The post-LGM deglaciation in Central and Southeast Switzerland: New insights from surface exposure dating

NASA Astrophysics Data System (ADS)

Boxleitner, Max; Maisch, Max; Brandova, Dagmar; Egli, Markus; Ochs, Susan Ivy; Christl, Marcus

2017-04-01

The deglaciation of the Alps after the Last Glacial Maximum was not a linear process. Moraines as traces of glacier re-advances show that the climate within the general Late-Pleistocene-warming is characterized by repeated cold intervals. While moraine series resulting from these cold spells have been already described for many Alpine valleys at the beginning of the 20th century, absolute chronologies of the Lateglacial climate and glacier development are still fragmentary. The advent of surface exposure dating as a new absolute dating method some 30 years ago made it possible to directly target the deposition-age of moraines. But still many questions regarding the local-to-regional glacier development and its coupling to the overall climate change remain open. In the framework of my PhD-project we study key sites in Central (Uri) and Southeast (Engadine) Switzerland with the aim to develop an absolute post-LGM chronology. More than 50 rock-samples from boulders of different moraine complexes from both regions have been analyzed using 10Be-surface-expsure-dating. Our results show that especially the Younger Dryas plays not unexpected an important role as a very pronounced cold interval. With our results we will refine the understanding of the glacier development in the Swiss Alps during the Lateglacial and the Holocene and improve estimates of equilibrium lines of altitude (ELA) of glaciers from the LGM to the beginning of the Holocene.

Rapid response of alpine timberline vegetation to the Younger Dryas climate oscillation in the Colorado Rocky Mountains, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reasoner, M.A.; Jodry, M.A.

2000-01-01

Paleobotanical records from two high-altitude (>3,300 m) sites in Colorado show a clear and immediate response to the Younger Dryas climate oscillation. The Black Mountain Lake and Sky Pond records indicate that alpine timberline migrated upslope to near-modern elevations during the late Bolling-Allerod (13.6--12.9 ka). Subsequent declines in arboreal pollen percentages and accumulation rates during the Younger Dryas interval (12.9--11.7 ka) reflect a downslope displacement of the alpine timberline ecotone of 60--120 m in elevation. This change translates to a cooling of summer temperature by {approximately}0.4--0.9 C and is consistent with proposed Younger Dryas advances of alpine glaciers in themore » Rocky Mountains to positions close to Little Ice Age maxima. Alpine timberline readvanced upslope to elevations above both sites between 11.7 and 11.4 ka. The concomitant response of temperature-sensitive alpine timberline vegetation in Colorado and late-glacial changes in North Atlantic thermohaline circulating implicates a rapid, widespread atmospheric transmission of the Younger Dryas climate oscillation.« less

Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes.

PubMed

McManus, J F; Francois, R; Gherardi, J-M; Keigwin, L D; Brown-Leger, S

2004-04-22

The Atlantic meridional overturning circulation is widely believed to affect climate. Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies, but their impact on climate is difficult to assess because such reconstructions provide insufficient constraints on the rate of overturning. Here we report measurements of 231Pa/230Th, a kinematic proxy for the meridional overturning circulation, in a sediment core from the subtropical North Atlantic Ocean. We find that the meridional overturning was nearly, or completely, eliminated during the coldest deglacial interval in the North Atlantic region, beginning with the catastrophic iceberg discharge Heinrich event H1, 17,500 yr ago, and declined sharply but briefly into the Younger Dryas cold event, about 12,700 yr ago. Following these cold events, the 231Pa/230Th record indicates that rapid accelerations of the meridional overturning circulation were concurrent with the two strongest regional warming events during deglaciation. These results confirm the significance of variations in the rate of the Atlantic meridional overturning circulation for abrupt climate changes.

Deep Arctic Ocean warming during the last glacial cycle

USGS Publications Warehouse

Cronin, T. M.; Dwyer, G.S.; Farmer, J.; Bauch, H.A.; Spielhagen, R.F.; Jakobsson, M.; Nilsson, J.; Briggs, W.M.; Stepanova, A.

2012-01-01

In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1–2 °C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

An Arctic Ocean freshwater event as the trigger of the Younger Dryas stadial? Answers from Arctic deep-sea sediment cores

NASA Astrophysics Data System (ADS)

Spielhagen, Robert F.

2017-04-01

At ca. 12.8-11.5 ka the northern hemisphere climate experienced a dramatic fall-back to quasi-glacial conditions. Since the late 1980s, a major meltwater ejection to the North Atlantic through the Gulf of St.Lawrence was considered the most likely trigger for this "Younger Dryas event". It may have caused a slowdown of the Atlantic meridional overturning circulation (AMOC) and a diminished heat transport to the northern latitudes. However, field evidence from the potential meltwater route in North America has been discussed controversially in the last years, and the detection of a freshwater signal in marine sediments off the St.Lawrence river rendered difficult. More recently, the idea of an "Arctic route" of meltwater originating from proglacial lake Agassiz was put forward (Tarasov & Peltier, Nature 2005) and has gained further attraction through evidence from radiogenic isotopes (Not and Hillaire-Marcel; Nature Comm., 2012) and through modelling results of Condron and Winsor (PNAS, 2012) which showed that only a freshwater outflow through Fram Strait was capable of triggering a climate perturbation like the Younger Dryas. Here I present a review of isotopic records from the Arctic Ocean, the Fram Strait, and the Greenland Sea in search of evidence for a strong freshwater event in the Arctic Ocean at the onset of the Younger Dryas, supporting an Arctic origin of the trigger. A number of Arctic cores show a light planktic oxygen isotope spike at 13 ka. For several of them the age model is detailed enough to exclude a confusion with other deglacial spikes. On the central Arctic Lomonosov Ridge there is even evidence for a diminshed intermediate/bottom water circulation immediately following the freshwater event. On the other hand, there are many records which do not show a meltwater spike in the critical time interval, most likely because of low temporal resolution, a thick ice cover and/or a habitat change of the planktic foraminifers. The largest uncertainty is introduced by arguable reservoir corrections which may need to be applied to radiocarbon datings from the last glacial termination. Nevertheless, since isotopic evidence for a freshwater event at ca. 13 ka is found also in the Greenland Sea, support for an "Arctic trigger" weakening the AMOC is accumulating and may add to the establishment of a new paradigm for the origin of the Younger Dryas cold event.

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis.

PubMed

Pigati, Jeffrey S; Latorre, Claudio; Rech, Jason A; Betancourt, Julio L; Martínez, Katherine E; Budahn, James R

2012-05-08

The Younger Dryas impact hypothesis contends that an extraterrestrial object exploded over North America at 12.9 ka, initiating the Younger Dryas cold event, the extinction of many North American megafauna, and the demise of the Clovis archeological culture. Although the exact nature and location of the proposed impact or explosion remain unclear, alleged evidence for the fallout comes from multiple sites across North America and a site in Belgium. At 6 of the 10 original sites (excluding the Carolina Bays), elevated concentrations of various "impact markers" were found in association with black mats that date to the onset of the Younger Dryas. Black mats are common features in paleowetland deposits and typically represent shallow marsh environments. In this study, we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern United States and the Atacama Desert of northern Chile. At 10 of 13 sites, we found elevated concentrations of iridium in bulk and magnetic sediments, magnetic spherules, and/or titanomagnetite grains within or at the base of black mats, regardless of their age or location, suggesting that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event.

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

PubMed Central

Pigati, Jeffrey S.; Latorre, Claudio; Rech, Jason A.; Betancourt, Julio L.; Martínez, Katherine E.; Budahn, James R.

2012-01-01

The Younger Dryas impact hypothesis contends that an extraterrestrial object exploded over North America at 12.9 ka, initiating the Younger Dryas cold event, the extinction of many North American megafauna, and the demise of the Clovis archeological culture. Although the exact nature and location of the proposed impact or explosion remain unclear, alleged evidence for the fallout comes from multiple sites across North America and a site in Belgium. At 6 of the 10 original sites (excluding the Carolina Bays), elevated concentrations of various “impact markers” were found in association with black mats that date to the onset of the Younger Dryas. Black mats are common features in paleowetland deposits and typically represent shallow marsh environments. In this study, we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern United States and the Atacama Desert of northern Chile. At 10 of 13 sites, we found elevated concentrations of iridium in bulk and magnetic sediments, magnetic spherules, and/or titanomagnetite grains within or at the base of black mats, regardless of their age or location, suggesting that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event. PMID:22529347

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

USGS Publications Warehouse

Pigati, Jeffrey S.; Latorre, Claudio; Rech, Jason A.; Betancourt, Julio L.; Martinez, Katherine E.; Budahn, James R.

2012-01-01

The Younger Dryas impact hypothesis contends that an extraterrestrial object exploded over North America at 12.9 ka, initiating the Younger Dryas cold event, the extinction of many North American megafauna, and the demise of the Clovis archeological culture. Although the exact nature and location of the proposed impact or explosion remain unclear, alleged evidence for the fallout comes from multiple sites across North America and a site in Belgium. At 6 of the 10 original sites (excluding the Carolina Bays), elevated concentrations of various "impact markers" were found in association with black mats that date to the onset of the Younger Dryas. Black mats are common features in paleowetland deposits and typically represent shallow marsh environments. In this study, we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern United States and the Atacama Desert of northern Chile. At 10 of 13 sites, we found elevated concentrations of iridium in bulk and magnetic sediments, magnetic spherules, and/or titanomagnetite grains within or at the base of black mats, regardless of their age or location, suggesting that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event.

Climatic oscillations in central Italy during the Last Glacial-Holocene transition: the record from Lake Accesa

NASA Astrophysics Data System (ADS)

Magny, Michel; de Beaulieu, Jacques-Louis; Drescher-Schneider, Ruth; Vannière, Boris; Walter-Simonnet, Anne-Véronique; Millet, Laurent; Bossuet, Gilles; Peyron, Odile

2006-05-01

This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake-level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial-early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north-central Italy). On the basis of an age-depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas-Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700-11 650 cal. yr BP. Four sub-millennial scale cooling phases were recognised from pollen data at ca. 14 300-14 200, 13 900-13 700, 13 400-13 100 and 11 350-11 150 cal.yrBP. The last three may be Mediterranean equivalents to the Older Dryas (GI-1d), Intra-Allerød (GI-1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice-core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra-Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake-level record shows that the sub-millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2ka cold reversal. Copyright

The loess/paleosol record and the nature of the younger dryas climate in central China

USGS Publications Warehouse

Madsen, D.B.; Jingzen, L.; Elston, R.G.; Cheng, X.; Bettinger, R.L.; Kan, G.; Jeff, Brantingham P.; Kan, Z.

1998-01-01

The use of latest Pleistocene-Holocene paleosols in defining Chinese climatic sequences is plagued by poor chronological controls caused primarily by the use of radiocarbon dates derived from bulk soil carbon. Dating of a post-glacial aeolian/paleosol sequence in the Pigeon Mountain basin of north-central China, using culturally deposited charcoal, support a wide array of other data suggesting the Younger Dryas was a period of cooler dryer conditions marked by wide-spread aeolian deposition. Periods of soil formation and higher lake levels bracket this climatic event. Climatic variability immediately before, during and immediately after the Younger Dryas interval is associated with rapid technological elaboration and innovation in the production and use of chipped stone tools, and perhaps, ground stone. ?? 1998 John Wiley & Sons, Inc.

Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

2017-05-01

Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

Deglacial climate variability in central Florida, USA

USGS Publications Warehouse

Willard, D.A.; Bernhardt, C.E.; Brooks, G.R.; Cronin, T. M.; Edgar, T.; Larson, R.

2007-01-01

Pollen and ostracode evidence from lacustrine sediments underlying modern Tampa Bay, Florida, document frequent and abrupt climatic and hydrological events superimposed on deglacial warming in the subtropics. Radiocarbon chronology on well-preserved mollusk shells and pollen residue from core MD02-2579 documents continuous sedimentation in a variety of non-marine habitats in a karst-controlled basin from 20 ka to 11.5 ka. During the last glacial maximum (LGM), much drier and cooler-than-modern conditions are indicated by pollen assemblages enriched in Chenopodiaceae and Carya, with rare Pinus (Pinus pollen increased to 20–40% during the warming of the initial deglaciation (∼ 17.2 ka), reaching near modern abundance (60–80%) during warmer, moister climates of the Bølling/Allerød interval (14.7–12.9 ka). Within the Bølling/Allerød, centennial-scale dry events corresponding to the Older Dryas and Intra-Allerød Cold Period indicate rapid vegetation response (

Evidence for early postglacial warming in Mount Field National Park, Tasmania

NASA Astrophysics Data System (ADS)

Rees, Andrew B. H.; Cwynar, Les C.

2010-02-01

Situated between the Western Pacific Warm Pool to the north and Antarctica to the south, Tasmania is an ideal location to study both postglacial and Holocene paleoclimates. Few well-dated, quantitative temperature reconstructions exist for the region so that important questions about the occurrence and magnitude of events, such as the Antarctic Cold Reversal and Younger Dryas, in Tasmania remain unanswered. Here, we provide chironomid-based reconstructions of temperature of the warmest quarter (TWARM) for two small subalpine lakes, Eagle and Platypus Tarns, Mount Field National Park. Shortly after deglaciation, TWARM reached modern values by approximately 15 000 cal a BP and remained high until 13 000 cal a BP after which temperatures began to cool steadily, reaching a minimum by 11 100-10 000 cal a BP. These results are consistent with sea surface temperature (SST) reconstructions from south of Tasmania but are in stark contrast to temperature inferences drawn from vegetation reconstructions based on pollen data that indicate cool initial temperatures followed by a broad warm period between 11 600-6800 cal a BP (10 000-6000 14C a BP). The chironomid record broadly matches the summer insolation curve whereas the vegetation record and associated climate inferences mirror winter insolation. The Antarctic Cold Reversal and Younger Dryas cold events are not evident in the chironomid-inferred temperatures, but the Antarctic Cold Reversal is evident in the loss-on-ignition curves.

Stable isotope (O and C) and pollen trends in eastern Lake Erie, evidence for a locally-induced climatic reversal of Younger Dryas age in the Great Lakes basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, C.F.M.; Anderson, T.W.

A cool period from about 11000 to 10500 BP (11 to 10.5 ka) is recognized in pollen records from the southern Great Lakes area by the return of Picea and Abies dominance and by the persistence of herbs. The area of cooling appears centred on the Upper Great Lakes. A high-resolution record (ca. 9 mm/y) from a borehole in eastern Lake Erie reveals, in the same time interval, this pollen anomaly, isotope evidence of melt-water presence (a-3 per mil shift in {delta} {sup 18}O and a + 1.1 per mil shift in {delta}{sup 13}C), increased sand, and reduced detrital calcitemore » content, all suggesting concurrent cooling of Lake Erie. The onset of cooling is mainly attributed to the effect of enhanced meltwater inflow on the relatively large upstream Main Lake Agassiz. Termination of the cooling coincides with drainage of Lake Algonquin, and is attributed to loss of its cooling effectiveness associated with a substantial reduction in its surface area. It is hypothesized that that the cold extra in-flow effectively prolonged the seasonal presence of lake ice and the period of spring overturn in Lake Algonquin. The deep mixing would have greatly increased the thermal conductive capacity of this extensive lake, causing suppression of summer surface lakewater temperatures and reduction of onshore growing-degree days. Alternatively, a rapid flow of meltwater, buoyed on sediment-charged (denser) lakewater, may have kept the lake surface cold in summer. Other factors such as wind-shifted pollen deposition and possible effects from the Younger Dryas North Atlantic cooling could have contributed to the Great Lakes climatic reversal, but further studies are needed to resolve their relative significance. 51 refs., 5 figs.« less

The Younger Dryas phase of Great Salt Lake, Utah, USA

USGS Publications Warehouse

Oviatt, Charles G.; Miller, D.M.; McGeehin, J.P.; Zachary, C.; Mahan, S.

2005-01-01

Field investigations at the Public Shooting Grounds (a wildlife-management area on the northeastern shore of Great Salt Lake) and radiocarbon dating show that the Great Salt Lake rose to the Gilbert shoreline sometime between 12.9 and 11.2 cal ka. We interpret a ripple-laminated sand unit exposed at the Public Shooting Grounds, and dated to this time interval, as the nearshore sediments of Great Salt Lake deposited during the formation of the Gilbert shoreline. The ripple-laminated sand is overlain by channel-fill deposits that overlap in age (11.9-11.2 cal ka) with the sand, and by wetland deposits (11.1 to 10.5 cal ka). Consistent accelerator mass spectrometry radiocarbon ages were obtained from samples of plant fragments, including those of emergent aquatic plants, but mollusk shells from spring and marsh deposits yielded anomalously old ages, probably because of a variable radiocarbon reservoir effect. The Bonneville basin was effectively wet during at least part of the Younger Dryas global-cooling interval, however, conflicting results from some Great Basin locations and proxy records indicate that the regional effects of Younger Dryas cooling are still not well understood. ?? 2005 Elsevier B.V. All rights reserved.

Terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest Ohio, USA

USGS Publications Warehouse

Campbell, M.C.; Fisher, T.G.; Goble, R.J.

2011-01-01

Optically stimulated luminescence dated sand dunes and Pleistocene beach ridges in northwest Ohio are used to reconstruct landscape modification more than 5000. yr after deglaciation. Four of the OSL ages (13.3-11.1. ka) cluster around the Younger Dryas cold event, five ages (10.8-8.2. ka) cluster around the Preboreal, one young age (0.9-0.7. ka) records more recent aeolian activity, and one age of 15.1-13.1. ka dates a barrier spit in Lake Warren. In northwest Ohio, both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the Younger Dryas. However, the climate conditions during the Preboreal resulting in aeolian activity are not recorded in the available pollen records. From this, we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler, drier episodes of climate and can complement pollen data. Younger Dryas and Preboreal aged aeolian activity in northwestern Ohio coincides with aeolian records elsewhere in the Great Lakes region east of the prairie-forest ecotone. ?? 2011 University of Washington.

Paradigms and proboscideans in the southern Great Lakes region, USA

USGS Publications Warehouse

Saunders, J.J.; Grimm, E.C.; Widga, C.C.; Campbell, G.D.; Curry, B. Brandon; Grimley, D.A.; Hanson, P.R.; McCullum, J.P.; Oliver, J.S.; Treworgy, J.D.

2010-01-01

Thirteen new chronometric dates for Illinois proboscideans are considered in relation to well-dated pollen records from northeastern and central Illinois. These dates span an interval from 21,228 to 12,944 cal BP. When compared to pollen spectra, it is evident that Mammut americanum inhabited spruce (Picea) and black ash (Fraxinus nigra) forest during the B??lling-Aller??d (14,700-12,900 cal BP) and early Younger Dryas (12,900-11,650 cal BP) chronozones. Both Mammuthus jeffersonii and Mammuthus primigenius inhabited spruce dominated open-woodland during the Oldest Dryas chronozone, while M.??primigenius persisted in a forest of predominantly black ash during the Aller??d chronozone. A newly discovered specimen from Lincoln, IL, clarifies the taxonomic distinction between M. primigenius and M.??jeffersonii. Hitherto, a paradigm of proboscidean succession during the full- to late-glacial periods was based on the vegetation succession of steppe tundra-like vegetation to spruce forest to spruce-deciduous forest. The presumed proboscidean succession was that of cold, dry steppe-adapted M. primigenius succeeded by more mesic-tolerant M. jeffersonii that in turn was succeeded by the wet forest-adapted M.??americanum. Reported data do not support this view and indicate a need for re-evaluation of assumptions of proboscidean ecology and history, e.g., the environmental tolerances and habits of M.??primigenius in regions south of 55??N, and its dynamic relationship with other proboscidean taxa. ?? 2009 Elsevier Ltd and INQUA.

Tree-ring records of near-Younger Dryas time in central North America - Preliminary results from the Lincoln quarry site, central Illinois, USA

USGS Publications Warehouse

Panyushkina, Irina P.; Leavitt, Steven W.; Wiedenhoeft, A.; Noggle, S.; Curry, B.; Grimm, E.

2004-01-01

The abrupt millennial-scale changes associated with the Younger Dryas (YD) event ("chronozone") near the dawn of the Holocene are at least hemispheric, if not global, in extent. Evidence for the YD cold excursion is abundant in Europe but fairly meager in central North America. We are engaged in an investigation of high-resolution environmental changes in mid-North America over several millennia (about 10,000 to 14,000 BP) during the Late Glacial-Early Holocene transition, including the YD interval. Several sites containing logs or stumps have been identified and we are in the process of initial sampling or re-sampling them for this project. Here, we report on a site in central Illinois containing a deposit of logs initially thought to be of YD age preserved in alluvial sands. The assemblage of wood represents hardwood (angiosperm) trees, and the ring-width characteristics are favorable to developing formal tree-ring chronologies. However, 4 new radiocarbon dates indicate deposition of wood may have taken place over at least 8000 14C yr (6000-14,000 BP). This complicates the effort to develop a single floating chronology of several hundred years at this site, but it may provide wood from a restricted region over a long period of time from which to develop a sequence of floating chronologies, the timing of deposition and preservation of which could be related to paleoclimatic events and conditions.

Glacier retreat in New Zealand during the Younger Dryas stadial.

PubMed

Kaplan, Michael R; Schaefer, Joerg M; Denton, George H; Barrell, David J A; Chinn, Trevor J H; Putnam, Aaron E; Andersen, Bjørn G; Finkel, Robert C; Schwartz, Roseanne; Doughty, Alice M

2010-09-09

Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (approximately 12.9 to approximately 11.7 kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand's glaciers retreated after approximately 13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent approximately 1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision (10)Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO(2). The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand's cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO(2) release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

Centennial and millennial-scale hydroclimate changes in northwestern Patagonia since 16,000 yr BP

NASA Astrophysics Data System (ADS)

Moreno, Patricio I.; Videla, Javiera

2016-10-01

We examine hydroclimate changes at centennial/millennial timescales since 16,000 yr BP in northwestern Patagonia based on the pollen and charcoal record from Lago El Salto, a small closed-basin lake located in the Chilean Lake District (41°38‧48.02″S, 73° 5‧48.42″W). We observe cold/wet conditions between 14,500-16,000 yr BP, followed by further cooling with increased precipitation until 13,000 yr BP, enhanced precipitation seasonality and/or variability between 11,600-13,000 yr BP, and an extended warm-and-dry interval between 7600 and 11,300 yr BP with peak paleofire activity. Colder-and-wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr BP, followed by alternating cold/wet and centennial-scale warm/dry phases starting at 5300 yr BP with three conspicuous megadroughts since 2500 yr BP. The most recent megadrought occurred during the Medieval Climate Anomaly. We identify a cold reversal that spans the Antarctic Cold Reversal (ACR) and the Younger Dryas (YD) chrons with stronger-than-present westerly influence during the former and enhanced variability during the latter. These results extend the northern limit of strong cooling and increase in precipitation during the ACR and the southern limit of influence of strong hydrologic variations during the YD in terrestrial environments, suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes. An extended warm southern westerly wind (SWW)-minimum interval is evident between 7600 and 11,300 yr BP, followed by a rapid shift to cool-moist conditions between 5300 and 7600 yr BP brought by a mid-Holocene SWW maximum. Since then we observe centennial-scale hydroclimate variability, which has driven biodiversity and fire-regime shifts of evergreen temperate rainforests.

Insights from a synthesis of old and new climate-proxy data from the Pyramid and Winnemucca lake basins for the period 48 to 11.5 cal ka

USGS Publications Warehouse

Benson, Larry; Smoot, J.P.; Lund, S.P.; Mensing, S.A.; Foit, F.F.; Rye, R.O.

2013-01-01

A synthesis of old and new paleoclimatic data from the Pyramid and Winnemucca lake basins indicates that, between 48.0 and 11.5·103 calibrated years BP (hereafter ka), the climate of the western Great Basin was, to a degree, linked with the climate of the North Atlantic. Paleomagnetic secular variation (PSV) records from Pyramid Lake core PLC08-1 were tied to the GISP2 ice-core record via PSV matches to North Atlantic sediment cores whose isotopic and(or) carbonate records could be linked to the GISP2 δ18O record. Relatively dry intervals in the western Great Basin were associated with cold Heinrich events and relatively wet intervals were associated with warm Dansgaard-Oeschger (DO) oscillations. The association of western Great Basin dry events with North Atlantic cold events (and vice versa) switched sometime after the Laurentide Ice Sheet (LIS) reached its maximum extent. For example, the Lahontan highstand, which culminated at 15.5 ka, and a period of elevated lake level between 13.1 and 11.7 ka were associated with cold North Atlantic conditions, the latter period with the Youngest Dryas event. Relatively dry periods were associated with the Bølling and Allerød warm events. A large percentage of the LIS may have been lost to the North Atlantic during Heinrich events 1 and 2 and may have resulted in the repositioning of the Polar Jet Stream over North America. The Trego Hot Springs, Wono, Carson Sink, and Marble Bluff tephras found in core PLC08-1 have been assigned GISP2 calendar ages of respectively, 29.9, 33.7, 34.1, and 43.2 ka. Given its unique trace-element chemistry, the Carson Sink Bed is the same as Wilson Creek Ash 15 in the Mono Lake Basin. This implies that the Mono Lake magnetic excursion occurred at approximately 34 ka and it is not the Laschamp magnetic excursion. The entrance of the First Americans into the northern Great Basin is dated to approximately 14.4 ka, a time when the climate was relatively dry. Evidence for human occupation of the Great Basin is lacking for the next 1100 years (y); i.e., the oldest western stemmed point site in the Great Basin dates to 13.3 ka. Two hypotheses are suggested for this cultural hiatus: (1) the climate had deteriorated to the point that people vacated the Great Basin, or (2) people moved to basin-bottom wetlands that persisted during the dry period, and then the subsequent Younger Dryas wet event erased the archaeological evidence deposited around the low-elevation wetland sites.

Meltwater and precipitation runoff to the North Atlantic, Arctic, and Gulf of Mexico from the Laurentide Ice Sheet and adjacent regions during the Younger Dryas

NASA Astrophysics Data System (ADS)

Teller, James T.

1990-12-01

Runoff from North America may have played a significant role in ocean circulation and climate change during the last deglaciation. Because the driving force behind such changes may have been related to salinity of the north flowing Atlantic Ocean conveyor circulation, it is critical to know the volume, timing, and location of fresh water entering the North Atlantic from the melting Laurentide Ice Sheet. During the Younger Dryas cold episode, 11,000-10,000 years B.P., there was a two-fold increase in the volume of meltwater plus precipitation runoff, to more than 1700 km³ yr-1, flowing through the St. Lawrence valley to the North Atlantic, mainly because retreating ice allowed the glacial Lake Agassiz basin to drain eastward into the Great Lakes at this time. There was a corresponding decline in discharge from Lake Agassiz through the Mississippi River to the Gulf of Mexico. Runoff to the Arctic Ocean also increased at about the beginning of the Younger Dryas, from 740 to 900 km³ yr-1, because of the capture of what is now the headwater region of the Mackenzie River watershed. This, in combination with rising sea level and warming climate, may have increased the amount of pack ice reaching the North Atlantic through the Norwegian Sea from the Arctic Ocean. At 10,000 years B.P., eastward overflow from the western interior of North America was blocked by advancing ice, again forcing overflow to the Gulf of Mexico and, possibly, to the northwest into the Arctic Ocean. Although total runoff to the oceans from all regions draining from the Laurentide Ice Sheet did not vary substantially between 12,000 and 9000 years B.P., if discharge to the Gulf of Mexico is excluded, fresh water reaching the North Atlantic averaged 4000 km³ yr-1 during the Younger Dryas, in contrast to 2870 km³ yr-1 just before this cold episode and 3440 km³ yr-1 just after it.

A Younger Dryas re-advance of local glaciers in north Greenland

NASA Astrophysics Data System (ADS)

Larsen, Nicolaj K.; Funder, Svend; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Xu, Sheng; Kjær, Kurt H.

2016-09-01

The Younger Dryas (YD) is a well-constrained cold event from 12,900 to 11,700 years ago but it remains unclear how the cooling and subsequent abrupt warming recorded in ice cores was translated into ice margin fluctuations in Greenland. Here we present 10Be surface exposure ages from three moraines in front of local glaciers on a 50 km stretch along the north coast of Greenland, facing the Arctic Ocean. Ten ages range from 11.6 ± 0.5 to 27.2 ± 0.9 ka with a mean age of 12.5 ± 0.7 ka after exclusion of two outliers. We consider this to be a minimum age for the abandonment of the moraines. The ages of the moraines are furthermore constrained using Optically Stimulated Luminescence (OSL) dating of epishelf sediments, which were deposited prior to the ice advance that formed the moraines, yielding a maximum age of 12.4 ± 0.6 ka, and bracketing the formation and subsequent abandonment of the moraines to within the interval 11.8-13.0 ka ago. This is the first time a synchronous YD glacier advance and subsequent retreat has been recorded for several independent glaciers in Greenland. In most other areas, there is no evidence for re-advance and glaciers were retreating during YD. We explain the different behaviour of the glaciers in northernmost Greenland as a function of their remoteness from the Atlantic Meridional Overturning Circulation (AMOC), which in other areas has been held responsible for modifying the YD drop in temperatures.

Termination of the Last Glaciation in the Iberian Peninsula Inferred from the Pollen Sequence of Quintanar de la Sierra

NASA Astrophysics Data System (ADS)

Peñalba, M. Cristina; Arnold, Maurice; Guiot, Joël; Duplessy, Jean-Claude; de Beaulieu, Jacques-Louis

1997-09-01

A 4.5-m-thick late-glacial pollen sequence, supported by 17 AMS 14C dates, has been investigated at the Quintanar de la Sierra marshland (Iberian cordillera, north-central Spain). Pollen zones were defined that correspond to successive phases in vegetation history during the end of the Late Würm, late-glacial interstade, and Younger Dryas periods. A transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data. A first expansion of Juniperusand Hippophae,about 13,500 14C yr B.P., indicates the beginning of the late-glacial interstade which is characterized by a Juniperus-Betula-Pinussuccession that suggests higher temperatures and moisture than during full-glacial time. The Younger Dryas interval is recorded by a 120-cm-thick sediment unit that is dominated by herbaceous pollen. Transfer function estimates suggest that the climate during this period was cold, with low precipitation during most of the year, although not in summer. The Holocene arboreal recolonization in the area started about 10,000 14C yr B.P., with a renewed Juniperus-Betula-Pinussuccession related to a strong increase in annual temperature and precipitation. The start of this process was synchronous with mean sea-surface temperature changes, as recorded from the nearby SU 81-18 marine core. The strong affinity with other European late-glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial-interglacial transition was similar in both northwestern and southwestern Europe.

Climate variability at the onset of the Younger Dryas as reflected in annually resolved tree-ring stable isotope chronologies

NASA Astrophysics Data System (ADS)

Pieper, H.; Helle, G.; Brauer, A.; Kaiser, K. F.; Miramont, C.

2013-12-01

The Younger Dryas interval during the Last Glacial Termination was an abrupt return to glacial-like conditions punctuating the transition to a warmer, interglacial climate. Despite recent advances in the layer counting of ice-core records of the termination, the timing and length of the Younger Dryas remain controversial. Late Glacial and early Holocene tree-ring chronologies are rare, however, they contain valuable information about past environmental conditions at annual time resolution. Changes in tree-ring growth rates can be related to past climate anomalies and changes in the carbon and oxygen isotope composition of tree-ring cellulose reflect atmospheric and hydrospheric changes. We are investigating a 860-year (13200 - 12340 cal BP) dated dendrochronological record of Late Glacial and Early Holocene chronologies of scots pine (Pinus sylvestris L.) from subfossil tree remnants from Barbiers River (Moyenne Durance, Southern French Alps), as well as from Swiss (Dättnau, Landikon and Gänziloh) sites. Dendro-ecological parameters, such as ring width and stable isotope variations (δ 13C und δ 18O) are used to infer past environmental conditions. We will present our first carbon and oxygen isotope records from tree rings reflecting the environmental changes at the Alleröd/Younger Dryas -transition.

Cold Reversal on Kodiak Island, Alaska, Correlated with the European Younger Dryas by Using Variations of Atmospheric C-14 Content

NASA Technical Reports Server (NTRS)

Hajdas, Irka; Bonani, Georges; Boden, Per; Peteet, Dorothy M.; Mann, Daniel H.

1999-01-01

High-resolution AMS (accelerator-mass-spectrometer) radiocarbon dating was performed on late-glacial macrofossils in lake sediments from Kodiak Island, Alaska, and on shells in marine sediments from southwest Sweden. In both records, a dramatic drop in radiocarbon ages equivalent to a rise in the atmospheric C-14 by approximately 70%. coincides with the beginning of the cold period at 11000 yr B.P. (C-14 age). Thus our results show that a close correlation between climatic records around the globe is possible by using a global signature of changes in atmospheric C-14 content.

Younger Dryas cooling and the Greenland climate response to CO2.

PubMed

Liu, Zhengyu; Carlson, Anders E; He, Feng; Brady, Esther C; Otto-Bliesner, Bette L; Briegleb, Bruce P; Wehrenberg, Mark; Clark, Peter U; Wu, Shu; Cheng, Jun; Zhang, Jiaxu; Noone, David; Zhu, Jiang

2012-07-10

Greenland ice-core δ(18)O-temperature reconstructions suggest a dramatic cooling during the Younger Dryas (YD; 12.9-11.7 ka), with temperatures being as cold as the earlier Oldest Dryas (OD; 18.0-14.6 ka) despite an approximately 50 ppm rise in atmospheric CO(2). Such YD cooling implies a muted Greenland climate response to atmospheric CO(2), contrary to physical predictions of an enhanced high-latitude response to future increases in CO(2). Here we show that North Atlantic sea surface temperature reconstructions as well as transient climate model simulations suggest that the YD over Greenland should be substantially warmer than the OD by approximately 5 °C in response to increased atmospheric CO(2). Additional experiments with an isotope-enabled model suggest that the apparent YD temperature reconstruction derived from the ice-core δ(18)O record is likely an artifact of an altered temperature-δ(18)O relationship due to changing deglacial atmospheric circulation. Our results thus suggest that Greenland climate was warmer during the YD relative to the OD in response to rising atmospheric CO(2), consistent with sea surface temperature reconstructions and physical predictions, and has a sensitivity approximately twice that found in climate models for current climate due to an enhanced albedo feedback during the last deglaciation.

The Holocene environmental history of the Verkhoyansk Mountains region (northeastern Siberia, Russia) reconstructed from high-resolution pollen data

NASA Astrophysics Data System (ADS)

Müller, S.; Tarasov, P. E.; Andreev, A. A.; Diekmann, B.

2009-04-01

The study presented here is part of the IPY project 106 "Lake Records of late Quaternary Climate Variability in northeastern Siberia" and the German Research Foundation project RI 809/17-1,2 "Late Quaternary environmental history of interstadial and interglacial periods in the Arctic reconstructed from bioindicators in permafrost sequences in NE Siberia". Both projects focus on generating high-resolution vegetation and climate proxy records mainly from lacustrine sediments along a north-south transect from Yakutia, Republic of Russia. This region is known for its climate extremes, with the Verkhoyansk Mountain Range being the coldest area in the Northern Hemisphere - "Pole of Cold". Radiocarbon-dated pollen records from Lake Billyakh (65°17'N, 126°47'E; 340 m a.s.l.) located in the central part of the Verkhoyansk Mountains were used to reconstruct vegetation and climate changes. The longest and oldest sediment core from the lake reaches back to >30 kyr BP, thus covering the last two Late Pleistocene Interstadials in Siberia. The pollen record and pollen-based biome reconstruction of the core PG 1756, which covers the last 15 kyr BP, suggest that open cool steppe and grass and sedge tundra communities with Poaceae, Cyperaceae, Artemisia, Chenopodiaceae, Caryophyllaceae and Selaginella rupestris dominated the area from 15 to 13.5 kyr BP. On the other hand, the constant presence of Larix pollen in quantities comparable to today's values points to the constant presence of boreal deciduous conifer trees in the regional vegetation during the last glaciation. A major spread of shrub tundra communities, including birch (Betula sect. Nanae), alder (Duschekia fruticosa) and willow (Salix) species, is dated to 13.5-12.7 kyr BP, indicating a noticeable increase in precipitation toward the end of the last glaciation, particularly during the Allerød Interstadial. Between 12.7 and 11.4 kyr BP pollen percentages of herbaceous taxa rapidly increased, whereas shrub taxa percentages decreased, suggesting strengthening of the steppe communities associated with the cold and dry Younger Dryas Stadial. However, the pollen data in hand indicate that Younger Dryas climate was less severe than the climate during the earlier interval from 15 to 13.5 kyr BP. The onset of the Holocene is marked in the pollen record by the highest values of shrub and lowest values of herbaceous taxa, suggesting a return of warmer and wetter conditions after 11.4 kyr BP. Percentages of tree taxa increase gradually and reach maximum values after 7 kyr BP, reflecting the spread of boreal cold deciduous and taiga forests in the region. An interval between 7 and 2 kyr BP is noticeable for the highest percentages of Scots pine (Pinus subgen. Diploxylon), spruce (Picea) and fir (Abies) pollen, indicating mid-Holocene spread of boreal forest communities in response to climate amelioration and degradation of the permafrost layer.

Heinrich 0 at the Younger Dryas Termination Offshore Newfoundland

NASA Astrophysics Data System (ADS)

Pearce, C.; Andrews, J. T.; Jennings, A. E.; Bouloubassi, I.; Seidenkrantz, M. S.; Kuijpers, A.; Hillaire-Marcel, C.

2014-12-01

The last deglaciation was marked by intervals of rapid climatic fluctuations accompanied by glacial advances and retreats along the eastern edge of the Laurentide ice sheet. The most severe of these events, the Younger Dryas cold reversal, was accompanied by the major detrital carbonate (DC) event generally referred to as "Heinrich event 0" (H0) in the westernmost and southern Labrador Sea. A detrital carbonate layer was observed in a high resolution marine sediment record from southern Newfoundland and the onset of the event was dated to 11,600 ± 70 cal. yrs. BP (local ΔR = 140 yrs.). A variety of different proxies was applied to investigate the transport mechanisms for deposition of the layer and provenance of the carbonates. Elevated concentrations of dolomite and calcite based on quantitative X-ray diffraction measurements, combined with the presence of several mature petrogenic biomarkers limit the source of the H0 detrital input to Palaeozoic carbonate outcrops in north-eastern Canada. The event is attributed to the rapid ice retreat from the Hudson Strait directly following the warming at the onset of the Holocene. Based on additional proxy data published earlier from the same record, the event succeeded the early Holocene resumption of the Atlantic Meridional Overturning Circulation (AMOC), indicating that the Hudson Strait meltwater event had probably no significant impact on the AMOC. The detrital carbonate layer can be found in other marine sediment records along the Labrador Current pathway, from Hudson Strait to the Grand Banks and the southern Newfoundland slope. By using the onset of deposition of the carbonates as a time-synchronous marker, the DC layer has great potential for improving marine chronologies of late glacial age in the region and evaluating spatial variations in ΔR values.

Recognizing the Palynological Signal of Heinrich Event H1

NASA Astrophysics Data System (ADS)

Delusina, I.

2017-12-01

One of the most challenging intervals for paleo-vegetation reconstruction of the post-Glacial environment is the transition that occurred at the beginning and the end of Heinrich event H1 and that stretched up to the beginning of the Younger Dryas. The main ambiguity is related to the magnitude and timing of H1 and the non-linear response of the Earth system to the Heinrich event itself in different geographical locations. We consider the H1 event as the entire transition interval since 18 to 14.5 Kya. The main problem that arises is the uncertainty in the interpretation of the pollen assemblages due to their mixed nature, particularly the presence of both "warm" and "cold" pollen. We have compared the pollen signal from the beginning to the end of the H1 event along a tropic to subpolar transect, using data from our own studies and the published literature. We find that despite regional peculiarities, most of the pollen assemblages demonstrate a similar sequence of patterns. One of the most prominent common features, seen at the beginning and the end of H1, is the appearance of saw-tooth like shapes in the variables of the pollen diagram, independent of location, vegetation composition and other factors. The most noticeable "saw-tooth" occurs after H1, between about 14 and 12 Kya, the interval that roughly corresponds to the Bølling/Allerød. The common features of a "saw-tooth" for both the beginning and the end of the H1 event, appear in this order: 1) increase in ferns, usually coinciding with or followed by an increased percentage of conifer pollen. 2) The beginning of dominance of xerophyte assemblages, again as a "saw-tooth" which lasts for about 2 Kya. 3) Each "saw-tooth", no matter where it occurs, terminates with the beginning of an increase in arboreal (or steppe) vegetation. For all of the different sites, the isotopic evidence is that this was a period of warming, but the pollen records tell a more complex story. Despite the local individualities of each pollen record, they all indicate that the response to global warming was not monotonic but resulted in rapid, almost chaotic changes in vegetation, until ultimately terminated with the Younger Dryas cooling.

The response of southern California ecosystems to Younger Dryas-like rapid climate change: Comparison of glacial terminations 1 and 5.

NASA Astrophysics Data System (ADS)

Heusser, L. E.; Hendy, I. L.

2015-12-01

The Younger Dryas is a well-known rapid climatic cooling that interrupted the Marine Isotope Stage (MIS) 1-2 deglacial warming of Termination 1. This cool event has been associated with ice sheet readvance, meridional overturning, circulation changes, and southward movement of the Intertropical Convergence Zone. In Southern California, the Younger Dryas has been associated with cooler SST, low marine productivity, a well-ventilated oxygen minimum zone, and a wetter climate. Similar rapid cooling events have been found at other terminations including Termination 5 at the MIS 11-12 deglaciation (~425 Ka) identified by ice rafting events in the North Atlantic. Here we present new pollen census data from a unique suite of cores taken from the sub-oxic sediments of Santa Barbara Basin (MV0508-15JC, MV0805-20JC, MV0508-33JC, 29JC and 21JC). These short cores, collected on a truncated anticline within SBB, provide the opportunity to examine the response of southern California terrestrial and marine ecosystems to rapid climate change during the MIS 11-12 deglaciation (Termination 5), which is identified by a bioturbated interval within a sequence of laminated sediments. During Termination 1, changes in Southern California precipitation are reflected in pollen- based reconstructions Southern California vegetation. The high precipitation of glacial montane-coniferous assemblages of pine (Pinus) and Juniper (Juniperus/Calocedrus) transitions into interglacial drought, as expresssed by arid oak (Quercus)/chaparral vegetation. The Younger Dryas interrupts the transition as a high-amplitude pulse in pine associated with increased Gramineae (grass). Termination 5 differs, as the high precipitation of glacial montane-coniferous assemblages do not transition into arid oak/chaparral vegetation. However, a Younger Dryas-like rapid climate event was associated with increased pine and grass.

Abrupt release of terrigenous organic carbon to the Laptev Sea at termination of the Younger Dryas

NASA Astrophysics Data System (ADS)

Tesi, T.; Muschitiello, F.; Smittenberg, R.; Jakobsson, M.; Vonk, J.; Hill, P.; Dudarev, O.; Semiletov, I. P.; Kirchner, N.; Noormets, R.; Andersson, A.; Gustafsson, O.

2015-12-01

Based on analysis of a piston core collected in 2014 from the Lena River paleo delta, now Laptev Sea, we show that rapid and massive organic carbon (OC) deposition took place into the marine system at the termination of the Younger Dryas when the Arctic region experienced a large and extremely fast climate change. The highly laminated strata with absence of bioturbation further confirm the rapid event-driven emplacement of this deposit which was largely dominated by terrigenous OC as indicated by depleted δ13C values and high concentrations of terrestrial fossil biomarkers (lignin phenols and cutin-derived products). Moreover, the hydrogen isotopic composition (δ2H) of HMW n-alkanes indicates that this terrestrially-derived translocated OC was produced in the watershed during a relatively cold period. The OC appears to be a few thousand years old at time of deposition (ca. 4-5000 radiocarbon years; reservoir age corrected), consistent with the radiocarbon age of pre-aged OC currently supplied by the Lena river. Altogether our results indicate that fast climate warming exerts first-order control on large-scale carbon redistribution. Because the Younger Dryas-Preboreal transition occurred within a few decades, we infer that the abrupt and large release of terrigenous OC was essentially driven by rapid changes in the permafrost stability (i.e., thermal collapse/thawing) and increase in precipitation over the Siberian watershed. Interestingly, only surface and sub-surface carbon pools (i.e., active layer) were remobilized while deep and old sources (radiocarbon dead) did not seem to have substantially contributed to the total land-to-ocean flux during the Younger Dryas-Preboreal transition.

The role of the Asian winter monsoon in the rapid propagation of abrupt climate changes during the last deglaciation

NASA Astrophysics Data System (ADS)

Chu, Guoqiang; Sun, Qing; Zhu, Qingzeng; Shan, Yabing; Shang, Wenyu; Ling, Yuan; Su, Youliang; Xie, Manman; Wang, Xishen; Liu, Jiaqi

2017-12-01

High-resolution temperature records spanning the last deglaciation from low latitudes are scarce; however, they are important for understanding the rapid propagation of abrupt climate events throughout the Northern Hemisphere and the tropics. Here, we present a branched GDGTs-based temperature reconstruction from the sediments of Maar Lake Huguangyan in tropical China. The record reveals that the mean temperature during the Oldest Dryas was 17.8 °C, which was followed by a two-step increase of 2-3 °C to the Bølling-Allerød, a decrease to 19.8 °C during the Younger Dryas, and a rapid warming at the onset of the Holocene. The Oldest Dryas was about 2 °C warmer than the Younger Dryas. The reconstructed temperature was weighted towards the wintertime since the lake is monomictic and the mixing process in winter supplies nutrients from the lake bottom to the entire water column, greatly promoting biological productivity. In addition, the winter-biased temperature changes observed in the study are more distinctive than the summer-biased temperature records from extra-tropical regions of East Asia. This implies that the temperature decreases during abrupt climatic events were mainly a winter phenomenon. Within the limits of the dating uncertainties, the broadly similar pattern of winter-weighted temperature change observed in both tropical Lake Huguangyan and in Greenland ice cores indicates the occurrence of tightly-coupled interactions between high latitude ice sheets and land areas in the tropics. We suggest that the winter monsoon (especially cold surges) could play an important role in the rapid transmission of the temperature signal from the Arctic to the tropics.

Post-glacial variability of sea ice cover, river run-off and biological production in the western Laptev Sea (Arctic Ocean) - A high-resolution biomarker study

NASA Astrophysics Data System (ADS)

Hörner, T.; Stein, R.; Fahl, K.; Birgel, D.

2016-07-01

Multi-proxy biomarker measurements were applied on two sediment cores (PS51/154, PS51/159) to reconstruct sea ice cover (IP25), biological production (brassicasterol, dinosterol) and river run-off (campesterol, β-sitosterol) in the western Laptev Sea over the last ∼17 ka with unprecedented temporal resolution. The absence of IP25 from 17.2 to 15.5 ka, in combination with minimum concentration of phytoplankton biomarkers, suggests that the western Laptev Sea shelf was mostly covered with permanent sea ice. Very minor river run-off and restricted biological production occurred during this cold interval. From ∼16 ka until 7.5 ka, a long-term decrease of terrigenous (riverine) organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western Laptev Sea, caused by the onset of the post-glacial transgression. Intensified river run-off and reduced sea ice cover characterized the time interval between 15.2 and 12.9 ka, including the Bølling/Allerød warm period (14.7-12.9 ka). Prominent peaks of the DIP25 Index coinciding with maximum abundances of subpolar foraminifers, are interpreted as pulses of Atlantic water inflow on the western Laptev Sea shelf. After the warm period, a sudden return to severe sea ice conditions with strongest ice-coverage between 11.9 and 11 ka coincided with the Younger Dryas (12.9-11.6 ka). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (reflected in a distinct drop in terrigenous and phytoplankton biomarkers) was detected. During the last 7 ka, the sea ice proxies reflect a cooling of the Laptev Sea spring/summer season. This cooling trend was superimposed by a short-term variability in sea ice coverage, probably representing Bond cycles (1500 ± 500 ka) that are related to solar activity changes. Hence, atmospheric circulation changes were apparently able to affect the sea ice conditions on the Laptev Sea shelf under modern sea level conditions.

Meltwater routing and the Younger Dryas.

PubMed

Condron, Alan; Winsor, Peter

2012-12-04

The Younger Dryas--the last major cold episode on Earth--is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318-321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC). More recently, Tarasov and Peltier [2005 Nature 435:662-665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenzie Valley ~4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ~3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling.

Decadal resolved leaf wax δD records of the Younger Dryas in central and eastern Europe

NASA Astrophysics Data System (ADS)

Aichner, Bernhard; Słowiński, Michał; Ott, Florian; Noryśkiewicz, Agnieszka M.; Wulf, Sabine; Brauer, Achim; Sachse, Dirk

2015-04-01

Annually laminated (varved) sediments with defined event-based age anchor points such as tephra layers enable the establishment of precise chronologies in lacustrine climate archives. This is especially useful to study subtle temporal differences in the consequences of mechanisms and feedbacks during abrupt climatic changes such as the Younger Dryas over larger spatial areas. To decipher the drivers of ecological changes across the Allerød/Younger Dryas transition in central Europe, we analyzed leaf wax biomarkers from Trzechowskie paleolake in northern Poland. Samples were taken in 10 years intervals across the onset of the Younger Dryas, with the Laacher See Tephra (12,880 yrs BP) as anchor point for age-calibration. Further, we applied compound specific hydrogen isotope analysis to infer past hydrological changes, in comparison to results from the well-dated Meerfelder Maar record located up 900 km to the southwest [1]. Between 12,750 and 12,600 yrs BP, ratios of terrestrial n-alkanes show a transition from a tree-dominated lake catchment (Pinus, Betula) to an environment mainly covered by Juniperus and grasses, which is in agreement with palynological data. δD values of n-alkanes indicate a rapid cooling and/or a change of moisture source together with a slight aridification between 12,680 and 12,600 yrs BP. This is synchronous to a rapid and strong aridification inferred for the beginning of the Younger Dryas at Meerfelder Maar (western Germany) [1] but ca. 170 yrs after the inferred onset of cooling at both Meerfelder Maar and the NGRIP ice core at 12,850 yrs BP. This highlights a different temporal succession and impact of hydrological and climatic changes in eastern compared to western Europe which could potentially be related to the stronger influence of the Fennoscandian icesheets and/or the Siberian High on atmospheric circulation patterns in the more continental climate influenced parts of eastern Europe. [1] Rach O, Brauer A, Wilkes H, Sachse D. Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe. Nat Geosci. Nature Publishing Group; 2014;7:109-112.

Sporo-pollen assemblage and paleoclimate events in shelf area of the southern Yellow Sea since 15 ka B. P.

NASA Astrophysics Data System (ADS)

Meng, Guanglan; Han, Yousong; Wang, Shaoqing; Wang, Zhenyan

2004-03-01

Based on the authors’ 1986 to 1994 sporo-pollen assemblage analysis in the southern Yellow Sea area, data from 3 main cores were studied in combination with14C, palaeomagnetic and thermoluminescence data. The evolution of the paleoclimate environments in the southern Yellow Sea since 15ka B. P. was revealed that, in deglaciation of the last glacial period, the climate of late glaciation transformed into that of postglaciation, accompanied by a series of violent climate fluctuations. These evolution events happened in a global climate background and related to the geographic changes in eastern China. We distinguished three short-term cooling events and two warming events. Among them, the sporo-pollen assemblage of subzone A1 showed some cold climate features indicating that a cooling event occurred at about 15-14ka. B. P. in early deglaciation. This subzone corresponds to the Oldest Dryas. In subzone A3, many drought-enduring herbal pollens and some few pollens of cold-resistant Picea, Abies, etc. were found, which indicated that a cooling event, with cold and arid climate, occurred at about 12-11ka. B. P. in late deglaciation. This subzone corresponds to the Younger Dryas. The sporo-pollen assemblage of zone B showed warm and arid climate features in postglaciation. Although the assemblage of subzone B2 indicated a cold and arid climate environment, the development of flora in subzone B2 climate was less cold than that in A3. Subzone B2 indicated a cooling event which occurred at about 9ka B. P. in early olocene. Subzone A2, with some distinct differences from subzone A1 and A3, indicated a warming event which occurred at 14-13ka. B.P. and should correspond to a warming fluctuation. The sporo-pollen assemblage of zone C showed features of warn-moist flora and climate, and indicated a warming event which universally occurred along the coast of eastern China at 8-3 ka B. P. in middle Holocene, and its duration was longer than that of any climate events mentioned above. This period was climatic optimum and belonged to an altithermal period in postglaciation.

Late-Glacial to Early Holocene Climate Changes from a Central Appalachians Pollen and Macrofossil Record

NASA Technical Reports Server (NTRS)

Kneller, Margaret; Peteet, Dorothy

1997-01-01

A Late-glacial to early Holocene record of pollen, plant macrofossils and charcoal, based on two cores, is presented for Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed upon the overall warming trend from 14,200 to 7,500 C-14 yr B.P. This site shows cold, moist conditions from approximately 14,200 to 12,700 C-14 yr B.P., with warming at 12,730, 11,280 and 10,050 C-14 yr B.P. A decrease in deciduous broad-leaved tree taxa and Pinus strobus (haploxylon) pollen, simultaneous with a re-expansion of Abies denotes a brief, cold reversal from 12,260 to 12,200 C-14 yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 7,500 C-14 yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland, and northwestern Europe. Warming at 11,280 C-14 yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.

Meltwater routing and the Younger Dryas

DOE PAGES

Condron, Alan; Winsor, Peter

2012-12-04

The Younger Dryas -- the last major cold episode on Earth -- is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318–321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC).More recently, Tarasov and Peltier [2005 Nature 435:662–665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenziemore » Valley ~4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ~3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling.« less

A 130 ka reconstruction of rainfall on the Bolivian Altiplano

NASA Astrophysics Data System (ADS)

Placzek, C. J.; Quade, J.; Patchett, P. J.

2013-02-01

New efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the Bolivian Altiplano. On the Southern Altiplano, 10 lake oscillations have been identified from this new unified chronology, each coincident with North Atlantic cold events such as Heinrich Events H5, H2, H1, and the Younger Dryas. By coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the Southern Bolivian Altiplano over the last 130 ka. These modeling efforts underscore the relative aridity of the Altiplano during the rare and small lake cycles occurring between 80 and 20 ka, when colder temperatures combined with little or no change in rainfall produced smaller paleolakes. Relative aridity between 80 and 20 ka contrasts with the immense Tauca lake cycle (18.1-14.1 ka), which was six times larger than modern Lake Titicaca and coincided with Heinrich Event 1. This improved paleolake record from the Southern Altiplano reveals a strong link between central Andean climate and Atlantic sea-surface temperature gradients during the late Pleistocene, even though today rainfall variability is driven mostly by Pacific sea-surface temperature anomalies associated with El Niño/Southern Oscillation. However, not all Heinrich Events appear to result in lake expansions, most conspicuously during the global cold interval between 80 and 20 ka when the Altiplano and Amazon Basin were relatively arid.

Ziwundaschg - 10Be dating an Older Dryas cirque glacier moraine in the middle of the Eastern Alps

NASA Astrophysics Data System (ADS)

Moran, Andrew; Ivy-Ochs, Susan; Kerschner, Hanns

2017-04-01

Alpine glacier extents during the Oldest Dryas period (>14.7 ka) are still largely unknown. Moraines from that period are comparatively rare and usually attributed to the "Gschnitz Stadial", which marks the alpine glacier reaction to the first part of Heinrich event 1. In many valleys, in the absence of clear geomorphological evidence, estimates for the glacier extent during that period range between large dendritic valley glacier systems with a well defined, albeit unknown glacier end on the one hand and numerous local valley and cirque glaciers on the other hand. In this context well dated local glacier extents may play an important role, as they provide boundary conditions for the altitude of the equilibrium line (an important palaeoclimatic parameter) and thus limit possible speculations about glacier extents in their vicinity. "Ziwundaschg" is the place name for a cirque in the western Ötztal Mountains near the upper Inn valley and Reschenpass. It is situated more or less in the centre of the Eastern Alps. The cirque floor is at an altitude of about 2000 m and the highest mountains in the back of the cirque are around 2750 m. They were not glacierized during the Little Ice Age, and even a glacierization during the Younger Dryas cold phase was likely limited to a few small ice patches. Further down at the cirque floor, a beautifully developed end moraine with lateral moraines is preserved. 10Be ages from boulders on the moraine cluster around the transition from the Oldest Dryas to the Bølling Interstadial, suggesting moraine stabilization due to the rapid warming at that time. The ELA of the glacier was at about 2200 m a.s.l., roughly 600 - 650 m lower than during the LIA. This value can be taken as representative for the mountain ranges in its vicinity and can form the basis for estimates of glacier extent during the early Lateglacial period in the central Eastern Alps.

Lateglacial vegetation dynamics in the eastern Baltic region between 14,500 and 11,400 cal yr BP: A complete record since the Bølling (GI-1e) to the Holocene

NASA Astrophysics Data System (ADS)

Veski, Siim; Amon, Leeli; Heinsalu, Atko; Reitalu, Triin; Saarse, Leili; Stivrins, Normunds; Vassiljev, Jüri

2012-04-01

This paper discusses a complete record of vegetation history since the Bølling (GI-1e) warming (14,500 cal yr BP) up to the Holocene in Latvia. To date, this is the only complete record of such age in the eastern Baltic area and the northernmost area for which Bølling records are present. Combining pollen evidence, pollen accumulation rates (PAR) and plant macrofossil data, we assess the local and regional vegetation development, and we attempt to separate the true Lateglacial vegetation signal by removing the obviously redeposited thermophilous pollen; however, we remove not only their signal, we discuss the possibilities of separating the redeposition signal of the so-called "local Lateglacial trees", pine and birch, by looking at their corrosion and degradation. The results show that the Bølling warming in the eastern Baltic area was a treeless tundra community consisting of the shrubs Betula nana, Dryas octopetala and Salix polaris. The Older Dryas cold spell is clearly recognised as a decline in the total concentration of plant macrofossils and PARs at between 14,200 and 13,500 cal yr BP. At 13,460 cal yr BP, the B. nana macrofossils disappear, and tree birch (Betula sect. Albae) appears, marking the start of tree birch forest. The presence of pine forest is confirmed by a variety of macrofossils, including bark, wood, needles and seeds, since 13,400 cal yr BP, at the same time at which pine stomata are found. The first identified pine stomata finds are associated with a Pinus PAR over 3000 grains cm-2 yr-1 and pine macrofossil finds with a Pinus PAR over 4000 grains cm-2 yr-1. During the warmest period of the GI-1a (Allerød) at 13,000-12,700 cal yr BP, a pine forest with deciduous trees (birch -Betula pendula and aspen -Populus tremula) developed in the study area. The Younger Dryas (GS-1) cooling strongly affected the floral composition in eastern Latvia. The PAR of the tree taxa declined abruptly from a maximum value at 12,700 to below 1000 grains cm-2 yr-1 at 12,600 cal yr BP. The response time for the pine forest to collapse was 100 years according to the PAR data. Pine macrofossils disappear simultaneously with the pollen signal at 12,600 cal yr BP, yet occasional Pinus stomata are recorded throughout the Younger Dryas (GS-1). The landscape was treeless shrub tundra again, with D. octopetala, S. polaris, B. nana and Juniperus present. Picea is introduced in the region within the cold Younger Dryas and is represented by stomata (12,400-12,200 cal yr BP), needles, seeds and wood (since 12,050 cal yr BP up to the Holocene). The Pleistocene/Holocene boundary at 11,650 cal yr BP is marked by changes both in vegetation composition and sediment type. The organic rich gyttja accumulated instead of silts and clays, and the start of the Holocene warm period permitted forest re-expansion in eastern Latvia.

Evidence for a bi-partition of the Younger Dryas Stadial in East Asia associated with inversed climate characteristics compared to Europe.

PubMed

Schlolaut, Gordon; Brauer, Achim; Nakagawa, Takeshi; Lamb, Henry F; Tyler, Jonathan J; Staff, Richard A; Marshall, Michael H; Bronk Ramsey, Christopher; Bryant, Charlotte L; Tarasov, Pavel E

2017-03-31

The Younger Dryas Stadial (YDS) was an episode of northern hemispheric cooling which occurred within the Last Glacial Interglacial Transition (LGIT). A major driver for the YDS climate was a weakening of the Atlantic Meridional Overturning Circulation (AMOC). It has been inferred that the AMOC began to strengthen mid-YDS, producing a bipartite structure of the YDS in records from continental Europe. These records imply that the polar front and westerlies shifted northward, producing a warmer second phase of the YDS in Europe. Here we present multi-proxy data from the sediments of Lake Suigetsu (Japan), as evidence that a related bi-partition of the YDS also occurred in East Asia. Besides showing for the first time that the bi-partition was not limited to the North Atlantic/European region, the data also imply a climatic dipole between Europe and East Asia since the cold-warm characteristics are reversed at Lake Suigetsu. We suggest that changes in eastward moisture transport from the North Atlantic are the primary mechanism by which the teleconnection can be explained.

Deglacial and Holocene sea-ice variability north of Iceland and response to ocean circulation changes

NASA Astrophysics Data System (ADS)

Xiao, Xiaotong; Zhao, Meixun; Knudsen, Karen Luise; Sha, Longbin; Eiríksson, Jón; Gudmundsdóttir, Esther; Jiang, Hui; Guo, Zhigang

2017-08-01

Sea-ice conditions on the North Icelandic shelf constitute a key component for the study of the climatic gradients between the Arctic and the North Atlantic Oceans at the Polar Front between the cold East Icelandic Current delivering Polar surface water and the relatively warm Irminger Current derived from the North Atlantic Current. The variability of sea ice contributes to heat reduction (albedo) and gas exchange between the ocean and the atmosphere, and further affects the deep-water formation. However, lack of long-term and high-resolution sea-ice records in the region hinders the understanding of palaeoceanographic change mechanisms during the last glacial-interglacial cycle. Here, we present a sea-ice record back to 15 ka (cal. ka BP) based on the sea-ice biomarker IP25, phytoplankton biomarker brassicasterol and terrestrial biomarker long-chain n-alkanols in piston core MD99-2272 from the North Icelandic shelf. During the Bølling/Allerød (14.7-12.9 ka), the North Icelandic shelf was characterized by extensive spring sea-ice cover linked to reduced flow of warm Atlantic Water and dominant Polar water influence, as well as strong meltwater input in the area. This pattern showed an anti-phase relationship with the ice-free/less ice conditions in marginal areas of the eastern Nordic Seas, where the Atlantic Water inflow was strong, and contributed to an enhanced deep-water formation. Prolonged sea-ice cover with occasional occurrence of seasonal sea ice prevailed during the Younger Dryas (12.9-11.7 ka) interrupted by a brief interval of enhanced Irminger Current and deposition of the Vedde Ash, as opposed to abruptly increased sea-ice conditions in the eastern Nordic Seas. The seasonal sea ice decreased gradually from the Younger Dryas to the onset of the Holocene corresponding to increasing insolation. Ice-free conditions and sea surface warming were observed for the Early Holocene, followed by expansion of sea ice during the Mid-Holocene.

Pollen-based evidence of extreme drought during the last Glacial (32.6-9.0 ka) in coastal southern California

NASA Astrophysics Data System (ADS)

Heusser, Linda E.; Kirby, Matthew E.; Nichols, Jonathan E.

2015-10-01

High resolution pollen analyses of sediment core LEDC10-1 from Lake Elsinore yield the first well-dated, terrestrial record of sub-centennial-scale ecologic change in coastal southern California between ˜32 and 9 ka. In the Lake Elsinore watershed, the initial, mesic montane conifer forests dominated by Pinus, and Cupressaceae with trace amounts of Abies and Picea were replaced by a sequence of multiple, extended severe mega-droughts between ˜27.5 and ˜25.5 ka, in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake. This prolonged and extended dry interval, which corresponds with warm waters offshore, imply strengthening of the North Pacific High and persistent below-average winter precipitation. The subsequent, contrasting monotonic occurrence of montane conifers reflects little variation in cold, mesic climate until ˜15 ka. Postglacial development of Quercus woodland and chaparral mark the return to more xeric, warmer conditions at this time. A brief reversal at ˜13.1-˜12.1 ka, as reflected by an expansion of Pinus, is correlative with the Younger Dryas and interrupts development of warm, postglacial climate. Subsequent gradual expansion of xeric vegetation post - Younger Dryas denotes the establishment of a winter hydroclimate regime in coastal southern California that is more similar to modern conditions. Pollen-based reconstructions of temperature and precipitation at Lake Elsinore are generally correlative with pollen-based paleoclimatic reconstructions and foraminifera-based sea surface temperatures from Santa Barbara Basin in marine core ODP 893. The conspicuous absence of the ˜27.5-˜25.5 ka glacial "mega-drought" in the Santa Barbara Basin pollen record highlights the sensitivity of Lake Elsinore to hydroclimate change, and thus, the importance of this new record that indicates that mega-drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present.

Timing of last deglaciation in the Cantabrian Mountains (Iberian Peninsula; North Atlantic Region) based on in situ-produced 10Be exposure dating

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María José; Rinterknecht, Vincent; Pallàs, Raimon; Aumaître, Georges; Bourlès, Didier L.; Keddadouche, Karim; Aster Team

2017-09-01

The Last Glacial Termination led to major changes in ice sheet coverage that disrupted global patterns of atmosphere and ocean circulation. Paleoclimate records from Iberia suggest that westerly episodes played a key role in driving heterogeneous climate in the North Atlantic Region. We used 10Be Cosmic Ray Exposure (CRE) dating to explore the glacier response of small mountain glaciers (ca. 5 km2) that developed on the northern slope of the Cantabrian Mountains (Iberian Peninsula), an area directly under the influence of the Atlantic westerly winds. We analyzed twenty boulders from three moraines and one rock glacier arranged as a recessional sequence preserved between 1150 and 1540 m above sea level (a.s.l.) in the Monasterio valley (Redes Natural Park). Results complement previous chronologic data based on radiocarbon and optically stimulated luminescence from the Monasterio valley, which suggest a local Glacial Maximum (local GM) prior to 33 ka BP and a long-standing glacier advance at 24 ka coeval to the global Last Glacial Maximum (LGM). Resultant 10Be CRE ages suggest a progressive retreat and thinning of the Monasterio glacier over the time interval 18.1-16.7 ka. This response is coeval with the Heinrich Stadial 1, an extremely cold and dry climate episode initiated by a weakening of the Atlantic Meridional Overturning Circulation (AMOC). Glacier recession continued through the Bølling/Allerød period as indicate the minimum exposure ages obtained from a cirque moraine and a rock glacier nested within this moraine, which yielded ages of 14.0 and 13.0 ka, respectively. Together, they suggest that the Monasterio glacier experienced a gradual transition from glacier to rock glacier activity as the AMOC started to strengthen again. Glacial evidence ascribable to the Younger Dryas cooling was not dated in the Monasterio valley, but might have occurred at higher elevations than evidence dated in this work. The evolution of former glaciers documented in the Monasterio valley seems consistent with previous 10Be chronologies reported in other mountain ranges of the Iberian Peninsula, which have been recalculated according to a common production rate and scaling scheme. However, the re-evaluation of published 10Be chronologies has highlighted the fact that glacial evidence previously ascribed to the Younger Dryas might be more limited than previously thought and the need for additional studies to characterized the extent of glaciers during the Younger Dryas cooling.

Cold-climate slope deposits and landscape modifications of the Mid-Atlantic Coastal Plain, Eastern USA

USGS Publications Warehouse

Newell, Wayne L.; Dejong, B.D.

2011-01-01

The effects of Pleistocene cold-climate geomorphology are distributed across the weathered and eroded Mid-Atlantic Coastal Plain uplands from the Wisconsinan terminal moraine south to Tidewater Virginia. Cold-climate deposits and landscape modifications are superimposed on antecedent landscapes of old, weathered Neogene upland gravels and Pleistocene marine terraces that had been built during warm periods and sea-level highstands. In New Jersey, sequences of surficial deposits define a long history of repeating climate change events. To the south across the Delmarva Peninsula and southern Maryland, most antecedent topography has been obscured by Late Pleistocene surficial deposits. These are spatially variable and are collectively described as a cold-climate alloformation. The cold-climate alloformation includes time-transgressive details of climate deterioration from at least marine isotope stage (MIS) 4 through the end of MIS 2. Some deposits and landforms within the alloformation may be as young as the Younger Dryas. Southwards along the trend of the Potomac River, these deposits and their climatic affinities become diffused. In Virginia, a continuum of erosion and surficial deposits appears to be the product of ‘normal’ temperate, climate-forced processes. The cold-climate alloformation and more temperate deposits in Virginia are being partly covered by Holocene alluvium and bay mud.

Last Glacial Maximum and Lateglacial in the Polish High Tatra Mountains - Revised deglaciation chronology based on the 10Be exposure age dating

NASA Astrophysics Data System (ADS)

Makos, Michał; Rinterknecht, Vincent; Braucher, Régis; Tołoczko-Pasek, Anna; Arnold, Maurice; Aumaître, Georges; Bourlès, Didier; Keddadouche, Karim; Aster Team

2018-05-01

Deglaciation chronology of the Polish High Tatra Mountains has been reconstructed based on 10Be exposure age dating. Fifty-seven rock samples were collected from boulders located on the terminal and lateral moraines that limit the horizontal extent of the LGM and the Lateglacial glaciers in the Biała Woda and Sucha Woda catchments. The uncertainty-weighted mean age of 21.5 ± 2.5 ka obtained for the maximum terminal moraine in the Sucha Woda Valley indicates that the oldest preserved moraines were formed during the global LGM. The age population ranges between 15.1 ± 1.0 and 28.3 ± 2.0 ka, and suggests that glaciers reached their maximum position (LGM I) as early as 28-25 ka and the final stabilization of the form occurred much later possibly after melting of buried dead ice. The younger glacial oscillation (LGM II) occurred no later than 20.5 ka and is represented by well-preserved termino-lateral moraine systems in the Pańszczyca Valley. The first Lateglacial stage (LG1) in the study area is documented in the Rybi Potok Valley at the RP1 moraine (1300 m a.s.l.), which was stable at around 16.6 ± 0.3 ka. The younger LG2 stage has no defined absolute age, however, it is constrained between 16.5 and 15.5 ka by the timing of the LG3 stage. This cold event is represented by well-formed moraines in the Roztoka/Pięć Stawów Polskich, Rybi Potok and Pańszczyca valleys of which exposure age indicates their deposition between 15.0 ± 0.5 and 15.6 ± 0.1 ka. The LG1, LG2 and LG3 stages likely occurred during the Oldest Dryas cold stage (Greenland Stadial 2.1a) related to the North Atlantic cooling Heinrich Event 1. The youngest glacial oscillation is evidenced by moraines in the Pusta and Pańszczyca valleys. These moraines are composed of very large granitic blocks of which exposure ages often exhibit isotope inheritance. This is reflected by the youngest P3 moraine in the Pańszczyca Valley with a mean age of deposition close to the LGM. The R4 moraine system in the Pusta Valley, however, indicates two oscillations phases that occurred at around 13 ka and correlates well with the timing of RP5 moraine formation in the Za Mnichem Valley. The LG4 stage is related to the climate cooling during the Younger Dryas (Greenland Stadial 1). LGM ELAs reconstructed for the Biała Woda and Sucha Woda/Pańszczyca glaciers were located at 1460-1480 m a.s.l. During the Oldest Dryas stages, the ELA in the High Tatras rose from 1600 to 1650 m a.s.l. in the Rybi Potok Valley and from 1700 to 1800 m a.s.l. in the Roztoka/Pięć Stawów Polskich Valley. The Younger Dryas ELA, depending on glacier's exposition, was located between 1950 and 2000 m a.s.l. Climate modelling results show that the LGM glaciers (maximum advance) could have advanced in the High Tatras when the mean annual temperature was lower than today by 11-12 °C and precipitation was reduced by 40-60%. During the Lateglacial stages the temperature decrease in the study area changed from 10 °C during the Oldest Dryas to 6 °C during the Younger Dryas and precipitation lowering decreased from -50% to -30% or even -10%, respectively compare to modern conditions.

Human responses and non-responses to climatic variations during the last Glacial-Interglacial transition in the eastern Mediterranean

NASA Astrophysics Data System (ADS)

Roberts, Neil; Woodbridge, Jessie; Bevan, Andrew; Palmisano, Alessio; Shennan, Stephen; Asouti, Eleni

2018-03-01

We review and evaluate human adaptations during the last glacial-interglacial climatic transition in southwest Asia. Stable isotope data imply that climatic change was synchronous across the region within the limits of dating uncertainty. Changes in vegetation, as indicated from pollen and charcoal, mirror step-wise shifts between cold-dry and warm-wet climatic conditions, but with lag effects for woody vegetation in some upland and interior areas. Palaeoenvironmental data can be set against regional archaeological evidence for human occupancy and economy from the later Epipalaeolithic to the aceramic Neolithic. Demographic change is evaluated from summed radiocarbon date probability distributions, which indicating contrasting - and in some cases opposite - population trajectories in different regions. Abrupt warming transitions at ∼14.5 and 11.7 ka BP may have acted as pacemakers for rapid cultural change in some areas, notably at the start of the Natufian and Pre-Pottery Neolithic cultures. However temporal synchroneity does not mean that climatic changes had the same environmental or societal consequences in different regions. During cold-dry time intervals, regions such as the Levant acted as refugia for plant and animal resources and human population. In areas where socio-ecological continuity was maintained through periods of adverse climate (e.g. Younger Dryas) human communities were able to respond rapidly to subsequent climatic improvement. By contrast, in areas where there was a break in settlement at these times (e.g. central Anatolia), populations were slower to react to the new opportunities provided by the interglacial world.

Late Quaternary vegetation and climate history of the central Bering land bridge from St. Michael Island, western Alaska

USGS Publications Warehouse

Ager, T.A.

2003-01-01

Pollen analysis of a sediment core from Zagoskin Lake on St. Michael Island, northeast Bering Sea, provides a history of vegetation and climate for the central Bering land bridge and adjacent western Alaska for the past ???30,000 14C yr B.P. During the late middle Wisconsin interstadial (???30,000-26,000 14C yr B.P.) vegetation was dominated by graminoid-herb tundra with willows (Salix) and minor dwarf birch (Betula nana) and Ericales. During the late Wisconsin glacial interval (26,000-15,000 14C yr B.P.) vegetation was graminoid-herb tundra with willows, but with fewer dwarf birch and Ericales, and more herb types associated with dry habitats and disturbed soils. Grasses (Poaceae) dominated during the peak of this glacial interval. Graminoid-herb tundra suggests that central Beringia had a cold, arid climate from ???30,000 to 15,000 14C yr B.P. Between 15,000 and 13,000 14C yr B.P., birch shrub-Ericales-sedge-moss tundra began to spread rapidly across the land bridge and Alaska. This major vegetation change suggests moister, warmer summer climates and deeper winter snows. A brief invasion of Populus (poplar, aspen) occurred ca. 11,000-9500 14C yr B.P., overlapping with the Younger Dryas interval of dry, cooler(?) climate. During the latest Wisconsin to middle Holocene the Bering land bridge was flooded by rising seas. Alder shrubs (Alnus crispa) colonized the St. Michael Island area ca. 8000 14C yr B.P. Boreal forests dominated by spruce (Picea) spread from interior Alaska into the eastern Norton Sound area in middle Holocene time, but have not spread as far west as St. Michael Island. ?? 2003 University of Washington. Published by Elsevier Inc. All rights reserved.

Lake Level Changes in the Mono Basin During the Last Deglacial Period

NASA Astrophysics Data System (ADS)

Wang, X.; Ali, G.; Hemming, S. R.; Zimmerman, S. R. H.; Stine, S. W.; Hemming, G.

2014-12-01

Mono Basin, located in the southwestern corner of the US Great Basin, has long been known to have experienced large lake level changes, particularly during the last deglaciation. But until recently it was not possible to establish a reliable lake level time series. We discovered many visually clean, white, shiny, dense calcite samples in the basin, associated with tufa deposits from high terraces. Their low thorium, but high uranium contents allow precise and reproducible U/Th age determinations. A highly resolved history of a minimum lake level through the last deglaciation can therefore be inferred based on sample locations and their ages. We found that the lake level reached ~2030 m asl at ~20.4 ka, evidenced by calcite coatings on a tufa mound at the upper Wilson Creek. The lake then rose to ~2075 m by ~19.1 ka, shown by calcite cements on conglomerates from the Hansen Cut terrace. The lake climbed to at least ~2140 m at ~15.9 ka, indicated by beach calcites from the east Sierra slope. Such timing of the highest lake stand, occurring within Heinrich Stadial 1, is reinforced by U/Th dates on calcite coatings from widespread locations in the basin, including the Bodie Hills and Cowtrack Mountains. The lake then dropped rapidly to ~2075 m at ~14.5 ka. It stood near this height over the next ~300 years, evidenced by a few-centimeter thick, laminated calcite rims on the Goat Ranch tufa mounds. It subsequently plunged to ~2007 m at ~13.8 ka, indicated by calcite coatings from cemetery road tufa mounds. The lake level came back to ~2030 m at ~12.9 ka, as seen in upper Wilson Creek tufa mounds. The lake level had a few fluctuations within the Younger Dryas, and even shot up to ~2075 m at ~12.0 ka. It then fell to levels in accord with Holocene climatic conditions. Relative to the present lake level of ~1950 m, Mono Lake broadly stood high during Heinrich Stadial 1 and Younger Dryas, when the climate was extremely cold over the North Atlantic, and the Asian monsoon was much weakened. When the climate shifted from cold to warm, the lake dropped significantly, during the transition between Heinrich Stadial 1 and the Bølling time interval, and then during the Allerød period. The U/Th ages on the tufa samples therefore not only establish a highly resolved chronology of hydroclimate history in the Mono Basin, but also put the lake level oscillations in a global context.

Evidence for seasonal low salinity surface waters in the Gulf of Mexico over the last 16,000 years

NASA Astrophysics Data System (ADS)

Spero, Howard J.; Williams, Douglas F.

1990-12-01

Oxygen isotopic analyses of individual Orbulina universa from Orca Basin core EN32-PC6 document the presence of low salinity surface waters in the northern Gulf of Mexico over the past 16 kyr. Isotopic data from an interval immediately following the Younger Dryas Event indicate the rapid decrease in δ18O values at the conclusion of the Younger Dryas was due to a year-round return of meltwater to the Gulf of Mexico. Data indicate periodic or seasonal low-salinity waters existed over the region of the Orca Basin prior to the initiation of the meltwater spike. Estimates suggest O. universa grew its shell in salinities at least 4.5 ‰ below ambient. Since O. universa may have calcified deep in the mixed layer during periods of low salinity, surface salinities could have been even lower. Comparison of the average of individual O. universa oxygen isotopic values with data from multiple shell samples of white Gs. ruber from the same core samples demonstrates that the two species record similar values during the late Holocene. In contrast, O. universa records lower oxygen isotopic values during the late glacial/deglacial intervals, possibly due to differences in seasonal distribution or shell ontogeny between the two species.

A new concept for paleohydrological evolution of the Younger Dryas in NE Brazil

NASA Astrophysics Data System (ADS)

Bouimetarhan, Ilham; Prange, Matthias; Gonzalez, Catalina; Dupont, Lydie

2016-04-01

The late deglacial interval from approximately 13 to 11 kyr BP contains some of the best documented abrupt climate changes in the Past, the Younger Dryas (YD). It is also an interval when the bipolar climatic signature of millennial-scale changes in the Atlantic meridional overturning circulation (AMOC) is well expressed. Here we present a high-resolution palynological record from core GeoB16205-4 (1°21.11'N, 43°05.80'W), retrieved off the Parnaíba River mouth, southeast of the Amazon River (~1955 m water depth). Pollen and organic-walled dinoflagellate cyst assemblages indicate a predominantly wet climate during the YD in the nowadays semi-arid Nordeste, whereby a second phase between ~12.3 and 11.7 kyr BP is wetter than the period before. This is recorded by a strong increase in the concentrations of river plume dinoflagellate cyst assemblages indicative of a stratified surface water column and reduced salinity environments, as well as a drop in grass pollen and microcharcoal particle concentrations along with strong fluctuations in the representation of rain forest, gallery forest and tree ferns suggesting year-round humid conditions. This shift from a relatively wet first phase to a much wetter second phase is in agreement with the transient TRACE-21k coupled climate model simulation which shows a first pluvial Parnaíba stage from ~12.8 to 12.3 kyr BP and a second stronger pluvial stage between ~12.3 and 11.7 kyr BP to be related to a very weak AMOC due to meltwater pulses in the North Atlantic. The AMOC variation induces a steep temperature gradient between the Southern and the Northern Hemisphere which forces a southward shift of the Intertropical Convergence Zone (ITCZ) and its associated rainfall. The two-step hydroclimatic and environmental evolution during the Younger Dryas has not been documented previously in this region.

Minimal geological methane emissions during the Younger Dryas-Preboreal abrupt warming event.

PubMed

Petrenko, Vasilii V; Smith, Andrew M; Schaefer, Hinrich; Riedel, Katja; Brook, Edward; Baggenstos, Daniel; Harth, Christina; Hua, Quan; Buizert, Christo; Schilt, Adrian; Fain, Xavier; Mitchell, Logan; Bauska, Thomas; Orsi, Anais; Weiss, Ray F; Severinghaus, Jeffrey P

2017-08-23

Methane (CH 4 ) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions) and top-down approaches (measuring atmospheric mole fractions and isotopes) for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane ( 14 CH 4 ) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today, our results indicate that current estimates of today's natural geological methane emissions (about 52 teragrams per year) are too high and, by extension, that current estimates of anthropogenic fossil methane emissions are too low. Our results also improve on and confirm earlier findings that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas-Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates, permafrost and methane trapped under ice) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas-Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.

Minimal geological methane emissions during the Younger Dryas-Preboreal abrupt warming event

NASA Astrophysics Data System (ADS)

Petrenko, Vasilii V.; Smith, Andrew M.; Schaefer, Hinrich; Riedel, Katja; Brook, Edward; Baggenstos, Daniel; Harth, Christina; Hua, Quan; Buizert, Christo; Schilt, Adrian; Fain, Xavier; Mitchell, Logan; Bauska, Thomas; Orsi, Anais; Weiss, Ray F.; Severinghaus, Jeffrey P.

2017-08-01

Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions) and top-down approaches (measuring atmospheric mole fractions and isotopes) for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year) are too high and, by extension, that current estimates of anthropogenic fossil methane emissions are too low. Our results also improve on and confirm earlier findings that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas-Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates, permafrost and methane trapped under ice) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas-Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.

AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

NASA Astrophysics Data System (ADS)

Hajdas, Irena; Ivy, Susan D.; Beer, Jürg; Bonani, Georges; Imboden, Dieter; Lotted, André F.; Sturm, Michael; Suter, Martin

1993-12-01

For the extension of the radiocarbon calibration curve beyond 10000 14C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000 11000 14C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from 6000 to 12000 14C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230±140 14C y BP and 9407±44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986±69 cal y BP (Younger Dryas/Preboreal) and 1212±86 cal y BP (Alleröd/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 14C y BP, is estimated at 12350 ± 135 cal y BP. The oldest radiocarbon age of 14190±120 14C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000 12000 14C y BP) and the absolute time scale (11400 13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.

The Schmidt hammer as a relative-age dating tool and its potential for calibrated-age dating in Holocene glaciated environments

NASA Astrophysics Data System (ADS)

Shakesby, Richard A.; Matthews, John A.; Owen, Geraint

2006-11-01

The Schmidt hammer is a relatively cheap, portable, sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins. Early views were that its dating role was limited to distinguishing recently exposed from much older. Typically, either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied. More recently, calibration curves based on individual R-value means from small numbers (2-4) of sites of known ages have been used to estimate the ages of undated sites. We present Schmidt hammer rebound ( R-) values from 28 'Little Ice Age' (and younger), 23 Preboreal and 7 Younger Dryas glaciated surfaces in southern Norway in order, first, to test rigorously the robustness of the instrument as a relative-age dating tool. Despite being obtained from different surfaces (moraines, glaciofluvial deposits and bedrock) and varied metamorphic lithologies, the R-value overall means and 95% confidence intervals for the 'Little Ice Age', Preboreal and Younger Dryas age categories (respectively, 60.0±1.6, 41.6±1.4 and 34.2±2.0) are statistically significantly different. Only two outlying sites in the two younger age categories have overlapping confidence intervals, demonstrating remarkable robustness in differentiating early- and late-Holocene surfaces. The distinction between Preboreal and Younger Dryas sites (with terminal dates <2000 years apart) is less clear but still statistically significant, though possibly partly because of enhanced weathering conditions at the predominantly well vegetated Younger Dryas sites. Second, we examine the feasibility and desirability of controlling non-age-related factors, including some previously considered critical (instrument wear, operator bias, initial rock surface texture), which emerge either as less important than previously argued or as relatively unimportant, together with others previously unreported (e.g. long-term changes in lichen, soil, snow and vegetation covers). Third, we investigate the potential for calibrated-age dating by applying exploratory, linear rates of R-value decline to selected combinations of sites. The results suggest that error limits of ca ±700 to ±1600 years should be achievable over the Holocene timescale. This improved dating capability, however, will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages. Recommendations are made for a suitable sampling protocol for developing further the Schmidt hammer as a calibrated-age dating tool.

Lake ecosystem response to late Allerød climatic fluctuation (northern Poland)

NASA Astrophysics Data System (ADS)

Słowiński, Michał; Zawiska, Izabela; Ott, Florian; Noryśkiewicz, Agnieszka M.; Plessen, Birgit; Apolinarska, Karina; Lutyńska, Monika; Michczyńska, Danuta J.; Wulf, Sabine; Skubała, Piotr; Błaszkiewicz, Mirosław; Brauer, Achim

2014-05-01

The aim of this study is a better understanding, how local lake ecosystems responded to climate changes during the late Allerød - Younger Dryas transition. Therefore, we carried out a detailed high-resolution multi-proxy case study on the partly laminated sediments from the Trzechowskie palaeolake, located in the Pomeranian Lakeland, northern Poland (53°52'40"N, 18°12'93"E). We reconstructed the ecosystem response to climatic and environmental changes using biotic proxies (macrofossils, pollen, Cladocera, diatoms) and classical geochemical proxies (δ18O, δ13C, loss-on-ignition, CaCO3 content) in combination with high-resolution µ-XRF element core scanning. The core chronology has been established by biostratigraphy, AMS 14C-dating on plant macro remains, varve counting within the laminated intervals and the Laacher See Tephra (12880 varve yrs BP) as a precise isochrone. Framework of our investigation is a period covering 367 varve years of the late Allerød and the beginning of the Younger Dryas period where varve preservation gradually ceases. The pronounced changes at the late Allerød - Younger Dryas transition is well-reflected in all environmental indicators but with conspicuous leads and lags reflecting complex responses of lake ecosystems to climate variation. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association. The research was supported by the National Science Centre Poland (grants No. NN 306085037 and NCN 2011/01/B/ST10/07367).

Lithostratigraphy and microfacies analyses of the Lateglacial and early Holocene sediment record from Lake Haemelsee (Germany)

NASA Astrophysics Data System (ADS)

Haliuc, Aritina; Brauer, Achim; Dulski, Peter; Engels, Stefan; Lane, Christine

2015-04-01

Annually laminated sediments are unique continental archives holding essential paleoenvironmental and paleoclimatic information providing the opportunity (i) to evaluate the climate variability at inter-annual to decadal scale and (ii) to construct independent and reliable chronologies. Lake Haemelsee in northern Germany (19.5 m a.s.l) is a key site for tracing high-resolution climatic and environmental evolution in W Europe because of its partly varved sediments. Here, we apply lithostratigraphical, geochemical and micro-facies analyses for the bottom sediments (~1700 to 1300 cm sediment depth) in order to investigate the driving mechanisms, timing and amplitude of Lateglacial abrupt climate changes to the onset of the Holocene warming. Detailed investigation includes micro-facies analyses on petrographic thin sections combined with high-resolution µ-XRF element scanning on both fresh sediment core halves (200 µm resolution) and impregnated sediment blocks (50µm resolution). Based on these analyses, the sediment composite profile (378 cm) has been divided in ten lithozones, each exhibiting different sedimentation modes in response to regional and local climatic and environmental changes. Micro-facies analyses revealed that sediments consist of organic matter, siderite, calcite, clay/silt and sand. The basal sediments consist of glacio-fluvial material. Fine laminations are best preserved in lithozone 5 (1522-1573 cm), where minima in element proxies for detrital sediments (Ti, K, Si) and maxima in Fe and Mn indicate the prevalence of anoxic meromictic conditions. Three different varve facies types were distinguished: i) the clastic-organic varves are specific for the intervals 1571-1573 cm and 1536-1541 cm; ii) calcite/siderite-organic varves appear between 1568-1571 and 1541-1545 cm; iii) the siderite-organic varves are characteristic for the middle of the lithozone 5 spanning from 1545-1568 cm. These changes in varve facies reflect the complex answer of sedimentary conditions to climatic changes during Allerød and Allerød/Younger Dryas transition. An increased detrital sediment flux characterizes lithozone 6 and, most probably reflects the Younger Dryas cold interval. This interpretation is supported by the late Allerød Laacher See Tephra, an important chronostratigraphic marker horizon to link the floating 625 varve year chronology for the Allerød interstadial to an absolute time scale. Also, the preliminary pollen data provided the biostratigraphical information for establishing the lateglacial boundaries. Poorly preserved organic laminas are characteristic for lithozone 7 (1445-1474 cm). Our preliminary results demonstrate that the lake system responded sensitively to rapid and short-term climatic changes and these responses are well-expressed in sedimentological and geochemical variability.

Synchoronous inter-hemispheric alpine glacier advances during the Late Glacial?

NASA Astrophysics Data System (ADS)

Bakke, Jostein; Paasche, Øyvind

2016-04-01

The termination of the last glaciation in both hemispheres was a period of rapid climate swings superimposed on the overall warming trend, resulting from large-scale reorganizations of the atmospheric and oceanic circulation patterns in both hemispheres. Environmental changes during the deglaciation have been inferred from proxy records, as well as by model simulations. Several oscillations took place both in northern and southern hemispheres caused by melt water releases such as during the Younger Dryas in north and the Antarctic Cold Reversal in south. However, a consensus on the hemispheric linkages through ocean and atmosphere are yet to be reached. Here we present a new multi-proxy reconstruction from a sub-annually resolved lake sediment record from Lake Lusvatnet in Arctic Norway compared with a new reconstruction from the same time interval at South Georgia, Southern Ocean, suggesting inter-hemispheric climate linkages during the Bølling/Allerød time period. Our reconstruction of the alpine glacier in the lake Lusvatnet catchment show a synchronous glacier advance with the Birch-hill moraine complex in the Southern Alps, New Zealand during the Intra Allerød Cooling period. We propose these inter hemispheric climate swings to be forced by the northward migration of the southern Subtropical Front during the Antarctic Cold Reversal. Such a northward migration of the Subtropical Front is shown in model simulation and in palaeorecords to reduce the Agulhas leakage impacting the strength of the Atlantic meridional overturning circulation. We simply ask if this can be the carrier of rapid climate swings from one hemisphere to another? Our high-resolution reconstructions provide the basis for an enhanced understanding of the tiny balance between migration of the Subtropical Front in the Southern Ocean and the teleconnection to northern hemisphere.

Nanodiamonds and wildfire evidence in the Usselo horizon postdate the Allerød-Younger Dryas boundary

PubMed Central

van Hoesel, Annelies; Hoek, Wim Z.; Braadbaart, Freek; van der Plicht, Johannes; Pennock, Gillian M.; Drury, Martyn R.

2012-01-01

The controversial Younger Dryas impact hypothesis suggests that at the onset of the Younger Dryas an extraterrestrial impact over North America caused a global catastrophe. The main evidence for this impact—after the other markers proved to be neither reproducible nor consistent with an impact—is the alleged occurrence of several nanodiamond polymorphs, including the proposed presence of lonsdaleite, a shock polymorph of diamond. We examined the Usselo soil horizon at Geldrop-Aalsterhut (The Netherlands), which formed during the Allerød/Early Younger Dryas and would have captured such impact material. Our accelerator mass spectrometry radiocarbon dates of 14 individual charcoal particles are internally consistent and show that wildfires occurred well after the proposed impact. In addition we present evidence for the occurrence of cubic diamond in glass-like carbon. No lonsdaleite was found. The relation of the cubic nanodiamonds to glass-like carbon, which is produced during wildfires, suggests that these nanodiamonds might have formed after, rather than at the onset of, the Younger Dryas. Our analysis thus provides no support for the Younger Dryas impact hypothesis. PMID:22547791

Hunted gazelles evidence cooling, but not drying, during the Younger Dryas in the southern Levant

NASA Astrophysics Data System (ADS)

Hartman, Gideon; Bar-Yosef, Ofer; Brittingham, Alex; Grosman, Leore; Munro, Natalie D.

2016-04-01

The climatic downturn known globally as the Younger Dryas (YD; ∼12,900-11,500 BP) has frequently been cited as a prime mover of agricultural origins and has thus inspired enthusiastic debate over its local impact. This study presents seasonal climatic data from the southern Levant obtained from the sequential sampling of gazelle tooth carbonates from the Early and Late Natufian archaeological sites of Hayonim and Hilazon Tachtit Caves (western Galilee, Israel). Our results challenge the entrenched model that assumes that warm temperatures and high precipitation are synonymous with climatic amelioration and cold and wet conditions are combined in climatic downturns. Enamel carbon isotope values from teeth of human-hunted gazelle dating before and during the YD provide a proxy measure for water availability during plant growth. They reveal that although the YD was cooler, it was not drier than the preceding Bølling-Allerød. In addition, the magnitude of the seasonal curve constructed from oxygen isotopes is significantly dampened during the YD, indicating that cooling was most pronounced in the growing season. Cool temperatures likely affected the productivity of staple wild cereal resources. We hypothesize that human groups responded by shifting settlement strategies-increasing population mobility and perhaps moving to the warmer Jordan Valley where wild cereals were more productive and stable.

Precipitation variability in East Timor during Younger Dryas

NASA Astrophysics Data System (ADS)

Chen, J.; Shen, C.; Mii, H.; Sone, T.; Lin, Y.; Chen, Y.

2012-12-01

Here we present a δ18O record of stalagmite collected from Lekiraka cave, East Timor ( 8o47'10.8"S, 126o23'31.1"E; 626 m above sea level). This stalagmite stable oxygen isotope record, covering an age interval of 13.5-10.8 thousand years ago (ka, before 1950 AD) by an age model using 230Th dates. Featured with an increasing precipitation trend during Younger Dryas (YD), this record is similar to the Gunung Buda cave record in Borneo(Partin et al., Nature, 2007, 449, 452-455) and Liang Luar cave record from Flores(Griffiths et al., Nature Geosciences, 2009, 2, 636-639). However, the detailed YD precipitation variability in Lekiraka record is not completely consistent with that in the nearby Liang Luar record with a precipitation maximum at ~12.4 ka. We propose the intensified precipitation in YD period was attributed to an enhanced Australian-Indonesian summer monsoon and was responded to sea level rise and a southward shift of Intertropical Convergence Zone (ITCZ), which was driven by oceanic/atmospheric circulation change originally from the North Atlantic at the YD.

Younger Dryas Age advance of Franz Josef Glacier in the Southern Alps of New Zealand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denton, G.H.; Hendy, C.H.

1994-06-03

A corrected radiocarbon age of 11,050 [+-] 14 years before present for an advance of the Franz Josef Glacier to the Waiho Loop terminal moraine on the western flank of New Zealand's Southern Alps shows that glacier advance on a South Pacific island was synchronous with initiation of the Younger Dryas in the North Atlantic region. Hence, cooling at the beginning of the Younger Dryas probably reflects global rather than regional forcing. The source for Younger Dryas climatic cooling may thus lie in the atmosphere rather than in a North Atlantic thermohaline switch. 36 refs., 2 figs., 1 tab.

Identification of contrasting seasonal sea ice conditions during the Younger Dryas

NASA Astrophysics Data System (ADS)

Cabedo-Sanz, P.; Belt, S. T.; Knies, J.

2012-12-01

The presence of the sea ice diatom biomarker IP25 in Arctic marine sediments has been used in previous studies as a proxy for past spring sea ice occurrence and as an indicator of wider palaeoenvironmental conditions for different regions of the Arctic over various timescales [e.g. 1, 2]. The current study focuses on high-resolution palaeo sea ice reconstructions for northern Norway during the last ca. 15 cal. kyr BP. Within this study, particular emphasis has been placed on the identification of the sea ice conditions during the Younger Dryas and the application of different biomarker-based proxies to both identify and quantify seasonal sea ice conditions. Firstly, the appearance of the specific sea ice diatom proxy IP25 at ca. 12.9 cal. kyr BP in a marine sediment core (JM99-1200) obtained from Andfjorden has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the Younger Dryas stadial. The near continuous occurrence of IP25 for the next ca. 1400 yr demonstrates seasonal sea ice during this interval, although variable abundances suggest that the recurrent conditions in the early-mid Younger Dryas (ca. 12.9 - 11.9 cal. kyr BP) changed significantly from stable to highly variable sea ice conditions at ca. 11.9 cal. kyr BP and this instability in sea ice prevailed for the subsequent ca. 400 yr. At ca. 11.5 cal. kyr BP, IP25 disappeared from the record indicating ice-free conditions that signified the beginning of the Holocene. Similarly, a high resolution record from the Kveithola Through, western Barents Sea, showed clearly higher IP25 concentrations during the Younger Dryas stadial compared to the Holocene. For both marine records, the IP25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate PBIP25 data from which more quantitative measurements of sea ice were determined. The contrasting seasonal sea ice conditions during the Younger Dryas were further verified through a comparison of the concentrations of IP25 with those of another highly branched isoprenoid (HBI) alkene that is di-unsaturated and believed to also be produced by sea ice diatoms. The ratio of the HBI diene to IP25, termed DIP25, is believed to provide a useful indicator of stability or variability in sea ice conditions and complements the outcomes from the IP25 and PBIP25 index data. 1. Belt, S.T., Vare, L.L., Massé, G., Manners, H.R., Price, J.C., MacLachlan, S.E., Andrews, J.T. , Schmidt, S., 2010. Striking similarities in temporal changes to spring sea ice occurrence across the central Canadian Arctic Archipelago over the last 7000 years. Quaternary Science Reviews 29, 3489-3504. 2. Müller, J., Massé, G., Stein, R., Belt, S.T., 2009. Variability of sea-ice conditions in the Fram Strait over the past 30,000 years. Nature Geoscience 2, 772-776.

High-resolution IP25-based reconstruction of sea-ice variability in the western North Pacific and Bering Sea during the past 18,000 years

NASA Astrophysics Data System (ADS)

Méheust, Marie; Stein, Ruediger; Fahl, Kirsten; Max, Lars; Riethdorf, Jan-Rainer

2016-04-01

Due to its strong influence on heat and moisture exchange between the ocean and the atmosphere, sea ice is an essential component of the global climate system. In the context of its alarming decrease in terms of concentration, thickness and duration, understanding the processes controlling sea-ice variability and reconstructing paleo-sea-ice extent in polar regions have become of great interest for the scientific community. In this study, for the first time, IP25, a recently developed biomarker sea-ice proxy, was used for a high-resolution reconstruction of the sea-ice extent and its variability in the western North Pacific and western Bering Sea during the past 18,000 years. To identify mechanisms controlling the sea-ice variability, IP25 data were associated with published sea-surface temperature as well as diatom and biogenic opal data. The results indicate that a seasonal sea-ice cover existed during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas during warmer intervals (Bølling-Allerød and Holocene) reduced sea ice or ice-free conditions prevailed in the study area. The variability in sea-ice extent seems to be linked to climate anomalies and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea, especially the Alaskan Stream injection though the Aleutian passes.

Indications of a pan-hemispheric bi-partition of the Younger Dryas Stadial from Lake Suigetsu, Japan

NASA Astrophysics Data System (ADS)

Schlolaut, Gordon; Brauer, Achim; Nakagawa, Takeshi; Lamb, Henry; Marshall, Michael; Kato-Saito, Megumi; Staff, Richard; Bronk Ramsey, Christopher; Bryant, Charlotte

2016-04-01

The Younger Dryas Stadial marks the final succession of climatic fluctuations of the last Glacial. Whilst well studied in records from Europe and Greenland, few high resolution records are available from East Asia. Here we present a high resolution, multi-proxy study of the Lake Suigetsu (Japan) sediments using the 'SG06' composite profile. Utilising microfacies, μXRF, pollen and diatom analysis we characterise changes occurring in the timeframe corresponding to the Younger Dryas Stadial. Firstly, our results show that the climatic equivalent of the Younger Dryas at Lake Suigetsu shows no major lead or lag in comparison to records from the North Atlantic region, which was postulated by an earlier project on the Suigetsu sediments ('SG93'). Reason for this disagreement between the SG06 and SG93 core is that the SG93 core/chronology was compromised by gaps between individual cores and varve count uncertainties. Furthermore, some of the analysed proxies from the SG06 core show a sub-division of the Younger Dryas Stadial. The timing of this sub-division is similar to the bi-partition of the Younger Dryas Stadial observed in a number of European records (e.g. Lane et al., 2013). This bi-partition was related to a northward shift of the westerly wind jet in the North Atlantic region. Our findings imply that the underlying climatic mechanism operated on a hemispheric rather than just on a regional scale. References: Lane et al. 2013, Volcanic ash reveals time-transgressive abrupt climate change during the Younger Dryas, Geology 41, 1251-1254

Younger Dryas glacial stillstands on the Bolivian Altiplano: pattern and climatic implications

NASA Astrophysics Data System (ADS)

Martin, Léo; Blard, Pierre-Henri; Lave, Jérôme; Premaillon, Melody; Charreau, Julien; Jomelli, Vincent; Brunstein, Daniel

2014-05-01

Modifications of the global climate during the last deglaciation have been characterized by regional reorganization that may have in turn amplified or attenuated the global changes. Notably, the respective influences of the Southern and Northern Hemispheres are poorly understood in the Tropics. This underlines the importance of studying past climate variations in the Tropics, particularly in the poorly documented tropical moutain areas. Cosmogenic exposure dating applied to the glacial landscapes provides temporal constraints on glacier fluctuations in response of climate variations. This permits high-resolution reconstructions of regional climates. In this work we present new cosmogenic ages from two different locations of the Bolivian Altiplano, the Nevado Sajama volcano (S18.11° - W66.88°) and the Zongo Valley (S16.25°- W68.11°). On the Sajama, new cosmogenic 3He dates support a late local glacial maximum, synchronous with the plaeolake Tauca highstand (ca. 16 ka) and contemporary to the north Atlantic Heinrich 1 (H1) event, with an equilibrium line altitude (ELA) at ca. 5200 m. Our data document also several recession episodes with the youngest one, characterized by an ELA of 5350 m, that seems to correspond to the Younger Dryas (YD) stadial (ca. 12 ka). In the Zongo valley, two recessional moraines have indistinguishable cosmogenic 10Be ages of ca. 17 ka, synchronous with the transgression of the Lake Tauca, with respective ELA of 4760 and 4640 m. Upstream, we identified an intermediate recessional moraine that could either be synchronous with Heinrich 1 or with the Antarctic Cold Reversal episode. Upward along the valley, a Younger Dryas stadial is clearly established by well-clustered cosmogenic 10Be ages, yielding a moraine age of ca. 12 ka, contemporary with the paleolake Coipasa highstand, with an ELA of 5000 m. These results confirm the sensitivity of South Hemisphere tropical glaciers to North Atlantic climate events, such as H1 or the YD. These glacial stadials are probably strongly driven by the wet conditions that prevailed during the central Altiplano palaeolake episodes. The identification of a Younger Dryas stadial in the Zongo valley, and also probably on the Sajama and Tunupa volcanoes (dating dupliquates are still in progress), is an unprecedented report in this region. During the YD event, the ELAs were ~150m (Sajama) to ~300 m (Tunupa, Zongo valley) higher than during the H1 event. Whereas glaciers advances and paleolake data indicate that the YD in the tropical Altiplano was characterized by higher temperature and lower precipitation than during H1, the climatic conditions during the YD in the Southern Tropics must have been far colder and wetter than today. Indeed, present day ELAs are more than 400 m higher in the Zongo, and more than 600 m higher in the Sajama and the Tunupa than they were during the Younger Dryas.

Eastern Pacific cooling and Atlantic overturning circulation during the last deglaciation.

PubMed

Kienast, Markus; Kienast, Stephanie S; Calvert, Stephen E; Eglinton, Timothy I; Mollenhauer, Gesine; François, Roger; Mix, Alan C

2006-10-19

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America, as well as the Indian and East Asian monsoon systems, but not with tropical Pacific sea surface temperatures. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of approximately 1 degrees C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of approximately 0.5 degrees C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean-atmosphere interaction as suggested before.

Glacial cold-water coral growth in the Gulf of Cádiz: Implications of increased palaeo-productivity

NASA Astrophysics Data System (ADS)

Wienberg, Claudia; Frank, Norbert; Mertens, Kenneth N.; Stuut, Jan-Berend; Marchant, Margarita; Fietzke, Jan; Mienis, Furu; Hebbeln, Dierk

2010-10-01

A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial-interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.

Warm ocean surface led to ice margin retreat in central-eastern Baffin Bay during the Younger Dryas

NASA Astrophysics Data System (ADS)

Oksman, Mimmi; Weckström, Kaarina; Miettinen, Arto; Juggins, Stephen; Divine, Dmitry; Jackson, Rebecca; Korsgaard, Niels J.; Telford, Richard; Kucera, Michal

2017-04-01

The Greenland ice sheet stability is linked to fast-flowing ice streams that are influenced by sea surface temperatures (SSTs) at their front. One of the largest ice streams in West Greenland is the Jakobshavn Isbræ, which has been shown to have collapsed at ca. 12.2 kyr BP in the middle of the Younger Dryas (YD) cold period (12.9-11.7 kyr BP). The cause for this collapse is still unknown yet hypotheses, such as warm Atlantic water inflow, have been put forward to explain it. Here we present the first diatom-based high-resolution reconstruction of sea surface conditions in the central-eastern Baffin Bay between 14.0 and 10.2 kyr BP. The sea surface temperatures reveal warmer conditions beginning at ca. 13.4 kyr BP and leading to intensive calving and iceberg discharge from Jakobshavn Isbræ visible as increased sedimentation rates and deposition of coarse-grained material in our sediment stratigraphy. The warm YD ocean surface conditions in Baffin Bay are out of phase with the δ18O record from the North Greenland Ice Core Project (NGRIP) and other SST records from northern North-Atlantic. We show that the ocean has had significant interactions with the Greenland ice sheet in the past and emphasize its importance under the current warming of the North Atlantic.

Evidences of melting of terrestrial sediments and paleoenvironment changes during the Younger Dryas in tectonic lacustrine basins of Transmexican Volcanic Belt, Mexico.

NASA Astrophysics Data System (ADS)

Israde-Alcantara, I.

2017-12-01

It is well known in the sedimentary record of several parts of the world that during the Younger Dryas interval (YD) ocurred an abrupt environmental change between 12,900 and 11,700 cal yr BP (10,900 to 10,000 14C BP). In the lacustrine basins this changes are often preserved and in some Mexican lakes this is a distinctive stratigraphic marker for the YD. We analized the proxies of this event in cores of two lakes (Chapala, Cuitzeo) and three trenches of ex-lakes (Acambay,Texcoco and El Cedral). Deposits consist of fine detrital material with often Pleistocene fossil vertebrate assemblages. At the Chapala, Cuitzeo, Acambay, and Tocuila lacustrine environments are found in association with a distinctive dark organic layer showing sharp changes in the diatom, pollen, mineralogical and geochemical record. Includes also microscopic magnetic, Fe-rich spherules, silica melted droplets with aerodynamic shapes (tektites), followed by large amounts of charcoal, and sometimes nanodiamonds (Cuitzeo), that were deposited at the onset of the YD or in the limit Pleistocene-Holocene. These unusual materials are buried more than 2.50 meters and were not observed above or below the Younger Dryas sediments at these sites. The geochemistry of the microspherules indicates that they are not volcanic, anthropogenic or authigenic origin. A very distinctive feature is the shape of the spherules, ovoid, polygonal, filigreed or dendritic indicating melting and quenching infering that are product of an impact event. Their morphologies includes hollow shells caused by de-gassing of elements at very high temperatures causing a flattened side with a "skirt" structure by a high-velocity collision.Our results are consistent with the Firestone hypothesis.

Reply to comment by E. Bard et al. on "Younger Dryas sea level and meltwater pulse 1B recorded in Barbados reef crest coral Acropora palmata" by N. A. Abdul et al.

NASA Astrophysics Data System (ADS)

Mortlock, Richard A.; Abdul, Nicole A.; Wright, James D.; Fairbanks, Richard G.

2016-12-01

Abdul et al. (2016) presented a detailed record of sea level at Barbados (13.9-9 kyr B.P.) tightly constraining the timing and amplitude during the Younger Dryas and Meltwater Pulse 1B (MWP-1B) based on U-Th dated reef crest coral species Acropora palmata. The Younger Dryas slow stand and the large (14 m) rapid sea level jump are not resolved in the Tahiti record. Tahiti sea level estimates are remarkably close to the Barbados sea level curve between 13.9 and 11.6 kyr but fall below the Barbados sea level curve for a few thousand years following MWP-1B. By 9 kyr the Tahiti sea level estimates again converge with the Barbados sea level curve. Abdul et al. (2016) concluded that Tahiti reefs at the core sites did not keep up with intervals of rapidly rising sea level during MWP-1B. We counter Bard et al. (2016) by showing (1) that there is no evidence for a hypothetical fault in Oistins Bay affecting one of the Barbados coring locations, (2) that the authors confuse the rare occurrences of A. palmata at depths >5 m with the "thickets" of A. palmata fronds representing the reef-crest facies, and (3) that uncertainties in depth habitat proxies largely account for differences in Barbados and Tahiti sea level differences curves with A. palmata providing the most faithful proxy. Given the range in Tahiti paleodepth uncertainties at the cored sites, the most parsimonious explanation remains that Tahiti coralgal ridges did not keep up with the sea level rise of MWP-1B.

The Big Chills

NASA Astrophysics Data System (ADS)

Bond, G. C.; Dwyer, G. S.; Bauch, H. A.

2002-12-01

At the end of the last glacial, the Earth's climate system abruptly shifted into the Younger Dryas, a 1500-year long cold snap known in the popular media as the Big Chill. Following an abrupt warming ending the Younger Dryas about 11,600 years ago, the climate system has remained in an interglacial state, thought to have been relatively stable and devoid, with possibly one or two exceptions, of abrupt climate change. A growing amount of evidence suggests that this benign view of interglacial climate is incorrect. High resolution records of North Atlantic ice rafted sediment, now regarded as evidence of extreme multiyear sea ice drift, reveal abrupt shifts on centennial and millennial time scales. These have been traced from the end of the Younger Dryas to the present, revealing evidence of significant climate variability through all of the last two millennia. Correlatives of these events have been found in drift ice records from the Arctic's Laptev Sea, in the isotopic composition of North Grip ice, and in dissolved K from the GISP2 ice core, attesting to their regional extent and imprint in proxies of very different origins. Measurements of Mg/Ca ratios in planktic foraminifera over the last two millennia in the eastern North Atlantic demonstrate that increases in drifting multiyear sea ice were accompanied by abrupt decreases in sea surface temperatures, especially during the Little Ice Age. Estimated rates of temperature change are on the order of two degrees centigrade, more than thirty percent of the regional glacial to interglacial change, within a few decades. When compared at the same resolution, these interglacial variations are as abrupt as the last glacial's Dansgaard-Oeschger cycles. The interglacial abrupt changes are especially striking because they occurred within the core of the warm North Atlantic Current. The changes may have been triggered by variations in solar irradiance, but if so their large magnitude and regional extent requires amplifying mechanisms that have not yet been identified. While the Younger Dryas event is dramatic, the Big Chills of the Holocene are clearly significant abrupt changes in their own right. Because they were a recurring feature of the interglacial climate we live in presently, they are especially relevant to the prediction of sudden changes in the future, more so probably than abrupt changes during the last glacial which took place within boundary conditions that are not likely to occur again soon, perhaps within tens of thousands of years.

A Tree-Ring Chronology and Paleoclimate Record for the Younger Dryas-Early Holocene Transition from Northeastern North America

NASA Technical Reports Server (NTRS)

Griggs, Carol; Peteet, Dorothy; Kromer, Bernd; Grote, Todd; Southon, John

2017-01-01

Spruce and tamarack logs dating from the Younger Dryas and Early Holocene (YDEH; approx. 12.9 - 11.3k cal a BP) were found at Bell Creek in the Lake Ontario lowlands of the Great Lakes region, North America. A 211-year tree-ring chronology dates to approx. 11 755 -11 545 cal a BP, across the YDEH transition. A 23-year period of higher year-to-year ring-width variability dates to around 11 650 cal a BP, infers strong regional climatic perturbations and may represent the end of the YD. Tamarack and spruce were dominant species throughout the YD - EH interval at the site, indicating that boreal conditions persisted into the EH, in contrast to geographical regions immediately south and east of the lowlands, but consistent with the Great Lakes interior lowlands. This infers that Bell Creek was at the eastern boundary of a boreal ecotone, perhaps a result of its lower elevation and the non-analog dynamics of the Laurentide Ice Sheet. This finding suggests that the ecotone boundary extended farther east during the YD - EH transition than previously thought.

North Atlantic Storm Activity During the Younger Dryas

NASA Astrophysics Data System (ADS)

Toomey, M.

2015-12-01

The risks posed to cities along the Eastern Seaboard by a potential intensification of tropical cyclone activity over the coming decades remain poorly constrained, in part, due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Previous work in the Bahamas shows that coarse-grained, high-energy event layers in carbonate bank margin sediments: (1) closely track recent historic hurricane events and (2) that the sensitivity of this proxy may be less affected by the deglacial changes in sea level that have limited our ability to reconstruct past hurricane activity using overwash records from back-barrier beach settings. Here we present a record of storm triggered turbidite deposition from a suite of well dated (e.g. Lynch-Stieglitz et al., 2011, Paleoceanography) jumbo piston cores taken offbank (300-500 mbsl) the Dry Tortugas, Florida, that spans abrupt transitions in North Atlantic sea surface temperature and thermohaline circulation during the Younger Dryas (12.9 - 11.5 kyr BP). This record, along with General Circulation Model output (TraCE: NCAR-CGD), indicates strong hurricane activity may have occurred along Southeastern US coasts through this interval despite considerably colder North Atlantic SSTs.

First Younger Dryas moraines in Greenland

NASA Astrophysics Data System (ADS)

Funder, Svend; Larsen, Nicolaj K.; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Kjær, Kurt H.; Xu, Sheng

2016-04-01

Over the Greenland ice sheet the Younger Dryas (YD) cold climate oscillation (12.9-11.7 kaBP) began with up to 10°C drop in temperatures and ended with up to 12°C abrupt warming. In the light of the present warming and melting of the ice sheet, and its importance for future climate change, the ice sheet's response to these dramatic changes in the past is of great interest. However, even though much effort has gone into charting YD ice margin behaviour around Greenland in recent years, no clear-cut signal of response to the oscillation has been uncovered. Here we show evidence to suggest that three major outlets from a local ice cap at Greenland's north coast advanced and retreated synchronously during YD. The evidence comprises OSL (optically stimulated luminescence) dates from a marine transgression of the coastal valleys that preceded the advance, and exposure ages from boulders on the moraines, formed by glaciers that overrode the marine sediment. The OSL ages suggest a maximum age of 12.4 ±0.6 kaBP for the marine incursion, and 10 exposure ages on boulders from the three moraines provide an average minimum age of 12.5 ±0.7 kaBP for the moraines, implying that the moraines were formed within the interval 11.8-13.0 kaBP. Elsewhere in Greenland evidence for readvance has been recorded in two areas. Most notably, in the East Greenland fjord zone outlet glaciers over a stretch of 800 km coast advanced through the fjords. In Scoresby Sund, where the moraines form a wide belt, an extensive 14C and exposure dating programme has shown that the readvance here probably culminated before YD, while cessation of moraine formation and rapid retreat from the moraine belt did not commence until c. 11.5 kaBP, but no moraines have so far been dated to YD. Readvance is also seen in Disko Bugt, the largest ice sheet outlet in West Greenland. However, here the advance and retreat of the ice stream took place in mid YD times, and lasted only a few hundred years, while YD in general was characterised by large scale, more than 200 km, retreat on the shelf. Therefore, although readvance and retreat occurred in both areas, the readvance was apparently not triggered by the initial YD cooling nor was the retreat caused by the abrupt warming at the end. At all other sites with a record that run through or into YD - Southeast Greenland, South Greenland, northern West Greenland - the ice margins were apparently retreating through YD, leaving the north coast as the only area with evidence for a climatically conditioned YD readvance/retreat. The apparent mismatch between ice core temperatures and ice margin behaviour is generally seen as a function of reduced AMOC (Atlantic Meridional Overturning Circulation), inducing both higher seasonality with very cold winters and warm summers, and also occurrence of warm subsurface water to melt the ice sheet margin along some coasts. Therefore the ice margin response to the cold oscillation was to some extent determined by the nearness to the North Atlantic - with North Greenland being the farthest away. Although this may explain why glaciers advanced in North Greenland, while they melted in more southerly parts, it still leaves the question with a bearing on the future: why don't we see any ice margin response neither to the initial YD cooling, nor to the abrupt warming at the end?

Tropical climate changes at millennial and orbital timescales on the Bolivian Altiplano.

PubMed

Baker, P A; Rigsby, C A; Seltzer, G O; Fritz, S C; Lowenstein, T K; Bacher, N P; Veliz, C

2001-02-08

Tropical South America is one of the three main centres of the global, zonal overturning circulation of the equatorial atmosphere (generally termed the 'Walker' circulation). Although this area plays a key role in global climate cycles, little is known about South American climate history. Here we describe sediment cores and down-hole logging results of deep drilling in the Salar de Uyuni, on the Bolivian Altiplano, located in the tropical Andes. We demonstrate that during the past 50,000 years the Altiplano underwent important changes in effective moisture at both orbital (20,000-year) and millennial timescales. Long-duration wet periods, such as the Last Glacial Maximum--marked in the drill core by continuous deposition of lacustrine sediments--appear to have occurred in phase with summer insolation maxima produced by the Earth's precessional cycle. Short-duration, millennial events correlate well with North Atlantic cold events, including Heinrich events 1 and 2, as well as the Younger Dryas episode. At both millennial and orbital timescales, cold sea surface temperatures in the high-latitude North Atlantic were coeval with wet conditions in tropical South America, suggesting a common forcing.

Lacustrine Basal Ages Constrain the Last Deglaciation in the Uinta Mountains, Utah, USA

NASA Astrophysics Data System (ADS)

Munroe, Jeffrey; Laabs, Benjamin

2013-04-01

Basal radiocarbon ages from 21 high-elevation lakes limit the timing of final Pleistocene deglaciation in the Uinta Mountains of northeastern Utah, USA. The lakes are located in glacial valleys and cirques 5 to 20 km upstream from LGM terminal moraines at elevations from 2830 to 3475 m. Many are impounded behind recessional moraines. Cores were retrieved from a floating platform with a percussion corer driven to the point of refusal. All penetrated inorganic silty clay beneath gyttja. AMS radiocarbon analyses were made on terrestrial macrofossils, daphnia ephippia, pollen concentrates, and bulk sediment retrieved from the base of each core. No radiocarbon reservoir effect was observed when bulk dates were checked against terrestrial material. Radiocarbon results were converted to calendar years using the IntCal09 calibration curve in OxCal 4.1. Given the stratigraphy observed in the cores, these calibrated basal ages are considered close limits on the timing of the local deglaciation and lake formation. The oldest three lakes have basal radiocarbon ages that calibrate to a few centuries after the Bölling/Alleröd warming, indicating that the landscape was becoming ice free at this time. These are followed by an overlapping group of five lakes with basal ages between 13.5 and 13.0 ka BP. Five more cores, from four separate lakes, have basal ages tightly clustered between 13.0 and 12.5 ka BP. Three of these lakes are dammed by moraines, suggesting glacial activity during the early part of the Younger Dryas interval. The lone kettle lake in the study yielded a basal age of 12.3 ka BP, considerably younger than the basal age of 13.9 ka BP from a nearby lake filling a bedrock basin, indicating that buried ice may have been locally stable for more than a millennium after deglaciation. The remaining seven lakes have basal ages between 12.0 and 11.0 ka BP. Four of these lakes are also dammed by moraines. These two non-overlapping clusters of basal ages for moraine-dammed lakes, with maximum probabilities ca. 12.7 and 11.3 ka BP, suggest that active glaciers were present in the Uinta Mountains during the Younger Dryas, and that Younger Dryas glacier activity was concentrated in two separate intervals.

Termination-II interstadial/stadial climate change recorded in two stalagmites from the north European Alps

NASA Astrophysics Data System (ADS)

Moseley, Gina E.; Spötl, Christoph; Cheng, Hai; Boch, Ronny; Min, Angela; Edwards, R. Lawrence

2015-11-01

Understanding the sequence of events that take place during glacial-interglacial climate transitions is important for improving our knowledge of abrupt climate change. Here, we present a new stacked, high-resolution, precisely-dated speleothem stable isotope record from the northern Alps, which provides an important record of temperature and moisture-source changes between 134 and 111 ka for Europe and the wider North Atlantic realm. The record encompasses the penultimate deglaciation (Termination II (TII)), which lies beyond the limit of radiocarbon dating, thus providing an important new archive for a crucial period of rapid paleoclimate change. Warmer and wetter ice-free conditions were achieved by 134.1 ± 0.7 ka (modelled ages) as indicated by the presence of liquid water at the site. Temperatures warmed further at 133.7 ± 0.5 ka and led into an interstadial, synchronous with slightly elevated monsoon strength during the week monsoon interval. The interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in Atlantic Meridional Overturning Circulation (AMOC) and a reduction in North Atlantic Deep Water (NADW) formation. The interstadial ended with a more extreme cold reversal lasting 500 years in which NADW formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards. The main warming associated with TII was very rapid, taking place between 130.9 ± 0.9 and 130.7 ± 0.9 ka coeval with initial monsoon strengthening. Temperatures then plateaued before being interrupted by a 600-year cold event at 129.1 ± 0.6 ka, associated once again with penetration of polar waters southwards into the North Atlantic and a slowdown in monsoon strengthening. Sub-orbital climate oscillations were thus a feature of TII in the north Atlantic realm, which broadly resemble the Bølling/Allerød-Younger Dryas-8.2 ka event pattern of change observed in Termination I despite monsoon records indicating strong differences between the last and penultimate deglaciation.

Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

PubMed Central

Kennett, James P.; Kennett, Douglas J.; Culleton, Brendan J.; Aura Tortosa, J. Emili; Bischoff, James L.; Bunch, Ted E.; Daniel, I. Randolph; Erlandson, Jon M.; Ferraro, David; Firestone, Richard B.; Goodyear, Albert C.; Israde-Alcántara, Isabel; Johnson, John R.; Jordá Pardo, Jesús F.; Kimbel, David R.; LeCompte, Malcolm A.; Lopinot, Neal H.; Mahaney, William C.; Moore, Andrew M. T.; Moore, Christopher R.; Ray, Jack H.; Stafford, Thomas W.; Tankersley, Kenneth Barnett; Wittke, James H.; Wolbach, Wendy S.; West, Allen

2015-01-01

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835–12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer. PMID:26216981

The record of deglaciation in the Sulu Sea: Evidence for the Younger Dryas Event in the tropical western Pacific

NASA Astrophysics Data System (ADS)

Linsley, Braddock K.; Thunell, Robert C.

1990-12-01

A high-resolution, accelerator mass spectroscopy 14C dated sediment record from the Sulu Sea clearly indicates that the Younger Dryas event affected the western equatorial Pacific. Planktonic foraminiferal δ18O and abundance data both record significant changes during Younger Dryas time. In particular, a 0.4‰ increase in the δ18O value of Globigerinoides ruber and the reappearance of the cool water planktonic foraminifera, Neogloboquadrina pachyderma, occur during the Younger Dryas at this location. These isotopic and faunal changes are a response to either surface water temperature or salinity changes, or some combination of the two. Changes in surface salinities could have been accomplished through either local or global processes. Intensification of the monsoon climate system and increased precipitation at approximately 11 ka is one mechanism that may have resulted in local changes in salinity. A meltwater pulse derived from the Tibetan Plateau is another mechanism which may have caused local changes in salinity. The presence of the Younger Dryas in the tropical western Pacific clearly indicates that this climatic event is not restricted to the North Atlantic or high latitudes, but rather is global in extent.

Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents

NASA Astrophysics Data System (ADS)

Kennett, James P.; Kennett, Douglas J.; Culleton, Brendan J.; Emili Aura Tortosa, J.; Bischoff, James L.; Bunch, Ted E.; Daniel, I. Randolph, Jr.; Erlandson, Jon M.; Ferraro, David; Firestone, Richard B.; Goodyear, Albert C.; Israde-Alcántara, Isabel; Johnson, John R.; Jordá Pardo, Jesús F.; Kimbel, David R.; LeCompte, Malcolm A.; Lopinot, Neal H.; Mahaney, William C.; Moore, Andrew M. T.; Moore, Christopher R.; Ray, Jack H.; Stafford, Thomas W., Jr.; Barnett Tankersley, Kenneth; Wittke, James H.; Wolbach, Wendy S.; West, Allen

2015-08-01

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents.

PubMed

Kennett, James P; Kennett, Douglas J; Culleton, Brendan J; Aura Tortosa, J Emili; Bischoff, James L; Bunch, Ted E; Daniel, I Randolph; Erlandson, Jon M; Ferraro, David; Firestone, Richard B; Goodyear, Albert C; Israde-Alcántara, Isabel; Johnson, John R; Jordá Pardo, Jesús F; Kimbel, David R; LeCompte, Malcolm A; Lopinot, Neal H; Mahaney, William C; Moore, Andrew M T; Moore, Christopher R; Ray, Jack H; Stafford, Thomas W; Tankersley, Kenneth Barnett; Wittke, James H; Wolbach, Wendy S; West, Allen

2015-08-11

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼ 100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

Multiple oscillations during the Lateglacial as recorded in a multi-proxy, high-resolution record of the Moervaart palaeolake (NW Belgium)

NASA Astrophysics Data System (ADS)

Bos, Johanna A. A.; De Smedt, Philippe; Demiddele, Hendrik; Hoek, Wim Z.; Langohr, Roger; Marcelino, Vera; Van Asch, Nelleke; Van Damme, Dirk; Van der Meeren, Thijs; Verniers, Jacques; Boeckx, Pascal; Boudin, Mathieu; Court-Picon, Mona; Finke, Peter; Gelorini, Vanessa; Gobert, Stefan; Heiri, Oliver; Martens, Koen; Mostaert, Frank; Serbruyns, Lynn; Van Strydonck, Mark; Crombé, Philippe

2017-04-01

This paper presents the results of multi-disciplinary research carried out on the deposits of Moervaart depression, NW Belgium, one of the largest palaeolakes (∼25 km2) that existed during the Lateglacial interstadial in NW Europe. The multi-proxy study, including physical (organic matter and calcium carbonate, magnetic susceptibility, micromorphological), botanical (pollen, macrofossils, diatoms), zoological (ostracods, molluscs, chironomids) and chemical analyses (stable carbon and oxygen isotopes) has resulted in a detailed reconstruction of the Lateglacial landscape as well of the local conditions that prevailed in the lake itself. A chronology of the record was provided by radiocarbon dating and comparison with radiocarbon dates of the nearby Rieme site. These yielded a good match with the regional biostratigraphy. During the Lateglacial, vegetation and geomorphology of the landscape in general changed from a tundra landscape to a boreal forest. The vegetation development, however, was interrupted by a number of cold reversals. Three centennial-scale cold oscillations are present in the record: 1) the so-called Older Dryas corresponding to GI-1d in the Greenland ice-cores, 2) a short and pronounced cold event during the early Allerød, which could be correlated to GI-1c2 and 3) a cooling event during the late Allerød probably corresponding to the Intra Allerød Cold Period (IACP) or GI-1b. The latter most likely was responsible for the disappearance of the Moervaart palaeolake.

Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics.

PubMed

Partin, J W; Quinn, T M; Shen, C-C; Okumura, Y; Cardenas, M B; Siringan, F P; Banner, J L; Lin, K; Hu, H-M; Taylor, F W

2015-09-02

Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10-100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland.

Snow cover and extreme winter warming events control flower abundance of some, but not all species in high arctic Svalbard

PubMed Central

Semenchuk, Philipp R; Elberling, Bo; Cooper, Elisabeth J

2013-01-01

Abstract The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes. Winter warming events, often occurring together with rain, can substantially remove snow cover and thereby expose plants to cold winter air. Depending on morphology, different parts of the plant can be directly exposed. On this picture, we see Dryas octopetala seed heads from the previous growing season protrude through the remaining ice layer after a warming event in early 2010. The rest of the plant, including meristems and flower primordia, are still somewhat protected by the ice. In the background we can see a patch of Cassiope tetragona protruding through the ice; in this case, the whole plant including flower primordia is exposed, which might be one reason why this species experienced a loss of flowers the following season. Photograph by Philipp Semenchuk. PMID:24567826

Younger Dryas glaciers in the High Atlas, Morocco

NASA Astrophysics Data System (ADS)

Hughes, Philip; Fink, David

2016-04-01

Twelve cirque glaciers formed during the Younger Dryas on the mountains of Aksoual (3912 m a.s.l.) and Adrar el Hajj (3129 m a.s.l.) in the Marrakesh High Atlas. Moraines in two separate cirques on these mountains have been dated using 10Be and 36Cl exposure dating. In both cirques the age scatter is relatively small (13.8-10.1 ka) and all ages overlap within error with the Younger Dryas (12.9-11.7 ka). The glaciers were small and covered <2 km2 and formed on north-facing slopes. However, the altitudinal range of the glaciers was very large, with equilibrium line altitudes (ELAs) ranging from 2470 and 3560 m. This large range is attributed to local topoclimatic factors with the lowest glacier (confirmed as Younger Dryas in age by 3 exposure ages) occupying a very steep cirque floor where a combination of steep glacier gradient and a large potential avalanche catchment enabled its low-lying position. This indicates that caution should be taken when using single glacier sites for reconstructing regional palaeoclimate, especially those formed in steep catchments that have strong topoclimatic controls. The average ELA of the twelve Younger Dryas glaciers was c. 3109 m a.s.l. (St Dev = 325 m) and this represents an ELA depression of > 1000 m from the modern theoretical regional ELA. Under precipitation values similar to today this would require a mean annual temperature depression of 9°C. Moreover, the glacier-climate modelling indicates that it is very unlikely that climate was drier than today during the Younger Dryas in the Marrakesh High Atlas.

Sediment geochemical records of productivity and oxygen depletion along the margin of western North America during the past 60,000 years: teleconnections with Greenland Ice and the Cariaco Basin

USGS Publications Warehouse

Dean, W.E.

2007-01-01

Many sediment records from the margins of the Californias (Alta and Baja) collected in water depths between 60 and 1200 m contain anoxic intervals (laminated sediments) that can be correlated with interstadial intervals as defined by the oxygen-isotope composition of Greenland ice (Dansgaard-Oeschger, D-O, cycles). These intervals include all or parts of Oxygen Isotope Stage 3 (OIS3; 60-24 cal ka), the Bo??lling/Allero??d warm interval (B/A; 15-13 cal ka), and the Holocene. This study uses organic carbon (Corg) and trace-element proxies for anoxia and productivity, namely elevated concentrations and accumulation rates of molybdenum and cadmium, in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom-water oxygen (BWO) conditions on open, highly productive continental margins. The main conclusion from these proxies is that during the last glacial interval (LGI; 24-15 cal ka) and the Younger Dryas cold interval (YD; 13-11.6 cal ka) productivity was lower and BWO levels were higher than during OIS3, the B/A, and the Holocene on all margins of the Californias. The Corg and trace-element profiles in the LGI-B/A-Holocene transition in the Cariaco Basin on the margin of northern Venezuela are remarkably similar to those in the transition on the northern California margin. Correlation between D-O cycles in Greenland ice with gray-scale measurements in varved sediments in the Cariaco Basin also is well established. Synchronous climate-driven changes as recorded in the sediments on the margins of the Californias, sediments from the Cariaco Basin, and in the GISP-2 Greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka. Millennial-scale cycles in productivity and oxygen depletion on the margins of the Californias demonstrate that the California Current System was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern North Pacific Ocean. It is likely that the Pacific and Atlantic Oceans were linked through the atmosphere. Warmer air temperatures during interstadials would have strengthened Hadley and Walker circulations, which, in turn, would have strengthened the subtropical high pressure systems in both the North Pacific and the North Atlantic, producing increased rainfall over the Cariaco Basin and increased upwelling along the margins of the Californias. ?? 2006 Elsevier Ltd. All rights reserved.

60,000 Year Climate and Vegetation History of Southeast Alaska

NASA Astrophysics Data System (ADS)

Wilcox, Paul S.

Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until 14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between 13,000 and 11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 +/- 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on delta13C and delta18O values spanning the interval from 60,000 yr. BP to 11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative delta13 C values are attributed to predominance of angiosperms in the vegetation above the cave at 22,000 yr. BP and between 53,000 and 46,000 yr. BP while more positive delta13C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data suggest limited or no ice cover above El Capitan Cave for the duration of the record, possibly indicating that this region was a nunatak during glacial periods.

Some new forms of pyemotes (Acarina:pyemotidae) from forest insects, with remarks on polymorphism

Treesearch

Earle A. Cross; John C. Moser; Gisela Rack

1981-01-01

Three new species of Pyemotes, P. giganticus, P. tuberculatus and P. emarginatus are described, as is the male of P. dryas (Vitzthum, 1923). Male P. dryas and both sexes of P. giganticus are polymorphic. A short, general discussion of...

Some new forms of Pysmotes (Acarina: Pyemotidae) from forest insects with remarks on polymorphism

Treesearch

Earle A. Cross; John C. Moser; Gisela Rack

1981-01-01

Three new species of Pyemotes, P. giganticus, P. tuberculatus and P. emarginatus are described, as is the male of P. dryas (Vitzthum, 1923). Male P. dryas and both sexes of P. giganticus are polymorphic. A short, general discussion of...

Glacial chronology and palaeoclimate in the Bystra catchment, Western Tatra Mountains (Poland) during the Late Pleistocene

NASA Astrophysics Data System (ADS)

Makos, Michał; Rinterknecht, Vincent; Braucher, Régis; Żarnowski, Michał

2016-02-01

Deglaciation chronology of the Bystra catchment (Western Tatra Mountains) has been reconstructed based on 10Be exposure age dating. Fourteen rock samples were collected from boulders located on three moraines that limit the horizontal extent of the LGM maximum advance and the Lateglacial recessional stage. The oldest preserved, maximum moraine was dated at 15.5 ± 0.8 ka, an age that could be explained more likely by post-depositional erosion of the moraine. Such scenario is supported by geomorphologic and palaeoclimatological evidence. The younger cold stage is represented by well-preserved termino-lateral moraine systems in the Kondratowa and Sucha Kasprowa valleys. The distribution of the moraine ridges in both valleys suggest a complex history of deglaciation of the area. The first Late-glacial re-advance (LG1) was followed by a cold oscillation (LG2), that occurred at around 14.0 ± 0.7-13.7 ± 1.2 ka. Glaciers during both stages had nearly the same horizontal extent, however, their thickness and geometry changed significantly, mainly due to local climatic conditions triggered by topography, controlling the exposition to solar radiation. The LG1 stage occurred probably during the pre-Bølling cold stage (Greenland Stadial 2.1a), however, the LG2 stage can be correlated with the cooling at around 14 ka during the Greenland Interstadial 1 (GI-1d - Older Dryas). This is the first chronological evidence of the Older Dryas in the Tatra Mountains. The ELA of the maximum Bystra glacier was located at 1480 m a.s.l. in accordance with the ELA in the High Tatra Mountains during the LGM. During the LG1 and LG2 stages, the ELA in the catchment rose up to 1520-1530 m a.s.l. and was located approximately 100-150 m lower than in the eastern part of the massif. Climate modelling results show that the Bystra glacier (maximum advance) could have advanced in the catchment when mean annual temperature was lower than today by 11-12 °C and precipitation was reduced by 40-60%. This is in accordance with LGM conditions previously reported for the High Tatras. During the LG1 and LG2 stages the temperature decrease in the study area reached 10 °C and precipitation was lower by ∼30% compare to modern conditions. This resulted in slightly higher accumulation (20-30%) in the Western Tatra Mountains compare to the High Tatra Mountains.

Ribbed moraine stratigraphy and formation in southern Finnish Lapland

NASA Astrophysics Data System (ADS)

Sarala, Pertti

2006-05-01

Characteristics of ribbed moraines, the dominating moraine type in southern Finnish Lapland, have been studied in detail. The ridges are composed of several till units, of which the bottommost units consist of mature basal tills and the surficial parts are enriched with local, short-transport rock fragments and boulders in till and at the surface of ridges. As a result of this re-examination a two-step model of the formation process of ribbed moraines is presented. In the first stage, while cold-based conditions prevailed, both the bottommost part of the ice sheet and the frozen, substrate fractured under compressive ice flow. Following glacial transport of fractured blocks and formation of the transverse ridge morphology, erosion between the ridges continued owing to freeze-thaw process under variable pressure conditions. In the areas with a low pre-existing till sheet, the process caused quarrying of the bedrock surface and subsequent deposition of rock fragments and boulders under high pressure on the next ridge. The most suitable conditions for ribbed moraine formation existed during Late Weichselian deglaciation, after the Younger Dryas when the climate warmed very quickly, leading to an imbalance between a warm glacier surface and a cold base. Copyright

The history of South American tropical precipitation for the past 25,000 years.

PubMed

Baker, P A; Seltzer, G O; Fritz, S C; Dunbar, R B; Grove, M J; Tapia, P M; Cross, S L; Rowe, H D; Broda, J P

2001-01-26

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.

Loess record of the Pleistocene-Holocene transition on the northern and central Great Plains, USA

USGS Publications Warehouse

Mason, J.A.; Miao, X.; Hanson, P.R.; Johnson, W.C.; Jacobs, P.M.; Goble, R.J.

2008-01-01

Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene-Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the B??lling-Aller??d episode (approximately 14.7-12.9 cal ka) and all of the Younger Dryas episode (12.9-11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5-9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture. Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess-paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the B??lling-Aller??d and Younger Dryas episodes in the North Atlantic region. ?? 2008 Elsevier Ltd. All rights reserved.

Quantifying the distribution of nanodiamonds in pre-Younger Dryas to recent age deposits along Bull Creek, Oklahoma Panhandle, USA

NASA Astrophysics Data System (ADS)

Bement, Leland C.; Madden, Andrew S.; Carter, Brian J.; Simms, Alexander R.; Swindle, Andrew L.; Alexander, Hanna M.; Fine, Scott; Benamara, Mourad

2014-02-01

High levels of nanodiamonds (nds) have been used to support the transformative hypothesis that an extraterrestrial (ET) event (comet explosion) triggered Younger Dryas changes in temperature, flora and fauna assemblages, and human adaptations [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104(41):16016-16021]. We evaluate this hypothesis by establishing the distribution of nds within the Bull Creek drainage of the Beaver River basin in the Oklahoma panhandle. The earlier report of an abundance spike of nds in the Bull Creek I Younger Dryas boundary soil is confirmed, although no pure cubic diamonds were identified. The lack of hexagonal nds suggests Bull Creek I is not near any impact site. Potential hexagonal nds at Bull Creek were found to be more consistent with graphene/graphane. An additional nd spike is found in deposits of late Holocene through the modern age, indicating nds are not unique to the Younger Dryas boundary. Nd distributions do not correlate with depositional environment, pedogenesis, climate perturbations, periods of surface stability, or cultural activity.

Terrestrial Plant Biomarkers Preserved in Cariaco Basin Sediments: Records of Abrupt Tropical Vegetation Response to Rapid Climate Changes

NASA Astrophysics Data System (ADS)

Hughen, K. A.; Eglinton, T. I.; Makou, M.; Xu, L.; Sylva, S.

2004-12-01

Organic-rich sediments from the anoxic Cariaco Basin, Venezuela, preserve high concentrations of biomarkers for reconstruction of terrestrial environmental conditions. Molecular-level investigations of organic compounds provide a valuable tool for extracting terrestrial signals from these annually laminated marine sediments. Differences in hydrogen isotopic fractionation between C16-18 and C24-30 n-alkanoic acids suggest a marine source for the shorter chain lengths and a terrestrial source for the longer chains. Records of carbon and hydrogen isotopes, as well as average carbon chain length (ACL), from long-chain n-alkanoic acids parallel millennial-scale changes in vegetation and climate between the late Glacial and Preboreal periods, 15,000 to 10,000 years ago. Data from all terrestrial chain lengths were combined to produce single δ D and δ 13C indices through deglaciation, exhibiting enrichment during the late Glacial and Younger Dryas and depletion during the Bolling-Allerod and Preboreal periods. δ D reflects the hydrogen isotopic composition of environmental water used for plant growth, combined with evaporative enrichment within leaf spaces, and as such may act as a proxy for local aridity. Leaf wax δ 13C, which is a proxy for C3 versus C4 metabolic pathways, indicates that C3 plants predominated in the Cariaco watershed during warm/wet Bolling-Allerod and Holocene periods, and C4 plant biomass proliferated during cool/dry Glacial and Younger Dryas intervals. Coupled carbon and hydrogen isotopic measurements together clearly distinguish deglacial climatic periods as wetter with C3 vegetation versus drier with C4 vegetation. High resolution biomarker records reveal the rapidity of vegetation changes in northern South America during the last deglaciation. The leaf wax data reveal that local vegetation biomass, although not necessarily entire assemblages, shifted between arid grassland and wetter forest taxa on timescales of decades. Comparison of ACL versus δ 13C for Cariaco Basin and NW African leaf waxes indicate that biomarkers reflect real changes in local South American vegetation and not contamination from long-distance transport during cold windy climates. The precise temporal relationship between tropical vegetation shifts and climate changes is measured by direct comparison of terrestrial vegetation and climate proxies from the same core. Abrupt deglacial climate shifts in tropical and high-latitude North Atlantic regions were synchronous, whereas changes in tropical vegetation consistently lagged climate shifts by several decades.

An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis.

PubMed

Surovell, Todd A; Holliday, Vance T; Gingerich, Joseph A M; Ketron, Caroline; Haynes, C Vance; Hilman, Ilene; Wagner, Daniel P; Johnson, Eileen; Claeys, Philippe

2009-10-27

Based on elevated concentrations of a set of "impact markers" at the onset of the Younger Dryas stadial from sedimentary contexts across North America, Firestone, Kennett, West, and others have argued that 12.9 ka the Earth experienced an impact by an extraterrestrial body, an event that had devastating ecological consequences for humans, plants, and animals in the New World [Firestone RB, et al. (2007) Proc. Natl. Acad. Sci. USA 104:16016-16021]. Herein, we report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact.

Younger-Dryas cooling and sea-ice feedbacks were prominent features of the Pleistocene-Holocene transition in Arctic Alaska

USGS Publications Warehouse

Gaglioti, Benjamin V.; Mann, Daniel H.; Wooller, Matthew J.; Jones, Benjamin M.; Wiles, Gregory C.; Groves, Pamela; Kunz, Michael L.; Baughman, Carson; Reanier, Richard E.

2017-01-01

Declining sea-ice extent is currently amplifying climate warming in the Arctic. Instrumental records at high latitudes are too short-term to provide sufficient historical context for these trends, so paleoclimate archives are needed to better understand the functioning of the sea ice-albedo feedback. Here we use the oxygen isotope values of wood cellulose in living and sub-fossil willow shrubs (δ18Owc) (Salix spp.) that have been radiocarbon-dated (14C) to produce a multi-millennial record of climatic change on Alaska's North Slope during the Pleistocene-Holocene transition (13,500–7500 calibrated 14C years before present; 13.5–7.5 ka). We first analyzed the spatial and temporal patterns of δ18Owc in living willows growing at upland sites and found that over the last 30 years δ18Owc values in individual growth rings correlate with local summer temperature and inter-annual variations in summer sea-ice extent. Deglacial δ18Owcvalues from 145 samples of subfossil willows clearly record the Allerød warm period (∼13.2 ka), the Younger Dryas cold period (12.9–11.7 ka), and the Holocene Thermal Maximum (11.7–9.0 ka). The magnitudes of isotopic changes over these rapid climate oscillations were ∼4.5‰, which is about 60% of the differences in δ18Owc between those willows growing during the last glacial period and today. Modeling of isotope-precipitation relationships based on Rayleigh distillation processes suggests that during the Younger Dryas these large shifts in δ18Owc values were caused by interactions between local temperature and changes in evaporative moisture sources, the latter controlled by seaice extent in the Arctic Ocean and Bering Sea. Based on these results and on the effects that sea-ice have on climate today, we infer that ocean-derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of Arctic Alaska during warm times in the past. Today, isotope values in willows on the North Slope of Alaska are similar to those growing during the warmest times of the Pleistocene-Holocene transition, which were times of widespread permafrost thaw and striking ecological changes.

Younger-Dryas cooling and sea-ice feedbacks were prominent features of the Pleistocene-Holocene transition in Arctic Alaska

NASA Astrophysics Data System (ADS)

Gaglioti, Benjamin V.; Mann, Daniel H.; Wooller, Matthew J.; Jones, Benjamin M.; Wiles, Gregory C.; Groves, Pamela; Kunz, Michael L.; Baughman, Carson A.; Reanier, Richard E.

2017-08-01

Declining sea-ice extent is currently amplifying climate warming in the Arctic. Instrumental records at high latitudes are too short-term to provide sufficient historical context for these trends, so paleoclimate archives are needed to better understand the functioning of the sea ice-albedo feedback. Here we use the oxygen isotope values of wood cellulose in living and sub-fossil willow shrubs (δ18Owc) (Salix spp.) that have been radiocarbon-dated (14C) to produce a multi-millennial record of climatic change on Alaska's North Slope during the Pleistocene-Holocene transition (13,500-7500 calibrated 14C years before present; 13.5-7.5 ka). We first analyzed the spatial and temporal patterns of δ18Owc in living willows growing at upland sites and found that over the last 30 years δ18Owc values in individual growth rings correlate with local summer temperature and inter-annual variations in summer sea-ice extent. Deglacial δ18Owc values from 145 samples of subfossil willows clearly record the Allerød warm period (∼13.2 ka), the Younger Dryas cold period (12.9-11.7 ka), and the Holocene Thermal Maximum (11.7-9.0 ka). The magnitudes of isotopic changes over these rapid climate oscillations were ∼4.5‰, which is about 60% of the differences in δ18Owc between those willows growing during the last glacial period and today. Modeling of isotope-precipitation relationships based on Rayleigh distillation processes suggests that during the Younger Dryas these large shifts in δ18Owc values were caused by interactions between local temperature and changes in evaporative moisture sources, the latter controlled by sea ice extent in the Arctic Ocean and Bering Sea. Based on these results and on the effects that sea-ice have on climate today, we infer that ocean-derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of Arctic Alaska during warm times in the past. Today, isotope values in willows on the North Slope of Alaska are similar to those growing during the warmest times of the Pleistocene-Holocene transition, which were times of widespread permafrost thaw and striking ecological changes.

Microfossils, a Key to Unravel Cold-Water Carbonate Mound Evolution through Time: Evidence from the Eastern Alboran Sea

PubMed Central

Stalder, Claudio; Vertino, Agostina; Rosso, Antonietta; Rüggeberg, Andres; Pirkenseer, Claudius; Spangenberg, Jorge E.; Spezzaferri, Silvia; Camozzi, Osvaldo; Rappo, Sacha; Hajdas, Irka

2015-01-01

Cold-water coral (CWC) ecosystems occur worldwide and play a major role in the ocean's carbonate budget and atmospheric CO2 balance since the Danian (~65 m.y. ago). However their temporal and spatial evolution against climatic and oceanographic variability is still unclear. For the first time, we combine the main macrofaunal components of a sediment core from a CWC mound of the Melilla Mounds Field in the Eastern Alboran Sea with the associated microfauna and we highlight the importance of foraminifera and ostracods as indicators of CWC mound evolution in the paleorecord. Abundances of macrofauna along the core reveal alternating periods dominated by distinct CWC taxa (mostly Lophelia pertusa, Madrepora oculata) that correspond to major shifts in foraminiferal and ostracod assemblages. The period dominated by M. oculata coincides with a period characterized by increased export of refractory organic matter to the seafloor and rather unstable oceanographic conditions at the benthic boundary layer with periodically decreased water energy and oxygenation, variable bottom water temperature/density and increased sediment flow. The microfaunal and geochemical data strongly suggest that M. oculata and in particular Dendrophylliidae show a higher tolerance to environmental changes than L. pertusa. Finally, we show evidence for sustained CWC growth during the Alleröd-Younger-Dryas in the Eastern Alboran Sea and that this period corresponds to stable benthic conditions with cold/dense and well oxygenated bottom waters, high fluxes of labile organic matter and relatively strong bottom currents PMID:26447699

Hydrological and vegetational response to the Younger Dryas climatic oscillations: a high resolution case study from Quoyloo Meadow, Orkney, Scotland

NASA Astrophysics Data System (ADS)

Maas, David; Abrook, Ashley; Timms, Rhys; Matthews, Ian; Palmer, Adrian; Milner, Alice; Candy, Ian; Sachse, Dirk

2016-04-01

The Younger Dryas (Loch Lomond) Stadial is a well defined period of cold climate that in North West Europe punctuated the climatic amelioration during the Last Glacial - Interglacial Transition (LGIT ca. 16-8 ka). A palaeolake record from Quoyloo Meadow, Orkney Islands (N59.067, E-3.309) has been analysed for pollen and stable isotopes on biomarker lipids. n-Alkanes from terrestrial and aquatic sources are present throughout the core. The average chain length (ACL) is relatively low during the interstadial (~28.0) and shows a distinct increase during the Younger Dryas (to 29.0 +), attributed to an increase in grasses and drought resistant shrubs (e.g. Artemisia, Castañeda et al., 2009, Bunting, 1994). At the beginning of the Holocene, the ACL rapidly drops to 28.3 and from thereon gently increases again to ~29.0. There is a continued odd-over-even n-alkane predominance, although even n-alkanes are present in greater quantities in the interstadial, indicating an increasing terrestrial contribution in the Holocene. Ongoing deuterium isotope measurements of the n-alkanes will give independent evidence for palaeohydrological changes and can be compared to the other proxy evidence within the same core. Using a combination of nC29 and nC23 (terrestrial and aquatic end-members, respectively), a change in relative humidity (rH) can be qualified. This is based on the idea that terrestrial vegetation is affected by evapotranspiration processes, whereas aquatic vegetation is not (Rach et al., 2014). This data is supported by a high resolution palynological study; the contiguously sampled record demonstrates ecosystem/environmental responses to millennial-scale climatic change and allows for the possible detection of vegetation shifts at the sub-millennial scale. Vegetation aside, the pollen data can further aid in the interpretation of the recorded n-alkanes and isotopic analyses. This data is placed within a chronological framework derived from a high resolution crypto- and macrotephra study (Timms et al in prep). References: Bunting, M.J., 1994, Vegetation history of Orkney, Scotland: pollen records from two small basins in west Mainland, New Phytologist, Vol 128, p 771-792 Castañeda, I.S., Mulitza, S., Schefuß, E., Lopes dos Santos, R.A., Sinninghe Damsté, J.S. and Schouten, S. (2009) Wet phases in the Sahara/Sahel region and human migration patterns in North Africa, Proceedings of the National Academy of Sciences, Vol 106, p 20159 - 20163, Supporting Information: 10.1073/pnas.0905771106 Rach, O., Brauer, A., Wilkes, H. and Sachse, D. (2014) Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe, Nature Geoscience, Vol 7, p 109 - 112 Timms, R.G.O., Matthews, I.P., Palmer, A.P., and Candy, I (in prep), A high resolution tephrostratigraphy from Quoyloo Meadow, Orkney, Scotland: Implications for tephrostratigraphic refinement in the Last Glacial - Interglacial Transition (ca. 16-8 ka) [working title

Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago

NASA Astrophysics Data System (ADS)

Meltzer, David J.; Holliday, Vance T.; Cannon, Michael D.; Miller, D. Shane

2014-05-01

According to the Younger Dryas Impact Hypothesis (YDIH), ∼12,800 calendar years before present, North America experienced an extraterrestrial impact that triggered the Younger Dryas and devastated human populations and biotic communities on this continent and elsewhere. This supposed event is reportedly marked by multiple impact indicators, but critics have challenged this evidence, and considerable controversy now surrounds the YDIH. Proponents of the YDIH state that a key test of the hypothesis is whether those indicators are isochronous and securely dated to the Younger Dryas onset. They are not. We have examined the age basis of the supposed Younger Dryas boundary layer at the 29 sites and regions in North and South America, Europe, and the Middle East in which proponents report its occurrence. Several of the sites lack any age control, others have radiometric ages that are chronologically irrelevant, nearly a dozen have ages inferred by statistically and chronologically flawed age-depth interpolations, and in several the ages directly on the supposed impact layer are older or younger than ∼12,800 calendar years ago. Only 3 of the 29 sites fall within the temporal window of the YD onset as defined by YDIH proponents. The YDIH fails the critical chronological test of an isochronous event at the YD onset, which, coupled with the many published concerns about the extraterrestrial origin of the purported impact markers, renders the YDIH unsupported. There is no reason or compelling evidence to accept the claim that a cosmic impact occurred ∼12,800 y ago and caused the Younger Dryas.

Rapid continental-scale vegetation response to the Younger Dryas Cool Episode

NASA Astrophysics Data System (ADS)

Peros, M.; Gajewski, K.; Viau, A.

2006-12-01

The Younger Dryas Cool Episode had rapid and widespread effects on flora and fauna throughout the Americas. Fossil pollen records document how plant communities responded to this event, although such data are generally only representative of changes at local- to regional-scales. We use a new approach to provide insight into vegetation responses to the Younger Dryas at a continental-scale, by focusing on data extracted for a single taxon (Populus poplar, cottonwood, aspen) from pollen diagrams throughout North America. We show that Populus underwent a rapid and continent-wide decline as the climate rapidly cooled and dried. At the termination of the Younger Dryas, Populus underwent another widespread decline, this time in response to competition from boreal and temperate taxa as the climate abruptly warmed. Late glacial-early Holocene pollen assemblages with high quantities of Populus pollen often lack modern analogues and thus confound quantitative paleoclimatic reconstructions; our results provide a context to interpret these assemblages. Furthermore, while Populus may continue to expand in the future in response to human disturbance and increasing temperatures, its sensitivity to competition may eventually put it at risk as global warming accelerates.

An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis

PubMed Central

Surovell, Todd A.; Holliday, Vance T.; Gingerich, Joseph A. M.; Ketron, Caroline; Haynes, C. Vance; Hilman, Ilene; Wagner, Daniel P.; Johnson, Eileen; Claeys, Philippe

2009-01-01

Based on elevated concentrations of a set of “impact markers” at the onset of the Younger Dryas stadial from sedimentary contexts across North America, Firestone, Kennett, West, and others have argued that 12.9 ka the Earth experienced an impact by an extraterrestrial body, an event that had devastating ecological consequences for humans, plants, and animals in the New World [Firestone RB, et al. (2007) Proc. Natl. Acad. Sci. USA 104:16016–16021]. Herein, we report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact. PMID:19822748

Climate change, adaptive cycles, and the persistence of foraging economies during the late Pleistocene/Holocene transition in the Levant.

PubMed

Rosen, Arlene M; Rivera-Collazo, Isabel

2012-03-06

Climatic forcing during the Younger Dryas (∼12.9-11.5 ky B.P.) event has become the theoretical basis to explain the origins of agricultural lifestyles in the Levant by suggesting a failure of foraging societies to adjust. This explanation however, does not fit the scarcity of data for predomestication cultivation in the Natufian Period. The resilience of Younger Dryas foragers is better illustrated by a concept of adaptive cycles within a theory of adaptive change (resilience theory). Such cycles consist of four phases: release/collapse (Ω); reorganization (α), when the system restructures itself after a catastrophic stimulus through innovation and social memory--a period of greater resilience and less vulnerability; exploitation (r); and conservation (K), representing an increasingly rigid system that loses flexibility to change. The Kebarans and Late Natufians had similar responses to cold and dry conditions vs. Early Natufians and the Pre-Pottery Neolithic A responses to warm and wet climates. Kebarans and Late Natufians (α-phase) shifted to a broader-based diet and increased their mobility. Early Natufian and Pre-Pottery Neolithic A populations (r- and K-phases) had a growing investment in more narrowly focused, high-yield plant resources, but they maintained the broad range of hunted animals because of increased sedentism. These human adaptive cycles interlocked with plant and animal cycles. Forest and grassland vegetation responded to late Pleistocene and early Holocene climatic fluctuations, but prey animal cycles reflected the impact of human hunting pressure. The combination of these three adaptive cycles results in a model of human adaptation, showing potential for great sustainability of Levantine foraging systems even under adverse climatic conditions.

How Synchronous was the Transition into the Younger Dryas across the Euro-Atlantic Region?

NASA Astrophysics Data System (ADS)

Schenk, F.; Muschitiello, F.; Heikkilä, M. P.; Väliranta, M.; Tarasov, L.; Brandefelt, J.; Johansson, A. V.; Naslund, J. O.; Wohlfarth, B.

2015-12-01

Observations of a currently weakening subpolar gyre south of Greenland has again increased scientific attention regarding the role of the Atlantic Meridional Overturning Circulation (AMOC) for the regional to global climate. The rapid climate shift of the Younger Dryas (YD, GS-1) cold reversal during the last deglaciation is attributed to an abrupt slowdown or collapse of the AMOC due to a strong meltwater pulse and/or the rapid disintegration of the Laurentide Ice sheet. Although such a dramatic event is not expected for the future, the spatiotemporal climatic response to such a slowdown is an interesting test case. Two recently well dated proxy records around the North Sea region suggest a non-synchronous early cooling/onset of the YD compared to Greenland (NGRIP). Presentation #61803 discusses the hypothesis of a local cooling as a response to increased ice berg calving and/or meltwater from Fenno-Scandinavian Ice Sheet (FIS) during the late Alleröd warm phase (GI-1a). Here we study CCSM3 model output from the quasi-transient atmosphere-ocean simulation (TraCE) where no strong contribution from FIS is considered from the late Alleröd into the YD. We evaluate to which extent the spatiotemporal temperature response to the AMOC slowdown of the simulation is synchronous over the Euro-Atlantic region and how atmospheric teleconnections reorganize during the rapid shift into the YD. In addition, we run time-slice experiments at high spatial resolution of around 100 km with the Community Earth System Model CESM1.0.5 for the late Alleröd and YD to compare spatial climatic differences for both periods taking into account the regional influence from continental ice sheets in more detail.

Oxygen Isotopes and Meltwater: Younger Dryas and 8.2 ka Event

NASA Astrophysics Data System (ADS)

Keigwin, L. D.

2015-12-01

Delta 18-O is one of our most powerful and widely used proxies, with, arguably, the fewest likely unknown unknowns. Here I will consider the d18-O evidence for the two best-known floods of mostly liquid water to the ocean, the Younger Dryas (YD) and the 8.2 ka event. The first d18-O signal of a meltwater flood in the ocean was reported 40 years ago by Kennett and Shackleton (1975) and that paper led directly to the meltwater diversion hypothesis for the origin of the YD cooling. It was later suggested by Rooth (1982) that such a flood could interrupt Nordic seas convection and trigger the YD cold episode. It was reported at this meeting last year that a candidate flood has been found in the Mackenzie River region of the western Arctic based on low d18-O and multiple other lines of evidence. The 8.2 ka event was about one-tenth the duration of the YD but with possibly higher transport, and is more difficult to detect in open marine sediments. As with the YD, it has been modeled by hosing and low salinities have been derived by temperature correcting the d18-O. The resulting low salinity was shown not to follow the prediction of the highest resolution modeling, and theory, that the fresh water would be transported mostly equatorward along the continental shelf. However, I report here that the low d18-O signal of the 8.2 ka flooding is present in new cores from near Logan Canyon on the Scotian shelf break, and in Jordan Basin, Gulf of Maine. These results substantially validate the modeling of Condron and Winsor that fresh water transport must have been along the continental shelf.

Evaluating Pyemotes dryas (Vitzthum 1923)(Acari: Pyemotidae) as a parasite of the southern pine beetle

Treesearch

John C. Moser; B. Kielczewski; J. Wisniewski; S. Balazy

1978-01-01

Populations of Pyemotes dryas (Vitzthum 1923) from Poland were bioassayed for potential use in the biological control of the southern pine beetle in the United States. The mite apparently rides and attacks a wide range of European bark beetles that attack conifers and readily consumes brood of the southern pine beetle. However, it is not phoretic on...

Oxygen Isotopes in Fresh Water Biogenic Opal: Northeastern US Alleroed-Younger Dryas Temperature Shift

NASA Technical Reports Server (NTRS)

Shemesh, Aldo; Peteet, Dorothy

1997-01-01

The first oxygen isotope analysis of biogenic opal from lake sediments, from the Allerod/Younger Dryas transition in a core from Linsley Pond, Connecticut, gives an average estimate of a 6 C drop in temperature during the Younger Dryas. This shift represents temperatures during the bloom season, and may be less than the winter temperature drop. The sharp transition itself, with a duration of about 200 years, suggests that the temperature decrease may have been as large as 12 C. Previous estimates of the Allerod/Younger Dryas temperature shifts are controversial, and range from 3-20 C, suggesting that further interdisciplinary research on the same samples is warranted. One way that global climate change manifests itself is by redistributing energy throughout the globe. The Northern Hemisphere latitudinal temperature gradient during the late-glacial is at present a controversial topic. The magnitude of air temperature shifts during the Allerod/Younger Dryas (YD) oscillation are estimated from mid-latitude pollen records surrounding the North Atlantic to be 3-5 C in Europe [Lowe et al., 19941 and 3-4 C in the eastern US [Peteet et al., 1993]. In contrast, lake temperatures estimates derived from aquatic midge larvae in the Canadian eastern maritimes and Maine range from 6-20 C, with larger shifts at more southern sites [Levesque et al., 1997]. The magnitude of YD cooling in Greenland ice cores ranges from at least 7 C from the Bolling warming [Dansgaard et al., 1989] to 15 C - a more recent estimate from borehole temperatures [Cuffey et al., 1995]. The ice core geochemical records reveal that massive frequent and short-term (decadal or less) changes in atmospheric composition occurred throughout this event, suggesting a very dynamic circulation [Mayewski et al., 1993).

Nasal mites from birds of a Guatemalan cloud forest (Acarina: rhinonyssidae)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spicer, G.S.

1984-01-01

A survey of the nasal mites from Guatemalan cloud forest birds is reported. Seventy-eight birds, representing 10 families and 18 species, were examined. Prevalence of infection was 24%. Two new species are described: Sternostoma darlingi from Mitrephanes phaeocercus (Tyrannidae) and S. pencei from Empidonax flavescens (Tyrannidae). New host records are reported for S. priangae from Chlorospingus opthalmicus (Thraupidae), S. hutsoni from Catharus dryas (Turdidae), Ptilonyssus sairae from Chlorospingus opthalmicus (Thraupidae), and Myioborus miniatus (Parulidae), P. euroturdi from Catharus dryas (Turdidae), P. tyrannus from Empidonax flavescens and Mitrephanes phaeocercus (both Tyannidae), and Tinaminyssus ixoreus from Catharus dryas (Turdidae). The subspecies Ptilonyssusmore » euroturdi mimicola Fain and Hyland is synonymized with the nominate subspecies. Data are presented to suggest that the Rhinonyssidae may be a polyphyletic assemblage. 35 references, 12 figures, 1 table.« less

Lateglacial landscape and vegetation change and the younger dryas climatic oscillation in New Zealand

NASA Astrophysics Data System (ADS)

McGlone, M. S.

Lateglacial sequences in New Zealand show progressive afforestation and landscape stabilization reflecting a warming climate. Between 14,500 BP and 11,500 BP, afforestation and landscape stability was achieved throughout most of the North Island and the northwest sector of the South Island. In the South Island, scrub and tree ferns were replacing previous grasslands in the east by 11,000 BP, and broadleaved forest was spreading in the west. No significant reversals of these trends occurred and afforestation was complete by 9500 BP. Glaciers of the high central part of the Southern Alps made a series of advances between 14,000 and 9000 BP Most of these advances are poorly dated but two moraines are of Younger Dryas age. Glacial advances in the face of the general Lateglacial warming trend may have been driven by stronger westerly winds increasing snowfall on high altitude névés, and by reduced ablation as a consequence of moist, cloudy, low insolation summers. The cause of the northern hemisphere Younger Dryas cooling is still uncertain, and expected Southern Hemisphere responses may differ according to the mechanism proposed for the cooling. Poor chronological resolution and apparent conflict between the various types of evidence for climatic change make detection of an unambiguous Younger Dryas in New Zealand problematical.

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

USGS Publications Warehouse

Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

2013-01-01

Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

Radiocarbon age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change

USGS Publications Warehouse

Gaglioti, Benjamin V.; Mann, Daniel H.; Jones, Benjamin M.; Pohlman, John W.; Kunz, Michael L.; Wooller, Matthew J.

2014-01-01

Continued warming of the Arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon (OC), thereby accentuating global warming. However, it is unclear if recent warming has raised the current rates of permafrost OC release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing. Here we use a time series of radiocarbon age-offsets (14C) between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost OC release over the last 14,500 years. The lake traps and archives OC imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age-offsets. Today, the age-offset (2 ka; thousand of calibrated years before A.D. 1950) and the depositional rate of ancient OC from the watershed into the lake are relatively low and similar to those during the Younger Dryas cold interval (occurring 12.9–11.7 ka). In contrast, age-offsets were higher (3.0–5.0 ka) when summer air temperatures were warmer than present during the Holocene Thermal Maximum (11.7–9.0 ka) and Bølling-Allerød periods (14.5–12.9 ka). During these warm times, permafrost thaw contributed to ancient OC depositional rates that were ~10 times greater than today. Although permafrost OC was vulnerable to climate warming in the past, we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release. As a result, the temperature threshold to trigger widespread permafrost OC release is higher than during previous warming events.

A six-stalagmite composite record of East Asian Summer Monsoon in northern China since 11.5 thousand years ago

NASA Astrophysics Data System (ADS)

Shen, C. C.; Dong, J.; Kong, X.; WU, C. C.; Ren, H. A.; Wang, Y.

2017-12-01

Here we present replicated carbonate δ18O records of six stalagmites with sub-decadal to multi-decadal resolutions from Lianhua Cave (38º10'N, 113º43'E), Shanxi Province, to reveal a detailed evolution of the East Asian Summer Monsoon (EASM) intensity in northern China since 11.5 thousand years ago (ka BP, before 1950 AD). This composite record shows that solar forcing dominated hydroclimatic changes, including an intensified monsoon at the Holocene Optimum from the termination of Younger Dryas to 6.5 ka BP, and a subsequent multi-millennial weakening of monsoon intensity, that agree with cave records in central and southern China. However, the EASM has retreated southwards more rapidly than the Indian summer monsoon after 6.5 ka BP, resulting in aridity conditions occurring at 4.0 ka BP in northern China, which is almost 2000-year earlier than in central and southern China. This asynchroneity may be related to the different regional responses among the coupling of the EASM, Indian summer monsoon, the solar forcing, and the differences in thermal forcing due to complex geographical configurations. In addition, a relative enrichment of 1‰ in 18O data of Lianhua record from 9.5 to 8.1 ka BP shows that the Holocene Optimum was punctuated by a millennial-long weak monsoon interval, which is not registered among previous cave records in central and southern China. The fresh water-induced cold climate conditions in the North Atlantic region could create stronger East Asian winter monsoon and induce a weakened EASM and a southward shift of rain belt in northern China. Therefore, it shall not be surprised that there are strong heterogeneities among regional hydroclimatic conditions across monsoonal China in the Holocene.

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

NASA Astrophysics Data System (ADS)

Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

2013-06-01

Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

Root tensile strength assessment of Dryas octopetala L. and implications for its engineering mechanism on lateral moraine slopes (Turtmann Valley, Switzerland)

NASA Astrophysics Data System (ADS)

Eibisch, Katharina; Eichel, Jana; Dikau, Richard

2015-04-01

Geomorphic processes and properties are influenced by vegetation. It has been shown that vegetation cover intercepts precipitation, enhances surface detention and storage, traps sediment and provides additional surface roughness. Plant roots impact the soil in a mechanical and hydrological manner and affect shear strength, infiltration capacity and moisture content. Simultaneously, geomorphic processes disturb the vegetation development. This strong coupling of the geomorphic and ecologic system is investigated in Biogeomorphology. Lateral moraine slopes are characterized by a variety of geomorphic processes, e. g. sheet wash, solifluction and linear erosion. However, some plant species, termed engineer species, possess specific functional traits which allow them to grow under these conditions and also enable them to influence the frequency, magnitude and even nature of geomorphic processes. For lateral moraine slopes, Dryas octopetala L., an alpine dwarf shrub, was identified as a potential engineer species. The engineering mechanism of D. octopetala, based on its morphological (e.g., growth form) and biomechanical (e.g., root strength) traits, yet remains unclear and only little research has been conducted on alpine plant species. The objectives of this study are to fill this gap by (A) quantifying D. octopetala root tensile strength as an important trait considering anchorage in and stabilization of the slope and (B) linking plant traits to the geomorphic process they influence on lateral moraine slopes. D. octopetala traits were studied on a lateral moraine slope in Turtmann glacier forefield, Switzerland. (A) Root strength of single root threads of Dryas octopetala L. were tested using the spring scale method (Schmidt et al., 2001; Hales et al., 2013). Measurement equipment was modified to enable field measurements of roots shortly after excavation. Tensile strength of individual root threads was calculated and statistically analyzed. First results show that Dryas roots appear to be quite strong compared to other alpine species with a mean tensile strength of 22,63 N mm -². (B) On a micro scale, morphological and biomechanical features of above and below-ground biomass were qualitatively studied through field observations on D. octopetala individuals. Findings indicate that D. octopetala's dense cushions, covering many square meters of the moraines surface, traps fine sediment, stores moisture and significantly reduces erosion through wind and water. Furthermore, Dryas is well adapted to rock fall or burial by forming stabilized patches of ground despite steep slope inclinations and strong, episodic surface runoff and creep processes. Anchorage is provided by its strong root, which in all studied cases grew upslope parallel to the moraines surface. Insights from this study allow to relate root tensile strength and other specific plant traits of Dryas octopetala to an engineering mechanism and effect on geomorphic processes on lateral moraine slopes. Knowledge about Dryas as an engineering species may help to understand its biotic influence on the geomorphic system of a lateral moraine and aid in the selection of species for erosion control or rehabilitation of ecosystems, where Dryas is native.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stephan Harrison; Ann V. Rowan; Neil F. Glasser

It is widely believed that the last glaciers in the British Isles disappeared at the end of the Younger Dryas stadial (12.9–11.7 cal. kyr BP). Here, we use a glacier–climate model driven by data from local weather stations to show for the first time that glaciers developed during the Little Ice Age (LIA) in the Cairngorm Mountains. Our model is forced from contemporary conditions by a realistic difference in mean annual air temperature of -1.5 degrees C and an increase in annual precipitation of 10%, and confirmed by sensitivity analyses. These results are supported by the presence of small bouldermore » moraines well within Younger Dryas ice limits, and by a dating programme on a moraine in one cirque. As a result, we argue that the last glaciers in the Cairngorm Mountains (and perhaps elsewhere in upland Britain) existed in the LIA within the last few hundred years, rather than during the Younger Dryas.« less

The impact of climate and environmental processes on vegetation pattern in the Czechowskie lake catchment Czechowo Region (Northern Tuchola Pinewoods) during the Younger Dryas cooling

NASA Astrophysics Data System (ADS)

Noryśkiewicz, Agnieszka Maria; Kramkowski, Mateusz; Słowiński, Michał; Zawiska, Izabela; Lutyńska, Monika; Błaszkiewicz, Mirosław; Brauer, Achim

2014-05-01

Czechowskie lake is located in the northern part of the Tuchola Pinewoods District (Northern Poland) in a young glacial landscape. At present, the majority of the area is forested or used for agricultural purposes, but among them a high amount of basins filled with biogenic sediments are present. This area is very suitable for the postglacial vegetation development investigation because of the LST ash and laminated sediments which we found in the Trzechowskie palaeolake and Czechowskie Lake (Wulf et. all 2013). The aim of the research was to reconstruct the past landscape and vegetation response to Younger Dryas cooling and we present the results of the palinological analysis done for 6 core of biogenic sediments. Our main objective was to determine whether local factors such as topography and soil cover have a significant impact on the vegetation, eutrophy and sedimentation rate at this time. In the lake Czechowskie lake catchment we have six cores that cover postglacial succession (Lake Czechowskie small basin - profile JC-12-s; Lake Czechowskiego terrace - profile TK; Lake Czechowskie vicinity - profile "Oko and Cz/80; Trzechowskie paleolake - profile T/trz; Valley between paleolake Trzechowskie and Lake Czechowskie - profile DTCZ-4). The paleoecological research carried out involved an analysis of pollen, macrofossils, Cladocera, diatom, loss-on-ignition and CaCO3 content. The results show, that the dominant plant communities during the Youngers Dryas in the region nearby Lake Czechowskie are heliophytes xeric herb vegetation with juniper (Juniperus communis) shrubs and birch (Betula) and pine (Pinus sylvestris). In the pollen diagrams there was the difference noted in the participation of the dominant pollen, the juniper pollen was always high but varied from 18 to 37%, birch average pollen share was between 17-27%. The thickness and type of the sediment accumulated in Younger Dryas in the presented profiles differs significantly. In the profiles which comprise the whole succession of the Younger Dryas ("Oko", T/trz, JC-12-s) the thickest sediments are in "Oko" profile (1 m) and thinness in the profile from the lake Czechowskie small basin JC-12-s (45 cm). In Cz/80 profile the lake sedimentation stopped at the beginning of the Younger Dryas. The conclusion is that the all pollen results show the same main patterns during the Younger Dryas cooling. Nevertheless the local factors had an influence on the vegetation and this reflected in the different participation of species among sites. The sediment type and sedimentation rate was strongly influenced by the local factors. The combined approach of fossil pollen data and contemporary distribution of substrate and relief allowed to reconstruct of Younger Dryas vegetation patterns and relief in Czechowskie lake catchment Czechowo region. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution Analysis -ICLEA- of the Helmholtz Association. The research was supported by the National Science Centre Poland (grants No. NN 306085037 and NCN 2011/01/B/ST10/07367). Literature: Wulf S., Ott F., Słowiński M., Noryśkiewicz A. M., Drager N., Martin-Puertas C., Czymzik M., Neugebauer I., Dulski P., Bourne A., Błaszkiewicz M., Brauer A. 2013. Tracing the Laacher See Tephra in the varved sediment record of the Trzechowskie palaeolake in central Northern Poland. Quaternary Science Reviews, s. 129-139.

Late Pleistocene Climate Events and The Origin of Agriculture In SW Asia

NASA Astrophysics Data System (ADS)

Rossignol-Strick, M.

In the Eastern Mediterranean sea, the climate succession of the last deglaciation is documented and dated in marine cores by the d18-O variation of foraminiferal cal- cite and pollen records. The Last Glacial Maximum is identified by a large abundance of grass pollen from a prairie-type vegetal cover with low annual precipitation in the mountainous north and east borderlands of the sea, where the pollen mainly origi- nates. During the first phase of the last deglaciation, the Bolling/Allerod chronozone, the moisture availability increases and makes possible the spread of a deciduous for- est, as shown by the increasing pollen abundance of the deciduous oak. The cold and arid Younger Dryas is identified by a reversal to semi-desert conditions, with the in- crease of sage-brush (Artemisia) and the saline-tolerant Chenopodiaceae. The climate of the earliest Holocene is Optimum for at least 3000 years (9000-6000yr BP), with the largest spread of the deciduous forest at low-middle elevations signalling wet sum- mers and of the Pistacia woodland at low elevations signalling mild, no-frost winters. This is the time when the most recent sapropel deposited in the eastern Mediterranean under anoxic bottom conditions generated by a surface lid of lower salinity due to the concomitant largest floods of the Nile River fed by the strongest African monsoon rains in the Ethiopian Highlands. In SW Asia, the pollen records of lakes and marshes have been correlated with those of the marine cores, thereby obtaining a robust time-frame. In that area, the archaeo- logical data of human settlements are independently dated by 14C. Thus the archaeo- logical succession can be securely set against the well-dated climatic succession. The Late Palaeolithic populations of SW Asia were wandering hunter-gatherers in the prairies of the Last Glacial Maximum, where they already collected wild wheat, barley and fruit. With the Bolling/Allerod wetter and warmer climate, they began to settle in favourable locations, on a year-long or semi-permanent basis. They exploited, proba- bly more widely, the vegetal food resources of wild cereals and pulses. In Palestine, this culture is called Natufian. In Syria on the Middle Euphrates, the settlement at Tel Abu Hureira displays a first phase of occupation that yielded wild emmer wheat and two-row barley. These wild varieties of cereals are characterized by a brittle rachis of the ear that insures the wide dispersion of the spikelets at maturity. This Phase I came to an end with the abandonment of the site for several hundred years. The following occupation Phase II immediately yields the domesticated form of cereals, which are 1 mainly identified by the non-brittle, solid rachis at maturity. This mutant form makes possible for man to more efficiently collect the seeds with a sickle or a stick. Based on the local 14C dates, the settlement interruption is coeval with the cold, arid Younger Dryas, and the incipience of Phase II is coeval with the Climate Optimum of the early Holocene. It is striking that the domestication of emmer wheat appears to have taken place during the Younger Dryas. This strong climatic shift must somehow have constrained this most fundamental step in the globally earliest emergence of agriculture, that of SW Asia. The accumulation of grain surplus supported the human population increase that eventually led to the earliest emergence of urban civilization in SW Asia. 2

Spatial variability and trends in Younger Dryas equilibrium line altitudes across the European Alps using a hypsometrically based ELA model: results and implications

NASA Astrophysics Data System (ADS)

Keeler, D. G.; Rupper, S.; Schaefer, J. M.; Finkel, R. C.; Maurer, J. M.

2016-12-01

Alpine glaciers constitute an important component of terrestrial paleoclimate records due to, among other characteristics, their high sensitivity to climate change, near global extent, and their integration of myriad climate variables into a single, easily detected signal. Because the glacier equilibrium line altitude (ELA) provides a more explicit representation of climate than many other glacier properties, ELA methods allow for more direct comparisons of multiple glaciers within or between regions. Such comparisons allow for more complete investigations of the ultimate causes of mountain glaciation during specific events. Many studies however tend to focus on a limited number of sites, and employ a large variety of different techniques for ELA reconstruction between studies, making wider climate implications more tenuous. Methods of ELA reconstruction that can be rapidly and consistently applied to an arbitrary number of paleo-glaciers would provide a more accurate portrayal of the changes in climate across a given region. Here we present ELA reconstructions from Egesen Stadial moraines across the European Alps using an ELA model accounting for differences in glacier width, glacier shape, bed topography, ice thickness, and glacier length, including several glaciers constrained to the Younger Dryas using surface exposure dating techniques. We compare reconstructed Younger Dryas ELA values to modern ELA values using the same model, or using end of summer snowline estimates where no glacier is currently present. We further provide uncertainty estimates on the ΔELA using bootstrapped Monte Carlo simulations for the various input parameters. Preliminary results compare favorably to previous glacier studies of the European Younger Dryas, but provide greater context from many glaciers across the region as a whole. Such results allow for a more thorough investigation of the spatial variability and trends in climate during the Younger Dryas across the European Alps, and comparisons of other regions in the future.

Daily average temperature and mortality among the elderly: a meta-analysis and systematic review of epidemiological evidence

NASA Astrophysics Data System (ADS)

Yu, Weiwei; Mengersen, Kerrie; Wang, Xiaoyu; Ye, Xiaofang; Guo, Yuming; Pan, Xiaochuan; Tong, Shilu

2012-07-01

The impact of climate change on the health of vulnerable groups such as the elderly has been of increasing concern. However, to date there has been no meta-analysis of current literature relating to the effects of temperature fluctuations upon mortality amongst the elderly. We synthesised risk estimates of the overall impact of daily mean temperature on elderly mortality across different continents. A comprehensive literature search was conducted using MEDLINE and PubMed to identify papers published up to December 2010. Selection criteria including suitable temperature indicators, endpoints, study-designs and identification of threshold were used. A two-stage Bayesian hierarchical model was performed to summarise the percent increase in mortality with a 1°C temperature increase (or decrease) with 95% confidence intervals in hot (or cold) days, with lagged effects also measured. Fifteen studies met the eligibility criteria and almost 13 million elderly deaths were included in this meta-analysis. In total, there was a 2-5% increase for a 1°C increment during hot temperature intervals, and a 1-2 % increase in all-cause mortality for a 1°C decrease during cold temperature intervals. Lags of up to 9 days in exposure to cold temperature intervals were substantially associated with all-cause mortality, but no substantial lagged effects were observed for hot intervals. Thus, both hot and cold temperatures substantially increased mortality among the elderly, but the magnitude of heat-related effects seemed to be larger than that of cold effects within a global context.

Geoarchaeological and paleohydrological evidence for a clovis-age drought in North America and its bearing on extinction

NASA Astrophysics Data System (ADS)

Haynes, C. Vance

1991-05-01

At the Murray Springs Clovis site in southeastern Arizona, stratigraphic and geomorphic evidence indicates that an abnormally low water table 10,900 yr B.P. was followed soon thereafter by a water-table rise accompanied by the deposition of an algal mat (the black mat) that buried mammoth tracks, Clovis artifacts, and a well. This water-table fluctuation correlates with pluvial lake fluctuations in the Great Basin during and immediately following Clovis occupation of that region. Many elements of Pleistocene megafauna in North America became extinct during the dry period. Oxygen isotope records show a marked decrease in δ18O correlated with the Younger Dryas cold-dry event of northern Europe which ended 10,750 yr B.P., essentially the same time as the water table began to rise in southeastern Arizona. Clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress. If so, both climate and human predation contributed to Pleistocene extinction in America.

Surface (sea floor) and near-surface (box cores) sediment mineralogy in Baffin Bay as a key to sediment provenance and ice sheet variations

USGS Publications Warehouse

Andrews, John T.; Eberl, D.D.

2011-01-01

To better understand the glacial history of the ice sheets surrounding Baffin Bay and to provide information on sediment pathways, samples from 82 seafloor grabs and core tops, and from seven box cores were subjected to quantitative X-ray diffraction weight percent (wt.%) analysis of the 2000 m) all show an abrupt drop in calcite wt.% (post-5 cal ka BP?) following a major peak in detrital carbonate (mainly dolomite). This dolomite-rich detrital carbonate (DC) event in JR175BC06 is possibly coeval with the Younger Dryas cold event. Four possible glacial-sourced end members were employed in a compositional unmixing algorithm to gain insight into down core changes in sediment provenance at the deep central basin. Estimates of the rates of sediment accumulation in the central basin are only in the range of 2 to 4 cm/cal ka, surprisingly low given the glaciated nature of the surrounding land.

Flood of October 8 and 9, 2005, on Cold River in Walpole, Langdon, and Alstead and on Warren Brook in Alstead, New Hampshire

USGS Publications Warehouse

Olson, Scott A.

2006-01-01

Southwestern New Hampshire experienced damaging flooding on October 8 and 9, 2005. The flooding was the result of a storm producing at least 7 inches of rain in a 30-hour period. The heavy, intense rainfall resulted in runoff and severe flooding, especially in regions of steep topography that are vulnerable to flash flooding. Some of the worst property damage was in the towns of Alstead, Langdon, and Walpole, New Hampshire along Cold River and Warren Brook. Warren Brook was severely flooded and had flows that exceeded a 100-year recurrence interval upstream of Cooper Hill Road. Downstream of Cooper Hill Road, the flooding was worsened as a result of a sudden release of impounded water, making the flood levels greater than what would be experienced from a 500-year recurrence-interval flood. Along Cold River, upstream of its confluence with Warren Brook, flooding was at approximately a 100-year recurrence interval. Downstream of the confluence of Cold River and Warren Brook, the streamflows, which were swollen by the surge of water from Warren Brook, exceeded a 500year recurrence interval.

North Atlantic forcing of tropical Indian Ocean climate.

PubMed

Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; Lückge, Andreas

2014-05-01

The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.

Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences

PubMed Central

Moore, Christopher R.; West, Allen; LeCompte, Malcolm A.; Brooks, Mark J.; Daniel, I. Randolph; Goodyear, Albert C.; Ferguson, Terry A.; Ivester, Andrew H.; Feathers, James K.; Kennett, James P.; Tankersley, Kenneth B.; Adedeji, A. Victor; Bunch, Ted E.

2017-01-01

Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control. PMID:28276513

Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown

USGS Publications Warehouse

Toomey, Michael; Korty, Robert L.; Donnelly, Jeffrey P.; van Hengstum, Peter J.; Curry, William B.

2017-01-01

The risk posed by intensification of North Atlantic hurricane activity remains controversial, in part due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Here we present a record of storm-triggered turbidite deposition offshore the Dry Tortugas, south Florida, USA, that spans abrupt transitions in North Atlantic sea-surface temperature and Atlantic Meridional Overturning Circulation (AMOC) during the Younger Dryas (12.9–11.7 ka). Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at that time, our record and numerical experiments suggest that strong hurricanes may have regularly affected Florida. Less severe surface cooling at mid-latitudes (∼20°–40°N) than across much of the tropical North Atlantic (∼10°–20°N) in response to AMOC reduction may best explain strong hurricane activity during the Younger Dryas near the Dry Tortugas and possibly along the entire southeastern coast of the United States.

Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences

NASA Astrophysics Data System (ADS)

Moore, Christopher R.; West, Allen; Lecompte, Malcolm A.; Brooks, Mark J.; Daniel, I. Randolph; Goodyear, Albert C.; Ferguson, Terry A.; Ivester, Andrew H.; Feathers, James K.; Kennett, James P.; Tankersley, Kenneth B.; Adedeji, A. Victor; Bunch, Ted E.

2017-03-01

Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.

Differential response of vegetation in Hulun Lake region at the northern margin of Asian summer monsoon to extreme cold events of the last deglaciation

NASA Astrophysics Data System (ADS)

Zhang, Shengrui; Xiao, Jule; Xu, Qinghai; Wen, Ruilin; Fan, Jiawei; Huang, Yun; Yamagata, Hideki

2018-06-01

The response of vegetation to extreme cold events during the last deglaciation is important for assessing the impact of possible extreme climatic events on terrestrial ecosystems under future global warming scenarios. Here, we present a detailed record of the development of regional vegetation in the northern margin of Asian summer monsoon during the last deglaciation (16,500-11,000 cal yr BP) based on a radiocarbon-dated high-resolution pollen record from Hulun Lake, northeast China. The results show that the regional vegetation changed from subalpine meadow-desert steppe to mixed coniferous and deciduous forest-typical steppe during the last deglaciation. However, its responses to the Heinrich event 1 (H1) and the Younger Dryas event (YD) were significantly different: during the H1 event, scattered sparse forest was present in the surrounding mountains, while within the lake catchment the vegetation cover was poor and was dominated by desert steppe. In contrast, during the YD event, deciduous forest developed and the proportion of coniferous forest increased in the mountains, the lake catchment was occupied by typical steppe. We suggest that changes in Northern Hemisphere summer insolation and land surface conditions (ice sheets and sea level) caused temperature and monsoonal precipitation variations that contributed to the contrasting vegetation response during the two cold events. We conclude that under future global warming scenarios, extreme climatic events may cause a deterioration of the ecological environment of the Hulun Lake region, resulting in increased coniferous forest and decreased total forest cover in the surrounding mountains, and a reduction in typical steppe in the lake catchment.

Radiocarbon dating with annual-resolution of subfossil trees from the Younger Dryas event in the southern French Alps

NASA Astrophysics Data System (ADS)

Capano, Manuela; Miramont, Cécile; Guibal, Frédéric; Kromer, Bernd; Tuna, Thibaut; Fagault, Yoann; Bard, Edouard

2017-04-01

Tree rings are an important archive for the calibration of radiocarbon data. The younger part of the IntCal curve is based essentially on tree-ring chronologies, absolutely dated by dendrochronological analysis. For the Northern Hemisphere (NH), a gap still exists between the absolutely dated sequences and a floating chronology. Based on the Southern Hemisphere (SH) tree-ring chronologies a link has been previously proposed (Reimer et al. 2013, Radiocarbon; see also update in Hogg et al. 2016, Radiocarbon). By measuring radiocarbon at annual resolution in French subfossil pines (Pinus sylvestris L.) we propose to improve the connection between the absolute chronology and the floating chronology. Several subfossil pines have been found in the Southern French Alps; they were buried by flood deposits, allowing their preservation. Some trees discovered in the Barbier riverbed were dated to the Younger Dryas periods by previous decadal radiocarbon measurements, performed in Heidelberg and Mannheim. The trees selected for our new study are Barb12 and Barb17 (analyzed sequences of 163 and 152 rings, respectively). These sequences were sampled at annual resolution when permitted by the ring width. As a first step, every third ring was pretreated for radiocarbon analysis. These samples were sliced in small pieces and pretreated by using the ABA-B method before being combusted, graphitized with the AGE system and measured with AixMICADAS (Bard et al. 2015, Nucl. Instr. Meth. B). From the comparison with the kauri sequence, the Barb12-17 sequence can be dated from about 12835 to 12606 cal. BP. It can also be used to calculate the interhemispheric gradient (IHG) over the overlapping period. In order to reduce the inter-annual variability, the Barb12-17 record was smoothed, grouped and averaged over the same decades as in the Kauri record. On the basis of twenty values, a mean IHG value of ca. 60 years was calculated. Quantification of the IHG around 50 yr is particularly robust during the two "age plateaux" corresponding to the time intervals 12820-12760 and 12660-12630 cal. BP. Overall, the IHG stayed relatively high throughout the studied period corresponding to the beginning of the Younger Dryas climatic event.

Pleistocene environmental dynamics recorded in the loess of the middle and lower Danube basin

NASA Astrophysics Data System (ADS)

Fitzsimmons, Kathryn E.; Marković, Slobodan B.; Hambach, Ulrich

2012-05-01

The substantial loess deposits of the middle and lower Danube basin in southeastern Europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent, yet are also the least well understood. Environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions, which nevertheless reflect oscillations between relatively warm-humid (“interglacial”) and cold-dry (“glacial”) intervals. This relative environmental stability may have proven important for hominins migrating into and through the region. The loess stratigraphy comprises distinct loess-paleosol sequences, reflecting glacial-interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry. These phases are emphasised by variations in vegetation and malacofauna which respond to climatic change. The loess deposits demonstrate broadly similar sedimentological characteristics across the basin. Danubian loess deposits initiated in response to the tectonic formation of the Pannonian basin, retreat of the large palaeolakes, and increased sediment supply from the Danube. The period from ˜1 Ma-500 ka (MIS 27-13) was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively, in response to relatively humid, forested conditions. This period represents the opening of the Danube corridor and provides the backdrop for initial hominin arrival into Europe. After ˜500 ka, and particularly after MIS 9, loess accumulation rates increased in response to relatively more steppic, arid, environments. MIS 9 and 13-15 were the most humid phases of the last ˜600 ky. The MIS 5 interglacial period was the warmest, and relatively most humid, period preceding the Holocene, and was followed by substantially increased loess accumulation during MIS 4, which may be linked to North Atlantic circulation. The complexity of the MIS 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time. MIS 3 corresponds with the first arrival of anatomically modern humans to Europe. The last glacial maximum and Younger Dryas of MIS 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the North Atlantic, although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota, as may also have been the case for most of the Pleistocene glacial cycles. The Holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial.

Sea ice cover variability and river run-off in the western Laptev Sea (Arctic Ocean) since the last 18 ka

NASA Astrophysics Data System (ADS)

Hörner, T.; Stein, R.; Fahl, K.; Birgel, D.

2015-12-01

Multi-proxy biomarker measurements were performed on two sediment cores (PS51/154, PS51/159) with the objective reconstructing sea ice cover (IP25, brassicasterol, dinosterol) and river-runoff (campesterol, β-sitosterol) in the western Laptev Sea over the last 18 ka with unprecedented temporal resolution. The sea ice cover varies distinctly during the whole time period. The absence of IP25 during 18 and 16 ka indicate that the western Laptev Sea was mostly covered with permanent sea ice (pack ice). However, a period of temporary break-up of the permanent ice coverage occurred at c. 17.2 ka (presence of IP25). Very little river-runoff occurred during this interval. Decreasing terrigenous (riverine) input and synchronous increase of marine produced organic matter around 16 ka until 7.5 ka indicate the gradual establishment of a marine environment in the western Laptev Sea related to the onset of the post-glacial transgression of the shelf. Strong river run-off and reduced sea ice cover characterized the time interval between 15.2 and 12.9 ka, including the Bølling/Allerød warm period (14.7 - 12.9 ka). Moreover, the DIP25 Index (ratio of HBI-dienes and IP25) might document the presence of Atlantic derived water at the western Laptev Sea shelf area. A sudden return to severe sea ice conditions occurred during the Younger Dryas (12.9 - 11.6 ka). This abrupt climate change was observed in the whole circum-Arctic realm (Chukchi Sea, Bering Sea, Fram Strait and Laptev Sea). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (deep drop in terrigenous and phytoplankton biomarkers) may document the entry of a giant freshwater plume, possibly relating to the Lake Agassiz outburst at 13 ka. IP25 concentrations increase and higher values of the PIP25 Index during the last 7 ka reflect a cooling of the Laptev Sea spring season. Moreover, a short-term variability of c. 1.5 thousand years occurred during the last 12 ka, most probably following Bond Cycles.

Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective

NASA Astrophysics Data System (ADS)

Shibahara, Akihiko; Ohkushi, Ken'ichi; Kennett, James P.; Ikehara, Ken

2007-09-01

A strong oxygen minimum zone (OMZ) currently exists at upper intermediate water depths on the northern Japanese margin, NW Pacific. The OMZ results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters. We investigated late Quaternary history (last 34 kyr) of ocean floor oxygenation and the OMZ using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off Shimokita Peninsula and Tokachi, northern Japan, at water depths between 975 and 1363 m. These cores are well located within the present-day OMZ, a region of high surface water productivity, and in close proximity to the source region of North Pacific Intermediate Water. Late Quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments. Foraminiferal assemblages are interpreted to represent three main groups representing oxic, suboxic, and dysoxic conditions. Assemblage changes in all three cores and hence in bottom water oxygenation coincided with late Quaternary climatic episodes, similar to that known for the southern California margin. These episodes, in turn, are correlated with orbital and millennial climate episodes in the Greenland ice core including the last glacial episode, Bølling-Ållerød (B/A), Younger Dryas, Preboreal (earliest Holocene), early Holocene, and late Holocene. The lowest oxygen conditions, marked by dysoxic taxa and laminated sediments in one core, occurred during the B/A and the Preboreal intervals. Suboxic taxa dominated mainly during the last glacial, the Younger Dryas, and most of the Holocene. Dysoxic conditions during the B/A and Preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern Pacific. Remarkable similarities are evident in the late Quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern Japan and southern California. The oscillations in OMZ strength, reflected by these faunal changes, were widespread and apparently synchronous over wide areas of the North Pacific, reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late Quaternary climate change on millennial and orbital timescales.

Evidence for insolation and Pacific forcing of late glacial through Holocene climate in the Central Mojave Desert (Silver Lake, CA)

NASA Astrophysics Data System (ADS)

Kirby, Matthew E.; Knell, Edward J.; Anderson, William T.; Lachniet, Matthew S.; Palermo, Jennifer; Eeg, Holly; Lucero, Ricardo; Murrieta, Rosa; Arevalo, Andrea; Silveira, Emily; Hiner, Christine A.

2015-09-01

Silver Lake is the modern terminal playa of the Mojave River in southern California (USA). As a result, it is well located to record both influences from the winter precipitation dominated San Bernardino Mountains - the source of the Mojave River - and from the late summer to early fall North American monsoon at Silver Lake. Here, we present various physical, chemical and biological data from a new radiocarbon-dated, 8.2 m sediment core taken from Silver Lake that spans modern through 14.8 cal ka BP. Texturally, the core varies between sandy clay, clayey sand, and sand-silt-clay, often with abrupt sedimentological transitions. These grain-size changes are used to divide the core into six lake status intervals over the past 14.8 cal ka BP. Notable intervals include a dry Younger Dryas chronozone, a wet early Holocene terminating 7.8 - 7.4 cal ka BP, a distinct mid-Holocene arid interval, and a late Holocene return to ephemeral lake conditions. A comparison to potential climatic forcings implicates a combination of changing summer - winter insolation and tropical and N Pacific sea-surface temperature dynamics as the primary drivers of Holocene climate in the central Mojave Desert.

From valley to marginal glaciation in alpine-type relief: Lateglacial glacier advances in the Pięć Stawów Polskich/Roztoka Valley, High Tatra Mountains, Poland

NASA Astrophysics Data System (ADS)

Zasadni, Jerzy; Kłapyta, Piotr

2016-01-01

The Pięć Stawów Polskich-Roztoka Valley in the High Tatras (Western Carpathians) features typical alpine-type relief with a deeply incised glacial trough and large, compound trough head cirque. The prominent hypsographic maximum in the valley (1680-2000 m) along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms, specifically the most recent Lateglacial advances. The valley has been intensively studied before in the context of glacial chronology. In this paper, we re-establish the post-Last Glacial Maximum (LGM) glacial chronology of the valley via detailed geomorphologic mapping, equilibrium line altitude (ELA) reconstruction, and Schmidt hammer (SH) dating, along with a critical review of previously published cosmogenic exposure age data (36Cl) and lacustrine sediment chronology. Our results indicate that the first four of the five distinguished Lateglacial stages (Roztoka I-III, Pusta I) occurred before the Bølling/Allerød (B/A) interstadial; thus, virtually the entire valley became deglaciated in course of the Oldest Dryas cold phase. A distinct reorganization of deglacial patterns from valley-type to marginal-type occurred before B/A warming when the ELA increased above the valley hypsographic maximum concentrated at the cirque bottom elevation. It shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing. This points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions. We infer that glaciers vanished in the Tatra Mountains during the B/A interstadial. Later, a renewed advance during the Younger Dryas (Pusta II) formed a nearly continuous, festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls. Furthermore, we discus some paleoenvironmental significance of the geomorphological record in the valley, as well, the applicability of SH dating in constructing glacial chronology.

A Digital 3D-Reconstruction of the Younger Dryas Baltic Ice Lake

NASA Astrophysics Data System (ADS)

Jakobsson, M.; Alm, G.; Bjorck, S.; Lindeberg, G.; Svensson, N.

2005-12-01

A digital 3D-reconstruction of the final stage of the ice dammed Baltic Ice Lake (BIL), dated to the very end of the Younger Dryas cold period (ca. 11 600 cal. yr BP) has been compiled using a combined bathymetric-topographic Digital Terrain Model (DTM), Scandinavian ice sheet limits, Baltic Sea Holocene bottom sediment thickness information, and a paleoshoreline database maintained at the Lund University. The combined bathymetric-topographic Digital Terrain Model (DTM) model used to reconstruct the ice dammed lake was compiled specifically for this study from publicly available data sets. The final DTM is in the form of a digital grid on Lamberts Equal Area projection with a resolution of 500 x 500 m, which permits a much more detailed reconstruction of the BIL than previously made. The lake was constructed through a series of experiments where mathematical algorithms were applied to fit the paleolake's surface through the shoreline database. The accumulated Holocene bottom sediments in the Baltic Sea were subsequently subtracted from the present bathymetry in our reconstruction. This allows us to estimate the Baltic Ice Lake's paleobathymetry, area, volume, and hypsometry, which will comprise key input data to lake/climate modeling exercises following this study. The Scandinavian ice sheet margin eventually retreated north of Mount Billingen, which was the high point in terrain of Southern central Sweden bordering to lower terrain further to the North. As a consequence, the BIL was catastrophically drained through this area, resulting in a 25 m drop of the lake level. With our digital BIL model we estimate that approximately 7, 800 km3 of water drained during this event and that the ice dammed lake area was reduced with ca 18 percent. The digital BIL reconstruction is analyzed using 3D-visualization techniques that provide new detailed information on the paleogeography in the area, both before and after the lake drainage, with implications for interpretations of geological records concerning the post-glacial environmental development of southern Scandinavia.

Sensitivity of the Younger Dryas climate to changes in orbtial, greenhouse gas, and freshwater forcing in CESM1

NASA Astrophysics Data System (ADS)

Hughlett, T. M.; Winguth, A. M. E.; Rosenbloom, N. A.; He, F.

2016-12-01

The Younger Dryas cooling event ( 12,900 years before present) was the most recent abrupt climate change in the geologic record where climate for the Northern Hemisphere returned to a near-glacial state. The cause of this cooling event is widely controversial, and no consensus has been found as to why the onset of the cooling occurred. Of the several hypotheses proposed, the freshening of the North Atlantic Ocean due to meltwater discharge from the retreating Lake Agassiz and subsequent changes in Atlantic meridional oceanic circulation (AMOC) is the most widely accepted one. In this study, the Community Earth System Model version 1 was used to perform sensitivity experiments to test how the AMOC responds to a freshwater discharge into the Northern Atlantic Ocean over the course of 1,000 years. This study is the first fully coupled, moderate-resolution simulation that implements a 13.1ka ice sheet (ICE-5G) along with Younger Dryas boundary and initial conditions. With the addition of the 13.1ka ice sheet and a 0.3 Sverdrup (Sv) freshwater discharge into the Northern Atlantic Ocean, the AMOC reduces by approximately 20 Sv, coming to a substantially slowed-down state of approximately 5 Sv. This reduction of the AMOC causes a decrease in surface air temperature of approximately 15 °C, which is in agreement with surface air temperature reconstructions from the Greenland Ice Sheet Project 2. Overall, the simulation presented in this study accurately represents the climatic state of the Younger Dryas cooling event.

Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis

USGS Publications Warehouse

Israde-Alcántara, Isabel; Bischoff, James L.; Domínguez-Vázquez, Gabriela; Li, Hong-Chun; DeCarli, Paul S.; Bunch, Ted E.; Wittke, James H.; Weaver, James C.; Firestone, Richard B.; West, Allen; Kennett, James P.; Mercer, Chris; Xie, Sujing; Richman, Eric K.; Kinzie, Charles R.; Wolbach, Wendy S.

2012-01-01

We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact. These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial. Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences. Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record. This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core. Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond: n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance. This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe. We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism. It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.

Evidence from Central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis

USGS Publications Warehouse

Israde-Alcántaraa, Isabel; Bischoff, James L.; Domínguez-Vázquez, Gabriela; Li, Hong-Chun; DeCarli, Paul S.; Bunch, Ted E.; Wittke, James H.; Weaver, James C.; Firestone, Richard B.; West, Allen; Kennett, James P.; Mercer, Chris; Xie, Sujing; Richman, Eric K.; Kinzie, Charles R.; Wolbach, Wendy S.; Stanley, Steven M.

2012-01-01

We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact. These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial. Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences. Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record. This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core. Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond: n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance. This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe. We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism. It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.

Ice ingestion with a long rest interval increases the endurance exercise capacity and reduces the core temperature in the heat.

PubMed

Naito, Takashi; Iribe, Yuka; Ogaki, Tetsuro

2017-01-05

The timing in which ice before exercise should be ingested plays an important role in optimizing its success. However, the effects of differences in the timing of ice ingestion before exercise on cycling capacity, and thermoregulation has not been studied. The aim of the present study was to assess the effect of length of time after ice ingestion on endurance exercise capacity in the heat. Seven males ingested 1.25 g kg body mass -1 of ice (0.5 °C) or cold water (4 °C) every 5 min, six times. Under three separate conditions after ice or water ingestion ([1] taking 20 min rest after ice ingestion, [2] taking 5 min rest after ice ingestion, and [3] taking 5 min rest after cold water ingestion), seven physically active male cyclists exercised at 65% of their maximal oxygen uptake to exhaustion in the heat (35 °C, 30% relative humidity). Participants cycled significantly longer following both ice ingestion with a long rest interval (46.0 ± 7.7 min) and that with a short rest interval (38.7 ± 5.7 min) than cold water ingestion (32.3 ± 3.2 min; both p < 0.05), and the time to exhaustion was 16% (p < 0.05) longer for ice ingestion with a long rest interval than that with a short rest interval. Ice ingestion with a long rest interval (-0.55 ± 0.07 °C; both p < 0.05) allowed for a greater drop in the core temperature than both ice ingestion with a short rest interval (-0.36 ± 0.16 °C) and cold water ingestion (-0.11 ± 0.14 °C). Heat storage under condition of ice ingestion with a long rest interval during the pre-exercise period was significantly lower than that observed with a short rest interval (-4.98 ± 2.50 W m -2 ; p < 0.05) and cold water ingestion (2.86 ± 4.44 W m -2 ). Therefore, internal pre-cooling by ice ingestion with a long rest interval had the greatest benefit on exercise capacity in the heat, which is suggested to be driven by a reduced rectal temperature and heat storage before the start of exercise.

Revised Quaternary glacial succession and post-LGM recession, southern Wind River Range, Wyoming, USA

NASA Astrophysics Data System (ADS)

Dahms, Dennis; Egli, Markus; Fabel, Derek; Harbor, Jon; Brandová, Dagmar; de Castro Portes, Raquel; Christl, Marcus

2018-07-01

We present here a more complete cosmogenic chronology of Pleistocene glacial deposits for the Wind River Range, Wyoming, USA. Fifty-one new and thirty-nine re-calculated 10Be and 26Al exposure ages from Sinks and North Fork canyons, Stough Basin, Cirque of the Towers and the Temple Lake valley allow us to more tightly constrain the timing and sequence of glacial alloformations in the southern portion of the range. Moraines, diamicts and bedrock exposures here have previously been correlated with as many as five Pleistocene and four Holocene glacial events. Exposure ages from Pleistocene alloformations associated with trunk glaciers in Sinks Canyon and North Fork Canyon generally confirm earlier age estimates. Cosmogenic radionuclide (CRN, 10Be and 26Al) ages from moraines and striated bedrock surfaces previously mapped as Pinedale correspond to MIS2, while boulder exposure ages from moraines mapped as Bull Lake correspond generally to MIS5-MIS6. Geomorphic data from a moraine previously mapped as Younger pre-Sacagawea Ridge appears to correspond most closely to the Sacagawea Ridge glacial episode (MIS-16), but the uncertainty of a single 10Be exposure age suggests the unit could be as young as MIS-10 or as old as MIS-18. Boulders from a diamict on Table Mountain previously reported as Older pre-Sacagawea Ridge yield two 10Be exposure ages that suggest the presence of Early Pleistocene glacial activity here possibly older than 1-2 Ma (>MIS-30). Bedrock exposure ages within Sinks Canyon suggest the Pinedale valley glacier had retreated from the floor of Sinks Canyon to above PopoAgie Falls by ca. 15.3 ka. Cirque glaciers in Stough Basin appear to have retreated behind their riegels by ca. 16 ka, which suggests the cirque glaciers were decoupling across their riegels from the valley glaciers below at this time, prior to their readvance to form Lateglacial moraines. New 10Be boulder exposure ages from moraines previously correlated to the Temple Lake and Alice Lake allostratigraphic units in the cirques of Stough Basin and Cirque of the Towers show general equivalence to the stadial event just prior to the onset of the Bølling interstadial (17.5-14.7 ka) and to the Intra-Allerød Cold Period-Younger Dryas stadial phase (13.9-11.7 ka), respectively. From this evidence, the Temple Lake Alloformation of the Wind River Mountains now should correspond to the INTIMATE GS-2.1a (Oldest Dryas) stadial event while the Alice Lake Alloformation should correspond to the INTIMATE GS-2 stadial (IACP-Younger Dryas). Thus, we consider that evidence no longer exists for early-to mid-Holocene glacial events in the southern Wind River Range.

Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert

NASA Astrophysics Data System (ADS)

Roperch, Pierrick; Gattacceca, Jerome; Valenzuela, Millarca; Devouard, Bertrand; Lorand, Jean-Pierre; Arriagada, Cesar; Rochette, Pierre; Latorre, Claudio

2017-04-01

Melted rocks are a common feature in many of the 175 recognized terrestrial impact structures [1]. However, some glasses, like the Dakhleh Glass [2] or the Edeowie Glass [3] are also attributed to impacts despite the lack of other direct evidence. These cases have been attributed to low-altitude airbursts of cosmic bodies (asteroids, comets) during their entry in the Earth's atmosphere but the identification and mechanism of formation of these glasses are however debated. Massive glass blocks were recently discovered [4] in the Tamarugal-Llamara basin of the Atacama desert in Chile. We show that these glasses, found near the town of Pica at four localities separated by up to 70 km, are neither fulgurites, nor volcanic glasses, nor metallurgical slags related to anthropic activity, but show close similarities with other glasses, which have been attributed to large airbursts. However, most glasses contain numerous plant imprints and some glasses are mainly made of partially melted silicified plant twigs and field observations indicate that the glasses are restricted to specific Late Pleistocene wetlands. Large oases did indeed form in the hyperarid Atacama desert due to elevated groundwater discharge and increased recharge during the Central Andean Pluvial Event (roughly coeval with the Mystery interval and Younger Dryas). 14C dating and paleomagnetic data indicate that the glasses were formed during at least two distinct periods. The strong environmental control on the distribution of the glasses and large differences in ages rule out the hypothesis of a single large airburst as the cause of surface melting. The available data suggest that the Atacama desert surface glasses were formed in situ by natural fires in soils rich in dry organic matter and siliceous biological remains, at a time of strong climate oscillations between wet (organic matter accumulation in soils) and dry periods (triggering fires) in desert wetlands. Our interpretation likely applies to other cases of silicate glasses attributed to airbursts, challenging the high airburst rate as well as the interpretation of fossils and organic matter in "impact glasses" [5]. Our study also demonstrates that exotic mineralogy with glass containing spherules of iron sulphides, metallic iron or iron phosphides may not necessarily imply an impact origin. This in turn cast doubts on some studies relating impact and climate change triggering the Younger Dryas cold event at the end of the Pleistocene [6]. 1. French, B. M. & Koeberl, C. Earth-Sci. Rev. 98, 123-170 (2010). 2. Osinski, G. R. et al. Meteorit. Planet. Sci. 43, 2089-2107 (2008). 3. Haines, P. W., Jenkins, R. J. F. & Kelley, S. P. Geology 29, 899 (2001). 4. Blanco, N. & Tomlinsson, A. J. Carta Guatacondo, Región de Tarapacá. (2013). 5. Schultz, P. H., Harris, R. S., Clemett, S. J., Thomas-Keprta, K. L. & Zarate, M. Geology 42, 515-518 (2014). 6. Firestone, R. B. et al. Proc. Natl. Acad. Sci. 104, 16016-16021 (2007).

Variations of the Antarctic Circumpolar Current (ACC) in the Kerguelen Sector during the Last Deglaciation : sedimentological and geochemical evidences

NASA Astrophysics Data System (ADS)

Bout-Roumazeilles, V.; Beny, F.; Mazaud, A.; Michel, E.; Crosta, X.; Davies, G. R.; Bory, A. J. M.

2017-12-01

High-resolution sedimentological and geochemical records were obtained from two sediment cores recovered by the French R/V Marion Dufresne during the INDIEN-SUD-ACC cruises near the sub-Antarctic Kerguelen Islands (49°S). This area is ideal to record past oceanic and atmospheric changes in the Southern Ocean because they are currently located in the northern branch of the Antarctic Circumpolar Current and under the direct influence of Southern Hemisphere Westerly wind belt. This study focuses on the last termination, with specific emphasis on the impact of severe climatic events (Heinrich Stadial 1, Antarctic Cold Reversal, Younger Dryas) onto the ocean-atmospheric exchange. Results indicates that most of the sediment is derived from the Kerguelen Plateau, characterized by high smectite content. Periodically, a minor contribution of Antarctica is noticeable. In particular, illite variations suggest fast and short northward incursions of Antarctic Bottom Water, probably formed in the Prydz Bay during the last glaciation. Grainsize repartition combined to magnetic parameters show a southward migration of the ACC and the fronts associated from the beginning of the deglaciation, which is consistent with Southern Hemisphere climate variations. On the opposite, it highlights an asynchronous decrease of the ACC strength, with a large drop during the Antarctic Cold Reversal when atmospheric CO2 increase was slowed down. Thus, at least in the studied area, the ACC strength and the Antarctic Climate were not synchronous during the last deglaciation.

Simulated influences of Lake Agassiz on the climate of central North America 11,000 years ago

USGS Publications Warehouse

Hostetler, S.W.; Bartlein, P.J.; Clark, P.U.; Small, E.E.; Solomon, A.M.

2000-01-01

Eleven thousand years ago, large lakes existed in central and eastern North America along the margin of the Laurentide Ice Sheet. The large-scale North American climate at this time has been simulated with atmospheric general circulation models, but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere, ice sheet, and proglacial lakes. Here we present simulations of the climate of central and eastern North America 11,000 years ago with a high-resolution, regional climate model nested within a general circulation model. The simulated climate is in general agreement with that inferred from palaeoecological evidence. Our experiments indicate that through mesoscale atmospheric feedbacks, the annual delivery of moisture to the Laurentide Ice Sheet was diminished at times of a large, cold Lake Agassiz relative to periods of lower lake stands. The resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin, thus affecting the routing of fresh water to the North Atlantic Ocean. A retreating ice margin during periods of high lake level may have opened an outlet for discharge of Lake Agassiz into the North Atlantic. A subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet, thereby reducing discharge to the North Atlantic. These variations may have been decisive in causing the Younger Dryas cold even.

Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, Douglas Howe

Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relativemore » weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before ~13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic 10Be and 26Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.« less

Deglacial climatic oscillations in the Gulf of California

NASA Astrophysics Data System (ADS)

Keigwin, L. D.; Jones, G. A.

1990-12-01

A high-resolution, accelerator radiocarbon dated climate record of the interval 8,000-18,000 years B.P. from Deep Sea Drilling Project site 480 (Guaymas Basin, Gulf of California) shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation. Nonlaminated sediments are associated with cooler climatic conditions during the late glacial (up to 13,000 years B.P.), and from 10,300 to 10,800 years B.P., equivalent to the Younger Dryas event of the North Atlantic region. We propose that the changes from laminated (varved) to nonlaminated sediments resulted from increased oxygen content in Pacific intermediate waters during the glacial and the Younger Dryas episodes, and that the forcing for the latter event was global in scope. Prominent events of low δ18O are recorded in benthic foraminifera from 8,000 to 10,000 and at 12,000 years B.P.; evidence for an earlier event between 13,500 and 15,000 years B.P. is weaker. Maximum δ18O is found to have occurred 10,500, 13,500, and 15,000 years ago (and beyond). Oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of Pacific waters of intermediate depth during deglaciation or environmental changes within the Gulf of California region. Several lines of evidence suggest that during deglaciation the climate of the American southwest was marked by increased precipitation that could have lowered salinity in the Gulf of California. Recent modelling studies show that cooling of the Gulf of Mexico due to glacial meltwater injection, which is believed to have occurred at least twice during deglaciation, would have resulted in increased precipitation with respect to evaporation in the American southwest during summertime. The timing of deglacial events in the Gulf of Mexico and the Gulf of California supports such an atmospheric teleconnection.

The remnants of Younger Dryas lithalsas on the Hautes Fagnes Plateau in Belgium and elsewhere in the world

NASA Astrophysics Data System (ADS)

Pissart, Albert

2003-05-01

This paper summarizes all the available information about the "viviers" of the Hautes Fagnes, i.e., closed and ramparted depressions which are numerous above 500 m a.s.l. on the highest Belgian plateau. These features and cross-sections in the ramparts are described. The ramparts are the result of both mass wasting on the slopes of the mounds and toppling of inside material. 14C dating of a peat layer preserved under a rampart, Alleröd volcanic ashes and palynological studies have proved that the "viviers" formed their origin during the Younger Dryas. In the first place, the depressions were interpreted as excavations by prehistoric men; from 1956 on, they were interpreted as pingo remnants. The pingo hypothesis is now abandoned. The "viviers" are remnants of mineral palsas (lithalsas), features which nowadays exist in Hudsony (Canada). Present-day lithalsas are solely known in subarctic Quebec and in Lapland. They form in the discontinuous permafrost zone, close to the tree line, i.e., in zones where mean annual temperature (MAT) ranges from -4 to -6 °C and where the average temperature of the warmest month is between +9 and +11.5 °C. Such climatic conditions are rarely encountered nowadays in periglacial regions. Remnants of lithalsas are very infrequent, too. They appear like ramparted depressions forming clusters. Such traces, dating from the Younger Dryas, have been described only at elevation above 500 m a.s.l. on the Belgian Hautes Fagnes Plateau, around 250 m a.s.l. in Wales and at sea level in Ireland. In these few places, according to R. Isarin's palaeoclimatic results, climatic conditions during the Younger Dryas were similar to present-day conditions in subarctic Quebec, where lithalsas are numerous.

Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis.

PubMed

Israde-Alcántara, Isabel; Bischoff, James L; Domínguez-Vázquez, Gabriela; Li, Hong-Chun; DeCarli, Paul S; Bunch, Ted E; Wittke, James H; Weaver, James C; Firestone, Richard B; West, Allen; Kennett, James P; Mercer, Chris; Xie, Sujing; Richman, Eric K; Kinzie, Charles R; Wolbach, Wendy S

2012-03-27

We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact. These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial. Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences. Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record. This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core. Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond: n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance. This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe. We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism. It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.

Understanding Colds: Anatomy of the Nose

MedlinePlus

... nasal secretions. (13) This interval is called the incubation period. Cold symptoms can also begin shortly after virus is first produced in the nose (10-12 hours). (13) The time from the beginning of the infection to the ...

Teasing Apart Regional Climate and Meltwater Influences on Florida Straits Sea Surface Temperature and Salinity over the past 40 kyr

NASA Astrophysics Data System (ADS)

Schmidt, M. W.; Lynch-Stieglitz, J.

2008-12-01

Recent reconstructions of North Atlantic salinity variability over the last glacial cycle show that abrupt climate events are linked to major reorganizations in the low-latitude hydrologic cycle, affecting large-scale changes in evaporation minus precipitation (E-P) patterns. Although there is general agreement that the Intertropical Convergence Zone (ITCZ) migrates southward during cold stadials, it remains unclear how this shift affects the net E-P budget in the North Atlantic. In order to reconstruct a high resolution record of past sea surface temperature (SST) and salinity (SSS) in the Florida Straits across abrupt climate events of the last 40 kyr, we combine Mg/Ca paleothermometry and δ18O measurements in shells from the surface-dwelling foraminifera Globigerinoides ruber in cores KNR166-2-JPC29 (24°17'N, 83°16'W; 648 m depth; 8-20 cm/kyr sed. rate) and JPC26 (24°19.61'N, 83°15.14'W; 546 m depth; 18-240 cm/kyr sed. rate) and calculate δ18OSEAWATER (δ18OSW) variability. Removal of the δ18OSW signal due to continental ice volume variation results in the ice volume-free (IVF) δ18OSW record (a proxy for SSS variability). Although most waters flowing through the Florida Straits today originate in the tropical western Atlantic, major meltwater discharges from the Mississippi River across the last deglacial period also influenced SST and SSS in the Florida Straits. To constrain periods of increased meltwater discharge, we measured Ba/Ca ratios in G. ruber from select intervals. Because riverine waters have a much higher dissolved Ba+2 concentration relative to seawater, foraminifera Ba/Ca ratios can be used as an additional proxy to constrain periods of increase riverine discharge. Initial results suggest the hydrographic history of the Florida Straits is influenced by both meltwater discharge and regional climate variability linked to the high-latitude North Atlantic. Both the IVF- δ18OSW and Ba/Ca records reveal a prolonged period from 16.0-13.0 kyr when elevated meltwater discharge was the dominant influence on surface water conditions in the Florida Straits. It is likely that SSS in the Florida Straits was significantly fresher than today during this interval. In contrast, periods of minimal meltwater influence (such as the Younger Dryas and across D-O cycles of MIS 3) are characterized by abrupt SST and SSS shifts that covary with the NGRIP δ18Oice record. SSTs in the Florida Straits cool by 1.5-2.0 °C and regional salinity increases (IVF-δ18OSW increase of 0.5-0.7‰) at the initiation of cold stadial events as the ITCZ shifts south. The most likely explanation for these rapid shifts in IVF-δ18OSW values is that moisture transport out of the North Atlantic increases when the North Atlantic cools and the ITCZ shifts southward.

Geochronology and paleoclimatic implications of the last deglaciation of the Mauna Kea Ice Cap, Hawaii

USGS Publications Warehouse

Anslow, Faron S.; Clark, P.U.; Kurz, M.D.; Hostetler, S.W.

2010-01-01

We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a shift in the ITCZ would have allowed midlatitude cyclones to reach Mauna Kea more frequently which would have increased precipitation at high elevations and caused additional cooling. ?? 2010 Elsevier B.V.

Ocean forcing of Ice Sheet retreat in central west Greenland from LGM to the early Holocene

NASA Astrophysics Data System (ADS)

Jennings, Anne E.; Andrews, John T.; Ó Cofaigh, Colm; Onge, Guillaume St.; Sheldon, Christina; Belt, Simon T.; Cabedo-Sanz, Patricia; Hillaire-Marcel, Claude

2017-08-01

Three radiocarbon dated sediment cores from trough mouth fans on the central west Greenland continental slope were studied to determine the timing and processes of Greenland Ice Sheet (GIS) retreat from the shelf edge during the last deglaciation and to test the role of ocean forcing (i.e. warm ocean water) thereon. Analyses of lithofacies, quantitative x-ray diffraction mineralogy, benthic foraminiferal assemblages, the sea-ice biomarker IP25, and δ18 O of the planktonic foraminifera Neogloboquadrina pachyderma sinistral from sediments in the interval from 17.5-10.8 cal ka BP provide consistent evidence for ocean and ice sheet interactions during central west Greenland (CWG) deglaciation. The Disko and Uummannaq ice streams both retreated from the shelf edge after the last glacial maximum (LGM) under the influence of subsurface, warm Atlantic Water. The warm subsurface water was limited to depths below the ice stream grounding lines during the LGM, when the GIS terminated as a floating ice shelf in a sea-ice covered Baffin Bay. The deeper Uummannaq ice stream retreated first (ca. 17.1 cal ka BP), while the shallower Disko ice stream retreated at ca. 16.2 cal ka BP. The grounding lines were protected from accelerating mass loss (calving) by a buttressing ice shelf and by landward shallowing bathymetry on the outer shelf. Calving retreat was delayed until ca. 15.3 cal ka BP in the Uummannaq Trough and until 15.1 cal ka BP in the Disko Trough, during another interval of ocean warming. Instabilities in the Laurentide, Innuitian and Greenland ice sheets with outlets draining into northern Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed GIS melt. During the Younger Dryas, the CWG records document strong cooling, lack of GIS meltwater, and an increase in iceberg rafted material from northern Baffin Bay. The ice sheet remained in the cross-shelf troughs until the early Holocene, when it retreated rapidly by calving and strong melting under the influence of atmosphere and ocean warming and a steep reverse slope toward the deep fjords. We conclude that ocean warming played an important role in the palaeo-retreat dynamics of the GIS during the last deglaciation.

Paleoceanography of the Gulf of Alaska during the past 15,000 years: results from diatoms, silicoflagellates, and geochemistry

USGS Publications Warehouse

Barron, John A.; Bukry, David; Dean, Walter E.; Addison, Jason A.; Finney, Bruce

2009-01-01

High-resolution records of diatoms, silicoflagellates, and geochemistry covering the past 15,000 years were studied in three cores from the Gulf of Alaska (GOA). Core EW0408-85JC in an oceanic setting on the Kayak Slope displays a paleoceanographic record similar to that at several locations on the California margin during deglaciation. Biologic productivity as reconstructed using geochemical and microfossil proxies increased abruptly during the Bølling–Alleröd (Bø–Al) warm interval (14.7–12.9 cal ka), declined during the Younger Dryas (YD) cold interval (12.9 to 11.7 cal kyr BP), and rose again during the earliest Holocene. At this site, the record after ~ 11 cal kyr BP is dominated by oceanic diatoms and silicoflagellates, with geochemical proxies displaying more subtle variation. Cores EW0408-66JC in the Yakobi Sea Valley near Cross Sound and EW0408-11JC in the Gulf of Esquibel contain an expanded, composite record along the southeast Alaskan margin. Core 66JC contains a detailed record of the Bø–Al and YD. Diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the Bø–Al but declined during the YD. Sea ice-related diatoms increased in abundance during the YD, indicating cooler, but less productive waters. The glacial to biogenic marine sediment transition in core 11JC occurs at 1280 cmbsf (centimeters below sea floor), probably representing rising sea level and deglaciation early in the Bø–Al. Freshwater and sea-ice related diatoms are common in the lower part of the core (Bø–Al and YD), but upwelling-related diatoms and silicoflagellates quickly increased in relative abundance up-core, dominating the record of the past 11,000 years. Low oxygen conditions in the bottom water as reconstructed using geochemical proxies (U and Mo concentration) were most intense between ~ 6.5 and 2.8 cal kyr BP, the beginning of which is coincident with increases in abundance of upwelling-related diatoms. The records from these three cores jointly thus made it possible to reconstruct paleoclimatic and paleoceanographic conditions at high northern Pacific latitudes during the last 15 kyr.

Molybdenum accumulation in Cariaco basin sediment over the past 24 k.y.: A record of water-column anoxia and climate

USGS Publications Warehouse

Dean, W.E.; Piper, D.Z.; Peterson, L.C.

1999-01-01

Molybdenum (Mo) concentrations in a sediment core from the Cariaco basin on the Venezuelan continental shelf can be partitioned between a marine fraction and a terrigenous fraction. The accumulation rate of the marine fraction of Mo increased abruptly 15 000 calendar years ago (15 ka), from 4 ??g ?? cm-2 ?? yr-1, and then decreased abruptly at 9 ka. The accumulation rate remained high throughout this 6 k.y. period, but exhibited maxima at 15-14 and 12.5 ka, corresponding in time to meltwater pulse IA into the Gulf of Mexico and the onset of the Younger Dryas cold event, respectively. The marine fraction of Mo is interpreted in terms of redox conditions of bottom water, as dictated by both the flux of settling organic matter and bottom-water residence time. Correspondence between geochemical extremes in this core with changes in sea level and global climate demonstrates the high degree to which this ocean-margin basin has responded to the paleoceanographic regime throughout the past 24 k.y.

Interhemispheric correlation of late pleistocene glacial events.

PubMed

Lowell, T V; Heusser, C J; Andersen, B G; Moreno, P I; Hauser, A; Heusser, L E; Schlüchter, C; Marchant, D R; Denton, G H

1995-09-15

A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and >/=33,500 carbon-14 years before present ((14)C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000(14)C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720(14)C yr B.P., and at the beginning of the Younger Dryas at 11,050 (14)C yr B. P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges.

The micromorphology of Younger Dryas-aged black mats from Nevada, Arizona, Texas and New Mexico

NASA Astrophysics Data System (ADS)

Harris-Parks, Erin

2016-01-01

Black mats are organic-rich sediments and soils that form in wet environments associated with spring discharge. Micromorphological and geochemical analyses of 25 black mats dating to the Younger Dryas Chronozone (12.9-11.7 ka) and early Holocene were conducted to determine their composition and depositional environment. Samples were collected from Arizona, New Mexico, Texas and Nevada. Micromorphological analyses were conducted on thin sections using polarized and blue fluorescent light. These analyses determined that black mats contain humic acids, fine (5-20 μm) plant fragments, diatoms, phytoliths, and gastropods. The dominant type of organic matter in black mats is derived from herbaceous plants, contradicting previous studies that supported algal or charcoal sources. Differences in the micromorphological characteristics of the samples revealed that black mats formed as three different types, organic horizons, moist soils and, ponded sediments, depending on their topographic position in relation to the water table. The microscopic evidence found in black mats supports the presence of widespread wet environments in Nevada and Arizona during the Younger Dryas Chronozone, clearly indicating a sustained period of greater effective moisture, optimal for spring discharge and black mat formation.

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America

NASA Astrophysics Data System (ADS)

Woodman, Neal; Beavan Athfield, Nancy

2009-11-01

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000-10,000 14C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190-10,530 14C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000-10,000 14C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon ( Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 14C yr BP and 10,032 ± 40 14C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.

The Lateglacial to Holocene transition as recorded by glacier fluctuations

NASA Astrophysics Data System (ADS)

Schindelwig, I.; Akçar, N.; Kubik, P. W.; Schlüchter, C.

2009-04-01

Examination of glacier associated records may contribute to a better understanding of the ice-continent-ocean-atmosphere interactions, since glacial deposits related to short-term temperature fluctuations, driven by climate change, might be preserved. Surface exposure dating (SED) of such glacial deposits can improve the chronology of climate records. The western Swiss Alps repeatedly hosted mountain glaciers during the Pleistocene, and even during the Last Glacial-Interglacial transition, with abundant stadial and interstadial transitions during the Lateglacial (e.g. Björck et al. 1998). In this study, the adjacent valleys of Belalp and Great Aletsch (catchment area is generally south facing) in the western Swiss Alps are investigated. The slow responding Great Aletsch valley glacier shows only one confirmed moraine ridge related to the Lateglacial (Egesen stadial) (Kelly et al. 2004). However, the rather fast responding Unnerbäch cirque (recent) glacier at the Belalp (a similarly exposed - and tributary - valley to the Great Aletsch valley), features 6 individual lateral-terminal moraine ridges related to Lateglacial and early Holocene times. In the Belalp valley, 22 erratic boulders from four out of six well-preserved moraines were sampled in order to establish a detailed chronological framework. From the Great Aletsch valley four samples (boulder and ice moulded bedrock) of the lateral moraine were collected for SED. Our 10Be exposure dates suggest a stabilization of the Great Aletsch moraine related to the Egesen advance in the beginning of the Younger Dryas, assuming that the ages of the oldest erratic boulders on a single moraine ridge are representative for the time of moraine stabilization (Putkonen & Swanson, 2003). According to our investigations on the right-lateral moraine and the dataset (recalculated from Kelly et al. 2004) for the left-lateral moraine, the Egesen stadial is the first preserved re-advance after the last deglaciation. In contrast, the glacier at the Belalp shows multiple advances during the Lateglacial to early Holocene. 10Be exposure age data suggest that the outer moraine ridge can be an advance older than the Egesen stadial and younger than the LGM. This is in concert with other Younger Dryas related glacial landsystems in Switzerland (reviewing the outer moraine ages e.g. Julier Pass, Ivy-Ochs et al. 1996, 2008). A large number of Lateglacial moraines have been identified and relative correlations on the basis of elevation, equilibrium line altitude (Gross et al. 1977; Maisch, 1987) and morphological characteristics have been established. Nevertheless, it remains important to refine the absolute chronology in order to put further temporal constraints on these relative frameworks. This allows the allocation of such absolutely dated deposits to distinguished cold phases (Preboreal oscillation, Younger Dryas, Aegelsee oscillation) thus underlining their potential significance in the context of regional, as well as global Lateglacial climate conditions. The 10Be exposure ages from an inner moraine ridge are in a good agreement with the recalculated previously published 10Be exposure ages from the Egesen moraines in the Alps. This suggests a synchronicity of the Egesen stadial in the European Alps at the end of the Younger Dryas cold phase. REFERENCES Björck, S., Walker, M. J.C., Cwynar, L.C., Johnson, S., Knudsen, K-L., Lowe, J. J. & Wohlfarth, B. (1998): An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group. Journal of Quarternary Science, 13, 283-292. Gross, G., Kerschner, H. & Patzelt, G. (1977): Methodische Untersuchungen über die Schneegrenze in alpinen Gletschergebieten. Zeitschrift für Gletscherkunde und Glazialgeologie, 12, 223-251. Ivy-Ochs, S., Kerschner, H., Reuther, A., Preusser, F., Heine, K., Maisch, M., Kubik, P.W. & Schlüchter, C. (2008): Chronology of the last glacial cycle in the European Alps. Journal of Quaternary Science, 23, 559-573. Ivy-Ochs, S., Schlüchter, C., Kubik, P. W., Synal, H.-A., Beer, J., Kerschner, H. (1996): The exposure age of an Egesen moraine at Julier Pass, Switzerland, measured with the cosmogenic radionuclides 10Be, 26Al and 36Cl. Eclogae geol. Helv., 89, 1049-1063. Kelly, M.A., Kubik, P.W., von Blanckenburg, F. & Schlüchter, C. (2004): Surface exposure dating of the Great Aletsch Glacier Egesen moraine system, western Swiss Alps, using the cosmogenic nuclide 10Be. Journal of Quarternary Science, 19, 431-441. Maisch, M. (1987): Zur Gletschergeschichte des alpinen Spätglazials: Analyse und Interpretation von Schneegrenzdaten. Geographica Helvetica, 42, 63-71. Putkonen, J. & Swanson, T. (2003): Accuracy of cosmogenic ages for moraines. Quarternary Research, 59, 255-261.

Cosmogenic Surface-Exposure Dating of Boulders on Last-Glacial and Late-Glacial Moraines, Lago Buenos Aires, Argentina: Interpretive Strategies and Paleoclimate Implications

NASA Astrophysics Data System (ADS)

Douglass, D. C.; Singer, B. S.; Kaplan, M. R.; Mickelson, D. M.; Caffee, M.

2005-12-01

The most substantial and least quantifiable source of uncertainty in cosmogenic surface-exposure datasets is the variable exposure histories of boulders from the same landform. The development of precise and accurate chronologies requires distinguishing boulders that best reflect the age of the landform from those which are outliers. We use the Mean Square of Weighted Deviates statistic and cumulative frequency plots to identify groups of samples that have statistically similar ages based on the number of samples and the uncertainty associated with the analyses. This group of samples most likely represents the best estimate of the landform age. We use these tools to interpret 49 surface-exposure ages from six last-glacial and late-glacial moraines at Lago Buenos Aires, Argentina (LBA; 71.0W, 46.5S). Seven of the orty-nine samples are identified as anomalously young, and are interpreted to have been exhumed after moraine deposition. The remaining samples indicate that glacial advances or still-stands of the ice margin occurred at 22.7±0.9, 21.4±1.9, 19.8±1.1, 17.0±0.8, 15.7±0.6, and 14.4±0.9 ka (±2 σ). This maximum ice extent is roughly synchronous with maximum global ice volume and several of the re-advances are contemporaneous with Heinrich events and other Northern Hemisphere cold periods. The late-glacial readvance at ca. 14.4 ka is contemporaneous with the Antarctic Cold Reversal (ACR), and precedes the Younger Dryas Chronozone (YD). No evidence for a Younger Dryas glacial advance has been found in the Lago Buenos Aires basin. This precise glacial chronology indicates there were significant and important differences in climate across southern South America. The timing of maximum ice extent and onset of deglaciation at LBA occur ~4000 years later than in the Chilean Lake District (41S). Fossil pollen from the CLD area indicates cooler conditions between ca. 14.2 and 11.2, and increased silt in a nearby lake core provides indirect evidence for glacial advances at this time. The onset of this late-glacial cool period precedes the YD, but post-dates the ACR. The LBA glacial record is in better accord with the Strait of Magellan (SM; 52S) than with the CLD. There ice reached its maximum around 25 ka, and a significant late-glacial re-advance occurred between ca. 15 and 11.5 ka. Both LBA and the SM have climate records similar to Antarctica, whereas the climate records from the CLD are combinations of Antarctic and Northern Hemisphere signals.

The temperature and precipitation reconstructions on Swiss stalagmites with a special emphasis on altitude gradient using noble-gases, δO-18 and δD of fluid inclusions

NASA Astrophysics Data System (ADS)

Ghadiri, Elaheh; Brennwald, Matthias; Kipfer, Rolf

2017-04-01

We present the results of an application of 'Combined Vacuum Crushing and Sieving (CVCS)' system (e.g., allowing to crush samples to defined grain size in vacuum) for the first time to stalagmites grown in cold climates during the last glacial-interglacial transition, but at different altitudes. Recently, concentrations of dissolved atmospheric noble gases in fluid inclusions of stalagmites were used to reconstruct past ambient cave temperatures, the annual mean temperature and hydrological conditions when the water was trapped. To reconstruct temperatures from noble gases (noble gas temperature: NGT) in water-filled inclusions, we processed samples from Swiss stalagmites M6 from Milandre cave (400 m.a.s.l) and GEF1 from Grotte aux Fées cave (895 m.a.s.l) covering the climatic transitions Allerød-Younger Dryas-Holocene. Water content. The amount of water extracted per unit mass of calcite fabric (e.g., 'water yield': WT) was shown to be a measure of the total water content. The data shows that the WT systematically changes with δ18Ocalcite of the calcite. We therefore conclude that WT records can be linked on changes in drip rates and thus can be used to track changes of past precipitation even in cold regions. Noble gases. Noble gas analysis shows that the annual mean temperatures in Milandre cave were 2.2±2.0°C during the late Allerød and dropped to 0±2°C at the Younger Dryas. Such temperatures close 0°C indicate that drip water supply stopped in response to the formation of permafrost conditions around the cave preventing further stalagmite growth. However, one late Holocene sample gave a cave temperature of 8.7±1.4°C agreeing generally with present day annual mean temperature. The annual mean temperature of 5.7±1.3°C from GEF1 was determined for the early Holocene. The observed data show systematic variations with sample elevation, e.g., higher temperature from lower altitude and vice versa. Combining the isotopic composition of water in fluid inclusions (δ18Owater, δDwater) and the NGTs allows determining the δ18O-T relation ('laps rate') in the past as both δ18O and T scale with altitude. This calibration is key as paleo-temperatures are often reconstructed from δ18O, δD data whereby it is implicitly assumed that the modern Δ(δ18Owater, δDwater)-ΔT relation is also valid for the past. Our study makes an argument that noble gas analysis in stalagmites can also be a new route to address this fundamental hypothesis of past climate reconstruction.

Variability in Organic-Carbon Sources and Sea-Ice Coverage North of Iceland (Subarctic) During the Past 15,000 Years

NASA Astrophysics Data System (ADS)

Xiao, X.; Zhao, M.; Knudsen, K. L.; Eiriksson, J.; Gudmundsdottir, E. R.; Jiang, H.; Guo, Z.

2017-12-01

Sea ice, prevailing in the polar region and characterized by distinct seasonal and interannual variability, plays a pivotal role in Earth's climate system (Thomas and Dieckmann, 2010). Studies of spatial and temporal changes in modern and past sea-ice occurrence may help to understand the processes controlling the recent decrease in Arctic sea-ice cover. Here, we determined the concentrations of sea-ice diatom-derived biomarker "IP25" (monoene highly-branched isoprenoid with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarker brassicasterol and terrigenous biomarker long-chain n-alkanols in a sediment core from the North Icelandic shelf to reconstruct the high-resolution sea-ice variability and the organic-matter sources during the past 15,000 years. During the Bølling/Allerød, the North Icelandic shelf was characterized by extensive spring sea-ice cover linked to reduced flow of warm Atlantic Water and dominant Polar water influence; the input of terrestrial and sea-ice organic matters was high while the marine organic matter derived from phytoplankton productivity was low. Prolonged sea-ice cover with occasional occurrence of seasonal sea ice prevailed during the Younger Dryas interrupted by a brief interval of enhanced Irminger Current; the organic carbon input from sea-ice productivity, terrestrial matter and phytoplankton productivity all decreased. The seasonal sea ice decreased gradually from the Younger Dryas to the onset of the Holocene corresponding to increasing insolation. Therefore, the sea-ice productivity decreased but the phytoplankton productivity increased during this time interval. The biomarker records from this sediment core give insights into the variability in sea ice and organic-carbon sources in the Arctic marginal area during the last deglacial and Holocene. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Org. Geochem. 38, 16-27. Knudsen, K.L. and Eiriksson, J., 2002. Application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in Holocene and Late Glacial shelf sediments off North Iceland. Marine Geology 191, 165-188. Thomas, D. N. and Dieckmann, G. S., 2010. Sea Ice, Blackwell Publ., Oxford, U. K.

Ecosystem responses during Late Glacial period recorded in the sediments of Lake Łukie (East Poland)

NASA Astrophysics Data System (ADS)

Zawiska, Izabela; Słowiński, Michał; Correa-Metrio, Alex; Obremska, Milena; Luoto, Tomi; Nevalainen, Liisa; Woszczyk, Michał; Milecka, Krystyna

2014-05-01

The main objectives of this study was to reconstruct climate impact on the functioning of Lake Łukie and its catchment (Łęczna Włodawa Lake District, East European Plain) during Late Glacial period. In order to reconstruct climatic fluctuations and corresponding ecosystem responses, we analysed lake sediments for pollen, subfossil Cladocera, plant macrofossils and chemical composition of the sediment. Of these, plant macrofossils and Cladocera were used to infer minimum and mean July temperatures and ordination analysis was used to examine biotic community shifts. Multiproxy analyses of late-glacial sediments of Lake Łukie clearly show that the main driver of aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate variation. The history of the lake initiated during the Older Dryas. In that period, Łęczna Włodawa Lake District was covered by open habitats dominated by grasses (Poaceae), humid sites were occupied by tundra plant communities with less clubmoss (Selaginella selaginoides), dry sites by dominated by steppe-like vegetation with light-demanding species such as Helianthemum, Artemisia, Chenopodiaceae, and juniper bushes (Juniperus). Cold climate limited the growth and development of organisms in the lake, Cladocera community species composition was poor, with only few species present there all the time. During this time period, permafrost was still present in the ground limiting infiltration of rainwater and causing high erosion in the catchment area. Surface runoff is confirmed by the presence of sclerotia of Cenococcum geophilum and high terrigenous silica content. The warming of the early Allerød caused a remarkable change in the natural environment of this area. This is in accordance with the temperature rise reconstructed with the use of plant macrofossils though the Cladocera reconstruction did not recorded the rise than. This temperature increase resulted in turnover of vegetation in the catchment of Lake Łukie, pioneer birch-pine forests dominated, later replaced by pine-birch forests. Consequently this limited the erosion. The results of all proxy suggest the water-lever rise in lake Łukie. The Younger Dryas cooling in the region began about 12 630 14C years BP and recorded in significant drop in temperature reconstructed with plant macrofossils and Cladocera. The cooling resulted in a decline of forest communities and development of open habitats with grasses (Poaceae), Artemisia, and Chenopodiaceae), as well as juniper thickets (Juniperus) At the end of the Younger Dryas, plant communities changed, the non-arborescent pollen declined, while pollen of trees (especially Pinus) became more abundant. This change was more abruptly reflected in Cladocera and aquatic pollen results and is probably related to gradual climate warming. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association, projects UMO-2011/01/B/ST10/07367 and N N306 036436 founded by National Science Center, Poland.

Vegetation and Climate Change during the Last Deglaciation in the Great Khingan Mountain, Northeastern China

PubMed Central

Wu, Jing; Liu, Qiang; Wang, Luo; Chu, Guo-qiang; Liu, Jia-qi

2016-01-01

The Great Khingan Mountain range, Northeast China, is located on the northern limit of modern East Asian Summer Monsoon (EASM) and thus highly sensitive to the extension of the EASM from glacial to interglacial modes. Here, we present a high-resolution pollen record covering the last glacial maximum and the early Holocene from a closed crater Lake Moon to reconstruct vegetation history during the glacial-interglacial transition and thus register the evolution of the EASM during the last deglaciation. The vegetation history has gone through distinct changes from subalpine meadow in the last glacial maximum to dry steppe dominated by Artemisia from 20.3 to 17.4 ka BP, subalpine meadow dominated by Cyperaceae and Artemisia between 17.4 and 14.4 ka BP, and forest steppe dominated by Betula and Artemisia after 14.4 ka BP. The pollen-based temperature index demonstrates a gradual warming trend started at around 20.3 ka BP with interruptions of several brief events. Two cold conditions occurred around at 17.2–16.6 ka BP and 12.8–11.8 ka BP, temporally correlating to the Henrich 1 and the Younger Dryas events respectively, 1and abrupt warming events occurred around at 14.4 ka BP and 11.8 ka BP, probably relevant to the beginning of the Bølling-Allerød stages and the Holocene. The pollen-based moisture proxy shows distinct drought condition during the last glacial maximum (20.3–18.0 ka BP) and the Younger Dryas. The climate history based on pollen record of Lake Moon suggests that the regional temperature variability was coherent with the classical climate in the North Atlantic, implying the dominance of the high latitude processes on the EASM evolution from the Last Glacial Maximum (LGM) to early Holocene. The local humidity variability was influenced by the EASM limitedly before the Bølling-Allerød warming, which is mainly controlled by the summer rainfall due to the EASM front covering the Northeast China after that. PMID:26730966

Vegetation and Climate Change during the Last Deglaciation in the Great Khingan Mountain, Northeastern China.

PubMed

Wu, Jing; Liu, Qiang; Wang, Luo; Chu, Guo-qiang; Liu, Jia-qi

2016-01-01

The Great Khingan Mountain range, Northeast China, is located on the northern limit of modern East Asian Summer Monsoon (EASM) and thus highly sensitive to the extension of the EASM from glacial to interglacial modes. Here, we present a high-resolution pollen record covering the last glacial maximum and the early Holocene from a closed crater Lake Moon to reconstruct vegetation history during the glacial-interglacial transition and thus register the evolution of the EASM during the last deglaciation. The vegetation history has gone through distinct changes from subalpine meadow in the last glacial maximum to dry steppe dominated by Artemisia from 20.3 to 17.4 ka BP, subalpine meadow dominated by Cyperaceae and Artemisia between 17.4 and 14.4 ka BP, and forest steppe dominated by Betula and Artemisia after 14.4 ka BP. The pollen-based temperature index demonstrates a gradual warming trend started at around 20.3 ka BP with interruptions of several brief events. Two cold conditions occurred around at 17.2-16.6 ka BP and 12.8-11.8 ka BP, temporally correlating to the Henrich 1 and the Younger Dryas events respectively, 1and abrupt warming events occurred around at 14.4 ka BP and 11.8 ka BP, probably relevant to the beginning of the Bølling-Allerød stages and the Holocene. The pollen-based moisture proxy shows distinct drought condition during the last glacial maximum (20.3-18.0 ka BP) and the Younger Dryas. The climate history based on pollen record of Lake Moon suggests that the regional temperature variability was coherent with the classical climate in the North Atlantic, implying the dominance of the high latitude processes on the EASM evolution from the Last Glacial Maximum (LGM) to early Holocene. The local humidity variability was influenced by the EASM limitedly before the Bølling-Allerød warming, which is mainly controlled by the summer rainfall due to the EASM front covering the Northeast China after that.

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America

USGS Publications Warehouse

Woodman, N.; Beavan, Athfield N.

2009-01-01

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000-10,000??14C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190-10,530??14C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000-10,000??14C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ?? 40??14C yr BP and 10,032 ?? 40??14C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction. ?? 2009 University of Washington.

Differential proxy responses to late Allerød and early Younger Dryas climatic change recorded in varved sediments of the Trzechowskie palaeolake in Northern Poland

NASA Astrophysics Data System (ADS)

Słowiński, Michał; Zawiska, Izabela; Ott, Florian; Noryśkiewicz, Agnieszka M.; Plessen, Birgit; Apolinarska, Karina; Rzodkiewicz, Monika; Michczyńska, Danuta J.; Wulf, Sabine; Skubała, Piotr; Kordowski, Jarosław; Błaszkiewicz, Mirosław; Brauer, Achim

2017-02-01

High-resolution biological proxies (pollen, macrofossils, Cladocera and diatoms), geochemical data (μ-XRF element scans, TOC, C/N ratios, δ18Ocarb and δ13Corg values) and a robust chronology based on varve counting, AMS 14C dating and tephrochronology were applied to reconstruct lake system responses to rapid climatic and environmental changes of the Trzechowskie palaeolake (TRZ; Northern Poland) during the late Allerød - Younger Dryas (YD) transition. Palaeoecological and geochemical data at 5-15 years temporal resolution allowed tracing the dynamics of short-term shifts of the ecosystem triggered by abrupt climate change. The robust age control together with the high-resolution sampling allowed the detection of leads and lags between different proxies to the climate shift at the Allerød-Younger Dryas transition. Our results indicate (1) a water level decrease and an increase in wind activities during the late Allerød and the Allerød-YD transition, which caused intensified erosion in the catchment, (2) a two-decades delayed vegetation response in comparison to the lake depositional system. Comparison with the Lake Meerfelder Maar record revealed slightly different vegetation responses of the Trzechowskie palaeolake at the YD onset.

Holocene climatic variations in the Western Cordillera of Colombia: A multiproxy high-resolution record unravels the dual influence of ENSO and ITCZ

NASA Astrophysics Data System (ADS)

Muñoz, Paula; Gorin, Georges; Parra, Norberto; Velásquez, Cesar; Lemus, Diego; Monsalve-M., Carlos; Jojoa, Marcela

2017-01-01

The Páramo de Frontino (3460 m elevation) in Colombia is located approximately halfway between the Pacific and Atlantic oceans. It contains a 17 kyr long, stratigraphically continuous sedimentary sequence dated by 30 AMS 14C ages. Our study covers the last 11,500 cal yr and focuses on the biotic (pollen) and abiotic (microfluorescence-X or μXRF) components of this high mountain ecosystem. The pollen record provides a proxy for temperature and humidity with a resolution of 20-35 yr, and μXRF of Ti and Fe is a proxy for rainfall with a sub-annual (ca. 6-month) resolution. Temperature and humidity display rapid and significant changes over the Holocene. The rapid transition from a cold (mean annual temperature (MAT) 3.5 °C lower than today) and wet Younger Dryas to a warm and dry early Holocene is dated at 11,410 cal yr BP. During the Holocene, MAT varied from ca. 2.5 °C below to 3.5° above present-day temperature. Warm periods (11,410-10,700, 9700-6900, 4000-2400 cal yr BP) were separated by colder intervals. The last 2.4 kyr of the record is affected by human impact. The Holocene remained dry until 7500 cal yr BP. Then, precipitations increased to reach a maximum between 5000 and 4500 cal yr BP. A rapid decrease occurred until 3500 cal yr BP and the late Holocene was dry. Spectral analysis of μXRF data show rainfall cyclicity at millennial scale throughout the Holocene, and at centennial down to ENSO scale in more specific time intervals. The highest rainfall intervals correlate with the highest activity of ENSO. Variability in solar output is possibly the main cause for this millennial to decadal cyclicity. We interpret ENSO and ITCZ as the main climate change-driving mechanisms in Frontino. Comparison with high-resolution XRF data from the Caribbean Cariaco Basin (a proxy for rainfall in the coastal Venezuelian cordilleras) demonstrates that climate in Frontino was Pacific-driven (ENSO-dominated) during the YD and early Holocene, whereas it was Atlantic-driven in Cariaco (ITCZ-dominated). From ca. 8000 cal yr BP, climate in both areas was under the dual influence of ENSO and ITCZ, thereby showing existing teleconnections between the tropical Pacific and Atlantic oceans. The Frontino record is to date the highest-resolution Holocene study in NW Colombia. An implication of these results is that new records should be analyzed with multiproxy tools, in particular those providing high resolution time series, such as μXRF.

Late-glacial and Holocene Vegetation and Climate Variability, Including Major Droughts, in the Sky Lakes Region of Southeastern New York State

NASA Technical Reports Server (NTRS)

Menking, Kirsten M.; Peteet, Dorothy M.; Anderson, Roger Y.

2012-01-01

Sediment cores from Lakes Minnewaska and Mohonk in the Shawangunk Mountains of southeastern New York were analyzed for pollen, plantmacrofossils, macroscopic charcoal, organic carbon content, carbon isotopic composition, carbon/nitrogen ratio, and lithologic changes to determine the vegetation and landscape history of the greater Catskill Mountain region since deglaciation. Pollen stratigraphy generally matches the New England pollen zones identified by Deevey (1939) and Davis (1969), with boreal genera (Picea, Abies) present during the late Pleistocene yielding to a mixed Pinus, Quercus and Tsuga forest in the early Holocene. Lake Minnewaska sediments record the Younger Dryas and possibly the 8.2 cal kyr BP climatic events in pollen and sediment chemistry along with an 1400 cal yr interval of wet conditions (increasing Tsuga and declining Quercus) centered about 6400 cal yr BP. BothMinnewaska andMohonk reveal a protracted drought interval in themiddle Holocene, 5700-4100 cal yr BP, during which Pinus rigida colonized the watershed, lake levels fell, and frequent fires led to enhanced hillslope erosion. Together, the records show at least three wet-dry cycles throughout the Holocene and both similarities and differences to climate records in New England and central New York. Drought intervals raise concerns for water resources in the New York City metropolitan area and may reflect a combination of enhanced La Niña, negative phase NAO, and positive phase PNA climatic patterns and/or northward shifts of storm tracks.

Nanodiamonds do not provide unique evidence for a Younger Dryas impact

PubMed Central

Tian, H.; Schryvers, D.; Claeys, Ph.

2011-01-01

Microstructural, δ13C isotope and C/N ratio investigations were conducted on excavated material from the black Younger Dryas boundary in Lommel, Belgium, aiming for a characterisation of the carbon content and structures. Cubic diamond nanoparticles are found in large numbers. The larger ones with diameters around or above 10 nm often exhibit single or multiple twins. The smaller ones around 5 nm in diameter are mostly defect-free. Also larger flake-like particles, around 100 nm in lateral dimension, with a cubic diamond structure are observed as well as large carbon onion structures. The combination of these characteristics does not yield unique evidence for an exogenic impact related to the investigated layer. PMID:21173270

Reconstruction of the Amazon Basin effective moisture availability over the past 14,000 years.

PubMed

Maslin, M A; Burns, S J

2000-12-22

Quantifying the moisture history of the Amazon Basin is essential for understanding the cause of rain forest diversity and its potential as a methane source. We reconstructed the Amazon River outflow history for the past 14,000 years to provide a moisture budget for the river drainage basin. The oxygen isotopic composition of planktonic foraminifera recovered from a marine sediment core in a region of Amazon River discharge shows that the Amazon Basin was extremely dry during the Younger Dryas, with the discharge reduced by at least 40% as compared with that of today. After the Younger Dryas, a meltwater-driven discharge event was followed by a steady increase in the Amazon Basin effective moisture throughout the Holocene.

Climate Events and Cycles During the Last Glacial-Interglacial Transition

NASA Astrophysics Data System (ADS)

Lee, Eun Hee; Lee, Dae-Young; Park, Mi-Young

2017-09-01

During the last glacial-interglacial transition, there were multiple intense climatic events such as the Bølling-Allerød warming and Younger Dryas cooling. These events show abrupt and rapid climatic changes. In this study, the climate events and cycles during this interval are examined through wavelet analysis of Arctic and Antarctic ice-core 18O and tropical marine 14C records. The results show that periods of 1383-1402, 1029-1043, 726-736, 441-497 and 202-247 years are dominant in the Arctic region, whereas periods of 1480, 765, 518, 311, and 207 years are prominent in the Antarctic TALDICE. In addition, cycles of 1019, 515, and 209 years are distinct in the tropical region. Among these variations, the de Vries cycle of 202-209 years, correlated with variations in solar activity, was detected globally. In particular, this cycle shows a strong signal in the Antarctic between about 13,000 and 10,500 yr before present (BP). In contrast, the Eddy cycle of 1019-1043 years was prominent in Greenland and the tropical region, but was not detected in the Antarctic TALDICE records. Instead, these records showed that the Heinrich cycle of 1480 year was very strong and significant throughout the last glacial-interglacial interval.

Mood and selective attention in the cold: the effect of interval versus continuous exercise.

PubMed

Muller, Matthew D; Muller, Sarah M; Kim, Chul-Ho; Ryan, Edward J; Gunstad, John; Glickman, Ellen L

2011-07-01

Both mood and cognitive function are altered in cold environments. Body warming through exercise may improve Stroop interference score and lessen total negative mood. The purpose of this study was to determine the effect of equal caloric bouts of interval (INT) and continuous (CONT) exercise on mood and selective attention in the cold. Eleven young men underwent two experimental trials in 5°C air. Both trials consisted of 90 min acute cold exposure (ACE), 30 min exercise (INT vs. CONT), and 60 min recovery (REC). The Profile of Mood States (POMS) and Stroop Color Word Test (SCWT) were administered at four time points. Mean body temperature decreased during ACE, increased during exercise, and decreased during REC. Repeated measures analysis of variance revealed a main effect for time for several of the POMS sub scores. In particular, negative mood was significantly decreased after exercise relative to ACE and then significantly increased during REC. Further, CONT appears to be more effective than INT at decreasing negative mood. Components of the SCWT supported both the arousal and distraction theories for simple perception, but no significant effects were shown for the interference score. In the cold, exercise decreases negative mood but does not appear to affect selective attention. Further mechanistic studies could determine the best mode and intensity of exercise for improving cognitive function in the cold.

Oceanic link between abrupt changes in the North Atlantic Ocean and the African monsoon

NASA Astrophysics Data System (ADS)

Chang, Ping; Zhang, Rong; Hazeleger, Wilco; Wen, Caihong; Wan, Xiuquan; Ji, Link; Haarsma, Reindert J.; Breugem, Wim-Paul; Seidel, Howard

2008-07-01

Abrupt changes in the African monsoon can have pronounced socioeconomic impacts on many West African countries. Evidence for both prolonged humid periods and monsoon failures have been identified throughout the late Pleistocene and early Holocene epochs. In particular, drought conditions in West Africa have occurred during periods of reduced North Atlantic thermohaline circulation, such as the Younger Dryas cold event. Here, we use an ocean-atmosphere general circulation model to examine the link between oceanographic changes in the North Atlantic Ocean and changes in the strength of the African monsoon. Our simulations show that when North Atlantic thermohaline circulation is substantially weakened, the flow of the subsurface North Brazil Current reverses. This leads to decreased upper tropical ocean stratification and warmer sea surface temperatures in the equatorial South Atlantic Ocean, and consequently reduces African summer monsoonal winds and rainfall over West Africa. This mechanism is in agreement with reconstructions of past climate. We therefore suggest that the interaction between thermohaline circulation in the North Atlantic Ocean and wind-driven currents in the tropical Atlantic Ocean contributes to the rapidity of African monsoon transitions during abrupt climate change events.

Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America

PubMed Central

Vanneste, Heleen; De Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

2015-01-01

Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions. PMID:26126739

Earth orbital variations and vertebrate bioevolution

NASA Technical Reports Server (NTRS)

Mclean, Dewey M.

1988-01-01

Cause of the Pleistocene-Holocene transition mammalian extinctions at the end of the last age is the subject of debate between those advocating human predation and climate change. Identification of an ambient air temperature (AAT)-uterine blood flow (UBF) coupling phenomenon supports climate change as a factor in the extinctions, and couples the extinctions to earth orbital variations that drive ice age climatology. The AAT-UBF phenomenon couples mammalian bioevolution directly to climate change via effects of environmental heat upon blood flow to the female uterus and damage to developing embryos. Extinctions were in progress during climatic warming before the Younger Dryas event, and after, at times when the AAT-UBF couple would have been operative; however, impact of a sudden short-term cooling on mammals in the process of adapting to smaller size and relatively larger S/V would have been severe. Variations in earth's orbit, and orbital forcing of atmospheric CO2 concentrations, were causes of the succession of Pleistocene ice ages. Coincidence of mammalian extinctions with terminations of the more intense cold stages links mammalian bioevolution to variations in earth's orbit. Earth orbital variations are a driving source of vertebrate bioevolution.

Deglacial palaeoclimate at Puerto del Hambre, subantarctic Patagonia, Chile

NASA Astrophysics Data System (ADS)

Heusser, Calvin J.; Heusser, Linda E.; Lowell, Thomas V.; Moreira M., Andrés; Moreira M., Simón

2000-02-01

The primary objective of this study is to further substantiate multistep climatic forcing of late-glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes-Bahía Inútil. Pollen assemblages at 2-cm intervals in a core of the mire at Puerto del Hambre (53°3621S, 70°5553W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262-cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 14C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455-13 000 14C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100-yr-long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 14C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass-dominated steppe. The Bølling-Allerød (13 000-11 000 14C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000-10 000 14C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes-Bahía Inútil is dated close to 14 455 14C yr BP, invalidating earlier dates of between 15 800 and 16 590 14C yr BP.

A ~25 ka Indian Ocean monsoon variability record from the Andaman Sea

USGS Publications Warehouse

Rashid, H.; Flower, B.P.; Poore, R.Z.; Quinn, T.M.

2007-01-01

Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ18O of seawater (δ18Osw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ18Osw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ18Osw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.

Combining gene expression and genetic analyses to identify candidate genes involved in cold responses in pea.

PubMed

Legrand, Sylvain; Marque, Gilles; Blassiau, Christelle; Bluteau, Aurélie; Canoy, Anne-Sophie; Fontaine, Véronique; Jaminon, Odile; Bahrman, Nasser; Mautord, Julie; Morin, Julie; Petit, Aurélie; Baranger, Alain; Rivière, Nathalie; Wilmer, Jeroen; Delbreil, Bruno; Lejeune-Hénaut, Isabelle

2013-09-01

Cold stress affects plant growth and development. In order to better understand the responses to cold (chilling or freezing tolerance), we used two contrasted pea lines. Following a chilling period, the Champagne line becomes tolerant to frost whereas the Terese line remains sensitive. Four suppression subtractive hybridisation libraries were obtained using mRNAs isolated from pea genotypes Champagne and Terese. Using quantitative polymerase chain reaction (qPCR) performed on 159 genes, 43 and 54 genes were identified as differentially expressed at the initial time point and during the time course study, respectively. Molecular markers were developed from the differentially expressed genes and were genotyped on a population of 164 RILs derived from a cross between Champagne and Terese. We identified 5 candidate genes colocalizing with 3 different frost damage quantitative trait loci (QTL) intervals and a protein quantity locus (PQL) rich region previously reported. This investigation revealed the role of constitutive differences between both genotypes in the cold responses, in particular with genes related to glycine degradation pathway that could confer to Champagne a better frost tolerance. We showed that freezing tolerance involves a decrease of expression of genes related to photosynthesis and the expression of a gene involved in the production of cysteine and methionine that could act as cryoprotectant molecules. Although it remains to be confirmed, this study could also reveal the involvement of the jasmonate pathway in the cold responses, since we observed that two genes related to this pathway were mapped in a frost damage QTL interval and in a PQL rich region interval, respectively. Copyright © 2013 Elsevier GmbH. All rights reserved.

Benthic foraminiferal faunal and geochemical proxies as tracers for paleoenvironmental and paleoceanographic changes in the western Mediterranean over the last 24 ka

NASA Astrophysics Data System (ADS)

Pérez-Asensio, José N.; Cacho, Isabel; Frigola, Jaime; Pena, Leopoldo D.; Sierro, Francisco J.; Asioli, Alessandra; Kuhlmann, Jannis; Huhn, Katrin

2017-04-01

Paleoenvironmental and paleoceanographic changes in the western Mediterranean are reconstructed for the last 24 ka using a combination of benthic foraminiferal assemblages and geochemical proxies measured on benthic foraminiferal shells (Mg/Ca-deep water temperatures and stable isotopes). The studied materials are sediment cores HER-GC-UB06 and MD95-2043recovered at 946 m and 1841 m, respectively, from the Alboran Sea. At present, both core sites are bathed by the Western Mediterranean Deep Water (WMDW), although UB06 core is close to the boundary with the overlying Levantine Intermediate Water (LIW). Therefore, past variability of both water masses can potentially be recorded by the benthic foraminiferal proxies from the studied sites. Benthic foraminiferal assemblages and geochemical data show fluctuations in bottom-water ventilation, organic matter accumulation and deep-water temperatures related to WMDW and LIW circulation. During the glacial interval, an alternation of events showing better ventilation (higher abundance of Cibicides pachyderma) with lower temperatures and events of warmer deep water temperatures with poorer ventilation (Nonionella iridea assemblage, lower abundance of C. pachyderma) are observed. This variability might reflect stronger WMDW formation during the Last Glacial Maximum (LGM) and Heinrich Stadial 1. During the Bølling-Allerød and Younger Dryas (YD) periods, cold temperatures and the lowest oxygenation rates are recorded coinciding with the highest abundance of deep infaunal taxa on both UB06 and MD95-2043 cores. This interval was coetaneous to the deposition of an Organic Rich Layer in the Alboran Sea. However, a re-ventilation trend started at the end of the YD in the shallower site (UB06 core) whereas low-oxygen conditions prevailed until the end of the early Holocene in the deep site (MD95-2043 core). During the early Holocene a significant deep water temperature increase occurred at the shallower site suggesting the replacement of WMDW by warmer water mass, likely LIW. In the middle Holocene, highly variable bottom-water oxygenation and temperatures are observed showing warmer deep waters with less oxygen content (higher deep and intermediate infaunal abundances). The late Holocene (last 4 ka) was characterized by slightly cooler deep water temperatures and enhanced oxygen levels supporting that WMDW became dominant at the shallower site. These observations reveal that Mediterranean thermohaline system has been highly variable during the studied period supporting its high sensitivity to changing climate conditions. These results open a new insight into the Mediterranean sensitivity to Holocene climate variability.

Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka, and Little Ice Age events

USGS Publications Warehouse

Benson, L.; Madole, R.; Kubik, P.; McDonald, R.

2007-01-01

Surface-exposure (10Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ???3.0 10Be ka.11Surface-exposure ages in this paper are labeled 10Be; radiocarbon ages are labeled 14C ka, calendar and calibrated radiocarbon ages are labeled cal ka, and layer-based ice-core ages are labeled ka. 14C ages, calibrated 14C ages, and ice core ages are given relative to AD 1950, whereas 10Be ages are given relative to the sampling date. Radiocarbon ages were calibrated using CALIB 5.01 and the INTCAL04 data base Stuiver et al. (2005). Ages estimated using CALIB 5.01 are shown in terms of their 1-sigma range. Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 10Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0-11.7 10Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation.

Positive anomaly in platinum group elements and the presence of shocked diamonds: Two question marks at the Younger Dryas

NASA Astrophysics Data System (ADS)

Claeys, P. F.; Schryvers, D.; Tian, H.; Goderis, S.

2009-12-01

Recently, a large size impact was proposed as the cause of the global changes taking place at the Younger Dryas (YD) some 12,9 kyr ago. Impact evidence was reported in a C-rich black layer of broad geographic distribution. The impact markers consist of a large anomaly in the concentration of platinum group elements (PGE) and the presence of nanodiamonds, in particular lonsdaleite, which hexagonal structure is believed to be of shock origin. The impact is proposed to have occurred on the North American continent. A crater large enough (> 150 km) to induce a mass extinction some ~12.9 ka ago, formed in a geologically well-known area, is unlikely to have escaped detection. Therefore, an alternative hypothesis is that a cometary projectile exploded fully within the atmosphere spreading PGE and shock formed diamonds, without any target rock contribution, all around the Northern hemisphere. So far, PGE measurements failed to reproduce the elevated (> ppb) concentrations reported previously at Younger Dryas sites containing the black layer. In Lommel (Belgium) where the first study detected up to 117 ppb Ir, the Ir concentration is below the detection limit of the method (NiS fire assay + ICP-MS) used (0.06 ppb). At all sites analyzed the PGE pattern is typical of that of the continental crust. In several craters (Popigai, Ries) or at the KT boundary nanodiamonds have been reported associated with shocked materials. Several types of carbon components occur in the black layer of the Lommel section such as i) flakes reaching up to 1 µm, ii) nano particles of cubic diamond, 1 to 10 nm in size and iii) larger carbon onion-ring structures, which core can act as a nanoscopic pressure cell leading to the formation of nanodiamond by self- compression. The Lommel nanodiamonds present in the Younger Dryas layer do resemble nanodiamonds found in carbon spherules of unknown origin previously reported in top soil from several localities in Belgium and Germany. The C stable isotopic signature measured in the C-rich black layer is clearly produced by organic matter of terrestrial origin (-29‰).

Paleolimnology of Lake Ontario: AN Assessment of Glacial Meltwater Influx

NASA Astrophysics Data System (ADS)

Hladyniuk, R.; Longstaffe, F. J.

2010-12-01

The timing and extent of glacial meltwater outbursts from the Laurentide Ice Sheet (LIS) may provide insight into their potential role in initiating and/or sustaining the Younger Dryas (YD) cooling event. It has been previously proposed that meltwater from the LIS suppressed thermohaline circulation in the Atlantic Ocean, leading to an abrupt change in climate (Broecker et al. 1989). Several pathways for transport of glacial meltwater to the Atlantic Ocean have been suggested in the past, including eastern flow through the St. Lawrence River system and discharge into the Arctic Ocean via a northwestern outlet (Murton et al. 2010). Glacial meltwater contributions to Lake Ontario and its ancient equivalents during the last ~14,000 cal BP have been evaluated using the oxygen-isotope compositions of ostracode shells from three sediment cores in Lake Ontario. Glacial Lake Iroquois (~12,500 cal BP) δ18O values as low as -18‰ suggest significant contribution of glacial meltwater runoff from the LIS. This glacial sediment is characterized by occasional grains of sand and gravel. These ice-rafted particles indicate how far icebergs floated and suggest close proximity to the LIS. Early Lake Ontario sediment (~12,000 cal BP) exhibits thicker laminations, suggestive of increased winter ice cover and perhaps a colder climate, and is characterized by slightly lower δ18O values (-19.5‰). The end of glacial-dominated sedimentation at ~11,800 cal BP is demarcated by a significant increase in lakewater δ18O values (-12.0‰), reflecting mixing between regional precipitation in the watershed and upstream inflow into Lake Ontario. At ~10,800 cal BP, the δ18O value of Lake Ontario decreased to ~-15‰. This change reflects the main Algonquin highstand in Lake Huron, which flooded into Lake Ontario from both the Fenelon Falls and Port Huron outlets at this time. Shortly thereafter, the opening of the North Bay outlet and isostatic rebound at the Port Huron outlet limited discharge from the upper Great Lakes to Lakes Erie and Ontario. From ~10,500 to 7,500 cal BP, closed-basin conditions prevailed in Lake Ontario (Lewis et al. 2010). Extreme evaporation and a dry climate associated with the Holocene Thermal Maximum, beginning at ~8,000 cal BP, led to a further shift to higher δ18O values (-7.0‰). The ostracode record then ends at ~4,000 cal BP, coincident with return of significant drainage from the Upper Great Lakes. Broecker W.S., Kennett J.P., Flower B.P., Teller J.T., Trumbore S., Bonani G., Wolfli W. (1989) Routing of meltwater from the Laurentide Ice Sheet during the Younger Dryas cold episode. Nature 341, 318-321. Lewis C.F.M., Anderson T.W., Cameron G., King J.W., Heil Jr. C.W. (2010) The reduced Lakes Erie and Ontario, a severe response to past drier climate. 53rd Annual International Association for Great Lakes Research-Conference Abstract. Murton J.B., Bateman M.D., Dallimore S.R., Teller J.T., Yang Z. (2010) Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean. Nature Letters 434, 740-743.

Aridity of Central Asia through the Holocene

NASA Astrophysics Data System (ADS)

Aizen, E. M.; Aizen, V. B.; Mayewski, P. A.; Zhou, H.; Rodda, C.; Joswiak, D.; Takeuchi, N.; Fujita, K.; Kurbatov, A.; Grigholm, B. O.

2017-12-01

The dynamics of aridity in Central Asia for over the past 12,000 years has been analyzed using deep ice core records recovered from the Siberian Altai, Tien Shan and Pamir glaciers. An analysis of aridity in the 20-21 centuries based on the long-term meteorological observations complements the paleo- climate reconstruction. The goal of our research is to examine an aridity (at low and high temperatures) in Central Asia as a complex of characteristics including air temperature-precipitation relationship (Koppen, 1918, Geiger, 1961, Mezencev, 1973), intensity of dust loading and biomass burning. The stable isotope ratio, soluble ionic and insoluble particulate geochemical components and oxalate preserved in ice were considered in relation to climatic and environmental changes; and to determine the main aerosol sources using ground- and upper-level meteorological data. Multivariate statistical methods were employed for examination of the main geo-chemical components responsible for the preserved aridity variability. Insoluble particle concentrations preserved in the ice core were affected mainly by precipitation regimes and wind speed. Concentration of all size particles was found to be negatively correlated with monthly temperatures indicating low temperatures during the dry particle deposition. Two abrupt depletions in stable isotope records, i.e., Younger Dryas and Centurial Sever Drought (CSD), occurred during cold, dry, windy periods of intensified dust storms in large desert areas. When climate became colder and drier, the Central Asian deserts extended, wind speeds increased loading mineral dust to atmosphere, which formed inversion while the convection processes and precipitation occurrence were limited. Warmer and wetter conditions are associated with less dust loading that occurred during the Holocene climate optimum, medieval warm and modern warm periods. The sudden climate transitions are accompanied by the most intensifying mineral dust loading. From the middle of 20th century, the potassium and nitrate ion concentrations significantly increased and reaches almost the same level as it was at the beginning of Holocene and before CSD that was caused by extended forest fires under air temperature growth. Interval between intensive biomass burning decreased during the 20th century.

A temperature reversal within the rapid Younger Dryas-Holocene warming in the North Atlantic?

NASA Astrophysics Data System (ADS)

Vincent, Jessie H.; Cwynar, Les C.

2016-12-01

The onset of the Holocene has been generally considered rapid and uninterrupted in the circum-Atlantic region. Loss-on-ignition (LOI - an index of organic carbon) profiles from 18 lateglacial-aged lakes in Nova Scotia, Canada, together with chironomid-inferred temperature reconstructions at 5 sites, demonstrate that the rapid warming from the Younger Dryas (GS-1) to the Holocene was interrupted by a cooling of 1.6-6.4 °C in summer surface lake water temperature. The resulting inflection or reversal on the rising temperature curve has also been identified at 35 sites outside Nova Scotia from terrestrial and marine settings, indicating that this cool step is a robust feature throughout the North Atlantic and is likely the result of major oceanic and atmospheric reorganization of the Holocene climate system.

Chironomid record of Late Quaternary climatic and environmental changes from two sites in Central Asia (Tuva Republic, Russia)—local, regional or global causes?

NASA Astrophysics Data System (ADS)

Ilyashuk, Boris P.; Ilyashuk, Elena A.

2007-03-01

Sediment cores from two mountain lakes (Lake Grusha at 2413 m a.s.l. and Ak-Khol at 2204 m a.s.l.) situated in the Tuva Republic (southern Siberia, Russia), just north of Mongolia, were studied for chironomid fossils in order to infer post-glacial climatic changes and to investigate responses of the lake ecosystems to these changes. The results show that chironomids are responding both to temperature and to changing lake depth, which is regarded as a sensitive proxy of regional effective moisture. The post-glacial history of this mountain region in Central Asia can be divided into seven successive climatic phases: the progressive warming during the last glacial-interglacial transition (ca 15.8-14.6 cal kyr BP), the warm and moist Bølling-Allerød-like interval (ca 14.6-13.1 cal kyr BP), the cool and dry Younger Dryas-like event (ca 13.1-12.1 cal kyr BP), warmer and wetter conditions during ca 12.1-8.5 cal kyr BP, a warm and dry phase ca 8.5-5.9 cal kyr BP, cold and wet conditions during ca 5.9-1.8 cal kyr BP, as well as cold and dry climate within the last 1800 years. The chironomid records reveal patterns of climatic variability during the Late-glacial and Holocene, which can be correlated with abrupt climatic events in the North Atlantic and the Asian monsoon-dominated regimes. Apparently, the water balance of the studied lakes is controlled by the interrelation between the dominant westerly system and the changing influence of the summer monsoon, as well as the influence of alpine glacier meltwater supply. It is possible that monsoon tracks could have reached the southwest Tuva, resulting in an increase in precipitation at ca 14.6-13.1 and ca 12.1-8.5 cal kyr BP, whereas cyclonic westerlies from the North Atlantic were likely responsible for considerable moisture transport accompanying the global Neoglacial cooling at ca 5.9-1.8 cal kyr BP. These events suggest the changes of the regional pattern of atmospheric circulation, which could be in turn induced by the global climatic shifts. Some discrepancies compared with other reconstructions from Central Asia may be associated with regional (spatial) differences between the changing predominant circulation mechanisms and with local differences in uplift and descent of air masses within the complicated mountain landscape. In this paper, we also discuss the possibilities and perspectives for using chironomids in reconstructions of past temperatures and climate-induced changes in water depth of lakes in Central Asia.

Cold-induced bradycardia in man during sleep in Arctic winter nights

NASA Astrophysics Data System (ADS)

Buguet, A. G. C.

1987-03-01

Two young male Caucasians volunteered for a study on the effects of cold exposure during night sleep in winter in the Arctic. The 14-day experiment was divided in three consecutive periods, baseline (2 nights), cold exposure (10 night) and recovery (2 nights). Both baseline and recovery data were obtained in neutral thermal conditions in a laboratory. The subjects slept in a sleeping bag under an unheated tent during the cold exposure. Apart from polysomnographic and body temperature recordings, electrocardiograms were taken through a telemetric system for safety purposes. Heart rates were noted at 5-min intervals and averaged hourly. In both environmental conditions, heart rate decreased within the first two hours of sleep. Comparison of the data obtained during cold exposure vs. thermal neutrality revealed lower values of heart rate in the cold, while body temperatures remained within normal range. This cold-induced bradycardia supervening during night sleep is discussed in terms of the occurrence of a vagal reflex preventing central blood pressure to rise.

Early and abrupt retreat of the Laurentide Ice Sheet margin from the Mackenzie River valley, southern Northwest Territories

NASA Astrophysics Data System (ADS)

Margold, Martin; Froese, Duane G.; Gosse, John C.; Yang, Guang; McKenna, Jillian; Hidy, Alan J.

2017-04-01

The detachment of the Laurentide Ice Sheet margin from the Canadian Cordillera opened the present-day drainage route of the Mackenzie River to the Arctic Ocean and an ice-free corridor that allowed for migration of species between Beringia and the mid-latitudes of North America. The existing ice-margin chronology depicts the southern reach of the Mackenzie River between 61 and 63° N as glaciated until about 13 ka, representing the last portion of the Laurentide Ice Sheet margin abutting the eastern foot of the Cordillera. A substantial retreat of the ice sheet margin in this region has been suggested to have occurred during the subsequent Younger Dryas cold period, despite the fact that in many other regions ice masses stabilised or even re-grew at this time. However, until now, deglacial chronometry for this region and the western LIS margin is sparse and consists mostly of minimum-limiting macrofossil and bulk C-14 ages from organics materials overlying glacial sediment. With the aim to bring new data on the deglaciation history of the Mackenzie River valley, we collected samples for Be-10 exposure dating from glacial erratic boulders in the southern Franklin Mountains that bound the Mackenzie River valley from the east. The sampling elevations ranged between 1480 and 800 m a.s.l., however, the measured ages show only a weak correlation with elevation. Instead, 10 out of 12 measured samples cluster tightly around 15 ka, with the remaining two samples likely containing Be-10 inherited from previous periods of exposure. Our results thus indicate a pre-Younger Dryas rapid down-wasting of the ice sheet surface, which we infer was accompanied by an ice margin retreat to the southeast. The southern reach of the Mackenzie River valley at the eastern foot of the Cordillera was, according to our results, ice free shortly after 15 ka, with the prospect that the ice-free corridor might have opened significantly earlier than hitherto anticipated. Further research is required in the region south of our study area to establish a firm chronological control on the separation of the Cordilleran and Laurentide ice sheets and the opening of the ice free corridor.

Late Pleistocene-Holocene deglaciation history in the Baffin Bay from radiogenic isotope provenance studies

NASA Astrophysics Data System (ADS)

Kirillova, V.; Lucassen, F.; Kasemann, S.

2016-12-01

Ice sheets dynamics as well as corresponding meltwater pulses and iceberg calving events play a major role in the delivery and dispersion of continental detritus into the ocean in glaciated environments. To trace Greenland, and potentially, Innuitian and Laurentian ice sheet history and freshwater routing during late Pleistocene to Holocene climate transition, we generate strontium (Sr), neodymium (Nd) and lead (Pb) isotope records as proxies for the provenance of continental detritus on sediment cores from the Baffin Bay: GeoTÜ SL 170, from the Greenland side, covering the last 18.000 years of climate history and GeoTÜ SL 174, close to the western coast, covering 48.000 years. For SL 170, a pronounced shift can be observed in all three isotope systems at 12 ka, what coincides with the Younger Dryas cold event. 87Sr/86Sr is around 0.74 before the event and reaches up to 0.72 during it. Nd isotope composition (IC) changes from ɛNd -32 to -26, and the 206Pb/204Pb values range from 18 to 17. The shift suggests a change in the continental sources from the Archean Southern West Greenland to a slightly younger Proterozoic source of the Nagssugtoqidian Mobile Belt in the Central West Greenland. These results allow us to estimate patterns and timings of deglaciation for different regions of the western Greenland Ice Sheet. In core SL174 variations in ɛNd ( -24 to -30) and 206Pb/204Pb ( 17 to 19) provide no clear evidence for a change of the sediment source within the Younger Dryas, despite the similar range of the values as in core SL 170. 87Sr/86Sr is more radiogenic than in SL 170, reaching values of up to 0.75, but without a systematic relation to the deposition age. Since SL 174 core is located closer to the coast and to the LGM (last glacial maximum) ice sheet border, it was possibly exposed to the direct influence of the marine-terminating ice sheet, which supplied material from enhanced glacial and subglacial erosion. Therefore, radiogenic isotope results for this core could be affected by the variable supply of minerals (e.g., micas) delivering radiogenic Sr signature.

Spatiotemporal Patterns of Hydrological Changes During the Younger Dryas Onset from Decadally-Resolved Lacustrine Biomarker Records: a W-E European Transect

NASA Astrophysics Data System (ADS)

Collins, J.; Aichner, B.; Engels, S.; Lane, C.; Maas, D.; Neugebauer, I.; Ott, F.; Slowinski, M. M.; Wulf, S.; Plessen, B.; Brauer, A.; Sachse, D.

2016-12-01

Future projections of European hydroclimate change remain uncertain, highlighting the need for an improved understanding of past abrupt European hydroclimate change, particularly in terms of identifying vulnerable regions. However, most existing continental paleohydrological records are not of sufficiently high resolution and/or sufficiently well dated for the assessment of leads and lags across the European continent and with the Greenland ice cores. To better understand mechanisms and feedbacks of hydrological changes during the last major abrupt climate change, the Younger Dryas (YD) cold period, we measured biomarker hydrogen isotopes (δD values) from terrestrial and aquatic sources on four high-resolution lacustrine sediment profiles. The sites span a 900km W-E transect from western Germany to eastern Poland and include: Meerfelder Maar, western Germany [MFM]; Hämelsee, northern-central Germany [HÄM]; Rehwiese, eastern Germany [RW]; Trzechowskie, central Poland [TRZ]. These sediments are annually laminated and contain common tephra layers, permitting a direct comparison of each site and allowing the identification of leads and lags in the response of the hydrological cycle to YD cooling on decadal timescales. We observed a decrease in biomarker δD values, likely reflecting cooling, that coincided with the onset of Greenland Stadial 1 in the NGRIP ice core at 12,846 years BP in the western European sites, with a progressive lag of several decades in the more easterly sites. Furthermore, we observed that the onset of aridification at all four sites occurred later but at roughly at the same time, coinciding with the biostratigraphically-defined onset of the YD at 12,679. A decrease in the magnitude of changes in biomarker δD values and aridification from W to E suggests a less strong aridification in eastern Europe. Our results suggest that hydrological changes at the onset of the YD were not uniform and were strongest and most abrupt in western Europe, where a substantial increase in aridity occurred over just 80 years, resulting in widespread environmental changes. These differences in magnitude and the distinct temporal succession could be related to the influence of the Fennoscandian ice sheets and/or the Siberian High on atmospheric circulation in eastern Europe.

Deglacial Tropical Atlantic subsurface warming links ocean circulation variability to the West African Monsoon.

PubMed

Schmidt, Matthew W; Chang, Ping; Parker, Andrew O; Ji, Link; He, Feng

2017-11-13

Multiple lines of evidence show that cold stadials in the North Atlantic were accompanied by both reductions in Atlantic Meridional Overturning Circulation (AMOC) and collapses of the West African Monsoon (WAM). Although records of terrestrial change identify abrupt WAM variability across the deglaciation, few studies show how ocean temperatures evolved across the deglaciation. To identify the mechanism linking AMOC to the WAM, we generated a new record of subsurface temperature variability over the last 21 kyr based on Mg/Ca ratios in a sub-thermocline dwelling planktonic foraminifera in an Eastern Equatorial Atlantic (EEA) sediment core from the Niger Delta. Our subsurface temperature record shows abrupt subsurface warming during both the Younger Dryas (YD) and Heinrich Event 1. We also conducted a new transient coupled ocean-atmosphere model simulation across the YD that better resolves the western boundary current dynamics and find a strong negative correlation between AMOC strength and EEA subsurface temperatures caused by changes in ocean circulation and rainfall responses that are consistent with the observed WAM change. Our combined proxy and modeling results provide the first evidence that an oceanic teleconnection between AMOC strength and subsurface temperature in the EEA impacted the intensity of the WAM on millennial time scales.

Deglacial development of (sub) sea surface temperature and salinity in the subarctic northwest Pacific: Implications for upper-ocean stratification

NASA Astrophysics Data System (ADS)

Riethdorf, Jan-Rainer; Max, Lars; Nürnberg, Dirk; Lembke-Jene, Lester; Tiedemann, Ralf

2013-01-01

Based on models and proxy data, it has been proposed that salinity-driven stratification weakened in the subarctic North Pacific during the last deglaciation, which potentially contributed to the deglacial rise in atmospheric carbon dioxide. We present high-resolution subsurface temperature (TMg/Ca) and subsurface salinity-approximating (δ18Oivc-sw) records across the last 20,000 years from the subarctic North Pacific and its marginal seas, derived from combined stable oxygen isotopes and Mg/Ca ratios of the planktonic foraminiferal species Neogloboquadrina pachyderma (sin.). Our results indicate regionally differing changes of subsurface conditions. During the Heinrich Stadial 1 and the Younger Dryas cold phases, our sites were subject to reduced thermal stratification, brine rejection due to sea-ice formation, and increased advection of low-salinity water from the Alaskan Stream. In contrast, the Bølling-Allerød warm phase was characterized by strengthened thermal stratification, stronger sea-ice melting, and influence of surface waters that were less diluted by the Alaskan Stream. From direct comparison with alkenone-based sea surface temperature estimates (SSTUk'37), we suggest deglacial thermocline changes that were closely related to changes in seasonal contrasts and stratification of the mixed layer. The modern upper-ocean conditions seem to have developed only since the early Holocene.

Precision Spectroscopy in Cold Molecules: The Lowest Rotational Interval of He2 + and Metastable He2

NASA Astrophysics Data System (ADS)

Jansen, Paul; Semeria, Luca; Hofer, Laura Esteban; Scheidegger, Simon; Agner, Josef A.; Schmutz, Hansjürg; Merkt, Frédéric

2015-09-01

Multistage Zeeman deceleration was used to generate a slow, dense beam of translationally cold He2 molecules in the metastable a 3Σu+ state. Precision measurements of the Rydberg spectrum of these molecules at high values of the principal quantum number n have been carried out. The spin-rotational state selectivity of the Zeeman-deceleration process was exploited to reduce the spectral congestion, minimize residual Doppler shifts, resolve the Rydberg series around n =200 and assign their fine structure. The ionization energy of metastable He2 and the lowest rotational interval of the X+ 2Σu+ (ν+=0 ) ground state of 4He2+ have been determined with unprecedented precision and accuracy by Rydberg-series extrapolation. Comparison with ab initio predictions of the rotational energy level structure of 4He2+ [W.-C. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012)] enabled us to quantify the magnitude of relativistic and quantum-electrodynamics contributions to the fundamental rotational interval of He2+ .

Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: Pollen-based climatic reconstruction

USGS Publications Warehouse

Willard, D.A.; Bernhardt, C.E.; Korejwo, D.A.; Meyers, S.R.

2005-01-01

We present paleoclimatic evidence for a series of Holocene millennial-scale cool intervals in eastern North America that occurred every ???1400 years and lasted ???300-500 years, based on pollen data from Chesapeake Bay in the mid-Atlantic region of the United States. The cool events are indicated by significant decreases in pine pollen, which we interpret as representing decreases in January temperatures of between 0.2??and 2??C. These temperature decreases include excursions during the Little Ice Age (???1300-1600 AD) and the 8 ka cold event. The timing of the pine minima is correlated with a series of quasi-periodic cold intervals documented by various proxies in Greenland, North Atlantic, and Alaskan cores and with solar minima interpreted from cosmogenic isotope records. These events may represent changes in circumpolar vortex size and configuration in response to intervals of decreased solar activity, which altered jet stream patterns to enhance meridional circulation over eastern North America. ?? 2004 Elsevier B.V. All rights reserved.

Lead and Lags of Lake System Responses to Late Allerød and Early Younger Dryas Climatic Fluctuation - an Example from Varved Lake Sediments from Northern Poland (Central Europe)

NASA Astrophysics Data System (ADS)

Slowinski, M. M.; Zawiska, I.; Ott, F.; Noryśkiewicz, A. M.; Plessen, B.; Apolinarska, K.; Lutyńska, M.; Michczynska, D. J.; Wulf, S.; Skubała, P.; Błaszkiewicz, M.; Brauer, A.

2014-12-01

The transition from the warmer Allerød to the cooler Younger Dryas period is well understood to represent sudden and extreme climate changes during the end of the last glaciation. Thus, lake sediment studies within paleoclimatic and paleoecological research on this transition are ideal to enhance the knowledge about "lead and lags" of lake system responses to abrupt climate changes through applying multi-proxy sediment analyses. In this study, we present the results of high-resolution studies on varved late glacial sediments from the Trzechowskie paleolake, located in the northern Poland (center Europe). High-resolution bio-proxies (pollen, macrofossils, Cladocera and diatoms), geochemical analyses (µ-XRF data, TOC, C/N ratios, δ18Ocarb and δ13Corg stable isotopes) and a robust chronology based on varve counting, AMS 14C dating and tephrochronology were used to reconstruct the lake system responses to rapid climatic and environmental changes of Trzechowskie paleolake during the late Allerød - Younger Dryas transition. Paleoecological and geochemical analyses, which were carried out in a 4 to 16 years temporal sample resolution, allowed to defining short-termed shifts of the ecosystem that were triggered by abrupt climate changes. The rapid and pronounced cooling at the beginning of the Younger Dryas had a major impact on the lake and its catchment as clearly reflected by not synchronous changes of both, biotic and geochemical proxies. The results of high-resolution analysis indicate (a) an increased precipitation during the Allerød-YD transition, which is responsible for an increase of soil erosion in the catchment during this period, (b) a delayed response of the vegetation compared to the lake depositional system at the YD onset of 20 years, and (c) a non-synchronicity of vegetation responses between Western (Lake Meerfelder Maar) and Eastern European sites (Trzechowskie palaeolake) at the YD onset. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association. The research was supported by the National Science Centre Poland (grants No. NN 306085037 and NCN 2011/01/B/ST10/07367).

Evidence for an Extraterrestrial Impact Event 12,900 years ago that Contributed to Megafaunal Extinctions and the Younger Dryas Cooling

NASA Astrophysics Data System (ADS)

Firestone, R. B.; West, A.; Kennett, J. P.; Becker, L.; Bunch, T. E.; Revay, Z.; Schultz, P. H.; Belgya, T.; Dickenson, O. J.; Erlandson, J. M.; Goodyear, A. C.; Harris, R. S.; Howard, G. A.; Kennett, D. J.; Kloosterman, J. B.; Lechler, P.; Montgomery, J.; Poreda, R.; Darrah, T.; Que Hee, S. S.; Smith, A. R.; Stich, A.; Topping, W.; Wittke, J. H.; Wolbach, W. S.

2007-05-01

The Younger Dryas event boundary (YDB) is a thin sedimentary layer of 12.9 ka age containing an assemblage of materials formed due to a major ET impact centered over northern North America. The event coincided with the megafaunal extinctions and the Younger Dryas cooling episode. The YDB layer contains peaks in magnetic grains, microspherules, and iridium, in addition to charcoal and soot that resulted from extensive wildfires. Two impact-related carbon-rich markers, glass-like carbon and carbon spherules, have not been reported previously in North America. Vesicular, glass-like carbon, in pieces up to several cm, occurs in the YDB at 22 sites with concentrations ranging up to 16 g/kg. Their glassy texture suggests melting during formation, with some fragments grading into charcoal, and CF-IRMS analysis reveals a composition of >70 percent carbon. One sample exhibited a strong fullerene signature containing ET helium with a ratio of 84× that of air, comparable to the Tagish Lake meteorite (90×). Similar glass-like carbon has been reported from the Azuara crater in Spain (Ernstson, et al. 2001). Carbon spherules (0.15-2.5 mm) are black, highly vesicular, low-density, subspherical-to-spherical objects found in 18 widely distributed sites at varying concentrations up to 1500/kg. SEM analysis shows that the spherules have cracked and patterned surfaces, honeycombed cells, no inclusions, and sometimes display hollow cores. SEM/EDS and microprobe analyses show the carbon spherules to be >75 percent carbon. Similar carbon spherules are reported from the a crater in Germany (Rösler, et al., 2005). The carbon spherules most likely are either ablation products from the impactor or combustion products of the impact. Sediment samples were analyzed for Ir, and YDB samples from 9 sites exhibited elevated Ir values up to 3.75 ppb, while there was no detectable Ir above or below the YDB. Extracted magnetic grains have values up to 117 ppb, which is 25 percent that of typical chondrites and up to 5000× crustal abundance. The YDB layer, representing a major ET impact event at 12.9 ka, appears to coincide with the late Pleistocene megafaunal extinction and the onset of Younger Dryas cooling. We propose that neither this cooling nor the extinction would have occurred in the absence of this impact event.

Glacier-derived climate for the Younger Dryas in Europe

NASA Astrophysics Data System (ADS)

Pellitero, Ramon; Rea, Brice R.; Spagnolo, Matteo; Hughes, Philip; Braithwaite, Roger; Renssen, Hans; Ivy-Ochs, Susan; Ribolini, Adriano; Bakke, Jostein; Lukas, Sven

2016-04-01

We have reconstructed and calculated the glacier equilibrium line altitudes (ELA) for 120 Younger Dryas palaeoglaciers from Morocco in the south to Svalbard in the north and from Ireland in the west to Turkey in the east. The chronology of these landform were checked and, when derived from cosmogenic dates, these were recalculated based on newer production rates. Frontal moraines/limits for the palaeoglaciers were used to reconstruct palaeoglacier extent by using a GIS tool which implements a discretised solution for the assumption of perfect-plasticity ice rheology for a single flowline and extents this out to a 3D ice surface. From the resulting equilibrium profile, palaeoglaciers palaeo-ELAs were calculated using another GIS tool. Where several glaciers were reconstructed in a region, a single ELA value was generated following the methodology of Osmaston (2005). In order to utilise these ELAs for quantitative palaeo-precipitation reconstructions an independent regional temperature analysis was undertaken. A database of 121 sites was compiled where the temperature was determined from palaeoproxies other than glaciers (e.g. pollen, diatoms, choleoptera, chironimids…) in both terrestrial and offshore environments. These proxy data provides estimates of average annual, summer and winter temperatures. These data were merged and interpolated to generate maps of average temperature for the warmest and coldest months and annual average temperature. From these maps the temperature at the ELA was obtained using a lapse rate of 0.65°C/100m. Using the ELA temperature range and summer maximum in a degree-day model allows determination of the potential melt which can be taken as equivalent to precipitation given the assumption a glacier is in equilibrium with climate. Results show that during the coldest part of the Younger Dryas precipitation was high in the British Isles, the NW of the Iberian Peninsula and the Vosges. There is a general trend for declining precipitation to the east with some regional exceptions. Local rain shadow effects can be seen in NW Scotland, NW Iberian Peninsula, the Balkans and the Alps. Precipitation is lowest for glaciers in N Norway, which appear to have had their Younger Dryas maxima later in the stadial. This is interpreted to be the result of limited precipitation north of the polar front due to the presence of a near permanent sea ice cover.

Testing the Younger Dryas impact hypothesis with platinum-group elements (PGE), Re, and Os isotopes in sediments from Hall's Cave and Freidken Archaeological site, Texas

NASA Astrophysics Data System (ADS)

Sun, N.; Brandon, A. D.; Forman, S. L.

2017-12-01

The Younger Dryas impact hypothesis suggests that extraterrestrial (ET) object(s) hit and exploded over North America 12,900 years ago and triggered the onset of Younger Dryas (YD) cooling and widespread megafaunal extinctions and the demise of the Clovis archeological culture. Supporting signatures such as concentrated carbon spherules and enlogaes, magnetic grains and spherules, nanodiamonds, and Ir-enrichment have been reported, but over time their lack of reproducibility of results at different locations have brought into question the impact hypothesis. Among the impact signatures investigated by previous studies, only few researchers included Re and platinum group element (PGE: Os, Ir, Ru, Rh, Pt, and Pd) characteristic concentrations, and 187Os/188Os ratios for ET mixing in terrestrial materials. Less than 1% of ET materials can provide enriched PGE concentrations, such that PGE are a sensitive tool to identify ET input in terrestrial materials. Because of the large difference between chondritic and continental crust 187Os/188Os ratios, 0.127 and >1.4, respectively, the 187Os/188Os ratios are also highly sensitive indicators of an extraterrestrial component in terrestrial and marine sediments. In this study, we examine sediments associated with the YD from two reported sites in North America, Hall's Cave and the Freidken Archaeological site in Central Texas, using the PGE and Re geochemical approach to test the evidence of the extraterrestrial projectiles during Younger Dryas period. Our current data show at Hall's Cave the PGE concentrations and patterns do not confirm the presence of an elevated meteoritic contribution. However, the 187Os/188Os depth profile shows a sudden 187Os/188Os decrease from 2.28 2.45 to 1.64 at the YD boundary layer, consistent with an increase in material derived from ET projectiles with chondritic 187Os/188Os ratios contaminating the Earth surface at the time of the YD extinction. Additional samples from the YD boundary at the Freidken site will also be presented in order to determine if a change in the 187Os/188Os signature occurs here as well. The combination of data across the YD boundary in both locales allows for a better evaluation of the possible causes for the YD extinction.

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene.

PubMed

Lambeck, Kurt; Rouby, Hélène; Purcell, Anthony; Sun, Yiying; Sambridge, Malcolm

2014-10-28

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet's dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to -134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 10(6) km(3) greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka(-1) punctuated by periods of greater, particularly at 14.5-14.0 ka BP at ≥40 mm⋅y(-1) (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100-150 y ago, with no evidence of oscillations exceeding ∼15-20 cm in time intervals ≥200 y from 6 to 0.15 ka BP.

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

PubMed Central

Lambeck, Kurt; Rouby, Hélène; Purcell, Anthony; Sun, Yiying; Sambridge, Malcolm

2014-01-01

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet’s dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 106 km3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka−1 punctuated by periods of greater, particularly at 14.5–14.0 ka BP at ≥40 mm⋅y−1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100–150 y ago, with no evidence of oscillations exceeding ∼15–20 cm in time intervals ≥200 y from 6 to 0.15 ka BP. PMID:25313072

Quaternary ecological and geomorphic changes associated with rainfall events in presently semi-arid northeastern Brazil

NASA Astrophysics Data System (ADS)

Auler, Augusto S.; Wang, Xianfeng; Edwards, R. Lawrence; Cheng, Hai; Cristalli, Patrícia S.; Smart, Peter L.; Richards, David A.

2004-10-01

Several geomorphic features and palaeobiotic remains in now semi-arid northeastern Brazil indicate major palaeoenvironmental changes during past periods of increased rainfall. 230Th mass spectrometric ages of speleothems and travertines have allowed the determination of the timing and duration of wetter than present conditions. The data demonstrate that wet events have occurred throughout much of the Pleistocene, present dry conditions having been established at the end of the Younger Dryas. A markedly different fauna comprising megafaunal elements not adapted to the present low arboreal scrubland caatinga vegetation existed in the area. Palaeobotanical remains embedded in travertine indicate forested vegetation at these wetter intervals, suggesting that the caatinga was then replaced or mixed with a semi-deciduous forest. Due to the abundance of travertine sites containing fossil botanical remains in northeastern Brazil, it is believed that forest expansion occurred over large areas of the now semi-arid zone, showing that the long hypothesised forested links between biodiversity-rich Amazon and Atlantic rainforests may indeed have existed during these moister phases. Copyright

Comparing apples and oranges: When is an interglacial not an interglacial?

NASA Astrophysics Data System (ADS)

Barker, S.; Conn, S.; Lordsmith, S.; Newman, D.; Knorr, G.

2017-12-01

In order to compare attributes among previous interglacials it is necessary to define the beginning (and end) of interglacial conditions. Here we suggest that the onset of some past interglacials could be adjusted by thousands of years if (quasi) equilibrium of the AMOC (Atlantic Meridional Overturning Circulation) is considered as a prerequisite for defining an interglacial state. Specifically we use continuous proxy records of NE Atlantic surface temperature and ice rafting to characterise every glacial to interglacial transition (including all glacial terminations) of the past 1.2Myr. Our results suggest that climate reversals (such as the Younger Dryas and 8.2ka event) are a common feature of terminations, with associated climate instability often lasting thousands of years beyond the start of interglacial conditions as traditionally defined. Accounting for these intervals within the process of deglaciation highlights the transient nature of greenhouse gas (CO2 and CH4) overshoots associated with the onset of some interglacials. As such we should perhaps consider these overshoots a part of the deglaciation process rather than part of the subsequent interglacial.

A pollen-based biome reconstruction over the last 3.562 million years in the Far East Russian Arctic - new insights into climate-vegetation relationships at the regional scale

NASA Astrophysics Data System (ADS)

Tarasov, P. E.; Andreev, A. A.; Anderson, P. M.; Lozhkin, A. V.; Leipe, C.; Haltia, E.; Nowaczyk, N. R.; Wennrich, V.; Brigham-Grette, J.; Melles, M.

2013-12-01

The recent and fossil pollen data obtained under the frame of the multi-disciplinary international El'gygytgyn Drilling Project represent a unique archive, which allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could be potentially present in this region during the past. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) long phases of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals in the study region within the past million years. During the late Pliocene-early Pleistocene interval (i.e., ~3.562-2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation from generally warmer/wetter environments of the earlier (i.e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction indicates that the taxon-rich cool mixed and cool conifer forest biomes are mostly characteristic of the time prior to MIS G16, whereas the tundra biome becomes a prominent feature starting from MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to ~2.730 Ma. The cold- and drought-tolerant steppe biome first appears in the reconstruction ~3.298 Ma during the tundra-dominated MIS M2, whereas the tundra biome initially occurs between ~3.379 and ~3.378 Ma within MIS MG4. Prior to ~2.800 Ma, several other cold stages during this generally warm Pliocene interval were characterized by the tundra biome.

Chronicles from the End of the Word: the Holocene climate variability in Tierra del Fuego

NASA Astrophysics Data System (ADS)

Waldmann, N.; Ariztegui, D.; Anselmetti, F.; Austin, J.; Moy, C.; Borromei, A.; Coronato, A.; Recasens, C.; Dunbar, R.; Martinez, M.; Olivera, D.

2008-12-01

Latest advances in the chronology and environmental importance of Antarctic paleoclimate records point towards a larger heterogeneity than previously thought. Thus, realistic inter-hemispheric correlations rely in the development of a tight array of well constrained records with a dense latitudinal coverage. Climatic records from southernmost Patagonia are hence critical corner-stones to link these Antarctic paleoclimatic archives with their South American counterparts. At 55° S on the Island of Tierra del Fuego, Lago Fagnano is located in one of the most substantially and extensively glaciated regions of southernmost South America during the Late Pleistocene. This elongated lake is the largest (~110 km long) and southernmost non-ice covered water body in the world. Existing on-shore geomorphological reconstructions combined with new lacustrine subsurface data, allowed us to better constrain the magnitude and chronology of the Fagnano glacier fluctuations since the LGM. The former Fagnano glacier flowed eastwards from the Darwin Cordillera fed by more than 50 tributary glaciers. The glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins directly into the Atlantic Ocean. During the maximum ice-expansion, the ice-covered area was ca. 4000 km2 with a maximum length of ca. 132 km. A set of submerged frontal moraines covered by lacustrine infilling identified in the seismic survey suggests occasional eastward re-advances of the paleo-glacier within the overall westward deglaciation pattern. These re-advances may correspond to cold events such as the Antarctic Cold Reversal (ACR), the Huelmo- Mascardi Cold Event (HMCE) and/or the Younger Dryas Chronozone (YDC). The ongoing development of a robust age model blended with a multi-proxy dataset will potentially clarify remaining controversial issues dealing with the geographical extension and chronology of these cold episodes during the last deglaciation. A multi-proxy study of selected cores retrieved from the deepest part of the lacustrine basin allows characterizing the Holocene sedimentary record. Detailed petrophysical, sedimentological and geochemical studies of a complete laminated sequence reveal fluctuations in major and trace elements, as well as total organic matter content and palynological data suggesting an apparent cyclicity. These results provide a unique dataset that can be compared with other marine and continental archives to improve our understanding of the forcing mechanisms behind climate change and to validate the outcome of existing ocean and atmospheric climatic models for the Southern Hemisphere.

Diatoms as paleoecological indicators of environmental change in the Lake Czechowskie catchments ecosystem (Northern Tuchola Pinewoods, Poland)

NASA Astrophysics Data System (ADS)

Rzodkiewicz, Monika; Zawiska, Izabela; Noryśkiewicz, Agnieszka Maria; Obremska, Milena; Ott, Florian; Kramkowski, Mateusz; Słowiński, Michał; Błaszkiewicz, Mirosław; Brauer, Achim

2016-04-01

In this study we investigated four cores of biogenic sediments from the lakes located in close vicinity. Three cores are situated along a transect in the Lake Czechowskie basin from its deepest point towards a former lake bay. The fourth sediment core was retrieved from the nearby Trzechowskie paleolake. Lake Czechowskie is located in the northern part of the Tuchola Pinewoods District (Northern Poland) in a young glacial landscape. At present, the majority of the area is forested or used for agriculture. The main focus was of the study was Late Glacial and early Holocene period. We performed diatom, Cladocera and pollen analyses, the chronology was established by varve counting, confirmed by AMS 14C dating and Laacher See Tephra (Wulf et. all 2013). In this study we focused on the results of diatom analyses. Diatom assemblages are integrated indicators of environmental change because their distributions are closely linked to water quality parameters including such as nutrient availability. At the beginning of Allerød there are more eutrophic diatom taxa such as Staurosira construens, Pseudostaurosira brevistriata, Staurosira pinnata. These species are widely distributed in the littoral mainly freshwater, many of which are species of epiphytic, preferring water rich in nutrients. At the end of the Allerød we observe significant changes within diatom assemblages. The increase of planktonic Cyclotella comensis together with the decrease of benthic Stauroseria construens indicate the shortening of time with ice cove on the lake and longer time with summer stratification. In the Younger Dryas cooling we can see the increase of the abundance of diatom Staurosira construens which indicate cold spring and late ice-out (Bradbury et al., 2002). At the early Holocene planktonic diatoms increase in particular Cyclotella comensis, Punciculata radiosa and Cyclotella praetermissa. Some of Aulacoseira species at the end of Younger Dryas. The Holocene sediments showed no variation of the species composition. Planktonic diatoms dominate in all studied location, expecially Cyclotella comensis, Punciculata radiosa, Cyclotella praetermissa and Stephanodiscus parvus. The results of our research shows that diatom communities were sensitive to climatic changes, which are well reflected in lake environment conditions. The strongest shifts in species assemblagess were noted at the beginning of the Allerød, the Younger Dryas onset and the transition into the early Holocene. The Late Glacial climate fluctuations caused more abrupt lake environment changes than during the Early Holocene. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association. The research was supported by the National Science Centre Poland (grant NCN 2011/01/B/ST10/07367). Literature: Bradbury, P., Cumming, B., Laird, K., 2002. A 1500-year record of climatic and environmental change in ElkLake, Minnesota III: measures of past primary productivity. Journal of Paleolimnology 27, 321-340 Wulf S., Ott F., Słowiński M., Noryśkiewicz A. M., Drager N., Martin-Puertas C., Czymzik M., Neugebauer I., Dulski P., Bourne A., Błaszkiewicz M., Brauer A. 2013. Tracing the Laacher See Tephra in the varved sediment record of the Trzechowskie palaeolake in central Northern Poland. Quaternary Science Reviews, s. 129-139.

Fever: exchange of shivering by nonshivering pyrogenesis in cold-acclimated guinea pigs.

PubMed

Blatteis, C M

1976-01-01

The pyrogenic response of adult, unanesthetized guinea pigs to 2 mug/kg iv of Salmonella enteritidis endotoxin was measured at 27 and 7 degrees C ambient temperatures, both before and after an 8-wk exposure to 7 degrees C. There were no significant differences between the onset, maximum height, and total duration of the fevers produced before and after cold acclimation in both thermal environments. However, in 27 degrees C, before cold acclimation, fever production was associated with vigorous shivering activity; two temperature maxima typically developed. After cold acclimation, visible shivering was not detectable during pyrogenesis; moreover, only a single maximum occurred, culminating during the interval between the two rises previously. In 7 degrees C, shivering occurred in both the non-cold- and cold-acclimated endotoxin-treated guinea pigs, but the increase in oxygen consumption was significantly greater in the latter. These results indicated, therefore, that nonshivering (NST) replaces shivering thermogenesis (ST) in a thermoneutral, while ST is added onto NST in a cold, environment in cold-acclimated guinea pigs in supplying the necessary heat for fever production, and that these effects involve alterations in the character of the febrile course.

A New Evaluation Method of Stored Heat Effect of Reinforced Concrete Wall of Cold Storage

NASA Astrophysics Data System (ADS)

Nomura, Tomohiro; Murakami, Yuji; Uchikawa, Motoyuki

Today it has become imperative to save energy by operating a refrigerator in a cold storage executed by external insulate reinforced concrete wall intermittently. The theme of the paper is to get the evaluation method to be capable of calculating, numerically, interval time for stopping the refrigerator, in applying reinforced concrete wall as source of stored heat. The experiments with the concrete models were performed in order to examine the time variation of internal temperature after refrigerator stopped. In addition, the simulation method with three dimensional unsteady FEM for personal-computer type was introduced for easily analyzing the internal temperature variation. Using this method, it is possible to obtain the time variation of internal temperature and to calculate the interval time for stopping the refrigerator.

The Rock Magnetic Record Across the 12.9 ka Younger Dryas Boundary: Evidence for Impact?

NASA Astrophysics Data System (ADS)

Nadel, M.; Feinberg, J. M.; Waters, M.

2012-12-01

The cause/s of the onset of the Younger Dryas (YD) climactic event at 12.9 ka and the corresponding extinction of Pleistocene megafauna and drastic changes in human subsistence patterns in the Americas remain a geologic mystery. Firestone et. al. (2007) proposed a bolide impact on the Laurentide ice sheet to explain these dramatic environmental changes, citing as evidence an increase in the concentration of magnetic spherules (MSp) and magnetic grains, among several other parameters. Over the five and a half years since the idea was first proposed it has evolved and matured, and many of the original lines of evidence are no longer argued. However, peaks in MSp concentrations (along with the presence of nanodiamonds) continue to be central to pro-impact arguments. Soils and lacustrine sediments are the most common recording media across the YD time interval, and the sample procedure used by previous workers to isolate the magnetic component is noteworthy. Disaggregated sediment was suspended in water and a plastic-covered hand magnet was used to stir the suspension and attract magnetic grains. Adhered grains were transferred into a separate container, and the process was repeated until grains were no longer attracted to the magnet. The total magnetic fraction was weighed and MSp were hand-picked under a microscope, to quantify concentration. Here we present an alternative approach that uses a comprehensive suite of highly sensitive rock magnetic measurements on in-situ samples to examine two early human archaeological sites: the Debra L. Friedkin site in central Texas and the Topper site in South Carolina (one of the original sites in the Firestone et al. (2007) study). The depositional history at both sites is constrained by optically stimulated luminescence ages, and the stratigraphic position of the 12.9 ka YD event is non-controversial. Two continuous soil profiles were collected at Friedkin, using 9 cm3 plastic boxes as well as a separate 20 cm U-channel core spanning the YD interval, later sub-sampled at 0.5 cm intervals. At Topper we collected bulk samples to be used in the hand magnet method described by Israde-Alcántara et al., (2012) and in 9 cm3 plastic boxes. Samples were analyzed for low- and high-field χ, frequency dependence of χ, NRM, ARM, and IRM intensities, and major hysteresis loops. The magnetic parameters collected from Friedkin provide a clear record of pedogenesis, but exhibit no obvious magnetic anomalies that can be correlated with either the onset of the YD or the potential environmental aftermath of a bolide impact. While we observe minor peaks in Hcr and the Mr/Ms ratio close to but not coincident with the YD, these peaks are no greater in magnitude than those in other portions of the profile. Analyses of the samples from the Topper site are not complete at the time of writing, but will provide a direct comparison between data acquired using the two competing methods. This additional data will allow us to evaluate the robustness of MSp concentrations as evidence for a bolide impact at 12.9 ka.

The Effect of the Younger Dryas on Paleoindian Occupations in Eastern North America Evidence from Artifactual, Pollen, and Radiocarbon Records

NASA Astrophysics Data System (ADS)

Anderson, D. G.; Meeks, S. C.; Miller, D. S.; Yerka, S. J.; Gillam, J. C.; Goodyear, A. C.; Johanson, E. N.; West, A.

2008-12-01

The Younger Dryas appears to have been a period when human populations in Eastern North America were undergoing significant stress. Attribute and locational data on Paleoindian materials from across the continent is available from the Paleoindian Database of the Americas or PIDBA, available on-line at http://pidba.utk.edu. Tallying the diagnostic projectile point sample from PIDBA in the on-line "entire sample" dated 24 April 2008, suggests that a population decline followed by a rebound may have occurred, particularly in southeastern North America. Following Clovis, fluted points with deeply indented bases and short to full flutes occur in many areas, such as the Redstone, Barnes, Cumberland, and Folsom types. In southeastern North America, these are thought to have been replaced by unfluted lanceolate and waisted forms, including the Beaver Lake, Suwannee/Simpson, and Quad types, which are in turn replaced by Dalton forms. Within the Southeast, a significant decline occurs between Clovis (N=1993 points) and presumably immediate post-Clovis full fluted forms (N=947 points). This may correspond to a similar decline in population, assuming the point types occurred for comparable periods of time, and were used in a similar fashion. Goodyear noted a similar pattern between Clovis (n=179) and presumed immediate post-Clovis Redstone (n=40) forms in South Carolina. Comparable declines have also been observed in North Carolina by Daniel and Goodyear ( and in Virginia by MacAvoy. In the PIDBA database across the Southeast, projectile point numbers increase following the immediate post Clovis decline, from 947 full fluted to 1717 unfluted and then 2594 Dalton points. The increase in the latter part of the Younger Dryas may actually be even more pronounced, since Dalton points, which are quite widespread, are only systematically recorded in a few states. Radiocarbon dates from Paleoindian and Early Archaic assemblages reveal a similar pattern. Dates falling in the initial centuries of the Younger Dryas are decidedly uncommon in the Southeast and over the larger region. In a sample of 218 dates from the Southeast and adjoining areas, only seven fall between 10,900 and 10,570 14C yr BP or between ca. 12,850 and 12,600 cal yr BP, and all of these are at the recent end of this range, between 10,570 and 10,710 14C yr BP. In the Southeast, at least, there appears to be a ca. 250-300 year 'gap' in the distribution of radiocarbon dates, with few reported from ca. 12,900-12,600 cal yr BP. Finally, analyses of fossil pollen records from the southeastern United States, although admittedly few in number, indicate that major vegetational shifts, both abrupt and characterized by oscillations, were occurring across the region during the Pleistocene/Holocene transition and that these shifts appear to be synchronic or quasi-synchronic with the Younger Dryas. The results suggests that the earliest inhabitants in the southeastern United States were faced with an environment that was anything but stable.

Sedimentological characteristics of lake sediment of the Lake Jelonek (North Poland)

NASA Astrophysics Data System (ADS)

Kramkowski, Mateusz; Filbrandt-Czaja, Anna; Ott, Florian; Słowiński, Michał; Tjallingii, Rik; Błaszkiewicz, Mirosław; Brauer, Achim

2016-04-01

Lake Jelonek is located in Northern Poland (53°45'58N, 18°23'30E). The lake is surrounded by forest, covers an area of 19,9 ha and has a maximum depth of 13,8 m. In 2013 and 2014 three overlapping and parallel series of long sediment cores JEL14-A-(1445 cm), JEL14-B-(1430 cm), JEL14-C-(1435 cm) and seven short gravity cores JEL13 (K1-K7) have been recovered from the deepest part of the lake. A continuous composite profile JEL14 covering 1426 cm has been established by correlation based on 28 distinct macroscopic marker layers. The sediment sequence can be divided into 15 (I-XV) lithological units. These units comprise biochemical calcite varves, homogeneous calcite-rich gyttja, homogeneous organic-diatomaceous gyttja, and sandy layers. The chronology established so far is based on 14 AMS 14C dates from terrestrial plant remains and tephrochronology (Askja AD-1875) and covers the interval from the Younger Dryas to present times. Based on the chronology and sedimentological characteristics the composite profile has been correlated to a previous core from which a detailed pollen diagram had been established (Filbrandt-Czaja 2009). Here we present initial results from thin section analyses for two intervals from the new composite record JEL14, (I) the uppermost 0-256 cm and (II) the interval from 768-1296 cm. Intercalated between these two varved interval is a thick section (512 cm) of homogeneous organic-ditomaceous sediments. We present varve micro-facies data in combination with μ-XRF element scanning for comprehensive reconstruction of the sedimentation processes in Lake Jelonek. Preliminary varve counting reveals that the uppermost 256 cm varved sediments comprise ca 925 years (2008-1083 AD), while the lower floating varve interval covers the time period from 1850 - 10500 cal a BP. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution Analysis -ICLEA- of the Helmholtz Association; grant number VH-VI-415. References: Filbrandt-Czaja, A. 2009: Studia nad historią szaty roślinnej i krajobrazu Borów Tucholskich. pp. Wydawnictwo Naukowe Uniwersytetu Mikołaja Kopernika.

Calcareous nannoplankton and foraminiferal response to global Oligocene and Miocene climatic oscillations: a case study from the Western Carpathian segment of the Central Paratethys

NASA Astrophysics Data System (ADS)

Holcová, Katarína

2017-06-01

The reactions of foraminiferal and calcareous nannoplankton assemblages to global warming and cooling events in the time intervals of ca. 27 to 19 Ma and 13.5 to 15 Ma (Oligocene and Miocene) were studied in subtropical epicontinental seas influenced by local tectonic and palaeogeographic events (the Central Paratethys). Regardless of these local events, global climatic processes significantly influenced the palaeoenvironment within the marine basin. Warm intervals are characterized by a stable, humid climate and a high-nutrient regime, due primarily to increased continental input of phytodetritus and also locally due to seasonal upwelling. Coarse clastics deposited in a hyposaline environment characterize the marginal part of the basin. Aridification events causing decreased riverine input and consequent nutrient decreases, characterized cold intervals. Apparent seasonality, as well as catastrophic climatic events, induced stress conditions and the expansion of opportunistic taxa. Carbonate production and hypersaline facies characterize the marginal part of the basins. Hypersaline surface water triggered downwelling circulation and mixing of water masses. Decreased abundance or extinction of K-specialists during each cold interval accelerated their speciation in the subsequent warm interval. Local tectonic events led to discordances between local and global sea-level changes (tectonically triggered uplift or subsidence) or to local salt formation (in the rain shadows of newly-created mountains).

Vaccines for the common cold.

PubMed

Simancas-Racines, Daniel; Franco, Juan Va; Guerra, Claudia V; Felix, Maria L; Hidalgo, Ricardo; Martinez-Zapata, Maria José

2017-05-18

The common cold is a spontaneously remitting infection of the upper respiratory tract, characterised by a runny nose, nasal congestion, sneezing, cough, malaise, sore throat, and fever (usually < 37.8º C). The widespread morbidity caused by the common cold worldwide is related to its ubiquitousness rather than its severity. The development of vaccines for the common cold has been difficult because of antigenic variability of the common cold virus and the indistinguishable multiple other viruses and even bacteria acting as infective agents. There is uncertainty regarding the efficacy and safety of interventions for preventing the common cold in healthy people. This is an update of a Cochrane review first published in 2011 and previously updated in 2013. To assess the clinical effectiveness and safety of vaccines for preventing the common cold in healthy people. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (September 2016), MEDLINE (1948 to September 2016), Embase (1974 to September 2016), CINAHL (1981 to September 2016), and LILACS (1982 to September 2016). We also searched three trials registers for ongoing studies and four websites for additional trials (February 2017). We included no language or date restrictions. Randomised controlled trials (RCTs) of any virus vaccines compared with placebo to prevent the common cold in healthy people. Two review authors independently evaluated methodological quality and extracted trial data. We resolved disagreements by discussion or by consulting a third review author. We found no additional RCTs for inclusion in this update. This review includes one RCT dating from the 1960s with an overall high risk of bias. The RCT included 2307 healthy participants, all of whom were included in analyses. This trial compared the effect of an adenovirus vaccine against placebo. No statistically significant difference in common cold incidence was found: there were 13 (1.14%) events in 1139 participants in the vaccines group and 14 (1.19%) events in 1168 participants in the placebo group (risk ratio 0.95, 95% confidence interval 0.45 to 2.02; P = 0.90). No adverse events related to the live vaccine were reported. The quality of the evidence was low due to limitations in methodological quality and a wide 95% confidence interval. This Cochrane Review was based on one study with low-quality evidence. We found no conclusive results to support the use of vaccines for preventing the common cold in healthy people compared with placebo. We identified a need for well-designed, adequately powered RCTs to investigate vaccines for the common cold in healthy people. Any future trials on medical treatments for preventing the common cold should assess a variety of virus vaccines for this condition. Outcome measures should include common cold incidence, vaccine safety, and mortality related to the vaccine.

Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary

PubMed Central

Wu, Yingzhe; Sharma, Mukul; LeCompte, Malcolm A.; Demitroff, Mark N.; Landis, Joshua D.

2013-01-01

One or more bolide impacts are hypothesized to have triggered the Younger Dryas cooling at ∼12.9 ka. In support of this hypothesis, varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the Younger Dryas boundary (YDB). We show that bulk sediment and/or magnetic grains/microspherules collected from the YDB sites in Arizona, Michigan, New Mexico, New Jersey, and Ohio have 187Os/188Os ratios ≥1.0, similar to average upper continental crust (= 1.3), indicating a terrestrial origin of osmium (Os) in these samples. In contrast, bulk sediments from YDB sites in Belgium and Pennsylvania exhibit 187Os/188Os ratios <<1.0 and at face value suggest mixing with extraterrestrial Os with 187Os/188Os of ∼0.13. However, the Os concentration in bulk sample and magnetic grains from Belgium is 2.8 pg/g and 15 pg/g, respectively, much lower than that in average upper continental crust (=31 pg/g), indicating no meteoritic contribution. The YDB site in Pennsylvania is remarkable in yielding 2- to 5-mm diameter spherules containing minerals such as suessite (Fe-Ni silicide) that form at temperatures in excess of 2000 °C. Gross texture, mineralogy, and age of the spherules appear consistent with their formation as ejecta from an impact 12.9 ka ago. The 187Os/188Os ratios of the spherules and their leachates are often low, but Os in these objects is likely terrestrially derived. The rare earth element patterns and Sr and Nd isotopes of the spherules indicate that their source lies in 1.5-Ga Quebecia terrain in the Grenville Province of northeastern North America. PMID:24009337

Lateglacial retreat chronology of the Scandinavian Ice Sheet in Finnmark, northern Norway, reconstructed from surface exposure dating of major end moraines

NASA Astrophysics Data System (ADS)

Romundset, Anders; Akçar, Naki; Fredin, Ola; Tikhomirov, Dmitry; Reber, Regina; Vockenhuber, Christof; Christl, Marcus; Schlüchter, Christian

2017-12-01

We report results from a comprehensive surface exposure dating campaign in eastern Finnmark, located in the northernmost part of Norway and close to the Norwegian-Russian border. This is a palaeo-glaciologically important region as it sits near the proposed border-zone between the former Scandinavian and Barents Sea Ice Sheets. However, until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice-marginal deposits with isostatically raised shorelines and marine sediment cores. We measured the content of 10Be (N = 22) and 36Cl (N = 17) from boulders located at the crest of major moraine ridges at four localities; Kjæs, Kongsfjorden, Vardø and Kirkenes. These are key localities of existing regional reconstructions of ice recession in this area. Despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating, the large numbers of samples from each site except Kjæs still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat. Our results show that the Kongsfjorden and Vardø moraines were deposited 14.3 ± 1.7 ka and 13.6 ± 1.4 ka, respectively, and thus point to a Older Dryas age of the proposed 'Outer Porsanger' deglaciation sub-stage. Moraine ridges belonging to the 'Main' sub-stage near Kirkenes were dated to 11.9 ± 1.2 ka, corresponding well with the ice retreat chronology farther west in northern Norway and suggesting that the maximum Younger Dryas ice sheet extent was attained in the late Younger Dryas along a more than 500 km long stretch in northernmost Scandinavia.

Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

USGS Publications Warehouse

Flynn, Robert H.

2006-01-01

This report presents water-surface elevations and profiles as determined using the U.S. Army Corps of Engineers (USACE) one-dimensional Hydrologic Engineering Center River Analysis System, also known as HEC-RAS. Steady flow water-surface profiles were developed for two stream reaches: the Cold River from its confluence with the Connecticut River in Walpole, through Alstead to the McDermott Bridge in Langdon, NH, and Warren Brook from its confluence with the Cold River to Warren Lake in Alstead, NH. Flood events of a magnitude, which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval), were modeled using HEC-RAS as these flood events are recognized as being significant for flood-plain management, determination of flood insurance rates, and design of structures such as bridges and culverts. These flood events are referred to as the 10-, 50-, 100-, and 500-year floods and have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled or exceeded during any year. The recurrence intervals represent the long-term average between floods of a specific magnitude. The risk of experiencing rare floods at short intervals or within the same year increases when periods greater than one year are considered. The analyses in this study reflect the flooding potentials based on conditions existing in the communities of Walpole, Alstead and Langdon at the time of completion of this study.

An experimental study of the role of subsurface plumbing on geothermal discharge

USGS Publications Warehouse

Namiki, Atsuko; Ueno, Yoshinori; Hurwitz, Shaul; Manga, Michael; Munoz-Saez, Carolina; Murphy, Fred

2016-01-01

In order to better understand the diverse discharge styles and eruption intervals observed at geothermal features, we performed three series of laboratory experiments with differing plumbing geometries. A single, straight conduit that connects a hot water bath (flask) to a vent (funnel) can originate geyser-like periodic eruptions, continuous discharge like a boiling spring, and fumarole-like steam discharge, depending on the conduit length and radius. The balance between the heat loss from the conduit walls and the heat supplied from the bottom determines whether and where water can condense which in turn controls discharge style. Next, we connected the conduit to a cold water reservoir through a branch, simulating the inflow from an external water source. Colder water located at a higher elevation than a branching point can flow into the conduit to stop the boiling in the flask, controlling the periodicity of the eruption. When an additional branch is connected to a second cold water reservoir, the two cold reservoirs can interact. Our experiments show that branching allows new processes to occur, such as recharge of colder water and escape of steam from side channels, leading to greater variation in discharge styles and eruption intervals. This model is consistent with the fact that eruption duration is not controlled by emptying reservoirs. We show how differences in plumbing geometries can explain various discharge styles and eruption intervals observed in El Tatio, Chile, and Yellowstone, USA.

Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Zhang, Enlou; Wang, Yongbo; Sun, Weiwei; Shen, Ji

2016-02-01

We present the results of pollen analyses from a 1105 cm long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed humid period in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño-Southern Oscillation strength in the tropical Pacific.

Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Zhang, E.; Wang, Y.; Sun, W.; Shen, J.

2015-10-01

We present the results of pollen analyses from a 1105-cm-long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed strengthening of the ISM in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño Southern Oscillation strength in the tropical Pacific.

Sedimentary evidence of landscape and climate history since the end of MIS 3 in the Krkonoše Mountains, Czech Republic

NASA Astrophysics Data System (ADS)

Engel, Zbyněk; Nývlt, Daniel; Křížek, Marek; Treml, Václav; Jankovská, Vlasta; Lisá, Lenka

2010-04-01

A sedimentary core recovered from the cirque basin of Labský důl valley (1039 m a.s.l.) in the Krkonoše Mountains reflects the environmental history for approximately the last 30,000 years. Analyses of magnetic susceptibility, carbon content, pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of Lateglacial and Holocene vegetation history in Sudetes region of the Czech Republic. The succession of sedimentary units in the lower part of the core suggests that the cirque was ice-free before the onset of the last glaciation at the beginning of marine isotope stage 2. Highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka BP. Cold climates persisted until the Lateglacial period, evidenced by an identified warming and subsequent cooling event correlated with the Younger Dryas period. Sparse, treeless vegetation dominated in the catchment area at that time. The sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12.5-10.8 cal ka BP. Subsequently, the alpine treeline ecotone gradually shifted above the cirque floor. Palaeoclimatic conditions in the early Holocene fluctuated strongly, whereas since 5.1 cal ka BP conditions have been more stable. Pollen-based climate reconstructions suggest significant cooling at around 9.8-9.3, 7.7-7.5 and 4.0-3.3 cal ka BP. Spruce forests have dominated the site since 5.0 cal ka BP when the vegetation became similar to the modern one. Two phases of increased sedimentation were identified within the Holocene culminating about 9.2-7.5 cal ka BP and 5.8-5.5 cal ka BP. Sediment yield was as high as 2.4 mm yr -1 during the period, reflecting environmental changes during the Atlantic/Sub-Boreal transition.

The response of the Okhotsk Sea environment to the orbital-millennium global climate changes during the Last Glacial Maximum, deglaciation and Holocene

NASA Astrophysics Data System (ADS)

Gorbarenko, Sergey A.; Artemova, Antonina V.; Goldberg, Evgeniy L.; Vasilenko, Yuriy P.

2014-05-01

Reconstruction of regional climate and the Okhotsk Sea (OS) environment for the Last Glacial Maximum (LGM), deglaciation and Holocene was performed on the basis of high-resolution records of ice rafted debris (IRD), СаСО3, opal, total organic carbon (TOС), biogenic Ba (Ba_bio) and redox sensitive element (Mn, Mo) content, and diatom and pollen results of four cores that form a north-southern transect. Age models of the studied cores were earlier established by AMS 14C data, oxygen-isotope chronostratigraphy and tephrochronology. According to received results, since 25 ka the regional climate and OS environmental conditions have changed synchronously with LGM condition, cold Heinrich event 1, Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Pre-Boreal (PB) warming recorded in the Greenland ice core, North Atlantic sediment, and China cave stalagmites. Calculation of IRD MAR in sediment of north-south transect cores indicates an increase of sea ice formation several times in the glacial OS as compared to the Late Holocene. Accompanying ice formation, increased brine rejection and the larger potential density of surface water at the north shelf due to a drop of glacial East Asia summer monsoon precipitation and Amur River run off, led to strong enhancement of the role of the OS in glacial North Pacific Intermediate Water (NPIW) formation. The remarkable increase in OS productivity during BA and PB warming was probably related with significant reorganisation of the North Pacific deep water ventilation and nutrient input into the NPIW and OS Intermediate Water (OSIW). Seven Holocene OS millennial cold events based on the elevated values of the detrended IRD stack record over the IRD broad trend in the sediments of the studied cores have occurred synchronously with cold events recorded in the North Atlantic, Greenland ice cores and China cave stalagmites after 9 ka. Diatom production in the OS was mostly controlled by sea ice cover changes and surface water stratification induced by sea-ice melting; therefore significant opal accumulation in sediments of this basin begin from 4 to 6 ka ago simultaneously with a remarkable decrease of sea ice cover.

Lateglacial climate reconstruction on the Bolivian Altiplano inferred from paleoglaciers and paleolakes

NASA Astrophysics Data System (ADS)

Martin, Léo; Blard, Pierre-Henri; Lavé, Jérôme; Prémaillon, Mélody; Jomelli, Vincent; Brunstein, Daniel; Lupker, Maarten; Charreau, Julien; Mariotti, Véronique; Condom, Thomas; Bourles, Didier

2016-04-01

Recent insights shed light on the global mechanisms involved in the abrupt oscillations of the Earth climate for the Late Glacial Maximum (LGM) to Holocene period (Zhang et al., 2014; Banderas et al., 2015). Yet the concomitant patterns of regional climate reorganization on continental areas are for now poorly documented. Particularly, few attempts have been made to propose temporal reconstructions of the regional climate variables in the High Tropical Andes, a region under the influence of multiple global climate forcings (Jomelli et al., 2014). We present new glacial chronologies from four sites of the Bolivian Altiplano: the Wara-Wara valley (17.3°S - 66.1°W), the Zongo valley (16.3°S - 68.1°W), the Cerro Tunupa (19.8°S - 67.6°W) and the Nevado Sajama (18.1°S 68.9°W). These chronologies are based on Cosmic Ray Exposure dating (CRE) from an exceptional suite of recessive moraines. These new data permitted to refine existing chronologies of Smith et al., 2005; Zech et al., 2010 and Blard et al., 2009. In both sites, glaciers recorded stillstand episodes synchronous with cold events such as the Henrich 1 event, the Younger Dryas and the Antarctic Cold Reversal. Since the nearby Altiplano basin registered lake level variations over the same period, we were able to apply a joint modelling of glaciers Equilibrium Line Altitude (ELA) and lake budget. This method permits to derive a temporal evolution of temperature and precipitation for the four sites. These new reconstructions show for all sites that glaciers of the Tropical Andes were influenced by the major climatic events of the Northern and Southern Hemispheres. Furthermore, the temperature variability observed at high latitudes results in these tropical latitudes in major precipitation variability whereas the lateglacial temperature patterns remain globally monotonic. This conversion of global temperature variability into regional precipitation variability support the idea that North Hemisphere cold events are coeval with an important southward deflexion of the Intertropical Convergence Zone (ITCZ) due to the inter-hemispheric temperature gradient (Schneider et al., 2014). Such a southward shift would lead to an increased moist supply of the subequatorial Amazonian basin (Montade et al., 2015) and thus an increased easterly driven moist transport over the Altiplano.

Cold periods and coronary events: an analysis of populations worldwide

PubMed Central

Barnett, A.; Dobson, A.; McElduff, P.; Salomaa, V.; Kuulasmaa, K.; Sans, S.; t for

2005-01-01

Study objective: To investigate the association between cold periods and coronary events, and the extent to which climate, sex, age, and previous cardiac history increase risk during cold weather. Design: A hierarchical analyses of populations from the World Health Organisation's MONICA project. Setting: Twenty four populations from the WHO's MONICA project, a 21 country register made between 1980 and 1995. Patients: People aged 35–64 years who had a coronary event. Main results: Daily rates of coronary events were correlated with the average temperature over the current and previous three days. In cold periods, coronary event rates increased more in populations living in warm climates than in populations living in cold climates, where the increases were slight. The increase was greater in women than in men, especially in warm climates. On average, the odds for women having an event in the cold periods were 1.07 higher than the odds for men (95% posterior interval: 1.03 to 1.11). The effects of cold periods were similar in those with and without a history of a previous myocardial infarction. Conclusions: Rates of coronary events increased during comparatively cold periods, especially in warm climates. The smaller increases in colder climates suggest that some events in warmer climates are preventable. It is suggested that people living in warm climates, particularly women, should keep warm on cold days. PMID:15965137

Vegetation and climate history in the Laptev Sea region (arctic Siberia) during Late Quaternary inferred from pollen records

NASA Astrophysics Data System (ADS)

Andreev, A.; Schirrmeister, L.; Tarasov, P.

2009-04-01

A number of permafrost sections dated by 14C, TL, IRSL, and 230U/Th were analysed for pollen. Pollen spectra suggest that wet grass-sedge tundra habitats dominated during an interstadial c. 200-170 ka ago. The climate was rather wet and cold. The pollen spectra reflect sparser grass-sedge vegetation cover during the Late Saalian stadial, c. 170-130 ka BP. Environmental conditions were much more severe compared with the previous interstadial. Open Poaceae and Artemisia communities dominated at the beginning of the Last Interglacial. Some shrubs (Alnus fruticosa, Salix, Betula nana) grew in more protected and wetter places. Climate was rather warm (similar to modern conditions)during this time. Shrub tundra with Alnus fruticosa and Betula nana s.l. dominated in the area during the Eemian climatic optimum, when summer temperatures were 4-5°C higher than today. Early Weichselian pollen records reflect harsh environmental conditions; sparser vegetation (mostly grass and sedge communities) during this time. Middle Weichselian (Karginsky) Interstadial records with dominance of Cyperaceae and Poaceae with some Artemisia and Salix reflects tundra- and steppe-like associations with willow shrubs dominated the area. The climate was relatively moist and warm. A rather high content of algae colonies in the sediments indicates shallow water habitats (e.g. centres of ice wedge polygons). Dominance of Poaceae, Cyperaceae, Artemisia, and Caryophyllaceae pollen with some other herbs is typical for the 40-32 ka BP (climatic optimum) old sediments when open herb dominated the area. High pollen concentrations reflect that dense grass-sedge dominated vegetation; presence of Salix is also characteristic. The records point to climate amelioration during the Middle Weichselian compared to the Early Weichselian. Climate conditions became colder and drier c. 30-26 ka BP. Pollen spectra reflect that sedge-grass-Artemisia with some Caryophyllaceae and Asteraceae dominated the vegetation. Mostly grass conenoses with some Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris predominated during the late Weichselian (Sartan), ca 26-16 ka BP. Climate was very cold and dry. Later, 16-12 ka BP, grass and sedge associations with Caryophyllaceae, Asteraceae, and Cichoriaceae dominated the vegetation. Climate was significantly warmer and moister than during the previous interval. Accumulation of Ice Complex sediments stopped ca 12 ka BP, at the beginning of Allerød. Higher pollen concentration, the presence of willow and birch pollen points to a relatively warm climate between 12 and 11 ka BP reflecting significant climate amelioration. Pollen of shrubs disappeared from the Younger Dryas spectra pointing to the harsher climate. Early Holocene spectra are dominated by alder, birch, Poaceae, and Cyperaceae. Climate reconstruction inferred a temperature substantially warmer than present (up to 12°C). Shrubs gradually disappeared from the area after 7.6 14C ka BP and vegetation cover became similar to modern tundra.

Variations in productivity and eolian fluxes in the northeastern Arabian Sea during the past 110 ka

NASA Astrophysics Data System (ADS)

Pourmand, Ali; Marcantonio, Franco; Schulz, Hartmut

2004-04-01

High-resolution (one to two samples/ka) radionuclide proxy records from core 93KL in the northeastern Arabian Sea provide evidence for millennial climate variability over the past 110 ka. We interpret 230Th-normalized 232Th fluxes as a proxy for eolian input, and authigenic uranium concentrations as a proxy for past productivity. We attribute orbital and suborbital variations in both proxies to changes in the intensity of the southwest Indian Ocean monsoon. The highest 230Th-normalized 232Th fluxes occur at times that are consistent with the timing of the Younger Dryas, Heinrich events 1-7 and cold Dansgaard-Oeschger stadial events recorded in the GISP2 ice core. Such high dust fluxes may be due to a weakened southwest monsoon in conjunction with strengthened northwesterlies from the Arabian Peninsula and Mesopotamia. Authigenic uranium concentrations, on the other hand, are highest during warm Dansgaard-Oeschger interstadials when the southwest monsoon is intensified relative to the northwesterly winds. Our results also indicate that on orbital timescales maximum average eolian fluxes coincide with the timing of marine isotopic stage (MIS) 2 and 4, while minimum fluxes occur during MIS 1, 3 and 5. Although the forcing mechanism(s) controlling suborbital variabilities in monsoonal intensity is still debated, our findings suggest an atmospheric teleconnection between the low-latitude southwest monsoon and North Atlantic climate.

Paleobiology of the Sand Beneath the Valders Diamicton at Valders, Wisconsin

NASA Astrophysics Data System (ADS)

Maher, Louis J.; Miller, Norton G.; Baker, Richard G.; Curry, B. Brandon; Mickelson, David M.

1998-03-01

Previously undescribed pollen, plant macrofossils, molluscs, and ostracodes were recovered from a 2.5-m-thick glaciolacustrine unit of silty sand and clay at Valders, Wisconsin. The interstadial sediment was deposited about 12,200 14C yr B.P. after retreat of the Green Bay lobe that deposited diamicton of the Horicon Formation, and before advance of the Lake Michigan lobe that deposited the red-brown diamicton of the Valders Member of the Kewaunee Formation. Fluctuations of abundance of Candona subtriangulata, Cytherissa lacustris,and three other species define four ostracode biozones in the lower 1.7 m, suggesting an open lake environment that oscillated in depth and proximity to glacial ice. Pollen is dominated by Piceaand Artemisia,but the low percentages of many other types of long-distance origin suggest that the terrestrial vegetation was open and far from the forest border. The upper part of the sediment, a massive sand deposited in either a shallow pond or a sluggish stream, contains a local concentration of plant macrofossils. The interpretation of a cold open environment is supported by the plant macrofossils of more than 20 species, dominated by those of open mineral soils ( Arenaria rubella, Cerastium alpinumtype, Silene acaulis, Sibbaldia procumbens, Dryas integrifolia, Vaccinium uliginosumvar. alpinum, Armeria maritima,etc.) that in North America occur largely in the tundra and open tundra-forest ecotone of northern Canada. Ice-wedge casts occur in the sand.

Abrupt climate change and collapse of deep-sea ecosystems

USGS Publications Warehouse

Yasuhara, Moriaki; Cronin, T. M.; Demenocal, P.B.; Okahashi, H.; Linsley, B.K.

2008-01-01

We investigated the deep-sea fossil record of benthic ostracodes during periods of rapid climate and oceanographic change over the past 20,000 years in a core from intermediate depth in the northwestern Atlantic. Results show that deep-sea benthic community "collapses" occur with faunal turnover of up to 50% during major climatically driven oceanographic changes. Species diversity as measured by the Shannon-Wiener index falls from 3 to as low as 1.6 during these events. Major disruptions in the benthic communities commenced with Heinrich Event 1, the Inter-Aller??d Cold Period (IACP: 13.1 ka), the Younger Dryas (YD: 12.9-11.5 ka), and several Holocene Bond events when changes in deep-water circulation occurred. The largest collapse is associated with the YD/IACP and is characterized by an abrupt two-step decrease in both the upper North Atlantic Deep Water assemblage and species diversity at 13.1 ka and at 12.2 ka. The ostracode fauna at this site did not fully recover until ???8 ka, with the establishment of Labrador Sea Water ventilation. Ecologically opportunistic slope species prospered during this community collapse. Other abrupt community collapses during the past 20 ka generally correspond to millennial climate events. These results indicate that deep-sea ecosystems are not immune to the effects of rapid climate changes occurring over centuries or less. ?? 2008 by The National Academy of Sciences of the USA.

10Be exposure age chronology of the last glaciation in the Krkonoše Mountains, Central Europe

NASA Astrophysics Data System (ADS)

Engel, Zbyněk; Braucher, Régis; Traczyk, Andrzej; Laetitia, Léanni; AsterTeam

2014-02-01

A new chronology of the last glaciation is established for the Krkonoše (Giant) Mountains, Central Europe, based on in-situ produced 10Be in moraine boulders. Exposure ages and Schmidt Hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the Last Glacial Maximum (LGM). Large moraines at the outlet of the Snowy Cirques (Śnieżne Kotły) and in the middle part of the Úpa (Obří důl) trough were deposited around 21 ka while a series of smaller moraines above the LGM deposits represent readvances that occurred no later than 18.1 ± 0.6 ka, 15.7 ± 0.5 ka, 13.5 ± 0.5 ka and 12.9 ± 0.7 ka. An exposure age of 13.8 ± 0.4 ka obtained for protalus ramparts at the foot of the Úpská jáma Cirque headwall indicates that glaciers advanced only in north- to east-facing cirques during the Lateglacial. The last glacier fluctuation was synchronous with the Younger Dryas cold event. The timing of local glacier advances during the last glacial episode correlates with the late Weichselian glacier phases in the Alps and in the Bavarian/Bohemian Forest.

High resolution dating of moraines on Kodiak Island, Alaska links Atlantic and North Pacific climatic changes during the late glacial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mann, D.H.

1992-01-01

Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice capmore » occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.« less

Multi-scale Holocene Asian monsoon variability deduced from a twin-stalagmite record in southwestern China

NASA Astrophysics Data System (ADS)

Huang, Wei; Wang, Yongjin; Cheng, Hai; Edwards, Richard Lawrence; Shen, Chuan-Chou; Liu, Dianbing; Shao, Qingfeng; Deng, Chao; Zhang, Zhenqiu; Wang, Quan

2016-07-01

We present two isotopic (δ18O and δ13C) sequences of a twin-stalagmite from Zhuliuping Cave, southwestern China, with 230Th dates from 14.6 to 4.6 ka. The stalagmite δ18O record characterizes orbital- to decadal-scale variability of Asian summer monsoon (ASM) intensity, with the Holocene optimum period (HOP) between 9.8 and 6.8 ka BP which is reinforced by its co-varying δ13C data. The large multi-decadal scale amplitude of the cave δ18O indicates its high sensitivity to climate change. Four centennial-scale weak ASM events during the early Holocene are centered at 11.2, 10.8, 9.1 and 8.2 ka. They can be correlated to cold periods in the northern high latitudes, possibly resulting from rapid dynamics of atmospheric circulation associated with North Atlantic cooling. The 8.2 ka event has an amplitude more than two-thirds that of the Younger Dryas (YD), and is significantly stronger than other cave records in the Asia monsoon region, likely indicating a more severe dry climate condition at the cave site. At the end of the YD event, the δ13C record lags the δ18O record by 300-500 yr, suggesting a multi-centennial slow response of vegetation and soil processes to monsoon enhancement.

The nature of abrupt climate change during the last glacial period from detailed isotopic records from the NGRIP ice core

NASA Astrophysics Data System (ADS)

Popp, T. J.; Svensson, A.; Steffensen, J. P.; Johnsen, S. J.; White, J. W. C.

2009-04-01

Isotopic and chemical impurity records from Greenland ice cores with sub-annual resolution across three fast climate transitions of the last deglacial termination reveal complex patterns of environmental change for the onset of Greenland Interstadial 1 (GI-1 or Bølling), the onset of Greenland Stadial 1 (GS-1 or Younger Dryas), and the onset of the Holocene. In the NGRIP ice core each of these transitions is initiated by a 1-3 year mode shift in deuterium excess, which is a proxy for the Greenland precipitation moisture source. These mode shifts in deuterium excess are decoupled in time from the isotopic (deuterium and oxygen-18) transitions from which they are derived. In general the abrupt isotopic transitions follow the corresponding deuterium excess shifts and span decades rather than years. Similar data from GISP2 confirms the clear deuterium excess mode shifts for transitions from cold states to warm states; however the abrupt deuterium excess transition at the onset of GS-1 is not expressed in a similar way at GISP2. Ironically, it appears that this cooling at the beginning of the Younger Dryas, for which we have theories of the triggering event, is less clearly recorded than warming events, the triggering of which is still poorly understood. Along with other available paleo-data, these results indicate that the sum of an abrupt climate change is composed of multiple responses from different parts of the climate system. These responses can be separated by as little as a single year to a few decades and the collection of these responses result in a variety of abrupt transitions giving each a unique anatomy. Here we expand this type of analysis with new isotope, deuterium excess, and accumulation rate time series from NGRIP across the abrupt transitions associated with several interstadial events of the Last Glacial period (Dansgaard-Oeschger events). Indeed the temporal phasing of deuterium excess and the isotopic content of the ice can vary from one event to the next and emerging patterns may depend on the conditions associated with specific events such as Heinrich Events and ice volume boundary conditions. Together with modeling and chemical impurity data, these patterns will provide clues to the timing and origin of ocean and atmospheric changes that comprise an abrupt climate change. The emerging picture indicates that abrupt climate changes have both a temporal and geographic anatomy that can change from one event to the next in how they are recorded across Greenland.

Lacustrine records of Holocene climate and environmental change from the Lofoten Islands, Norway

NASA Astrophysics Data System (ADS)

Balascio, Nicholas L.

Lakes sediments from the Lofoten Islands, Norway, can be used to generate well resolved records of past climate and environmental change. This dissertation presents three lacustrine paleoenvironmental reconstructions that show evidence for Holocene climate changes associated with North Atlantic climate dynamics and relative sea-level variations driven by glacio-isostatic adjustment. This study also uses distal tephra deposits (cryptotephra) from Icelandic volcanic eruptions to improve the chronologies of these reconstructions and explores new approaches to crypto-tephrochronology. Past and present conditions at Vikjordvatnet, Fiskebolvatnet, and Heimerdalsvatnet were studied during four field seasons conducted from 2007--2010. Initially, each lake was characterized by measuring water column chemistry, logging annual temperature fluctuations, and conducting bathymetric and seismic surveys. Sediment cores were then collected and analyzed using multiple techniques, including: sediment density, magnetic susceptibility, loss-on-ignition, total carbon and nitrogen, delta13C and delta 15N of organic matter, and elemental compositions acquired by scanning X-ray fluorescence. Chronologies were established using radiocarbon dating and tephrochronology. A 13.8 cal ka BP record from Vikjordvatnet provides evidence for glacial activity during the Younger Dryas cold interval and exhibits trends in Ti, Fe, and organic content during the Holocene that correlate with regional millennial-scale climate trends and provide evidence for more rapid events. A 9.7 cal ka BP record from Fiskebolvatnet shows a strong signal of sediment inwashing likely driven by local geomorphic conditions, although there is evidence that increased inwashing at the onset of the Neoglacial could have been associated with increased precipitation. Heimerdalsvatnet provides a record of relative sea-level change. A 7.8 cal ka BP sedimentary record reflects changes in salinity and water column conditions as the lake was isolated and defines sea-level regression following the Tapes transgression. Cryptotephra horizons were identified in sediments of Heimerdalsvatnet, Vikjordvatnet, and Sverigedalsvatn. They were also found in a Viking-age boathouse excavated along the shore of Inner Borgpollen. These include the GA4-85, BIP-24a, SILK-N2, Askja, 860 Layer B, Hekla 1158, Hekla 1104, Vedde Ash, and Saksunarvatn tephra. This research project also explored the use of scanning XRF to locate cryptotephra in lacustrine sediments and presents experimental results of XRF scans of tephra-spiked synthetic sediment cores.

Early Wisconsinan (MIS 4) Arctic ground squirrel middens and a squirrel-eye-view of the mammoth-steppe

NASA Astrophysics Data System (ADS)

Zazula, Grant D.; Froese, Duane G.; Elias, Scott A.; Kuzmina, Svetlana; Mathewes, Rolf W.

2011-08-01

Fossil arctic ground squirrel ( Spermophilus parryii) middens were recovered from ice-rich loess sediments in association with Sheep Creek-Klondike and Dominion Creek tephras (ca 80 ka) exposed in west-central Yukon. These middens provide plant and insect macrofossil evidence for a steppe-tundra ecosystem during the Early Wisconsinan (MIS 4) glacial interval. Midden plant and insect macrofossil data are compared with those previously published for Late Wisconsinan middens dating to ˜25-29 14C ka BP (MIS 3/2) from the region. Although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils, the co-occurrence of steppe-tundra plants and insects (e.g., Elymus trachycaulus, Kobresia myosuroides, Artemisia frigida, Phlox hoodii, Connatichela artemisiae) provides evidence for successive reestablishment of the zonal steppe-tundra habitats during cold stages of the Late Pleistocene. Arctic ground squirrels were well adapted to the cold, arid climates, steppe-tundra vegetation and well-drained loessal soils that characterize cold stages of Late Pleistocene Beringia. These glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of Alaska and Yukon, including the Klondike, where they are absent today. Arctic ground squirrels have endured numerous Quaternary climate oscillations by retracting populations to disjunct "interglacial refugia" during warm interglacial periods (e.g., south-facing steppe slopes, well-drained arctic and alpine tundra areas) and expanding their distribution across the mammoth-steppe biome during cold, arid glacial intervals.

Prenatal exposure to ambient temperature variation increases the risk of common cold in children.

PubMed

Lu, Chan; Miao, Yufeng; Zeng, Ji; Jiang, Wei; Shen, Yong-Ming; Deng, Qihong

2018-06-15

Common cold is a frequent upper respiratory tract infection, but the role of ambient temperature in the infection is unclear. We investigated the role of prenatal exposure to diurnal temperature variation (DTV), the difference between the daily maximal and minimal temperatures, in the risk of common cold in children. We conducted a cohort study of 2598 preschool children in Changsha, China. Occurrence of common cold during the past year was surveyed using questionnaire. We then estimated each child's prenatal exposure to DTV during pregnancy. Multivariate logistic regression model was used to examine the association between occurrence of common cold and prenatal exposure to DTV in terms of odds ratios (OR) and 95% confidence interval (CI). About 45% children have common cold (≥3 times) during the past year. We found that common cold in children was associated with maternal DTV exposure during pregnancy, particularly during the first trimester with adjusted OR (95% CI) = 1.27 (1.10-1.46). Male and atopic children were more susceptible to the effect of DTV during pregnancy. The risk of common cold due to DTV is higher in children living in the suburban areas and the bigger houses and in those exposed to environmental tobacco smoke, mold/dampness, new furniture and redecoration. We observed that the risk of common cold in children has been increased in recent years due to increasing DTV. Common cold in children was associated with maternal exposure to temperature variation during pregnancy, suggesting that the risk of common cold may originate in pregnancy. Copyright © 2018 Elsevier Inc. All rights reserved.

Association of cold temperature and mortality and effect modification in the subtropical plateau monsoon climate of Yuxi, China.

PubMed

Ding, Zan; Li, Liujiu; Wei, Ruqin; Dong, Wenya; Guo, Pi; Yang, Shaoyi; Liu, Ju; Zhang, Qingying

2016-10-01

Consistent evidence has shown excess mortality associated with cold temperature, but some important details of the cold-mortality association (e.g. slope and threshold) have not been adequately investigated and few studies focused on the cold effect in high-altitude areas of developing countries. We attempted to quantify the cold effect on mortality, identify the details, and evaluate effect modification in the distinct subtropical plateau monsoon climate of Yuxi, a high plateau region in southwest China. From daily mortality and meteorological data during 2009-2014, we used a quasi-Poisson model combined with a "natural cubic spline-natural cubic spline" distributed lag non-linear model to estimate the temperature-mortality relationship and then a simpler "hockey-stick" model to investigate the cold effect and details. Cold temperature was associated with increased mortality, and the relative risk of cold effect (1st relative to 10th temperature percentile) on non-accidental, cardiovascular, and respiratory mortality for lag 0-21 days was 1.40 (95% confidence interval: 1.19-1.66), 1.61 (1.28-2.02), and 1.13 (0.78-1.64), respectively. A 1°C decrease below a cold threshold of 9.1°C (8th percentile) for lags 0-21 was associated with a 7.35% (3.75-11.09%) increase in non-accidental mortality. The cold-mortality association was not significantly affected by cause-specific mortality, gender, age, marital status, ethnicity, occupation, or previous history of hypertension. There is an adverse impact of cold on mortality in Yuxi, China, and a temperature of 9.1°C is an important cut-off for cold-related mortality for residents. Copyright © 2016 Elsevier Inc. All rights reserved.

Recovery benefits of using a heat and moisture exchange mask during sprint exercise in cold temperatures.

PubMed

Seifert, John G; Frost, Jeremy; St Cyr, John A

2017-01-01

Breathing cold air can lead to bronchoconstriction and peripheral vasoconstriction, both of which could impact muscular performance by affecting metabolic demands during exercise. Successful solutions dealing with these physiological changes during exercise in the cold has been lacking; therefore, we investigated the influence of a heat and moisture exchange mask during exercise in the cold. There were three trial arms within this study: wearing the heat and moisture exchange mask during the rest periods in the cold, no-mask application during the rest periods in the cold, and a trial at room temperature (22°C). Eight subjects cycled in four 35 kJ sprint sessions with each session separated by 20 min rest period. Workload was 4% of body mass. Mean sprint times were faster with heat and moisture exchange mask and room temperature trial than cold, no-mask trial (133.8 ± 8.6, 134.9 ± 8.8, and 138.0 ± 8.4 s (p = 0.001)). Systolic blood pressure and mean arterial pressure were greater during the cold trial with no mask (15% and 13%, respectively), and heart rate was 10 bpm less during the third rest or recovery period during cold, no mask compared to the heat and moisture exchange mask and room temperature trials. Subjects demonstrated significant decreases in vital capacity and peak expiratory flow rate during the cold with no mask applied during the rest periods. These negative responses to cold exposure were alleviated by the use of a heat and moisture exchange mask worn during the rest intervals by minimizing cold-induced temperature stress on the respiratory system with subsequent maintenance of cardiovascular function.

How typical are the last 20,000 years of climatic and vegetation change in the tropical Andes?

NASA Astrophysics Data System (ADS)

Gosling, W. D.; Urrego, D. H.; Hanselman, J. A.; Valencia, B.; Bush, M. B.; Silman, M. R.

2006-12-01

A consensus of global circulation models highlights the southern tropical Andes as the biodiversity hotspot most likely to experience biome shift in the next century. The pace of the ongoing change finds its nearest parallel in that of the Younger Dryas at high latitudes. However, in the tropical Andes of Peru and Bolivia we find that there was no such rapid temperature change within the last 40,000 years. Rates of temperature change across the deglacial interval (which may begin as early as c. 22,000 cal. yr BP) are one to two orders of magnitude slower than those forecasted for the next century, and differed little from those of the full glacial. Indeed, the fastest rates of vegetation change are responses to Holocene drought and human activity, not Pleistocene/Holocene warming. Sedimentary data from long records on the Altiplano provide records of earlier interglacials (MIS 5e, 7 and 9), but do not have the chronological control to provide assessments of rate of change. Nevertheless, those records do provide evidence of marked similarities in the development of each interglacial, with some divergence seen at full interglacial conditions.

U and Th isotope constraints on the duration of Heinrich events H0-H4 in the southeastern Labrador Sea

NASA Astrophysics Data System (ADS)

Veiga-Pires, C. C.; Hillaire-Marcel, C.

1999-04-01

The duration and sequence of events recorded in Heinrich layers at sites near the Hudson Strait source area for ice-rafted material are still poorly constrained, notably because of the limit and uncertainties of the 14C chronology. Here we use high-resolution 230Th-excess measurements, in a 6 m sequence raised from Orphan Knoll (southern Labrador Sea), to constrain the duration of the deposition of the five most recent Heinrich (H) layers. On the basis of maximum/minimum estimates for the mean glacial 230Th-excess flux at the studied site a minimum/maximum duration of 1.0/0.6, 1.4/0.8, 1.3/0.8, 1.5/0.9, and 2.1/1.3 kyr is obtained for H0 (˜Younger Dryas), Hl, H2, H3, and H4, respectively. Thorium-230-excess inventories and other sedimentological features indicate a reduced but still significant lateral sedimentary supply by the Western Boundary Undercurrent during the glacial interval. U and Th series systematics also provide insights into source rocks of H layer sediments (i.e., into distal Irminger Basin/local Labrador Sea supplies).

Multiple cold resistance loci confer the high cold tolerance adaptation of Dongxiang wild rice (Oryza rufipogon) to its high-latitude habitat.

PubMed

Mao, Donghai; Yu, Li; Chen, Dazhou; Li, Lanying; Zhu, Yuxing; Xiao, Yeqing; Zhang, Dechun; Chen, Caiyan

2015-07-01

Dongxiang wild rice is phylogenetically close to temperate japonica and contains multiple cold resistance loci conferring its adaptation to high-latitude habitat. Understanding the nature of adaptation in wild populations will benefit crop breeding in the development of climate-resilient crop varieties. Dongxiang wild rice (DXWR), the northernmost common wild rice known, possesses a high degree of cold tolerance and can survive overwintering in its native habitat. However, to date, it is still unclear how DXWR evolved to cope with low-temperature environment, resulting in limited application of DXWR in rice breeding programs. In this study, we carried out both QTL mapping and phylogenetic analysis to discern the genetic mechanism underlying the strong cold resistance. Through a combination of interval mapping and single locus analysis in two genetic populations, at least 13 QTLs for seedling cold tolerance were identified in DXWR. A phylogenetic study using both genome-wide InDel markers and markers associated with cold tolerance loci reveals that DXWR belongs to the Or-III group, which is most closely related to cold-tolerant Japonica rice rather than to the Indica cultivars that are predominant in the habitat where DXWR grows. Our study paves the way toward an understanding of the nature of adaptation to a northern habitat in O. rufipogon. The QTLs identified in DXWR in this study will be useful for molecular breeding of cold-tolerant rice.

An ultra-high resolution last deglacial marine sediment records of the Northwest Atlantic Ocean

NASA Astrophysics Data System (ADS)

Rashid, H.; Piper, D.; Marche, B.; Vermooten, M.; Lazar, K.; Brockway, B.

2016-12-01

Lack of high sedimentation rate records of past changes pertaining to the late Pleistocene Laurentide ice-sheet (LIS) dynamics has prevented efforts to differentiate the various forcings in modulating abrupt climate changes. Here, we present an ultra-high resolution sediment record spanning approximately 1,500 km of the Eastern Canadian continental margin. The new record comprises four sediment cores which were collected from the northwest Labrador Sea (i.e., Saglek Bank) to southwestern Flemish Pass to the southeast Grand Banks in outer shelf and slope settings. Fifty new 14C-accelerator mass spectrometric dates were obtained to construct the stratigraphy. The total sediment thickness of the new record is 41 m covering the past 26 ka with 1.58/ka mean sediment rate, the highest sediment rate ever reported from the Northwest Atlantic Ocean for this time interval. Further, the temporal resolution of the record varies from a couple of decades to centuries depending on the time interval. X-ray fluorescence (XRF) data in conjunction with physical properties of sediments and petrology allowed us to distinguish sediment delivered by major ice-streams of the LIS namely the Hudson Strait, Hopedale Saddle, and Cumberland Sound ice streams. Heinrich layers 1 and 2 are well identified by their Labrador Sea specific characteristics. The so-called Younger Dryas equivalent Heinrich layer H0 was identified in these cores but the timing of onset of H0 has an offset by nearly 1,000 years with that of the 12.9 ka, suggesting that the YD event was not initiated by the Hudson Strait compared to other Heinrich events.

Study of RCR Catalogue Radio Source Integral Spectra

NASA Astrophysics Data System (ADS)

Zhelenkova, O. P.; Majorova, E. K.

2018-04-01

We present the characteristics of the sources found on the averaged scans of the "Cold" experiment 1980-1999 surveys in the right-ascension interval 2h< RA < 7h. Thereby, a refinement of the parameters of the RC catalog sources (RATANCold) for this interval is complete. To date, the RCR catalog (RATAN Cold Refined) covers the right-ascension interval 2h< RA < 17h and includes 830 sources. The spectra are built for them with the use of new data in the range of 70-230 MHz. The dependence between the spectral indices α 0.5, α 3.94 and integral flux density at the frequencies of 74 and 150 MHz, at 1.4, 3.94 and 4.85 GHz is discussed.We found that at 150 MHz in most sources the spectral index α 0.5 gets steeper with increasing flux density. In general, the sources with flat spectra are weaker in terms of flux density than the sources with steep spectra, which especially differs at 150 MHz. We believe that this is due to the brightness of their extended components, which can be determined by the type of accretion and the neighborhood of the source.

Late Glacial vegetation reconstruction based on leaf waxes from the Gemündener Maar, Germany

NASA Astrophysics Data System (ADS)

Wüthrich, Lorenz; Lutz, Selina; Zech, Michael; Hepp, Johannes; Sirocko, Frank; Zech, Roland

2015-04-01

Lake sediments are valuable archives for the reconstruction of past changes in climate and vegetation. In the present study, we analyse samples from the Gemündener Maar, a lake situated in the western Eiffel, Germany, for their leaf wax composition: In the bottom part of the core, corresponding to the Oldest Dryas (i.e. older than ~15 ka), n-alkanes have a high average chain length (ACL), which points to a vegetation dominated by grass. During the Bölling/Alleröd, a decrease of the ACL can be interpreted as signal of more deciduous trees. During the Younger Dryas (~12.8 to 11.5 ka), the ACL increases again. Trees probably became again less abundant, before finally, the ACL records the return of deciduous trees during the early Holocene. In general, the total concentrations of both, n-alkanes and sugar biomarkers are high enough to measure compound-specific isotopes on n-alkanes (deuterium) and sugars (18-O). Combined, these two isotopes might help to obtain more information about the relative humidity and mean air temperature during the late glacial.

Late Pleistocene and Early Holocene lake-level fluctuations in the Lahontan Basin, Nevada: Implications for the distribution of archaeological sites

USGS Publications Warehouse

Adams, K.D.; Goebel, Thomas; Graf, K.; Smith, G.M.; Camp, A.J.; Briggs, R.W.; Rhode, D.

2008-01-01

The Great Basin of the western U.S. contains a rich record of late Pleistocene and Holocene lake-level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial-temporal relationships between these records in the Lahontan basin to consider whether lake-level fluctuations across the Pleistocene-Holocene transition controlled distribution of archaeological sites. We use the reasonably well-dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230-1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief Paleoindian and early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (???1220-1225 in) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. ?? 2008 Wiley Periodicals, Inc.

Inferring the Provenance of an Alien Species with DNA Barcodes: The Neotropical Butterfly Dryas iulia in Thailand

PubMed Central

Burg, Noah A.; Pradhan, Ashman; Gonzalez, Rebecca M.; Morban, Emely Z.; Zhen, Erica W.; Sakchoowong, Watana; Lohman, David J.

2014-01-01

The Neotropical butterfly Dryas iulia has been collected from several locations in Thailand and Malaysia since 2007, and has been observed breeding in the wild, using introduced Passiflora foetida as a larval host plant. The butterfly is bred by a butterfly house in Phuket, Thailand, for release at weddings and Buddhist ceremonies, and we hypothesized that this butterfly house was the source of wild, Thai individuals. We compared wing patterns and COI barcodes from two, wild Thai populations with individuals obtained from this butterfly house. All Thai individuals resemble the subspecies D. iulia modesta, and barcodes from wild and captive Thai specimens were identical. This unique, Thai barcode was not found in any of the 30 specimens sampled from the wild in the species' native range, but is most similar to specimens from Costa Rica, where many exporting butterfly farms are located. These data implicate the butterfly house as the source of Thailand's wild D. iulia populations, which are currently so widespread that eradication efforts are unlikely to be successful. PMID:25119899

Inferring the provenance of an alien species with DNA barcodes: the neotropical butterfly Dryas iulia in Thailand.

PubMed

Burg, Noah A; Pradhan, Ashman; Gonzalez, Rebecca M; Morban, Emely Z; Zhen, Erica W; Sakchoowong, Watana; Lohman, David J

2014-01-01

The Neotropical butterfly Dryas iulia has been collected from several locations in Thailand and Malaysia since 2007, and has been observed breeding in the wild, using introduced Passiflora foetida as a larval host plant. The butterfly is bred by a butterfly house in Phuket, Thailand, for release at weddings and Buddhist ceremonies, and we hypothesized that this butterfly house was the source of wild, Thai individuals. We compared wing patterns and COI barcodes from two, wild Thai populations with individuals obtained from this butterfly house. All Thai individuals resemble the subspecies D. iulia modesta, and barcodes from wild and captive Thai specimens were identical. This unique, Thai barcode was not found in any of the 30 specimens sampled from the wild in the species' native range, but is most similar to specimens from Costa Rica, where many exporting butterfly farms are located. These data implicate the butterfly house as the source of Thailand's wild D. iulia populations, which are currently so widespread that eradication efforts are unlikely to be successful.

Exploring the Human Ecology of the Younger Dryas Extraterrestrial Impact Event

NASA Astrophysics Data System (ADS)

Kennett, D. J.; Erlandson, J. M.; Braje, T. J.; Culleton, B. J.

2007-05-01

Several lines of evidence now exist for a major extraterrestrial impact event in North America at 12.9 ka (the YDB). This impact partially destabilized the Laurentide and Cordilleran ice sheets, triggered abrupt Younger Dryas cooling and extensive wildfires, and contributed to megafaunal extinction. This event also occurred soon after the well established colonization of the Americas by anatomically modern humans. Confirmation of this event would represent the first near-time extraterrestrial impact with significant effects on human populations. These likely included widespread, abrupt human mortality, population displacement, migration into less effected or newly established habitats, loss of cultural traditions, and resource diversification in the face of the massive megafaunal extinction and population reductions in surviving animal populations. Ultimately, these transformations established the context for the special character of plant and animal domestication and the emergence of agricultural economies in North America. We explore the Late Pleistocene archaeological record in North America within the context of documented major biotic changes associated with the YDB in North America and of the massive ecological affects hypothesized for this event.

Evaluation of the memory effect on gold-coated silica adsorption tubes used for the analysis of gaseous mercury by cold vapor atomic absorption spectrometry.

PubMed

Rahman, Mohammad Mahmudur; Brown, Richard J C; Kim, Ki-Hyun; Yoon, Hye-On; Phan, Nhu-Thuc

2013-01-01

In an effort to reduce the experimental bias involved in the analysis of gaseous elemental mercury (Hg(o)), the blank response from gold-coated adsorption tubes has been investigated using cold vapor atomic absorption spectrometry (CVAAS). Our study has been compared with our recent investigation on memory effect in a cold vapour atomic fluorescence spectrometry (CVAFS). The pattern of blank responses was quantified after loading different amounts of mercury and after different time intervals of 1, 14, and 45 days. In case of the one day interval, the result of five to six instant blank heating cycles confirmed successful liberation of mercury following the second and third blank heating cycles. The results of 14 or 45 days generally suggest that liberation of excess mercury is affected by both the initial loading amount and the length of storage time prior to analysis. We have demonstrated a possibly effective way to reduce memory effects. Some similarities of these results with those from CVAFS experiment suggests that the blank response is caused by a combination of mercury absorbed within the bulk gold and micro- and nanoparticles liberated during heating and not from coabsorbing interfering gaseous species.

Evaluation of the Memory Effect on Gold-Coated Silica Adsorption Tubes Used for the Analysis of Gaseous Mercury by Cold Vapor Atomic Absorption Spectrometry

PubMed Central

Rahman, Mohammad Mahmudur; Brown, Richard J. C.; Yoon, Hye-On; Phan, Nhu-Thuc

2013-01-01

In an effort to reduce the experimental bias involved in the analysis of gaseous elemental mercury (Hgo), the blank response from gold-coated adsorption tubes has been investigated using cold vapor atomic absorption spectrometry (CVAAS). Our study has been compared with our recent investigation on memory effect in a cold vapour atomic fluorescence spectrometry (CVAFS). The pattern of blank responses was quantified after loading different amounts of mercury and after different time intervals of 1, 14, and 45 days. In case of the one day interval, the result of five to six instant blank heating cycles confirmed successful liberation of mercury following the second and third blank heating cycles. The results of 14 or 45 days generally suggest that liberation of excess mercury is affected by both the initial loading amount and the length of storage time prior to analysis. We have demonstrated a possibly effective way to reduce memory effects. Some similarities of these results with those from CVAFS experiment suggests that the blank response is caused by a combination of mercury absorbed within the bulk gold and micro- and nanoparticles liberated during heating and not from coabsorbing interfering gaseous species. PMID:23589708

Holocene and latest Pleistocene climate and glacier fluctuations in Iceland

NASA Astrophysics Data System (ADS)

Geirsdóttir, Áslaug; Miller, Gifford H.; Axford, Yarrow; Ólafsdóttir, Sædís

2009-10-01

Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1-2 °C compared to the AD 1961-1990 average. Steep north-south and west-east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland.

Plant-wax D/H ratios in the southern European Alps record multiple aspects of climate variability

NASA Astrophysics Data System (ADS)

Wirth, Stefanie B.; Sessions, Alex L.

2016-09-01

We present a Younger Dryas-Holocene record of the hydrogen isotopic composition of sedimentary plant waxes (δDwax) from the southern European Alps (Lake Ghirla, N-Italy) to investigate its sensitivity to climatic forcing variations in this mid-latitude region (45°N). A modern altitudinal transect of δD values of river water and leaf waxes in the Lake Ghirla catchment is used to test present-day climate sensitivity of δDwax. While we find that altitudinal effects on δDwax are minor at our study site, temperature, precipitation amount, and evapotranspiration all appear to influence δDwax to varying extents. In the lake-sediment record, δDwax values vary between -134 and -180‰ over the past 13 kyr. The long-term Holocene pattern of δDwax parallels the trend of decreasing temperature and is thus likely forced by the decline of northern hemisphere summer insolation. Shorter-term fluctuations, in contrast, may reflect both temperature and moisture-source changes. During the cool Younger Dryas and Little Ice Age (LIA) periods we observe unexpectedly high δDwax values relative to those before and after. We suggest that a change towards a more D-enriched moisture source is required during these intervals. In fact, a shift from northern N-Atlantic to southern N-Atlantic/western Mediterranean Sea sources would be consistent with a southward migration of the Westerlies with climate cooling. Prominent δDwax fluctuations in the early and middle Holocene are negative and potentially associated with temperature declines. In the late Holocene (<4 kyr BP), excursions are partly positive (as for the LIA) suggesting a stronger influence of moisture-source changes on δDwax variation. In addition to isotopic fractionations of the hydrological cycle, changes in vegetation composition, in the length of the growing season, and in snowfall amount provide additional potential sources of variability, although we cannot yet quantitatively assess these in the paleo-record. We conclude that while our δDwax record from the Alps does contain climatic information, it is a complicated record that would require additional constraints to be robustly interpreted. This also has important implications for other water-isotope-based proxy records of precipitation and hydro-climate from this region, such as cave speleothems.

Cosmic impact: What are the odds?

NASA Astrophysics Data System (ADS)

Harris, A. W.

2009-12-01

Firestone et al. (PNAS 104, 16016-16021, 2007) propose that the impact of a ~4 km diameter comet (or multiple bodies making up a similar mass) led to the Younger Dryas cooling and extinction of megafauna in North America, 12,900 years ago. Even more provocatively, Firestone et al. (Cycle of Cosmic Catastrophes, Bear & Co. Books, 2006, 392pp), suggest that a nearby supernova may have produced a comet shower leading to the impact event, either by disturbing the Oort Cloud or by direct injection of 4-km comet-like bodies to the solar neighborhood. Here we show: (a) A supernova shockwave or mass ejection is not capable of triggering a shower of comets from the Oort Cloud. (b) An Oort Cloud shower from whatever cause would take 100,000 years or more for the perturbed comets to arrive in the inner solar system, and the peak flux would persist for some hundreds of thousands more years. (c) Even if all 20 solar masses or so of ejected matter from a SN were in the form of 4-km diameter balls, the probability of even one such ball hitting the Earth from an event 100 light years away would be about 3e-5. (d) A 4-km diameter ball traveling fast enough to get here from 100 LY away in some tens of thousands of years would deliver the energy of a 50 km diameter impactor traveling at typical Earth-impact velocity (~20 km/sec). We review the current impact flux on the Earth from asteroids and comets, and show that the probability of an impact of a 4-km diameter asteroid in an interval of 13,000 years is about one in a thousand, and the probability of a comet impact of that size is a few in a million. An "impact shower" caused by the injection or breakup of comets or asteroids in the inner solar system by whatever means would take tens to hundreds of thousands of years to clear out, thus the population of NEOs we see now with our telescopic surveys is what we’ve had for the last few tens of thousands of years, at least. Faced with such low odds, the evidence that such a large cosmic impact is the cause of the Younger Dryas boundary and cooling, and that there is no other possible cause, needs to be extraordinary indeed.

The biome reconstruction approach as a tool for interpretation of past vegetation and climate changes: application to modern and fossil pollen data from Lake El'gygytgyn, Far East Russian Arctic

NASA Astrophysics Data System (ADS)

Tarasov, P. E.; Andreev, A. A.; Anderson, P. M.; Lozhkin, A. V.; Haltia, E.; Nowaczyk, N. R.; Wennrich, V.; Brigham-Grette, J.; Melles, M.

2013-06-01

The modern and fossil pollen data obtained under the framework of the multi-disciplinary international "El'gygytgyn Drilling Project" represent a unique archive that allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate since ~3.58 Ma. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could potentially have been present in this region during the past. When applied to the modern surface pollen spectra from the lake, the method shows a dominance of the tundra biome that currently characterizes the Lake El'gygytgyn area. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) a long phase of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals within the past million years. During the late Pliocene-early Pleistocene interval (i.e., ~3.562-2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation which suggest a step-like transition from generally warmer/wetter environments of the earlier (i.e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction of most of the species-rich cool mixed and cool conifer forest biomes is particularly noticeable prior to MIS G16, whereas tundra becomes a prominent feature after MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to ~2.730 Ma. The biomization results also suggest that the transition from mostly forested to mostly open landscape was not gradual, but rather occurred in step-like fashion. Thus, the cold and drought tolerant steppe biome first appears in the reconstruction ca. 3.298 Ma during the tundra dominated MIS M2, whereas the tundra biome initially occurs between ~3.379 and ~3.378 Ma within MIS MG4. Prior to ~2.800 Ma, several other cold stages during this generally warm Pliocene interval experienced a dominance of tundra and a great reduction of tree populations in the regional vegetation.

Salinity history of the northern Atlantic during the last deglaciation

NASA Astrophysics Data System (ADS)

Broecker, Wallace S.

1990-08-01

The claim has been made (see Broecker et al., 1988) that production of North Atlantic Deep Water terminated during Younger Dryas time and that the onset of this termination occurred about 11,000 years ago when the flow of meltwater from a large segment of the southern margin of the Laurentide ice sheet was diverted from the Mississippi to the St. Lawrence drainage. Fairbanks [1989] points out a serious weakness in this argument. Based on a sea level curve derived from radiocarbon dates on coral obtained from borings made off the Barbados coast, he suggests that a lull in the melting of the ice caps during Younger Dryas time may have more than compensated for the impact of the diversion. The purpose of this paper is to reassess the situation regarding the origin of the Younger Dryas in light of this new evidence. Currently the salinity of surface waters in the northern Atlantic is influenced by three fluxes. Water vapor transport from the Atlantic drainage basin to the Pacific-Indian basin tends to raise the salinity of the entire Atlantic. The excess over evaporation of precipitation and runoff poleward of 40°N tends to reduce the salinity of waters in this region relative to the Atlantic average. The conveyor circulation of the Atlantic trades more salty waters of the Atlantic with less salty waters outside the Atlantic tending to drive down the Atlantic's salinity. The conveyor circulation also flushes the northern Atlantic, pushing its salinity toward the mean for the Atlantic. During the period of deglaciation meltwater emanating from the Laurentide and Scandinavian ice sheets was also important. This flux tended to lower not only the salinity of the entire Atlantic but also the salinity of surface waters in the northern Atlantic relative to the Atlantic's mean. As deepwater formation in the northern Atlantic depends critically on the salinity of surface waters, the interactions among these fluxes can change the strength of the conveyor.

Self-Rated Health in Healthy Adults and Susceptibility to the Common Cold.

PubMed

Cohen, Sheldon; Janicki-Deverts, Denise; Doyle, William J

2015-01-01

To explore the association of self-rated health (SRH) with host resistance to illness after exposure to a common cold virus and identify mechanisms linking SRH to future health status. We analyzed archival data from 360 healthy adults (mean [standard deviation] age = 33.07 [10.69] years, 45.6% women). Each person completed validated questionnaires that assessed SRH (excellent, very good, good, fair, poor), socioemotional factors, and health practices and was subsequently exposed to a common cold virus and monitored for 5 days for clinical illness (infection and objective signs of illness). Poorer SRH was associated in a graded fashion with greater susceptibility to developing clinical illness (good/fair versus excellent: odds ratio = 3.21, 95% confidence interval = 1.47-6.99; very good versus excellent: odds ratio = 2.60, 95% confidence interval = 1.27-5.32), independent of age, sex, race, prechallenge immunity (specific antibody), body mass, season, education, and income. Greater illness risk was not attributable to infection, but to increased likelihood of developing objective signs of illness once infected. Poorer SRH also correlated with poorer health practices, increased stress, lower positive emotions, and other socioemotional factors. However, none of these (alone or together) accounted for the association between SRH and host resistance. Additional data (separate study) indicated that history of having colds was unrelated to susceptibility and hence also did not account for the SRH link with immunocompetence. Poorer SRH is associated with poorer immunocompetence, possibly reflecting sensitivity to sensations associated with premorbid immune dysfunction. In turn, poorer immune function may be a major contributing mechanism linking SRH to future health.

40 CFR 63.7733 - What procedures must I use to establish operating limits?

Code of Federal Regulations, 2010 CFR

2010-07-01

... combustion device applied to emissions from a scrap preheater or TEA cold box mold or core making line... and record the scrubbing liquid flow rate during each TEA sampling run in intervals of no more than 15...

Cold-Induced Impairment of Delayed Matching in Rats

DTIC Science & Technology

1991-01-01

rather than a decrease at longer delay intervals (cf. Roitblat & Harley, 1988; White, 1985). However, the contribution of interference, either...Journal of Experimental Psychology: Animal Behavior Processes. 4, 219-236. Roitblat , H. L., & Harley, H. E. (1988). Spatial delayed matching-to-sample

Effectiveness of cold therapy in reducing pain, trismus, and oedema after impacted mandibular third molar surgery: a randomized, self-controlled, observer-blind, split-mouth clinical trial.

PubMed

Zandi, M; Amini, P; Keshavarz, A

2016-01-01

Cold therapy is a conventional and widely used modality for reducing pain, trismus, and oedema after dentoalveolar surgeries. However, information reported in the literature on its effectiveness is insufficient and controversial. This study was performed to evaluate the effect of local cold application in reducing pain, trismus, and swelling after impacted mandibular third molar surgery. Thirty patients (seven males and 23 females) with bilateral symmetrical mandibular impacted third molars were enrolled in this randomized, self-controlled, observer-blind clinical trial. The patients were aged between 18 and 30 years. After surgical removal of the tooth on one side (intervention), ice pack therapy was given for 24h after surgery; for the other side (control), no cold therapy was given. The time interval between the two surgeries was at least 4 weeks. The amount of pain, trismus, and facial swelling was measured on days 2 and 7 postoperative, and patient satisfaction with the cold therapy vs. no cold therapy was assessed. The amount of pain, trismus, and facial swelling, and the extent of patient satisfaction were not significantly different between the intervention and control sides. Cold therapy had no beneficial effects on postoperative sequelae after impacted mandibular third molar surgery. Copyright © 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

White fingers, cold environment, and vibration--exposure among Swedish construction workers.

PubMed

Burström, Lage; Järvholm, Bengt; Nilsson, Tohr; Wahlström, Jens

2010-11-01

The aim of this study was to examine the association between white fingers, cold environment, and exposure to hand-arm vibration (HAV). The hypothesis was that working in cold climate increases the risk of white fingers. The occurrence of white fingers was investigated as a cross-sectional study in a cohort of Swedish male construction workers (N=134 757). Exposure to HAV was based on a job-exposure matrix. Living in the north or south of Sweden was, in a subgroup of the cohort, used as an indicator of the exposure to cold environment (ie, living in the north meant a higher exposure to cold climate). The analyses were adjusted for age and use of nicotine products (smoking and snuff). HAV-exposed workers living in a colder climate had a higher risk for white fingers than those living in a warmer climate [odds ratio (OR) 1.71, 95% confidence interval (95% CI) 1.42-2.06]. As expected, we found that HAV-exposed workers had an increased risk compared to controls (OR 2.02, 95% CI 1.75-2.34). The risk for white fingers increased with increased level of exposure to HAV and also age. Cold environment increases the risk for white fingers in workers occupationally exposed to HAV. The results underscore the need to keep exposure to HAV at workplaces as low as possible especially in cold climate.

The impact of temperature on mortality in a subtropical city: effects of cold, heat, and heat waves in São Paulo, Brazil

NASA Astrophysics Data System (ADS)

Son, Ji-Young; Gouveia, Nelson; Bravo, Mercedes A.; de Freitas, Clarice Umbelino; Bell, Michelle L.

2016-01-01

Understanding how weather impacts health is critical, especially under a changing climate; however, relatively few studies have investigated subtropical regions. We examined how mortality in São Paulo, Brazil, is affected by cold, heat, and heat waves over 14.5 years (1996-2010). We used over-dispersed generalized linear modeling to estimate heat- and cold-related mortality, and Bayesian hierarchical modeling to estimate overall effects and modification by heat wave characteristics (intensity, duration, and timing in season). Stratified analyses were performed by cause of death and individual characteristics (sex, age, education, marital status, and place of death). Cold effects on mortality appeared higher than heat effects in this subtropical city with moderate climatic conditions. Heat was associated with respiratory mortality and cold with cardiovascular mortality. Risk of total mortality was 6.1 % (95 % confidence interval 4.7, 7.6 %) higher at the 99th percentile of temperature than the 90th percentile (heat effect) and 8.6 % (6.2, 11.1 %) higher at the 1st compared to the 10th percentile (cold effect). Risks were higher for females and those with no education for heat effect, and males for cold effect. Older persons, widows, and non-hospital deaths had higher mortality risks for heat and cold. Mortality during heat waves was higher than on non-heat wave days for total, cardiovascular, and respiratory mortality. Our findings indicate that mortality in São Paulo is associated with both cold and heat and that some subpopulations are more vulnerable.

Parenthood and host resistance to the common cold.

PubMed

Sneed, Rodlescia S; Cohen, Sheldon; Turner, Ronald B; Doyle, William J

2012-01-01

To determine whether parenthood predicts host resistance to the common cold among healthy volunteers experimentally exposed to a common cold virus. Participants were 795 healthy volunteers (age range = 18-55 years) enrolled in one of three viral-challenge studies conducted from 1993 to 2004. After reporting parenthood status, participants were quarantined, administered nasal drops containing one of four common cold viruses, and monitored for the development of a clinical cold (infection in the presence of objective signs of illness) on the day before and for 5 to 6 days after exposure. All analyses included controls for immunity to the experimental virus (prechallenge specific antibody titers), viral strain, season, age, sex, race/ethnicity, marital status, body mass, study, employment status, and education. Parents were less likely to develop colds than nonparents were (odds ratio [OR] = 0.48, 95% confidence interval [CI] = 0.31-0.73). This was true for both parents with one to two children (OR = 0.52, 95% CI = 0.33-0.83) and three or more children (OR = 0.39, 95% CI = 0.22-0.70). Parenthood was associated with a decreased risk of colds for both those with at least one child living at home (OR = 0.46, 95% CI = 0.24-0.87) and those whose children all lived away from home (OR = 0.27, 95% CI = 0.12-0.60). The relationship between parenthood and colds was not observed in parents aged 18 to 24 years but was pronounced among older parents. Parenthood was associated with greater host resistance to common cold viruses.

Who is more vulnerable to death from extremely cold temperatures? A case-only approach in Hong Kong with a temperate climate

NASA Astrophysics Data System (ADS)

Qiu, Hong; Tian, Linwei; Ho, Kin-fai; Yu, Ignatius T. S.; Thach, Thuan-Quoc; Wong, Chit-Ming

2016-05-01

The short-term effects of ambient cold temperature on mortality have been well documented in the literature worldwide. However, less is known about which subpopulations are more vulnerable to death related to extreme cold. We aimed to examine the personal characteristics and underlying causes of death that modified the association between extreme cold and mortality in a case-only approach. Individual information of 197,680 deaths of natural causes, daily temperature, and air pollution concentrations in cool season (November-April) during 2002-2011 in Hong Kong were collected. Extreme cold was defined as those days with preceding week with a daily maximum temperature at or less than the 1st percentile of its distribution. Logistic regression models were used to estimate the effects of modification, further controlling for age, seasonal pattern, and air pollution. Sensitivity analyses were conducted by using the 5th percentile as cutoff point to define the extreme cold. Subjects with age of 85 and older were more vulnerable to extreme cold, with an odds ratio (OR) of 1.33 (95 % confidence interval (CI), 1.22-1.45). The greater risk of extreme cold-related mortality was observed for total cardiorespiratory diseases and several specific causes including hypertensive diseases, stroke, congestive heart failure, chronic obstructive pulmonary disease (COPD), and pneumonia. Hypertensive diseases exhibited the greatest vulnerability to extreme cold exposure, with an OR of 1.37 (95 % CI, 1.13-1.65). Sensitivity analyses showed the robustness of these effect modifications. This evidence on which subpopulations are vulnerable to the adverse effects of extreme cold is important to inform public health measures to minimize those effects.

Deep-sea benthic response to rapid climatic oscillations of the last glacial cycle in the SE Bay of Biscay

NASA Astrophysics Data System (ADS)

Rodriguez-Lazaro, J.; Pascual, A.; Cacho, I.; Varela, Z.; Pena, L. D.

2017-12-01

Paleoclimatic evolution of the last 140 ka (Marine Isotopic Stages MIS 1 to MIS 5) in the South Bay of Biscay has been studied by considering microfossil changes in sediment samples of deep core PP10-17. This core was retrieved at 2882 m water depth (mwd) in the Landas Plateau and is formed by 1792 cm of clay-silt continuously deposited sediment. For this study, a total of 114 samples have been examined, yielding approximately 60 thousands of specimens of foraminifers (181 benthic species, BF) and ostracods (70 spp.). Reconstruction of the benthic response is based on the main foraminifer and ostracod species by considering their oxic/anoxic character as well as other ecological features of the assemblages. Detailed quantification of microfossils (planktonic and benthic foraminifers, ostracods) together with grain size analyses and magnetic susceptibility of the sediments allow us to characterize many of the climatic events registered in this core. Based on a robust chronostratigraphy by correlation with reference core MD95-2002 and Greenland ice core records (GICC05modelext), we are able to characterize a detailed response of benthic environments to cooling/warming, oxygen-content and productivity cycles in the region. MIS 5 has been characterized by oscillations of the planktonic/benthic foraminifer ratio (Oceanity index, OI; 60-90%); this index was higher (90-100%) and stable through the MIS 4-MIS 3 intervals. We found BF species indicators of different climatic-related events. Thus, MIS 5a, c, e interstadials are evidenced by Bulimina gibba and B. aculeata while the stadials MIS 5b, d are shown by the occurrence of Melonis pompilioides. Heinrich events, with massive iceberg discharges into the N Atlantic Ocean, are indicated by presence of Globobulimina affinis, particularly during the MIS 4 to MIS 2 interval. The beginning of MIS 4 is indicated by the appearance of new species of BF and an increase of Cassidulina laevigata. Krithe spp. and C. laevigata are good indicators of the LGM (Last Glacial Maximum, 19-23 ka) when the OI decreased. Other cooling periods (e.g. Younger Dryas, YD, around 12-13 ka) are shown as well by an increase of M. pompilioides, similar to that of the MIS 5d stadial. The Holocene (11.5 ka to present) is marked by an increase in the oceanity index, disappearance of cold-water indicators and the occurrence of Uvigerina peregrina. A shallow infaunal microhabitat of benthics foraminifers (Cibicides, Cassidulina, Uvigerina) and ostracods (Krithe, Argilloecia) has been linked to favorable bottom conditions, with oxic to slightly suboxic conditions (high diversity and equitability of assemblages) reflecting an active Atlantic Meridional Overturning Circulation (AMOC) during many D/O interstadials. The opposite conditions were established for deep infaunal BF (Bulimina, Globobulimina) where the strong dysoxic bottom conditions are indicative of poor ventilation produced by a reduction or shutdown of the AMOC during Heinrich stadials.

Minocycline Prevents Muscular Pain Hypersensitivity and Cutaneous Allodynia Produced by Repeated Intramuscular Injections of Hypertonic Saline in Healthy Human Participants.

PubMed

Samour, Mohamad Samir; Nagi, Saad Saulat; Shortland, Peter John; Mahns, David Anthony

2017-08-01

Minocycline, a glial suppressor, prevents behavioral hypersensitivities in animal models of peripheral nerve injury. However, clinical trials of minocycline in human studies have produced mixed results. This study addressed 2 questions: can repeated injections of hypertonic saline (HS) in humans induce persistent hypersensitivity? Can pretreatment with minocycline, a tetracycline antibiotic with microglial inhibitory effects, prevent the onset of hypersensitivity? Twenty-seven healthy participants took part in this double-blind, placebo-controlled study, consisting of 6 test sessions across 2 weeks. At the beginning of every session, pressure-pain thresholds of the anterior muscle compartment of both legs were measured to determine the region distribution and intensity of muscle soreness. To measure changes in thermal sensitivity in the skin overlying the anterior muscle compartment of both legs, quantitative sensory testing was used to measure the cutaneous thermal thresholds (cold sensation, cold pain, warm sensation, and heat pain) and a mild cooling stimulus was applied to assess the presence of cold allodynia. To induce ongoing hypersensitivity, repeated injections of HS were administered into the right tibialis anterior muscle at 48-hour intervals. In the final 2 sessions (days 9 and 14), only sensory assessments were done to plot the recovery after cessation of HS administrations and drug washout. By day 9, nontreated participants experienced a significant bilateral increase in muscle soreness (P < .0001), accompanied by the emergence of bilateral cold allodynia in 44% of participants, thus confirming the effectiveness of the model. Placebo-treated participants experienced a bilateral 35% alleviation in muscle soreness (P < .0001), with no changes to the prevalence of cold allodynia. In contrast, minocycline-treated participants experienced a bilateral 70% alleviation in muscle soreness (P < .0001), additionally, only 10% of minocycline-treated participants showed cold allodynia. This study showed that repeated injections of HS can induce a hypersensitivity that outlasts the acute response, and the development of this hypersensitivity can be reliably attenuated with minocycline pretreatment. Four repeated injections of HS at 48-hour intervals induce a state of persistent hypersensitivity in healthy human participants. This hypersensitivity was characterized by bilateral muscular hyperalgesia and cutaneous cold allodynia, symptoms commonly reported in many chronic pain conditions. Minocycline pretreatment abolished the development of this state. Crown Copyright © 2017. Published by Elsevier Inc. All rights reserved.

Deglaciation in the High Andes - a Record from Laguna Piuray (Cusco, Peru)

NASA Astrophysics Data System (ADS)

Nederbragt, A.; Thurow, J.; Brumsack, H.; Lowe, J.; Pearce, R.; Ramsey, C.

2007-12-01

The Peruvian Andes lie in a crucial location for paleoclimate investigation. Fluctuating Pacific and Atlantic air masses compete for long-term dominance of the region, with the El-Nino Southern Oscillation (ENSO) system causing further variability. A laminated glacial/interglacial sediment sequence (6m) exposed around the shores of Laguna Piuray, near Cusco, offers not only the potential to reconstruct the climate history of the area but also to test for strength and frequency of the Atlantic monsoonal and Pacific ENSO influence. A suite of continuous cores was collected from deep trenches. The sedimentary record is characterized by postglacial diatom-rich chalk overlying organic-rich clayey chalk. Between these units are 3 distinct organic layers (80% TOC) deposited between 12-14 cal. kyr BP (14C). The base of the record is probably as old as 25kyrs (U/Th). We obtained a multi- proxy record of the section including continuous XRF scanning data of the entire sequence, and stable isotopes, XRF, XRD, TOC, biogenic opal, and carbonate analysis of discrete samples as well as a relative paleotemperature record from analyses of soil biomarkers. All the data profiles we obtained show a pronounced increase in temperature and decrease in precipitation at 13.8kyrs and are in good correlation with published regional Andean records using single proxies. Our results confirm that the Deglaciation Cold Reversal in central South America is not identical to the Younger Dryas event in the Northern Hemisphere.

Paleobiology of the Sand Beneath the Valders Diamicton at Valders, Wisconsin

USGS Publications Warehouse

Maher, L.J.; Miller, N.G.; Baker, R.G.; Curry, B. Brandon; Mickelson, D.M.

1998-01-01

Previously undescribed pollen, plant macrofossils, molluscs, and ostracodes were recovered from a 2.5-m-thick glaciolacustrine unit of silty sand and clay at Valders, Wisconsin. The interstadial sediment was deposited about 12,200 14C yr B.P. after retreat of the Green Bay lobe that deposited diamicton of the Horicon Formation, and before advance of the Lake Michigan lobe that deposited the red-brown diamicton of the Valders Member of the Kewaunee Formation. Fluctuations of abundance of Candona subtriangulata, Cytherissa lacustris, and three other species define four ostracode biozones in the lower 1.7 m, suggesting an open lake environment that oscillated in depth and proximity to glacial ice. Pollen is dominated by Picea and Artemisia, but the low percentages of many other types of longdistance origin suggest that the terrestrial vegetation was open and far from the forest border. The upper part of the sediment, a massive sand deposited in either a shallow pond or a sluggish stream, contains a local concentration of plant macrofossils. The interpretation of a cold open environment is supported by the plant macrofossils of more than 20 species, dominated by those of open mineral soils (Arenaria rubella, Cerastium alpinum type, Silene acaulis, Sibbaldia procumbens, Dryas integrifolia, Vaccinium uliginosum var. alpinum, Armeria maritima, etc.) that in North America occur largely in the tundra and open tundra-forest ecotone of northern Canada. Ice-wedge casts occur in the sand. ?? 1998 University of Washington.

Cold-water immersion after training sessions: Effects on fiber type-specific adaptations in muscle K+ transport proteins to sprint-interval training in men.

PubMed

Christiansen, Danny; Bishop, David John; Broatch, James R; Bangsbo, Jens; McKenna, Michael John; Murphy, Robyn M

2018-05-10

Effects of regular use of cold-water immersion (CWI) on fiber type-specific adaptations in muscle K + transport proteins to intense training, along with their relationship to changes in mRNA levels after the first training session, were investigated in humans. Nineteen recreationally-active men (24{plus minus}6 y, 79.5{plus minus}10.8 kg, 44.6{plus minus}5.8 mL∙kg -1 ∙min -1 ) completed six weeks of sprint-interval cycling either without (passive rest; CON) or with training sessions followed by CWI (15 min at 10{degree sign}C; COLD). Muscle biopsies were obtained before and after training to determine abundance of Na + ,K + -ATPase isoforms (α 1-3 , β 1-3 ) and FXYD1, and after recovery treatments (+0h and +3h) on the first day of training to measure mRNA content. Training increased (p<0.05) the abundance of α 1 and β 3 in both fiber types, β 1 in type-II fibers, and decreased FXYD1 in type-I fibers, whereas α 2 and α 3 abundance was not altered by training (p>0.05). CWI after each session did not influence responses to training (p>0.05). However, α 2 mRNA increased after the first session in COLD (+0h, p<0.05), but not in CON (p>0.05). In both conditions, α 1 and β 3 mRNA increased (+3h; p <0.05), β 2 mRNA decreased (+3h; p<0.05), whereas α 3 , β 1 , and FXYD1 mRNA remained unchanged (p>0.05) after the first session. In summary, Na + ,K + -ATPase isoforms are differently regulated in type I and II muscle fibers by sprint-interval training in humans, which for most isoforms do not associate with changes in mRNA levels after the first training session. CWI neither impairs nor improves protein adaptations to intense training of importance for muscle K + regulation.

Clinical assessment of the warming sensation accompanying flavor 316282 in a cold and cough syrup containing paracetamol, phenylephrine hydrochloride, and guaifenesin

PubMed Central

Monnet, Joëlle

2014-01-01

Objective: The primary objective was to assess the warming sensation caused by flavor 316282 in a cold and cough product in the target population. Methods: A single-cohort, single-treatment arm, open-label study. Subjects received one 30-mL dose of syrup containing flavor 316282, paracetamol, phenylephrine hydrochloride, and guaifenesin and recorded onset and disappearance of any warming sensation in the mouth/throat. Subjects’ assessment of strength and appeal of the sensation, taste, texture, and acceptability of the product as a cold and cough remedy was investigated using questionnaires. Results: A total of 51 subjects were included; 47 (92.1%) experienced a warming sensation. The median duration of the warming sensation was 100 s (95% confidence interval = 82 s, 112 s). The majority of subjects rated the syrup as excellent, good, or fair for treatment of cough and cold symptoms (96.1%), taste (80.4%), and texture (98.0%). There were no safety concerns, and the syrup was well tolerated. Most subjects liked the warming sensation. Conclusions: Flavor 316282 in a cold and cough syrup is associated with a warming sensation. The syrup is well tolerated, safe, and palatable. PMID:26770699

40 CFR 1066.410 - Dynamometer test procedure.

Code of Federal Regulations, 2014 CFR

2014-07-01

... drive mode. (For purposes of this paragraph (g), the term four-wheel drive includes other multiple drive... Dynamometer test procedure. (a) Dynamometer testing may consist of multiple drive cycles with both cold-start...-setting part identifies the driving schedules and the associated sample intervals, soak periods, engine...

Late-glacial to Holocene environmental changes and climate variability: evidence from Voldafjorden, western Norway

NASA Astrophysics Data System (ADS)

Sejrup, H. P.; Haflidason, H.; Flatebø, T.; Klitgaard Kristensen, D.; Grøsfjeld, K.; Larsen, E.

2001-02-01

Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS 14C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine-grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9-7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large-scale sliding on the continental margin off Norway (the Storegga Tsunami).During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea-surface summer temperatures, possibly with year-round sea-ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea-surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4-9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4-0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large-scale oceanic circulation.

North Atlantic influence on 19th-20th century rainfall in the Dead Sea watershed, teleconnections with the Sahel, and implication for Holocene climate fluctuations

NASA Astrophysics Data System (ADS)

Kushnir, Yochanan; Stein, Mordechai

2010-12-01

The importance of understanding processes that govern the hydroclimate of the Mediterranean Basin is highlighted by the projected significant drying of the region in response to the increase in greenhouse gas concentrations. Here we study the long-term hydroclimatic variability of the central Levant region, situated in the eastern boundary of the Basin, as reveled by instrumental observations and the Holocene record of Dead Sea level variations. Observations of 19th and 20th century precipitation in the Dead Sea watershed region display a multidecadal, anti-phase relationship to North Atlantic (NAtl) sea surface temperature (SST) variability, such that when the NAtl is relatively cold, Jerusalem experiences higher than normal precipitation and vice versa. This association is underlined by a negative correlation to precipitation in the sub-Saharan Sahel and a positive correlation to precipitation in western North America, areas that are also affected by multidecadal NAtl SST variability. These observations are consistent with a broad range of Holocene hydroclimatic fluctuations from the epochal, to the millennial and centennial time scales, as displayed by the Dead Sea lake level, by lake levels in the Sahel, and by direct and indirect proxy indicators of NAtl SSTs. On the epochal time scale, the gradual cooling of NAtl SSTs throughout the Holocene in response to precession-driven reduction of summer insolation is associated with previously well-studied wet-to-dry transition in the Sahel and with a general increase in Dead Sea lake levels from low stands after the Younger Dryas to higher stands in the mid- to late-Holocene. On the millennial and centennial time scales there is also evidence for an anti-phase relationship between Holocene variations in the Dead Sea and Sahelian lake levels and with proxy indicators of NAtl SSTs. However the records are punctuated by abrupt lake-level drops, which appear to be in-phase and which occur during previously documented abrupt major cooling events in the Northern Hemisphere. We propose that the mechanisms by which NAtl SSTs affect precipitation in the central Levant is related to the tendency for high (low) pressure anomalies to persist over the eastern North Atlantic/Western Mediterranean region when the Basin is cold (warm). This, in turn, affects the likelihood of cold air outbreaks and cyclogenesis in the Eastern Mediterranean and, consequently, rainfall in the central Levant region. Depending on its phase, this natural mechanism can alleviate or exacerbate the anthropogenic impact on the regions' hydroclimatic future.

Late quaternary changes in lakes, vegetation, and climate in the Bonneville Basin reconstructed from sediment cores from Great Salt Lake: Chapter 11

USGS Publications Warehouse

Thompson, Robert S.; Oviatt, Charles G.; Honke, Jeffrey S.; McGeehin, John

2016-01-01

Sediment cores from Great Salt Lake (GSL) provide the basis for reconstructing changes in lakes, vegetation, and climate for the last ~ 40 cal ka. Initially, the coring site was covered by a shallow saline lake and surrounded by Artemisia steppe or steppe-tundra under a cold and dry climate. As Lake Bonneville began to rise (from ~ 30 to 28 cal ka), Pinus and subalpine conifer pollen percentages increased and Artemisia declined, suggesting the onset of wetter conditions. Lake Bonneville oscillated near the Stansbury shoreline between ~ 26 and ~ 24 cal ka, rose to the Bonneville shoreline by ~ 18 cal ka, and then fell to the Provo shoreline, which it occupied until ~ 15 cal ka. Vegetation changed during this time span, albeit not always with the same direction or amplitude as the lake. The pollen percentages of Pinus and subalpine conifers were high from ~ 25 to 21.5 cal ka, indicating cool and moist conditions during the Stansbury oscillation and for much of the rise toward the Bonneville shoreline. Pinus percentages then decreased and Artemisia became codominant, suggesting drier and perhaps colder conditions from ~ 21 to ~ 15 cal ka, when Lake Bonneville was at or near its highest levels.Lake Bonneville declined to a low level by ~ 13 cal ka, while Pinus pollen percentages increased, indicating that conditions remained cooler and moister than today. During the Younger Dryas interval, the brief Gilbert episode rise in lake level was followed by a shallow lake with a stratified water column. This lake rise occurred as Pinus pollen percentages were declining and those of Artemisia were rising (reflecting increasingly dry conditions), after which Artemisia pollen was at very high levels (suggesting cold and dry conditions) for a brief period.Since ~ 10.6 cal ka lacustrine conditions have resembled those of present-day GSL. Pollen spectra for the period from ~ 10.6 to 7.2 cal ka have low levels of conifer pollen and high (for the Holocene) levels of desert and steppe taxa, suggesting generally dry conditions with maximum aridity occurring prior to the deposition of the Mazama tephra (~ 7.6 cal ka). After ~ 10.6 cal ka, Juniperus pollen percentages began to increase and by ~ 7.2 cal ka juniper woodlands were well established on lower mountain slopes. From ~ 7 to 4 cal ka, pollen percentages fluctuated near their mean values for the entire Holocene. The neopluvial (~ 4 to 2 cal ka) was the wettest part of the Holocene, with higher levels of Juniperus pollen and lower levels for steppe and desert taxa than in older Holocene sediments. Pollen percentages for the last ~ 2 cal ka are variable, but generally indicate a return to drier conditions.

Heated, humidified air for the common cold.

PubMed

Singh, Meenu; Singh, Manvi

2013-06-04

Heated, humidified air has long been used by sufferers of the common cold. The theoretical basis is that steam may help congested mucus drain better and heat may destroy the cold virus as it does in vitro. To assess the effects of inhaling heated water vapour (steam) in the treatment of the common cold by comparing symptoms, viral shedding and nasal resistance. In this updated review we searched CENTRAL 2013, Issue 2, MEDLINE (1966 to February week 4, 2013), EMBASE (1990 to March 2013) and Current Contents (1994 to March 2013). Randomised controlled trials (RCTs) using heated water vapour in participants with the common cold or participants with experimentally induced common cold. The two review authors independently reviewed all retrieved articles and excluded any articles, editorials and abstracts with inadequate outcome descriptions. The studies we included were subjected to a methodological assessment. We included six trials (394 trial participants). Three trials in which patient data could be pooled found benefits of steam for symptom relief for the common cold (odds ratio (OR) 0.31; 95% confidence interval (CI) 0.16 to 0.60). However, results on symptom indices were equivocal. No studies demonstrated an exacerbation of clinical symptom scores. One study conducted in the USA demonstrated worsened nasal resistance, while an earlier Israeli study showed improvement. One study examined viral shedding and antibody titres in nasal washings; there was no change in either between treatment and placebo groups. Minor side effects (including discomfort or irritation of the nose) were reported in some studies. Steam inhalation has not shown any consistent benefits in the treatment of the common cold, hence is not recommended in the routine treatment of common cold symptoms until more double-blind, randomised trials with a standardised treatment modality are conducted.

Effects of extreme temperatures on cardiovascular emergency hospitalizations in a Mediterranean region: a self-controlled case series study.

PubMed

Ponjoan, Anna; Blanch, Jordi; Alves-Cabratosa, Lia; Martí-Lluch, Ruth; Comas-Cufí, Marc; Parramon, Dídac; Del Mar Garcia-Gil, María; Ramos, Rafel; Petersen, Irene

2017-04-04

Cold spells and heatwaves increase mortality. However little is known about the effect of heatwaves or cold spells on cardiovascular morbidity. This study aims to assess the effect of cold spells and heatwaves on cardiovascular diseases in a Mediterranean region (Catalonia, Southern Europe). We conducted a population-based retrospective study. Data were obtained from the System for the Development of Research in Primary Care and from the Catalan Meteorological Service. The outcome was first emergency hospitalizations due to coronary heart disease, stroke, or heart failure. Exposures were: cold spells; cold spells and 3 or 7 subsequent days; and heatwaves. Incidence rate ratios (IRR) and 95% confidence intervals were calculated using the self-controlled case series method. We accounted for age, time trends, and air pollutants; results were shown by age groups, gender or cardiovascular event type. There were 22,611 cardiovascular hospitalizations in winter and 17,017 in summer between 2006 and 2013. The overall incidence of cardiovascular hospitalizations significantly increased during cold spells (IRR = 1.120; CI 95%: 1.10-1.30) and the effect was even stronger in the 7 days subsequent to the cold spell (IRR = 1.29; CI 95%: 1.22-1.36). Conversely, cardiovascular hospitalizations did not increase during heatwaves, neither in the overall nor in the stratified analysis. Cold spells but not heatwaves, increased the incidence of emergency cardiovascular hospitalizations in Catalonia. The effect of cold spells was greater when including the 7 subsequent days. Such knowledge might be useful to develop strategies to reduce the impact of extreme temperature episodes on human health.

Intense cold and mortality in Castile-La Mancha (Spain): study of mortality trigger thresholds from 1975 to 2003

NASA Astrophysics Data System (ADS)

Miron, Isidro J.; Montero, Juan Carlos; Criado-Alvarez, Juan José; Linares, Cristina; Díaz, Julio

2012-01-01

Studies on temperature-mortality time trends especially address heat, so that any contribution on the subject of cold is necessarily of interest. This study describes the modification of the lagged effects of cold on mortality in Castile-La Mancha from 1975 to 2003, with the novelty of also approaching this aspect in terms of mortality trigger thresholds. Cross-correlation functions (CCFs) were thus established with 15 lags, after application of ARIMA models to the mortality data and minimum daily temperatures (from November to March), and the results for the periods 1975-1984, 1985-1994 and 1995-2003 were then compared. In addition, daily mortality residuals for the periods 1975-1989 and 1990-2003 were related to minimum temperatures grouped in 2°C intervals, with a cold threshold temperature being obtained in cases where such residuals increased significantly ( p < 0.05) with respect to the mean for the study period. A cold-related mortality trigger threshold of -3°C was obtained for Ciudad Real for the period 1990-2003. The significant number of lags ( p < 0.05) in the CCFs declined every 10 years in Toledo (5-2-0), Cuenca (4-2-0), Albacete (4-3-0) and Ciudad Real (3-2-1). This meant that, while the trend in cold-related mortality trigger thresholds in the region could not be ascertained, it was possible to establish a reduction in the lagged effects of cold on mortality, attributable to the improvement in socio-economic conditions over the study period. Evidence was shown of the effects of cold on mortality, a finding that renders the adoption of preventive measures advisable in any case where intense cold is forecast.

Effects of temperature on mortality in Hong Kong: a time series analysis

NASA Astrophysics Data System (ADS)

Yi, Wen; Chan, Albert P. C.

2015-07-01

Although interest in assessing the impacts of hot temperature and mortality in Hong Kong has increased, less evidence on the effect of cold temperature on mortality is available. We examined both the effects of heat and cold temperatures on daily mortality in Hong Kong for the last decade (2002-2011). A quasi-Poisson model combined with a distributed lag non-linear model was used to assess the non-linear and delayed effects of temperatures on cause-specific and age-specific mortality. Non-linear effects of temperature on mortality were identified. The relative risk of non-accidental mortality associated with cold temperature (11.1 °C, 1st percentile of temperature) relative to 19.4 °C (25th percentile of temperature) was 1.17 (95 % confidence interval (CI): 1.04, 1.29) for lags 0-13. The relative risk of non-accidental mortality associated with high temperature (31.5 °C, 99th percentile of temperature) relative to 27.8 °C (75th percentile of temperature) was 1.09 (95 % CI: 1.03, 1.17) for lags 0-3. In Hong Kong, extreme cold and hot temperatures increased the risk of mortality. The effect of cold lasted longer and greater than that of heat. People older than 75 years were the most vulnerable group to cold temperature, while people aged 65-74 were the most vulnerable group to hot temperature. Our findings may have implications for developing intervention strategies for extreme cold and hot temperatures.

Effects of temperature on mortality in Hong Kong: a time series analysis.

PubMed

Yi, Wen; Chan, Albert P C

2015-07-01

Although interest in assessing the impacts of hot temperature and mortality in Hong Kong has increased, less evidence on the effect of cold temperature on mortality is available. We examined both the effects of heat and cold temperatures on daily mortality in Hong Kong for the last decade (2002-2011). A quasi-Poisson model combined with a distributed lag non-linear model was used to assess the non-linear and delayed effects of temperatures on cause-specific and age-specific mortality. Non-linear effects of temperature on mortality were identified. The relative risk of non-accidental mortality associated with cold temperature (11.1 °C, 1st percentile of temperature) relative to 19.4 °C (25th percentile of temperature) was 1.17 (95% confidence interval (CI): 1.04, 1.29) for lags 0-13. The relative risk of non-accidental mortality associated with high temperature (31.5 °C, 99th percentile of temperature) relative to 27.8 °C (75th percentile of temperature) was 1.09 (95% CI: 1.03, 1.17) for lags 0-3. In Hong Kong, extreme cold and hot temperatures increased the risk of mortality. The effect of cold lasted longer and greater than that of heat. People older than 75 years were the most vulnerable group to cold temperature, while people aged 65-74 were the most vulnerable group to hot temperature. Our findings may have implications for developing intervention strategies for extreme cold and hot temperatures.

Evaluation of holmium laser versus cold knife in optical internal urethrotomy for the management of short segment urethral stricture.

PubMed

Jain, Sudhir Kumar; Kaza, Ram Chandra Murthy; Singh, Bipin Kumar

2014-10-01

SACHSE COLD KNIFE IS CONVENTIONALLY USED FOR OPTICAL INTERNAL URETHROTOMY INTENDED TO MANAGE URETHRAL STRICTURES AND HO: YAG laser is an alternative to it. The aim of this study was to evaluate the role of urethral stricture treatment outcomes, efficacy, and complications using cold knife and Ho: YAG (Holmium laser) for optical internal urethrotomy. In this prospective study included, 90 male patients age >18 years, with diagnosis of urethral stricture admitted for internal optical urethrotomy during April 2010 to March 2012. The patients were randomized into two groups containing 45 patients each using computer generated random number. In group A (Holmium group), internal urethrotomy was done with Holmium laser and in group B (Cold knife group) Sachse cold knife was used. Patients were followed up for 6 months after surgery in Out Patient Department on 15, 30 and 180 post-operative days. At each follow up visit physical examination, and uroflowmetry was performed along with noting complaints, if any. The peak flow rates (PFR) were compared between the two groups on each follow up. At 180 days (6 month interval) the difference between mean of PFR for Holmium and Cold knife group was statistically highly significant (P < 0.001). Complications were seen in 12.22% of cases. Both modalities are effective in providing immediate relief to patients with single and short segment (<2 cm long) urethral strictures but more sustained response was attained with Cold knife urethrotomy.

Lateglacial temperature reconstruction in the Eastern Tropical Andes (Bolivia) inferred from paleoglaciers and paleolakes

NASA Astrophysics Data System (ADS)

Martin, L.; Blard, P. H.; Lave, J.; Prémaillon, M.; Jomelli, V.; Brunstein, D.; Lupker, M.; Charreau, J.; Mariotti, V.; Condom, T.; Bourles, D. L.

2015-12-01

Recent insights shed light on the global mechanisms involved in the abrupt oscillations of the Earth climate for the Late Glacial Maximum (LGM) to Holocene period (Zhang et al., 2014; Banderas et al., 2015). Yet the concomitant patterns of regional climate reorganization on continental areas are for now poorly documented. Particularly, few attempts have been made to propose temporal reconstructions of the regional climate variables in the High Tropical Andes, a region under the direct influence of the upper part of the troposphere. We present new glacial chronologies from the Zongo (16.3°S - 68.1°W, Bolivia) and Wara-Wara (17.3°S - 66.1°W, Bolivia) valleys based on Cosmic Ray Exposure dating (CRE) from an exceptional suite of recessive moraines. These new data permitted to refine existing chronologies (Smith et al., 2005 ; Zech et al., 2010): the Zongo valley is characterized by an older local last glacial maximum than the Wara Wara valley. Both sites however exhibit similar glacier behaviours, with a progressive regression between 18 ka and the Holocene. In both sites, glaciers recorded stillstand episodes synchronous with the cold events of the Norther Hemisphere (Henrich 1 event, Younger Dryas). Since the nearby Altiplano basin registered lake level variations over the same period, we were able to apply a joint modelling of glaciers Equilibrium Line Altitude (ELA) and lake budget. This permits to derive a temporal evolution of temperature and precipitation for both sites. These new reconstructions show for both sites that glaciers of the Eastern Tropical Andes were both influenced by the major climatic events of the Northern and Southern Hemispheres. However, precipitation variability is more influenced by the Northern Atlantic events. This observation is in good agreement with the theories suggesting that North Hemisphere cold events are coeval with an important southward deflexion of the Intertropical Convergence Zone (ITCZ) due to the inter-hemispheric temperature gradient (Schneider et al., 2014). Such a southward shift would lead to an increased moist supply of the subequatorial Amazonian basin (Montade et al., 2015) and thus an increased easterly driven moist transport over the Altiplano.

Organic geochemical investigations of the Dali Lake sediments in northern China: Implications for environment and climate changes of the last deglaciation in the East Asian summer monsoon margin

NASA Astrophysics Data System (ADS)

Fan, Jiawei; Xiao, Jule; Wen, Ruilin; Zhang, Shengrui; Wang, Xu; Cui, Linlin; Yamagata, Hideki

2017-06-01

Millennial-scale environment and climate changes in the East Asian summer monsoon margin during the last deglaciation are reconstructed by systematic studies on the characteristic of sedimentary organic matter from Dali Lake in northern China. Concurrent increases in the TOC and TN concentrations indicate increases in terrestrial organic matter and nutrient inputs to the lake and a development of terrestrial vegetation and phytoplankton productivity related to increases in regional temperature and precipitation. C/N ratios reflect changes in the proportions of terrestrial and aquatic organic matter. Decreases in both δ13Corg and δ15N values indicate increases in the isotopically lighter, terrestrial carbon and nitrogen inputs to the lake, due to increases in surface runoffs; while a sharp decrease in the δ15N value implies a significant weakening in the biological activities of nitrifying and amonifying bacteria, due to abrupt decrease in the water temperature. The geochemical data indicate that regional temperature and precipitation exhibited increasing trends from 15,000 to 12,350 cal yr BP; temperature decreased abruptly at 12,350 cal yr BP and then maintained a low level from 12,350 to 11,400 cal yr BP, precipitation decreased to a relatively low level from 12,350 to 11,400 cal yr BP; and both temperature and precipitation returned to increase after 11,400 cal yr BP. The climate change in the Dali Lake region during the last deglaciation corresponds, within age uncertainties, to the Bølling-Allerød (BA) warm phase and Younger Dryas (YD) cold reversal occurring over northern high latitudes. However, the gradual and mild increasing trends of regional temperature and precipitation during the BA warm period contrasts with the general cooling trend in northern high latitude temperature, implying a dominant influence from increases in the Northern Hemisphere summer insolation; while the slight decreases in regional precipitation relative to the rapid and significant decreases in northern high latitude temperature during the YD cold period may have resulted from local moisture recycling or from an insensitive response of hydrology and ecology to the regional precipitation change.

Bay of Bengal Exhibits Warming Trend During the Younger Dryas: Implications of AMOC

NASA Astrophysics Data System (ADS)

Panmei, Champoungam; Divakar Naidu, Pothuri; Mohtadi, Mahyar

2017-12-01

A sharp decline in temperature during the Younger Dryas (YD) preceding the current warmer Holocene is well documented in climate archives from the Northern Hemisphere high latitudes. Although the magnitude of YD cooling varied spatially, the response of YD cooling was well documented in the Atlantic and Pacific Oceans but not in the Indian Ocean. Here we investigate whether the modern remote forcing of tropical Indian Ocean sea surface temperature (SST) by Northern Hemisphere climate changes holds true for events such as the YD. Our SST reconstruction from the western Bay of Bengal exhibits an overall warming of ˜1.8°C during the YD. We further compared our data with other existing Mg/Ca-based SST records from the Northern Indian Ocean and found no significant negative SST anomalies in both the Arabian Sea and the Bay of Bengal compared to pre- and post-YD, suggesting that no apparent cooling occurred during the YD in the Northern Indian Ocean. In contrast, most part of the YD exhibits positive SST anomalies in the Northern Indian Ocean that coincide with the slowdown of the Atlantic Meridional Overturning Circulation during this period.

Two episodes of meltwater influx from glacial Lake Agassiz into the Lake Michigan basin and their climatic contrasts

USGS Publications Warehouse

Colman, Steven M.; Keigwin, L.D.; Forester, R.M.

1994-01-01

Two episodes of meltwater influx from glacial Lake Agassiz are recorded as prominent sedimentologic, isotopic, magnetic, and faunal signatures in southern Lake Michigan profundal sediments. As a tributary to the main path of eastward Lake Agassiz flow, southern Lake Michigan recorded only the largest, catastrophic discharges. The distinctive Wilmette Bed, a massive gray mud that interrrupts laminated red glaciolacustrine clays, marks the first episode, which occurred near the beginning of the Younger Dryas cooling events. The associated discharge may have played a role in the inception or severity of the Younger Dryas event. An oxygen isotope excursion in biogenic carbonate and changes in ostracode assemblages mark the second episode, which appears to have had at least two pulses, dated by accelerator mass spectrometer 14C ages on biogenic carbonate at about 8.9 and 8.6 ka. The second episode occurred during the early Holocene peak in global meltwater discharge and apparently had little widespread climatic or oceanographic effect. The contrast between the effects associated with these two episodes of meltwater discharge emphasizes the complexity of the ice sheet-ocean-climate system. -Authors

Thermomechanical treatment of alloys

DOEpatents

Bates, John F.; Brager, Howard R.; Paxton, Michael M.

1983-01-01

An article of an alloy of AISI 316 stainless steel is reduced in size to predetermined dimensions by cold working in repeated steps. Before the last reduction step the article is annealed by heating within a temperature range, specifically between 1010.degree. C. and 1038.degree. C. for a time interval between 90 and 60 seconds depending on the actual temperature. By this treatment the swelling under neutron bombardment by epithermal neutrons is reduced while substantial recrystallization does not occur in actual use for a time interval of at least of the order of 5000 hours.

Psychological job demands as a risk factor for common cold in a Dutch working population.

PubMed

Mohren, D C; Swaen, G M; Borm, P J; Bast, A; Galama, J M

2001-01-01

We investigated the effect of Psychological Job Demands (PJD) on the occurrence of the clinical symptoms of common cold. Subjects, participating in a large prospective cohort study on psychological determinants of fatigue at work, were asked to fill in a questionnaire on the occurrence of common cold during the previous four months. High PJD were considered as a potential risk factor. Other factors such as age, gender, and having young children were considered as potential confounders. In logistic regression analysis, the adjusted odds ratio (OR) for having a recent cold in subjects reporting high PJD vs. those reporting low PJD was 1.20 (95% confidence interval (CI), 1.08-1.33). A higher risk emerged among those with young children (OR, 1.70; 95% CI, 1.47-1.96), those having a history of asthma (OR, 1.69; 95% CI, 1.28-2.22), or being under the age of 40 (OR, 1.28; 95% CI, 1.14-1.43) and among smokers (OR, 1.23; 95% CI, 1.09-1.38). The results support an association between PJD and common cold. In spite of the almost inevitable shortcoming of a large cohort study using questionnaires, this study gave us the opportunity to study the relationship between common cold and work-related factors in a nonexperimental setting with participants observed in a natural environment with all the normal everyday hassles.

Microplastic Deformation of Submicrocrystalline Copper at Room and Elevated Temperatures

NASA Astrophysics Data System (ADS)

Dudarev, E. F.; Pochivalova, G. P.; Tabachenko, A. N.; Maletkina, T. Yu.; Skosyrskii, A. B.; Osipov, D. A.

2017-02-01

of investigations of submicrocrystalline copper subjected to cold rolling after abc pressing by methods of backscatter electron diffraction and x-ray diffraction analysis are presented. It is demonstrated that after such combined intensive plastic deformation, the submicrocrystalline structure with average grain-subgrain structure elements having sizes of 0.63 μm is formed with relative fraction of high-angle grain boundaries of 70% with texture typical for rolled copper. Results of investigation of microplastic deformation of copper with such structure at temperatures in the interval 295-473 K and with submicrocrystalline structure formed by cold rolling of coarse-grained copper are presented.

Improving vaccination cold chain in the general practice setting.

PubMed

Page, Sue L; Earnest, Arul; Birden, Hudson; Deaker, Rachelle; Clark, Chris

2008-10-01

This study compared temperature control in different types of vaccine storing refrigerators in general practice and tested knowledge of general practice staff in vaccine storage requirements. Temperature data loggers were set to serially record the temperature within vaccine refrigerators in 28 general practices, recording at 12 minute intervals over a period of 10 days on each occasion. A survey of vaccine storage knowledge and records of divisions of general practice immunisation contacts were also obtained. There was a significant relationship between type of refrigerator and optimal temperature, with the odds ratio for bar style refrigerator being 0.005 (95% CI: 0.001-0.044) compared to the purpose built vaccine refrigerators. Score on a survey of vaccine storage was also positively associated with optimal storage temperature. General practices that invest in purpose built vaccine refrigerators will achieve standards of vaccine cold chain maintenance significantly more reliably than can be achieved through regular cold chain monitoring and practice supports.

First-principles molecular dynamics simulations of anorthite (CaAl2Si2O8) glass at high pressure

NASA Astrophysics Data System (ADS)

Ghosh, Dipta B.; Karki, Bijaya B.

2018-06-01

We report first-principles molecular dynamics study of the equation of state, structural, and elastic properties of CaAl2Si2O8 glass at 300 K as a function of pressure up to 155 GPa. Our results for the ambient pressure glass show that: (1) as with other silicates, Si atoms remain mostly (> 95%) under tetrahedral oxygen surroundings; (2) unlike anorthite crystal, presence of high-coordination (> 4) Al atoms with 30% abundance; (3) and significant presence of both non-bridging (8%) and triply (17%) coordinated oxygen. To achieve the glass configurations at various pressures, we use two different simulation schedules: cold and hot compression. Cold compression refers to sequential compression at 300 K. Compression at 3000 K and subsequent isochoric quenching to 300 K is considered as hot compression. At the initial stages of compression (0-10 GPa), smooth increase in bond distance and coordination occurs in the hot-compressed glass. Whereas in cold compression, Si (also Al to some extent) displays mainly topological changes (without significantly affecting the average bond distance or coordination) in this pressure interval. Further increase in pressure results in gradual increases in mean coordination, with Si-O (Al-O) coordination eventually reaching and remaining 6 (6.5) at the highest compression. Similarly, the ambient pressure Ca-O coordination of 5.9 increases to 9.5 at 155 GPa. The continuous pressure-induced increase in the proportion of oxygen triclusters along with the appearance and increasing abundance of tetrahedral oxygens results in mean O-T (T = Si and Al) coordination of > 3 from a value of 2.1 at ambient pressure. Due to the absence of kinetic barrier, the hot-compressed glasses consistently produce greater densities and higher coordination numbers than the cold compression cases. Decompressed glasses show irreversible compaction along with retention of high-coordination species when decompressed from pressure ≥ 10 GPa. The different density retention amounts (12, 17, and 20% when decompressed from 12, 40, and 155 GPa, respectively) signifies that the degree of irreversibility depends on the peak pressure of decompression. The calculated compressional and shear wave velocities (5 and 3 km/s at 0 GPa) for the cold-compressed case display sluggish pressure response in the 0-10 GPa interval as opposed to smooth increase in the hot-compressed one. Shear velocity saturates rather rapidly with a value of 5 km/s, whereas compressional wave velocity displays continuous increase, reaching/exceeding 12.5 km/s at 155 GPa. These structural details suggest that the pressure response of the cold-compressed glasses is not only inherently different at the 0-10 GPa interval, the density, coordination, and wave velocity data are consistently lower than the hot-compressed glasses. Hot-compressed glasses may, therefore, be the better analog in the study of high-pressure silicate melts.

Century and Millennial-scale Changes in the Western Equatorial Pacific Thermocline in Relationship to Higher Latitude Processes

NASA Astrophysics Data System (ADS)

Weiss, T. L. C.; Linsley, B. K.

2017-12-01

The last several glacial-interglacial cycles provide the perfect laboratory for investigating sea level, ocean circulation, and regional climate variability during pronounced global climate transitions. During the most recent deglaciation, the paleo-evidence for the Younger Dryas cold event and preceding meltwater pulse 1A (MWP-1A) and subsequent possible meltwater pulse 1B (MWP-1B) suggests rapid climate variability, in sharp contrast to the gradual deglacial forcing. MWP-1A has been documented in several locations, but there remains a controversy about whether deglacial MWP-1B existed and how much sea level rose across the interval from 11,450 to 11,000 kyr B.P. Due to its location and unusual bathymetry, the Sulu Sea is uniquely situated to monitor western Pacific boundary current (WBC) variability and changes in the proportion of North Pacific vs. South Pacific water in the far western Pacific near the entrance to the Indonesian Throughflow (ITF). Though the Sulu Sea is a relatively deep basin (>4,000 m), it is isolated from the South China Sea to the North and Sulawesi Sea to the south by shallow sills no deeper than 570 m that limit deepwater ventilation to the basin. As a result, deep basin water below the thermocline is a constant 10° C, a direct function of the ventilating WBCs. Observing past changes in thermocline conditions in the Sulu Sea should provide insight into WBC variability in addition to climate and circulation driven temperature and salinity variability in the South China and Sulawesi Seas. We will present δ18O evidence from the thermocline dwelling planktonic foraminifera Globorotalia tumida extracted from sediment core MD972141 in the Sulu Sea that the thermocline rapidly warmed and/or freshened near the time of MWP-1B. Our new G. tumida δ18O data indicates a 50% larger decrease in δ18O in the thermocline than observed in the surface dwelling Globigerinoides ruber. The Sulu Sea G. tumida δ18O results also indicate relatively cool and salty thermocline conditions from 10,000 kyr BP to 8,400 kyr BP. We will also present new G. tumida and benthic foraminifera Oridorsalis umbonatus δ18O and δ13C results from core MD972141 spanning the last 150 kyr and compare these records to existing G. ruber data from the same core with a focus on comparing Pacific WBC variability across Terminations I and II.

The rise and fall of Lake Bonneville between 45 and 10.5 ka

USGS Publications Warehouse

Benson, L.V.; Lund, S.P.; Smoot, J.P.; Rhode, D.E.; Spencer, R.J.; Verosub, K.L.; Louderback, L.A.; Johnson, C.A.; Rye, R.O.; Negrini, R.M.

2011-01-01

A sediment core taken from the western edge of the Bonneville Basin has provided high-resolution proxy records of relative lake-size change for the period 45.1-10.5 calendar ka (hereafter ka). Age control was provided by a paleomagnetic secular variation (PSV)-based age model for Blue Lake core BL04-4. Continuous records of ??18O and total inorganic carbon (TIC) generally match an earlier lake-level envelope based on outcrops and geomorphic features, but with differences in the timing of some hydrologic events/states. The Stansbury Oscillation was found to consist of two oscillations centered on 25 and 24 ka. Lake Bonneville appears to have reached its geomorphic highstand and began spilling at 18.5 ka. The fall from the highstand to the Provo level occurred at 17.0 ka and the lake intermittently overflowed at the Provo level until 15.2 ka, at which time the lake fell again, bottoming out at ~14.7 ka. The lake also fell briefly below the Provo level at ~15.9 ka. Carbonate and ??18O data indicate that between 14.7 and 13.1 ka the lake slowly rose to the Gilbert shoreline and remained at about that elevation until 11.6 ka, when it fell again. Chemical and sedimentological data indicate that a marsh formed in the Blue Lake area at 10.5 ka.Relatively dry periods in the BL04-4 records are associated with Heinrich events H1-H4, suggesting that either the warming that closely followed a Heinrich event increased the evaporation rate in the Bonneville Basin and (or) that the core of the polar jet stream (PJS) shifted north of the Bonneville Basin in response to massive losses of ice from the Laurentide Ice Sheet (LIS) during the Heinrich event. The second Stansbury Oscillation occurred during Heinrich event H2, and the Gilbert wet event occurred during the Younger Dryas cold interval. Several relatively wet events in BL04-4 occur during Dansgaard-Oeschger (DO) warm events.The growth of the Bear River glacier between 32 and 17 ka paralleled changes in the values of proxy indicators of Bonneville Basin wetness and terminal moraines on the western side of the Wasatch Mountains have ages ranging from 16.9 to 15.2 ka. This suggests a near synchroneity of change in the hydrologic and cryologic balances occurring in the Bonneville drainage system and that glacial extent was linked to lake size. ?? 2010.

Heated, humidified air for the common cold.

PubMed

Singh, M

2006-07-19

Heated, humidified air has long been used by common cold sufferers. The theoretical basis is that steam may help congested mucus drain better and heat may destroy cold virus as it does in vitro. To assess the effects of inhaling heated water vapour (steam), in the treatment of the common cold by comparing symptoms, viral shedding and nasal resistance. In this updated review we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library issue 4, 2005); MEDLINE (2003 to December Week 2 2005); EMBASE (July 2003 to September 2005); and Current Contents (current five years). Randomized controlled trials (RCTs) using heated water vapor in patients with the common cold or volunteers with experimentally induced common cold. All the articles retrieved were initially subjected to a review for inclusion or exclusion criteria. Review articles, editorials and abstracts with inadequate outcome descriptions were excluded. Studies selected for inclusion were subjected to a methodological assessment. Six trials were included. Three found benefits of steam for symptom relief with the common cold (odds ratio (OR) 95% confidence interval (CI) 0.31; 0.16 to 0.60; relative risk (RR) 0.56; 95% CI 0.4 to 0.79). Results on symptom indices were equivocal. No studies demonstrated an exacerbation of clinical symptom scores. One USA study demonstrated worsened nasal resistance, while an earlier Israeli one showed improvement. One study examined viral shedding and antibody titres in nasal washings: there was no change of either between treatment and placebo groups. Minor side effects (including discomfort or irritation of the nose) were reported in some studies. Steam inhalation are not recommended in the routine treatment of common cold symptoms until more double-blind RCT trials are conducted.

Interaction of the Left Dorsolateral Prefrontal Cortex (l-DLPFC) and Right Orbitofrontal Cortex (OFC) in Hot and Cold Executive Functions: Evidence from Transcranial Direct Current Stimulation (tDCS).

PubMed

Nejati, Vahid; Salehinejad, Mohammad Ali; Nitsche, Michael A

2018-01-15

An organizing principle which has recently emerged proposes that executive functions (EF) can be divided into cognitive (cold) and affective/reward-related (hot) processes related to the dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex (OFC) respectively. A controversial question is whether cold and hot EF are functionally and structurally independent or not. This study investigated how the left DLPFC (l-DLPFC) and right OFC (r-OFC) interact in hot and cold EF using transcranial direct current stimulation (tDCS). Twenty-four healthy male subjects received anodal, cathodal and sham tDCS (20 min, 1.5 mA) over the l-DLPFC (F3) and r-OFC (Fp2) with a 72-h interval between each stimulation condition. After five minutes of stimulation, participants underwent a series of cold and hot EF tasks including the Go/No-Go and Tower of Hanoi (TOH) as measures of cold EF and the BART and temporal discounting tasks as measures of hot EF. Inhibitory control mostly benefited from anodal l-DLPFC/cathodal r-OFC tDCS. Planning and problem solving were more prominently affected by anodal l-DLPFC/cathodal r-OFC stimulation, although the reversed electrode position with the anode positioned over the r-OFC also affected some aspects of task performance. Risk-taking behavior and risky decision-making decreased under both anodal l-DLPFC/cathodal r-OFC and anodal r-OFC/cathodal l-DLPFC tDCS. Cold EF rely on DLPFC activation while hot EF rely on both, DLPFC and OFC activation. Results suggest that EF are placed on continuum with lateral and mesial prefrontal areas contributing to cold and hot aspects respectively. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

Zinc Acetate Lozenges May Improve the Recovery Rate of Common Cold Patients: An Individual Patient Data Meta-Analysis.

PubMed

Hemilä, Harri; Fitzgerald, James T; Petrus, Edward J; Prasad, Ananda

2017-01-01

A previous meta-analysis of 3 zinc acetate lozenge trials estimated that colds were on average 40% shorter for the zinc groups. However, the duration of colds is a time outcome, and survival analysis may be a more informative approach. The objective of this individual patient data (IPD) meta-analysis was to estimate the effect of zinc acetate lozenges on the rate of recovery from colds. We analyzed IPD for 3 randomized placebo-controlled trials in which 80-92 mg/day of elemental zinc were administered as zinc acetate lozenges to 199 common cold patients. We used mixed-effects Cox regression to estimate the effect of zinc. Patients administered zinc lozenges recovered faster by rate ratio 3.1 (95% confidence interval, 2.1-4.7). The effect was not modified by age, sex, race, allergy, smoking, or baseline common cold severity. On the 5th day, 70% of the zinc patients had recovered compared with 27% of the placebo patients. Accordingly, 2.6 times more patients were cured in the zinc group. The difference also corresponds to the number needed to treat of 2.3 on the 5th day. None of the studies observed serious adverse effects of zinc. The 3-fold increase in the rate of recovery from the common cold is a clinically important effect. The optimal formulation of zinc lozenges and an ideal frequency of their administration should be examined. Given the evidence of efficacy, common cold patients may be instructed to try zinc acetate lozenges within 24 hours of onset of symptoms. © The Author 2017. Published by Oxford University Press on behalf of Infectious Diseases Society of America.

Behaviorally Assessed Sleep and Susceptibility to the Common Cold.

PubMed

Prather, Aric A; Janicki-Deverts, Denise; Hall, Martica H; Cohen, Sheldon

2015-09-01

Short sleep duration and poor sleep continuity have been implicated in the susceptibility to infectious illness. However, prior research has relied on subjective measures of sleep, which are subject to recall bias. The aim of this study was to determine whether sleep, measured behaviorally using wrist actigraphy, predicted cold incidence following experimental viral exposure. A total of 164 healthy men and women (age range, 18 to 55 y) volunteered for this study. Wrist actigraphy and sleep diaries assessed sleep duration and sleep continuity over 7 consecutive days. Participants were then quarantined and administered nasal drops containing the rhinovirus, and monitored over 5 days for the development of a clinical cold (defined by infection in the presence of objective signs of illness). Logistic regression analysis revealed that actigraphy- assessed shorter sleep duration was associated with an increased likelihood of development of a clinical cold. Specifically, those sleeping < 5 h (odds ratio [OR] = 4.50, 95% confidence interval [CI], 1.08-18.69) or sleeping between 5 to 6 h (OR = 4.24, 95% CI, 1.08-16.71) were at greater risk of developing the cold compared to those sleeping > 7 h per night; those sleeping 6.01 to 7 h were at no greater risk (OR = 1.66; 95% CI 0.40-6.95). This association was independent of prechallenge antibody levels, demographics, season of the year, body mass index, psychological variables, and health practices. Sleep fragmentation was unrelated to cold susceptibility. Other sleep variables obtained using diary and actigraphy were not strong predictors of cold susceptibility. Shorter sleep duration, measured behaviorally using actigraphy prior to viral exposure, was associated with increased susceptibility to the common cold. © 2015 Associated Professional Sleep Societies, LLC.

Reconstructing lake evaporation history and the isotopic composition of precipitation by a coupled δ18O-δ2H biomarker approach

NASA Astrophysics Data System (ADS)

Hepp, Johannes; Tuthorn, Mario; Zech, Roland; Mügler, Ines; Schlütz, Frank; Zech, Wolfgang; Zech, Michael

2015-10-01

Over the past decades, δ18O and δ2H analyses of lacustrine sediments became an invaluable tool in paleohydrology and paleolimnology for reconstructing the isotopic composition of past lake water and precipitation. However, based on δ18O or δ2H records alone, it can be challenging to distinguish between changes of the precipitation signal and changes caused by evaporation. Here we propose a coupled δ18O-δ2H biomarker approach that provides the possibility to disentangle between these two factors. The isotopic composition of long chain n-alkanes (n-C25, n-C27, n-C29, n-C31) were analyzed in order to establish a 16 ka Late Glacial and Holocene δ2H record for the sediment archive of Lake Panch Pokhari in High Himalaya, Nepal. The δ2Hn-alkane record generally corroborates a previously established δ18Osugar record reporting on high values characterizing the deglaciation and the Older and the Younger Dryas, and low values characterizing the Bølling and the Allerød periods. Since the investigated n-alkane and sugar biomarkers are considered to be primarily of aquatic origin, they were used to reconstruct the isotopic composition of lake water. The reconstructed deuterium excess of lake water ranges from +57‰ to -85‰ and is shown to serve as proxy for the evaporation history of Lake Panch Pokhari. Lake desiccation during the deglaciation, the Older Dryas and the Younger Dryas is affirmed by a multi-proxy approach using the Hydrogen Index (HI) and the carbon to nitrogen ratio (C/N) as additional proxies for lake sediment organic matter mineralization. Furthermore, the coupled δ18O and δ2H approach allows disentangling the lake water isotopic enrichment from variations of the isotopic composition of precipitation. The reconstructed 16 ka δ18Oprecipitation record of Lake Panch Pokhari is well in agreement with the δ18O records of Chinese speleothems and presumably reflects the Indian Summer Monsoon variability.

Impacts of cold weather on all-cause and cause-specific mortality in Texas, 1990-2011.

PubMed

Chen, Tsun-Hsuan; Li, Xiao; Zhao, Jing; Zhang, Kai

2017-06-01

Cold weather was estimated to account for more than half of weather-related deaths in the U.S. during 2006-2010. Studies have shown that cold-related excessive mortality is especially relevant with decreasing latitude or in regions with mild winter. However, only limited studies have been conducted in the southern U.S. The purpose of our study is to examine impacts of cold weather on mortality in 12 major Texas Metropolitan Areas (MSAs) for the 22-year period, 1990-2011. Our study used a two-stage approach to examine the cold-mortality association. We first applied distributed lag non-linear models (DLNM) to 12 major MSAs to estimate cold effects for each area. A random effects meta-analysis was then used to estimate pooled effects. Age-stratified and cause-specific mortalities were modeled separately for each MSA. Most of the MSAs were associated with an increased risk in mortality ranging from 0.1% to 5.0% with a 1 °C decrease in temperature below the cold thresholds. Higher increased mortality risks were generally observed in MSAs with higher average daily mean temperatures and lower latitudes. Pooled effect estimate was 1.58% (95% Confidence Interval (CI) [0.81, 2.37]) increase in all-cause mortality risk with a 1 °C decrease in temperature. Cold wave effects in Texas were also examined, and several MSAs along the Texas Gulf Coast showed statistically significant cold wave-mortality associations. Effects of cold on all-cause mortality were highest among people over 75 years old (1.86%, 95% CI [1.09, 2.63]). Pooled estimates for cause-specific mortality were strongest in myocardial infarction (4.30%, 95% CI [1.18, 7.51]), followed by respiratory diseases (3.17%, 95% CI [0.26, 6.17]) and ischemic heart diseases (2.54%, 95% CI [1.08, 4.02]). In conclusion, cold weather generally increases mortality risk significantly in Texas, and the cold effects vary with MSAs, age groups, and cause-specific deaths. Copyright © 2017 Elsevier Ltd. All rights reserved.

El Nino-like events during Miocene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casey, R.E.; Nelson, C.O.; Weinheimer, A.L.

El Nino-like events have been recorded from the Miocene laminated siliceous facies of the Monterey Formation. These El Nino-like Miocene events are compared to El Nino events recorded from Holocene varved sediments deposited within the anoxic Santa Barbara basin. Strong El Nino events can be recognized from Holocene Santa Barbara basin sediments by increases in radiolarian flux to the sea floor during those events. For the last 100-plus years, frequency of strong El Ninos has been on the order of one extremely strong event about every 100 years, and one easily recognizable event about every 18 years. Frequencies in themore » laminated (varved) Miocene range from about every 4-5 years to over 20 years. The higher frequencies occur within generally warm intervals and the lower frequencies within generally cold intervals. Perhaps the frequencies of these events may, in fact, be an important indicator in determining whether the intervals were cold or warm. Reconstructions of the paleo-California Current system during El Nino-like periods have been made for the west coast from the Gulf of California to northern California. Strong El Nino-like events occurred 5.5 and 8 Ma, and a strong anti-El Nino-like event occurred at about 6.5 Ma. Evidence from the 5.5 and 8 Ma events combined with other evidence suggests that modern El Ninos, similar to today's, were initiated at 5.5 Ma or earlier.« less

Cold-provocation testing for the vascular component of hand-arm vibration syndrome in health surveillance.

PubMed

Poole, Kerry; Elms, Joanne; Mason, Howard

2006-10-01

The aim was to investigate whether the use of infra-red thermography (I-R) and measurement of temperature gradients along the finger could improve the diagnostic accuracy of cold-provocation testing (15 degrees C for 5 min) in vascular hand-arm vibration syndrome (HAVS). Twenty-one controls and 33 individuals with stages 2/3V HAVS were studied. The standard measurement of time to rewarm by 4 degrees C (T4 degrees C) and temperature gradients between the finger tip, base and middle (measured using I-R) were calculated. Receiver Operating Characteristics (ROC) analysis to distinguish between the two groups revealed that for T4 degrees C the area under the ROC curve was not statistically significantly different from 0.5 (0.64 95% confidence interval 0.49-0.76). The difference between the tip and middle portion of the finger during the sixth minute of recovery was the most promising gradient with an area of 0.76 (95% confidence interval 0.62-0.87), and sensitivity and specificity of 57.6% and 85.7% respectively. However, this was not significantly different from that for the time to rewarm by 4 degrees C. In conclusion, the cold-provocation test used in this study does not appear to discriminate between individuals with stage 2/3V HAVS and controls and this is not improved by the measurement of temperature gradients along the fingers using I-R.

Effectiveness of Mouthrinse formulated from Aqueous Extract of Terminalia chebula on Salivary Streptococcus mutans Count and pH among 8- to 12-year-old School Children of Karnataka: A Randomized Clinical Trial.

PubMed

Palit, Madhuchanda; Hegde, Sundeep K; Bhat, Sham S

2016-01-01

The aim of the present study was to evaluate the anticar-iogenic efficacy of hot and cold aqueous extracts of Terminalia chebula against Streptococcus mutans as an oral rinse and also to discover the acceptability of the mouthwash in children. Sixty children between 8 and 12 years with high caries risk were selected. 10% concentration of hot and cold aqueous extracts were prepared. Children were randomly divided into extract and control group. Baseline salivary samples were taken, and the samples were re-collected at 10, 60, and 90 minutes interval after rinsing. Microbial and pH analysis were done. An acceptability questionnaire was filled. Tukey's multiple comparison test. The results show statistically significant difference in S. mutans counts at 10, 60, and 90 minutes interval when compared with negative control. However, when the hot and cold extracts were compared, there was no significant difference. Acceptability questionnaire showed 65 to 75% overall acceptability for both types of extract. Results of this study showed that both types of aqueous extract of T. chebula may be used as potential anticariogenic mouthwash with acceptable taste in children. Palit MC, Hegde SK, Bhat SS. Effectiveness of Mouthrinse formulated from Aqueous Extract of Terminalia chebula on Salivary Streptococcus mutans Count and pH among 8- to 12-year-old School Children of Karnataka: A Randomized Clinical Trial. Int J Clin Pediatr Dent 2016;9(4):349-354.

The effects of cold water immersion with different dosages (duration and temperature variations) on heart rate variability post-exercise recovery: A randomized controlled trial.

PubMed

Almeida, Aline C; Machado, Aryane F; Albuquerque, Maíra C; Netto, Lara M; Vanderlei, Franciele M; Vanderlei, Luiz Carlos M; Junior, Jayme Netto; Pastre, Carlos M

2016-08-01

The aim of the present study was to investigate the effects of cold water immersion during post-exercise recovery, with different durations and temperatures, on heart rate variability indices. Hundred participants performed a protocol of jumps and a Wingate test, and immediately afterwards were immersed in cold water, according to the characteristics of each group (CG: control; G1: 5' at 9±1°C; G2: 5' at 14±1°C; G3: 15' at 9±1°C; G4: 15' at 14±1°C). Analyses were performed at baseline, during the CWI recuperative technique (TRec) and 20, 30, 40, 50 and 60min post-exercise. The average HRV indices of all RR-intervals in each analysis period (MeanRR), standard deviation of normal RR-intervals (SDNN), square root of the mean of the sum of the squares of differences between adjacent RR-intervals (RMSSD), spectral components of very low frequency (VLF), low frequency (LF) and high frequency (HF), scatter of points perpendicular to the line of identity of the Poincaré Plot (SD1) and scatter points along the line of identity (SD2) were assessed. Mean RR, VLF and LF presented an anticipated return to baseline values at all the intervention groups, but the same was observed for SDNN and SD2 only in the immersion for 15min at 14°C group (G4). In addition, G4 presented higher values when compared to CG. These findings demonstrate that if the purpose of the recovery process is restoration of cardiac autonomic modulation, the technique is recommended, specifically for 15min at 14°C. Copyright © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Dynamics of Productivity-Related Oxygen Minimum Zone along the Shirshov Ridge, Western Bering Sea, during the Last Glacial Termination

NASA Astrophysics Data System (ADS)

Ovsepyan, E.; Ivanova, E. V.; Tiedemann, R.

2017-12-01

Seasonally sea-ice covered Bering Sea is known to be a sensitive region to study rapid climatic oscillations. Based on benthic (BF) and planktic (PF) foraminiferal data from two sediment cores SO201-2-85KL (85KL, w.d. 968 m) and SO201-2-77KL (77KL, w.d. 2163 m) we reconstruct variations in intensity of oxygen minimum zone (OMZ) and its relation to sea-surface bioproductivity in the central and southern parts of the Shirshov Ridge, western Bering Sea, during the Termination I. A prevalence of suboxic BF group (Kaiho, 1994) in both cores mirrors moderately oxygenated intermediate and deep waters during LGM-Heinrich I interval. Rapid increase in percentages of dysoxic group is registered in the core 77KL at the onset of Bølling/Allerød. This implies that relatively low-oxygen conditions developed at 2 km water depths in the southwestern Bering Sea, but occurrence (20-30%) of suboxic group suggests that oxygen depletion was not dramatic. Simultaneous spikes of high-productivity species point to a bioproductivity rise above the southern part of the ridge. Increase in bioproductivity and decrease in oxygen content are detected 0.9 kyr later above the central part of Shirshov Ridge than above the southern one. This delay might reflect a gradual sea ice retreat from station 77 KL to 85KL during the global warming and sea level rise. Moderate bottom-water oxygenation is suggested for the intermediate depths of 1 km whereas no changes in relative oxygen content are found at 2 km below sea level during the Younger Dryas. Concurrent decrease in bioproductivity is reconstructed from BF records from the core 85KL. However, presence of high-productivity species and elevated BF accumulation rates in the core 77KL point to higher organic matter flux to the sea floor in the southern part of the ridge at the end of Younger Dryas. For the Early Holocene, bioproductivity rise and oxygen depletion in the intermediate waters are inferred from BF data. Strong dominance of dysoxic group in the 85KL indicates that oxygen content at the intermediate depths was much lower during the Early Holocene than during the Bølling/Allerød. The results provide evidence for complex development of OMZ in the western Bering Sea during the Termination I. They also demonstrate high potential to extend such studies to the North Pacific realm.

Limnological and climatic environments at Upper Klamath Lake, Oregon during the past 45 000 years

USGS Publications Warehouse

Bradbury, J.P.; Colman, Steven M.; Dean, W.E.

2004-01-01

Upper Klamath Lake, in south-central Oregon, contains long sediment records with well-preserved diatoms and lithological variations that reflect climate-induced limnological changes. These sediment archives complement and extend high resolution terrestrial records along a north-south transect that includes areas influenced by the Aleutian Low and Subtropical High, which control both marine and continental climates in the western United States. The longest and oldest core collected in this study came from the southwest margin of the lake at Caledonia Marsh, and was dated by radiocarbon and tephrochronology to an age of about 45 ka. Paleolimnological interpretations of this core, based upon geochemical and diatom analyses, have been augmented by data from a short core collected from open water environments at nearby Howards Bay and from a 9-m core extending to 15 ka raised from the center of the northwestern part of Upper Klamath Lake. Pre- and full-glacial intervals of the Caledonia Marsh core are characterized and dominated by lithic detrital material. Planktic diatom taxa characteristic of cold-water habitats (Aulacoseira subarctica and A. islandica) alternate with warm-water planktic diatoms (A. ambigua) between 45 and 23 ka, documenting climate changes at millennial scales during oxygen isotope stage (OIS) 3. The full-glacial interval contains mostly cold-water planktic, benthic, and reworked Pliocene lacustrine diatoms (from the surrounding Yonna Formation) that document shallow water conditions in a cold, windy environment. After 15 ka, diatom productivity increased. Organic carbon and biogenic silica became significant sediment components and diatoms that live in the lake today, indicative of warm, eutrophic water, became prominent. Lake levels fell during the mid-Holocene and marsh environments extended over the core site. This interval is characterized by high levels of organic carbon from emergent aquatic vegetation (Scirpus) and by the Mazama ash (7.55 ka), generated by the eruption that created nearby Crater Lake. For a brief time the ash increased the salinity of Upper Klamath Lake. High concentrations of molybdenum, arsenic, and vanadium indicate that Caledonia Marsh was anoxic from about 7 to 5 ka. After the mid-Holocene, shallow, but open-water environments returned to the core site. The sediments became dominated (>80%) by biogenic silica. The open-water cores show analogous but less extreme limnological and climatic changes more typical of mid-lake environments. Millennial-scale lake and climate changes during OIS 3 at Upper Klamath Lake contrast with a similar record of variation at Owens Lake, about 750 km south. When Upper Klamath Lake experienced cold-climate episodes during OIS 3, Owens Lake had warm but wet episodes; the reverse occurred during warmer intervals at Upper Klamath Lake. Such climatic alternations apparently reflect the variable position and strength of the Aleutian Low during the mid-Wisconsin.

Late Pleistocene paleohydrology near the boundary of the Sonoran and Chihuahuan Deserts, southeastern Arizona, USA

USGS Publications Warehouse

Pigati, Jeffery S.; Bright, Jordon E.; Shanahan, Timothy M.; Mahan, Shannon

2009-01-01

Ground-water discharge (GWD) deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation. Where preserved, these deposits contain information on the timing and elevation of past ground-water fluctuations. Here we report on the investigation of a series of GWD deposits that are exposed in discontinuous outcrops along a ???150-km stretch of the San Pedro Valley in southeastern Arizona, near the boundary of the Sonoran and Chihuahuan Deserts. Chronologic, isotopic, geochemical, faunal assemblage (ostracodes and gastropods), and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate ???50 ka ago and remained relatively high for the next ???35 ka before falling during the B??lling-Aller??d warm period, rebounding briefly during the Younger Dryas cold event, and falling again at the onset of the Holocene. The timing of these hydrologic changes coincides closely with variations in ??18O values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial Lake Cochise to the east. Thus, in southeastern Arizona, the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated. The timing of these changes also broadly coincides with variations in the GISP2 ??18O record, which supports the hypothesis that atmospheric teleconnections existed between the North Atlantic and the deserts of the American Southwest during the late Pleistocene.

Late Quaternary high resolution micropaleontological and sedimentological records in the Gulf of Cadiz.

NASA Astrophysics Data System (ADS)

Balestra, B.; Ducassou, E.; Zarikian, C.; Bout-Roumazeilles, V.; Flores, J. A.; Paytan, A.

2017-12-01

We present preliminary micropaleontological and sedimentological data from IODP Site U1390 (Expedition 339), located in the central middle slope of the Gulf of Cadiz, since the last glaciation. This site has been targeted for reconstruction of regional paleo-circulation as it shows particularly high sedimentation rates, throughout the Holocene and the Last Glacial Maximum (LGM). We use micropaleontological and sedimentological proxies to understand the bottom current variations through time and the ecological conditions at the sea surface (planktonic foraminifer, pteropod and nannofossil assemblages), and the sea bottom (ostracod assemblages). Eleven samples, chosen at transitions of planktonic foraminifer assemblages, have been dated by AMS radiocarbon analyses. Preliminary results from benthic ostracod assemblages show variations in bottom water ventilation and food supply. Planktonic foraminifer assemblages clearly show the well-known cold events of this period such as the Younger Dryas and Heinrich stadial associated to coarser sediment, and warmer phases such as the Bölling-Allerød associated to muddy sediment. Other bio-events within the Holocene period are also recorded. The preservation of the coccolithophore assemblages is good to moderate. Coccolith abundances (expressed in coccoliths/gr of sediment) show higher values during the Holocene and generally are like assemblages previously reported for the same area. Implications for characterization of the Holocene, the last termination and LGM ecological conditions at high resolution and their potential fluctuations (i.e. amplitude and magnitude) under the influence of the lower core of the Mediterranean Outflow Water (MOW), with this multi proxy approach based on sedimentological, and paleontological data will be discussed.

New tree-ring evidence for the Late Glacial period from the northern pre-Alps in eastern Switzerland

NASA Astrophysics Data System (ADS)

Reinig, Frederick; Nievergelt, Daniel; Esper, Jan; Friedrich, Michael; Helle, Gerhard; Hellmann, Lena; Kromer, Bernd; Morganti, Sandro; Pauly, Maren; Sookdeo, Adam; Tegel, Willy; Treydte, Kerstin; Verstege, Anne; Wacker, Lukas; Büntgen, Ulf

2018-04-01

The rate and magnitude of temperature variability at the transition from the Last Glacial Maximum into the early Holocene represents a natural analog to current and predicted climate change. A limited number of high-resolution proxy archives, however, challenges our understanding of environmental conditions during this period. Here, we present combined dendrochronological and radiocarbon evidence from 253 newly discovered subfossil pine stumps from Zurich, Switzerland. The individual trees reveal ages of 41-506 years and were growing between the Allerød and Preboreal (∼13‧900-11‧300 cal BP). Together with previously collected pines from this region, this world's best preserved Late Glacial forest substantially improves the earliest part of the absolutely dated European tree-ring width chronology between 11‧300 and 11‧900 cal BP. Radiocarbon measurements from 65 Zurich pines between ∼12‧320 and 13‧950 cal BP provide a perspective to prolong the continuous European tree-ring record by another ∼2000 years into the Late Glacial era. These data will also be relevant for pinpointing the Laacher See volcanic eruption (∼12‧900 cal BP) and two major Alpine earthquakes (∼13‧770 and ∼11‧600 cal BP). In summary, this study emphasizes the importance of dating precision and multi-proxy comparison to disentangle environmental signals from methodological noise, particularly during periods of high climate variability but low data availability, such as the Younger Dryas cold spell (∼11‧700 and 12‧900 cal BP).

Wisconsinan and early Holocene glacial dynamics of Cumberland Peninsula, Baffin Island, Arctic Canada

NASA Astrophysics Data System (ADS)

Margreth, Annina; Gosse, John C.; Dyke, Arthur S.

2017-07-01

Three glacier systems-an ice sheet with a large marine-based ice stream, an ice cap, and an alpine glacier complex-coalesced on Cumberland Peninsula during the Late Wisconsinan. We combine high-resolution mapping of glacial deposits with new cosmogenic nuclide and radiocarbon age determinations to constrain the history and dynamics of each system. During the Middle Wisconsinan (Oxygen Isotope Stage 3, OIS-3) the Cumberland Sound Ice Stream of the Laurentide Ice Sheet retreated well back into Cumberland Sound and the alpine ice retreated at least to fiord-head positions, a more significant recession than previously documented. The advance to maximal OIS-2 ice positions beyond the mouth of Cumberland Sound and beyond most stretches of coastline remains undated. Partial preservation of an over-ridden OIS-3 glaciomarine delta in a fiord-side position suggests that even fiord ice was weakly erosive in places. Moraines formed during deglaciation represent stillstands and re-advances during three major cold events: H-1 (14.6 ka), Younger Dryas (12.9-11.7 ka), and Cockburn (9.5 ka). Distinctly different responses of the three glacial systems are evident, with the alpine system responding most sensitively to Bølling-Allerød warming whereas the larger systems retreated mainly during Pre-Boreal warming. While the larger ice masses were mainly influenced by internal dynamics, the smaller alpine glacier system responded sensitively to local climate effects. Asymmetrical recession of the alpine glacier complex indicates topoclimatic control on deglaciation and perhaps migration of the accumulation area toward moisture source.

The chronology of Late Pleistocene thermal contraction cracking derived from sand wedge OSL dating in central and southern France

NASA Astrophysics Data System (ADS)

Andrieux, Eric; Bateman, Mark D.; Bertran, Pascal

2018-03-01

Much of France remained unglaciated during the Late Quaternary and was subjected to repeated phases of periglacial activity. Numerous periglacial features have been reported but disentangling the environmental and climatic conditions they formed under, the timing and extent of permafrost and the role of seasonal frost has remained elusive. The primary sandy infillings of relict sand-wedges and composite-wedge pseudomorphs record periglacial activity. As they contain well-bleached quartz-rich aeolian material they are suitable for optically stimulated luminescence dating (OSL). This study aims to reconstruct when wedge activity took place in two regions of France; Northern Aquitaine and in the Loire valley. Results from single-grain OSL measurements identify multiple phases of activity within sand wedges which suggest that wedge activity in France occurred at least 11 times over the last 100 ka. The most widespread events of thermal contraction cracking occurred between ca. 30 and 24 ka (Last Permafrost Maximum) which are concomitant with periods of high sand availability (MIS 2). Although most phases of sand-wedge growth correlate well with known Pleistocene cold periods, the identification of wedge activity during late MIS 5 and the Younger Dryas strongly suggests that these features do not only indicate permafrost but also deep seasonal ground freezing in the context of low winter insolation. These data also suggest that the overall young ages yielded by North-European sand-wedges likely result from poor record of periglacial periods concomitant with low sand availability and/or age averaging inherent with standard luminescence methods.

Frequent alcohol drinking is associated with lower prevalence of self-reported common cold: a retrospective study.

PubMed

Ouchi, Eriko; Niu, Kaijun; Kobayashi, Yoritoshi; Guan, Lei; Momma, Haruki; Guo, Hui; Chujo, Masahiko; Otomo, Atsushi; Cui, Yufei; Nagatomi, Ryoichi

2012-11-16

Alcohol intake has been associated with reduced incidence of common cold symptoms in 2 European studies. However, no study has addressed the association between the frequency of alcohol intake and the incidence of common cold. This study aimed to investigate the association between the amount and frequency of alcohol drinking and the retrospective prevalence of common cold in Japanese men. This retrospective study included men who participated in an annual health examination conducted in Sendai, Japan. The frequency of common cold episodes in the previous year was self-reported. The weekly frequency and amount of alcohol consumed, as well as the type of alcoholic drink, were reported by a brief-type self-administered diet history questionnaire. Logistic regression models were used to analyze the association between the amount and frequency of alcohol intake and the retrospective prevalence of common cold. Among 899 men, 83.4% of the subjects reported drinking alcohol, and 55.4% of the subjects reported having experienced at least one episode of common cold in the previous year. Compared with non-drinkers, the adjusted odds ratios (ORs) with 95% confidence intervals (CIs) for having had 1 or more episodes of common cold during the past year across categories of alcohol intake frequency of 3 or less, 4-6, and 7 days/week were 0.827 (0.541-1.266), 0.703 (0.439-1.124), and 0.621 (0.400-0.965), respectively (P for trend = 0.025); the adjusted ORs with 95% CIs for having had of 2 or more episodes of common cold across the same categories were 0.642 (0.395-1.045), 0.557 (0.319-0.973), and 0.461 (0.270-0.787), respectively (P for trend = 0.006). Compared with subjects who consumed 11.5-35.8 g of alcohol per day, the non-drinkers were significantly more likely to experience 2 or more episodes of common cold (OR, 1.843; 95% CI, 1.115-3.047). The frequency, not the amount, of alcohol intake was significantly related to lower prevalence of self-reported common cold episodes in Japanese men.

Heated, humidified air for the common cold.

PubMed

Singh, Meenu; Singh, Manvi

2011-05-11

Heated, humidified air has long been used by sufferers of the common cold. The theoretical basis is that steam may help congested mucus drain better and heat may destroy the cold virus as it does in vitro. To assess the effects of inhaling heated water vapour (steam) in the treatment of the common cold by comparing symptoms, viral shedding and nasal resistance. In this updated review we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 3), which contains the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to July Week 1, 2010), EMBASE (1990 to July 2010) and Current Contents (1994 to July 2010). Randomised controlled trials (RCTs) using heated water vapour in participants with the common cold or participants with experimentally-induced common cold. We reviewed all retrieved articles and excluded any articles, editorials and abstracts with inadequate outcome descriptions. The studies we included were subjected to a methodological assessment. Six trials (394 trial participants) were included. Three trials in which patient data could be pooled found benefits of steam for symptom relief for the common cold (odds ratio (OR) 0.31; 95% confidence interval (CI) 0.16 to 0.60). However, results on symptom indices were equivocal. No studies demonstrated an exacerbation of clinical symptom scores. One study conducted in the USA demonstrated worsened nasal resistance, while an earlier Israeli study showed improvement. One study examined viral shedding and antibody titres in nasal washings; there was no change in either between treatment and placebo groups. Minor side effects (including discomfort or irritation of the nose) were reported in some studies. Steam inhalation has not shown any consistent benefits in the treatment of the common cold, hence is not recommended in the routine treatment of common cold symptoms until more double-blind, randomized trials with a standardised treatment modality are conducted.

Behaviorally Assessed Sleep and Susceptibility to the Common Cold

PubMed Central

Prather, Aric A.; Janicki-Deverts, Denise; Hall, Martica H.; Cohen, Sheldon

2015-01-01

Study Objectives: Short sleep duration and poor sleep continuity have been implicated in the susceptibility to infectious illness. However, prior research has relied on subjective measures of sleep, which are subject to recall bias. The aim of this study was to determine whether sleep, measured behaviorally using wrist actigraphy, predicted cold incidence following experimental viral exposure. Design, Measurements, and Results: A total of 164 healthy men and women (age range, 18 to 55 y) volunteered for this study. Wrist actigraphy and sleep diaries assessed sleep duration and sleep continuity over 7 consecutive days. Participants were then quarantined and administered nasal drops containing the rhinovirus, and monitored over 5 days for the development of a clinical cold (defined by infection in the presence of objective signs of illness). Logistic regression analysis revealed that actigraphy- assessed shorter sleep duration was associated with an increased likelihood of development of a clinical cold. Specifically, those sleeping < 5 h (odds ratio [OR] = 4.50, 95% confidence interval [CI], 1.08–18.69) or sleeping between 5 to 6 h (OR = 4.24, 95% CI, 1.08–16.71) were at greater risk of developing the cold compared to those sleeping > 7 h per night; those sleeping 6.01 to 7 h were at no greater risk (OR = 1.66; 95% CI 0.40–6.95). This association was independent of prechallenge antibody levels, demographics, season of the year, body mass index, psychological variables, and health practices. Sleep fragmentation was unrelated to cold susceptibility. Other sleep variables obtained using diary and actigraphy were not strong predictors of cold susceptibility. Conclusions: Shorter sleep duration, measured behaviorally using actigraphy prior to viral exposure, was associated with increased susceptibility to the common cold. Citation: Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally assessed sleep and susceptibility to the common cold. SLEEP 2015;38(9):1353–1359. PMID:26118561

A large drop in atmospheric [sup 14]C/[sup 12]C and reduced melting in the younger dryas, documented with [sup 230]Th ages of corals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edwards, R.L.; Beck, J.W.; Burr, G.S.

1993-05-14

Paired carbon-14 ([sup 14]C) and thorium-230 ([sup 230]Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the [sup 14]C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the [sup 14]C and [sup 230]Th ages suggests that the atmospheric [sup 14]C/[sup 12]C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YDmore » may have caused an increase in the rate of ocean ventilation, which caused the atmospheric [sup 14]C/[sup 12]C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event. 41 refs., 5 figs., 1 tab.« less

Bottom-water oxygenation and environmental change in Santa Monica Basin, southern California during the last 22 kyr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balestra, Barbara; Krupinksi, Nadine Quintana; Erhoina, Tzvetina

The Southern California Borderland (SCB) is a region that experiences strong natural variations in bottom water oxygen and pH. Here, we use marine sediments from the Santa Monica Basin (SMB) to reconstruct environmental conditions and changes in the basin's bottom water oxygenation from the Last Glacial Maximum (LGM) to present, and compare the records to the adjacent Santa Barbara Basin (SBB) and Santa Lucia Slope (SLS). High-resolution records of benthic foraminiferal oxygen and carbon isotopes (δ 18O and δ 13C), benthic foraminiferal assemblages, and bulk sedimentary organic matter geochemistry records exhibit major changes associated with late Quaternary millennial-scale global climatemore » oscillations. Our data show the dominance of low-oxygen benthic foraminifera assemblages during warm intervals, and assemblages representing higher dissolved oxygen during cooler intervals, as also seen in SBB and SLS. But, our record shows a stronger and longer-lasting oxygen minimum zone (OMZ) between the end of the Bølling-Allerød (B-A) and the Early Holocene (including the Younger Dryas) than at neighboring sites, indicated by dominance of Bolivina tumida (characteristic of major hypoxia) in the assemblage. The middle to late Holocene (from ~ 8.8 to 0 ka) had weaker hypoxia than the early Holocene, with assemblages mainly composed of Bolivina argentea and Uvigerina peregrina. The SMB remains mostly slightly low in oxygen throughout the studied interval, with differences in the degree of hypoxia relative to SBB and SLS (especially from the B-A to the Early Holocene) likely due to its greater depth and its more southern geographic position and therefore decreased exposure to North Pacific Intermediate Water current. Regional effects, such as changing intermediate water source and/or changing ventilation (oxygenation) of the intermediate water source, also affect SMB deep water. Our analysis utilizing parallel geochemical and micropaleontological records brings new insights into bottom water and climate conditions in SMB, indicating regional similarities and differences with adjacent basins, and provides insight into the causes for changes in bottom water oxygenation.« less

Bottom-water oxygenation and environmental change in Santa Monica Basin, southern California during the last 22 kyr

DOE PAGES

Balestra, Barbara; Krupinksi, Nadine Quintana; Erhoina, Tzvetina; ...

2017-09-29

The Southern California Borderland (SCB) is a region that experiences strong natural variations in bottom water oxygen and pH. Here, we use marine sediments from the Santa Monica Basin (SMB) to reconstruct environmental conditions and changes in the basin's bottom water oxygenation from the Last Glacial Maximum (LGM) to present, and compare the records to the adjacent Santa Barbara Basin (SBB) and Santa Lucia Slope (SLS). High-resolution records of benthic foraminiferal oxygen and carbon isotopes (δ 18O and δ 13C), benthic foraminiferal assemblages, and bulk sedimentary organic matter geochemistry records exhibit major changes associated with late Quaternary millennial-scale global climatemore » oscillations. Our data show the dominance of low-oxygen benthic foraminifera assemblages during warm intervals, and assemblages representing higher dissolved oxygen during cooler intervals, as also seen in SBB and SLS. But, our record shows a stronger and longer-lasting oxygen minimum zone (OMZ) between the end of the Bølling-Allerød (B-A) and the Early Holocene (including the Younger Dryas) than at neighboring sites, indicated by dominance of Bolivina tumida (characteristic of major hypoxia) in the assemblage. The middle to late Holocene (from ~ 8.8 to 0 ka) had weaker hypoxia than the early Holocene, with assemblages mainly composed of Bolivina argentea and Uvigerina peregrina. The SMB remains mostly slightly low in oxygen throughout the studied interval, with differences in the degree of hypoxia relative to SBB and SLS (especially from the B-A to the Early Holocene) likely due to its greater depth and its more southern geographic position and therefore decreased exposure to North Pacific Intermediate Water current. Regional effects, such as changing intermediate water source and/or changing ventilation (oxygenation) of the intermediate water source, also affect SMB deep water. Our analysis utilizing parallel geochemical and micropaleontological records brings new insights into bottom water and climate conditions in SMB, indicating regional similarities and differences with adjacent basins, and provides insight into the causes for changes in bottom water oxygenation.« less

Susceptibility of different life stage of Tribolium confusum and Oryzaephilus surinamensis to cold treatment

USDA-ARS?s Scientific Manuscript database

Laboratory tests were carried out to examine the efficacy of different exposure intervals (2 h, 4 h, 8 h, 1 d, 2 d, 3 d and 7 d) on different life stages (adults, pupae, larvae, eggs) of Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), the confused flour beetle, and O. surinamensis (...

Glaciation in the Andes during the Lateglacial and Holocene

NASA Astrophysics Data System (ADS)

Rodbell, Donald T.; Smith, Jacqueline A.; Mark, Bryan G.

2009-10-01

This review updates the chronology of Andean glaciation during the Lateglacial and the Holocene from the numerous articles and reviews published over the past three decades. The Andes, which include some of the world's wettest and driest mountainous regions, offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68-degree meridional transect. The geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad-scale atmospheric circulation and consequent regional moisture patterns. Glaciers in the tropical Andes and in the mid-latitude Andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical Andes. Broad-scale temporal and spatial patterns of glaciation during the Lateglacial are apparent. In the southernmost Andes, the Lateglacial chronology appears to have a strong Antarctic signature with the best-dated moraines correlating closely with the Antarctic Cold Reversal. The southernmost Andes do not appear to have experienced a significant ice advance coeval with the Younger Dryas (YD) climatic reversal. At the other end of the Andes, from ˜0 to 9°N, a stronger YD connection may exist, but critical stratigraphic and geochronologic work is required before a YD ice advance can be fully demonstrated. In the central Andes of Peru, well-dated moraines record a significant ice readvance at the onset of the YD, but ice was retreating during much of the remaining YD interval. The spatial-temporal pattern of Holocene glaciation exhibits tantalizing but incomplete evidence for an Early to Mid-Holocene ice advance(s) in many regions, but not in the arid subtropical Andes, where moraines deposited during or slightly prior to the Little Ice Age (LIA) record the most extensive advance of the Holocene. In many regions, there is strong evidence for Neoglacial advances in the interval between 1.0 and 2.5 ka. Moraines that correlate with the LIA of the Northern Hemisphere are seen in all presently glacierized mountain ranges; most of these date to within the past 450 years. Outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the LIA. Priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies. For the Lateglacial these gaps include the arid regions of northern Chile and Argentina, the southern Peruvian Andes between 11.5°and 13.5°S, and the Andes of northern Peru and southern Ecuador between 3° and 9°S. Areas in need of better representation in regional datasets of Holocene glaciation include all of the Andes north of the Equator. Specific chronologic priorities include the need for close bracketing radiocarbon ages for purported Early and Mid-Holocene moraines, and the increased application of cosmogenic radionuclide dating to Lateglacial and Early Holocene moraines that are already constrained by maximum-limiting radiocarbon ages.

Differences between the most used equations in BAT-human studies to estimate parameters of skin temperature in young lean men.

PubMed

Martinez-Tellez, Borja; Sanchez-Delgado, Guillermo; Acosta, Francisco M; Alcantara, Juan M A; Boon, Mariëtte R; Rensen, Patrick C N; Ruiz, Jonatan R

2017-09-05

Cold exposure is necessary to activate human brown adipose tissue (BAT), resulting in heat production. Skin temperature is an indirect measure to monitor the body's reaction to cold. The aim of this research was to study whether the most used equations to estimate parameters of skin temperature in BAT-human studies measure the same values of temperature in young lean men (n = 11: 23.4 ± 0.5 years, fat mass: 19.9 ± 1.2%). Skin temperature was measured with 26 ibuttons at 1-minute intervals in warm and cold room conditions. We used 12 equations to estimate parameters of mean, proximal, and distal skin temperature as well as skin temperature gradients. Data were analysed with Temperatus software. Significant differences were found across equations to measure the same parameters of skin temperature in warm and cold room conditions, hampering comparison across studies. Based on these findings, we suggest to use a set of 14 ibuttons at anatomical positions reported by ISO STANDARD 9886:2004 plus five ibuttons placed on the right supraclavicular fossa, right middle clavicular bone, right middle upper forearm, right top of forefinger, and right upper chest.

5000 Meter Run Performance is not Enhanced 24 Hrs After an Intense Exercise Bout and Cold Water Immersion.

PubMed

Stenson, Mary C; Stenson, Matthew R; Matthews, Tracey D; Paolone, Vincent J

2017-06-01

Cold water immersion (CWI) is used by endurance athletes to speed recovery between exercise bouts, but little evidence is available on the effects of CWI on subsequent endurance performance. The purpose of this study was to investigate the effects of CWI following an acute bout of interval training on 5000 m run performance 24 hrs after interval training, perceived muscle soreness (PMS), range of motion (ROM), thigh circumference (TC), and perceived exertion (RPE). Nine endurance-trained males completed 2 trials, each consisting of an interval training session of 8 repetitions of 1200 m at a running pace equal to 75% of VO 2 peak, either a control or CWI treatment, and a timed 5000 m run 24 hrs post interval training session. CWI was performed for 12 min at 12 degrees Celsius on the legs. Recovery treatments were performed in a counterbalanced design. Run time for 5000 m was not different between the CWI and control trials (CWI = 1317.33 ± 128.33 sec, control = 1303.44 ± 105.53 sec; p = 0.48). PMS increased significantly from baseline to immediately post exercise (BL = 1.17 ± 0.22, POST = 2.81 ± 0.52; p = 0.02) and remained elevated from baseline to 24 hrs post exercise (POST24 = 2.19 ± 0.32; p = 0.02), but no difference was observed between the treatments. No differences were observed for the interaction between time and treatment for TC (λ = 0.73, p = 0.15) and ROM (λ = 0.49; p = 0.10). CWI performed immediately following an interval training exercise bout did not enhance subsequent 5000 m run performance or reduce PMS. CWI may not provide a recovery or performance advantage when athletes are accustomed to the demands of the prior exercise bout.

Socioenvironmental factors associated with heat and cold-related mortality in Vadu HDSS, western India: a population-based case-crossover study

NASA Astrophysics Data System (ADS)

Ingole, Vijendra; Kovats, Sari; Schumann, Barbara; Hajat, Shakoor; Rocklöv, Joacim; Juvekar, Sanjay; Armstrong, Ben

2017-10-01

Ambient temperatures (heat and cold) are associated with mortality, but limited research is available about groups most vulnerable to these effects in rural populations. We estimated the effects of heat and cold on daily mortality among different sociodemographic groups in the Vadu HDSS area, western India. We studied all deaths in the Vadu HDSS area during 2004-2013. A conditional logistic regression model in a case-crossover design was used. Separate analyses were carried out for summer and winter season. Odds ratios (OR) and 95% confidence intervals (CI) were estimated for total mortality and population subgroups. Temperature above a threshold of 31 °C was associated with total mortality (OR 1.48, CI = 1.05-2.09) per 1 °C increase in daily mean temperature. Odds ratios were higher among females (OR 1.93; CI = 1.07-3.47), those with low education (OR 1.65; CI = 1.00-2.75), those owing larger agricultural land (OR 2.18; CI = 0.99-4.79), and farmers (OR 1.70; CI = 1.02-2.81). In winter, per 1 °C decrease in mean temperature, OR for total mortality was 1.06 (CI = 1.00-1.12) in lag 0-13 days. High risk of cold-related mortality was observed among people occupied in housework (OR = 1.09; CI = 1.00-1.19). Our study suggests that both heat and cold have an impact on mortality particularly heat, but also, to a smaller degree, cold have an impact. The effects may differ partly by sex, education, and occupation. These findings might have important policy implications in preventing heat and cold effects on particularly vulnerable groups of the rural populations in low and middle-income countries with hot semi-arid climate.

The effect of exercise on prevention of the common cold: a meta-analysis of randomized controlled trial studies.

PubMed

Lee, Hyun Kun; Hwang, In Hong; Kim, Soo Young; Pyo, Se Young

2014-05-01

Because there is no specific treatment for the common cold, many previous studies have focused on prevention of the common cold. There were some studies reporting that regular, moderate-intensity exercise increases immunity and prevents the common cold. We conducted a meta-analysis to determine the effects of exercise on prevention of the common cold. We searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL for studies released through June 2013. We manually searched the references. Two authors independently extracted the data. To assess the risk of bias of included literature, Cochrane Collaboration's tool for assessing risk of bias was used. Review Manager ver. 5.2 (RevMan, Cochrane Collaboration) was used for statistical analysis. Four randomized controlled trials were identified. A total of 281 participants, 134 in the exercise group and 147 in the control group, were included. The effect of exercise on the prevention of the common cold had a relative risk (RR) of 0.73 (95% confidence interval [CI], 0.56 to 0.95; I(2) = 7%). The mean difference of mean illness days between exercise group and control group was -3.50 (95% CI, -6.06 to -0.94; I(2) = 93%). In the subgroup analysis, the RR of under 16 weeks exercise was 0.79 (95% CI, 0.58 to 1.08). In this meta-analysis, regular, moderate-intensity exercise may have an effect on the prevention of the common cold. But numbers of included studies and participants were too small and quality of included studies was relatively poor. Subsequent well-designed studies with larger sample size are needed to clarify the association.

Effect of cold compress application on tissue temperature in healthy dogs.

PubMed

Millard, Ralph P; Towle-Millard, Heather A; Rankin, David C; Roush, James K

2013-03-01

To measure the effect of cold compress application on tissue temperature in healthy dogs. 10 healthy mixed-breed dogs. Dogs were sedated with hydromorphone (0.1 mg/kg, IV) and diazepam (0.25 mg/kg, IV). Three 24-gauge thermocouple needles were inserted to a depth of 0.5 (superficial), 1.0 (middle), and 1.5 (deep) cm into a shaved, lumbar, epaxial region to measure tissue temperature. Cold (-16.8°C) compresses were applied with gravity dependence for periods of 5, 10, and 20 minutes. Tissue temperature was recorded before compress application and at intervals for up to 80 minutes after application. Control data were collected while dogs received identical sedation but with no cold compress. Mean temperature associated with 5 minutes of application at the superficial depth was significantly decreased, compared with control temperatures. Application for 10 and 20 minutes significantly reduced the temperature at all depths, compared with controls and 5 minutes of application. Twenty minutes of application significantly decreased temperature at only the middle depth, compared with 10 minutes of application. With this method of cold treatment, increasing application time from 10 to 20 minutes caused a further significant temperature change at only the middle tissue depth; however, for maximal cooling, the minimum time of application should be 20 minutes. Possible changes in tissue temperature and adverse effects of application > 20 minutes require further evaluation.

Vaccines for the common cold.

PubMed

Simancas-Racines, Daniel; Guerra, Claudia V; Hidalgo, Ricardo

2013-06-12

The common cold is a spontaneously remitting infection of the upper respiratory tract, characterised by a runny nose, nasal congestion, sneezing, cough, malaise, sore throat and fever (usually < 37.8˚C). The widespread morbidity it causes worldwide is related to its ubiquitousness rather than its severity. The development of vaccines for the common cold has been difficult because of antigenic variability of the common cold virus and the indistinguishable multiple other viruses and even bacteria acting as infective agents. There is uncertainty regarding the efficacy and safety of interventions for preventing the common cold in healthy people. To assess the clinical effectiveness and safety of vaccines for preventing the common cold in healthy people. We searched CENTRAL (2012, Issue 12), MEDLINE (1948 to January week 1, 2013), EMBASE (1974 to January 2013), CINAHL (1981 to January 2013) and LILACS (1982 to January 2013). Randomised controlled trials (RCTs) of any virus vaccines to prevent the common cold in healthy people. Two review authors independently evaluated methodological quality and extracted trial data. Disagreements were resolved by discussion or by consulting a third review author. This review included one RCT with 2307 healthy participants; all of them were analysed. This trial compared the effect of an adenovirus vaccine against a placebo. No statistically significant difference in common cold incidence was found: there were 13 events in 1139 participants in the vaccines group and 14 events in 1168 participants in the placebo group; risk ratio (RR) 0.95, 95% confidence interval (CI) 0.45 to 2.02, P = 0.90). No adverse events related to the live vaccine were reported. This Cochrane review has found a lack of evidence on the effects of vaccines for the common cold in healthy people. Only one RCT was found and this did not show differences between comparison groups; it also had a high risk of bias. There are no conclusive data to support the use of vaccines for preventing the common cold in healthy people. We identified the need for well-designed, adequately powered RCTs to investigate vaccines for the common cold in healthy people. Unless RCTs provide evidence of a treatment effect and the trade-off between potential benefits and harms is established, policy-makers, clinicians and academics should not recommend the use of vaccines for preventing the common cold in healthy people. Any future trials on medical treatments for preventing the common cold should assess a variety of virus vaccines for this condition. Outcome measures should include common cold incidence, vaccine safety and mortality related to the vaccine.

High-frequency rock temperature data from hyper-arid desert environments in the Atacama and the Antarctic Dry Valleys and implications for rock weathering

NASA Astrophysics Data System (ADS)

McKay, Christopher P.; Molaro, Jamie L.; Marinova, Margarita M.

2009-09-01

In desert environments with low water and salt contents, rapid thermal variations may be an important source of rock weathering. We have obtained temperature measurements of the surface of rocks in hyper-arid hot and cold desert environments at a rate of 1/s over several days. The values of temperature change over 1-second intervals were similar in hot and cold deserts despite a 30 °C difference in absolute rock surface temperature. The average percentage of the time dT/dt > 2 °C/min was ~ 8 ± 3%, > 4 °C/min was 1 ± 0.9%, and > 8 °C/min was 0.02 ± 0.03%. The maximum change over a 1-second interval was ~ 10 °C/min. When sampled to simulate data taken over intervals longer than 1 s, we found a reduction in time spent above the 2 °C/min temperature gradient threshold. For 1-minute samples, the time spent above any given threshold was about two orders of magnitude lower than the corresponding value for 1-second sampling. We suggest that a rough measure of efficacy of weathering as a function of frequency is the product of the percentage of time spent above a given threshold value multiplied by the damping depth for the corresponding frequency. This product has a broad maximum for periods between 3 and 10 s.

Abrupt intensification of the SW Indian Ocean monsoon during the last deglaciation: constraints from Th, Pa, and He isotopes

NASA Astrophysics Data System (ADS)

Marcantonio, Franco; Anderson, Robert F.; Higgins, Sean; Fleisher, Martin Q.; Stute, Martin; Schlosser, Peter

2001-01-01

Sediments from western Arabian Sea core 74KL representing the last 23 ka were analyzed for helium, thorium, and protactinium isotopes. Assuming global average fluxes of extraterrestrial 3He and 230Th, the average 3He-derived sediment mass accumulation rate (MAR) is a factor of 1.8 higher than the average 230Th-derived MAR. 3He- and 230Th-derived MARs converge, however, during the Younger Dryas (YD) and during the peak of the early Holocene humid interval. These features, not seen anywhere else in the world, probably reflect a combination of climate-driven changes in the flux of 230Th and 3He. Ratios of xs 231Pa/xs 230Th, proxies of paleoproductivity, are lowest during the last glacial maximum (LGM), and increase abruptly during the Bolling-Allerod. Later, following a sudden decrease to near-LGM values during the YD, they rise abruptly to maximum values for the entire record in the early Holocene. We hypothesize that low xs 231Pa/xs 230Th ratios reflect low productivity due to the decreased intensity of the SW monsoon, whereas the opposite is true for high ratios. The correlation between Arabian Sea productivity and monsoonal upwelling, on the one hand, and North Atlantic climate variability, on the other, suggests a linkage between high- and low-latitude climates caused by changing patterns of atmospheric circulation.

Variability of Indonesian Throughflow and Borneo Runoff During the Last 14 kyr

NASA Astrophysics Data System (ADS)

Hendrizan, Marfasran; Kuhnt, Wolfgang; Holbourn, Ann

2017-10-01

We present a high-resolution ( 20 to 100 years temporal resolution) reconstruction of hydrological changes in the Makassar Strait over the last 14 kyr from Core SO217-18517 retrieved off the Mahakam Delta (1°32.198'S, 117°33.756'E; 698 m water depth) during the SO217 Makassar-Java Cruise. Sea surface temperatures, based on Mg/Ca of Globigerinoides ruber and alkenone UK'37, and seawater δ18O reconstructions, based on G. ruber δ18O and Mg/Ca, in combination with sortable silt grain size measurements and X-ray fluorescence (XRF) core scanner derived elemental data provide evidence for increased precipitation during the Bølling-Allerød (BA) and early Holocene and for warmer and more saline surface waters and a decrease in the intensity of the Indonesian Throughflow (ITF) during the Younger Dryas (YD). XRF derived Log (Zr/Rb) records, sortable silt data and increased sedimentation rates indicate decreased winnowing, interpreted as a slowdown of the ITF thermocline flow during the YD. We attribute this decline in ITF intensity to slowdown of the Atlantic meridional overturning circulation during the YD. We suggest that changes in Makassar Strait surface hydrology during this interval of Northern Hemisphere cooling and Southern Hemisphere warming were related to a southward displacement of the Intertropical Convergence Zone.

The Southern Ocean as a driver of centennial to millenial timescale radiocarbon variations

NASA Astrophysics Data System (ADS)

Rodgers, K. B.; Bianchi, D.; Galbraith, E.; Gnanadesikan, A.; Iudicone, D.; Mikaloff Fletcher, S.; Sarmiento, J. L.; Slater, R. D.

2009-04-01

Paleo-proxy records reveal large delta-c14 variations for both the atmosphere and the ocean on centennial to millenial timescales. One of the most pronounced examples is the onset phase of the Younger Dryas, when atmospheric delta-c14 rose by 70 per mil in only 200 years. Another is the most recent deglaciation (and the associated "Mystery Interval"). Many of the significant centennial to millenial transients in atmospheric delta-c14 are reflected in ocean interior delta-c14 at intermediate depths in the Pacific over the last 50kyrs. An ocean model has been used to test the idea that only modest perturbations to Southern Ocean winds provides a means to link the oceanic and atmospheric delta-c14 variations. Perturbations to the winds over the Southern Ocean are able to drive sizable decoupling of the fluxes of 14CO2 and 12CO2 over the Southern Ocean, thus modifying atmospheric delta-c14. These same perturbations are able to perturb rapidly the depth of intermediate water horizons in the North Pacific through the passage of baroclinic planetary (Rossby) waves. This sensitivity is significantly stronger than what previous studies have found for perturbations to the Meridional Overturning Circulation (MOC) in the North Atlantic. It is suggested that delta-c14 may provide a powerful tracer for understanding past variations in the climate system.

A 60,000-year record of hydrologic variability in the Central Andes from the hydrogen isotopic composition of leaf waxes in Lake Titicaca sediments

NASA Astrophysics Data System (ADS)

Fornace, Kyrstin L.; Hughen, Konrad A.; Shanahan, Timothy M.; Fritz, Sherilyn C.; Baker, Paul A.; Sylva, Sean P.

2014-12-01

A record of the hydrogen isotopic composition of terrestrial leaf waxes (δDwax) in sediment cores from Lake Titicaca provides new insight into the precipitation history of the Central Andes and controls of South American Summer Monsoon (SASM) variability since the last glacial period. Comparison of the δDwax record with a 19-kyr δD record from the nearby Illimani ice core supports the interpretation that precipitation δD is the primary control on δDwax with a lesser but significant role for local evapotranspiration and other secondary influences on δDwax. The Titicaca δDwax record confirms overall wetter conditions in the Central Andes during the last glacial period relative to a drier Holocene. During the last deglaciation, abrupt δDwax shifts correspond to millennial-scale events observed in the high-latitude North Atlantic, with dry conditions corresponding to the Bølling-Allerød and early Holocene periods and wetter conditions during late glacial and Younger Dryas intervals. We observe a trend of increasing monsoonal precipitation from the early to the late Holocene, consistent with summer insolation forcing of the SASM, but similar hydrologic variability on precessional timescales is not apparent during the last glacial period. Overall, this study demonstrates the relative importance of high-latitude versus tropical forcing as a dominant control on glacial SASM precipitation variability.

Achieving the classical Carnot efficiency in a strongly coupled quantum heat engine

NASA Astrophysics Data System (ADS)

Xu, Y. Y.; Chen, B.; Liu, J.

2018-02-01

Generally, the efficiency of a heat engine strongly coupled with a heat bath is less than the classical Carnot efficiency. Through a model-independent method, we show that the classical Carnot efficiency is achieved in a strongly coupled quantum heat engine. First, we present the first law of quantum thermodynamics in strong coupling. Then, we show how to achieve the Carnot cycle and the classical Carnot efficiency at strong coupling. We find that this classical Carnot efficiency stems from the fact that the heat released in a nonequilibrium process is balanced by the absorbed heat. We also analyze the restrictions in the achievement of the Carnot cycle. The first restriction is that there must be two corresponding intervals of the controllable parameter in which the corresponding entropies of the work substance at the hot and cold temperatures are equal, and the second is that the entropy of the initial and final states in a nonequilibrium process must be equal. Through these restrictions, we obtain the positive work conditions, including the usual one in which the hot temperature should be higher than the cold, and a new one in which there must be an entropy interval at the hot temperature overlapping that at the cold. We demonstrate our result through a paradigmatic model—a two-level system in which a work substance strongly interacts with a heat bath. In this model, we find that the efficiency may abruptly decrease to zero due to the first restriction, and that the second restriction results in the control scheme becoming complex.

Achieving the classical Carnot efficiency in a strongly coupled quantum heat engine.

PubMed

Xu, Y Y; Chen, B; Liu, J

2018-02-01

Generally, the efficiency of a heat engine strongly coupled with a heat bath is less than the classical Carnot efficiency. Through a model-independent method, we show that the classical Carnot efficiency is achieved in a strongly coupled quantum heat engine. First, we present the first law of quantum thermodynamics in strong coupling. Then, we show how to achieve the Carnot cycle and the classical Carnot efficiency at strong coupling. We find that this classical Carnot efficiency stems from the fact that the heat released in a nonequilibrium process is balanced by the absorbed heat. We also analyze the restrictions in the achievement of the Carnot cycle. The first restriction is that there must be two corresponding intervals of the controllable parameter in which the corresponding entropies of the work substance at the hot and cold temperatures are equal, and the second is that the entropy of the initial and final states in a nonequilibrium process must be equal. Through these restrictions, we obtain the positive work conditions, including the usual one in which the hot temperature should be higher than the cold, and a new one in which there must be an entropy interval at the hot temperature overlapping that at the cold. We demonstrate our result through a paradigmatic model-a two-level system in which a work substance strongly interacts with a heat bath. In this model, we find that the efficiency may abruptly decrease to zero due to the first restriction, and that the second restriction results in the control scheme becoming complex.

Associations between mental disorders and the common cold in adults: a population-based cross-sectional study.

PubMed

Adam, Yuki; Meinlschmidt, Gunther; Lieb, Roselind

2013-01-01

To investigate the association between specific mental disorders and the common cold. Negative binomial regression analyses were applied to examine cross-sectional associations of a broad range of mental disorders according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) employing the standardized Munich Composite International Diagnostic Interview, with the self-reported number of occurrences of the common cold during the past 12 months in a representative population sample of 4022 German adults aged 18-65 years. After adjustment for covariates including age, gender, and marital and socioeconomic status, having any 12-month DSM-IV mental disorder (incidence rate ratio [IRR]=1.44, 95% confidence interval [CI]=1.29-1.60), any substance abuse or dependence (IRR=1.32, 95% CI=1.14-1.52), possible psychotic disorder (IRR=1.43, 95% CI=1.09-1.87), any mood disorder (IRR=1.35, 95% CI=1.16-1.56), any anxiety disorder (IRR=1.40, 95% CI=1.23-1.59), or any somatoform disorder (IRR=1.38, 95% CI=1.18-1.62) was shown to be positively associated with the number of occurrences of a cold during the past 12 months. The presence of a DSM-IV mental disorder was associated with a 44% higher risk of having experienced a cold in the past 12 months. Further studies are needed to explore potential common risk factors for incidence of mental disorders and the common cold, since the pathway connecting them has not been fully determined. Copyright © 2012 Elsevier Inc. All rights reserved.

Temperature-related mortality in 17 large Chinese cities: how heat and cold affect mortality in China.

PubMed

Ma, Wenjuan; Chen, Renjie; Kan, Haidong

2014-10-01

Few multicity studies have been conducted to investigate the acute health effects of cold and hot temperatures in China. We aimed to examine the relationship between temperature and daily mortality in 17 large Chinese cities. We first calculated city-specific effect of temperature using time-series regression models combined with distributed lag nonlinear models; then we pooled the city-specific estimates with the Bayesian hierarchical models. The cold effects lasted longer than the hot effects. For the cold effects, a 1 °C decrease from the 25th to 1st percentiles of temperature over lags 0-14 days was associated with increases of 1.69% [95% posterior intervals (PI): 1.01%, 2.36%], 2.49% (95% PI: 1.53%, 3.46%) and 1.60% (95% PI: 0.32%, 2.87%) in total, cardiovascular and respiratory mortality, respectively. For the hot effects, a 1 °C increase from the 75th to 99th percentiles of temperature was associated with corresponding increases of 2.83% (95% PI: 1.42%, 4.24%), 3.02% (95% PI: 1.33%, 4.71%) and 4.64% (95% PI: 1.96%, 7.31%). The latitudes, number of air conditioning per household and disposable income per capita were significant modifiers for cold effects; the proportion of the elderly was a significant modifier for hot effects. This largest epidemiological study of temperature to date in China suggested that both cold and hot temperatures were associated with increased mortality. Our findings may have important implications for the public health policies in China. Copyright © 2014 Elsevier Inc. All rights reserved.

Cold season emissions dominate the Arctic tundra methane budget

NASA Astrophysics Data System (ADS)

Zona, Donatella; Gioli, Beniamino; Commane, Róisín; Lindaas, Jakob; Wofsy, Steven C.; Miller, Charles E.; Dinardo, Steven J.; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y.-W.; Henderson, John M.; Murphy, Patrick C.; Goodrich, Jordan P.; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D.; Kimball, John S.; Lipson, David A.; Oechel, Walter C.

2016-01-01

Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y-1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

Cold season emissions dominate the Arctic tundra methane budget.

PubMed

Zona, Donatella; Gioli, Beniamino; Commane, Róisín; Lindaas, Jakob; Wofsy, Steven C; Miller, Charles E; Dinardo, Steven J; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y-W; Henderson, John M; Murphy, Patrick C; Goodrich, Jordan P; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D; Kimball, John S; Lipson, David A; Oechel, Walter C

2016-01-05

Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥ 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y(-1), ∼ 25% of global emissions from extratropical wetlands, or ∼ 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

Conversion of Nuclear Waste into Nuclear Waste Glass: Experimental Investigation and Mathematical Modeling

DOE PAGES

Hrma, Pavel

2014-12-18

The melter feed, slurry, or calcine charged on the top of a pool of molten glass forms a floating layer of reacting material called the cold cap. Between the cold-cap top, which is covered with boiling slurry, and its bottom, where bubbles separate it from molten glass, the temperature changes by up to 1000 K. The processes that occur over this temperature interval within the cold cap include liberation of gases, conduction and consumption of heat, dissolution of quartz particles, formation and dissolution of intermediate crystalline phases, and generation of foam and gas cavities. These processes have been investigated usingmore » thermal analyses, optical and electronic microscopies, x-ray diffraction, as well as other techniques. Properties of the reacting feed, such as heat conductivity and density, were measured as functions of temperature. Investigating the structure of quenched cold caps produced in a laboratory-scale melter complemented the crucible studies. The cold cap consists of two main layers. The top layer contains solid particles dissolving in the glass-forming melt and open pores through which gases are escaping. The bottom layer contains bubbly melt or foam where bubbles coalesce into larger cavities that move sideways and release the gas to the atmosphere. The feed-to-glass conversion became sufficiently understood for representing the cold-cap processes via mathematical models. These models, which comprise heat transfer, mass transfer, and reaction kinetics models, have been developed with the final goal to relate feed parameters to the rate of glass melting.« less

Cold season emissions dominate the Arctic tundra methane budget

PubMed Central

Zona, Donatella; Gioli, Beniamino; Lindaas, Jakob; Wofsy, Steven C.; Miller, Charles E.; Dinardo, Steven J.; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y.-W.; Henderson, John M.; Murphy, Patrick C.; Goodrich, Jordan P.; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D.; Kimball, John S.; Lipson, David A.; Oechel, Walter C.

2016-01-01

Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y−1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming. PMID:26699476

Temporal prolongation of decreased skin blood flow causes cold limbs in Parkinson's disease.

PubMed

Shindo, Kazumasa; Kobayashi, Fumikazu; Miwa, Michiaki; Nagasaka, Takamura; Takiyama, Yoshihisa; Shiozawa, Zenji

2013-03-01

To unravel the pathogenesis of cold limbs in Parkinson's disease, we evaluated cutaneous vasomotor neural function in 25 Parkinson's disease patients with or without cold limbs and 20 healthy controls. We measured resting skin sympathetic nerve activity, as well as reflex changes of skin blood flow and skin sympathetic nerve activity after electrical stimulation, with the parameters including skin sympathetic nerve activity frequency at rest, the amplitude of reflex bursts, the absolute decrease and percent reduction of blood flow, and the recovery time which was calculated as the interval from the start of blood flow reduction until the return to baseline cutaneous blood flow. The resting frequency of skin sympathetic nerve activity was significantly lower in patients with Parkinson's disease than in controls (p < 0.01). There were no significant differences between the patients and controls with respect to the amplitude of skin sympathetic nerve activity and the absolute decrease or percent reduction of blood flow volume. In the controls, the recovery time (9.4 ± 1.2), which was similar to Parkinson's disease patients without cold limbs (9.0 ± 0.7), while the recovery time ranged (15.7 ± 3.2) in Parkinson's disease patients with cold limbs. Recovery was significantly slower in these patients compared with the other groups (p < 0.05). It is possible that cold limbs might arise due to impaired circulation based on prolonged vasoconstriction by peripheral autonomic impairments, in addition to central autonomic dysfunction in Parkinson's disease.

Cold season emissions dominate the Arctic tundra methane budget

DOE PAGES

Zona, Donatella; Gioli, Beniamino; Commane, Róisín; ...

2015-12-22

Arctic terrestrial ecosystems are major global sources of methane (CH 4); hence, it is important to understand the seasonal and climatic controls on CH 4 emissions from these systems. Here, we report year-round CH 4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥ 50% of the annual CH 4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0more » °C. The zero curtain may persist longer than the growing season, and CH 4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH 4 derived from aircraft data demonstrate the large spatial extent of late season CH 4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH 4 y –1, ~25% of global emissions from extratropical wetlands, or ~6% of total global wetland methane emissions. Here, the dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH 4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.« less

The common cold in patients with a history of recurrent sinusitis: increased symptoms and radiologic sinusitislike findings.

PubMed

Alho, O P; Ylitalo, K; Jokinen, K; Laitinen, J; Suramo, I; Tuokko, H; Koskela, M; Uhari, M

2001-01-01

We evaluated whether the symptoms and signs and radiologic findings during a common cold are similar in patients who have and have not suffered from recurrent sinusitis. We recruited 2 series of volunteer cases from February 1, 1996, to December 31, 1996. Twenty-three adults who claimed to have suffered from recurrent sinusitis and 25 who had never had sinusitis were examined during the period of a self-diagnosed cold of 48 to 96 hours' duration and again after 21 days. Symptom scores were recorded, nasoendoscopy and computed tomography scans were performed, and viral and bacterial specimens were taken. The patients with a history of sinusitis had significantly higher symptom scores than the control patients (P=.04) and had radiologic sinusitislike changes more often (65% [15] vs 36% [9]; difference 29% [95% confidence interval, 2%-56%]; P=.04). The viral etiology of the common cold (verified in 67% of the episodes) was similar in both groups. Pathogenic bacteria were isolated from the middle meatus in 24% (6) of the control patients and only 9% (2) of the sinusitis-prone patients (P=.15). On the basis of the symptomatology, radiologic findings, and bacterial cultures only 2 patients in the sinusitis-prone group should have been treated with antimicrobials. Some patients are susceptible to both sinusitislike symptoms and radiologic findings during viral common colds. This may cause them to consult their physicians earlier and more often during viral colds, which may result in unnecessary antibiotic treatments. Nasopharyngeal bacteriological cultures may prove to be useful in ruling out bacterial sinusitis.

Late-glacial and early Holocene changes in vegetation and lake-level at Hauterive/Rouges-Terres, Lake Neuchâtel (Switzerland)

NASA Astrophysics Data System (ADS)

Magny, Michel; Thew, Nigel; Hadorn, Philippe

2003-01-01

Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges-Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake-level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus-Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb-2, first part of the Bølling, ca. 14 650-14 450 cal. yr BP) was characterised by a generally low lake-level. A weak rise occurred during this zone. The Juniperus-Hippophaë to Betula zone transition coincided with a lake-level lowering, interrupted by a short-lived but marked phase of higher lake-level recorded at the neighbouring site of Hauterive-Champréveyres, but not present at Hauterive/Rouges-Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb-3, second part of the Bølling, ca 14 450-14 000 cal. yr BP), a marked rise in lake-level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake-level associated with raised values in Artemisia and other non-arboreal pollen. The last part of RPAZ CHb-3 saw a fall in lake-level. The lower lake-levels during RPAZ CHb-2 to early RPAZ CHb-3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake-level punctuating the GI 1e might be linked to the so-called Intra-Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen-isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges-Terres lake-level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1-Preboreal (RPAZ CHb-4b-4c) transition (except for a rise at ca. 11 450-11 400 cal. yr BP), and at the RPAZ CHb-4c-5 (Preboreal-Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake-levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges-Terres lake-level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake-level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content.

Millennial-scale northern Hemisphere Atlantic-Pacific climate teleconnections in the earliest Middle Pleistocene.

PubMed

Hyodo, Masayuki; Bradák, Balázs; Okada, Makoto; Katoh, Shigehiro; Kitaba, Ikuko; Dettman, David L; Hayashi, Hiroki; Kumazawa, Koyo; Hirose, Kotaro; Kazaoka, Osamu; Shikoku, Kizuku; Kitamura, Akihisa

2017-08-30

Suborbital-scale climate variations, possibly caused by solar activity, are observed in the Holocene and last-glacial climates. Recently published bicentennial-resolution paleoceanic environmental records reveal millennial-scale high-amplitude oscillations postdating the last geomagnetic reversal in the Marine Isotope Stage (MIS) 19 interglacial. These oscillations, together with decoupling of post-reversal warming from maximum sea-level highstand in mid-latitudes, are key features for understanding the climate system of MIS 19 and the following Middle Pleistocene. It is unclear whether the oscillations are synchronous, or have the same driver as Holocene cycles. Here we present a high resolution record of western North Pacific submarine anoxia and sea surface bioproductivity from the Chiba Section, central Japan. The record reveals many oxic events in MIS 19, coincident with cold intervals, or with combined cold and sea-level fall events. This allows detailed correlations with paleoceanic records from the mid-latitude North Atlantic and Osaka Bay, southwest Japan. We find that the millennial-scale oscillations are synchronous between East and West hemispheres. In addition, during the two warmest intervals, bioproductivity follows the same pattern of change modulated by bicentennial cycles that are possibly related to solar activity.

Relationships between cold-temperature indices and all causes and cardiopulmonary morbidity and mortality in a subtropical island.

PubMed

Lin, Yu-Kai; Wang, Yu-Chun; Lin, Pay-Liam; Li, Ming-Hsu; Ho, Tsung-Jung

2013-09-01

This study aimed to identify optimal cold-temperature indices that are associated with the elevated risks of mortality from, and outpatient visits for all causes and cardiopulmonary diseases during the cold seasons (November to April) from 2000 to 2008 in Northern, Central and Southern Taiwan. Eight cold-temperature indices, average, maximum, and minimum temperatures, and the temperature humidity index, wind chill index, apparent temperature, effective temperature (ET), and net effective temperature and their standardized Z scores were applied to distributed lag non-linear models. Index-specific cumulative 26-day (lag 0-25) mortality risk, cumulative 8-day (lag 0-7) outpatient visit risk, and their 95% confidence intervals were estimated at 1 and 2 standardized deviations below the median temperature, comparing with the Z score of the lowest risks for mortality and outpatient visits. The average temperature was adequate to evaluate the mortality risk from all causes and circulatory diseases. Excess all-cause mortality increased for 17-24% when average temperature was at Z=-1, and for 27-41% at Z=-2 among study areas. The cold-temperature indices were inconsistent in estimating risk of outpatient visits. Average temperature and THI were appropriate indices for measuring risk for all-cause outpatient visits. Relative risk of all-cause outpatient visits increased slightly by 2-7% when average temperature was at Z=-1, but no significant risk at Z=-2. Minimum temperature estimated the strongest risk associated with outpatient visits of respiratory diseases. In conclusion, the relationships between cold temperatures and health varied among study areas, types of health event, and the cold-temperature indices applied. Mortality from all causes and circulatory diseases and outpatient visits of respiratory diseases has a strong association with cold temperatures in the subtropical island, Taiwan. Copyright © 2013 Elsevier B.V. All rights reserved.

Extreme climatic conditions and health service utilisation across rural and metropolitan New South Wales

NASA Astrophysics Data System (ADS)

Jegasothy, Edward; McGuire, Rhydwyn; Nairn, John; Fawcett, Robert; Scalley, Benjamin

2017-08-01

Periods of successive extreme heat and cold temperature have major effects on human health and increase rates of health service utilisation. The severity of these events varies between geographic locations and populations. This study aimed to estimate the effects of heat waves and cold waves on health service utilisation across urban, regional and remote areas in New South Wales (NSW), Australia, during the 10-year study period 2005-2015. We divided the state into three regions and used 24 over-dispersed or zero-inflated Poisson time-series regression models to estimate the effect of heat waves and cold waves, of three levels of severity, on the rates of ambulance call-outs, emergency department (ED) presentations and mortality. We defined heat waves and cold waves using excess heat factor (EHF) and excess cold factor (ECF) metrics, respectively. Heat waves generally resulted in increased rates of ambulance call-outs, ED presentations and mortality across the three regions and the entire state. For all of NSW, very intense heat waves resulted in an increase of 10.8% (95% confidence interval (CI) 4.5, 17.4%) in mortality, 3.4% (95% CI 0.8, 7.8%) in ED presentations and 10.9% (95% CI 7.7, 14.2%) in ambulance call-outs. Cold waves were shown to have significant effects on ED presentations (9.3% increase for intense events, 95% CI 8.0-10.6%) and mortality (8.8% increase for intense events, 95% CI 2.1-15.9%) in outer regional and remote areas. There was little evidence for an effect from cold waves on health service utilisation in major cities and inner regional areas. Heat waves have a large impact on health service utilisation in NSW in both urban and rural settings. Cold waves also have significant effects in outer regional and remote areas. EHF is a good predictor of health service utilisation for heat waves, although service needs may differ between urban and rural areas.

Application of Alkenone 14C-Based chronostratigraphy in carbonate barren sediments on the Peru Margin.

NASA Astrophysics Data System (ADS)

Higginson, M. J.; Altabet, M. A.; Herbert, T. D.

2003-04-01

Despite the availability of high-quality sediment cores in key locations, little paleoclimatic information exists for the Peru margin largely because poor carbonate preservation severely restricts the use of traditional carbonate-based proxies for stratigraphy, dating, and paleo-environmental reconstruction. Many sites also include hiatuses produced by the variable influence of undercurrents on sediment accumulation. To overcome these difficulties, we have developed (in collaboration with T. Eglinton, WHOI) a laboratory facility to successfully extract and purify haptophyte-derived alkenones for compound specific 14C AMS dating (modified from OHKOUCHI et al., 2002). This avoids potential problems with dating bulk organic carbon which we assume, even in an upwelling environment as highly productive as the Peru margin, is not a priori solely of marine origin. In a recently collected, mid-Peru Margin core (ODP Leg 201 Site 1228D), comparison of our alkenone 14C dates with bulk sediment organic carbon dates and known stratigraphic markers produces a very well constrained, curvilinear age-depth relationship for at least the last 14 Kyr. A discrete ash layer at Site 1228D with an adjacent alkenone 14C age of 3890 ± 350 yr, is within error identical to the 14C age of a prominent ash layer (3800 ± 50 yr) found west of the large Peruvian El Misti volcano (16^o18'S, 71^o24'W). In summary, these results show that the Peru margin alkenones are autochthonous (i.e. not from an older, distant source) and provide sufficient dating precision to permit, for the first time, high-resolution paleoceanographic studies in this highly important marine province. Based upon this new chronology, synchronous changes in alkenone-derived SST estimates in two of our independently-dated records are the first to record at high-resolution (a) a large LGM-Holocene SST range in the Tropics (up to 7.8 ^oC during brief events in this upwelling location); and (b) sharp coolings (4 ^oC) consistent with the timing of the Younger Dryas. We presume that the enlarged SST amplitude of these sites comes from the sensitivity of the Peru margin to the dominant upwelling signal and its proximity to the Andes, from which there is evidence for a Younger Dryas response. The appearance of a Bolling-Allerod/Younger Dryas SST reversal consistent with published dates is further verification of our chronostratigraphic methods.

Atmospheric dynamics over Europe during the Younger Dryas revealed by palaeoglaciers.

NASA Astrophysics Data System (ADS)

Rea, Brice; Pellitero, Ramon; Spagnolo, Matteo; Hughes, Philip; Braithwaite, Roger; Renssen, Hans; Ivy-Ochs, Susan; Ribolini, Adriano; Bakke, Jostein; Lukas, Sven

2017-04-01

A dataset of 120 palaeoglaciers ranging from Morocco in the south to Svalbard in the north and from Ireland in the west to Turkey in the east, has been assembled from the literature. A robust quality control on the chronology was undertaken and, when derived from cosmogenic nuclides, ages were recalculated using the most up-to-date production rates. All the reconstructed glaciers date to the Younger Dryas. Frontal moraines/limits were used to initiate the palaeoglacier reconstructions using GlaRe, a GIS tool which generates an equilibrium profile ice surface along a single flowline and extrapolates this to out to a 3D ice surface. From the resulting glacier surfaces palaeo-ELAs were calculated within the GIS. Where multiple glaciers were reconstructed within in a region, a single ELA value was generated. Results show that ELAs decrease with latitude but have a more complex pattern with longitude. A database of 121 sites, spanning the same geographical range as the palaeoglaciers, was compiled for Younger Dryas temperature, determined from palaeoproxies, for example pollen, diatoms, coleoptera, chironimids etc. These proxy data were merged and interpolated to generate maps of average temperature for the warmest and coldest months and annual average temperature. Results show that, in general, temperature decreases with latitude. Temperature at the palaeo-ELAs were determined from the temperature maps using a lapse rate of 0.65°C/100m and the precipitation required for equilibrium was calculated. Positive precipitation anomalies are found along much of the western seaboard of Europe, with the most striking positive anomalies present in the eastern Mediterranean. Negative precipitation anomalies appear on the northern side of the Alps. This pattern is interpreted to represent a southward displaced polar frontal jet stream with a concomitant track of Atlantic mid-latitude depressions, leading to more frequent incursions of low pressure systems especially over the relatively warm eastern Mediterranean, enhancing cyclogenesis. This is similar to the modern Scandinavia (SCAND) pattern which, in its positive phase, is characterised by a high pressure anomaly over Fennoscandia and western Russia, negative pressure anomalies around the Iberian Peninsula and enhanced cyclogenesis in the central and eastern Mediterranean. During the YD the Fennoscandian Ice Sheet and permafrost across much of northern continental Europe and Russia would have generated a high pressure region leading to a persistent, enhanced SCAND circulation.

Time constraints for post-LGM landscape response to deglaciation in Val Viola, Central Italian Alps

NASA Astrophysics Data System (ADS)

Scotti, Riccardo; Brardinoni, Francesco; Crosta, Giovanni Battista; Cola, Giuseppe; Mair, Volkmar

2017-12-01

Across the northern European Alps, a long tradition of Quaternary studies has constrained post-LGM (Last Glacial Maximum) landscape history. The same picture remains largely unknown for the southern portion of the orogen. In this work, starting from existing 10Be exposure dating of three boulders in Val Viola, Central Italian Alps, we present the first detailed, post-LGM reconstruction of landscape (i.e., glacial, periglacial and paraglacial) response south of the Alpine divide. We pursue this task through Schmidt-hammer exposure-age dating (SHD) at 34 sites including moraines, rock glaciers, protalus ramparts, rock avalanche deposits and talus cones. In addition, based on the mapping of preserved moraines and on the numerical SHD ages, we reconstruct the glacier extent of four different stadials, including Egesen I (13.1 ± 1.1 ka), Egesen II (12.3 ± 0.6 ka), Kartell (11.0 ± 1.4 ka) and Kromer (9.7 ± 1.4 ka), whose chronologies agree with available counterparts from north of the Alpine divide. Results show that Equilibrium Line Altitude depressions (ΔELAs) associated to Younger Dryas and Early Holocene stadials are smaller than documented at most available sites in the northern Alps. These findings not only support the hypothesis of a dominant north westerly atmospheric circulation during the Younger Dryas, but also suggest that this pattern could have lasted until the Early Holocene. SHD ages on rock glaciers and protalus ramparts indicate that favourable conditions to periglacial landform development occurred during the Younger Dryas (12.7 ± 1.1 ka), on the valley slopes above the glacier, as well as in newly de-glaciated areas, during the Early Holocene (10.7 ± 1.3 and 8.8 ± 1.8 ka). The currently active rock glacier started to develop before 3.7 ± 0.8 ka and can be associated to the Löbben oscillation. Four of the five rock avalanches dated in Val Viola cluster within the Early Holocene, in correspondence of an atmospheric warming phase. By contrast, the timing of the main Val Viola rock avalanche, 7.7 ± 0.3 ka during the Holocene Thermal Optimum, suggests a possible causal linkage to permafrost degradation. Overall, Schmidt-hammer proved to be an effective, inexpensive and versatile tool for improving the spatial resolution of Val Viola post-LGM landscape history, starting from existing numerical age constrains.

Climate Reconstructions of the Younger Dryas: An ELA Model Investigating Variability in ELA Depressions, Temperature, and Precipitation Changes for the Graubϋnden Alps

NASA Astrophysics Data System (ADS)

Keeler, D. G.; Rupper, S.; Schaefer, J. M.; Finkel, R. C.

2015-12-01

The high sensitivity of mountain glaciers to even small perturbations in climate, combined with a near global distribution, make alpine glaciers an important target for terrestrial paleoclimate reconstructions. The geomorphic remnant of past glaciers can yield important insights into past climate, particularly in regions where other methods of reconstruction are not possible. The quantitative conversion of these changes in geomorphology to a climate signal, however, presents a significant challenge. A particular need exists for a versatile climate reconstruction method applicable to diverse glacierized regions around the globe. Because the glacier equilibrium line altitude (ELA) provides a more explicit comparison of climate than properties such as glacier length or area, ELA methods lend themselves well to such a need, and allow for a more direct investigation of the primary drivers of mountain glaciations during specific events. Here, we present an ELA model for quantifying changes in climate based on changes in glacier extent, while accounting for differences in glacier width, glacier shape, bed topography, ice thickness, and glacier length. The model furthermore provides bounds on the ΔELA using Monte Carlo simulations. These methods are validated using published mass balances and ELA measurements from 4 modern glaciers in the European Alps. We then use this ELA model, combined with a surface mass and energy balance model, to estimate the changes in temperature/precipitation between the Younger Dryas (constrained by 10Be surface exposure ages) and the present day for three glacier systems in the Graubϋnden Alps. Our results indicate an ELA depression in this area of 257 m ±45 m during the Younger Dryas (YD) relative to today. This corresponds to a 1.3 °C ±0.36 °C decrease in temperature or a 156% ±30% increase in precipitation relative to today. These results indicate the likelihood of a predominantly temperature-driven change rather than a strong dependence on precipitation. We apply these same methods to additional areas around the globe to obtain preliminary, self-consistent estimates of temperature/precipitation for multiple regions. These methods and results enhance our understanding of the global and regional patterns in the climate system during the YD.

Late Pleistocene Megafaunal Extinction Consistent With YDB Impact Hypothesis at Younger Dryas Onset

NASA Astrophysics Data System (ADS)

Kennett, J. P.; Kennett, D. J.

2008-12-01

At least 35 mammal and 19 bird genera became extinct across North America near the end of the Pleistocene. Modern increases in stratigraphic and dating resolution suggest that this extinction occurred relatively rapidly near 12.9 ka (11 radiocarbon kyrs). Within the context of a long-standing debate about its cause, Firestone et al., (2007) proposed that this extinction resulted from an extraterrestrial (ET) impact over North America at 12.9 ka. This hypothesis predicts that the extinction of most of these animals should have occurred abruptly at 12.9 ka. To test this hypothesis, we have critically examined radiocarbon ages and the extinction stratigraphy of these taxa. From a large data pool, we selected only radiocarbon dates with low error margins with a preference for directly dated biological materials (e.g., bone, dung, etc.) and modern chemical purification techniques. A relatively small number of acceptable dates indicate that at least 16 animal genera and several other species became extinct close to 12.9 ka. These taxa include the most common animals of the late Pleistocene such as horses, camels, and mammoths. Also, the remains of extinct taxa are reportedly found up to, but not above, the base of a widely distributed carbon-rich layer called the black mat. This stratum forms an abrupt, major biostratigraphic boundary at the Younger Dryas onset (12.9 ka), which also contains multiple ET markers comprising the impact layer (the YDB). Surviving animal populations were abruptly reduced at the YDB (e.g., Bison), with major range restrictions and apparent evolutionary bottlenecks. The abruptness of this major extinction is inconsistent with the hypotheses of human overkill and climatic change. We argue that extinction ages older than 12.9 ka for many less common species result from the Signor-Lipps effect, but the impact hypothesis predicts that as new dates are acquired, they will approach ever closer to 12.9 ka. The megafaunal extinction is strongly associated with abrupt and major vegetation changes, abrupt cooling, and widespread biomass burning at the onset of the Younger Dryas over North America. The stratigraphic and chronologic data are consistent with megafaunal extinction being caused by continental-scale ecosystem disruption due to an ET impact.

Processes controlling trace element geochemistry of Arabian Sea sediments during the last 25,000 years

NASA Astrophysics Data System (ADS)

Sirocko, Frank; Garbe-Schönberg, Dieter; Devey, Colin

2000-11-01

Thirty seven deep-sea sediment cores from the Arabian Sea were studied geochemically (49 major and trace elements) for four time slices during the Holocene and the last glacial, and in one high sedimentation rate core (century scale resolution) to detect tracers of past variations in the intensity of the atmospheric monsoon circulation and its hydrographic expression in the ocean surface. This geochemical multi-tracer approach, coupled with additional information on the grain size composition of the clastic fraction, the bulk carbonate and biogenic opal contents makes it possible to characterize the sedimentological regime in detail. Sediments characterized by a specific elemental composition (enrichment) originated from the following sources: river suspensions from the Tapti and Narbada, draining the Indian Deccan traps (Ti, Sr); Indus sediments and dust from Rajasthan and Pakistan (Rb, Cs); dust from Iran and the Persian Gulf (Al, Cr); dust from central Arabia (Mg); dust from East Africa and the Red Sea (Zr/Hf, Ti/Al). C org, Cd, Zn, Ba, Pb, U, and the HREE are associated with the intensity of upwelling in the western Arabian Sea, but only those patterns that are consistently reproduced by all of these elements can be directly linked with the intensity of the southwest monsoon. Relying on information from a single element can be misleading, as each element is affected by various other processes than upwelling intensity and nutrient content of surface water alone. The application of the geochemical multi-tracer approach indicates that the intensity of the southwest monsoon was low during the LGM, declined to a minimum from 15,000-13,000 14C year BP, intensified slightly at the end of this interval, was almost stable during the Bölling, Alleröd and the Younger Dryas, but then intensified in two abrupt successions at the end of the Younger Dryas (9900 14C year BP) and especially in a second event during the early Holocene (8800 14C year BP). Dust discharge by northwesterly winds from Arabia exhibited a similar evolution, but followed an opposite course: high during the LGM with two primary sources—the central Arabian desert and the dry Persian Gulf region. Dust discharge from both regions reached a pronounced maximum at 15,000-13,000 14C year. At the end of this interval, however, the dust plumes from the Persian Gulf area ceased dramatically, whereas dust discharge from central Arabia decreased only slightly. Dust discharge from East Africa and the Red Sea increased synchronously with the two major events of southwest monsoon intensification as recorded in the nutrient content of surface waters. In addition to the tracers of past dust flux and surface water nutrient content, the geochemical multi-tracer approach provides information on the history of deep sea ventilation (Mo, S), which was much lower during the last glacial maximum than during the Holocene. The multi-tracer approach—i.e. a few sedimentological parameters plus a set of geochemical tracers widely available from various multi-element analysis techniques—is a highly applicable technique for studying the complex sedimentation patterns of an ocean basin, and, specifically in the case of the Arabian Sea, can even reveal the seasonal structure of climate change.

Frequent alcohol drinking is associated with lower prevalence of self-reported common cold: a retrospective study

PubMed Central

2012-01-01

Background Alcohol intake has been associated with reduced incidence of common cold symptoms in 2 European studies. However, no study has addressed the association between the frequency of alcohol intake and the incidence of common cold. This study aimed to investigate the association between the amount and frequency of alcohol drinking and the retrospective prevalence of common cold in Japanese men. Methods This retrospective study included men who participated in an annual health examination conducted in Sendai, Japan. The frequency of common cold episodes in the previous year was self-reported. The weekly frequency and amount of alcohol consumed, as well as the type of alcoholic drink, were reported by a brief-type self-administered diet history questionnaire. Logistic regression models were used to analyze the association between the amount and frequency of alcohol intake and the retrospective prevalence of common cold. Results Among 899 men, 83.4% of the subjects reported drinking alcohol, and 55.4% of the subjects reported having experienced at least one episode of common cold in the previous year. Compared with non-drinkers, the adjusted odds ratios (ORs) with 95% confidence intervals (CIs) for having had 1 or more episodes of common cold during the past year across categories of alcohol intake frequency of 3 or less, 4–6, and 7 days/week were 0.827 (0.541–1.266), 0.703 (0.439–1.124), and 0.621 (0.400–0.965), respectively (P for trend = 0.025); the adjusted ORs with 95% CIs for having had of 2 or more episodes of common cold across the same categories were 0.642 (0.395–1.045), 0.557 (0.319–0.973), and 0.461 (0.270–0.787), respectively (P for trend = 0.006). Compared with subjects who consumed 11.5–35.8 g of alcohol per day, the non-drinkers were significantly more likely to experience 2 or more episodes of common cold (OR, 1.843; 95% CI, 1.115–3.047). Conclusion The frequency, not the amount, of alcohol intake was significantly related to lower prevalence of self-reported common cold episodes in Japanese men. PMID:23158193

Smoking, leisure-time exercise and frequency of self-reported common cold among the general population in northeastern China: a cross-sectional study.

PubMed

Zhou, Ge; Liu, Hongjian; He, Minfu; Yue, Mengjia; Gong, Ping; Wu, Fangyuan; Li, Xuanxuan; Pang, Yingxin; Yang, Xiaodi; Ma, Juan; Liu, Meitian; Li, Jinghua; Zhang, Xiumin

2018-02-27

Physical activity (PA) and smoking have been reported to be associated with the duration and severity of common cold symptoms. However, few studies have addressed the associations between the frequency of leisure-time exercise, cigarette smoking status and the frequency of the common cold in a cold area. This study was designed to investigate these issues in northeastern China. This cross-sectional study included individuals who participated in a regular health examination conducted in Jilin Province, China. Information on episodes of the common cold, the frequency of leisure-time exercise and cigarette smoking status in the past year were collected by self-administered health questionnaires. Ordinal logistic regression models were used to analyse the associations between the frequency of leisure-time exercise, cigarette smoking status and the retrospective frequency of common cold. A total of 1413 employees participated in the study, with an average age of 38.92 ± 9.04 years and 44.4% of them were male. Of all participants, 80.8% reported having experienced the common cold in the past year. After adjustment, the risk of suffering from the common cold more than once (odds ratios (ORs), 1.59; 95% confidence interval (CI), 1.27-1.99) in passive smokers was 1.59 times as high as that in non-smokers. Nevertheless, the results of the adjusted analysis showed no statistically significant relation between current smoking and the frequency of the common cold. A high frequency of leisure-time exercise (≥3 days/week) was associated with a 26% reduced risk of having at least one episode of the common cold (OR, 0.74; 95% CI, 0.55-0.98) compared with a low frequency group (< 4 days/month). For current and passive smokers, the protective effect of a high frequency of leisure-time exercise appears not to be obvious (current smokers: OR, 0.68; 95% CI, 0.33-1.43; passive smokers: OR, 1.15; 95% CI, 0.69-1.93). Passive smoking was associated with a higher risk of having self-reported common cold at least once, while a high frequency of leisure-time exercise was related to a lower risk of reporting more than one episode of the disease in Chinese.

Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California

USGS Publications Warehouse

Pigati, J.S.; Miller, D.M.; Bright, J.E.; Mahan, S.A.; Nekola, J.C.; Paces, J.B.

2011-01-01

groundwater supported persistent and long-lived desert wetlands in many broad valleys and basins in the American Southwest. When active, these systems provided important food and water sources for local fauna, supported hydrophilic and phreatophytic vegetation, and acted as catchments for eolian and alluvial sediments. Desert wetlands are represented in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits. Groundwater discharge deposits contain information on the timing and magnitude of past changes in water-table levels and, thus, are a source of paleohydrologic and paleoclimatic information. Here, we present the results of an investigation of extensive groundwater discharge deposits in the central Mojave Desert at Valley Wells, California. We used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at Valley Wells, which we dated using radiocarbon, luminescence, and uranium-series techniques. We also analyzed the sediments and microfauna (ostracodes and gastropods) to reconstruct the specific environments in which they formed. Our results suggest that the earliest episode of high water-table conditions at Valley Wells began ca. 60 ka (thousands of calendar yr B.P.), and culminated in peak discharge between ca. 40 and 35 ka. During this time, cold (4-12 ??C) emergent groundwater supported extensive wetlands that likely were composed of a wet, sedge-rush-tussock meadow mixed with mesic riparian forest. After ca. 35 ka, the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the Last Glacial Maximum (LGM). The water table dropped further after the LGM, and xeric conditions prevailed until modest wetlands returned briefly during the Younger Dryas cold event (13.0-11.6 ka). We did not observe any evidence of wet conditions during the Holocene at Valley Wells. The timing of these fluctuations is consistent with changes in other paleowetland systems in the Mojave Desert, the nearby Great Basin Desert, and in southeastern Arizona, near the border of the Sonoran and Chihuahuan Deserts. The similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late Pleistocene in desert wetlands scattered throughout the American Southwest were likely driven by synopticscale climate processes. ?? 2011 Geological Society of America.

Asynchronous Glacial Chronologies in the Central Andes (15-40°S) and Paleoclimatic Implications

NASA Astrophysics Data System (ADS)

Zech, R.; Kull, C.; Kubik, P. W.; Veit, H.

2006-12-01

We have established glacial chronologies along a N-S transect over the Central Andes using 10Be surface exposure dating. Our results show that maximum glacial advances occurred asynchronously and reflect the varying influence and shifts of the major atmospheric circulation systems during the Late Quaternary: the tropical circulation in the north and the westerlies in the south. In Bolivia (three research areas in the Cordillera Real and the Cordillera Cochabamba, ~15°S) glacial advances could be dated to ~20 and 12 ka BP. This is in good agreement with published exposure age data from moraines in Bolivia and Peru (provided that all ages are calculated following the same scaling system). Accordingly, the maximum glaciation there probably occurred roughly synchronous to the temperature minimum of the global Last Glacial Maximum (LGM) and the lateglacial cold reversals. Strict correlation with neither the Younger Dryas in the northern hemisphere, nor the Antarctic Cold Reversal is possible due to the current systematic exposure age uncertainties (~10%). Glacier-Climate-Modelling corroborates the sensitivity of the reconstructed glaciers to temperature changes, rather than precipitation. On the contrary, there is good evidence for the dominant role of precipitation changes on the glacial chronologies in the lee of the Cordillera Occidental, i.e. on the Altiplano and further south. The pronounced lateglacial wet phase, which is well documented in lake transgression phases as far south as 28°S (-> tropical moisture source), seems to have caused glacial advances even at ~30°S. In two research areas in Chile at that latitude, we were able to date several lateglacial moraines. Besides, the maximum datable glaciation there occurred at ~30 ka BP. That is significantly earlier than the LGM (sensu strictu) and points to favourable climate conditions for glaciation at that time (particularly increased precipitation). We conclude that the westerlies were more intensive or shifted northward at ~30 ka BP. We have not yet been able to date LGM moraines as far south as ~40°, which would indicate the transition of precipitation- to temperature-sensitive glaciers. Instead, our preliminary exposure age chronology from Valle Rucachoroi (~39°S, Argentina) suggests that the maximum glaciation there occurred also at ~30 ka BP, but that the valleys became ice-free only by ~15 ka BP. Samples from moraines in the cirques are currently in progress and may document lateglacial re-advances.

Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California

USGS Publications Warehouse

Pigati, Jeffrey S.; Miller, David M.; Bright, Jordon E.; Mahan, Shannon; Nekola, Jeffrey C.; Paces, James B.

2011-01-01

During the late Pleistocene, emergent groundwater supported persistent and long-lived desert wetlands in many broad valleys and basins in the American Southwest. When active, these systems provided important food and water sources for local fauna, supported hydrophilic and phreatophytic vegetation, and acted as catchments for eolian and alluvial sediments. Desert wetlands are represented in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits. Groundwater discharge deposits contain information on the timing and magnitude of past changes in water-table levels and, thus, are a source of paleohydrologic and paleoclimatic information. Here, we present the results of an investigation of extensive groundwater discharge deposits in the central Mojave Desert at Valley Wells, California. We used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at Valley Wells, which we dated using radiocarbon, luminescence, and uranium-series techniques. We also analyzed the sediments and microfauna (ostracodes and gastropods) to reconstruct the specific environments in which they formed. Our results suggest that the earliest episode of high water-table conditions at Valley Wells began ca. 60 ka (thousands of calendar yr B.P.), and culminated in peak discharge between ca. 40 and 35 ka. During this time, cold (4–12 °C) emergent groundwater supported extensive wetlands that likely were composed of a wet, sedge-rush-tussock meadow mixed with mesic riparian forest. After ca. 35 ka, the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the Last Glacial Maximum (LGM). The water table dropped further after the LGM, and xeric conditions prevailed until modest wetlands returned briefly during the Younger Dryas cold event (13.0–11.6 ka). We did not observe any evidence of wet conditions during the Holocene at Valley Wells. The timing of these fluctuations is consistent with changes in other paleowetland systems in the Mojave Desert, the nearby Great Basin Desert, and in southeastern Arizona, near the border of the Sonoran and Chihuahuan Deserts. The similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late Pleistocene in desert wetlands scattered throughout the American Southwest were likely driven by synoptic-scale climate processes.

Tropical Climate Variability From the Last Glacial Maximum to the Present

DTIC Science & Technology

2005-09-01

between the tropics and extrat- ropics remains an open question. Over the course of the glacial-interglacial cycles of the past 800,000 years, the high...roughly 80% of the total CSEs. The remaining 12 Younger Dryas in the Cariaco Basin. CSE peaks are consistently smaller than those mentioned [29] CSEs I...33] CSEs 8 and 15 remain unidentified. It is evident record. Identification and downcore analysis of these CSE from their downcore trends, however

Evidence from Central Mexico Supporting the Younger Dryas Extraterrestrial Impact Hypothesis

DTIC Science & Technology

2012-03-05

identified glassy spherules, CSps, high- temperature melt- rocks , shocked quartz, and a YDB black mat analogue in the Venezuelan Andes. Those authors...debate, we have examined a diverse assemblage of YDB markers at Lake Cuitzeo using a more comprehensive array of analytical techniques than in previous...accelerator mass spectroscopy (AMS) 14C dates on bulk sediment and used in a linear interpolation with the YD onset identified at approximately 2.8 m. To

Too early and too northerly: evidence of temperate trees in northern Central Europe during the Younger Dryas.

PubMed

Robin, Vincent; Nadeau, Marie-Josée; Grootes, Pieter M; Bork, Hans-Rudolf; Nelle, Oliver

2016-10-01

This paper presents highly unexpected paleobotanical data. Eight (14) C-accelerator mass spectrometry (AMS) dates of soil macrocharcoal pieces, identified taxonomically, indicate the presence of oak and beech in the Younger Dryas, and pine in the Allerød, in the northernmost low mountain range of Central Europe, the Harz Mountains, in Germany. If the presence of pine at such latitude and periods is not surprising, the presence of temperate-adapted trees is highly improbable, because they are assumed to have reached the area from a southern location several thousand years later. Two hypotheses are postulated to explain this record. Both are related to the warm periods of the Bølling and Allerød: the classically 'short' duration of this warm period makes the migration of the temperate trees from the identified refuge areas in the southern location implausible, and so the presence of intermediary microrefugia at a medium latitude in Central Europe is postulated; recent data reveal that the warm period of the Late Glacial phase was much longer than considered in the classical view and, thus, would be long enough for a northward migration of temperate-adapted trees. Although our dataset does not permit disentanglement of these hypotheses, it provides significant innovative insights for the biogeography of Central Europe. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Lacustrine lignin biomarker record reveals a severe drought during the late Younger Dryas in southern Taiwan

NASA Astrophysics Data System (ADS)

Ding, Xiaodong; Bao, Hongyan; Zheng, Liwei; Li, Dawei; Kao, Shuh-Ji

2017-03-01

The Younger Dryas (YD) event, which punctuated the last glacial-Holocene transition period and had a profound impact on global climate, is the most well studied millennial-scale climate event although the triggering mechanism remains debate. Weakened Asian summer monsoon during the YD is recorded in oxygen isotopes of stalagmite from Mainland China. However, lacustrine climate record of the YD event has not been reported from the subtropical land-ocean boundary of the Asian continent near the Pacific warm pool. We provide a lignin biomarker record covering the last deglaciation and early Holocene (17-9 ka BP) from the Dongyuan Lake, southern Taiwan, located at the frontal zone of typhoon invasion. The lignin phenol ratio S/V shows that the vegetation in the catchments had shifted from gymnosperm dominant to angiosperm dominant plants since 12.2 ka BP. Significantly decreased lignin concentrations (TLP and λ8) and elevated lignin degradation parameters ((Ad/Al)v, P/(V + S), DHBA/V) in combination with other organic proxies (TOC, δ13Corg) during the late YD suggest a severe drought had occurred in southern Taiwan during this specific period. Changes in the lignin proxies from the Dongyuan Lake lagged the climate changes registered in stalagmite records by around 500-800 years, suggesting a slow response of vegetation and soil processes to rapid climate changes.

Numerical modeling of late Glacial Laurentide advance of ice across Hudson Strait: Insights into terrestrial and marine geology, mass balance, and calving flux

USGS Publications Warehouse

Pfeffer, W.T.; Dyurgerov, M.; Kaplan, M.; Dwyer, J.; Sassolas, C.; Jennings, A.; Raup, B.; Manley, W.

1997-01-01

A time-dependent finite element model was used to reconstruct the advance of ice from a late Glacial dome on northern Quebec/Labrador across Hudson Strait to Meta Incognita Peninsula (Baffin Island) and subsequently to the 9.9-9.6 ka 14C Gold Cove position on Hall Peninsula. Terrestrial geological and geophysical information from Quebec and Labrador was used to constrain initial and boundary conditions, and the model results are compared with terrestrial geological information from Baffin Island and considered in the context of the marine event DC-0 and the Younger Dryas cooling. We conclude that advance across Hudson Strait from Ungava Bay to Baffin Island is possible using realistic glacier physics under a variety of reasonable boundary conditions. Production of ice flux from a dome centered on northeastern Quebec and Labrador sufficient to deliver geologically inferred ice thickness at Gold Cove (Hall Peninsula) appears to require extensive penetration of sliding south from Ungava Bay. The discharge of ice into the ocean associated with advance and retreat across Hudson Strait does not peak at a time coincident with the start of the Younger Dryas and is less than minimum values proposed to influence North Atlantic thermohaline circulation; nevertheless, a significant fraction of freshwater input to the North Atlantic may have been provided abruptly and at a critical time by this event.

A 2000-yr-long multi-proxy lacustrine record from eastern Baffin Island, Arctic Canada reveals first millennium AD cold period

NASA Astrophysics Data System (ADS)

Thomas, Elizabeth K.; Briner, Jason P.; Axford, Yarrow; Francis, Donna R.; Miller, Gifford H.; Walker, Ian R.

2011-05-01

We generate a multi-proxy sub-centennial-scale reconstruction of environmental change during the past two millennia from Itilliq Lake, Baffin Island, Arctic Canada. Our reconstruction arises from a finely subsectioned 210Pb- and 14C-dated surface sediment core and includes measures of organic matter (e.g., chlorophyll a; carbon-nitrogen ratio) and insect (Diptera: Chironomidae) assemblages. Within the past millennium, the least productive, and by inference coldest, conditions occurred ca. AD 1700-1850, late in the Little Ice Age. The 2000-yr sediment record also reveals an episode of reduced organic matter deposition during the 6th-7th century AD; combined with the few other records comparable in resolution that span this time interval from Baffin Island, we suggest that this cold episode was experienced regionally. A comparable cold climatic episode occurred in Alaska and western Canada at this time, suggesting that the first millennium AD cold climate anomaly may have occurred throughout the Arctic. Dramatic increases in aquatic biological productivity at multiple trophic levels are indicated by increased chlorophyll a concentrations since AD 1800 and chironomid concentrations since AD 1900, both of which have risen to levels unprecedented over the past 2000 yr.

Impacts of an Extreme Early-Season Freeze Event in the Interior Pacific Northwest (30 October-3 November 2002) on Western Juniper Woodlands.

NASA Astrophysics Data System (ADS)

Knapp, Paul A.; Soulé, Peter T.

2005-07-01

In mid-autumn 2002, an exceptional 5-day cold spell affected much of the interior Pacific Northwest, with minimum temperatures averaging 13°C below long-term means (1953-2002). On 31 October, minimum temperature records occurred at 98 of the 106 recording stations, with records lowered in some locations by 9°C. Calculation of recurrence intervals of minimum temperatures shows that 50% of the stations experienced a >500-yr event. The synoptic conditions responsible were the development of a pronounced high pressure ridge over western Canada and an intense low pressure area centered in the Intermountain West that promoted strong northeasterly winds. The cold spell occurred near the end of the growing season for an ecologically critical and dominant tree species of the interior Pacific Northwest—western juniper—and followed an extended period of severe drought. In spring 2003, it became apparent that the cold had caused high rates of tree mortality and canopy dieback in a species that is remarkable for its longevity and resistance to climatic stress. The cold event altered western juniper dominance in some areas, and this alteration may have long-term impacts on water budgets, fire intensities and frequencies, animal species interrelationships, and interspecific competition among plant species.

Immunogenic yeast-based fermentate for cold/flu-like symptoms in nonvaccinated individuals.

PubMed

Moyad, Mark A; Robinson, Larry E; Zawada, Edward T; Kittelsrud, Julie; Chen, Ding-Geng; Reeves, Stuart G; Weaver, Susan

2010-02-01

The common cold has a profound impact on employee attendance and productivity. Seasonal influenza is responsible for approximately 200,000 hospitalizations and 36,000 deaths per year in the United States alone. Over-the-counter medication efficacy has been questioned, and seasonal vaccination compliance issues abound. Our previously reported randomized trial of an oral fermentation product found an adjuvant benefit for vaccinated individuals in terms of a significantly reduced incidence and duration of cold and flu-like symptoms. A concurrent 12-week, randomized, double-blind, placebo-controlled clinical trial of 116 subjects with no recent history of seasonal influenza vaccination was conducted. Participants received once-daily supplementation with 500 mg of a dried modified Saccharomyces cerevisiae oral fermentate (EpiCor) or placebo. Clinical outcome measurements included periodic interval-based in-clinic examinations and serologic analysis at baseline, 6 weeks, and 12 weeks. Participants utilized a standardized self-report symptom diary. Subjects receiving the intervention experienced a statistically significant reduction in the incidence (p = 0.01), a nonsignificant reduction in duration (p = 0.10), and no impact on the severity (p = 0.90) of colds or flu-like symptoms, but a more favorable safety profile compared with subjects receiving placebo. This nutritional-based fermentate appeared to be safe and efficacious in a unique at-risk population and should receive more clinical research as a potential method to reduce the incidence of cold and flu-like symptoms, in individuals with and without a history of influenza vaccination.

Carbonate mound development in contrasting settings on the Irish margin

NASA Astrophysics Data System (ADS)

van der Land, Cees; Eisele, Markus; Mienis, Furu; de Haas, Henk; Hebbeln, Dierk; Reijmer, John J. G.; van Weering, Tjeerd C. E.

2014-01-01

Cold-water coral carbonate mounds, formed by framework building cold-water corals, are found in several mound provinces on the Irish margin. Differences in cold-water coral mound development rates and sediment composition between mounds at the southwest Rockall Trough margin and the Galway Mound in the Porcupine Seabight are investigated. Variations in sediment composition in the two mound provinces are related to the local environmental conditions and sediment sources. Mound accumulation rates are possibly higher at the Galway Mound probably due to a higher influx of hemipelagic fine grained non-carbonate sediments. In both cold-water coral mound areas, mound growth has been continuous for the last ca 11,000 years, before this period several hiatuses and unconformities exist in the mound record. The most recent unconformity can be correlated across multiple mounds and mound provinces at the Irish margin on the basis of apparent age. On the southwest Rockall Trough margin these hiatuses/unconformities are associated with post-depositional aragonite dissolution in, and lithification of, certain intervals, while at Galway Mound no lithification occurs. This study revealed that the influx and types of material transported to cold-water coral mounds may have a direct impact on the carbonate mound accumulation rate and on post-depositional processes. Significantly, the Logachev Mounds on the SW Rockall Trough margin accumulate slower but, because they contain lithified layers, are less susceptible to erosion. This net effect may account for their larger size compared to the Belgica Mounds.

Effect of cold indoor environment on physical performance of older women living in the community.

PubMed

Lindemann, Ulrich; Oksa, Juha; Skelton, Dawn A; Beyer, Nina; Klenk, Jochen; Zscheile, Julia; Becker, Clemens

2014-07-01

the effects of cold on older persons' body and mind are not well documented, but with an increased number of older people with decreasing physical performance, these possible effects need to be understood. to investigate the effect of cold indoor environment on physical performance of older women. cross-sectional experimental study with two test conditions. movement laboratory in a climate chamber. eighty-eight community-dwelling, cognitively unimpaired older women (mean age 78 years). participants were exposed to moderately cold (15°C) and warm/normal (25°C) temperature in a climate chamber in random order with an interval of 1 week. The assessment protocol included leg extensor power (Nottingham Power Rig), sit-to-stand performance velocity (linear encoder), gait speed, walk-ratio (i.e. step length/cadence on an instrumented walk way), maximal quadriceps and hand grip strength. physical performance was lower in 15°C room temperature compared with 25°C room temperature for leg extensor power (P < 0.0001), sit-to-stand performance velocity (P < 0.0001), gait speed (P < 0.0001), walk-ratio (P = 0.016) and maximal quadriceps strength (P = 0.015), but not for hand grip strength. in healthy older women a moderately cold indoor environment decreased important physical performance measures necessary for independent living. © The Author 2014. Published by Oxford University Press on behalf of the British Geriatrics Society. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Tropical African Glacier Fluctuations During Termination 1

NASA Astrophysics Data System (ADS)

Jackson, M. S.; Kelly, M. A.; Russell, J. M.; Doughty, A. M.; Howley, J. A.; Zimmerman, S. R. H.

2017-12-01

As the primary source of latent heat and water vapor to the atmosphere, the tropics are a key element of Earth's climate system. However, the potential role of the tropics in past climate change, and particularly abrupt climate changes, is uncertain. A first step to assessing the role of the low latitudes in both past and future climate is to determine the timing and spatial variability of past climate change in the tropics. Termination 1, the time of most rapid global warming of the last glacial cycle, is an ideal period on which to focus. We present a 10Be chronology of glaciation from the Rwenzori Mountains, Uganda, which elucidates the timing and magnitude of deglacial warming in the African tropics through the Termination, from the Last Glacial Maximum (LGM) to the Holocene. Ice retreated from its maximum LGM extent by 20.7 ka. In the Bujuku valley, a series of nested moraines deposited between 15-14 ka attest to late-glacial ice extent. In both the Bujuku and Nyamugasani valleys, moraine sequences and erratic boulders indicate glacier retreat following the Younger Dryas (YD) and during the early Holocene. The preliminary chronology from these moraines suggests that glaciers were more extensive during the Antarctic Cold Reversal (ACR) than during the YD. This chronology is similar to that observed in the South American tropics, where expanded glaciers during the ACR are recognized across the high Andes. This suggests that glaciers across the tropics responded to a common forcing during Termination 1, likely temperature. Possible mechanisms to induce such temperature change include global climate boundary conditions, and greenhouse gas forcing in particular, as well as tropical ocean variability.

Diatom-based inference of Asian monsoon precipitation from a volcanic lake in southwest China for the last 18.5 ka

NASA Astrophysics Data System (ADS)

Li, Yanling; Chen, Xu; Xiao, Xiayun; Zhang, Hucai; Xue, Bin; Shen, Ji; Zhang, Enlou

2018-02-01

Diatom in the volcanic lake provides proxy evidence for pH changes that are characterized by variations in the percentage of acidophilous diatom species. The information regarding the hydrology of the lake, derived from a previous publication and survey of one year on the lake, indicate that pH is low during the wet season and higher during the dry season. Therefore, variations in lake water pH may be considered as a proxy record for past changes in precipitation. In the sediment, high/low relative abundance of acidophilous diatom species indicates high/low precipitation. The diatom record of the past 18.5 ka BP shows that precipitation decrease during the periods 17.0-15.0, 13.3-11.3, and 0.7-0.3 ka BP corresponding to the Heinrich Event 1 (H1), the Younger Dryas cold event (YD), and the Little Ice Age (LA). A marked precipitation increase between 15.0 and 14.5 ka BP occurred at the end of H1 and before the Bølling-Allerød (BA), which indicates a strong pre-Bølling wetting. The start of the Holocene is recorded at 11.3 ka BP. The climate was the wettest between 11.3 and 7.5 ka BP., then the wetter between 7.5 and 3.4 ka BP. Between 3.4 and 0.7 ka BP, the precipitation decrease in general, but in the period from 1.3 to 0.8 ka BP the precipitation was higher corresponding to the Medieval Warm Period (MWP). Our results support the hypothes that the Indian Summer Monsoon (ISM) was strongest during the Early Holocene.

Timing and east-west correlation of south Swedish ice marginal lines during the Late Weichselian

NASA Astrophysics Data System (ADS)

Lundqvist, Jan; Wohlfarth, Barbara

2000-01-01

The retreat of the Late Weichselian ice sheet over the southern part of Sweden is marked along the southwest coast by distinct marginal moraine ridges. Their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines. Along the southeastern side of the peninsula, the ice recession has been reconstructed based on a combination of clay-varve chronology, pollen and radiocarbon stratigraphy. A morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west-coast moraines cannot be followed through the central part of the peninsula towards the east coast. This paper is an attempt to reconstruct an age-equivalent west-east extension of the ice-recession lines on the basis of existing data sets. For our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon-dated clay-varve chronology on the east coast. We conclude that the two oldest moraines on the west coast formed at ˜18,000-16,000 and ˜15,400-14,500 cal yr BP, respectively. During the following rapid deglaciation, which may have coincided with the beginning of the Bølling pollen zone, large parts of southernmost Sweden became ice free, except for higher elevated areas, where stagnant ice remained for another 400-500 yr. A best guess is that the formation of the next younger ice marginal lines may have occurred at ˜14,400-14,200, ˜14,200 and ˜13,400 cal yr BP and during the Younger Dryas cold event.

Revisiting Lake Hämelsee: reconstructing abrupt Lateglacial climate transitions using state- of-the-art palaeoclimatological proxies

NASA Astrophysics Data System (ADS)

Engels, Stefan; Hoek, Wim; Lane, Christine; Sachse, Dirk; Wagner-Cremer, Friederike

2015-04-01

Lake Hämelsee (Germany) is one of the northernmost sites in NW Europe that has varved sediments throughout large parts of its Lateglacial and Early Holocene sediment sequence. Previous research on this site has shown its potential, in terms of chronological resolution and palaeoecological reconstructions, for reconstructing the abrupt transitions into and out of the Younger Dryas, the last cold period of the last glacial. The site was revisited during a 1-week summer school for Early Stage Researchers (2013), within the INTIMATE Example training and research project, supported by EU Cost Action ES0907. Two overlapping sediment sequences were retrieved from the centre of the lake during the summer school. These sediments have since formed the basis for follow-up research projects, which have sparked the collaboration of around 30 researchers in 12 laboratories across Europe. A chronological framework for the core has been composed from a combination of varve counting, radiocarbon dating and tephrochronology. Tephrostratigraphic correlations allow direct correlation and precise comparison of the record to marine and ice core records from the North Atlantic region, and other terrestrial European archives. Furthermore, the core is has been subjected to multiple sedimentological (e.g. XRF, loss-on-ignition), geochemical (e.g. lipid biomarkers, GDGTs) and palaeoecological (e.g. pollen, chironomids) proxy-based reconstructions of past environmental and climatic conditions. The results provide important insights into the nature of the abrupt climate transitions of the Lateglacial and Early Holocene, both locally and on a continental scale. The INTIMATE Example participants: Illaria Baneschi, Achim Brauer, Christopher Bronk Ramsey, Renee de Bruijn, Siwan Davies, Aritina Haliuc, Katalin Hubay, Gwydion Jones, Meike Müller, Johanna Menges, Josef Merkt, Tom Peters, Francien Peterse, Anneke ter Schure, Kathrin Schuetrumpf, Richard Staff, Falko Turner, Valerie van den Bos.

The Younger Dryas Main Line on Leka, Norway, as determined from a high resolution digital elevation model derived from airborne LiDAR data

NASA Astrophysics Data System (ADS)

Høgaas, Fredrik; Sveian, Harald

2015-02-01

The Main Line is a conspicuous late glacial erosive feature along parts of the Norwegian coastline. Although the shoreline has been much studied, the genesis of the ancient raised sea-level is still somewhat unaccounted for. In this study, the Main Line on Leka, Norway, is illuminated through a high resolution (1 m pixel size) digital elevation model (DEM) derived from airborne LiDAR data. The DEM allows a detailed mapping of the shoreline's dimensions and actual distribution and hence provides an improved foundation for interpreting the pronounced features. A new method for estimating cliff degradation during shoreline formation is presented. The Main Line is found from 106-112 m asl on Leka. Varying platform morphology across the island points to different shore-eroding mechanisms. The shoreline is thought to be developed through the interaction of sea-ice processes and freeze-thaw mechanisms, where the former agent is considered to be of particular importance where the platforms are most levelled. A bulge on the outermost part of the shoreline features is described for the first time and interpreted as a consequence of freeze-on plucking. Mean platform widths range from 9-29 m, while mean cliff degradation is estimated to be 140 m3 m- 1. By adapting the age span of Main Line formation reported elsewhere, maximum erosion rates over 1 Ma totals to 58 km. The study sheds light on the Main Line's potential as a reference level when assessing postglacial landscape development and highlights the significance of episodic erosional events in cold climate regimes.

Searching for Abrupt Circulation Shifts in Marine Isotope Stage 2 and 3

NASA Astrophysics Data System (ADS)

Henry, L. E.; Lynch-Stieglitz, J.; Schmidt, M. W.

2008-12-01

During Marine Isotope Stage 3, DO events were recorded in the Greenland ice cores and North Atlantic Ocean sediment records. Some cold DO stadials have been associated with massive freshwater inputs, termed Heinrich Events. These Heinrich Events are frequently associated with "drop dead" circulation periods in which the production of North Atlantic Deep Water is greatly diminished. DO events are thought to result from a restructuring of the overturning circulation. We explore these proposed changes in Atlantic Ocean circulation by examining changes in seawater density in the Florida Straits. The density is inferred from the δ18O of the benthic foraminifera C. pachyderma and P. ariminensis taken from core-sites on the Florida and Greater Bahamas Bank margins. The flow through the Florida Straits is in near- geostrophic balance. This means that the vertical shear in the current is reflected in a strong density gradient across the Straits. During the Younger Dryas and the Last Glacial Maximum the density gradient was reduced consistent with weaker flow through the Straits at these times. A weakening of the Florida Current would be expected if the large scale Atlantic Meridional Overturning Circulation weakened, as has been proposed based on other studies. The Younger Dyras event manifests itself as well-correlated decreases in δ18O from the cores on the Florida margin, while their counterparts taken from the Bahamas remain relatively stable when adjusted for global ice volume. Here, we will present data extending back 32kyr, focusing on those cores taken from the Florida Margin which can resolve millennial scale changes during Marine Isotope Stage 2 and Late Stage 3. We will examine the relationship between circulation changes, as reflected in Florida Margin density, and the three most recent Heinrich events, as well as the most recent DO events.

Abrupt aridities in the Levant-Sahel linked with solar activities

NASA Astrophysics Data System (ADS)

Stein, M.; Kushnir, Y.

2012-04-01

Observations of 19th and 20th century precipitation in the Dead Sea watershed region display a multidecadal, anti-phase relationship to North Atlantic (NAtl) sea surface temperature (SST) variability, such that when the NAtl is relatively cold, Jerusalem experiences higher than normal precipitation and vice versa. This association is underlined by a negative correlation to precipitation in the sub-Saharan Sahel and a positive correlation to precipitation in western North America, areas that are also affected by multidecadal NAtl SST variability. These observations are consistent with broad range of Holocene hydroclimatic fluctuations from the epochal, to the millennial and centennial time scales, as displayed by the Dead Sea and Sahelian lake levels and by direct and indirect proxy indicators of NAtl SSTs. On the epochal time scale, the gradual cooling of NAtl SSTs throughout the Holocene in response to precession-driven reduction of summer insolation is associated with previously well-studied wet-to-dry transition in the Sahel and with a general increase in Dead Sea lake levels from low stands after the Younger Dryas to higher stands in the mid- to late-Holocene. On the millennial and centennial time scales there is also evidence for an antiphase relationship between Holocene variations in the Dead Sea and Sahelian lake levels and with proxy indicators of NAtl SSTs. However, the records are punctuated by abrupt lake-level drops and extensive expansion of the desert belt at ~8.1, 5.7, 3.3 and 1.4 ka cal BP, which appear to be in-phase and which occur during previously documented abrupt major cooling events in the Northern Hemisphere. We link these cooling to solar activity variations that were identified in the North Atlantic IRD and cosmogenic isotopes records.

Late Quaternary palaeolakes, rivers, and wetlands on the Bolivian Altiplano and their palaeoclimatic implications

NASA Astrophysics Data System (ADS)

Rigsby, Catherine A.; Platt Bradbury, J.; Baker, Paul A.; Rollins, Stephanie M.; Warren, Michelle R.

2005-10-01

Drill cores of sediments from the Rio Desaguadero valley, Bolivia, provide new information about the climate of tropical South America over the past 50 000 years. The modern Rio Desaguadero is fed by Lake Titicaca overflow (and by local tributaries) in the wetter northern Altiplano and discharges into Lake Poopo in the more arid central Altiplano. During the late Quaternary the Rio Desaguadero valley was the site of several generations of palaeolakes and wetlands that formed during periods of increased precipitation and local runoff, augmented by increased overflow from Lake Titicaca. Sediments recovered by drilling in eight localities along the 390-km long valley of the Rio Desaguadero yield a regional history of lacustrine sedimentation and effective precipitation. Lacustrine strata in the drill cores record 12 distinct wet periods in the past 50 000 years. Four of these wet periods resulted in the formation of major palaeolakes in the Rio Desaguadero valley: during the last glacial maximum from before 20 000 to 16 000 cal. yr BP, during the late glacial from about 14 000 to 12 000 cal. yr BP, in the early Holocene from about 10 000 to 7900 cal. yr BP, and in the late Holocene from 4500 cal. yrBP to present. The period that appears to have been most arid was between 7900 and 4500cal.yrBP. The Altiplano wet periods were generally synchronous with North Atlantic cold events (respectively, the last glacial maximum, the Younger Dryas, the 8200cal.yrBP event, and the Neoglacial) implying a relationship between past precipitation variability in tropical South America and North Atlantic sea-surface temperature.

Select, High-Resolution Windows Into Sub-Centennial-Scale Climate Variability in the Western Pacific Warm Pool Between 7 and 12 ka

NASA Astrophysics Data System (ADS)

Quinn, T. M.; Taylor, F. W.; Cheng, H.; Edwards, R. L.; Burr, G.; Chen, Y.

2004-12-01

Post-glacial, coral-based climate records from the Western Pacific Warm Pool (WPWP), a region that serves as a major heat and moisture source to the ocean-atmosphere system, provide sub-annually resolved windows into climate variability on interannual to multi-decadal timescales from this climatologically significant region. Paleoclimate reconstructions based on fossil corals require that the skeletal geochemistry be unaffected by diagenesis and that secular changes in seawater chemistry be known. Global seawater \\delta18O variations can be constrained using knowledge of past variations in ice volume, whereas much less is known about global seawater Sr/Ca variations, if they occur in the post-glacial interval. Our paleoclimate reconstructions are based on monthly resolved \\delta18O and Sr/Ca records in fossil Porites corals from the Western Solomon Islands ( ˜8° S, ˜157° E; Tetepare and Rendova). Post-depositional alteration of our fossil coral samples is minimal based on mineralogic (XRD), petrographic (SEM) and geochemical criteria (preservation of modern marine initial \\delta234U values). Four of these fossil coral time series are of particular interest: 99RND (age, 7,992±42; ~45 years), 01T-B (age, 7,647±73; ~65 years), 01T-AQ (age, 10,208±44; ~30 years), and 99TET-B (age, 11,987±69; ~ 30 years). We apply a model that uses simultaneous variations in coral \\delta18O and Sr/Ca in combination with estimates of post-glacial changes in seawater chemistry to reconstruct mean climate state during the early Holocene and the Younger Dryas. Model results indicate that on average SSTs in the WPWP were within 1° C of modern and that surface waters were more saline than modern during each of the four time intervals during which our fossil corals grew.

Late Quaternary Hydroclimate of Arid Northeastern Mexico: Response of Millennial-scale Global Climate Change and the Atlantic Warm Pool

NASA Astrophysics Data System (ADS)

Roy, P. D.; Shanahan, T. M.; Sánchez Zavala, J. L.; Lozano-SantaCruz, R.; Vera-Vera, G.

2017-12-01

Model projections suggest that drought-prone northeastern Mexico could experience an increase of more than 2 ºC in mean annual temperature and precipitation could decrease at least by 10-20% over the 21st century. The combination of drought and warmth would enhance the dryness of this water-stressed region in the coming decades. However, because of the lack of long continuous records from the region, little is known about the past controls on climate variability in northeast Mexico. In order to better understand the susceptibility of this climatically sensitive but data-poor region, we present a new multi-proxy record of past hydrological changes from paleo-lacustrine deposits in the Sandia Basin ( 24°N) over the last 32 cal ka BP. We reconstruct runoff from changes in the abundance of Al-bearing clastic minerals and local hydrological changes from the oxygen isotope composition of lacustrine carbonates, as well as gypsum/calcite abundances. During the cooler Heinrich Stadials (HS3, HS2 and HS1) and Younger Dryas, the basin received less runoff and the lake was more saline, though hydrological conditions varied significantly throughout these stadial events. The wettest interval in the record occurred coincident with the Bølling-Allerød (B/A) interstadial. Arid conditions returned during the Holocene, with low sedimentation rates, reduced proxy runoff indicators, and enhanced gypsum deposition suggesting this was the driest interval of the last 30 ka. Our observations are consistent with a growing number of records from across both northeastern Mexico and the southern Great Plains suggesting dry conditions associated with North Atlantic stadials and a sudden but transient shift to wetter conditions accompanying the strengthening of the overturning circulation during the B/A. We will evaluate the possible influence of Atlantic Warm Pool on hydroclimate of the region by comparing the different proxy records to the sea-surface temperature of Gulf of Mexico, Caribbean Sea and tropical Atlantic Ocean.

An improved chronology for the Lateglacial palaeoenvironmental record of Lake Haemelsee, Germany: challenges for independent site comparisons

NASA Astrophysics Data System (ADS)

Lane, Christine; Brauer, Achim; Ramsey Christopher, Bronk; Engels, Stefan; Haliuc, Aritina; Hoek, Wim; Hubay, Katalin; Jones, Gwydion; Sachse, Dirk; Staff, Richard; Turner, Falko; Wagner-Cremer, Frederike

2016-04-01

Exploring temporal and spatial variability of environmental response to climatic changes requires the comparison of widespread palaeoenvironmental sequences on their own, independently-derived, age models. High precision age-models can be constructed using statistical methods to combine absolute and relative age estimates measured using a range of techniques. Such an approach may help to highlight otherwise unrecognised uncertainties, where a single dating method has been applied in isolation. Radiocarbon dating, tephrochronology and varve counting have been combined within a Bayesian depositional model to build a chronology for a sediment sequence from Lake Haemelsee (Northern Germany) that continuously covers the entire Lateglacial and early Holocene. Each of the dating techniques used brought its own challenges. Radiocarbon dates provide the only absolute ages measured directly in the record, however a low macrofossil content led to small sample sizes and a limited number of low precision dates. A floating varved interval provided restricted but very precise relative dating for sediments covering the Allerød to Younger Dryas transition. Well-spaced, visible and crypto- tephra layers, including the widespread Laacher See , Vedde Ash, Askja-S and Saksunarvatn tephra layers, allow absolute ages for the tephra layers established in other locations to be imported into the Haemelsee sequence. These layers also provide multiple tie-lines that allow the Haemelsee sequences to be directly compared at particular moments in time, and within particular intervals, to other important Lateglacial archives. However, selecting the "best" published tephra ages to use in the Haemelsee age model is not simple and risks biasing comparison of the palaeoenvironmental record to fit one or another comparative archive. Here we investigate the use of multiple age models for the Haemelsee record, in order to retain an independent approach to investigating the environmental transitions of the Lateglacial to Early Holocene.

Why were Past North Atlantic Warming Conditions Associated with Drier Climate in the Western United States?

NASA Astrophysics Data System (ADS)

Wong, C. I.; Potter, G. L.; Montanez, I. P.; Otto-Bliesner, B. L.; Behling, P.; Oster, J. L.

2014-12-01

Investigating climate dynamics governing rainfall over the western US during past warmings and coolings of the last glacial and deglaciation is pertinent to understanding how precipitation patterns might change with future global warming, especially as the processes driving the global hydrological reorganization affecting this drought-prone region during these rapid temperature changes remain unresolved. We present model climates of the Bølling warm event (14,500 years ago) and Younger Dryas cool event (12,200 years ago) that i) uniquely enable the assessment of dueling hypothesis about the atmospheric teleconnections responsible for abrupt temperature shifts in the North Atlantic region to variations in moisture conditions across the western US, and ii) show that existing hypotheses about these teleconnections are unsupported. Modeling results show no evidence for a north-south shift of the Pacific winter storm track, and we argue that a tropical moisture source with evolving trajectory cannot explain alternation between wet/dry conditions, which have been reconstructed from the proxy record. Alternatively, model results support a new hypothesis that variations in the intensity of the winter storm track, corresponding to its expansion/contraction, can account for regional moisture differences between warm and cool intervals of the last deglaciation. Furthermore, we demonstrate that the mechanism forcing the teleconnection between the North Atlantic and western US is the same across different boundary conditions. In our simulation, during the last deglaciation, and in simulations of future warming, perturbation of the Rossby wave structure reconfigures the atmospheric state. This reconfiguration affects the Aleutian Low and high-pressure ridge over and off of the northern North American coastline driving variability in the storm track. Similarity between the processes governing the climate response during these distinct time intervals illustrates the robust nature of the teleconnection, a novel result that provides context for understanding the climate processes governing the response of moisture variability to future climate change.

Development of microstructure and mechanical properties during annealing of a cold-swaged Co-Cr-Mo alloy rod.

PubMed

Mori, Manami; Sato, Nanae; Yamanaka, Kenta; Yoshida, Kazuo; Kuramoto, Koji; Chiba, Akihiko

2016-12-01

In this study, we investigated the evolution of the microstructure and mechanical properties during annealing of a cold-swaged Ni-free Co-Cr-Mo alloy for biomedical applications. A Co-28Cr-6Mo-0.14N-0.05C (mass%) alloy rod was processed by cold swaging, with a reduction in area of 27.7%, and then annealed at 1173-1423K for various periods up to 6h. The duplex microstructure of the cold-swaged rod consisted of a face-centered cubic γ-matrix and hexagonal closed-packed ε-martensite developed during cold swaging. This structure transformed nearly completely to the γ-phase after annealing and many annealing twin boundaries were observed as a result of the heat treatment. A small amount of the ε-phase was identified in specimens annealed at 1173K. Growth of the γ-grains occurred with increasing annealing time at temperatures ≥1273K. Interestingly, the grain sizes remained almost unchanged at 1173K and a very fine grain size of approximately 8μm was obtained. The precipitation that occurred during annealing was attributed to the limited grain coarsening during heat treatment. Consequently, the specimens treated at this temperature showed the highest tensile strength and lowest ductility among the specimens prepared. An elongation-to-failure value larger than 30% is sufficient for the proposed applications. The other specimens treated at higher temperatures possessed similar tensile properties and did not show any significant variations with different annealing times. Optimization of the present rod manufacturing process, including cold swaging and interval annealing heat treatment, is discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Risk of hospitalization for fire-related burns during extreme cold weather.

PubMed

Ayoub, Aimina; Kosatsky, Tom; Smargiassi, Audrey; Bilodeau-Bertrand, Marianne; Auger, Nathalie

2017-10-01

Environmental factors are important predictors of fires, but no study has examined the association between outdoor temperature and fire-related burn injuries. We sought to investigate the relationship between extremely cold outdoor temperatures and the risk of hospitalization for fire-related burns. We carried out a time-stratified case-crossover study of 2470 patients hospitalized for fire-related burn injuries during cold months between 1989 and 2014 in Quebec, Canada. The main exposure was the minimum outdoor temperature on the day of and the day before the burn. We computed odds ratios (OR) and 95% confidence intervals (CI) to evaluate the relationship between minimum temperature and fire-related burns, and assessed how associations varied across sex and age. Exposure to extreme cold temperature was associated with a significantly higher risk of hospitalization for fire-related burns. Compared with 0°C, exposure to a minimum temperature of -30°C was associated with an OR of 1.51 (95% CI 1.22-1.87) for hospitalization for fire-related burns. The associations were somewhat stronger for women, youth, and the elderly. Compared with 0°C, a minimum temperature of -30°C was associated with an OR for fire-related burn hospitalization of 1.65 for women (95% CI 1.13-2.40), 1.60 for age < 25 years (95% CI 1.02-2.52), and 1.73 for age ≥ 65 years (95% CI 1.08-2.77). Extremely cold outdoor temperature is a risk factor for fire-related burns. Measures to prevent fires should be implemented prior to the winter season, and enhanced during extreme cold. Copyright © 2017 Elsevier Inc. All rights reserved.

Chinese patent medicines for the treatment of the common cold: a systematic review of randomized clinical trials.

PubMed

Chen, Wei; Liu, Bo; Wang, Li-qiong; Ren, Jun; Liu, Jian-ping

2014-07-30

Many Chinese patent medicines (CPMs) have been authorized by the Chinese State of Food and Drug Administration for the treatment of the common cold. A number of clinical trials have been conducted and published. However, there is no systematic review or meta-analysis on their efficacy and safety for the common cold to justify their clinical use. We searched CENTRAL, MEDLINE, EMBASE, SinoMed, CNKI, VIP, China Important Conference Papers Database, China Dissertation Database, and online clinical trial registry websites for published and unpublished randomized clinical trials (RCTs) of CPMs for the common cold till 31 March 2013. Revman 5.2 software was used for data analysis with effect estimate presented as relative risk (RR) and mean difference (MD) with a 95% confidence interval (CI). A total of five RCTs were identified. All of the RCTs were of high risk of bias with flawed study design and poor methodological quality. All RCTs included children aged between 6 months to 14 years. Results of individual trials showed that Shuanghuanglian oral liquid (RR 4.00; 95% CI: 2.26 to 7.08), and Xiaoer Resuqing oral liquid (RR 1.43; 95% CI: 1.15 to 1.77) had higher cure rates compared with antivirus drugs. Most of the trials did not report adverse events, and the safety of CPMs was still uncertain. Some CPMs showed a potential positive effect for the common cold on cure rate. However, due to the poor methodology quality and the defects in the clinical design of the included RCTs, such as the lack of placebo controlled trials, the inappropriate comparison intervention and outcome measurement, the confirmative conclusions on the beneficial effect of CPMs for the common cold could not be drawn.

Expanding NevCAN capabilities: monitoring cold air drainage flow along a narrow wash within a Montane to PJ ecotone

NASA Astrophysics Data System (ADS)

Bird, B. M.; Devitt, D.

2012-12-01

Cold air drainage flows are a naturally occurring physical process of mountain systems. Plant communities that exist in cold air drainage basins respond to these localized cold air trends, and have been shown to be decoupled from larger global climate weather systems. The assumption that air temperature decreases with altitude is violated within these systems and climate model results based on this assumption would ultimately be inaccurate. In arid regions, high radiation loads lead to significant long wave radiation being emitted from the ground later in the day. As incoming radiation ceases, the surface very quickly loses energy through radiative processes, leading to surface inversions and enhanced cold air drainage opportunities. This study is being conducted in the Mojave desert on Sheep Mountain located between sites 3 and 4 of the NSF EPSCoR network. Monitoring of cold air drainage was initiated in September of 2011within a narrow ravine located between the 2164 and 2350 meter elevation. We have installed 25 towers (5 towers per location situated at the central low point in a ravine and at equal distances up the sides of the ravine on both the N and S facing slopes) to assess air temperatures from 0.1 meters to a height of 3 meters at 25m intervals. Our goal is to better understand the connection between cold air movement and plant physiological response. The species monitored in this study include: Pinus ponderosa (common name: Ponderosa Pine), Pinus pinyon (Pinyon Pine), Juniperus osteosperma (Utah juniper), Cercocarpus intricatus (Mountain Mahogany) and Symphoricarpos (snowberry). Hourly air temperature measurements within the wash are being captured from 100 ibuttons placed within PVC solar radiation shields. We are also developing a modeling approach to assess the three dimensional movement of cold air over time by incorporating wind vectors captured from 5 2D sonic anemometers. Wind velocities will be paired with air temperatures to better understand the thermal dynamics of cold air drainage. Granier probes were installed in the five test species to monitor transpirational flow relative to cold air movement. Mid day soil - plant - water measurements are also being taken on a monthly basis during the growing season at all locations. Measurements include: leaf xylem water potential, stomata conductance, chlorophyll index readings, canopy minus ambient temperatures and surface soil moisture contents. To date the monitoring system has revealed cold air drainage occurring during periods of every month. We will report the physiological response of the five plant species, with emphasis on assessing the linkages with cold air movement.

Spatial and seasonal characteristics of cold-air pools in the upper Zêzere valley (Serra da Estrela, Portugal)

NASA Astrophysics Data System (ADS)

Mora, Carla

2010-05-01

Occurrence, formation, spatial patterns and intensity of cold air pools/lakes were studied in the Serra da Estrela (40° 20'N 7° 35'W, 1993m, Central Portugal) from January to December 2000. Data was collected using a network of air temperature dataloggers installed at different topographic positions (interfluves, valley floors and slopes) recording at 2-h intervals. A k-means classification was applied to the dataset of instantaneous air temperatures, and 3 types of thermal patterns were identified. Type 1 (66% cases) shows events with decreasing air temperatures with altitude. Type 2 (27% cases) shows accumulation of cold air in the valleys with higher valley floors showing the lowest temperatures. Type 3 (7% cases) show accumulation of cold air, but with lowest air temperatures in the valleys at lower altitudes. Causal factors for the occurrence of the patterns were studied by applying discriminant analysis on meteorological and topographical variables. Type 1 occurs under atmospheric instability conditions, while types 2 and 3 relate to atmospheric stability. Types 2 and 3 are controlled by seasonality and local insolation/shadowing effects. For the detailed study of cold air accumulations, two approaches were followed: the analysis of temperature differences between a station in a crest and a station in a glacial cirque floor; and, the analysis of 5-min interval temperature data along a transect in the Zêzere valley.The differences in air temperature between the glacier cirque floor (Covão Cimeiro, 1620m) and the crest (Cântaro Gordo, 1870m) were classified into 9 types of regime. Thermal inversions in the cirque were found in 6 types (48%). These are characterized in detail and the geographical and meteorological controlling factors are analyzed using one-way ANOVA and discriminant analysis. The 6 types show different daily regimes and inversion intensities, as well as a seasonal trend. The maximum inversion intensity was 9 °C, and the minimum temperature -17 °C at the cirque floor. Simultaneoulsy, the ridge showed -9 °C. Thermal inversions show atmospheric stability with low wind speed and low cloudiness. The sequence of patterns throughout the year is controlled by topographic factors and insolation at the cirque floor. The formation of thermal inversions in a NNE-SSW direction valley (Zêzere valley), their durationand dissipation were studied in detail during 5 days of atmospheric stability using air temperature recorded at 5-min intervals. During the day, air temperature decreased with altitude (-0.7 °C/100m to -1 °C/100m), and during the night, the valley floor showed lower temperatures than the mountain summit. During the night a thermal belt formed and the valley floor was 3 °C colder than the top of the inversion layer. During the day there was an asymmetry in the distribution of temperatures along the valley controlled by solar radiation. Air temperatures ranged from -5 °C to 16 °C. The results show the effect of topography on air temperatures in situations of atmospheric stability and can be extrapolated to the mountains with similar climatic and topographic conditions. The identification of the shadowing effect induced by valleys and its impact on the maintenance of cold air lakes during the morning in the valleys of North-South orientation can be of special interest for planning and environmental impact studies.

Pattern of xylem phenology in conifers of cold ecosystems at the Northern Hemisphere.

PubMed

Rossi, Sergio; Anfodillo, Tommaso; Čufar, Katarina; Cuny, Henri E; Deslauriers, Annie; Fonti, Patrick; Frank, David; Gričar, Jožica; Gruber, Andreas; Huang, Jian-Guo; Jyske, Tuula; Kašpar, Jakub; King, Gregory; Krause, Cornelia; Liang, Eryuan; Mäkinen, Harri; Morin, Hubert; Nöjd, Pekka; Oberhuber, Walter; Prislan, Peter; Rathgeber, Cyrille B K; Saracino, Antonio; Swidrak, Irene; Treml, Václav

2016-11-01

The interaction between xylem phenology and climate assesses forest growth and productivity and carbon storage across biomes under changing environmental conditions. We tested the hypothesis that patterns of wood formation are maintained unaltered despite the temperature changes across cold ecosystems. Wood microcores were collected weekly or biweekly throughout the growing season for periods varying between 1 and 13 years during 1998-2014 and cut in transverse sections for assessing the onset and ending of the phases of xylem differentiation. The data set represented 1321 trees belonging to 10 conifer species from 39 sites in the Northern Hemisphere and covering an interval of mean annual temperature exceeding 14 K. The phenological events and mean annual temperature of the sites were related linearly, with spring and autumnal events being separated by constant intervals across the range of temperature analysed. At increasing temperature, first enlarging, wall-thickening and mature tracheids appeared earlier, and last enlarging and wall-thickening tracheids occurred later. Overall, the period of wood formation lengthened linearly with the mean annual temperature, from 83.7 days at -2 °C to 178.1 days at 12 °C, at a rate of 6.5 days °C -1 . April-May temperatures produced the best models predicting the dates of wood formation. Our findings demonstrated the uniformity of the process of wood formation and the importance of the environmental conditions occurring at the time of growth resumption. Under warming scenarios, the period of wood formation might lengthen synchronously in the cold biomes of the Northern Hemisphere. © 2016 John Wiley & Sons Ltd.

Cold Urticaria, Immunodeficiency, and Autoimmunity Related to PLCG2 Deletions

PubMed Central

Ombrello, Michael J.; Remmers, Elaine F.; Sun, Guangping; Freeman, Alexandra F.; Datta, Shrimati; Torabi-Parizi, Parizad; Subramanian, Naeha; Bunney, Tom D.; Baxendale, Rhona W.; Martins, Marta S.; Romberg, Neil; Komarow, Hirsh; Aksentijevich, Ivona; Kim, Hun Sik; Ho, Jason; Cruse, Glenn; Jung, Mi-Yeon; Gilfillan, Alasdair M.; Metcalfe, Dean D.; Nelson, Celeste; O'Brien, Michelle; Wisch, Laura; Stone, Kelly; Douek, Daniel C.; Gandhi, Chhavi; Wanderer, Alan A.; Lee, Hane; Nelson, Stanley F.; Shianna, Kevin V.; Cirulli, Elizabeth T.; Goldstein, David B.; Long, Eric O.; Moir, Susan; Meffre, Eric; Holland, Steven M.; Kastner, Daniel L.; Katan, Matilda; Hoffman, Hal M.; Milner, Joshua D.

2012-01-01

Background Mendelian analysis of disorders of immune regulation can provide insight into molecular pathways associated with host defense and immune tolerance. Methods We identified three families with a dominantly inherited complex of cold-induced urticaria, antibody deficiency, and susceptibility to infection and autoimmunity. Immunophenotyping methods included flow cytometry, analysis of serum immunoglobulins and autoantibodies, lymphocyte stimulation, and enzymatic assays. Genetic studies included linkage analysis, targeted Sanger sequencing, and next-generation whole-genome sequencing. Results Cold urticaria occurred in all affected subjects. Other, variable manifestations included atopy, granulomatous rash, autoimmune thyroiditis, the presence of antinuclear antibodies, sinopulmonary infections, and common variable immunodeficiency. Levels of serum IgM and IgA and circulating natural killer cells and class-switched memory B cells were reduced. Linkage analysis showed a 7-Mb candidate interval on chromosome 16q in one family, overlapping by 3.5 Mb a disease-associated haplotype in a smaller family. This interval includes PLCG2, encoding phospholipase Cγ2 (PLCγ2), a signaling molecule expressed in B cells, natural killer cells, and mast cells. Sequencing of complementary DNA revealed heterozygous transcripts lacking exon 19 in two families and lacking exons 20 through 22 in a third family. Genomic sequencing identified three distinct in-frame deletions that cosegregated with disease. These deletions, located within a region encoding an autoinhibitory domain, result in protein products with constitutive phospholipase activity. PLCG2-expressing cells had diminished cellular signaling at 37°C but enhanced signaling at subphysiologic temperatures. Conclusions Genomic deletions in PLCG2 cause gain of PLCγ2 function, leading to signaling abnormalities in multiple leukocyte subsets and a phenotype encompassing both excessive and deficient immune function. (Funded by the National Institutes of Health Intramural Research Programs and others.) PMID:22236196

Search for Extraterrestrial Osmium at the Allerod - Younger Dryas Boundary

NASA Astrophysics Data System (ADS)

Beets, C.; Sharma, M.; Kasse, K.; Bohncke, S.

2008-12-01

Ir and Os are excellent markers of extraterrestrial impact events, due to their high abundance in ET objects (Alvarez et al., 1980 Science; Turekian, 1982 Geol. Bull. Am. Spec. Pap.). Os has the advantage over Ir, in that the 187Os/188Os ratio also greatly differs between meteorites and upper continental crust (UCC). The combination of [Os] and 187Os/188Os analyses would be superior in detecting any ET contribution. Firestone et al (2007 PNAS) attributed a widespread 12.9 ka Ir containing black carbon layer to a potential extraterrestrial impact at the Allerød-Younger Dryas (A-YD) boundary. In order to test this inference, we measured [Os] and 187Os/188Os on a radiocarbon dated A-YD record (13.210 to 12.788 cal years BP) from the Netherlands. This location is close to Lommel, a Belgian site studied by Firestone et al.(2007). The organic-rich sequence was sampled continuously over a 12 cm interval at 2 cm resolution (~70 years). About 10 g samples were freeze-dried, ground and homogenized in a zirconia ball-mill. The samples mixed with 190Os tracer solutions were dissolved in carius tubes and Os extracted in liquid bromine. Os was further purified using micro-distillation. Os isotopes were measured using N-TIMS on Dartmouth Triton. The procedural blank was 7 fg/g Os with an isotopic composition of 0.41±0.01 The Allerød samples have an order of magnitude higher abundance than UCC (200 vs. 30 pg/g), but similar 187Os/188Os ratios, >1.1. The sample at the base of the YD (12.893±75 cal years BP) contains a similar amount of Os, but has a distinctly lower isotopic signature, 0.53±0.002. The high [Os] in the A-YD section possibly reflects enrichment by preferential partitioning into organic matter. The Os isotope composition of 0.53, sandwiched between values >1.1, implies contribution of a significant amount of non-radiogenic Os. Since the pollen spectra show no reworking, the non-radiogenic Os could only have been delivered as a discrete pulse at 12.893 cal yr BP. The observation of the non-radiogenic Os isotope composition would therefore be consistent with a meteorite impact. However, it is intriguing to note there was a small volcanic eruption of Laacher See tephra (LST) at this time (surface immediately below LST = 12.979±147 cal years BP, Bittmann, 2007 Veget Hist Archeobot) approximately 150 km away. The timing of this eruption has been traditionally placed in upper Allerød, about 200 years before the onset of YD. More work is needed to resolve the issue of ET Os at the YD boundary.

Effect of cold storage on total phenolics content, antioxidant activity and vitamin C level of selected potato clones.

PubMed

Külen, Oktay; Stushnoff, Cecil; Holm, David G

2013-08-15

Twelve Colorado-grown specialty potato clones were evaluated for total phenolic content, antioxidant activity and ascorbic acid content at harvest and after 2, 4, 6 and 7 months cold storage at 4 °C. Potato clones were categorized as pigmented ('CO97226-2R/R', 'CO99364-3R/R', 'CO97215-2P/P', 'CO97216-3P/P', 'CO97227-2P/P', 'CO97222-1R/R', 'Purple Majesty', 'Mountain Rose' and 'All Blue'), yellow ('Yukon Gold') and white fleshed ('Russet Nugget', 'Russet Burbank'). Folin-Ciocalteu reagent was used to estimate total phenolic content, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS(•+) ) and 2,2-diphenyl-1-picrylhydrazyl (DPPH(•) ) radical scavenging assays were used to estimate antioxidant capacity. Pigmented potato genotypes had significantly higher total phenolic content and antioxidant activity at all data points than yellow- and white-fleshed cultivars. Vitamin C content was higher in 'Yukon Gold' than in the other clones. The highest level of vitamin C in all clones was at harvest and after 2 months in cold storage. Vitamin C content in all potato clones dropped rapidly with longer intervals of cold storage. Although total phenolic content and antioxidant activity fluctuated during cold storage, after 7 months of cold storage their levels were slightly higher than at harvest. Total phenolic content was better correlated with Trolox equivalent antioxidant capacity (TEAC)/ABTS(•+) than the TEAC/DPPH(•) radical scavenging assay. Pigmented potato clones had significantly higher total phenolic content and antioxidant activity, while the yellow-fleshed potato cultivar 'Yukon Gold' had significantly higher vitamin C content. Vitamin C content decreased in all potato clones during cold storage, while total phenolics increased in pigmented clones. © 2013 Society of Chemical Industry.

C-reactive protein and cold-pressor tolerance in the general population: the Tromsø Study.

PubMed

Schistad, Elina Iordanova; Stubhaug, Audun; Furberg, Anne-Sofie; Engdahl, Bo Lars; Nielsen, Christopher Sivert

2017-07-01

The aim of this study was to examine whether increases in severity of subclinical inflammation, measured by high-sensitivity C-reactive protein (hs-CRP), increased experimental pain sensitivity, measured by cold-pressor tolerance, and to test whether this relationship is independent of chronic pain. A large population-based study from 2007 to 2008, the sixth Tromsø Study, provided data from 12,981 participants. For the present analysis, complete data for 10,274 participants (age: median 58 years) were available. The main outcome measure was cold-pressor tolerance, tested by placing the dominant hand in circulating cold water (3°C) for a maximum of 106 seconds. Cox proportional hazard models, treating hand withdrawal during the cold-pressor test as the event and enduring the full test time as censored data, were used to investigate the relationship between hs-CRP levels (≤3 or >3 mg/L) and cold-pressure tolerance. The fully adjusted model was controlled for age, sex, education, body mass index, smoking status, alcohol consumption, emotional distress, statin usage, and self-reported presence of chronic pain. Additional analysis was performed in participants without chronic pain. Higher levels of hs-CRP were negatively related to cold-pressor tolerance (hazard ratio [HR] = 1.24, 95% confidence interval [CI], 1.12-1.37, P < 0.001), adjusted for age and sex. This relationship remained essentially unaltered after controlling for potential confounders (HR = 1.22, 95% CI, 1.09-1.36, P < 0.001), as well as for the presence of chronic pain (HR = 1.22, 95% CI, 1.09-1.36, P < 0.001). The present data show that subclinical inflammation is related to increased pain sensitivity, suggesting a potential role of inflammation in experimental pain which may be of importance for the development of clinical pain.

Longer-Term Impact of High and Low Temperature on Mortality: An International Study to Clarify Length of Mortality Displacement

PubMed Central

Bell, Michelle L.; de Sousa Zanotti Stagliorio Coelho, Micheline; Leon Guo, Yue-Liang; Guo, Yuming; Goodman, Patrick; Hashizume, Masahiro; Honda, Yasushi; Kim, Ho; Lavigne, Eric; Michelozzi, Paola; Hilario Nascimento Saldiva, Paulo; Schwartz, Joel; Scortichini, Matteo; Sera, Francesco; Tobias, Aurelio; Tong, Shilu; Wu, Chang-fu; Zanobetti, Antonella; Zeka, Ariana; Gasparrini, Antonio

2017-01-01

Background: In many places, daily mortality has been shown to increase after days with particularly high or low temperatures, but such daily time-series studies cannot identify whether such increases reflect substantial life shortening or short-term displacement of deaths (harvesting). Objectives: To clarify this issue, we estimated the association between annual mortality and annual summaries of heat and cold in 278 locations from 12 countries. Methods: Indices of annual heat and cold were used as predictors in regressions of annual mortality in each location, allowing for trends over time and clustering of annual count anomalies by country and pooling estimates using meta-regression. We used two indices of annual heat and cold based on preliminary standard daily analyses: a) mean annual degrees above/below minimum mortality temperature (MMT), and b) estimated fractions of deaths attributed to heat and cold. The first index was simpler and matched previous related research; the second was added because it allowed the interpretation that coefficients equal to 0 and 1 are consistent with none (0) or all (1) of the deaths attributable in daily analyses being displaced by at least 1 y. Results: On average, regression coefficients of annual mortality on heat and cold mean degrees were 1.7% [95% confidence interval (CI): 0.3, 3.1] and 1.1% (95% CI: 0.6, 1.6) per degree, respectively, and daily attributable fractions were 0.8 (95% CI: 0.2, 1.3) and 1.1 (95% CI: 0.9, 1.4). The proximity of the latter coefficients to 1.0 provides evidence that most deaths found attributable to heat and cold in daily analyses were brought forward by at least 1 y. Estimates were broadly robust to alternative model assumptions. Conclusions: These results provide strong evidence that most deaths associated in daily analyses with heat and cold are displaced by at least 1 y. https://doi.org/10.1289/EHP1756 PMID:29084393

Randomized Trial of Machine Perfusion Versus Cold Storage in Recipients of Deceased Donor Kidney Transplants With High Incidence of Delayed Graft Function.

PubMed

Tedesco-Silva, Helio; Mello Offerni, Juliano Chrystian; Ayres Carneiro, Vanessa; Ivani de Paula, Mayara; Neto, Elias David; Brambate Carvalhinho Lemos, Francine; Requião Moura, Lúcio Roberto; Pacheco E Silva Filho, Alvaro; de Morais Cunha, Mirian de Fátima; Francisco da Silva, Erica; Miorin, Luiz Antonio; Demetrio, Daniela Priscila; Luconi, Paulo Sérgio; da Silva Luconi, Waldere Tania; Bobbio, Savina Adriana; Kuschnaroff, Liz Milstein; Noronha, Irene Lourdes; Braga, Sibele Lessa; Barsante, Renata Cristina; Mendes Moreira, João Cezar; Fernandes-Charpiot, Ida Maria Maximina; Abbud-Filho, Mario; Modelli de Andrade, Luis Gustavo; Dalsoglio Garcia, Paula; Tanajura Santamaria Saber, Luciana; Fernandes Laurindo, Alan; Chocair, Pedro Renato; Cuvello Neto, Américo Lourenço; Zanocco, Juliana Aparecida; Duboc de Almeida Soares Filho, Antonio Jose; Ferreira Aguiar, Wilson; Medina Pestana, Jose

2017-05-01

This study compared the use of static cold storage versus continuous hypothermic machine perfusion in a cohort of kidney transplant recipients at high risk for delayed graft function (DGF). In this national, multicenter, and controlled trial, 80 pairs of kidneys recovered from brain-dead deceased donors were randomized to cold storage or machine perfusion, transplanted, and followed up for 12 months. The primary endpoint was the incidence of DGF. Secondary endpoints included the duration of DGF, hospital stay, primary nonfunction, estimated glomerular filtration rate, acute rejection, and allograft and patient survivals. Mean cold ischemia time was high but not different between the 2 groups (25.6 ± 6.6 hours vs 25.05 ± 6.3 hours, 0.937). The incidence of DGF was lower in the machine perfusion compared with cold storage group (61% vs. 45%, P = 0.031). Machine perfusion was independently associated with a reduced risk of DGF (odds ratio, 0.49; 95% confidence interval, 0.26-0.95). Mean estimated glomerular filtration rate tended to be higher at day 28 (40.6 ± 19.9 mL/min per 1.73 m 2 vs 49.0 ± 26.9 mL/min per 1.73 m 2 ; P = 0.262) and 1 year (48.3 ± 19.8 mL/min per 1.73 m 2 vs 54.4 ± 28.6 mL/min per 1.73 m 2 ; P = 0.201) in the machine perfusion group. No differences in the incidence of acute rejection, primary nonfunction (0% vs 2.5%), graft loss (7.5% vs 10%), or death (8.8% vs 6.3%) were observed. In this cohort of recipients of deceased donor kidneys with high mean cold ischemia time and high incidence of DGF, the use of continuous machine perfusion was associated with a reduced risk of DGF compared with the traditional cold storage preservation method.

The effects of ambient temperature on cerebrovascular mortality: an epidemiologic study in four climatic zones in China

PubMed Central

2014-01-01

Background Little evidence is available about the association between temperature and cerebrovascular mortality in China. This study aims to examine the effects of ambient temperature on cerebrovascular mortality in different climatic zones in China. Method We obtained daily data on weather conditions, air pollution and cerebrovascular deaths from five cities (Beijing, Tianjin, Shanghai, Wuhan, and Guangzhou) in China during 2004-2008. We examined city-specific associations between ambient temperature and the cerebrovascular mortality, while adjusting for season, long-term trends, day of the week, relative humidity and air pollution. We examined cold effects using a 1°C decrease in temperature below a city-specific threshold, and hot effects using a 1°C increase in temperature above a city-specific threshold. We used a meta-analysis to summarize the cold and hot effects across the five cities. Results Beijing and Tianjin (with low mean temperature) had lower thresholds than Shanghai, Wuhan and Guangzhou (with high mean temperature). In Beijing, Tianjin, Wuhan and Guangzhou cold effects were delayed, while in Shanghai there was no or short induction. Hot effects were acute in all five cities. The cold effects lasted longer than hot effects. The hot effects were followed by mortality displacement. The pooled relative risk associated with a 1°C decrease in temperature below thresholds (cold effect) was 1.037 (95% confidence interval (CI): 1.020, 1.053). The pooled relative risk associated with a 1°C increase in temperature above thresholds (hot effect) was 1.014 (95% CI: 0.979, 1.050). Conclusion Cold temperatures are significantly associated with cerebrovascular mortality in China, while hot effect is not significant. People in colder climate cities were sensitive to hot temperatures, while people in warmer climate cities were vulnerable to cold temperature. PMID:24690204

Effects of temperature on mortality in Chiang Mai city, Thailand: a time series study

PubMed Central

2012-01-01

Background The association between temperature and mortality has been examined mainly in North America and Europe. However, less evidence is available in developing countries, especially in Thailand. In this study, we examined the relationship between temperature and mortality in Chiang Mai city, Thailand, during 1999–2008. Method A time series model was used to examine the effects of temperature on cause-specific mortality (non-external, cardiopulmonary, cardiovascular, and respiratory) and age-specific non-external mortality (<=64, 65–74, 75–84, and > =85 years), while controlling for relative humidity, air pollution, day of the week, season and long-term trend. We used a distributed lag non-linear model to examine the delayed effects of temperature on mortality up to 21 days. Results We found non-linear effects of temperature on all mortality types and age groups. Both hot and cold temperatures resulted in immediate increase in all mortality types and age groups. Generally, the hot effects on all mortality types and age groups were short-term, while the cold effects lasted longer. The relative risk of non-external mortality associated with cold temperature (19.35°C, 1st percentile of temperature) relative to 24.7°C (25th percentile of temperature) was 1.29 (95% confidence interval (CI): 1.16, 1.44) for lags 0–21. The relative risk of non-external mortality associated with high temperature (31.7°C, 99th percentile of temperature) relative to 28°C (75th percentile of temperature) was 1.11 (95% CI: 1.00, 1.24) for lags 0–21. Conclusion This study indicates that exposure to both hot and cold temperatures were related to increased mortality. Both cold and hot effects occurred immediately but cold effects lasted longer than hot effects. This study provides useful data for policy makers to better prepare local responses to manage the impact of hot and cold temperatures on population health. PMID:22613086

Using bacterial and necrophagous insect dynamics for post-mortem interval estimation during cold season: Novel case study in Romania.

PubMed

Iancu, Lavinia; Carter, David O; Junkins, Emily N; Purcarea, Cristina

2015-09-01

Considering the biogeographical characteristics of forensic entomology, and the recent development of forensic microbiology as a complementary approach for post-mortem interval estimation, the current study focused on characterizing the succession of necrophagous insect species and bacterial communities inhabiting the rectum and mouth cavities of swine (Sus scrofa domesticus) carcasses during a cold season outdoor experiment in an urban natural environment of Bucharest, Romania. We monitored the decomposition process of three swine carcasses during a 7 month period (November 2012-May 2013) corresponding to winter and spring periods of a temperate climate region. The carcasses, protected by wire cages, were placed on the ground in a park type environment, while the meteorological parameters were constantly recorded. The succession of necrophagous Diptera and Coleoptera taxa was monitored weekly, both the adult and larval stages, and the species were identified both by morphological and genetic characterization. The structure of bacterial communities from swine rectum and mouth tissues was characterized during the same time intervals by denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene fragments. We observed a shift in the structure of both insect and bacterial communities, primarily due to seasonal effects and the depletion of the carcass. A total of 14 Diptera and 6 Coleoptera species were recorded on the swine carcasses, from which Calliphora vomitoria and C. vicina (Diptera: Calliphoridae), Necrobia violacea (Coleoptera: Cleridae) and Thanatophilus rugosus (Coleoptera: Silphidae) were observed as predominant species. The first colonizing wave, primarily Calliphoridae, was observed after 15 weeks when the temperature increased to 13°C. This was followed by Muscidae, Fanniidae, Anthomyiidae, Sepsidae and Piophilidae. Families belonging to Coleoptera Order were observed at week 18 when temperatures raised above 18°C, starting with Cleridae, Silphidae, and followed by Histeridae, Staphylinidae and Dermestidae. For bacteria, 53 taxa belonging to phyla Proteobacteria (Gammaproteobacteria, Betaproteobacteria), Firmicutes and Bacteroidetes were identified from the mouth cavity (36 OTUs) and rectum cavity (17 OTUs). These shifts in insect and bacterial communities indicated their complementary role in the carcass decomposition process. These results represent the first forensic entomological and microbiological survey in Romania. This study shows the value of forensic entomology as a tool for forensic investigations in Romania and neighboring areas with similar biogeographical characteristics. Moreover, this study represents a novel approach for understanding taphonomy and estimating post-mortem interval during cold season by combining entomological and microbiological methods. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

European vegetation during Marine Oxygen Isotope Stage-3

NASA Astrophysics Data System (ADS)

Huntley, Brian; Alfano, Mary J. o.; Allen, Judy R. M.; Pollard, Dave; Tzedakis, Polychronis C.; de Beaulieu, Jacques-Louis; Grüger, Eberhard; Watts, Bill

2003-03-01

European vegetation during representative "warm" and "cold" intervals of stage-3 was inferred from pollen analytical data. The inferred vegetation differs in character and spatial pattern from that of both fully glacial and fully interglacial conditions and exhibits contrasts between warm and cold intervals, consistent with other evidence for stage-3 palaeoenvironmental fluctuations. European vegetation thus appears to have been an integral component of millennial environmental fluctuations during stage-3; vegetation responded to this scale of environmental change and through feedback mechanisms may have had effects upon the environment. The pollen-inferred vegetation was compared with vegetation simulated using the BIOME 3.5 vegetation model for climatic conditions simulated using a regional climate model (RegCM2) nested within a coupled global climate and vegetation model (GENESIS-BIOME). Despite some discrepancies in detail, both approaches capture the principal features of the present vegetation of Europe. The simulated vegetation for stage-3 differs markedly from that inferred from pollen analytical data, implying substantial discrepancy between the simulated climate and that actually prevailing. Sensitivity analyses indicate that the simulated climate is too warm and probably has too short a winter season. These discrepancies may reflect incorrect specification of sea surface temperature or sea-ice conditions and may be exacerbated by vegetation-climate feedback in the coupled global model.

Tear Fluid SIgA as a Noninvasive Biomarker of Mucosal Immunity and Common Cold Risk.

PubMed

Hanstock, Helen G; Walsh, Neil P; Edwards, Jason P; Fortes, Matthew B; Cosby, Sara L; Nugent, Aaron; Curran, Tanya; Coyle, Peter V; Ward, Mark D; Yong, Xin Hui Aw

2016-03-01

Research has not convincingly demonstrated the utility of saliva secretory immunoglobulin-A (SIgA) as a biomarker of upper respiratory tract infection (URTI) risk, and disagreement exists about the influence of heavy exercise ("open-window theory") and dehydration on saliva SIgA. Prompted by the search for viable alternatives, we compared the utility of tear and saliva SIgA to predict URTI prospectively (study 1) and assessed the influence of exercise (study 2) and dehydration (study 3) using a repeated-measures crossover design. In study 1, 40 subjects were recruited during the common-cold season. Subjects provided tear and saliva samples weekly and recorded upper respiratory symptoms (URS) daily for 3 wk. Real-time PCR confirmed common-cold pathogens in 9 of 11 subjects reporting URS (82%). Predictive utility of tear and saliva SIgA was explored by comparing healthy samples with those collected during the week before URS. In study 2, 13 subjects performed a 2-h run at 65% V˙O2peak. In study 3, 13 subjects performed exercise heat stress to 3% body mass loss followed by overnight fluid restriction. Tear SIgA concentration and secretion rate were 48% and 51% lower, respectively, during URTI and 34% and 46% lower the week before URS (P < 0.05), but saliva SIgA remained unchanged. The risk of URS the following week increased ninefold (95% confidence interval, 1.7-48) when the tear SIgA secretion rate was <5.5 μg·min(-1) and sixfold (95% confidence interval, 1.2-29) when the tear SIgA secretion rate decreased >30%. Tear SIgA secretion rate >5.5 μg·min(-1) or no decrease of >30% predicted subjects free of URS in >80% of cases. Tear SIgA concentration decreased after exercise (-57%, P < 0.05) in line with the "open-window theory" but was unaffected by dehydration. Saliva flow rate decreased and saliva SIgA concentration increased after exercise and during dehydration (P < 0.05). Tear SIgA has utility as a noninvasive biomarker of mucosal immunity and common-cold risk.

Vitamin C for preventing and treating the common cold.

PubMed

Hemilä, Harri; Chalker, Elizabeth

2013-01-31

Vitamin C (ascorbic acid) for preventing and treating the common cold has been a subject of controversy for 70 years. To find out whether vitamin C reduces the incidence, the duration or severity of the common cold when used either as a continuous regular supplementation every day or as a therapy at the onset of cold symptoms. We searched CENTRAL 2012, Issue 11, MEDLINE (1966 to November week 3, 2012), EMBASE (1990 to November 2012), CINAHL (January 2010 to November 2012), LILACS (January 2010 to November 2012) and Web of Science (January 2010 to November 2012). We also searched the U.S. National Institutes of Health trials register and WHO ICTRP on 29 November 2012. We excluded trials which used less than 0.2 g per day of vitamin C and trials without a placebo comparison. We restricted our review to placebo-controlled trials. Two review authors independently extracted data. We assessed 'incidence' of colds during regular supplementation as the proportion of participants experiencing one or more colds during the study period. 'Duration' was the mean number of days of illness of cold episodes. Twenty-nine trial comparisons involving 11,306 participants contributed to the meta-analysis on the risk ratio (RR) of developing a cold whilst taking vitamin C regularly over the study period. In the general community trials involving 10,708 participants, the pooled RR was 0.97 (95% confidence interval (CI) 0.94 to 1.00). Five trials involving a total of 598 marathon runners, skiers and soldiers on subarctic exercises yielded a pooled RR of 0.48 (95% CI 0.35 to 0.64).Thirty-one comparisons examined the effect of regular vitamin C on common cold duration (9745 episodes). In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%). In children, 1 to 2 g/day vitamin C shortened colds by 18%. The severity of colds was also reduced by regular vitamin C administration.Seven comparisons examined the effect of therapeutic vitamin C (3249 episodes). No consistent effect of vitamin C was seen on the duration or severity of colds in the therapeutic trials.The majority of included trials were randomised, double-blind trials. The exclusion of trials that were either not randomised or not double-blind had no effect on the conclusions. The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise. Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out. Nevertheless, given the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, and the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them. Further therapeutic RCTs are warranted.

Respiratory virus transmission dynamics determine timing of asthma exacerbation peaks: Evidence from a population-level model.

PubMed

Eggo, Rosalind M; Scott, James G; Galvani, Alison P; Meyers, Lauren Ancel

2016-02-23

Asthma exacerbations exhibit a consistent annual pattern, closely mirroring the school calendar. Although respiratory viruses--the "common cold" viruses--are implicated as a principal cause, there is little evidence to link viral prevalence to seasonal differences in risk. We jointly fit a common cold transmission model and a model of biological and environmental exacerbation triggers to estimate effects on hospitalization risk. Asthma hospitalization rate, influenza prevalence, and air quality measures are available, but common cold circulation is not; therefore, we generate estimates of viral prevalence using a transmission model. Our deterministic multivirus transmission model includes transmission rates that vary when school is closed. We jointly fit the two models to 7 y of daily asthma hospitalizations in adults and children (66,000 events) in eight metropolitan areas. For children, we find that daily viral prevalence is the strongest predictor of asthma hospitalizations, with transmission reduced by 45% (95% credible interval =41-49%) during school closures. We detect a transient period of nonspecific immunity between infections lasting 19 (17-21) d. For adults, hospitalizations are more variable, with influenza driving wintertime peaks. Neither particulate matter nor ozone was an important predictor, perhaps because of the large geographic area of the populations. The school calendar clearly and predictably drives seasonal variation in common cold prevalence, which results in the "back-to-school" asthma exacerbation pattern seen in children and indirectly contributes to exacerbation risk in adults. This study provides a framework for anticipating the seasonal dynamics of common colds and the associated risks for asthmatics.

Both low and high temperature may increase the risk of stroke mortality

PubMed Central

Chen, Renjie; Wang, Cuicui; Meng, Xia; Chen, Honglei; Thach, Thuan Quoc; Wong, Chit-Ming

2013-01-01

Objective: To examine temperature in relation to stroke mortality in a multicity time series study in China. Methods: We obtained data on daily temperature and mortality from 8 large cities in China. We used quasi-Poisson generalized additive models and distributed lag nonlinear models to estimate the accumulative effects of temperature on stroke mortality across multiple days, adjusting for long-term and seasonal trends, day of the week, air pollution, and relative humidity. We applied the Bayesian hierarchical model to pool city-specific effect estimates. Results: Both cold and hot temperatures were associated with increased risk of stroke mortality. The potential effect of cold temperature might last more than 2 weeks. The pooled relative risks of extreme cold (first percentile of temperature) and cold (10th percentile of temperature) temperatures over lags 0–14 days were 1.39 (95% posterior intervals [PI] 1.18–1.64) and 1.11 (95% PI 1.06–1.17), compared with the 25th percentile of temperature. In contrast, the effect of hot temperature was more immediate. The relative risks of stroke mortality over lags 0–3 days were 1.06 (95% PI 1.02–1.10) for extreme hot temperature (99th percentile of temperature) and 1.14 (95% PI 1.05–1.24) for hot temperature (90th percentile of temperature), compared with the 75th percentile of temperature. Conclusions: This study showed that both cold and hot temperatures were associated with increased risk of stroke mortality in China. Our findings may have important implications for stroke prevention in China. PMID:23946311

Both low and high temperature may increase the risk of stroke mortality.

PubMed

Chen, Renjie; Wang, Cuicui; Meng, Xia; Chen, Honglei; Thach, Thuan Quoc; Wong, Chit-Ming; Kan, Haidong

2013-09-17

To examine temperature in relation to stroke mortality in a multicity time series study in China. We obtained data on daily temperature and mortality from 8 large cities in China. We used quasi-Poisson generalized additive models and distributed lag nonlinear models to estimate the accumulative effects of temperature on stroke mortality across multiple days, adjusting for long-term and seasonal trends, day of the week, air pollution, and relative humidity. We applied the Bayesian hierarchical model to pool city-specific effect estimates. Both cold and hot temperatures were associated with increased risk of stroke mortality. The potential effect of cold temperature might last more than 2 weeks. The pooled relative risks of extreme cold (first percentile of temperature) and cold (10th percentile of temperature) temperatures over lags 0-14 days were 1.39 (95% posterior intervals [PI] 1.18-1.64) and 1.11 (95% PI 1.06-1.17), compared with the 25th percentile of temperature. In contrast, the effect of hot temperature was more immediate. The relative risks of stroke mortality over lags 0-3 days were 1.06 (95% PI 1.02-1.10) for extreme hot temperature (99th percentile of temperature) and 1.14 (95% PI 1.05-1.24) for hot temperature (90th percentile of temperature), compared with the 75th percentile of temperature. This study showed that both cold and hot temperatures were associated with increased risk of stroke mortality in China. Our findings may have important implications for stroke prevention in China.

Relationships between skin temperature and temporal summation of heat and cold pain.

PubMed

Mauderli, Andre P; Vierck, Charles J; Cannon, Richard L; Rodrigues, Anthony; Shen, Chiayi

2003-07-01

Temporal summation of heat pain during repetitive stimulation is dependent on C nociceptor activation of central N-methyl-d-aspartate (NMDA) receptor mechanisms. Moderate temporal summation is produced by sequential triangular ramps of stimulation that control skin temperature between heat pulses but do not elicit distinct first and second pain sensations. Dramatic summation of second pain is produced by repeated contact of the skin with a preheated thermode, but skin temperature between taps is not controlled by this procedure. Therefore relationships between recordings of skin temperature and psychophysical ratings of heat pain were evaluated during series of repeated skin contacts. Surface and subcutaneous recordings of skin temperatures revealed efficient thermoregulatory compensation for heat stimulation at interstimulus intervals (ISIs) ranging from 2 to 8 s. Temporal summation of heat pain was strongly influenced by the ISIs and cannot be explained by small increases in skin temperature between taps or by heat storage throughout a stimulus series. Repetitive brief contact with a precooled thermode was utilized to evaluate whether temporal summation of cold pain occurs, and if so, whether it is influenced by skin temperature. Surface and subcutaneous recordings of skin temperature revealed a sluggish thermoregulatory compensation for repetitive cold stimulation. In contrast to heat stimulation, skin temperature did not recover between cold stimuli throughout ISIs of 3-8 s. Psychophysically, repetitive cold stimulation produced an aching pain sensation that progressed gradually and radiated beyond the site of stimulation. The magnitude of aching pain was well related to skin temperature and thus appeared to be established primarily by peripheral factors.

Permafrost carbon as a missing link to explain CO 2 changes during the last deglaciation

NASA Astrophysics Data System (ADS)

Crichton, K. A.; Bouttes, N.; Roche, D. M.; Chappellaz, J.; Krinner, G.

2016-09-01

The atmospheric concentration of CO2 increased from 190 to 280 ppm between the last glacial maximum 21,000 years ago and the pre-industrial era. This CO2 rise and its timing have been linked to changes in the Earth’s orbit, ice sheet configuration and volume, and ocean carbon storage. The ice-core record of δ13CO2 (refs ,) in the atmosphere can help to constrain the source of carbon, but previous modelling studies have failed to capture the evolution of δ13CO2 over this period. Here we show that simulations of the last deglaciation that include a permafrost carbon component can reproduce the ice core records between 21,000 and 10,000 years ago. We suggest that thawing permafrost, due to increasing summer insolation in the northern hemisphere, is the main source of CO2 rise between 17,500 and 15,000 years ago, a period sometimes referred to as the Mystery Interval. Together with a fresh water release into the North Atlantic, much of the CO2 variability associated with the Bølling-Allerod/Younger Dryas period ~15,000 to ~12,000 years ago can also be explained. In simulations of future warming we find that the permafrost carbon feedback increases global mean temperature by 10-40% relative to simulations without this feedback, with the magnitude of the increase dependent on the evolution of anthropogenic carbon emissions.

Late Quaternary loess in northeastern Colorado: Part I - Age and paleoclimatic significance

USGS Publications Warehouse

Muhs, D.R.; Aleinikoff, J.N.; Stafford, Thomas W.; Kihl, R.; Been, J.; Mahan, S.A.; Cowherd, S.

1999-01-01

Loess in eastern Colorado covers an estimated 14000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20-14 ka) and correlates reasonably well with the culmination and retreat of Pinedale glaciers in the Colorado Front Range during the last glacial maximum. The second period of loess deposition occurred between ca. 11 000 and 9000 14C yr B.P. This interval may be Holocene or may correlate with a hypothesized Younger Dryas glacial advance in the Colorado Front Range. Sedimentologic, mineralogic, and geochemical data indicate that as many as three sources could have supplied loess in eastern Colorado. These sources include glaciogenic silt (derived from the Colorado Front Range) and two bedrock sources, volcaniclastic silt from the White River Group, and clays from the Pierre Shale. The sediment sources imply a generally westerly paleowind during the last glacial maximum. New carbon isotope data, combined with published faunal data, indicate that the loess was probably deposited on a cool steppe, implying a last glacial maximum July temperature depression, relative to the present, of at least 5-6??C. Overall, loess deposition in eastern Colorado occurred mostly toward the end of the last glacial maximum, under cooler and drier conditions, with generally westerly winds from more than one source.

Marine sediment cores database for the Mediterranean Basin: a tool for past climatic and environmental studies

NASA Astrophysics Data System (ADS)

Alberico, I.; Giliberti, I.; Insinga, D. D.; Petrosino, P.; Vallefuoco, M.; Lirer, F.; Bonomo, S.; Cascella, A.; Anzalone, E.; Barra, R.; Marsella, E.; Ferraro, L.

2017-06-01

Paleoclimatic data are essential for fingerprinting the climate of the earth before the advent of modern recording instruments. They enable us to recognize past climatic events and predict future trends. Within this framework, a conceptual and logical model was drawn to physically implement a paleoclimatic database named WDB-Paleo that includes the paleoclimatic proxies data of marine sediment cores of the Mediterranean Basin. Twenty entities were defined to record four main categories of data: a) the features of oceanographic cruises and cores (metadata); b) the presence/absence of paleoclimatic proxies pulled from about 200 scientific papers; c) the quantitative analysis of planktonic and benthonic foraminifera, pollen, calcareous nannoplankton, magnetic susceptibility, stable isotopes, radionuclides values of about 14 cores recovered by Institute for Coastal Marine Environment (IAMC) of Italian National Research Council (CNR) in the framework of several past research projects; d) specific entities recording quantitative data on δ18O, AMS 14C (Accelerator Mass Spectrometry) and tephra layers available in scientific papers. Published data concerning paleoclimatic proxies in the Mediterranean Basin are recorded only for 400 out of 6000 cores retrieved in the area and they show a very irregular geographical distribution. Moreover, the data availability decreases when a constrained time interval is investigated or more than one proxy is required. We present three applications of WDB-Paleo for the Younger Dryas (YD) paleoclimatic event at Mediterranean scale and point out the potentiality of this tool for integrated stratigraphy studies.

a Marine Record of Holocene Climate Events in Tropical South America

NASA Astrophysics Data System (ADS)

Haug, G. H.; Günther, D.; Hughen, K. A.; Peterson, L. C.; Röhl, U.

2002-12-01

Metal concentration data (Ti, Fe) from the anoxic Cariaco Basin off the Venezuelan coast record with subdecadal to seasonal resolution variations in the hydrological cycle over tropical South America during the last 14 ka. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene `thermal maximum'. Since ~5.4 ka, a trend towards drier conditions is evident from the data, with high amplitude fluctuations and precipitation minima during the time interval 3.8 to 2.8 ka and during the `Little Ice Age'. O pronouced increase in precipitation coincides with the phase sometimes referred to as the `Medieval Warm Period'. These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The variations recorded in Cariaco Basin sediments coincide with events in societal evolution that have been suggested previously to be motivated by environmental change. Regionally, the Cariaco record supports the notion that the collapse of this civilization between 800 and 1000 AD coincided with an extended period of drier conditions, implying that the rapid growth of Mayan culture from 600 to 800 AD may have resulted in a population operating at the fringes of the environment's carrying capacity. The Cariaco Basin record also hints at tropical climate events similar in timing to high latitude changes in the North Atlantic often invoked as pivotal to societal developments in Europe.

Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

USGS Publications Warehouse

Addison, Jason A.; Finney, Bruce P.; Dean, Walter E.; Davies, Maureen H.; Mix, Alan C.; Jaeger, John M.

2012-01-01

Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration (∼10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values (∼6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values (∼3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values (∼5000 g cm−2 kyr−1) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary δ15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ15N (6.3 ± 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced terrestrial runoff; and/or the intermittent presence of seasonal sea ice resulting from altered ocean/atmospheric circulation during the B-A in the Gulf of Alaska.

Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

USGS Publications Warehouse

Addison, Jason A.; Finney, Bruce P.; Dean, Walter E.; Davies, Maureen H.; Mix, Alan C.; Stoner, Joseph S.; Jaeger, John M.

2012-01-01

Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration (∼10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values (∼6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values (∼3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values (∼5000 g cm−2 kyr−1) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary δ15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ15N (6.3 ± 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced terrestrial runoff; and/or the intermittent presence of seasonal sea ice resulting from altered ocean/atmospheric circulation during the B-A in the Gulf of Alaska.

Century-scale climate-driven vegetation and environmental dynamics in southern Siberia during the last 47 kyr

NASA Astrophysics Data System (ADS)

Tarasov, Pavel; Bezrukova, Elena; Solovieva, Nadia; Riedel, Frank

2010-05-01

Radiocarbon-dated pollen and diatom records from Lake Kotokel in southern Siberia are used to reconstruct the environmental history of the area since ~47 kyr BP. Pollen data and reconstructed biome scores suggest predominance of a tundra-steppe vegetation and variable woody cover (5-20%) between ~47-30 kyr BP, indicating generally a harsh and unstable climate during this interval, conventionally regarded as the MIS3 interstadial. The short-term climate amelioration episodes in the glacial part of the records are marked by the peaks in taiga and corresponding minima in steppe biome scores and appear synchronously with the hemispheric temperature and precipitation changes recorded in the Greenland ice cores and Chinese stalagmites. The interval ~30-24 kyr BP was probably the driest and coldest of the whole record, as indicated by highest scores for steppe biome, woody coverage <5%, absence of diatoms and reduced size of the lake. A slight amelioration of the regional climate ~24-22 kyr BP was followed by a shorter than the previous and less pronounced deterioration phase. After 14.7 kyr BP the climate became warmer and wetter than ever during ~47-14.7 kyr BP, resulting in the deepening of the lake and increase in the woody coverage to 20-30% ~14.5-14 kyr and ~13.3-12.8 kyr BP. These two intervals correspond to the Meiendorf and Allerød interstadials, which until now were interpreted as part of the undifferentiated Bølling/Allerød interstadial complex in the Lake Baikal region. The increase in tundra biome scores and pronounced change in the diatom composition allow (for the first time) the unambiguous identification of the Younger Dryas (YD) in the region ~12.7-11.65 kyr BP, suggesting the synchronous onset of the YD and the Holocene interglacial across Eurasia. The maximal spread of the taiga communities in the region is associated with a warmer and wetter climate than the present prior to ~7 kyr BP. This was followed by a wide spread of Scots pine, indicating the onset of modern environments. These results are a contribution to the German Research Foundation project TA-540/1 and to the RFBF project 09-05-00123.

Environmental contamination with rhinovirus and transfer to fingers of healthy individuals by daily life activity.

PubMed

Winther, Birgit; McCue, Karen; Ashe, Kathleen; Rubino, Joseph R; Hendley, J Owen

2007-10-01

Rhinovirus infection may be acquired by inoculation of virus on fingertips to conjunctiva or nose (self-inoculation). The virus contaminating the fingertips may come from hand contact with someone with a cold or from virus in mucus on environmental surfaces. This study was designed to assess rhinovirus contamination of surfaces by adults with colds and rhinovirus transfer from surfaces to fingertips during normal daily activities. Fifteen adults with natural rhinovirus colds stayed overnight in a local hotel. Ten touched sites in each room were tested for rhinovirus RNA using RT-PCR. Transfer to fingertips of five subjects was examined by drying 10 microl of virus-containing mucus from each subject onto light switches, telephone dial buttons and telephone handsets. After an interval of 1 or 18 hr the subject flipped the light switch, pressed the button, held the handset. Fingertip rinses were tested for virus. Thirty five percent of the 150 environmental sites in the rooms were contaminated. Common virus-positive sites were door handles, pens, light switches, TV remote controls, faucets, and telephones. Rhinovirus was transferred from surfaces to fingertips in 18/30 (60%) trials 1 hr after contamination and in 10/30 (33%) of trials 18 hr (overnight) after contamination. Adults with colds commonly contaminate environmental surfaces with rhinovirus; virus on surfaces can be transferred to a fingertip during normal daily activities. (c) 2007 Wiley-Liss, Inc.

Effect of seasonal changes in use patterns and cold inlet water temperature on water-heating loads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abrams, D.W.; Shedd, A.C.

This paper presents long-term test data obtained in 20 commercial buildings and 16 residential sites. The information illustrates the effects of variations in hot water load determinants and the effect on energy use. It also is useful as a supplement to the load profiles presented in the ASHRAE Handbooks and other design references. The commercial facilities include supermarkets, fast-food restaurants, full-service restaurants, commercial kitchens, a motel, a nursing home, a hospital, a bakery, and laundry facilities. The residential sites ere selected to provide test sites with higher-than-average hot water use. They include 13 single-family detached residences, one 14-unit apartment building,more » and two apartment laundries. Test data are available at measurement intervals of 1 minute for the residential sites and 15 minutes for the commercial sites. Summary data in tabular and graphical form are presented for average daily volumetric hot water use and cold inlet water temperature. Measured cold inlet water temperature and volumetric hot water use figures are compared to values typically used for design and analysis. Conclusions are offered regarding the effect of cold water inlet temperature and variations in hot water use on water-heating load and energy use. Recommendations for the use of the information presented in water-heating system design, performance optimization, and performance analysis conclude the paper.« less

Constraining the sources of CH4 emissions during past abrupt climate change using CH4 triple isotopes mass balance from the ice core records

NASA Astrophysics Data System (ADS)

Dyonisius, M.; Petrenko, V. V.; Smith, A. W.; Hmiel, B.; Beck, J.; Seth, B.; Bock, M.; Hua, Q.; Yang, B.; Harth, C. M.; Beaudette, R.; Lee, J.; Erhardt, T.; Schmitt, J.; Brook, E.; Weiss, R. F.; Fischer, H.; Severinghaus, J. P.

2017-12-01

Methane (CH4) is the third most important greenhouse gas in the atmosphere after water vapor and CO2. Understanding how the natural CH4 budget has changed in response to changing climate in the past can provide insights on the sensitivity of the natural CH4 emissions to the current anthropogenic warming. CH4 isotopes (Δ14CH4, δ13C-CH4, and δD-CH4) from ice cores can be used to fingerprint the sources of CH4 increases in the past. We have successfully extracted 6 large volume (>1000kg) ice core samples from Taylor Glacier, Antarctica spanning the Oldest Dryas-Bølling transition ( 14.7ka) - the first abrupt warming and CH4 rise since the Last Glacial Maximum. Among the CH4 isotopes, our Δ 14CH4 data are unique in their ability to unambiguously distinguish between "old" CH4 sources (e.g. marine clathrate, geologic sources, old permafrost) and "modern" CH4 sources (e.g. tropical and boreal wetlands). Our Δ14CH4 data unambiguously rule out marine clathrate and old permafrost as the sources of the abrupt CH4 rise. Preliminary CH4 stable isotopes box modeling combined with interpolar CH4 concentration gradient from existing ice core records suggest that tropical wetlands were the dominant driver for the Oldest Dryas-Bølling CH4 rise.

Vitamin C and common cold-induced asthma: a systematic review and statistical analysis.

PubMed

Hemilä, Harri

2013-11-26

Asthma exacerbations are often induced by the common cold, which, in turn, can be alleviated by vitamin C. To investigate whether vitamin C administration influences common cold-induced asthma. Systematic review and statistical analysis of the identified trials. Medline, Scopus and Cochrane Central were searched for studies that give information on the effects of vitamin C on common cold-induced asthma. All clinically relevant outcomes related to asthma were included in this review. The estimates of vitamin C effect and their confidence intervals [CI] were calculated for the included studies. Three studies that were relevant for examining the role of vitamin C on common cold-induced asthma were identified. The three studies had a total of 79 participants. Two studies were randomized double-blind placebo-controlled trials. A study in Nigeria on asthmatics whose asthma attacks were precipitated by respiratory infections found that 1 g/day vitamin C decreased the occurrence of asthma attacks by 78% (95% CI: 19% to 94%). A cross-over study in former East-Germany on patients who had infection-related asthma found that 5 g/day vitamin C decreased the proportion of participants who had bronchial hypersensitivity to histamine by 52 percentage points (95% CI: 25 to 71). The third study did not use a placebo. Administration of a single dose of 1 gram of vitamin C to Italian non-asthmatic common cold patients increased the provocative concentration of histamine (PC20) 3.2-fold (95% CI: 2.0 to 5.1), but the vitamin C effect was significantly less when the same participants did not suffer from the common cold. The three reviewed studies differed substantially in their methods, settings and outcomes. Each of them found benefits from the administration of vitamin C; either against asthma attacks or against bronchial hypersensitivity, the latter of which is a characteristic of asthma. Given the evidence suggesting that vitamin C alleviates common cold symptoms and the findings of this systematic review, it may be reasonable for asthmatic patients to test vitamin C on an individual basis, if they have exacerbations of asthma caused by respiratory infections. More research on the role of vitamin C on common cold-induced asthma is needed.

Vitamin C and common cold-induced asthma: a systematic review and statistical analysis

PubMed Central

2013-01-01

Background Asthma exacerbations are often induced by the common cold, which, in turn, can be alleviated by vitamin C. Objective To investigate whether vitamin C administration influences common cold-induced asthma. Methods Systematic review and statistical analysis of the identified trials. Medline, Scopus and Cochrane Central were searched for studies that give information on the effects of vitamin C on common cold-induced asthma. All clinically relevant outcomes related to asthma were included in this review. The estimates of vitamin C effect and their confidence intervals [CI] were calculated for the included studies. Results Three studies that were relevant for examining the role of vitamin C on common cold-induced asthma were identified. The three studies had a total of 79 participants. Two studies were randomized double-blind placebo-controlled trials. A study in Nigeria on asthmatics whose asthma attacks were precipitated by respiratory infections found that 1 g/day vitamin C decreased the occurrence of asthma attacks by 78% (95% CI: 19% to 94%). A cross-over study in former East-Germany on patients who had infection-related asthma found that 5 g/day vitamin C decreased the proportion of participants who had bronchial hypersensitivity to histamine by 52 percentage points (95% CI: 25 to 71). The third study did not use a placebo. Administration of a single dose of 1 gram of vitamin C to Italian non-asthmatic common cold patients increased the provocative concentration of histamine (PC20) 3.2-fold (95% CI: 2.0 to 5.1), but the vitamin C effect was significantly less when the same participants did not suffer from the common cold. Conclusions The three reviewed studies differed substantially in their methods, settings and outcomes. Each of them found benefits from the administration of vitamin C; either against asthma attacks or against bronchial hypersensitivity, the latter of which is a characteristic of asthma. Given the evidence suggesting that vitamin C alleviates common cold symptoms and the findings of this systematic review, it may be reasonable for asthmatic patients to test vitamin C on an individual basis, if they have exacerbations of asthma caused by respiratory infections. More research on the role of vitamin C on common cold-induced asthma is needed. PMID:24279478

Thermohaline circulation and its box models simulation

NASA Astrophysics Data System (ADS)

Bazyura, Kateryna; Polonsky, Alexander; Sannikov, Viktor

2014-05-01

Ocean Thermochaline circulation (THC) is the part of large-scale World Ocean circulation and one of the main climate system components. It is generated by global meridional density gradients, which are controlled by surface heat and freshwater fluxes. THC regulates climate variability on different timescales (from decades to thousands years) [Stocker (2000), Clark (2002)]. Study of paleoclimatic evidences of abrupt and dramatic changes in ocean-atmosphere system in the past (such as, Dansgaard-Oeschger and Heinrich events or Younger Dryas, see e.g., [Rahmstorf (2002), Alley & Clark(1999)]) shows that these events are connected with THC regimes. At different times during last 120,000 years, three THC modes have prevailed in the Atlantic. They can be labeled as stadial, interstadial and Heinrich modes or as cold, warm and off mode. THC collapse (or thermohaline catastrophe) can be one of the consequences of global warming (including modern anthropogenic climate changes occurring at the moment). The ideas underlying different box-model studies, possibility of thermochaline catastrophe in present and past are discussed in this presentation. Response of generalized four box model of North Atlantic thermohaline circulation [developing the model of Griffies & Tzippermann (1995)] on periodic, stochastic and linear forcing is studied in details. To estimate climatic parameters of the box model we used monthly salinity and temperature data of ECMWF operational Ocean Reanalysis System 3 (ORA-S3) and data from atmospheric NCEP/NCAR reanalysis on precipitation, and heat fluxes for 1959-2011. Mean values, amplitude of seasonal cycle, amplitudes and periods of typical interdecadal oscillations, white noise level, linear trend coefficients and their significance level were estimated for every hydrophysical parameter. In response to intense freshwater or heat forcing, THC regime can change resulting in thermohaline catastrophe. We analyze relevant thresholds of external forcing in cases of using linear and nonlinear seawater state equation. In the frame of four-box model it is shown that: 1) The occurrence of the thermohaline catastrophe, which is likely happened at Younger Dryas period or developed as Heinrich events in the past, is improbable in modern climate epoch. 2) Choice of nonlinear seawater equitation of state leads to stabilization of warm mode of THC, which corresponds to modern climate state. 3) Typical white noise in heat and freshwater fluxes leads to generation of multidecadal oscillations of volume transport. Time-scale of these oscillations coincides with Atlantic Multidecadal oscillation periodicity. So, it is shown that that recent climate is characterized by quasi-periodical stable multidecadal THC warm regime. Stocker, T. F., 2000: Past and future reorganisations in the climate system. Quat. Sci.Rev, Vol. 19, P.301-319. Clark U., 2002: The role of the thermohaline circulation in abrupt climate change. Nature. Vol. 415, P.863-869. Rahmstorf S., 2002: Ocean circulation and climate during the past 120000 years. Nature. Vol. 419, P.207-214. Alley, R. B. & Clark, P. U., 1999: The deglaciation of the Northern Hemisphere: a global perspective. Annu.Rev. Earth Planet. Sci. Vol. 27, P.149-182. Griffies S.M., Tziperman E., 1995: A linear thermohaline oscillator driven by stochastic atmospheric forcing. Journal of Climate. Vol. 8. P. 2440-2453.

Younger Dryas equilibrium line altitudes and precipitation patterns in the Alps

NASA Astrophysics Data System (ADS)

Kerschner, Hanns; Moran, Andrew; Ivy-Ochs, Susan

2016-04-01

Moraine systems of the "Egesen Stadial" are widespread and easily identifiable features in the Alps. Absolute dating with terrestrial cosmogenic radionuclides shows that the maximum extent was reached during the early Younger Dryas (YD), probably as a reaction to the intense climatic downturn subsequent to Lateglacial Interstadial. In recent years, several new studies and the availability of high-quality laser-scan hillshades and orthophotos allowed a significant extension of the database of YD glaciers as "palaeoprecipitation gauges" to large hitherto unmapped regions in the Austrian and Swiss Alps. The equilibrium line altitude (ELA) of the glaciers and its lowering relative to the Little Ice Age ELA (dELA) shows a distinct and systematic spatial pattern. Along the northern slope of the Alps, dELAs are usually large (around 400 m and perhaps even more), while dELAs range around 200 m in the well sheltered areas of the central Alps, e.g. in the Engadine and in western Tyrol. Both stochastic glacier-climate models (e.g. Ohmura et al. 1992) and the heat- and mass balance equation (Kuhn 1981) allow the reconstruction of precipitation change under the assumption of a spatially constant summer temperature depression, which in turn can be estimated from biological proxies. This allows to draw the spatial pattern of precipitation change with considerable detail. Precipitation change is clearly controlled by the local relief like high mountain chains, deeply incised and long valleys and mountain passes. Generally the contrast between the northern fringe of the Alps and the interior was more pronounced than today. Climate in the Northern and and Northwestern Alps was rather wet with precipitation totals eventually exceeding modern annual sums. The central Alps received 20 - 30% less precipitation than today, mainly due to reduced winter precipitation. In the southern Alps, still scarce spatial information points to precipitation sums which were approximately similar to modern values. As winter precipitation was probably much smaller than today, seasonal contrasts were more pronounced. In total, the pattern of YD precipitation change is remarkably similar to precipitation patterns caused by westerly and northwesterly cyclonic airflow during the present-day hydrologic winter (October - March). Kerschner, H., G. Kaser, R. Sailer (2000): Alpine Younger Dryas glaciers as paleo-precipitation gauges. Annals of Glaciology 31, 80-84. Kerschner, H. and S. Ivy-Ochs (2007): Palaeoclimate from glaciers: Examples from the Eastern Alps during the Alpine Lateglacial and early Holocene. Global and Planetary Change 60, 58-71.

Vegetation and climate variability in tropical and subtropical South America during the late Quaternary

NASA Astrophysics Data System (ADS)

Behling, H.

2013-05-01

Detailed palynological studies from different ecosystems in tropical and subtropical South America reflect interesting vegetation and climate dynamics, in particular during glacial and late glacial times. Records from ecosystems such as the Amazon rainforest, savanna, Caatinga, Atlantic rainforest, Araucaria forest and grasslands provide interesting insight of past climate variability. The influence of events such as Dansgaard-Oeschger, Heinnrich stadials, changes in the thermohaline circulation (THC) will be discussed. In particular the Younger Dryas (YD) period shows at different places distinct vegetational changes, revealing unexpected past climatic conditions.

The association of extreme temperatures and the incidence of tuberculosis in Japan

NASA Astrophysics Data System (ADS)

Onozuka, Daisuke; Hagihara, Akihito

2015-08-01

Seasonal variation in the incidence of tuberculosis (TB) has been widely assumed. However, few studies have investigated the association between extreme temperatures and the incidence of TB. We collected data on cases of TB and mean temperature in Fukuoka, Japan for 2008-2012 and used time-series analyses to assess the possible relationship of extreme temperatures with TB incident cases, adjusting for seasonal and interannual variation. Our analysis revealed that the occurrence of extreme heat temperature events resulted in a significant increase in the number of TB cases (relative risk (RR) 1.20, 95 % confidence interval (CI) 1.01-1.43). We also found that the occurrence of extreme cold temperature events resulted in a significant increase in the number of TB cases (RR 1.23, 95 % CI 1.05-1.45). Sex and age did not modify the effect of either heat or cold extremes. Our study provides quantitative evidence that the number of TB cases increased significantly with extreme heat and cold temperatures. The results may help public health officials predict extreme temperature-related TB incidence and prepare for the implementation of preventive public health interventions.

Determining the spatial variability of crop yields of two different climatic regions in Southwest Germany

NASA Astrophysics Data System (ADS)

Eshonkulov, Ravshan; Poyda, Arne; Ingwersen, Joachim; Streck, Thilo

2017-04-01

Assessing the spatial variability of soil physical properties is crucial for agricultural land management. We determined the spatial variability within two agricultural fields in the regions of Kraichgau and Swabian Jura in Southwest Germany. We determined soil physical properties and recorded the temporal development of soil mineral nitrogen (N) and water content as well as that of plant variables (phenology, biomass, leaf area index (LAI), N content, green vegetation fraction (GVF). The work was conducted during the vegetation periods of 2015 and 2016 in winter wheat, and winter rapeseed in Kraichgau and winter barley and silage maize on Swabian Jura. Measurements were taken in three-weekly intervals. On each field, we identified three plots with reduced plant development using high-resolution (RapidEye) satellite images ("cold spots"). Measurements taken on these cold spots were compared to those from five established (long-term) reference plots representing the average field variability. The software EXPERT-N was used to simulate the soil crop system at both cold spots and reference plots. Sensitivity analyses were conducted to identify the most important parameters for the determination of spatial variability in crop growth dynamics.

The role of cold plasma and its composition on the growth of electromagnetic ion cyclotron waves in the inner magnetosphere

NASA Astrophysics Data System (ADS)

Snelling, J. M.; Johnson, J.; Engebretson, M. J.; Kim, E. H.; Tian, S.

2017-12-01

While it is currently well accepted that the free energy for growth of electromagnetic ion cyclotron (EMIC) waves in Earth's magnetosphere comes from unstable configurations of hot anisotropic ions that are injected into the ring current, several questions remain about what controls the instability. A recent study of the occurrence of EMIC waves relative to the plasmapause in Vallen Probes Data showed that plasma density gradients or enhancements were not the dominant factor in determining the site of EMIC wave generation [Tetrick et al. 2017]. However, the factors that control wave growth on each of the branches are not fully understood. For example, in some cases, the measured anisotropy is not adequate to explain local instability, and the relative importance of the density and composition of a cold plasma population is still uncertain. Several intervals of EMIC wave activity are analyzed to determine the role of a cold population in driving instability on each of the wave branches. This study utilizes the WHAMP (Waves in Homogeneous Anisotropic Magnetized Plasma) stability code with plasma distributions optimized to fit the observed distributions including temperature anisotropy, loss cone, and ring beam populations.

Optimizing donor heart outcome after prolonged storage with endothelial function analysis and continuous perfusion.

PubMed

Poston, Robert S; Gu, Junyan; Prastein, Deyanira; Gage, Fred; Hoffman, John W; Kwon, Michael; Azimzadeh, Agnes; Pierson, Richard N; Griffith, Bartley P

2004-10-01

By minimizing tissue ischemia, continuous perfusion (CP) during organ transport may increase the safety of "marginal donors." My colleagues and I investigated whether an analysis of donor heart viability predicts recovery of grafts challenged with a 24-hour preservation interval. Dog hearts underwent cold static storage (CS) for 8 hours (n = 8) or 24 hours (n = 2) or CP for 24 hours with cold asanguinous, oxygenated solution (n = 8). Myocardial systolic and diastolic function and oxygen and lactate consumption were assessed at base line, during CP, and after Langendorff blood reperfusion. Base line endothelial function was evaluated by the percentage transcoronary change ([coronary sinus - aorta]/aorta) in myeloperoxidase and by platelet function and coronary flow reserve after 20 seconds of coronary artery occlusion. During CP, the endothelium was assessed by transcoronary protein release and coronary resistance. Edema was assessed by weight gain and histology. Base line systolic and metabolic functions showed no relation to post-Langendorff function. Compared with CS, CP resulted in a greater recovery in systolic function (87% +/- 35% vs 65% +/- 15% of baseline; p = 0.05) and a shorter interval required for lactate consumption to exceed production (7.0 +/- 6.8 minutes vs 15.0 +/- 8.9 minutes; p = 0.06). Endothelial function was heterogeneous: coronary flow reserve, 2.7 +/- 0.7; percentage change in myeloperoxidase, -8.4% +/- 6.8%; and change in platelet function, 4.3% +/- 3.5%, as determined by thromboelastography angle at base line. Protein release during CP for 24 hours was 8.3 +/- 7.1 g. Two factors predicted more than 75% systolic pressure generation recovery: use of CP and normal endothelial function (p = 0.05; Fisher's exact test). However, CP led to edema according to histology, weight gain (72 +/- 29 g), and impaired diastolic function versus CS (end-diastolic pressure-volume relationship, 1.4 +/- 0.4 mm Hg/mL vs 0.8 +/- 0.3 mm Hg/mL; p = 0.08). Better systolic function despite 16 hours' more preservation than cold storage corroborates the idea that CP supports aerobic metabolism at physiologically important levels. Viability analysis focused on endothelial function and identified organs that were able to tolerate this 24-hour preservation interval.

Serum C-reactive protein levels predict regional brain responses to noxious cold stimulation of the hand in chronic whiplash associated disorders.

PubMed

Sterling, Michele; Head, Jessica; Cabot, Peter J; Farrell, Michael

2016-04-01

Whiplash Associated Disorders (WAD) are a costly health burden. The condition is characterised by sensory disturbances such as widespread hyperalgesia likely indicative of central hyperexcitability. Recently elevated levels of pro-inflammatory biomarkers have also found in acute and chronic WAD. The aim of this cross-sectional study was to investigate the relationship between inflammatory biomarkers and pain processing in people with persistent whiplash associated disorders (WAD). Twenty one participants with chronic whiplash (>3 months) were recruited. Venous blood samples were collected and assays performed for C-reactive protein (CRP) and TNF-α. Blood oxygen level-dependent (BOLD) contrast images of the brain were acquired with a Siemens 1.5T MRI scanner during repeated 24s stimulus blocks of innocuous or painful stimuli (thumbnail pressure and cold stimulation of dorsum of hand) separated by 36s inter-stimulus intervals. Stimulus intensities used during scanning were at the level of participants' thresholds for moderate pain. Parameter estimates representing BOLD signal increases during painful events from each participant were tested for associations with inflammatory biomarkers. Clinically relevant levels of CRP and TNF-α were found in 33% and 38% of participants. Levels of CRP showed a positive correlation with levels of cold pain activation in brain regions including the anterior insula, posterior parietal cortex, caudate and thalamus (p corrected <0.05). Levels of TNF-α were not related to activation levels during either noxious pressure or cold. Pressure pain activations also did not show a relationship with CRP levels. Shared variance between inflammation and increased levels of regional pain-related activation in people with persistent whiplash symptoms is apparent for cold, but not pressure stimuli. The results highlight cold pain processing as an important aspect of whiplash chronicity, although the implications of this modality-specific effect are not readily apparent. Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.

Effect of Cold Storage on Biological Traits of Psix saccharicola (Hymenoptera: Platygastridae), an Egg Parasitoid of Acrosternum arabicum (Hemiptera: Pentatomidae).

PubMed

Forouzan, Farzane; Jalali, Mohammad Amin; Ziaaddini, Mahdi; Hashemi Rad, Hamid

2018-05-28

Psix saccharicola (Mani) (Hymenoptera: Platygastridae) is a solitary egg parasitoid of the pistachio green stink bug, Acrosternum arabicum (Wagner) (Hemiptera: Pentatomidae), which is one of the most important pests of pistachio in Iran. Augmentation of P. saccharicola field populations using mass-reared individuals may provide an alternative to conventional pesticide use for pistachio green stink bug control. Cold storage is an important component of mass-rearing protocols for optimum timing of host egg parasitization and potentially extended storage of P. saccharicola pupae prior to adult emergence. The impact of cold storage on A. arabicum eggs for various time intervals at 4.0°C was investigated. Results indicated that host eggs stored at 4.0°C for up to 60 d could be exploited by P. sacchricola, whereas no offspring were produced when eggs were stored for 120 d. The emergence rates of the F1 and F2 generations declined with increased host egg storage time. Both sex ratio and survival rate of the F2 generation decreased as the refrigeration time of host eggs increased. The impact of cold storage on P. saccharicola pupae was evaluated. Reared pupae of P. saccharicola were held for 1 wk at three temperatures and compared with a control (27 ± 1°C). Psix saccharicola pupae were tolerant to cold storage at 8 and 12°C. Cold storage adversely affected mean adult emergence at 4°C, which decreased following low temperature exposure. Furthermore, mean percentage survivorship was unaffected by storage at low temperatures in the F1 generation, but was reduced at 4°C. The sex ratio of the F1 generation became more male-biased when held at lower storage temperatures. The highest female proportion was observed at 12°C.

Effective Hypothermic Storage of Human Pluripotent Stem Cell-Derived Cardiomyocytes Compatible With Global Distribution of Cells for Clinical Applications and Toxicology Testing

PubMed Central

Correia, Cláudia; Koshkin, Alexey; Carido, Madalena; Espinha, Nuno; Šarić, Tomo; Lima, Pedro A.; Alves, Paula M.

2016-01-01

To fully explore the potential of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), efficient methods for storage and shipment of these cells are required. Here, we evaluated the feasibility to cold store monolayers and aggregates of functional CMs obtained from different PSC lines using a fully defined clinical-compatible preservation formulation and investigated the time frame that hPSC-CMs could be subjected to hypothermic storage. We showed that two-dimensional (2D) monolayers of hPSC-CMs can be efficiently stored at 4°C for 3 days without compromising cell viability. However, cell viability decreased when the cold storage interval was extended to 7 days. We demonstrated that hPSC-CMs are more resistant to prolonged hypothermic storage-induced cell injury in three-dimensional aggregates than in 2D monolayers, showing high cell recoveries (>70%) after 7 days of storage. Importantly, hPSC-CMs maintained their typical (ultra)structure, gene and protein expression profile, electrophysiological profiles, and drug responsiveness. Significance The applicability of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) in the clinic/industry is highly dependent on the development of efficient methods for worldwide shipment of these cells. This study established effective clinically compatible strategies for cold (4°C) storage of hPSC-CMs cultured as two-dimensional (2D) monolayers and three-dimensional (3D) aggregates. Cell recovery of 2D monolayers of hPSC-CMs was found to be dependent on the time of storage, and 3D cell aggregates were more resistant to prolonged cold storage than 2D monolayers. Of note, it was demonstrated that 7 days of cold storage did not affect hPSC-CM ultrastructure, phenotype, or function. This study provides important insights into the cold preservation of PSC-CMs that could be valuable in improving global commercial distribution of hPSC-CMs. PMID:27025693

Effective Hypothermic Storage of Human Pluripotent Stem Cell-Derived Cardiomyocytes Compatible With Global Distribution of Cells for Clinical Applications and Toxicology Testing.

PubMed

Correia, Cláudia; Koshkin, Alexey; Carido, Madalena; Espinha, Nuno; Šarić, Tomo; Lima, Pedro A; Serra, Margarida; Alves, Paula M

2016-05-01

To fully explore the potential of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), efficient methods for storage and shipment of these cells are required. Here, we evaluated the feasibility to cold store monolayers and aggregates of functional CMs obtained from different PSC lines using a fully defined clinical-compatible preservation formulation and investigated the time frame that hPSC-CMs could be subjected to hypothermic storage. We showed that two-dimensional (2D) monolayers of hPSC-CMs can be efficiently stored at 4°C for 3 days without compromising cell viability. However, cell viability decreased when the cold storage interval was extended to 7 days. We demonstrated that hPSC-CMs are more resistant to prolonged hypothermic storage-induced cell injury in three-dimensional aggregates than in 2D monolayers, showing high cell recoveries (>70%) after 7 days of storage. Importantly, hPSC-CMs maintained their typical (ultra)structure, gene and protein expression profile, electrophysiological profiles, and drug responsiveness. The applicability of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) in the clinic/industry is highly dependent on the development of efficient methods for worldwide shipment of these cells. This study established effective clinically compatible strategies for cold (4°C) storage of hPSC-CMs cultured as two-dimensional (2D) monolayers and three-dimensional (3D) aggregates. Cell recovery of 2D monolayers of hPSC-CMs was found to be dependent on the time of storage, and 3D cell aggregates were more resistant to prolonged cold storage than 2D monolayers. Of note, it was demonstrated that 7 days of cold storage did not affect hPSC-CM ultrastructure, phenotype, or function. This study provides important insights into the cold preservation of PSC-CMs that could be valuable in improving global commercial distribution of hPSC-CMs. ©AlphaMed Press.

Development of models to predict early post-transplant recurrence of hepatocellular carcinoma that also integrate the quality and characteristics of the liver graft: A national registry study in China.

PubMed

Ling, Qi; Liu, Jimin; Zhuo, Jianyong; Zhuang, Runzhou; Huang, Haitao; He, Xiangxiang; Xu, Xiao; Zheng, Shusen

2018-04-27

Donor characteristics and graft quality were recently reported to play an important role in the recurrence of hepatocellular carcinoma after liver transplantation. Our aim was to establish a prognostic model by using both donor and recipient variables. Data of 1,010 adult patients (training/validation: 2/1) undergoing primary liver transplantation for hepatocellular carcinoma were extracted from the China Liver Transplant Registry database and analyzed retrospectively. A multivariate competing risk regression model was developed and used to generate a nomogram predicting the likelihood of post-transplant hepatocellular carcinoma recurrence. Of 673 patients in the training cohort, 70 (10.4%) had hepatocellular carcinoma recurrence with a median recurrence time of 6 months (interquartile range: 4-25 months). Cold ischemia time was the only independent donor prognostic factor for predicting hepatocellular carcinoma recurrence (hazard ratio = 2.234, P = .007). The optimal cutoff value was 12 hours when patients were grouped according to cold ischemia time at 2-hour intervals. Integrating cold ischemia time into the Milan criteria (liver transplantation candidate selection criteria) improved the accuracy for predicting hepatocellular carcinoma recurrence in both training and validation sets (P < .05). A nomogram composed of cold ischemia time, tumor burden, differentiation, and α-fetoprotein level proved to be accurate and reliable in predicting the likelihood of 1-year hepatocellular carcinoma recurrence after liver transplantation. Additionally, donor anti-hepatitis B core antibody positivity, prolonged cold ischemia time, and anhepatic time were linked to the intrahepatic recurrence, whereas older donor age, prolonged donor warm ischemia time, cold ischemia time, and ABO incompatibility were relevant to the extrahepatic recurrence. The graft quality integrated models exhibited considerable predictive accuracy in early hepatocellular carcinoma recurrence risk assessment. The identification of donor risks can further help understand the mechanism of different patterns of recurrence. Copyright © 2018 Elsevier Inc. All rights reserved.

Persistent post-surgical pain and experimental pain sensitivity in the Tromsø study: comorbid pain matters.

PubMed

Johansen, Aslak; Schirmer, Henrik; Stubhaug, Audun; Nielsen, Christopher S

2014-02-01

In a large survey incorporating medical examination (N=12,981), information on chronic pain and surgery was collected, and sensitivity to different pain modalities was tested. Tolerance to the cold pressor test was analysed with survival statistics for 10,486 individuals, perceived cold pressor pain intensity was calculated for 10,367 individuals, heat pain threshold was assessed for 4,054 individuals, and pressure pain sensitivity for 4,689 individuals. Persistent post-surgical pain, defined by self-report, was associated with lower cold pressor tolerance (sex-adjusted hazard ratio=1.34, 95% confidence interval=1.08-1.66), but not when adjusting for other chronic pain. Other experimental pain modalities did not differentiate between individuals with or without post-surgical pain. Of the individuals with chronic pain (N=3352), 6.2% indicated surgery as a cause, although only 0.5% indicated surgery as the only cause. The associations found between persistent post-surgical pain and cold pressor tolerance is largely explained by the co-existence of chronic pain from other causes. We conclude that most cases of persistent post-surgical pain are coexistent with other chronic pain, and that, in an unselected post-surgical population, persistent post-surgical pain is not significantly associated with pain sensitivity when controlling for comorbid pain from other causes. A low prevalence of self-reported persistent pain from surgery attenuates statistically significant associations. We hypothesize that general chronic pain is associated with central changes in pain processing as expressed by reduced tolerance for the cold pressor test. Copyright © 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

Effect of whole-body mild-cold exposure on arterial stiffness and central haemodynamics: a randomised, cross-over trial in healthy men and women.

PubMed

King, Sibella G; Ahuja, Kiran D K; Wass, Jezreel; Shing, Cecilia M; Adams, Murray J; Davies, Justin E; Sharman, James E; Williams, Andrew D

2013-05-01

Aortic pulse wave velocity (PWV) and augmentation index (AIx) are independent predictors of cardiovascular risk and mortality, but little is known about the effect of air temperature changes on these variables. Our study investigated the effect of exposure to whole-body mild-cold on measures of arterial stiffness (aortic and brachial PWV), and on central haemodynamics [including augmented pressure (AP), AIx], and aortic reservoir components [including reservoir and excess pressures (P ex)]. Sixteen healthy volunteers (10 men, age 43 ± 19 years; mean ± SD) were randomised to be studied under conditions of 12 °C (mild-cold) and 21 °C (control) on separate days. Supine resting measures were taken at baseline (ambient temperature) and after 10, 30, and 60 min exposure to each experimental condition in a climate chamber. There was no significant change in brachial blood pressure between mild-cold and control conditions. However, compared to control, AP [+2 mmHg, 95 % confidence interval (CI) 0.36-4.36; p = 0.01] and AIx (+6 %, 95 % CI 1.24-10.1; p = 0.02) increased, and time to maximum P ex (a component of reservoir function related to timing of peak aortic in-flow) decreased (-7 ms, 95 % CI -15.4 to 2.03; p = 0.01) compared to control. Yet there was no significant change in aortic PWV (+0.04 m/s, 95 % CI -0.47 to 0.55; p = 0.87) or brachial PWV (+0.36 m/s; -0.41 to 1.12; p = 0.35) between conditions. We conclude that mild-cold exposure increases central haemodynamic stress and alters timing of peak aortic in-flow without differentially affecting arterial stiffness.

Peritoneal Tumorigenesis and Inflammation are Ameliorated by Humidified-Warm Carbon Dioxide Insufflation in the Mouse.

PubMed

Carpinteri, Sandra; Sampurno, Shienny; Bernardi, Maria-Pia; Germann, Markus; Malaterre, Jordane; Heriot, Alexander; Chambers, Brenton A; Mutsaers, Steven E; Lynch, Andrew C; Ramsay, Robert G

2015-12-01

Conventional laparoscopic surgery uses CO2 that is dry and cold, which can damage peritoneal surfaces. It is speculated that disseminated cancer cells may adhere to such damaged peritoneum and metastasize. We hypothesized that insufflation using humidified-warm CO2, which has been shown to reduce mesothelial damage, will also ameliorate peritoneal inflammation and tumor cell implantation compared to conventional dry-cold CO2. Laparoscopic insufflation was modeled in mice along with anesthesia and ventilation. Entry and exit ports were introduced to maintain insufflation using dry-cold or humidified-warm CO2 with a constant flow and pressure for 1 h; then 1000 or 1 million fluorescent-tagged murine colorectal cancer cells (CT26) were delivered into the peritoneal cavity. The peritoneum was collected at intervals up to 10 days after the procedure to measure inflammation, mesothelial damage, and tumor burden using fluorescent detection, immunohistochemistry, and scanning electron microscopy. Rapid temperature control was achieved only in the humidified-warm group. Port-site tumors were present in all mice. At 10 days, significantly fewer tumors on the peritoneum were counted in mice insufflated with humidified-warm compared to dry-cold CO2 (p < 0.03). The inflammatory marker COX-2 was significantly increased in the dry-cold compared to the humidified-warm cohort (p < 0.01), while VEGFA expression was suppressed only in the humidified-warm cohort. Significantly less mesothelial damage and tumor cell implantation was evident from 2 h after the procedure in the humidified-warm cohort. Mesothelial cell damage and inflammation are reduced by using humidified-warm CO2 for laparoscopic oncologic surgery and may translate to reduce patients' risk of developing peritoneal metastasis.

Intraseasonal variability in the summer South China Sea: Wind jet, cold filament, and recirculations

NASA Astrophysics Data System (ADS)

Xie, Shang-Ping; Chang, Chueh-Hsin; Xie, Qiang; Wang, Dongxiao

2007-10-01

A recent study shows that the blockage of the southwest monsoon by the mountain range on the east coast of Indochina triggers a chain of ocean-atmospheric response, including a wind jet and cold filament in the South China Sea (SCS). We extend this climatological analysis by using higher temporal resolution (weekly) to study intraseasonal variability in summer. Our analysis shows that the development of the wind jet and cold filament is not a smooth seasonal process but consists of several intraseasonal events each year at about 45-day intervals. In a typical intraseasonal event, the wind jet intensifies to above 12 m/s, followed in a week by the development of a cold filament advected by an offshore jet east of South Vietnam on the boundary of a double gyre circulation in the ocean. The double gyre circulation itself also strengthens in response to the intraseasonal wind event via Rossby wave adjustment, reaching the maximum strength in 2 to 3 weeks. The intraseasonal cold filaments appear to influence the surface wind, reducing the local wind speed because of the increased static stability in the near-surface atmosphere. To first order, the above sequence of events may be viewed as the SCS response to atmospheric intraseasonal wind pulses, which are part of the planetary-scale boreal summer intraseasonal oscillation characterized by the northeastward propagation of atmospheric deep convection. The intraseasonal anomalies of sea surface temperature and precipitation are in phase over the SCS, suggesting an oceanic feedback onto the atmosphere. As wind variations are now being routinely monitored by satellite, the lags of 1-3 weeks in oceanic response offer useful predictability that may be exploited.

Hot and cold executive functions in youth with psychotic symptoms.

PubMed

MacKenzie, L E; Patterson, V C; Zwicker, A; Drobinin, V; Fisher, H L; Abidi, S; Greve, A N; Bagnell, A; Propper, L; Alda, M; Pavlova, B; Uher, R

2017-12-01

Psychotic symptoms are common in children and adolescents and may be early manifestations of liability to severe mental illness (SMI), including schizophrenia. SMI and psychotic symptoms are associated with impairment in executive functions. However, previous studies have not differentiated between 'cold' and 'hot' executive functions. We hypothesized that the propensity for psychotic symptoms is specifically associated with impairment in 'hot' executive functions, such as decision-making in the context of uncertain rewards and losses. In a cohort of 156 youth (mean age 12.5, range 7-24 years) enriched for familial risk of SMI, we measured cold and hot executive functions with the spatial working memory (SWM) task (total errors) and the Cambridge Gambling Task (decision-making), respectively. We assessed psychotic symptoms using the semi-structured Kiddie Schedule for Affective Disorders and Schizophrenia interview, Structured Interview for Prodromal Syndromes, Funny Feelings, and Schizophrenia Proneness Instrument - Child and Youth version. In total 69 (44.23%) youth reported psychotic symptoms on one or more assessments. Cold executive functioning, indexed with SWM errors, was not significantly related to psychotic symptoms [odds ratio (OR) 1.36, 95% confidence interval (CI) 0.85-2.17, p = 0.204). Poor hot executive functioning, indexed as decision-making score, was associated with psychotic symptoms after adjustment for age, sex and familial clustering (OR 2.37, 95% CI 1.25-4.50, p = 0.008). The association between worse hot executive functions and psychotic symptoms remained significant in sensitivity analyses controlling for general cognitive ability and cold executive functions. Impaired hot executive functions may be an indicator of risk and a target for pre-emptive early interventions in youth.

Clinical features and natural history of acquired cold urticaria in a tertiary referral hospital: a 10-year prospective study.

PubMed

Katsarou-Katsari, A; Makris, M; Lagogianni, E; Gregoriou, S; Theoharides, T; Kalogeromitros, D

2008-12-01

Acquired cold urticaria (ACU) represents a heterogeneous group of disorders that share a common clinical feature: the development of urticaria or angioedema after cold exposure. We present epidemiological and clinical data of subjects with ACU, natural progression and we examine possible parameters that could correlate with disease severity. During a 10-year period in all subjects with ACU, detailed record of personal history, laboratory testing, cold stimulation testing (CST), atopy assessment and disease severity took place. In a re-evaluation visit at the end of the surveillance period, ACU progression was assessed from patients in a subjective way. Four thousand one hundred fifty-seven individuals with chronic urticaria were referred, and 352 (198 males, 154 females, 8.47% of patients with chronic urticaria) presented definite symptoms of physical urticarias, while 95 individuals (49 males, 46 females, 27% of patients with physical urticarias) were detected with ACU. Sixty-two participants were included in study analysis. Thirty-two patients (51.6%) were female; the mean age was 41.5 +/- 15.6 years, while the mean age at disease onset was 32.5 +/- 15.6 years; half were < or = 30 years old at disease onset. The mean duration of surveillance was 9.0 +/- 6.9 years. During this time interval, 18 patients (29.0%) showed the same or even worse symptomatology, 26 patients reported some improvement (41.9%), while in 18 patients, symptoms resolved completely (29.0%); the mean time to resolution was 5.6 +/- 3.5 years. Disease severity was the only variable statistically significantly related to disease progression (P = 0.004). Cold urticaria is a chronic persistent disorder with occasional severe clinical manifestations.

Age scatter in cosmogenic exposure-age chronologies in the McMurdo Dry Valleys, Antarctica: implications for regional glacial history and sampling strategies

NASA Astrophysics Data System (ADS)

Swanger, K. M.; Schaefer, J. M.; Winckler, G.; Lamp, J. L.; Marchant, D. R.

2016-12-01

Based on surface exposure dating of moraines and drifts, East Antarctic outlet glaciers in the McMurdo Dry Valleys (MDV) advanced during the mid-Pliocene and/or early-Pleistocene. However, scatter in exposure ages is common for these deposits (and other glacial drifts throughout Antarctica), making it difficult to tie glacial advances to specific climate intervals. In order to constrain the sources of scatter, we mapped and dated 15 cold-based drifts in Taylor Valley and the Olympus Range in the MDV. A secondary goal was to build a regional climate record, for comparison with fluctuations of the local outlet glaciers. Our alpine drift record is confined to the late-Pleistocene, with glacial advances during interglacial periods. Based on 54 3He exposure dates on alpine drifts, age scatter is common in the MDV on both recent and ancient deposits. Where it occurs, age scatter is likely caused by inheritance of cosmogenic nuclides previous to glacial entrainment and stacking of multiple cold-based drifts. Nuclide inheritance of >1 Myr is possible, but this is relatively rare and confined to regions where englacial debris is sourced from stable, high-elevation plateaus. On the other hand, drifts associated with glaciers bound by steep cirque headwalls and arêtes exhibit significantly less age scatter. Given the cold-based nature of MDV alpine and outlet glaciers, deposition of multiple stacked drift sheets also contributes to age scatter, with the implication that it might be possible to date multiple advances of cold-based ice. These results serve to inform better sampling strategies on cold-based drifts throughout Antarctica.

Creation of heterogeneous materials on the basis of B4C and Ni powders by the method of cold spraying with subsequent layer-by-layer laser treatment

NASA Astrophysics Data System (ADS)

Fomin, V. M.; Golyshev, A. A.; Kosarev, V. F.; Malikov, A. G.; Orishich, A. M.; Ryashin, N. S.; Filippov, A. A.; Shikalov, V. S.

2017-09-01

A method is proposed for creating principally new functionally graded heterogeneous materials on the basis of B4C ceramic powders with different mass fractions in the original mixture and plastic metallic additive of Ni by a combined method of cold spraying with subsequent layer-by-layer laser treatment. Mechanical properties of the resultant tracks are examined. It is shown that the track microhardness increases with increasing B4C concentration in the original mixture. The track structure is found to depend on the size of ceramic particles in the interval from 3 to 75 μm. Reduction of the B4C particle size (approximately by a factor of 2-3) inside the track owing to fragmentation under the action of the laser beam is observed for the first time.

Changing Susceptibility to Non-Optimum Temperatures in Japan, 1972-2012: The Role of Climate, Demographic, and Socioeconomic Factors.

PubMed

Chung, Yeonseung; Yang, Daewon; Gasparrini, Antonio; Vicedo-Cabrera, Ana M; Fook Sheng Ng, Chris; Kim, Yoonhee; Honda, Yasushi; Hashizume, Masahiro

2018-05-02

Previous studies have shown that population susceptibility to non-optimum temperatures has changed over time, but little is known about the related time-varying factors that underlie the changes. Our objective was to investigate the changing population susceptibility to non-optimum temperatures in 47 prefectures of Japan over four decades from 1972 to 2012, addressing three aspects: minimum mortality temperature (MMT) and heat- and cold-related mortality risks. In addition, we aimed to examine how these aspects of susceptibility were associated with climate, demographic, and socioeconomic variables. We first used a two-stage time-series design with a time-varying distributed lag nonlinear model and multivariate meta-analysis to estimate the time-varying MMT, heat- and cold-related mortality risks. We then applied linear mixed effects models to investigate the association between each of the three time-varying aspects of susceptibility and various time-varying factors. MMT increased from 23.2 [95% confidence interval (CI): 23, 23.6] to 28.7 (27.0, 29.7) °C. Heat-related mortality risk [relative risk (RR) for the 99th percentile of temperature vs. the MMT] decreased from 1.18 (1.15, 1.21) to 1.01 (0.98, 1.04). Cold-related mortality risk (RR for the first percentile vs. the MMT) generally decreased from 1.48 (1.41, 1.54) to 1.35 (1.32, 1.40), with the exception of a few eastern prefectures that showed increased risk. The changing patterns in all three aspects differed by region, sex, and causes of death. Higher mean temperature was associated ( p <0.01) with lower heat risk, whereas higher humidity was associated with higher cold risk. A higher percentage of elderly people was associated with a higher cold risk, whereas higher economic strength of the prefecture was related to lower cold risk. Population susceptibility to heat has decreased over the last four decades in Japan. Susceptibility to cold has decreased overall except for several eastern prefectures where it has either increased or remained unchanged. Certain climate, demographic, and socioeconomic factors explored in the current study might underlie this changing susceptibility. https://doi.org/10.1289/EHP2546.

Acetaminophen (Paracetamol) Induces Hypothermia During Acute Cold Stress.

PubMed

Foster, Josh; Mauger, Alexis R; Govus, Andrew; Hewson, David; Taylor, Lee

2017-11-01

Acetaminophen is an over-the-counter drug used to treat pain and fever, but it has also been shown to reduce core temperature (T c ) in the absence of fever. However, this side effect is not well examined in humans, and it is unknown if the hypothermic response to acetaminophen is exacerbated with cold exposure. To address this question, we mapped the thermoregulatory responses to acetaminophen and placebo administration during exposure to acute cold (10 °C) and thermal neutrality (25 °C). Nine healthy Caucasian males (aged 20-24 years) participated in the experiment. In a double-blind, randomised, repeated measures design, participants were passively exposed to a thermo-neutral or cold environment for 120 min, with administration of 20 mg/kg lean body mass acetaminophen or a placebo 5 min prior to exposure. T c , skin temperature (T sk ), heart rate, and thermal sensation were measured every 10 min, and mean arterial pressure was recorded every 30 min. Data were analysed using linear mixed effects models. Differences in thermal sensation were analysed using a cumulative link mixed model. Acetaminophen had no effect on T c in a thermo-neutral environment, but significantly reduced T c during cold exposure, compared with a placebo. T c was lower in the acetaminophen compared with the placebo condition at each 10-min interval from 80 to 120 min into the trial (all p < 0.05). On average, T c decreased by 0.42 ± 0.13 °C from baseline after 120 min of cold exposure (range 0.16-0.57 °C), whereas there was no change in the placebo group (0.01 ± 0.1 °C). T sk , heart rate, thermal sensation, and mean arterial pressure were not different between conditions (p > 0.05). This preliminary trial suggests that acetaminophen-induced hypothermia is exacerbated during cold stress. Larger scale trials seem warranted to determine if acetaminophen administration is associated with an increased risk of accidental hypothermia, particularly in vulnerable populations such as frail elderly individuals.

The effect of temperature on the mechanical aspects of rigor mortis in a liquid paraffin model.

PubMed

Ozawa, Masayoshi; Iwadate, Kimiharu; Matsumoto, Sari; Asakura, Kumiko; Ochiai, Eriko; Maebashi, Kyoko

2013-11-01

Rigor mortis is an important phenomenon to estimate the postmortem interval in forensic medicine. Rigor mortis is affected by temperature. We measured stiffness of rat muscles using a liquid paraffin model to monitor the mechanical aspects of rigor mortis at five temperatures (37, 25, 10, 5 and 0°C). At 37, 25 and 10°C, the progression of stiffness was slower in cooler conditions. At 5 and 0°C, the muscle stiffness increased immediately after the muscles were soaked in cooled liquid paraffin and then muscles gradually became rigid without going through a relaxed state. This phenomenon suggests that it is important to be careful when estimating the postmortem interval in cold seasons. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Seasonal temperature extremes in Potsdam

NASA Astrophysics Data System (ADS)

Kundzewicz, Zbigniew; Huang, Shaochun

2010-12-01

The awareness of global warming is well established and results from the observations made on thousands of stations. This paper complements the large-scale results by examining a long time-series of high-quality temperature data from the Secular Meteorological Station in Potsdam, where observation records over the last 117 years, i.e., from January 1893 are available. Tendencies of change in seasonal temperature-related climate extremes are demonstrated. "Cold" extremes have become less frequent and less severe than in the past, while "warm" extremes have become more frequent and more severe. Moreover, the interval of the occurrence of frost has been decreasing, while the interval of the occurrence of hot days has been increasing. However, many changes are not statistically significant, since the variability of temperature indices at the Potsdam station has been very strong.

Effect of solar activity on the repetitiveness of some meteorological phenomena

NASA Astrophysics Data System (ADS)

Todorović, Nedeljko; Vujović, Dragana

2014-12-01

In this paper we research the relationship between solar activity and the weather on Earth. This research is based on the assumption that every ejection of magnetic field energy and particles from the Sun (also known as Solar wind) has direct effects on the Earth's weather. The impact of coronal holes and active regions on cold air advection (cold fronts, precipitation, and temperature decrease on the surface and higher layers) in the Belgrade region (Serbia) was analyzed. Some active regions and coronal holes appear to be in a geo-effective position nearly every 27 days, which is the duration of a solar rotation. A similar period of repetitiveness (27-29 days) of the passage of the cold front, and maximum and minimum temperatures measured at surface and at levels of 850 and 500 hPa were detected. We found that 10-12 days after Solar wind velocity starts significantly increasing, we could expect the passage of a cold front. After eight days, the maximum temperatures in the Belgrade region are measured, and it was found that their minimum values appear after 12-16 days. The maximum amount of precipitation occurs 14 days after Solar wind is observed. A recurring period of nearly 27 days of different phases of development for hurricanes Katrina, Rita and Wilma was found. This analysis confirmed that the intervals of time between two occurrences of some particular meteorological parameter correlate well with Solar wind and A index.

Improved arterial blood oxygenation following intravenous infusion of cold supersaturated dissolved oxygen solution.

PubMed

Grady, Daniel J; Gentile, Michael A; Riggs, John H; Cheifetz, Ira M

2014-01-01

One of the primary goals of critical care medicine is to support adequate gas exchange without iatrogenic sequelae. An emerging method of delivering supplemental oxygen is intravenously rather than via the traditional inhalation route. The objective of this study was to evaluate the gas-exchange effects of infusing cold intravenous (IV) fluids containing very high partial pressures of dissolved oxygen (>760 mm Hg) in a porcine model. Juvenile swines were anesthetized and mechanically ventilated. Each animal received an infusion of cold (13 °C) Ringer's lactate solution (30 mL/kg/hour), which had been supersaturated with dissolved oxygen gas (39.7 mg/L dissolved oxygen, 992 mm Hg, 30.5 mL/L). Arterial blood gases and physiologic measurements were repeated at 15-minute intervals during a 60-minute IV infusion of the supersaturated dissolved oxygen solution. Each animal served as its own control. Five swines (12.9 ± 0.9 kg) were studied. Following the 60-minute infusion, there were significant increases in PaO2 and SaO2 (P < 0.05) and a significant decrease in PaCO2 (P < 0.05), with a corresponding normalization in arterial blood pH. Additionally, there was a significant decrease in core body temperature (P < 0.05) when compared to the baseline preinfusion state. A cold, supersaturated dissolved oxygen solution may be intravenously administered to improve arterial blood oxygenation and ventilation parameters and induce a mild therapeutic hypothermia in a porcine model.

Stress-evoked opioid release inhibits pain in major depressive disorder.

PubMed

Frew, Ashley K; Drummond, Peter D

2008-10-15

To determine whether stress-evoked release of endogenous opioids might account for hypoalgesia in major depressive disorder (MDD), the mu-opioid antagonist naltrexone (50mg) or placebo was administered double-blind to 24 participants with MDD and to 31 non-depressed controls. Eighty minutes later participants completed a painful foot cold pressor test and, after a 5-min interval, began a 25-min arithmetic task interspersed with painful electric shocks. Ten minutes later participants completed a second cold pressor test. Negative affect was greater in participants with MDD than in non-depressed controls throughout the experiment, and increased significantly in both groups during mental arithmetic. Before the math task, naltrexone unmasked direct linear relationships between severity of depression, negative affect while resting quietly, and cold-induced pain in participants with MDD. In contrast, facilitatory effects of naltrexone on cold- and shock-induced pain were greatest in controls with the lowest depression scores. Naltrexone strengthened the relationship between negative affect and shock-induced pain during the math task, particularly in the depressed group, and heightened anxiety in both groups toward the end of the task. Thus, mu-opioid activity apparently masked a positive association between negative affect and pain in the most distressed participants. These findings suggest that psychological distress inhibits pain via stress-evoked release of opioid peptides in severe cases of MDD. In addition, tonic endogenous opioid neurotransmission could inhibit depressive symptoms and pain in people with low depression scores.

Holocene thermal optimal and climate variability of East Asian monsoon inferred from forest reconstruction of a subalpine pollen sequence, Taiwan

NASA Astrophysics Data System (ADS)

Liew, P. M.; Lee, C. Y.; Kuo, C. M.

2006-10-01

The East Asian monsoon Holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation. In this study we show Holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central Taiwan, based on modern analogues of various altitudinal biomes in the region. A warmer interval occurred between 8 and 4 ka BP (calibrated 14C years) when the subtropical forests were more extensive. The Holocene thermal optimum is represented by an altitudinal tropical forest at 6.1-5.9 ka BP and 6.9 ka BP and only the latter was accompanied by wet conditions, indicating decoupling of thermal and precipitation mechanism in the middle Holocene. Abrupt and relative severe cold phases, shown by biome changes, occurred at about 11.2-11.0 ka BP; 7.5 ka BP; 7.2 ka BP; 7.1 ka BP; 5.2 ka BP, 5.0 ka BP and 4.9 ka BP. A spectral analysis of pollen of a relatively cold taxon — Salix, reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of Indian and western Pacific Oceans. The cold-warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of Be-10.

Improved Arterial Blood Oxygenation Following Intravenous Infusion of Cold Supersaturated Dissolved Oxygen Solution

PubMed Central

Grady, Daniel J; Gentile, Michael A; Riggs, John H; Cheifetz, Ira M

2014-01-01

BACKGROUND One of the primary goals of critical care medicine is to support adequate gas exchange without iatrogenic sequelae. An emerging method of delivering supplemental oxygen is intravenously rather than via the traditional inhalation route. The objective of this study was to evaluate the gas-exchange effects of infusing cold intravenous (IV) fluids containing very high partial pressures of dissolved oxygen (>760 mm Hg) in a porcine model. METHODS Juvenile swines were anesthetized and mechanically ventilated. Each animal received an infusion of cold (13 °C) Ringer’s lactate solution (30 mL/kg/hour), which had been supersaturated with dissolved oxygen gas (39.7 mg/L dissolved oxygen, 992 mm Hg, 30.5 mL/L). Arterial blood gases and physiologic measurements were repeated at 15-minute intervals during a 60-minute IV infusion of the supersaturated dissolved oxygen solution. Each animal served as its own control. RESULTS Five swines (12.9 ± 0.9 kg) were studied. Following the 60-minute infusion, there were significant increases in PaO2 and SaO2 (P < 0.05) and a significant decrease in PaCO2 (P < 0.05), with a corresponding normalization in arterial blood pH. Additionally, there was a significant decrease in core body temperature (P < 0.05) when compared to the baseline preinfusion state. CONCLUSIONS A cold, supersaturated dissolved oxygen solution may be intravenously administered to improve arterial blood oxygenation and ventilation parameters and induce a mild therapeutic hypothermia in a porcine model. PMID:25249764

Intranasal ipratropium bromide for the common cold.

PubMed

Albalawi, Zaina H; Othman, Sahar S; Alfaleh, Khalid

2011-07-06

The common cold is one of the most common illnesses in humans and constitutes an economic burden both in terms of productivity and expenditure for treatment. There is no proven cure for the common cold and symptomatic relief is the mainstay of treatment. The use of intranasal ipratropium bromide (IB) has been addressed in several studies and might prove an effective treatment for the common cold. To determine the effect of IB versus placebo or no treatment on severity of rhinorrhoea and nasal congestion in children and adults with the common cold. Subjective overall improvement was another primary outcome and side effects were reported as a secondary outcome. We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2011, Issue 1) which contains the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1950 to January week 4, 2011), MEDLINE in-process and other non-indexed citations (February 2011), EMBASE (1974 to February 2011), AMED (1985 to February 2011), Biosis (1974 to February 2011) and LILACS (1985 to February 2011). Randomised controlled trials (RCTs) comparing IB to placebo or no treatment in children and adults with the common cold. Two review authors independently extracted data and assessed trial quality. We used a standardised form to extract relevant data and we contacted trial authors for additional information. Seven trials with a total of 2144 participants were included. Four studies (1959 participants) addressed subjective change in severity of rhinorrhoea. All studies were consistent in reporting statistically significant changes in favour of IB. Nasal congestion was reported in four studies and was found to have no significant change between the two groups. Two studies found a positive response in the IB group for the global assessment of overall improvement. Side effects were more frequent in the IB group, odds ratio (OR) 2.09 (95% confidence interval (CI) 1.40 to 3.11). Commonly encountered side effects included nasal dryness, blood tinged mucus and epistaxis. For people with the common cold, the existing evidence, which has some limitations, suggests that IB is likely to be effective in ameliorating rhinorrhoea. IB had no effect on nasal congestion and its use was associated with more side effects compared to placebo or no treatment although these appeared to be well-tolerated and self-limiting. There is a need for larger, high-quality trials to determine the effectiveness of IB in relieving common cold symptoms.

Wet and cold climate conditions recorded by coral geochemical proxies during the beginning of the first millennium CE in the northern South China Sea

NASA Astrophysics Data System (ADS)

Xiao, Hangfang; Deng, Wenfeng; Chen, Xuefei; Wei, Gangjian; Zeng, Ti; Zhao, Jian-xin

2017-03-01

The past two millennia include some distinct climate intervals, such as the Medieval Warm Period (MWP) and the Little Ice Age (LIA), which were caused by natural forcing factors, as well as the Current Warm Period (CWP) that has been linked to anthropogenic factors. Therefore, this period has been of great interest to climate change researchers. However, most studies are based on terrestrial proxy records, historical documentary data, and simulation results, and the ocean and the tropical record are very limited. The Eastern Han, Three Kingdoms, and Western Jin periods (25-316 CE) cover the beginning first millennium CE in China, and were characterized by a cold climate and frequent wars and regime changes. This study used paired Sr/Ca and δ18O series recovered from a fossil coral to reconstruct the sea surface water conditions during the late Eastern Han to Western Jin periods (167-309 CE) at Wenchang, eastern Hainan Island in the northern South China Sea (SCS), to investigate climate change at this time. The long-term sea surface temperature (SST) during the study interval was 25.1 °C, which is about 1.5 °C lower than that of the CWP (26.6 °C). Compared with the average value of 0.40‰ during the CWP, the long-term average seawater δ18O (-0.06‰) was more negative. These results indicate that the climate conditions during the study period were cold and wet and comparable with those of the LIA. This colder climate may have been associated with the weaker summer solar irradiance. The wet conditions were caused by the reduced northward shift of the intertropical convergence zone/monsoon rainbelt associated with the retreat of the East Asian summer monsoon. Interannual and interdecadal climate variability may also have contributed to the variations in SST and seawater δ18O recorded over the study period.

Whole Grain Consumption and Risk of Ischemic Stroke: Results From 2 Prospective Cohort Studies.

PubMed

Juan, Juan; Liu, Gang; Willett, Walter C; Hu, Frank B; Rexrode, Kathryn M; Sun, Qi

2017-12-01

Higher intake of whole grains may exert cardiometabolic benefits, although findings on stroke risk are inconclusive. The potentially differential effects of individual whole grain foods on ischemic stroke have not been examined. We analyzed whole grain consumption in relation to ischemic stroke among 71 750 women from the Nurses' Health Study and 42 823 men from the Health Professionals Follow-up Study who were free of cardiovascular disease, diabetes mellitus, and cancer at baseline (1984 and 1986, respectively) through 2010 using a Cox proportional hazards model. Validated semiquantitative food frequency questionnaires were used to assess consumption of whole grain intake, including whole grain cold breakfast cereal, dark bread, oatmeal, brown rice, popcorn, bran, and germ. Self-reported incident cases of ischemic stroke were confirmed through medical record review. During 2 820 128 person-years of follow-up in the 2 cohorts, 2458 cases of ischemic stroke were identified and confirmed. Intake of total whole grains was not associated with risk of ischemic stroke after adjustment for covariates: the pooled hazard ratio (95% confidence interval) comparing extreme intake levels was 1.04 (0.91-1.19). However, intake of whole grain cold breakfast cereal and total bran was inversely associated with ischemic stroke after multivariate adjustment: the pooled hazard ratios (95% confidence intervals) were 0.88 (0.80-0.96; P trend =0.008) and 0.89 (0.79-1.00; P trend =0.004), respectively. Other whole grain foods were not associated with a lower risk of ischemic stroke. Although overall consumption of whole grains was not associated with lower risk of ischemic stroke, greater consumption of whole grain cold breakfast cereal and bran was significantly associated with a lower risk of ischemic stroke. More studies are needed to replicate these associations between individual whole grain foods and risk of ischemic stroke among other populations. © 2017 American Heart Association, Inc.

Effects of cilnidipine, a novel dihydropyridine calcium antagonist, on autonomic function, ambulatory blood pressure and heart rate in patients with essential hypertension.

PubMed

Minami, J; Kawano, Y; Makino, Y; Matsuoka, H; Takishita, S

2000-12-01

The aim of the present study was to evaluate the effects of cilnidipine, a novel dihydropyridine calcium antagonist, on autonomic function, ambulatory blood pressure and heart rate in patients with essential hypertension. Ten inpatients with mild to moderate essential hypertension (four men and six women; age: 44-64 years) underwent a drug-free period for 7 days and a treatment period with cilnidipine 10 mg orally for another 7 days, in a randomized crossover study. On the sixth day of each period, they underwent autonomic function tests including a mental arithmetic test, a cold pressor test and a Valsalva manoeuvre. After these tests, 24 h ambulatory blood pressure, heart rate, and the electrocardiogram R-R intervals were monitored every 30 min. A power spectral analysis of R-R intervals was performed to obtain the low-and high-frequency components. Cilnidipine significantly decreased the 24 h blood pressure by 6.5 +/- 1.7 mm Hg systolic (mean +/- s.e.mean; P < 0.01) and 5.0 +/- 1.1 mmHg diastolic (P < 0.01), whereas cilnidipine did not change heart rate or any indices of power spectral components. During the cold pressor test, the maximum change in systolic blood pressure and percentage changes in both systolic and diastolic blood pressures were significantly lower during the treatment period with cilnidipine than during the drug-free period. The baroreflex sensitivity measured from the overshoot phase of the Valsalva manoeuvre did not differ significantly between the two periods. Cilnidipine is effective as a once-daily antihypertensive agent and causes little influence on heart rate and the autonomic nervous system in patients with mild to moderate essential hypertension. Moreover, it is suggested that cilnidipine has an additional clinical benefit in the inhibition of the pressor response induced by acute cold stress.

Optimizing Cold Water Immersion for Exercise-Induced Hyperthermia: A Meta-analysis.

PubMed

Zhang, Yang; Davis, Jon-Kyle; Casa, Douglas J; Bishop, Phillip A

2015-11-01

Cold water immersion (CWI) provides rapid cooling in events of exertional heat stroke. Optimal procedures for CWI in the field are not well established. This meta-analysis aimed to provide structured analysis of the effectiveness of CWI on the cooling rate in healthy adults subjected to exercise-induced hyperthermia. An electronic search (December 2014) was conducted using the PubMed and Web of Science. The mean difference of the cooling rate between CWI and passive recovery was calculated. Pooled analyses were based on a random-effects model. Sources of heterogeneity were identified through a mixed-effects model Q statistic. Inferential statistics aggregated the CWI cooling rate for extrapolation. Nineteen studies qualified for inclusion. Results demonstrate CWI elicited a significant effect: mean difference, 0.03°C·min(-1); 95% confidence interval, 0.03-0.04°C·min(-1). A conservative, observed estimate of the CWI cooling rate was 0.08°C·min(-1) across various conditions. CWI cooled individuals twice as fast as passive recovery. Subgroup analyses revealed that cooling was more effective (Q test P < 0.10) when preimmersion core temperature ≥38.6°C, immersion water temperature ≤10°C, ambient temperature ≥20°C, immersion duration ≤10 min, and using torso plus limbs immersion. There is insufficient evidence of effect using forearms/hands CWI for rapid cooling: mean difference, 0.01°C·min(-1); 95% confidence interval, -0.01°C·min(-1) to 0.04°C·min(-1). A combined data summary, pertaining to 607 subjects from 29 relevant studies, was presented for referencing the weighted cooling rate and recovery time, aiming for practitioners to better plan emergency procedures. An optimal procedure for yielding high cooling rates is proposed. Using prompt vigorous CWI should be encouraged for treating exercise-induced hyperthermia whenever possible, using cold water temperature (approximately 10°C) and maximizing body surface contact (whole-body immersion).

Paleohydrology of China Lake basin and the context of early human occupation in the northwestern Mojave Desert, USA

NASA Astrophysics Data System (ADS)

Rosenthal, Jeffrey S.; Meyer, Jack; Palacios-Fest, Manuel R.; Young, D. Craig; Ugan, Andrew; Byrd, Brian F.; Gobalet, Ken; Giacomo, Jason

2017-07-01

Considerable prior research has focused on the interconnected pluvial basins of Owens Lake and Searles Lake, resulting in a long record of paleohydrological change in the lower Owens River system. However, the published record is poorly resolved or contradictory for the period encompassing the terminal Pleistocene (22,000 to 11,600 cal BP) and early Holocene (11,600-8200 cal BP). This has resulted in conflicting interpretations about the timing of lacustrine high stands within the intermediate basin of China Lake, which harbors one of the most extensive records of early human occupation in the western Great Basin and California. Here, we report a broad range of radiocarbon-dated paleoenvironmental evidence, including lacustrine deposits and shoreline features, tufa outcrops, and mollusk, ostracode, and fish bone assemblages, as well as spring and other groundwater-related deposits (a.k.a. "black mats") from throughout China Lake basin, its outlet, and inflow drainages. Based on 98 radiocarbon dates, we develop independent evidence for five significant lake-level oscillations between 18,000 and 13,000 cal BP, and document the persistence of groundwater-fed wetlands from the beginning of the Younger Dryas through the early Holocene (12,900-8200 cal BP); including the transition from ground-water fed lake to freshwater marsh between about 13,000 and 12,600 cal BP. Results of this study support and refine existing evidence that shows rapid, high-amplitude oscillations in the water balance of the Owens River system during the terminal Pleistocene, and suggest widespread human use of China Lake basin began during the Younger Dryas.

Chronological and geomorphological investigation of fossil debris-covered glaciers in relation to deglaciation processes: A case study in the Sierra de La Demanda, northern Spain

NASA Astrophysics Data System (ADS)

Fernández-Fernández, José M.; Palacios, David; García-Ruiz, José M.; Andrés, Nuria; Schimmelpfennig, Irene; Gómez-Villar, Amelia; Santos-González, Javier; Álvarez-Martínez, Javier; Arnáez, José; Úbeda, José; Léanni, Laëtitia; Aumaître, Georges; Bourlès, Didier; Keddadouche, Karim; Aster Team

2017-08-01

In this study, fossil debris-covered glaciers are investigated and dated in the Sierra de la Demanda, northern Spain. They are located in glacial valleys of approximately 1 km in length, where several moraines represent distinct phases of the deglaciation period. Several boulders in the moraines and fossil debris-covered glaciers were selected for analysis of 10Be surface exposure dating. A minimum age of 17.8 ± 2.2 ka was obtained for the outermost moraine in the San Lorenzo cirque, and was attributed to the global Last Glacial Maximum (LGM) or earlier glacial stages, based on deglaciation dates determined in other mountain areas of northern Spain. The youngest moraines were dated to approximately 16.7 ± 1.4 ka, and hence correspond to the GS-2a stadial (Oldest Dryas). Given that the debris-covered glaciers fossilize intermediate moraines, it was deduced that they developed between the LGM and the Oldest Dryas, coinciding with a period of extensive deglaciation. During this deglaciation phase, the cirque headwalls likely discharged large quantities of boulders and blocks that covered the residual ice masses. The resulting debris-covered glaciers evolved slowly because the debris mantle preserved the ice core from rapid ablation, and consequently they remained active until the end of the Late Glacial or the beginning of the Holocene (for the San Lorenzo cirque) and the Holocene Thermal Maximum (for the Mencilla cirque). The north-facing part of the Mencilla cirque ensured longer preservation of the ice core.

Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America

NASA Astrophysics Data System (ADS)

Bahr, André; Hoffmann, Julia; Schönfeld, Joachim; Schmidt, Matthew W.; Nürnberg, Dirk; Batenburg, Sietske J.; Voigt, Silke

2018-01-01

Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America during periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we generated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indicate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions prevailed in northern South America, while eastern Brazil experienced maximally wet conditions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by reconfigurations of surface ocean currents in low latitudes. Our new records demonstrate the extreme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions.

Archaeal community changes in Lateglacial lake sediments: Evidence from ancient DNA

NASA Astrophysics Data System (ADS)

Ahmed, Engy; Parducci, Laura; Unneberg, Per; Ågren, Rasmus; Schenk, Frederik; Rattray, Jayne E.; Han, Lu; Muschitiello, Francesco; Pedersen, Mikkel W.; Smittenberg, Rienk H.; Yamoah, Kweku Afrifa; Slotte, Tanja; Wohlfarth, Barbara

2018-02-01

The Lateglacial/early Holocene sediments from the ancient lake at Hässeldala Port, southern Sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present Interglacial. The existing multi-proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes. Yet, it remains unclear how microorganisms, such as Archaea, which do not leave microscopic features in the sedimentary record, were affected by these climatic shifts. Here we present the metagenomic data set of Hässeldala Port with a special focus on the abundance and biodiversity of Archaea. This allows reconstructing for the first time the temporal succession of major Archaea groups between 13.9 and 10.8 ka BP by using ancient environmental DNA metagenomics and fossil archaeal cell membrane lipids. We then evaluate to which extent these findings reflect physical changes of the lake system, due to changes in lake-water summer temperature and seasonal lake-ice cover. We show that variations in archaeal composition and diversity were related to a variety of factors (e.g., changes in lake water temperature, duration of lake ice cover, rapid sediment infilling), which influenced bottom water conditions and the sediment-water interface. Methanogenic Archaea dominated during the Allerød and Younger Dryas pollen zones, when the ancient lake was likely stratified and anoxic for large parts of the year. The increase in archaeal diversity at the Younger Dryas/Holocene transition is explained by sediment infilling and formation of a mire/peatbog.

Late Quaternary glaciation history of monsoon-dominated Dingad basin, central Himalaya, India

NASA Astrophysics Data System (ADS)

Shukla, Tanuj; Mehta, Manish; Jaiswal, Manoj K.; Srivastava, Pradeep; Dobhal, D. P.; Nainwal, H. C.; Singh, Atul K.

2018-02-01

The study presents the Late Quaternary glaciation history of monsoon-dominated Dokriani Glacier valley, Dingad basin, central Himalaya, India. The basin is tested for the mechanism of landforms preservation in high relief and abundant precipitation regimes of the Higher Himalaya. Field geomorphology and remote sensing data, supported by Optical Stimulated Luminescence (OSL) dating enabled identification of five major glacial events of decreasing magnitude. The oldest glacial stage, Dokriani Glacial Stage I (DGS-I), extended down to ∼8 km (2883 m asl) from present-day snout (3965 m asl) followed by other four glaciations events viz. DGS-II, DGS-III, DGS-IV and DGS-V terminating at ∼3211, 3445, 3648 and ∼3733 m asl respectively. The DGS-I glaciation (∼25-∼22 ka BP) occurred during early Marine Isotope Stage (MIS) -2, characterized as Last Glacial Maximum (LGM) extension of the valley. Similarly, DGS-II stage (∼14-∼11 ka BP) represents the global cool and dry Older Dryas and Younger Dryas event glaciation. The DGS-III glaciation (∼8 ka BP) coincides with early Holocene 8.2 ka cooling event, the DGS-IV glaciations (∼4-3.7 ka BP) corresponds to 4.2 ka cool and drier event, DGS-V (∼2.7-∼1 ka BP) represents the cool and moist late Holocene glacial advancement of the valley. This study suggests that the Dokriani Glacier valley responded to the global lowering of temperature and variable precipitation conditions. This study also highlights the close correlation between the monsoon-dominated valley glaciations and Northern Hemisphere cooling events influenced by North Atlantic climate.

On the paleoenvironmental potential of 253 newly discovered pine stumps from Zurich, Switzerland

NASA Astrophysics Data System (ADS)

Reinig, Frederick; Nievergelt, Daniel; Esper, Jan; Friedrich, Michael; Helle, Gerhard; Hellmann, Lena; Kromer, Bernd; Morganti, Sandro; Pauly, Maren; Sookdeo, Adam; Tegel, Willy; Treydte, Kerstin; Wacker, Lukas; Büntgen, Ulf

2017-04-01

The transition from the last Ice Age to the early Holocene 15'000-10'000 BP represents a close natural analog to the ongoing and predicted rates of anthropogenic climate change. A reduced quality and quantity of high-resolution proxy archives during this period, however, limits our understanding of the magnitude and pace of Late Glacial (LG) environmental variability. Here, we present the world's best preserved, most replicated and oldest forest remains: A total of 253 subfossil pine stumps were recently discovered in Zurich. The combined approach of tree-ring and radiocarbon (14C) measurements results in an absolutely dated Preboreal Swiss tree-ring width chronology and eight floating chronologies. With tree ages ranging between 41 and 506 years, often including pith and bark, and a mean segment length of 163 years, this exceptional find is distributed over nearly 2'000 years between the Allerød and the Preboreal. Together with 200 previously collected LG pines from the greater Zurich region, this study sets a benchmark in terms of sample replication and dating precision for stable more dynamic climatic periods such as the Laacher See eruption, the Older and Younger Dryas. The paleoenvironmental significance would even increase when annually resolved 14C-measurements help fixing a major, Northern Hemispheric gap in the absolutely dated dendro time series during the Younger Dryas. While overcoming this interlude, our results further emphasize the importance of interdisciplinary research on these striking LG climatic shifts to better understand and assess their ecological and environmental impact.

Evidence for an extraterrestrial impact 12,900 years ago thatcontributed to megafaunal extinctions and the Younger Dryas cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Firestone, R.B.; West, A.; Kennett, J.P.

2007-08-06

A carbon-rich black layer, dating to ~;12.9 ka, has beenpreviously identified at ~;50 Clovis-age sites across North America andappears contemporaneous with the abrupt onset of Younger Dryas (YD)cooling. The in situ bones of extinct Pleistocene megafauna and Clovistool assemblages occur below this black layer but not within or above it.Causes for the extinctions, the YD cooling, and the termination of Clovisculture have long been controversial. In this paper, we provide evidencefor an extraterrestrial (ET) impact event at ?12.9 ka, which, wehypothesize, caused abrupt environmental changes that contributed to YDcooling, major ecological reorganization, broad-scale extinctions, andrapid human behavioral shifts at themore » end of the Clovis Period. Clovis-agesites in North American are overlain by a thin, discrete layer withvarying peak abundances of: (1) magnetic grains with iridium, (2)magnetic microspherules (3) charcoal, (4) soot, (5) carbon spherules, (6)glass-like carbon, and (7) fullerenes with ET helium, all of which areevidence for an ET impact and associated biomass burning at ~;12.9 ka.This layer also extends throughout at least fifteen Carolina Bays, whichare unique, elliptical wetlands, oriented to thenorthwest across theAtlantic Coastal Plain. We propose that one or more large, low-density ETobjects exploded over northern North America, partially destabilizing theLaurentide Ice Sheet and triggering YD cooling. The shock wave, thermalpulse, and event-related environmental effects (e.g., extensive biomassburning, food limitations) contributed to the end-Pleistocene megafaunalextinctions and adaptive shifts among PaleoAmericans in NorthAmerica.« less

Annual proxy data from Lago Grande di Monticchio (southern Italy) contributing to chronological constraints and abrupt climatic oscillations between 76 and 112 ka

NASA Astrophysics Data System (ADS)

Martin-Puertas, C.; Brauer, A.; Wulf, S.; Ott, F.; Lauterbach, S.; Dulski, P.

2014-06-01

We present annual sedimentological proxies and sub-annual element scanner data from the Lago Grande di Monticchio (MON) sediment record for the sequence 76-112 ka, which, combined with the decadal to centennial resolved pollen assemblage, allow a comprehensive reconstruction of six major abrupt cold and relatively humid spells (MON 1-6) in the central Mediterranean during early phase of the last glaciation. These climatic oscillations are defined by intervals of thicker varves and high Ti-counts and coincide with episodes of forest depletion interpreted as cold and wet oscillations. Based on the independent and slightly revised MON-2014 varve chronology (76-112 ka), a detailed comparison with the Greenland ice-core δ18O record (NGRIP) and northern Alps speleothem δ18O data (NALPS) is presented. Based on visual inspection of major changes in the proxy data, MON 2-6 are suggested to correlate with GS 25-20. MON 1 (Woillard event), the first and shortest cooling spell in the Mediterranean after a long phase of stable interglacial conditions, has no counterpart in the Greenland ice core, but coincides with the lowest isotope values at the end of the gradual decrease in δ18O in NGRIP during the second half of the GI 25. MON 3 is the least pronounced cold spell and shows gradual transitions, whereas its NGRIP counterpart GS 24 is characterized by sharp changes in the isotope records. MON 2 and MON 4 are the longest most pronounced oscillations in the MON sediments in good agreement with their counterparts in the ice and spelethem records. The length of MON 4 (correlating with GS 22) support the duration of this stadial proposed by the NALPS timescales and suggests ca. 500 yr longer duration than calculated by GICC05 and AICC2012, which would confirm a~possible underestimation in the ice-core. Absolute dating of the cold spells occurring from 112 to 100 ka (MON 1-3) in the MON-2014 chronology is in good agreement with the GICC05 and NALPS timescales but the younger oscillations (MON 4-6) are ca. 3500 yr younger in Monticchio suggesting a so far not recognized and explicable underestimation of varves within the interstadial interval between MON 3 and MON 4 (corresponding to GI 23-GI 22).

Zinc for the common cold.

PubMed

Singh, Meenu; Das, Rashmi R

2011-02-16

The common cold is one of the most widespread illnesses and is a leading cause of visits to the doctor and absenteeism from school and work. Trials conducted since 1984 investigating the role of zinc for the common cold symptoms have had mixed results. Inadequate treatment masking and reduced bioavailability of zinc from some formulations have been cited as influencing results. To assess the effect of zinc on common cold symptoms. We searched CENTRAL (2010, Issue 2) which contains the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to May week 3, 2010) and EMBASE (1974 to June 2010). Randomised, double-blind, placebo-controlled trials using zinc for at least five consecutive days to treat, or for at least five months to prevent the common cold. Two review authors independently extracted data and assessed trial quality. We included 13 therapeutic trials (966 participants) and two preventive trials (394 participants). Intake of zinc is associated with a significant reduction in the duration (standardized mean difference (SMD) -0.97; 95% confidence interval (CI) -1.56 to -0.38) (P = 0.001), and severity of common cold symptoms (SMD -0.39; 95% CI -0.77 to -0.02) (P = 0.04). There was a significant difference between the zinc and control group for the proportion of participants symptomatic after seven days of treatment (OR 0.45; 95% CI 0.2 to 1.00) (P = 0.05). The incidence rate ratio (IRR) of developing a cold (IRR 0.64; 95% CI 0.47 to 0.88) (P = 0.006), school absence (P = 0.0003) and prescription of antibiotics (P < 0.00001) was lower in the zinc group. Overall adverse events (OR 1.59; 95% CI 0.97 to 2.58) (P = 0.06), bad taste (OR 2.64; 95% CI 1.91 to 3.64) (P < 0.00001) and nausea (OR 2.15; 95% CI 1.44 to 3.23) (P = 0.002) were higher in the zinc group. Zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people. When supplemented for at least five months, it reduces cold incidence, school absenteeism and prescription of antibiotics in children. There is potential for zinc lozenges to produce side effects. In view of this and the differences in study populations, dosages, formulations and duration of treatment, it is difficult to make firm recommendations about the dose, formulation and duration that should be used.

Extraterrestrial Markers Found at Clovis Sites Across North America

NASA Astrophysics Data System (ADS)

West, A.; Firestone, R. B.; Kennett, J. P.; Becker, L.

2007-05-01

We present evidence for an extraterrestrial (ET) impact event with Earth at about 12.9 ka, which, we hypothesize, caused abrupt environmental changes that contributed to Younger Dryas (YD) cooling, major ecological reorganization, broad-scale extinctions, and the rapid human behavioral shifts evident at the end of the Clovis Period. Terminal Clovis-age sites in North American are marked by a thin, discrete layer, the YD boundary layer (YDB) with varying peak abundances of an array or ET markers, including magnetic grains, microspherules, carbon spherules, soot, fullerenes with ET helium, and iridium. We will present data from a number of well- known Clovis sites and other locations in support of the YD impact event. Gainey, north of Detroit, Michigan, is a PaleoAmerican campsite that was located a few tens of kilometers from the southern margin of the Laurentide Ice Sheet at 12.9 ka. Gainey gave its name to the distinctive fluted point style found there, and Gainey sediments contained some of the highest abundances of YDB markers found, suggesting that the YD impact was centered nearby. Murray Springs, near Sierra Vista, Arizona is one of the best known Clovis mammoth kill-sites. A distinctive carbonaceous layer, called a "black mat" and thought to be of algal origin, drapes conformably over the mammoth bones (Haynes and Huckell, 2007). A thin layer (about 2 mm), the YDB, containing Younger Dryas impact event markers, lies at the base of the black mat and immediately overlies the mammoth bones and Clovis artifacts. Blackwater Draw, New Mexico is southwest of the town of Clovis, which gave its name to the type of projectile points first found there. It was a PaleoAmerican hunting site on the bank of a spring-fed waterhole, and the black mat drapes over bones of butchered mammoths and Clovis artifacts. Topper, located on a high bank of the Savannah River near Allendale, South Carolina, was a Clovis-age flint quarry containing thousands of artifacts. YDB markers occur within an approximate 5-cm interval immediately above the distinct layer of Clovis artifacts. Wally`s Beach at St. Mary Reservoir, southwestern Alberta, Canada, at 12.9 ka, supported many species of now-extinct megafauna, including mammoths, camels, and horses (Kooyman, et al., 2001). YDB markers, including iridium at 51 ppb, occur inside an extinct horse skull at the Wally's Beach Clovis kill-site, suggesting rapid burial following the YD event. One other Clovis site examined was the Chobot site near Edmonton, AB, Canada. We also examined other sites that date to 12.9 ka: glacial Lake Hind in MB, Canada; an ice-aged drumlin at Morley, AB, Canada; Daisy Cave on the Channel Islands of California; and Lommel in Belgium. At all sites, the YDB layer was evident, dated to around 12.9 ka, and contained abundant ET markers.

Annealing Increases Stability Of Iridium Thermocouples

NASA Technical Reports Server (NTRS)

Germain, Edward F.; Daryabeigi, Kamran; Alderfer, David W.; Wright, Robert E.; Ahmed, Shaffiq

1989-01-01

Metallurgical studies carried out on samples of iridium versus iridium/40-percent rhodium thermocouples in condition received from manufacturer. Metallurgical studies included x-ray, macroscopic, resistance, and metallographic studies. Revealed large amount of internal stress caused by cold-working during manufacturing, and large number of segregations and inhomogeneities. Samples annealed in furnace at temperatures from 1,000 to 2,000 degree C for intervals up to 1 h to study effects of heat treatment. Wire annealed by this procedure found to be ductile.

Quantitative interpretation of atmospheric carbon records over the last glacial termination

NASA Astrophysics Data System (ADS)

KöHler, Peter; Fischer, Hubertus; Munhoven, Guy; Zeebe, Richard E.

2005-12-01

The glacial/interglacial rise in atmospheric pCO2 is one of the best known changes in paleoclimate research, yet the cause for it is still unknown. Forcing the coupled ocean-atmosphere-biosphere box model of the global carbon cycle BICYCLE with proxy data over the last glacial termination, we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (δ13C, Δ14C) observed in natural climate archives. The sensitivity of the Box model of the Isotopic Carbon cYCLE (BICYCLE) to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models, respectively. The processes considered here ranked by their contribution to the glacial/interglacial rise in pCO2 in decreasing order are: the rise in Southern Ocean vertical mixing rates (>30 ppmv), decreases in alkalinity and carbon inventories (>30 ppmv), the reduction of the biological pump (˜20 ppmv), the rise in ocean temperatures (15-20 ppmv), the resumption of ocean circulation (15-20 ppmv), and coral reef growth (<5 ppmv). The regrowth of the terrestrial biosphere, sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction, decreasing pCO2 during Termination I by ˜30 ppmv. According to our model the sequence of events during Termination I might have been the following: a reduction of aeolian iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase. After these events the reduced North Atlantic Deep Water (NADW) formation during the Heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the Bølling-Allerød warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of Termination I. We further deduce that a complete shutdown of the NADW formation during the Younger Dryas was very unlikely. Changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric δ13C after the Bølling-Allerød warm interval.

Trace-element deposition in the Cariaco Basin, Venezuela Shelf, under sulfate-reducing conditions: a history of the local hydrography and global climate, 20 ka to the present

USGS Publications Warehouse

Piper, David Z.; Dean, Walter E.

2002-01-01

A sediment core from the Cariaco Basin on the Venezuelan continental shelf, which recovered sediment that has been dated back to 20 ka (thousand years ago), was examined for its major-element-oxide and trace-element composition. Cadmium (Cd), chromium (Cr), copper (Cu), molybdenum (Mo), nickel (Ni), vanadium (V), and zinc (Zn) can be partitioned between a siliciclastic, terrigenous-derived fraction and two seawater-derived fractions. The two marine fractions are (1) a biogenic fraction represented by nutrient trace elements taken up mostly in the photic zone by phytoplankton, and (2) a hydrogenous fraction that has been derived from bottom water via adsorption and precipitation reactions. This suite of trace elements contrasts with a second suite of trace elements—barium (Ba), cobalt (Co), gallium (Ga), lithium (Li), the rare-earth elements, thorium (Th), yttrium (Y), and several of the major-element oxides—that has had solely a terrigenous source. The partitioning scheme, coupled with bulk sediment accumulation rates measured by others, allows us to determine the accumulation rate of trace elements in each of the three sediment fractions and of the fractions themselves. The current export of organic matter from the photic zone, redox conditions and advection of bottom water, and flux of terrigenous debris into the basin can be used to calculate independently trace-element depositional rates. The calculated rates show excellent agreement with the measured rates of the surface sediment. This agreement supports a model of trace-element accumulation rates in the subsurface sediment that gives a 20-kyr history of upwelling into the photic zone (that is, primary productivity), bottom-water advection and redox, and provenance. Correspondence of extrema in the geochemical signals with global changes in sea level and climate demonstrates the high degree to which the basin hydrography and provenance have responded to the paleoceanographic and paleoclimatic regimes of the last 20 kyr. The accumulation rate of the marine fraction of Mo increased abruptly at about 14.8 ka (calendar years), from less than 0.5 µg cm-2 yr-1 to greater than 4 µg cm-2 yr-1. Its accumulation rate remained high but variable until 8.6 ka, when it decreased sharply to 1 µg cm-2 yr-1. It continued to decrease to 4.0 ka, to its lowest value for the past 15 kyr, before gradually increasing to the present. Between 14.8 ka and 8.6 ka, its accumulation rate exhibited strong maxima at 14.4, 13.0, and 9.9 ka. The oldest maximum corresponds to melt-water pulse IA into the Gulf of Mexico. A relative minimum, centered at about 11.1 ka, corresponds to melt-water pulse IB; a strong maximum occurs in the immediately overlying sediment. The maximum at 13.0 ka corresponds to onset of the Younger Dryas cold event. This pattern to the accumulation rate of Mo (and V) can be interpreted in terms of its deposition from bottom water of the basin, the hydrogenous fraction, under SO42- -reducing conditions, during times of intense bottom-water advection 14.8 ka to 11.1 ka and significantly less intense bottom-water advection 11 ka to the present. The accumulation rate of Cd shows a pattern that is only slightly different from that of Mo, although its deposition was determined largely by the rain rate of organic matter into the bottom water, a biogenic fraction whose deposition was driven by upwelling of nutrient-enriched water into the photic zone. Its accumulation exhibits only moderately high rates, on average, during both melt-water pulses. Its highest rate, and that of upwelling, occurred during the Younger Dryas, and again following melt-water pulse IB. The marine fractions of Cu, Ni, and Zn also have a strong biogenic signal. The siliciclastic terrigenous debris, however, represents the dominant source, and host, of Cu, Ni, and Zn. All four trace elements have a consid-erably weaker hydrogenous signal than biogenic signal. Accumulation rates of the terrigenous fraction, as reflected by accumulation rates of Th and Ga, show strong maxima at 16.2 and 12.7 ka and minima at 14.1 and 11.1 ka. Co, Li, REE, and Y have a similar distribution. The minima occurred during melt-water pulses IA and IB, the maxima during the Younger Dryas and the rise in sea level following the last glacial maximum.

Time from cervical conization to pregnancy and preterm birth.

PubMed

Himes, Katherine P; Simhan, Hyagriv N

2007-02-01

To estimate whether the time interval between cervical conization and subsequent pregnancy is associated with risk of preterm birth. Our study is a case control study nested in a retrospective cohort. Women who underwent colposcopic biopsy or conization with loop electrosurgical excision procedure, large loop excision of the transformation zone, or cold knife cone and subsequently delivered at our hospital were identified with electronic databases. Variables considered as possible confounders included maternal race, age, marital status, payor status, years of education, self-reported tobacco use, history of preterm delivery, and dimensions of cone specimen. Conization was not associated with preterm birth or any subtypes of preterm birth. Among women who underwent conization, those with a subsequent preterm birth had a shorter conization-to-pregnancy interval (337 days) than women with a subsequent term birth (581 days) (P=.004). The association between short conization-to-pregnancy interval and preterm birth remained significant when controlling for confounders including race and cone dimensions. The effect of short conization-to-pregnancy interval on subsequent preterm birth was more persistent among African Americans when compared with white women. Women with a short conization-to-pregnancy interval are at increased risk for preterm birth. Women of reproductive age who must have a conization procedure can be counseled that conceiving within 2 to 3 months of the procedure may be associated with an increased risk of preterm birth. II.

A 2000-year tree ring record of annual temperatures in the Sierra Nevada Mountains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scuderi, L.A.

1993-03-05

Tree ring data have been used to reconstruct the mean late-season (June through January) temperature at a timberline site in the Sierra Nevada, California, for each of the past 2000 years. Long-term trends in the temperature reconstruction are indicative of a 125-year periodicity that may be liked to solar activity as reflected in radiocarbon and auroral records. The results indicate that both the warm intervals during the Medieval Warm Epoch ([approximately]A.D. 800 to 1200) and the cold intervals during the Little Ice Age ([approximately]A.D. 1200 to 1900) are closely associated with the 125-year period. Significant changes in the phase ofmore » the 125-year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior.« less

Cold Spraying of Cu-Al-Bronze for Cavitation Protection in Marine Environments

NASA Astrophysics Data System (ADS)

Krebs, S.; Gärtner, F.; Klassen, T.

2015-01-01

Traveling at high speeds, ships have to face the problem of rudder cavitation-erosion. At present, the problem is countered by fluid dynamically optimized rudders, synthetic, and weld-cladded coatings on steel basis. Nevertheless, docking and repair is required after certain intervals. Bulk Cu-Al-bronzes are in use at ships propellers to withstand corrosion and cavitation. Deposited as coatings with bulk-like properties, such bronzes could also enhance rudder life times. The present study investigates the coating formation by cold spraying CuAl10Fe5Ni5 bronze powders. By calculations of the impact conditions, the range of optimum spray parameters was preselected in terms of the coating quality parameter η on steel substrates with different temperatures. As-atomized and annealed powders were compared to optimize cavitation resistance of the coatings. Results provide insights about the interplay between the mechanical properties of powder and substrate for coating formation. Single particle impact morphologies visualize the deformation behavior. Coating performance was assessed by analyzing microstructures, bond strength, and cavitation resistance. These first results demonstrate that cold-sprayed bronze coatings have a high potential for ensuring a good performances in rudder protection. With further optimization, such coatings could evolve towards a competitive alternative to existing anti-cavitation procedures.

Sensitivity of sediment magnetic records to climate change during Holocene for the northern South China Sea

NASA Astrophysics Data System (ADS)

Ouyang, Tingping; Li, Mingkun; Zhao, Xiang; Zhu, Zhaoyu; Tian, Chengjing; Qiu, Yan; Peng, Xuechao; Hu, Qiao

2016-05-01

Magnetic property has been proved to be a sensitive proxy to climate change for both terrestrial and marine sediments. Based on the schedule frame established by AMS 14C dating of foraminifera, detail magnetic analyses were performed for core PC24 sediments at sampling intervals of 2 cm to discuss magnetic sensitivity of marine sediment to climate during Holocene for the northern South China Sea. The results indicated that: 1) Concentration dependent magnetic parameters are positive corresponding to variation of temperature. The frequency dependent susceptibility coefficient basically reflected the variation in humidity; 2) XARM/SIRM was more sensitive to detrital magnetite particles and SIRM/X was more effective to biogenic magnetite particles. Variations of XARM/SIRM and SIRM/X are corresponding to precipitation and temperature, respectively; 3) the Holocene Megathermal in the study area was identified as 7.5-3.4 cal. ka BP. The warmest stage of Holocene for the study area should be during 6.1 to 3.9 cal. ka BP; 4) The 8 ka cold event was characterized as cold and dry during 8.55 to 8.25 cal. ka BP; 5) During early and middle Holocene, the climate combinations were warm dry and cold wet. It turned to warm and wet after 2.7 cal. ka BP.

Malacological and palynological evidence of the Lower Pleistocene cold phase at the Carpathian Foothills (Southern Poland)

NASA Astrophysics Data System (ADS)

Stworzewicz, Ewa; Granoszewski, Wojciech; Wójcik, Antoni

2012-05-01

Early Pleistocene sediments bearing gastropod shells and pollen flora were found during coring at Jawornik (South Poland) at a depth interval of 54.30-39.00 m, beneath the oldest till of the Carpathians. Thirteen land-snail taxa identified in 55 samples of the core formed two molluscan assemblages. In the bottom part, typical cold-loving snails were found (e.g. Vallonia tenuilabris, Pupilla loessica, Vertigo genesii, Columella columella), whereas in the upper part only Semilimax kotulae was present. The succession of molluscan assemblages may suggest that at the site of deposition, after a phase of tundra, steppe-tundra or forest-steppe landscape with patches of wet habitats in cold climate, the climate became slightly milder but still cool, favourable to the spreading of boreal (coniferous) woodlands. Pollen analysis was performed only for the upper part of the profile. The pollen spectra, besides the Tertiary (Miocene) elements, contained sporomorphs common to the Tertiary and Quaternary floras. Among them, the highest percentages were noted for Pinus haploxylon t., P. diploxylon t., Picea, Quercus, Ericaceae, Betula, and Ulmus. The fact that the sediments with organic remains underlie the oldest Scandinavian till suggests that they are older than the oldest glacial unit of the South-Polish Complex (Narevian = Menapian, ~ 1.2 Ma).

Reliability estimation of a N- M-cold-standby redundancy system in a multicomponent stress-strength model with generalized half-logistic distribution

NASA Astrophysics Data System (ADS)

Liu, Yiming; Shi, Yimin; Bai, Xuchao; Zhan, Pei

2018-01-01

In this paper, we study the estimation for the reliability of a multicomponent system, named N- M-cold-standby redundancy system, based on progressive Type-II censoring sample. In the system, there are N subsystems consisting of M statistically independent distributed strength components, and only one of these subsystems works under the impact of stresses at a time and the others remain as standbys. Whenever the working subsystem fails, one from the standbys takes its place. The system fails when the entire subsystems fail. It is supposed that the underlying distributions of random strength and stress both belong to the generalized half-logistic distribution with different shape parameter. The reliability of the system is estimated by using both classical and Bayesian statistical inference. Uniformly minimum variance unbiased estimator and maximum likelihood estimator for the reliability of the system are derived. Under squared error loss function, the exact expression of the Bayes estimator for the reliability of the system is developed by using the Gauss hypergeometric function. The asymptotic confidence interval and corresponding coverage probabilities are derived based on both the Fisher and the observed information matrices. The approximate highest probability density credible interval is constructed by using Monte Carlo method. Monte Carlo simulations are performed to compare the performances of the proposed reliability estimators. A real data set is also analyzed for an illustration of the findings.

Test plan for evaluating the operational performance of the prototype nested, fixed-depth fluidic sampler

DOE Office of Scientific and Technical Information (OSTI.GOV)

REICH, F.R.

The PHMC will provide Low Activity Wastes (LAW) tank wastes for final treatment by a privatization contractor from two double-shell feed tanks, 241-AP-102 and 241-AP-104. Concerns about the inability of the baseline ''grab'' sampling to provide large volume samples within time constraints has led to the development of a nested, fixed-depth sampling system. This sampling system will provide large volume, representative samples without the environmental, radiation exposure, and sample volume impacts of the current base-line ''grab'' sampling method. A plan has been developed for the cold testing of this nested, fixed-depth sampling system with simulant materials. The sampling system willmore » fill the 500-ml bottles and provide inner packaging to interface with the Hanford Sites cask shipping systems (PAS-1 and/or ''safe-send''). The sampling system will provide a waste stream that will be used for on-line, real-time measurements with an at-tank analysis system. The cold tests evaluate the performance and ability to provide samples that are representative of the tanks' content within a 95 percent confidence interval, to sample while mixing pumps are operating, to provide large sample volumes (1-15 liters) within a short time interval, to sample supernatant wastes with over 25 wt% solids content, to recover from precipitation- and settling-based plugging, and the potential to operate over the 20-year expected time span of the privatization contract.« less

Respiratory virus transmission dynamics determine timing of asthma exacerbation peaks: Evidence from a population-level model

PubMed Central

Scott, James G.; Galvani, Alison P.; Meyers, Lauren Ancel

2016-01-01

Asthma exacerbations exhibit a consistent annual pattern, closely mirroring the school calendar. Although respiratory viruses—the “common cold” viruses—are implicated as a principal cause, there is little evidence to link viral prevalence to seasonal differences in risk. We jointly fit a common cold transmission model and a model of biological and environmental exacerbation triggers to estimate effects on hospitalization risk. Asthma hospitalization rate, influenza prevalence, and air quality measures are available, but common cold circulation is not; therefore, we generate estimates of viral prevalence using a transmission model. Our deterministic multivirus transmission model includes transmission rates that vary when school is closed. We jointly fit the two models to 7 y of daily asthma hospitalizations in adults and children (66,000 events) in eight metropolitan areas. For children, we find that daily viral prevalence is the strongest predictor of asthma hospitalizations, with transmission reduced by 45% (95% credible interval =41–49%) during school closures. We detect a transient period of nonspecific immunity between infections lasting 19 (17–21) d. For adults, hospitalizations are more variable, with influenza driving wintertime peaks. Neither particulate matter nor ozone was an important predictor, perhaps because of the large geographic area of the populations. The school calendar clearly and predictably drives seasonal variation in common cold prevalence, which results in the “back-to-school” asthma exacerbation pattern seen in children and indirectly contributes to exacerbation risk in adults. This study provides a framework for anticipating the seasonal dynamics of common colds and the associated risks for asthmatics. PMID:26858436

Retreat of the Southwest Labrador Sector of the Laurentide Ice Sheet During the Last Termination

NASA Astrophysics Data System (ADS)

Lowell, T. V.; Kelly, M. A.; Fisher, T. G.; Barnett, P. J.; Howley, J. A.; Zimmerman, S. R. H.

2016-12-01

Large ice sheets are suspected to have played a major role in forcing the transitions from glacial to interglacial conditions, known as terminations. To improve the understanding of the role of the Laurentide Ice Sheet in the last termination, we present a chronology of ice sheet recession from just subsequent to end of the Last Glacial Maximum (LGM) to the early Holocene. We focus on the retreat of the southwest Labrador Sector of the ice sheet in northern Minnesota and adjacent Ontario. Multiple moraines in this region mark an overall pattern of ice recession interrupted by stillstands and/or minor readvances. Radiocarbon and 10Be ages from 50 sites along this 400 km-long transect indicate that the oldest moraine complex, the Vermillion moraine, formed at 17.0 ka. Subsequently, the ice margin retreated with minor standstills until the Dog Lake moraine was deposited between 12.7 and 12.3 ka. Recession from the Dog Lake moraine began by 12.3 ka the ice margin receded 150 km to the north-northeast by 10.7 ka. In general, the radiocarbon and 10Be ages define a pattern of near-continuous ice sheet retreat. Deposition of the Vermillion and Dog Lake moraines occurred at the beginning of Heinrich stadials 1 ( 17.5-14.5 ka) and 0 ( 12.9-11.7 ka), respectively, but ice recession occurred throughout the remainder of these stadials. This pattern is different from climate conditions registered by Greenland ice cores which show cold conditions from the end of the LGM until the Bølling warming at 14.5 ka, and throughout the Younger Dryas ( 12.9-11.7 ka). We suggest that the pattern of ice sheet recession is more similar to mountain glaciers in the southern mid-latitudes and tropics, and that Heinrich stadials may have been characterized by warming at least in the summertime that influenced near global ice recession.

Deglacial Warming and Wetting of Northern Alaska

NASA Astrophysics Data System (ADS)

Daniels, W.; Russell, J. M.; Longo, W. M.; Giblin, A. E.; Holland-Stergar, P.; Morrill, C.; Huang, Y.

2015-12-01

Aeolian sand dunes swept across northern Alaska during the last glacial maximum. Today, summer temperatures are moderate and soils can remain waterlogged all summer long. How did the transition from a cold and dry glacial to a warm and wet interglacial take place? To answer this question we reconstructed temperature and precipitation changes during the last deglaciation using biomarker hydrogen isotopes from a new 28,000 year-long sediment core from Lake E5, located in the central Brooks Range of Alaska. We use terrestrial leaf waxes (dDterr, C28-acid), informed by dD measurements of modern vegetation, to infer dD of precipitation, an indicator of relative temperature change. Biomarkers from aquatic organisms (dDaq, C18-acid) are used as a proxy for lake water isotopes. The offset between the two (eterr-aq) is used to infer relative changes in evaporative enrichment of lake water, and by extension, moisture balance. dDterr during the last glacial period was -282‰ compared to -258‰ during the Holocene, suggesting a 5.6 ± 2.7 °C increase in summer temperature using the modern local temperature-dD relationship. Gradual warming began at ~18.5 ka, and temperature increased abruptly at 11.5 ka, at the end of the Younger Dryas. Warming peaked in the early Holocene from 11.5 to 9.1 ka, indicating a Holocene thermal maximum associated with peak summer insolation. The eterr-aq supports a dry LGM and moist Holocene. Other sediment proxies (TIC, TOC, redox-sensitive elements) support the eterr-aq, and reveal a shift to more positive P-E beginning around 17 ka, suggesting rising temperature led increases in precipitation during the last deglaciation. Moreover, differing patterns of dDterr and eterr-aq during the deglaciation suggest that the relationship between temperature and precipitation changed through time. Such decoupling, likely due to regional atmospheric reorganization as the Laurentide ice sheet waned, illustrates the importance of atmospheric dynamics in controlling Alaskan climate.

Past and future evolution of Abies alba forests in Europe - comparison of a dynamic vegetation model with palaeo data and observations.

PubMed

Ruosch, Melanie; Spahni, Renato; Joos, Fortunat; Henne, Paul D; van der Knaap, Willem O; Tinner, Willy

2016-02-01

Information on how species distributions and ecosystem services are impacted by anthropogenic climate change is important for adaptation planning. Palaeo data suggest that Abies alba formed forests under significantly warmer-than-present conditions in Europe and might be a native substitute for widespread drought-sensitive temperate and boreal tree species such as beech (Fagus sylvatica) and spruce (Picea abies) under future global warming conditions. Here, we combine pollen and macrofossil data, modern observations, and results from transient simulations with the LPX-Bern dynamic global vegetation model to assess past and future distributions of A. alba in Europe. LPX-Bern is forced with climate anomalies from a run over the past 21 000 years with the Community Earth System Model, modern climatology, and with 21st-century multimodel ensemble results for the high-emission RCP8.5 and the stringent mitigation RCP2.6 pathway. The simulated distribution for present climate encompasses the modern range of A. alba, with the model exceeding the present distribution in north-western and southern Europe. Mid-Holocene pollen data and model results agree for southern Europe, suggesting that at present, human impacts suppress the distribution in southern Europe. Pollen and model results both show range expansion starting during the Bølling-Allerød warm period, interrupted by the Younger Dryas cold, and resuming during the Holocene. The distribution of A. alba expands to the north-east in all future scenarios, whereas the potential (currently unrealized) range would be substantially reduced in southern Europe under RCP8.5. A. alba maintains its current range in central Europe despite competition by other thermophilous tree species. Our combined palaeoecological and model evidence suggest that A. alba may ensure important ecosystem services including stand and slope stability, infrastructure protection, and carbon sequestration under significantly warmer-than-present conditions in central Europe. © 2015 John Wiley & Sons Ltd.

Persistence of the North American Monsoon over the last 50,000 years in Arizona, USA

NASA Astrophysics Data System (ADS)

Cole, K. L.; Ironside, K. E.; Cobb, N. S.

2012-12-01

Reconstruction of monsoon rainfall in the American southwest over the last 50,000 years has been complicated by past massive shifts in temperature and winter precipitation, as well as the rarity of proxy sources. Paleogeographical analysis of plant species distributions from plant macrofossils contained within packrat middens and sediment cores portray substantial shifts that are most easily attributed to these larger changes in temperature and winter precipitation. But some species can be more reliably associated with summer precipitation through spatial analyses of their climate space within their contemporary habitat. For example, warm-season C4 grasses and summer annuals were infrequent in southern Arizona throughout the late Wisconsinan, likely because of much lower temperatures and much higher levels of winter rainfall. But other species, today typical of summer precipitation regions further north, were especially abundant during selected intervals. Macrofossils of Arizona single-leaf pinyon (Pinus edulis var. fallax) and one seed juniper (Juniperus monosperma) are abundant in middens from northern Arizona and southern Utah ranging from 30,400 to > 50,000 C14 yr BP, suggesting at least 200% of the current summer precipitation. The abundance of Arizona single-leaf pinyon throughout Arizona during the Allerød Interval (~13.9 ka to ~12.9 ka) suggests that summer precipitation was at least 120% of modern. The rapid expansion and dominance of the southwestern interior race of Ponderosa pine (Pinus ponderosa), as well as increases in Rocky Mountain Juniper (Juniperus scopulorum), during the earliest Holocene (~11.7 ka to ~10.2 Ka) portray summer precipitation somewhat greater than that of today. These paleobotanical conclusions are supported by a recent analysis of Deuterium isotopes from 120 middens in 5 regional series. These isotopic values should reflect the relative frequency of precipitation originating from Pacific winter cyclonic storms versus sub-tropical summer monsoonal convective precipitation. This correlation was supported by the analysis of 41 modern samples from throughout the region. Higher values, similar to modern levels, were recorded during the Allerød Interval and earliest Holocene. Much lower levels were recorded during the Full-glacial Wisconsinan and the Younger Dryas Period. These paleogeograpic records and isotopic analyses are temporally and spatially consistent. They suggest that the climate mechanisms responsible transport of summer moisture into Arizona have persisted at various times during the late Wisconsinan, although the amounts, transport dynamics, and moisture sources may have shifted from time to time.

N zooming into the Mediterranean outflow fossil moat during the 1.2-1.8 million years period (Early-Pleistocene) - An approach by radiogenic and stable isotopes

NASA Astrophysics Data System (ADS)

Lebreiro, Susana M.; Antón, Laura; Reguera, M. Isabel; Fernández, Marta; Conde, Estefanía; Barrado, Ana I.; Yllera, Abel

2015-12-01

The fossil Alvarez Cabral erosive Moat contains hemipelagite, contourite and turbidite facies where oceanography changes in the Mediterranean outflow are archived over the 1.2-1.8 Myr time period. Here we used Pb and Sr radiogenic isotopes to trace water masses and sediment source changes, for the first time in twenty glacial-interglacial (G-I) cycles of the Early-Pleistocene interval, and the last Glacial Maximum through Holocene cycle (including the Younger Dryas and Heinrich Stadial-1). A mixing line of Pb isotopes gives reliable low radiogenic 208Pb/204Pb, 206Pb/204Pb, and 206Pb/207Pb typical of Mediterranean Outflow Water (MOW) in one end-member and the signature of high radiogenic isotopes of Atlantic Waters (AW) towards the second end-member. The 87Sr/86Sr isotopes also display two end-members of the mixing line between eolian transport/dust source (0.71) and fluvial transport/weathering source (0.73) previously proposed in the Gulf of Cadiz. Combination of Pb and Sr radiogenic isotopes with O and C stable isotopes of planktonic and benthic foraminifera, and the response of foraminifera benthos over the Early-Pleistocene interval, reveals a direct link between water masses circulation and shifts in G-I. We found a persistent cyclic pattern of MOW circulation and fluvial deposition during glaciations and AW and aeolian influence during interglaciations. On site U1386B/C, the upper-MOW was less ventilated but productive and with high flux of organic flux matter during glacials, while Atlantic Waters were better ventilated, enriched in O, but less productive during interglacials. We infer that shifts in ocean and atmospheric processes in the Gulf of Cadiz were strongly controlled by Earth's obliquity (41 kyr-cycle) and 35°NH insolation during the Early-Pleistocene. We propose a correlation in changes in phase-relationship between precession and obliquity. In general terms, physical properties of fine sediments (glacials) show lower NGR, low reflectance and high magnetic susceptibility. These curves measured in a 20 cm sampling interval, on board ship, present a number of gaps due to non-recovery of sediment. To overcome this problem and obtain a complete lithological record the point-sensor curves of physical properties were correlated with down-hole logs of HSGR (standard total Gamma-ray in gAPI units) (Suppl. Fig. 1) and HROM (high resolution corrected bulk density in g/cm3) (IODP Expedition 339 by the Scientific Party, Logging Summaries).

Laurentide Ice Sheet meltwater and the Atlantic meridional overturning circulation since the last glacial maximum: A view from the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Flower, B. P.; Williams, C.; Brown, E. A.; Hastings, D. W.; Hendricks, J.; Goddard, E. A.

2010-12-01

The influence of ice sheet meltwater on the Atlantic meridional overturning circulation (AMOC) since the last glacial maximum represents an important issue in abrupt climate change. Comparison of Greenland and Antarctic ice core records has revealed a complex interhemispheric linkage and led to different models of ocean circulation including the “bipolar seesaw.” Meltwater input from the Laurentide Ice Sheet has been invoked as a cause of proximal sea-surface temperature (SST) and salinity change in the North Atlantic, and of regional to global climate change via its influence on the AMOC. We present published and new Mg/Ca, Ba/Ca, and δ18O data on the planktic foraminifer Globigerinoides ruber from northern Gulf of Mexico sediment cores that provide detailed records of SST, δ18O of seawater (δ18Osw), and inferred salinity for the 20-8 ka interval. Age control for Orca Basin core MD02-2550 is based on >40 AMS 14C dates on Globigerinoides ruber and documents continuous sedimentation at rates >35 cm/kyr. Early meltwater input is inferred from δ18Osw and Ba/Ca data prior to and during the Mystery Interval, consistent with a high sensitivity to solar insolation and greenhouse forcing. New bulk sediment δ18O data show major spikes reaching -5.5‰ ca. 14.6 and 12.6 ka. We speculate that these excursions represent fine carbonate sediment from Canadian Paleozoic marine carbonates, analogous to detrital carbonate in the North Atlantic which has a δ18O value of -5‰. Partial support for our hypothesis comes from SEM photomicrographs of bulk sediment from this section, which show no coccoliths or foraminifera in contrast to other intervals. The biogenic carbonate flux seems to have been greatly reduced by fine sediment input. Inferred peak meltwater flow appears to have been associated with the Bolling warming and meltwater pulse 1a. Finally, meltwater reduction at the start of the Younger Dryas supports models for a diversion to North Atlantic outlets and AMOC reduction ca. 12.9 ka, but alternatively could represent diminished ice melting. Overall, the relations between Gulf of Mexico meltwater input, Heinrich events, Antarctic warm events, and AMOC variability suggest bipolar warming and enhanced seasonality during meltwater episodes. We formulate a “meltwater capacitor” hypothesis for understanding enhanced seasonality in the North Atlantic region during abrupt climate change.

Continuous Transversus Abdominis Plane Nerve Blocks: Does Varying Local Anesthetic Delivery Method-Automatic Repeated Bolus Versus Continuous Basal Infusion-Influence the Extent of Sensation to Cold?: A Randomized, Triple-Masked, Crossover Study in Volunteers.

PubMed

Khatibi, Bahareh; Said, Engy T; Sztain, Jacklynn F; Monahan, Amanda M; Gabriel, Rodney A; Furnish, Timothy J; Tran, Johnathan T; Donohue, Michael C; Ilfeld, Brian M

2017-04-01

It remains unknown whether continuous or scheduled intermittent bolus local anesthetic administration is preferable for transversus abdominis plane (TAP) catheters. We therefore tested the hypothesis that when using TAP catheters, providing local anesthetic in repeated bolus doses increases the cephalad-caudad cutaneous effects compared with a basal-only infusion. Bilateral TAP catheters (posterior approach) were inserted in 24 healthy volunteers followed by ropivacaine 2 mg/mL administration for a total of 6 hours. The right side was randomly assigned to either a basal infusion (8 mL/h) or bolus doses (24 mL administered every 3 hours for a total of 2 bolus doses) in a double-masked manner. The left side received the alternate treatment. The primary end point was the extent of sensory deficit as measured by cool roller along the axillary line at hour 6 (6 hours after the local anesthetic administration was initiated). Secondary end points included the extent of sensory deficit as measured by cool roller and Von Frey filaments along the axillary line and along a transverse line at the level of the anterior superior iliac spine at hours 0 to 6. Although there were statistically significant differences between treatments within the earlier part of the administration period, by hour 6 the difference in extent of sensory deficit to cold failed to reach statistical significance along the axillary line (mean = 0.9 cm; SD = 6.8; 95% confidence interval -2.0 to 3.8; P = .515) and transverse line (mean = 2.5 cm; SD = 10.1; 95% confidence interval -1.8 to 6.8; P = .244). Although the difference between treatments was statistically significant at various early time points for the horizontal, vertical, and estimated area measurements of both cold and mechanical pressure sensory deficits, no comparison remained statistically significant by hour 6. No evidence was found in this study involving healthy volunteers to support the hypothesis that changing the local anesthetic administration technique (continuous basal versus hourly bolus) when using ropivacaine 0.2% and TAP catheters at 8 mL/h and 24 mL every 3 hours significantly influences the cutaneous effects after 6 hours of administration. Additional research is required to determine whether changing variables (eg, local anesthetic concentration, basal infusion rate, bolus dose volume, and/or interval) would provide different results.

The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis.

PubMed

Hemilä, Harri; Chalker, Elizabeth

2015-02-25

A previous meta-analysis found that high dose zinc acetate lozenges reduced the duration of common colds by 42%, whereas low zinc doses had no effect. Lozenges are dissolved in the pharyngeal region, thus there might be some difference in the effect of zinc lozenges on the duration of respiratory symptoms in the pharyngeal region compared with the nasal region. The objective of this study was to determine whether zinc acetate lozenges have different effects on the duration of common cold symptoms originating from different anatomical regions. We analyzed three randomized trials on zinc acetate lozenges for the common cold administering zinc in doses of 80-92 mg/day. All three trials reported the effect of zinc on seven respiratory symptoms, and three systemic symptoms. We pooled the effects of zinc lozenges for each symptom and calculated point estimates and 95% confidence intervals (95% CI). Zinc acetate lozenges shortened the duration of nasal discharge by 34% (95% CI: 17% to 51%), nasal congestion by 37% (15% to 58%), sneezing by 22% (-1% to 45%), scratchy throat by 33% (8% to 59%), sore throat by 18% (-10% to 46%), hoarseness by 43% (3% to 83%), and cough by 46% (28% to 64%). Zinc lozenges shortened the duration of muscle ache by 54% (18% to 89%), but there was no difference in the duration of headache and fever. The effect of zinc acetate lozenges on cold symptoms may be associated with the local availability of zinc from the lozenges, with the levels being highest in the pharyngeal region. However our findings indicate that the effects of zinc ions are not limited to the pharyngeal region. There is no indication that the effect of zinc lozenges on nasal symptoms is less than the effect on the symptoms of the pharyngeal region, which is more exposed to released zinc ions. Given that the adverse effects of zinc in the three trials were minor, zinc acetate lozenges releasing zinc ions at doses of about 80 mg/day may be a useful treatment for the common cold, started within 24 hours, for a time period of less than two weeks.

The cold effect of ambient temperature on ischemic and hemorrhagic stroke hospital admissions: A large database study in Beijing, China between years 2013 and 2014-Utilizing a distributed lag non-linear analysis.

PubMed

Luo, Yanxia; Li, Haibin; Huang, Fangfang; Van Halm-Lutterodt, Nicholas; Qin Xu; Wang, Anxin; Guo, Jin; Tao, Lixin; Li, Xia; Liu, Mengyang; Zheng, Deqiang; Chen, Sipeng; Zhang, Feng; Yang, Xinghua; Tan, Peng; Wang, Wei; Xie, Xueqin; Guo, Xiuhua

2018-01-01

The effects of ambient temperature on stroke death in China have been well addressed. However, few studies are focused on the attributable burden for the incident of different types of stroke due to ambient temperature, especially in Beijing, China. We purpose to assess the influence of ambient temperature on hospital stroke admissions in Beijing, China. Data on daily temperature, air pollution, and relative humidity measurements and stroke admissions in Beijing were obtained between 2013 and 2014. Distributed lag non-linear model was employed to determine the association between daily ambient temperature and stroke admissions. Relative risk (RR) with 95% confidence interval (CI) and Attribution fraction (AF) with 95% CI were calculated based on stroke subtype, gender and age group. A total number of 147, 624 stroke admitted cases (including hemorrhagic and ischemic types of stroke) were documented. A non-linear acute effect of cold temperature on ischemic and hemorrhagic stroke hospital admissions was evaluated. Compared with the 25th percentile of temperature (1.2 °C), the cumulative RR of extreme cold temperature (first percentile of temperature, -9.6 °C) was 1.51 (95% CI: 1.08-2.10) over lag 0-14 days for ischemic type and 1.28 (95% CI: 1.03-1.59) for hemorrhagic stroke over lag 0-3 days. Overall, 1.57% (95% CI: 0.06%-2.88%) of ischemic stroke and 1.90% (95% CI: 0.40%-3.41%) of hemorrhagic stroke was attributed to the extreme cold temperature over lag 0-7 days and lag 0-3 days, respectively. The cold temperature's impact on stroke admissions was found to be more obvious in male gender and the youth compared to female gender and the elderly. Exposure to extreme cold temperature is associated with increasing both ischemic and hemorrhagic stroke admissions in Beijing, China. Copyright © 2017 Elsevier Ltd. All rights reserved.

New Insights into the 8.2 ka Cold Event and Subsequent Climate Recovery in Central Europe Provided by a Precisely Dated Ostracod δ18O Record from Mondsee (Austria)

NASA Astrophysics Data System (ADS)

Lauterbach, S.; Andersen, N.; Brauer, A.; Erlenkeuser, H.; Danielopol, D. L.; Namiotko, T.; Huels, M.; Belmecheri, S.; Nantke, C.; Meyer, H.; Chapligin, B.; von Grafenstein, U.

2015-12-01

As evidenced by numerous palaeoclimate records worldwide, the Holocene warm period has been interrupted by several short, low-amplitude cold episodes. Among these, the so-called 8.2 ka cold event is the most prominent Holocene climate perturbation but despite extensive studies, knowledge about its synchrony in different areas and particularly about the dynamics of subsequent climate recovery is still limited. As this is of crucial importance for understanding the complex mechanisms that trigger rapid climate fluctuations and for testing the performance of climate models, new data on the 8.2 ka cold event are needed. Here we present a new sub-decadally resolved, precisely dated oxygen isotope (δ18O) record for the interval 7.7-8.7 ka BP obtained from benthic ostracods preserved in the varved lake sediments of Mondsee (Austria), providing new insights into climate development around the 8.2 ka cold event in Central Europe. The new high-resolution δ18O data set reveals the occurrence of a pronounced cold spell around 8.2 ka BP, whose amplitude (~1.0 ‰, equivalent to a 1.5-2.0 °C cooling), total duration (151 a) and absolute dating (8231-8080 a BP, i.e. calendar years before AD 1950) perfectly agree with results from other Northern Hemisphere palaeoclimate archives, e.g. the precisely dated Greenland ice cores. In addition, the Mondsee δ18O record also indicates a 75-year-long air temperature overshoot of ~0.7 °C directly after the 8.2 ka event (between 8080 and 8005 a BP), which is so far only poorly documented in the mid-latitudes. However, this observation is consistent with results from coupled climate models and high-latitude proxy records, thus likely reflecting a hemispheric-scale climate signal driven by enhanced resumption of the Atlantic meridional overturning circulation (AMOC), which apparently also caused synchronous migrations of atmospheric and oceanic front systems in the North Atlantic realm.

Intranasal ipratropium bromide for the common cold.

PubMed

AlBalawi, Zaina H; Othman, Sahar S; Alfaleh, Khalid

2013-06-19

The common cold is one of the most common illnesses in humans and constitutes an economic burden both in terms of productivity and expenditure for treatment. There is no proven cure for the common cold and symptomatic relief is the mainstay of treatment. The use of intranasal ipratropium bromide (IB) has been addressed in several studies and might prove an effective treatment for the common cold. To determine the effect of IB versus placebo or no treatment on severity of rhinorrhoea and nasal congestion in children and adults with the common cold. Subjective overall improvement was another primary outcome and side effects (for example, dry mucous membranes, epistaxis and systemic anticholinergic effects) were reported as a secondary outcome. In this updated review we searched CENTRAL 2013, Issue 3, MEDLINE (1950 to March week 4, 2013), MEDLINE in-process and other non-indexed citations (8 April 2013), EMBASE (1974 to April 2013), AMED (1985 to April 2013), Biosis (1974 to February 2011) and LILACS (1985 to April 2013). Randomised controlled trials (RCTs) comparing IB to placebo or no treatment in children and adults with the common cold. Two review authors independently extracted data and assessed trial quality. We used a standardised form to extract relevant data and we contacted trial authors for additional information. Seven trials with a total of 2144 participants were included. Four studies (1959 participants) addressed subjective change in severity of rhinorrhoea. All studies were consistent in reporting statistically significant changes in favour of IB. Nasal congestion was reported in four studies and was found to have no significant change between the two groups. Two studies found a positive response in the IB group for the global assessment of overall improvement. Side effects were more frequent in the IB group, odds ratio (OR) 2.09 (95% confidence interval (CI) 1.40 to 3.11). Commonly encountered side effects included nasal dryness, blood tinged mucus and epistaxis. The overall risk of bias in the included studies was moderate. For people with the common cold, the existing evidence, which has some limitations, suggests that IB is likely to be effective in ameliorating rhinorrhoea. IB had no effect on nasal congestion and its use was associated with more side effects compared to placebo or no treatment although these appeared to be well tolerated and self limiting. There is a need for larger, high-quality trials to determine the effectiveness of IB in relieving common cold symptoms.

Climatic factors associated with peripartum pig deaths during hot and humid or cold seasons.

PubMed

Iida, Ryosuke; Koketsu, Yuzo

2014-08-01

Our objective was to quantify the associations between climatic factors and a death occurrence of peripartum pigs from 16 to 19 weeks after successful service during hot and humid or cold seasons. The study used lifetime records of 93,837 females entered into 98 Japanese commercial herds from 2003 to 2007. The climate data were obtained from 21 weather stations close to the studied herds. Average daily maximum (HT) and minimum temperature (LT), and relative humidity for week 15 of gestation for each pregnant pig were coordinated with the respective pig's performance data. Multilevel logistic regression models were applied to two of the three separate datasets. One dataset included females due to farrow during the hot and humid season (June-September), and another comprised females due to farrow during the cold season (December-March). Of the 8381 females that died throughout the year, 11.5% of pregnant pigs died between 16 and 17 weeks after service, and 44.3% of farrowed females subsequently died from 16 to 19 weeks after service. Mean (ranges) HT in the hot and humid season and LT in the cold season were 28.7 (13.4-39.8) °C and 1.6 (-14.8 to 17.6) °C, respectively. Means of relative humidity in the hot and humid season and cold season were 73.6 (35-98)% and 64.9 (21-99)%, respectively. In the hot and humid season, a higher HT was associated with a higher occurrence of death for parity 0-1 females (P<0.05), but not for parity 2 or higher sows (P≥0.38). The odds ratio was 1.030 (95% confidence intervals: 1.005-1.056) for HT in parity 0-1 females. Also, higher relative humidity was associated with a higher occurrence of death for parity 0-3 females (P<0.05), but not parity 4 or higher sows (P≥0.21). In the cold season, a higher occurrence of death of parity 4 or higher sows was associated with lower LT (P<0.05). Also, the occurrence of death of parity 6 or higher sows was associated with higher relative humidity in the cold season (P<0.05). For parity 0-3 females, there were no associations between the occurrences of death and either LT or relative humidity during the cold season (P≥0.11). Therefore, it is recommended to install cooling systems and thick insulation to prevent increases in occurrences of pig deaths due to HT or LT. Copyright © 2014 Elsevier B.V. All rights reserved.

Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago.

PubMed

Bunch, Ted E; Hermes, Robert E; Moore, Andrew M T; Kennett, Douglas J; Weaver, James C; Wittke, James H; DeCarli, Paul S; Bischoff, James L; Hillman, Gordon C; Howard, George A; Kimbel, David R; Kletetschka, Gunther; Lipo, Carl P; Sakai, Sachiko; Revay, Zsolt; West, Allen; Firestone, Richard B; Kennett, James P

2012-07-10

It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica- and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe(3)Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO(2) glass, or lechatelierite, with flow textures (or schlieren) that form at > 2,200 °C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.

A regional tephrostratigraphic framework for central and southern European climate archives during the Last Glacial to Interglacial transition: comparisons north and south of the Alps

NASA Astrophysics Data System (ADS)

Lane, C. S.; Blockley, S. P. E.; Lotter, A. F.; Finsinger, W.; Filippi, M. L.; Matthews, I. P.

2012-03-01

This paper summarises the results of tephrochronological investigations into a suite of central and southern European records, which include: Rotmeer, southern Germany; Soppensee and Rotsee, central Swiss Plateau; Lago di Lavarone and Lago Piccolo di Avigliana, Italian southern Alpine foreland. These sites provide records of palaeoenvironmental changes for the Last Glacial to Interglacial Transition (LGIT) at the boundary between North Atlantic and Mediterranean climatic influences. Chemical characterisation of glass shards in volcanic ash layers indicates that multiple volcanic sources have contributed to the central European tephra record. Amongst other volcanic markers, the Laacher See Tephra, originating from the Eifel region of Germany c. 12.9 ± 0.1 ka, and the Vedde Ash from Iceland c. 12.1 ± 0.1 ka, are found co-located within the sediments of Rotmeer, Soppensee, Rotsee and Lago Piccolo di Avigliana. These key horizons, which bracket the onset of the Younger Dryas stadial, provide precise calendrically-dated tie points around which a detailed picture of the timing of local and regional environmental transitions can be constructed. Using the co-located tephra layers the re-colonisation of Northern Italian catchment areas by Quercus is shown to occur just prior to the deposition of the Laacher See Tephra layer, whereas to the North of the Alps Quercus and other thermophilous trees do not reappear until several centuries after the deposition of the Vedde Ash. Furthermore, the discovery of the Vedde Ash in Lago Piccolo di Avigliana and Lago di Lavarone is indicative of atmospheric transport of polar air into southern Europe during the Younger Dryas stadial, matching evidence proposed for such transport of polar air during the Last Glacial Maximum (LGM).

Changes in El Nino - Southern Oscillation (ENSO) conditions during the Younger Dryas revealed by New Zealand tree-rings.

NASA Astrophysics Data System (ADS)

Palmer, Jonathan; Turney, Chris; Cook, Edward; Fenwick, Pavla; Thomas, Zoë; Helle, Gerhard; Jones, Richard; Clement, Amy; Hogg, Alan; Southon, John; Bronk Ramsey, Christopher; Staff, Richard; Muscheler, Raimund; Corrège, Thierry; Hua, Quan

2017-04-01

The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remains uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning the YD, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a 'historic' 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Niño - Southern Oscillation (ENSO). We then focus our study to a 1010-year subfossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between 12,500 to 12,380 cal BP within the YD. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency in the changes to ENSO and Southern Hemisphere westerly airflow during this period. The drivers for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions.

Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records

USGS Publications Warehouse

Jakobsson, Martin; Pearce, Christof; Cronin, Thomas M.; Backman, Jan; Anderson, Leif G.; Barrientos, Natalia; Bjork, Goran; Coxhall, Helen; de Boer, Agatha; Mayer, Larry; Morth, Carl-Magnus; Nilsson, Johan; Rattray, Jayne; Sranne, Christian; Semiletov, Igor; O'Regan, Matt

2017-01-01

The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ∼  53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9–11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic–Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records

NASA Astrophysics Data System (ADS)

Jakobsson, Martin; Pearce, Christof; Cronin, Thomas M.; Backman, Jan; Anderson, Leif G.; Barrientos, Natalia; Björk, Göran; Coxall, Helen; de Boer, Agatha; Mayer, Larry A.; Mörth, Carl-Magnus; Nilsson, Johan; Rattray, Jayne E.; Stranne, Christian; Semiletov, Igor; O'Regan, Matt

2017-08-01

The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ˜ 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9-11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic-Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

Stratigraphy of the Younger Dryas Chronozone and paleoenvironmental implications: Central and Southern Great Plains

USGS Publications Warehouse

Holliday, V.T.; Meltzer, D.J.; Mandel, R.

2011-01-01

The Great Plains of the United States was the setting for some of the earliest research in North America into patterns and changes in the character of late Pleistocene environments and their effects on contemporary human populations. Many localities in the region have well-stratified records of terminal Pleistocene and early Holocene human (Paleoindian) activity and past environments. These have proven important in debates over the character of the Younger Dryas Chronozone (YDC; 11,000-10,000 14C BP; 12,900-11,700 cal BP) in the continental interior. This paper reviews the lithostratigraphic record of the YDC on the Central and Southern Great Plains and summarizes paleobiological records (largely isotopic). The goal is to determine if there is any uniformity in the timing, character, direction and/or magnitude of changes in depositional environments or broader geomorphic systems before, during or after the YDC in order to address the question of the character of environments through this time. The stratigraphic records of the late Pleistocene to early Holocene transition, and in particular, the stratigraphic records of the YDC vary through time and space. The data clearly show that a host of geomorphic processes produced the terminal Pleistocene and early Holocene stratigraphic records of the Great Plains. Moreover, the YDC is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils. The various geomorphic systems of the Great Plains did not behave synchronously in response to any common climate driver. These stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid-latitude climates in the terminal Pleistocene and early Holocene. ?? 2011 Elsevier Ltd and INQUA.

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling.

PubMed

Firestone, R B; West, A; Kennett, J P; Becker, L; Bunch, T E; Revay, Z S; Schultz, P H; Belgya, T; Kennett, D J; Erlandson, J M; Dickenson, O J; Goodyear, A C; Harris, R S; Howard, G A; Kloosterman, J B; Lechler, P; Mayewski, P A; Montgomery, J; Poreda, R; Darrah, T; Hee, S S Que; Smith, A R; Stich, A; Topping, W; Wittke, J H; Wolbach, W S

2007-10-09

A carbon-rich black layer, dating to approximately 12.9 ka, has been previously identified at approximately 50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at approximately equal 12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at approximately 12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.