These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Biogeomorphic interactions and patterns on Little Ice Age lateral moraines  

NASA Astrophysics Data System (ADS)

Glaciers and their forefields are strongly affected by climate change. This leads to increasing geomorphological and ecological dynamics in these environments. Glacier recession exposes high volumes of unconsolidated sediments, with lateral moraines being among the most important sediment storages. Their sediment is reworked by a variety of slope processes, e.g. sheet wash, debris flows or gullying. At the same time, these landforms are colonized by plants and other organisms, proceeding into vegetation succession. It is believed that this process ultimately leads to sediment stabilization which is an important factor for reservoir management in glacier forefields. Recent biogeomorphic research revealed a strong coupling of geomorphic and ecologic processes and complex feedbacks. Geomorphic processes disturb vegetation while at the same time, certain plant species, 'geomorphic-engineer species', can influence geomorphic properties and processes. The strength of these interactions changes during biogeomorphic succession. Corresponding patterns of vegetation and geomorphic forms and processes arise at the mesoscale. The resulting spatial heterogeneity can be mapped as patches. In our study, we investigate patterns of vegetation and geomorphic forms and processes on Little Ice Age lateral moraines in the Turtmann glacier forefield, Switzerland. Despite higher terrain age, these landforms show strongly heterogeneous vegetation as well as geomorphic activity patterns, indicating that sediment stabilization has not yet been accomplished. This could result from varying strengths of biogeomorphic interactions. To assess this influence, vegetation and geomorphic properties of 50 vegetation plots were sampled and statistically analyzed. Results showed that vegetation composition does not relate to terrain age, rather, geomorphic disturbances seem to be a dominant influencing factors, producing patch dynamics. Certain species compositions can be related to specific geomorphic forms and processes. Pioneer vegetation was found proximal to moraine crests with frequent sheet wash, linear erosion and occasional debris flows. Shrub vegetation (Salix spp.) occurs on polygenic cones at the moraine toe. Alpine grass communities with dwarf shrubs (Dryas octopetala) grow at various slope positions and are associated with solifluction forms and processes. With its adapted plant functional traits (strong roots, mat growth form) Dryas octopetala acts as scree-dammer. Thereby, this geomorphic-engineer species generates biogeomorphic interactions and could induce a transition from dominant sheet wash and linear erosion to solifluction. The specific combinations of vegetation and geomorphic properties and processes and related patterns can be seen as the emergent result of small-scale biogeomorphic interactions and as the spatial representation of different biogeomorphic succession phases. They can thus be categorized as 'biogeomorphic patches' that probably determine mesoscale sediment dynamics on lateral moraines.

Eichel, Jana; Schmidtlein, Sebastian; Dikau, Richard

2014-05-01

2

LICHENOMETRIC DATING OF LITTLE ICE AGE GLACIER MORAINES USING EXPLICIT DEMOGRAPHIC MODELS  

E-print Network

LICHENOMETRIC DATING OF LITTLE ICE AGE GLACIER MORAINES USING EXPLICIT DEMOGRAPHIC MODELS OF LICHEN of Little Ice Age glacier moraines using explicit demographic models of lichen colonization, growth surface age and maximum lichen sizes, rather than an understanding of lichen biology. To date three

Loso, Michael G.

3

On the accuracy of lichenometric dates: an assessment based on the 'Little Ice Age' moraine sequence of Nigardsbreen, southern Norway  

Microsoft Academic Search

Families of lichenometric dating curves are constructed using four historically-dated moraine ridges on the glacier foreland of Nigardsbreen (Jostedalsbreen ice cap), southern Norway. A further 20 'Little Ice Age' moraine ridges are dated in terms of median-predicted dates derived from the families of curves. Four approaches are used to assess the accuracy of the median-predicted dates: (1) the extent to

Richard W. Bickerton; John A. Matthews

1992-01-01

4

10Be dating of the Narsarsuaq moraine in southernmost Greenland: evidence for a late-Holocene ice advance exceeding the Little Ice Age maximum  

NASA Astrophysics Data System (ADS)

In southernmost Greenland near Narsarsuaq, the terminal Narsarsuaq moraine was deposited well outside of a historical Little Ice Age (LIA) moraine adjacent to the modern ice margin. Using 10Be surface exposure dating, we determine Narsarsuaq moraine abandonment at 1.51 ± 0.11 ka. A second set of 10Be ages from a more ice-proximal position shows that ice has been within or at its historical (i.e., LIA) extent since 1.34 ± 0.15 ka. Notably, Narsarsuaq moraine abandonment was coincident with climate amelioration in southern Greenland. Southern Greenland warming at ˜1.5 ka was also concurrent with the end of the Roman Warm Period as climate along the northern North Atlantic sector of Europe cooled into the Dark Ages. The warming of southern Greenland and retreat of ice from the Narsarsuaq moraine is consistent with studies suggesting possible anti-phase centennial-scale climate variability between northwestern Europe and southern Greenland. Other southernmost Greenland ice-margin records do not preclude a pre-LIA ice-margin maximum, potentially concurrent with a Narsarsuaq advance prior to ˜1.51 ka, but also lack sufficient ice-margin control to confirm such a correlation. We conclude that there is a clear need to further determine whether a late-Holocene pre-LIA maximum was a local phenomenon or a regional southern Greenland ice maximum, and if this advance and retreat reflects a regional fluctuation in climate.

Winsor, K.; Carlson, A. E.; Rood, D. H.

2014-08-01

5

Paraglacial and postglacial debris flows on a Little Ice Age terminal moraine: Jamapa Glacier, Pico de Orizaba (Mexico)  

Microsoft Academic Search

The study area is located on the northern face of Pico de Orizaba (Mexico, 5700 m ASL), on the terminal moraine of Jamapa Glacier, which dates from the Little Ice Age. Large debris flows are recurrent on the proglacial ramp. The comparison of lichen colonies growing on the deposits of the flows reveals that two generations of flows are present:

David Palacios; Gemma Parrilla; Jose J Zamorano

1999-01-01

6

Little Ice Age on the Tibetan Plateau and its bordering mountains: Evidence from moraine chronologies  

NASA Astrophysics Data System (ADS)

Knowledge of the Little Ice Age (LIA) on the Tibetan Plateau (TP) is of critical importance for understanding the climate changes over the past millennium. However, the data associated with the extents and chronologies of TP LIA moraines are highly dispersed in literature. Lack of systematic integration of these data hampers us to further understand the nature of the LIA, especially from a perspective of whole TP. The paper reviews multiple types of dating on LIA moraines to examine the timing and nature of the LIA on the TP. These include ages of radiocarbon 14C, lichenometry, and cosmogenic radionuclide (CRN), by which we can cross-date the same or morphostratigraphically similar landforms. LIA moraines on the TP are usually present a few hundred to thousand meters beyond the contemporary glaciers. The morphological and stratigraphic evidence indicates multiple periods of glacier advance during the last millennium (LIA). At present, available chronology evidence allows to fully compare the timing of the LIA maximum extents. The glaciers reached and retreated from their LIA maximum extents by an asynchronous pattern between different parts of the TP. The majority of glaciers advanced to their LIA maximum extents at late-14th and early-14th century on the southern and northwestern TP, respectively. The glaciers retreated from their LIA maximum extents during 16th to early-18th, late-14th to early-15th and early-16th century on the southern, northwestern, and northeastern TP, respectively. In addition, the glacier advance period of late-18th to early-19th centuries and retreat period of late-19th century are common on the whole TP. Comparison with ice core records suggests that on the TP, the glacier fluctuations responded more strongly to temperature than to precipitation. By comparison of the LIA chronologies from a global perspective, this paper also concludes that the LIA maximum extents occurred commonly earlier on the TP than in North Atlantic and Southern Hemisphere regions, despite of the variability in the timing of LIA maximum extents on the TP and in the North Atlantic regions. Further, more chronology programs, especially in the central TP, are necessarily needed to improve our understanding of the LIA glacier fluctuations.

Xu, Xiangke; Yi, Chaolu

2014-05-01

7

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

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.

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

2007-01-01

8

Analysis of plant colonization on an arctic moraine since the end of the Little Ice Age using remotely sensed data and a Bayesian approach  

Microsoft Academic Search

Young moraines less than 100 years old are considered as key areas for monitoring the effects of climate change since the end of the Little Ice Age. One way of documenting this change is by recognizing and characterizing the different plant colonization stages and trends that occur on these relatively new environments. Previous studies have shown that remotely sensed data

Myrtille Moreau; Dominique Laffly; Daniel Joly; Thierry Brossard

2005-01-01

9

Cosmogenic 10 Be ages on the Pomeranian Moraine, Poland  

E-print Network

Cosmogenic 10 Be ages on the Pomeranian Moraine, Poland VINCENT R. RINTERKNECHT, LESZEK MARKS, JAN (May): Cosmogenic 10 Be ages on the Pomeranian Moraine, Poland. Boreas, Vol. 34, pp. 186­191. Oslo in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS

Kurapov, Alexander

10

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

Microsoft Academic Search

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

Larry Benson; Richard Madole; Peter Kubik; Richard McDonald

2007-01-01

11

Glacier variations in Breheimen, southern Norway: dating Little Ice Age moraine sequences at seven low-altitude glaciers  

Microsoft Academic Search

Moraine sequences in front of seven relatively low-altitude glaciers in the Breheimen region of central southern Norway are described and dated using a multi-proxy approach to moraine stratigraphy. Lichenometric dating, based on the Rhizocarpon subgenus, is used to construct a composite moraine chronology, which indicates eight phases of synchronous moraine formation: AD 1793-1799, 1807-1813, 1845-1852, 1859-1862, 1879-1885, 1897-1898, 1906-1908 and

Stefan Winkler; John A. Matthews; Richard A. Shakesby; P. Quentin Dresser

2003-01-01

12

Nature and origin of a Pleistocene-age massive ground-ice body exposed in the Chapman Lake moraine complex, central Yukon Territory, Canada  

Microsoft Academic Search

A massive ground-ice body was found exposed in the headwall of a thaw flow developed within the Chapman Lake terminal moraine complex on the Blackstone Plateau (Ogilvie Mountains, central Yukon Territory), which is contemporaneous to the Reid glaciation. Based on visible cryostructures in the 4-m-high headwall, two units were identified: massive ground ice, overlain sharply by 2 m of icy diamicton.

Denis Lacelle; Bernard Lauriol; Ian D. Clark; Raphaelle Cardyn; Christian Zdanowicz

2007-01-01

13

Nature and origin of a Pleistocene-age massive ground-ice body exposed in the Chapman Lake moraine complex, central Yukon Territory, Canada  

NASA Astrophysics Data System (ADS)

A massive ground-ice body was found exposed in the headwall of a thaw flow developed within the Chapman Lake terminal moraine complex on the Blackstone Plateau (Ogilvie Mountains, central Yukon Territory), which is contemporaneous to the Reid glaciation. Based on visible cryostructures in the 4-m-high headwall, two units were identified: massive ground ice, overlain sharply by 2 m of icy diamicton. The nature and origin of the Chapman Lake massive ground ice was determined using cryostratigraphy, petrography, stable O-H isotopes and the molar concentration of occluded gases (CO 2, O 2, N 2 and Ar) entrapped in the ice, a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non-glacial intrasedimental ice. Collectively, the results indicate that the Chapman Lake massive ground ice formed by firn densification with limited melting-refreezing and underwent deformation near its margin. Given that the massive ground-ice body consists of relict glacier ice, it suggests that permafrost persisted, at least locally, on plateau areas in the central Yukon Territory since the middle Pleistocene. In addition, the d value of Chapman Lake relict glacier ice suggests that the ice covering the area during the Reid glaciation originated from a local alpine glaciation in the Ogilvie Mountains.

Lacelle, Denis; Lauriol, Bernard; Clark, Ian D.; Cardyn, Raphaelle; Zdanowicz, Christian

2007-09-01

14

Different rates of reworking of Little Ice Age lateral moraines in the Kaunertal valley, Austrian Alps: A morphometric and morphodynamic case study using multi-epoch LiDAR surveys  

NASA Astrophysics Data System (ADS)

Little Ice Age (LIA) moraines in the proglacial areas of the Gepatsch and Weißsee glaciers in the Kaunertal valley, Austria reveal different degrees of reworking by gully incision and debris flows. The state and intensity of reworking appears to depend not only on the time since deglaciation, but also on morphometric properties of the respective locations, such as slope gradient and slope length. Moreover, moraine locations with a high morphodynamic intensity are directly connected to the fluvial system. In these areas, where slope processes and fluvial processes overlap, the accumulation zones of the slope processes are prone to fluvial erosion. This leads to a regular disturbance of the slope gradient at the foot of the slopes. A series of aerial photos, dating back to 1953, was used as a basis for a geomorphological map, where coupling states of the investigated moraine locations are evident from the digitized process areas. Spatial changes of single gullies and headward migration of the upper moraine ridges were also monitored on base of the series of aerial photos. In order to estimate the time since deglaciation for different locations, spatial extents of the glaciers, dating back to 1850 were used to interpolate an age surface grid. Airborne LiDAR data were acquired and a digital elevation model was derived from the LiDAR point clouds in order to quantify minimum erosion volumes. These LiDAR data are also suitable for analysis of morphometric properties as well as morphodynamic intensities on the moraine locations. The study presented here is part of the multidisciplinary joint research project PROSA (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) which deals with the quantification of the sediment budget of the upper Kaunertal valley, with a focus on the proglacial area.

Neugirg, Fabian; Haas, Florian; Heckmann, Tobias; Hilger, Ludwig; Dusik, Jana-Marie; Becht, Michael

2014-05-01

15

Using blue-ice moraines to constrain elevation changes of the West Antarctic Ice Sheet in the southern Ellsworth Mountains  

NASA Astrophysics Data System (ADS)

Observations in the Weddell Sea sector of the Antarctic Ice Sheet have not yet allowed the dating of elevated glacier trimlines and associated deposits in the Ellsworth Mountains. This uncertainty limits the value of models of changing ice-sheet configuration, volume and, by extension, sea level during glacial cycles and earlier. Here we present the emerging results of a study into the origin and evolution of blue-ice moraines in the Heritage Range, southern Ellsworth Mountains, and begin to unravel the long record of ice-sheet history they hold. Our findings so far are: (a) Ground Penetrating Radar shows that the blue-ice moraines are equilibrium forms bringing basal debris to the ice surface; the compressive ice flow is caused by enhanced ablation at the mountain foot. (b) Moraines are concentrated in embayments that focus katabatic winds and their location is largely controlled by topography. (c) The elevated blue-ice moraines in the southern Ellsworth Mountains hold a continuous record of West Antarctic Ice Sheet history going back 600,000 years; so far we have not found evidence of de-glacial intervals. (d) Thinning since the LGM (~40 ka?) is < 450 m and agrees with views of modest changes in the Weddell Sea sector during glacial cycles; most thinning occurred in the Holocene (6-3 ka). (e) Downslope flow of debris-covered ice in embayments follows ice surface lowering; it transports old clasts downslope and exposes fresh clasts, thus complicating the interpretation of exposure ages. We hope that a second field season in 2014 to re-measure 90 stakes for horizontal movement and ablation will help quantify the rate of blue-ice moraine formation.

Sugden, David; Woodward, John; Dunning, Stuart; Hein, Andy; Marrero, Shasta; Le-Brocq, Anne

2014-05-01

16

A record of late-Holocene fluctuations of Quelccaya Ice Cap, Peru, based on glacial moraines and lake sediments  

NASA Astrophysics Data System (ADS)

The mechanisms which influenced climate variability during the late Holocene, including the Little Ice Age (LIA; ~AD 1300-1850), are still not well understood. The geographic distribution and timing of the climate variability may provide important information about possible mechanisms. Here we present a record of late Holocene climate in the southern tropics. This record is based on past extents of Quelccaya Ice Cap located in southeastern Peru (~14°S, 70°W) defined by surface exposure (10Be) dating of moraines, radiocarbon dating of organic material in stratigraphic sections and sediment cores from a glacially fed lake. These archives complement the existing high-resolution ice core records from Quelccaya Ice Cap, which register climate conditions during the past ~1500 yrs (Thompson et al., 1985, 2006). Our combined moraine and lake sediment records document two significant advances of Quelccaya Ice Cap during late Holocene time. A prominent set of moraines (the Huancane I moraines), located ~1 km from the modern ice margin, marks the most extensive ice advance during the Holocene. We dated the outermost and innermost moraines at 480±60 and 340±10 yr BP, respectively, using both 10Be and radiocarbon dating. These moraines ages indicate that QIC advanced during the LIA. 10Be ages of moraines outboard of the Huancane I moraines are all >11 ka. Based on radiocarbon dating of organic material in stratigraphic sections, another advance of QIC occurred at ~3000 yr BP, but was less extensive than the LIA ice cap extent. The ages of the Huancane I moraines are similar in timing to LIA advances of glaciers in Europe, Scandinavia and the Southern Alps of New Zealand, as well as to an advance in the nearby Cordillera Vilcabamba of Peru. The ages of the Huancane I moraines at QIC are contemporaneous within error with glacier advances in the Swiss Alps between ~570±50 and ~310±50 yr BP). The broad-scale similarity in the timing of the above mentioned glacial advances suggests a globally synchronous LIA.

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C.; Baranes, H. E.

2011-12-01

17

Evolution of a highly vulnerable ice-cored moraine: Col des Gentianes, Swiss Alps  

NASA Astrophysics Data System (ADS)

Rock mass movements are dominant in the morphodynamics of high mountain rock slopes and are at the origin of significant risks for people who attend these areas and for infrastructures that are built on (mountain huts, cable cars, etc.). These risks are becoming greater because of permafrost degradation and glacier retreat, two consequences of the global warming. These two commonly associated factors may affect slope stability by changing mechanical properties of the interstitial ice and modifying the mechanical constraints in these rock slopes. Between 1977 and 1979, significant works were carried out on the Little Ice Age moraine of the Tortin glacier at the Col des Gentianes (2894 m), in the Mont Fort area (Verbier, Switzerland), for the construction of a cable car station and a restaurant. Since the early 1980s, the glacier drastically retreated and the moraine became unstable: its inner slope has retreated for several meters. Various observations and geoelectric measurements indicate that significant volume of massive ice mass is still present within the moraine (ice-cored moraine). Its melting could therefore increase the instability of the moraine. Since 2007, the moraine is surveyed by terrestrial laser scanning (TLS) in order to characterize its evolution: 8 campaigns were conducted between July 2007 and October 2011. The comparison of the high resolution 3D models so obtained allowed the detection and quantification of mass movements that have affected the moraine over this period, essentially by calculating difference maps (shortest oblique distances between two models). Between July 2007 and October 2011, 7 landslides were measured, involving volumes between 87 and 1138 m3. The most important of these occurred during the summers 2009 and 2011. TLS data also allowed identifying: (i) two main areas affected by slower but sometimes substantial movements (displacements of blocks on more than 2 m during a summer period); (ii) significant deposits of anthropogenic materials and their mechanical readjustments; and (iii) a loss of thickness of the glacier approaching 10 m at the foot of the moraine. Except for the morphological changes related to the landscaping of ski-runs, mass movements identified by TLS since 2007 are mainly resulting from glacier retreat and, to a lesser extent, to permafrost creep and degradation.

Ravanel, L.; Lambiel, C.; Oppikofer, T.; Mazotti, B.; Jaboyedoff, M.

2012-04-01

18

Little Ice Age Fluctuations of Quelccaya Ice Cap, Peru  

NASA Astrophysics Data System (ADS)

A record of the past extents of Quelccaya Ice Cap (QIC) provides valuable information about tropical climate change from late glacial to recent time. Here, we examine the timing and regional significance of fluctuations of QIC during the Little Ice Age (LIA; ~1300-1850 AD). One prominent set of moraines, known as the Huancane I moraines, is located ~1 km from the present-day western ice cap margin and provides a near-continuous outline of the most recent advance of QIC. This moraine set was radiocarbon dated (~298 ± 134 and 831 ± 87 yr BP) by Mercer and Palacios (1977) and presented as some of the first evidence for cooling in the tropics during the Little Ice Age. Recent field investigations in the QIC region focused on refining the chronology of the Huancane I moraines. In 2008, new stratigraphic sections exposed by local lake-flooding events revealed multiple layers of peat within the Huancane I moraines. In both 2008 and 2009, samples were obtained for 10Be dating of boulders on Huancane I moraines. A combination of radiocarbon and 10Be ages indicate that the Huancane I moraines were deposited by ice cap expansion after ~3800 yr BP and likely by multiple advances at approximately 1000, 600, 400, and 200 yr BP. Radiocarbon and 10Be chronologies of the Huancane I moraines are compared with the Quelccaya ice core records (Thompson et al., 1985; 1986; 2006). Accumulation data from the ice core records are interpreted to indicate a significant wet period at ~1500-1700 AD followed by a significant drought at ~1720-1860 AD. We examine ice marginal fluctuations during these times to determine influence of such events on the ice cap extent.

Stroup, J. S.; Kelly, M. A.; Lowell, T.

2009-12-01

19

Surface Dating of Dynamic Landforms: Young Boulders on Aging Moraines  

Microsoft Academic Search

The dating of landforms is crucial to understanding the evolution, history, and stability of landscapes. Cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces. A pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data. Consideration of the dynamic nature

Bernard Hallet; Jaakko Putkonen

1994-01-01

20

Ice Ages  

NSDL National Science Digital Library

During most of the last one billion years the globe had no permanent ice. However, sometimes large areas of the globe were covered with vast ice sheets. Users can read and view pictures which help explain what ice ages are, when they occurred, and why they occur. This site, sponsored by the Illinois State Museum, has links to web pages on paleontology of the midwestern United States during the last ice age and to an animation showing the advance and retreat of the ice sheet in North America 20,000 years ago.

21

LITTLE ICE AGE HISTORY OF TZEETSAYTSUL GLACIER, TWEEDSMUIR PROVINCIAL PARK, BRITISH COLUMBIA  

Microsoft Academic Search

This paper describes licheno- metric and dendroglaciological investigations of Little Ice Age (LIA) deposits at Tzeetsaytsul Glacier, Tweedsmuir Provincial Park, British Columbia. The glacier originates from an ice- field on the northeast flank of Tzeetsaytsul Peak and terminates in a moraine-dammed lake. A stream draining the lake has incised the moraine dam and flows through nested moraines into a second

J. SMITH; Joseph R. DESLOGES; D. J. SMITH

22

Cosmogenic 10Be Exposure Age for the Cut Bank Creek terminal moraine, Glacier National Park, MT  

NASA Astrophysics Data System (ADS)

Mountain glaciers are highly sensitive to temperature and precipitation with geologic records that are superb proxies of climate change. In the Rocky Mountains of the western United States, abundant records of Late Pleistocene glaciation provide an opportunity for understanding paleoclimate throughout this region, especially in places where the chronology of glaciation is precisely known. Cosmogenic 10Be exposure dating has been widely applied to glacial deposits in the Rocky Mountains, providing precise numerical ages and improving the understanding of glacial chronologies in this region. Despite these improvements, the chronology of the last Pleistocene glaciation of the northernmost Rocky Mountains is not completely understood. Cosmogenic 10Be exposure dating was applied to the Cut Bank Creek valley in the Lewis Range of the Northern Rocky Mountains, where a discrete mountain glacier deposited a broad terminal moraine during the last Pleistocene glaciation. Exposure ages of eight quartzite and sandstone boulders at the crest of the ice-distal sector of the terminal moraine indicate that abandonment occurred at 15.6 ± 0.8 ka. This age is consistent with age limits of several terminal moraines elsewhere in the Northern Rocky Mountains, suggesting that the last Pleistocene glaciation culminated in this region after the global Last Glacial Maximum.

Quirk, B.; Laabs, B. J.; Leonard, E. M.; Caffee, M. W.

2012-12-01

23

Lateral moraine age in Park Valley, Tararua Range, New Zealand  

Microsoft Academic Search

Recent geomorphologie and sedimentologic investigations in Park Valley, in the central Tararua Range, have identified several landforms of glacial erosion and deposition, including cirque basins, a U?shaped glacial valley, and a lateral moraine ridge. The presence of Kawakawa tephra (Aokautere Ash) within loess c. 50 cm beneath the surface of the moraine has indicated that the moraine was formed prior

Martin S. Brook

2009-01-01

24

Relative dating of Quaternary moraines, Rongbuk valley, Mount Everest, Tibet: Implications for an ice sheet on the Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Relative-dating studies applied to high-altitude moraines (5000-5500 m) in the Rongbuk valley on the northern flank of Mt. Everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests. These differences serve to define three intervals of major Pleistocene glaciation that, on the basis of the degree of weathering, are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation. Either interpretation indicates that some of these moraines are considerably older than their previously assigned ages. The magnitude of equilibrium-line lowering during Neoglacial and late Pleistocene times is calculated to be ca. 50-100 and 350-450 m, respectively. The data described here are incompatible with the recently proposed model ( Kuhle, 1987) for large-scale ice-sheet development on the Tibetan Plateau. The reconstructed equilibrium-line lowering in the Everest region is only 30% of that cited in the ice-sheet model. Moreover, the flow patterns and geometry of the former Rongbuk glaciers are in opposition to those proposed by the model. Based on the data from the Everest region, it appears that valley glaciation, rather than ice-sheet growth, characterized the southern margin of the Tibetan Plateau during the middle and late Pleistocene glaciations.

Burbank, Douglas W.; Cheng, Kang Jian

1991-07-01

25

Surface Exposure Dating of the Huancané III Moraines in Peru: A Record of Quelccaya Ice Cap's Maximum Extent during the Last Glacial Period  

NASA Astrophysics Data System (ADS)

The climatic conditions that influenced the tropics during the height of the last glacial period are not well defined and controversial. There are disparities in estimates of temperature anomalies (e.g., MARGO, 2009; Rind and Peteet, 1985; CLIMAP, 1976), and critical terrestrial paleotemperature proxy records in tropical regions are poorly dated (e.g., Porter, 2001). Defining these conditions is important for understanding the mechanisms that cause major shifts in climate, as the tropics are a primary driver of atmospheric and oceanic circulation. This study aims to constrain the timing of maximum glacier extents in the Cordillera Oriental in southern Peru during the last glacial period by applying surface exposure (beryllium-10) dating to the Huancané III (Hu-III) moraines. The Hu-III moraines mark the maximum extent of Quelccaya Ice Cap (QIC) (13.93°S, 70.83°W), the largest tropical ice cap, during the last ice age. The eight beryllium-10 ages presented here yield 17,056 ± 520 yrs ago as a minimum age for the onset of recession from the ice cap advance marked by the Hu-III moraines. Comparing this age to other paleoclimate records indicates that the ice cap advance marked by the Hu-III moraines is more likely associated with a North Atlantic climate event known as Heinrich I (H1; 16,800 yrs ago, Bond et al., 1992, 1993) than with global cooling at the Last Glacial Maximum (LGM; ~21,000 yrs ago, Denton and Hughes, 1981). This result suggests that climate processes in the North Atlantic region are linked to climatic conditions in the tropical Andes. A mesoscale climate model and an ice-flow model are currently being developed for QIC. The moraine data presented in this study will be used with these two models to test response of QIC to North Atlantic and global climate events.

Baranes, H. E.; Kelly, M. A.; Stroup, J. S.; Howley, J. A.; Lowell, T. V.

2012-12-01

26

High resolution record of paleoclimate since the Little Ice Age from the Tibetan ice cores  

Microsoft Academic Search

Climate changes during the Little Ice Age were studied based on oxygen isotope values (?18O) measured from ice cores recovered on, and nearby, the Qinghai-Tibetan Plateau. Three cold periods have been identified and are supported by three widely existing moraine ridges formed during the Little Ice Age. Importantly, the amplitude of the three cold periods differ in the cores studied.

Tandong Yao; Yafeng Shi; L. G. Thompson

1997-01-01

27

Hydrogeophysical characterisation of ice-marginal moraines, with reference to moraine dam stability, Miage Glacial Lake, Italy  

NASA Astrophysics Data System (ADS)

In mountain regions, potentially hazardous glacial lakes are becoming increasingly common as a consequence of climatically driven glacier recession. Lakes can expand rapidly in the space between downwasting or receding glacier fronts and terminal or lateral moraines, and are prone to catastrophic drainage if the moraine dam is breached. Lake drainage can have severe impacts on both fragile mountain ecosystems and local economies. In addition to the moraine-dammed lakes currently in existence, it is likely that many more will form in the coming decades as more glaciers cross the threshold required for rapid lake expansion. A key factor in assessing the stability and future evolution of such systems is a better understanding of the subsurface structure and hydrology of the moraine dams. Here results are presented from electrical geophysical work carried out across the breach moraine complex at the Miage Glacial Lake, Italy. A combination of induced polarisation, normalised induced polarisation and self potentials have been used to characterise the local water table and to identify the subsurface connections between two moraines dammed glacial lakes. The results not only show the depth and distribution of subsurface flow but also the preferential flow pathways, indicating areas of maximum discharge. The results highlight the areas of the moraines where hydrological processes are causing internal degradation and impacting upon the longer term stability of the system. This model therefore, can be employed on much larger systems where the risk of outburst has far greater consequences.

Thompson, S. S.; Kulessa, B.

2010-12-01

28

Submerged Tioga and Tahoe age Moraines at Meeks Bay, Lake Tahoe, Calif. Implications to Late Pleistocene Lake Levels  

NASA Astrophysics Data System (ADS)

At Meeks Bay, a well-preserved right-lateral morainal complex is constructed of till from the Tioga (>20.4 +/- 0.7 ka B.P.) and Tahoe (>62.0 +/- 1.3 ka B.P.; Howle et al., 2005) glacial advances. High-resolution digital bathymetry merged with the terrestrial DEM reveals that the onshore Tioga and Tahoe moraines extend offshore below the modern lake level of 1,899m. Longitudinal profiles show that the sub-aerial moraine crests grade evenly with the submerged crests and that the slopes of the sub-aqueous crests match the profile of the adjacent submarine canyon. In the digital bathymetry, the Tioga and Tahoe moraines are recognizable to 1,844 and 1,768m respectively. In May of 2004 and 2005 the moraines were imaged with the remotely operated submersible Triton deployed from the UC Davis research vessel, John LeConte. The Tioga moraine goes down to 1,817m, and rests upon Pliocene (?) lacustrine sediments. Above 1,817m the moraine is comprised of unsorted gravel, cobbles, and angular granitic boulders up to 3m across, typical of the Tioga age till on land. The moraine crest is continuous from 1,817m up to the shoreline promontory where the Tioga till on land enters the lake. Between 1,868m and 1,838m, the submerged Tahoe moraine contains well-rounded granitic boulders up to 2m across. The degree of rounding is consistent with the Tahoe boulders on land. The lowest occurrence of the Tahoe moraine was not imaged, but the glacial origin of the crest was confirmed. The submerged Tioga and Tahoe lateral moraines place upper limiting constraints on lake elevation, because lateral moraines do not form in water deeper than the ice thickness. Instead, when the relatively thin terminal ice cliff of an ablating alpine glacier interacts with water the glacier either melts, disintegrates by calving, or detaches along crevasses and floats when submerged to about 0.9 of the ice thickness. Reconstructions of ice thickness at the lower limits of the Tioga and Tahoe moraines here yield estimates of the maximum lake elevations at the glacial maxima. During the Tioga and Tahoe glacial maxima (>20 and >62 ka B.P., respectively) the lake elevation was <1,810m and <1,765m. These data indicate that in the Tahoe basin, late Pleistocene lake low-stands occurred during the glacial maxima. Asynchrony between glacial and lacustrine maxima has also been documented at Pleistocene lakes Russell and Lahonton (Lajoie and Robinson, 1982). Evidence at Meeks Bay for a post-Tahoe and pre-Tioga high-stand between 1,914 and 1,920m is provided by a gently sloping bench cut into the Tahoe moraine. This correlates well with reports of a Tahoe age high-stand at 1,926m. Birkeland (1963) proposed a Tahoe age ice dam at that may have raised lake levels to about 1950m. However, there is no evidence of this at 1950m in the Tahoe moraine at Meeks Bay, and therefore any such high-stand must have predated the Tahoe maximum. Available data suggests that large fluctuations in lake elevation have occurred from a mid Pleistocene (?) high-stand of about 2073m (Birkeland, 1963) to <1,765m at the Tahoe glacial maximum, up to about 1,920m after the Tahoe advance, down to <1,810m at the Tioga glacial maximum, and finally up to elevations between 1876 and 1899m during the Holocene (Schweickert et al., 2000). We thank the IEEE Oceanic Engineering Society for partial funding and commend the engineering students of Santa Clara University for designing, building, and deploying the Triton. Special thanks to Bob Richards and Brant Allen, captains of the LeConte.

Howle, J. F.; Schweickert, R. A.; Finkel, R. C.; Kitts, C. A.; Ota, J.

2005-12-01

29

Blue-ice moraines in Antarctica: long-term formation and short-term change  

NASA Astrophysics Data System (ADS)

The Heritage Range at the southern end of the Ellsworth Mountains lies across the main flow of the West Antarctic Ice Sheet (WAIS) just 50 km from the grounding line of the Filchner-Ronne Ice Shelf. If the long-term record of ice sheet change can be understood from the Blue Ice Moraines (BIM) found along the hills it becomes a critical location to understand the past behaviour of the ice sheet, and therefore, to better understand the future behaviour of WAIS in a warming climate. We present integrated geophysical data from Unmanned Aerial Vehicles (UAV), Terrestrial Laser Scanning (TLS) and ground penetrating radar (GPR) that helps us understand the long-term formation, and short-term mophological changes of BIMs. BIMs along the front of Patriot Hills (part of the Heritage Range) are associated with katabatic winds enhancing ablation and sublimation to create depressions that are then compensated for by ice-flow from the main trunk glacier at right angles to the main flow direction. This ice flow brings basal debris from the trunk glacier that can reside for long-periods of time rather than being removed by the dominant mountain parallel ice-flow. Using GPR we have imaged debris bands from the trunk glacier arriving directly into the lowest BIMs, and also emerging at the ice surface as folded debris bands in the moraine-marginal depressions that do not have a dense enough debris cover to prevent ablation. High resolution elevation models derived from TLS, and a UAV quantify the changing topography associated with this debris arriving into the BIM, and the surface change over a summer melt season. This work was funded by NERC Standard Grant NE/I025840/1

Woodward, J.; Dunning, S.; Sugden, D.; Hein, A.; Marrero, S.

2013-12-01

30

Airborne SAR determination of relative ages of Walker Valley moraines, eastern Sierra Nevada  

NASA Technical Reports Server (NTRS)

A regional study of the distribution and elevations of Pleistocene moraines in the Andes requires a method of determining relative age from space. One of our primary objectives is to establish the relative chronology of major climatic events responsible for glaciation in the Andes and other regions that are difficult to access on the ground and where suitable material for absolute age determination is lacking. The sensitivity of radar to surface roughness makes it possible to develop a remotely-based relative dating technique for landforms for which surface age and roughness can be correlated. We are developing such a technique with Airborne Synthetic Aperture Radar (AIRSAR) imagery of the eastern Sierra Nevada where independent evidence is available for the ages and physical characteristics of moraines. The Sierra Nevada moraines are similar in form and environmental setting to Andean moraines that we have targeted for study during the pending Shuttle Imaging Radar-C (SIR-C) mission. SAR imagery is used to differentiate the ages of five moraine sequences of Walker Valley in the eastern Sierra Nevada. Other aspects of this investigation are briefly discussed.

Fox, A.; Isacks, B.; Bloom, A.; Fielding, E.; Mcmurry, D.

1991-01-01

31

Geology Fieldnotes: Ice Age National Scientific Preserve  

NSDL National Science Digital Library

This National Park Service (NPS) site gives information on the Ice Age National Scientific Preserve in Wisconsin, including geology, park maps, a photo album, and other media (books, videos, CDs). There is also a selection of links to other geologic and conservation organizations, and to information for visitors. This preserve contains a wealth of glacial features associated with the most recent Pleistocene continental glaciation including drumlins, kames, kettles, moraines, erratics, and eskers. It also contains a segment of the Ice Age National Scenic Trail, a 1000-plus mile hiking and backpacking trail that passes through this unique glacial landscape.

32

Dating of Little Ice Age glacier fluctuations in the tropical Andes: Charquini glaciers, Bolivia, 16°S  

Microsoft Academic Search

Fluctuations of the Charquini glaciers (Cordillera Real, Bolivia) have been reconstructed for the Little Ice Age (LIA) from a set of 10 moraines extending below the present glacier termini. A lichenometric method using the Rhizocarpon geographicum was used to date the moraines and reconstruct the main glacier fluctuations over the period. The maximum glacier extent occurred in the second half

Antoine Rabatel; Vincent Jomelli; Philippe Naveau; Bernard Francou; Delphine Grancher

2005-01-01

33

A chronology of the Little Ice Age in the tropical Andes of Bolivia (16°S) and its implications for climate reconstruction  

Microsoft Academic Search

Dating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries. Moraines were dated by performing statistical analysis of lichen measurements based on the extreme

Antoine Rabatel; Bernard Francou; Vincent Jomelli; Philippe Naveau; Delphine Grancher

2008-01-01

34

Paleo Slide Set: The Ice Ages  

NSDL National Science Digital Library

This slide show will aid in the quest to understand the cause of the Pleistocene ice ages, an example of how scientists have used different types of evidence to understand earth processes. It traces the history of investigation of the ice ages, from the discovery of glacial erratics and moraines in the 1800s, and the theories of orbital variations in solar radiation, to recent investigations of the glacial-interglacial cycles using evidence found in ice cores and deep sea sediments. This slide set emphasizes how different types of geologic evidence can be used to understand how earth climate has varied in the past. The set includes photos of evidence of glaciers, pictures and graphs from ice cores and marine sediment cores, and pictures illustrating changes in the earths orbit. Each is accompanied by a comprehensive narrative and can be enlarged for better viewing.

35

The Utility of Proximal-Accretion Stratigraphy in Lateral Moraines  

Microsoft Academic Search

Lateral-moraine stratigraphy is a valuable tool that can be used to constrain the timing and magnitude of alpine glacier fluctuations. Numerous lateral moraines, conventionally thought to have been constructed during the Little Ice Age (LIA), have been shown to be composite landforms that contain multiple till layers deposited by successively larger glacier advances. Organic matter and\\/or tephra sandwiched between the

M. A. Samolczyk; G. Osborn

2010-01-01

36

Ice-Cored Moraines and Ice Diapirs, Lake Miers, Victoria Land, Antarctica  

Microsoft Academic Search

Lake Miers is covered by a thick ice sheet which is domed over most of its area and thrust into sharp debris-covered ridges around its margin. Ridges result largely from compression generated in the ice raft by freeze and thaw. Apart from a narrow moat in summer the ice round the lake shore is frozen fast to the lake bed.

J. Bradley; D. F. Palmer

1967-01-01

37

Topographic control of equilibrium-line altitude depression on reconstructed 'Little Ice Age' glaciers, Grovabreen, western Norway  

Microsoft Academic Search

'Little Ice Age' marginal moraines in the Grovabreen area, inner Sunnfjord, are mapped and described. The modem and 'Little Ice Age' (mid-eighteenth century) equilibrium-line altitude (ELA) of the plateau glacier Grovabreen is calculated by the use of an accumulation-area ratio (AAR) of 0.6, giving a 'Little Ice Age' ELA depression of 125 m. AAR-ELA depression of the 'Little Ice Age'

Asbjørn Rune Aa

1996-01-01

38

Glaciotectonic deformation associated with the Orient Point-Fishers Island moraine, westernmost Block Island Sound: further evidence of readvance of the Laurentide ice sheet  

USGS Publications Warehouse

High-resolution seismic-reflection profiles collected across pro-glacial outwash deposits adjacent to the circa 18 ka b.p. Orient Point–Fishers Island end moraine segment in westernmost Block Island Sound reveal extensive deformation. A rhythmic seismic facies indicates the host outwash deposits are composed of fine-grained glaciolacustrine sediments. The deformation is variably brittle and ductile, but predominantly compressive in nature. Brittle deformation includes reverse faults and thrust faults that strike parallel to the moraine, and thrust sheets that extend from beneath the moraine. Ductile deformation includes folded sediments that overlie undisturbed deposits, showing that they are not drape features. Other seismic evidence for compression along the ice front consists of undisturbed glaciolacustrine strata that dip back toward and underneath the moraine, and angular unconformities on the sea floor where deformed sediments extend above the surrounding undisturbed correlative strata. Together, these ice-marginal glaciotectonic features indicate that the Orient Point–Fishers Island moraine marks a significant readvance of the Laurentide ice sheet, consistent with existing knowledge for neighboring coeval moraines, and not simply a stillstand as previously reported.

Poppe, Lawrence J.; Oldale, Robert N.; Foster, David S.; Smith, Shepard M.

2012-01-01

39

Ice Age Terminations  

NASA Astrophysics Data System (ADS)

230Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO2 and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO2 and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO2.

Cheng, Hai; Edwards, R. Lawrence; Broecker, Wallace S.; Denton, George H.; Kong, Xinggong; Wang, Yongjin; Zhang, Rong; Wang, Xianfeng

2009-10-01

40

The little ice age  

Microsoft Academic Search

The Little Ice Age, a period of glacier expansion in alpine regions that began sometime between the twelfth and sixteenth centuries and lasted until late in the nineteenth century, was recorded not only in glacial features dated by geologic techniques but also in historical documents such as field sketches, land values, and weather records, especially in the Alps. Indirect evidence

J. M. Grove

1988-01-01

41

The little ice age  

SciTech Connect

The Little Ice Age, a period of glacier expansion in alpine regions that began sometime between the twelfth and sixteenth centuries and lasted until late in the nineteenth century, was recorded not only in glacial features dated by geologic techniques but also in historical documents such as field sketches, land values, and weather records, especially in the Alps. Indirect evidence of its impact in other parts of the world includes the records of sea-ice extent near Iceland and Greenland, the fate of the Viking settlements in Greenland, and many other suggestions that the climate was colder in the recent past than it is today. Jean Grove's book is an authoritative, superbly documented, and excellently written summary of the abundant evidence of climatic change during the last few centuries in the context of broader climatic variations of the last 10,000 years. This summary provides a much-needed perspective for considering the magnitude and frequency of natural climatic variations in the past, given predictions for the future. In the final chapter, Grove notes that natural climatic variations, including another minor ice age, might be expected in the future but at the end of the Little Ice Age coincided with the increased burning of fossil fuels during the industralization of Europe and North America. This coincidence does indeed suggest that modern scientists already have had a significant impact on the global climate.

Grove, J.M.

1988-01-01

42

The Utility of Proximal-Accretion Stratigraphy in Lateral Moraines  

NASA Astrophysics Data System (ADS)

Lateral-moraine stratigraphy is a valuable tool that can be used to constrain the timing and magnitude of alpine glacier fluctuations. Numerous lateral moraines, conventionally thought to have been constructed during the Little Ice Age (LIA), have been shown to be composite landforms that contain multiple till layers deposited by successively larger glacier advances. Organic matter and/or tephra sandwiched between the till layers constrain times of advance and retreat; wood fragments within till may provide the age of the till. Observation of contemporary lateral moraines has lead to the recognition of two means of lateral moraine construction: (1) accretion of tills onto the distal flank of the pre-existing lateral moraine, and (2) accretion or plastering of tills onto the proximal flank of the pre-existing moraine. In composite lateral moraines, distal and proximal accretion result in paleosurfaces that trend parallel to the current distal and proximal slope, respectively. Published work using lateral-moraine stratigraphy, for example at Bugaboo and Stutfield glaciers in the Canadian Rockies, has used evidence only from distal-accretion moraines. However, proximal-accretion moraines that provide chronological information have been found at Nisqually Glacier on Mount Rainier in Washington State, USA, and Columbia Glacier, an outlet of the Columbia Icefield in the Canadian Rockies. A gully cut into the left-lateral moraine at Nisqually Glacier exposes a sandy seam, with associated wood fragments, that runs parallel to the proximal moraine flank for ~20 m. Wood collected from different elevations along the seam have radiocarbon ages of 1715±15, 1700±15, and 1670±50 14C yr BP, indicating that the seam is similar in age along its extent and likely marks a paleosurface separating older till below and till of the First Millennium advance above. At Columbia Glacier, some till exposures in the prominent right-lateral moraine show a fissility dipping variably 40 to 50° toward the valley axis; this orientation is semi-parallel to the proximal flank of the moraine, which however is steeper due to ongoing erosion. Five wood fragments encased in the till over a broad area of the flank, and exposed by gullying, have ages ranging from 1920±70 to 2340±70 14C yr BP. This suggests that (1) most of what appears to be a LIA moraine was deposited in earlier Neoglacial time, and (2) that the glacier was nearly as extensive ca. 2400-1900 ka as it was during the LIA.

Samolczyk, M. A.; Osborn, G.

2010-12-01

43

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines  

USGS Publications Warehouse

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

2007-01-01

44

Ice Age Floods Institute  

NSDL National Science Digital Library

Describes Ice Age glaciers and immense floods of glacial meltwater that swept across the Pacific Northwest (18,000-12,000 years ago and earlier), affecting the landscape from Montana to Washington and Oregon, sculpting the Columbia River Basin, and creating glacial lakes to rival the today's Great Lakes. This non-profit institute promotes scientific education about the floods, their causes and impacts. Proposes an interpretive geologic trail linking significant sites.

45

Upper Wisconsinan submarine end moraines off Cape Ann, Massachusetts  

NASA Astrophysics Data System (ADS)

Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England.

Oldale, R. N.

1985-09-01

46

Responses to climatic changes since the Little Ice Age on Maladeta Glacier (Central Pyrenees)  

Microsoft Academic Search

The evolution of Maladeta Glacier (Maladeta massif, central Spanish Pyrenees) since the Little Ice Age maximum is analyzed in this work. The extent of the glacier was mapped into 10 stages using morainic deposits and graphic documents. Climatic data (temperature and precipitation) were reconstructed by using dendroclimatic techniques complemented by recent instrumental records. The results thus obtained confirm the control

J. Chueca Cía; A. Julián Andrés; M. A. Saz Sánchez; J. Creus Novau

2005-01-01

47

A review of catastrophic drainage of moraine-dammed lakes in British Columbia  

Microsoft Academic Search

Moraine-dammed lakes are common in the high mountains of British Columbia. Most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the Little Ice Age. Many moraine dams in British Columbia are susceptible to failure because they are steep-sided, have relatively low width-to-height ratios, comprise loose, poorly sorted sediment, and may contain ice cores

John J. Clague; Stephen G. Evans

2000-01-01

48

Recent ice ages on Mars  

Microsoft Academic Search

A key pacemaker of ice ages on the Earth is climatic forcing due to variations in planetary orbital parameters. Recent Mars exploration has revealed dusty, water-ice-rich mantling deposits that are layered, metres thick and latitude dependent, occurring in both hemispheres from mid-latitudes to the poles. Here we show evidence that these deposits formed during a geologically recent ice age that

John F. Mustard; Mikhail A. Kreslavsky; Ralph E. Milliken; David R. Marchant; James W. Head

2003-01-01

49

Ice age paleotopography  

Microsoft Academic Search

A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred

W. R. Peltier

1994-01-01

50

A new moraine surface exposure chronology from the eastern Kunlun Shan (Lake Donggi Cona catchment, NE-Tibet): Early last glacial ice maxima and the 'missing' LGM  

NASA Astrophysics Data System (ADS)

Recent advances in obtaining reliable age control for late Pleistocene glaciations on the Tibetan Plateau and adjacent mountain areas have been critical for reconstructing past regional climate dynamics and long distance glacial correlations. In this debate, the analysis of mountain glacier records from the vast area of central and High Asia is particularly interesting as this region is influenced by several major atmospheric systems including the Siberian-Mongolian anticyclone, the mid-latitude Westerlies and the Asian Monsoon systems. During the late Quaternary, changes in the complex interplay between these systems caused substantial climatic variability, specifically in hydrological conditions, with major effects on the extent of regional glaciation. Pioneering studies from NE-Tibet (Anyemaqen Shan, Qilian Shan) have suggested significant late Pleistocene ice advances during MIS 3 and MIS 2 indicating that in some phases glacial mass balances responded strongly positive to increased monsoonal precipitation (during MIS 3) and at other times to insolation minima (during MIS 2). More recently, however, results from other areas of NE-Tibet (Bayan Shan) have shown that glaciation during MIS 2 was extremely limited or even missing, while the timing of the largest late Pleistocene glaciation remains unclear. To address this problem we collected a set of 23 rock samples from moraines in four glacial valleys of the eastern Kunlun Shan near Lake Donggi Cona on the northeastern Tibetan Plateau for in-situ 10Be exposure age dating. All samples were prepared and measured at the AMS laboratory of the Scottish Universities Environmental Research Centre (SUERC). Our results indicate that mountains in the northern part of the Donggi Cona catchment (up to 5000 m a.s.l.) experienced extensive glaciation between 100-90 ka (MIS 5) and between 60-50 ka (MIS 4) when valley glaciers advanced up to 20 km. By contrast, we find no evidence for any significant glaciation during MIS 2 or the LGM. In fact, results from a high resolution study conducted in one of the valleys where the entire up-valley directed moraine sequence was sampled, demonstrate that deglaciation had occurred by 40 ka and that the range remained essentially unglaciated since. We will present study details and discuss paleoclimatological implications.

Rother, Henrik; Lehmkuhl, Frank; Stauch, Georg; Freeman, Stewart; Davidson, Allan

2013-04-01

51

The morphology, structural evolution and significance of push moraines  

Microsoft Academic Search

Push moraines (glaciotectonic ice-marginal moraines) have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing Pleistocene ice sheets, providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland. To the wider earth science community, push moraines are of interest as analogues for thin-skin tectonics within orogenic belts. This paper reviews

Matthew R. Bennett

2001-01-01

52

Genesis of De Geer moraines in Finland  

NASA Astrophysics Data System (ADS)

The proposed model of the genesis of De Geer moraines in Finland is based mainly on the distribution of the moraine areas in relation to the palaeohydrological environment, and on the composition and two- and three-dimensional fabrics of the material. In order to shed some light on the geochronological problem involved, the distances between successive ridges in a number of De Geer moraine series are also compared with clay varve data on deglaciation rates in Finland. Granulometrically, petrographically and morphometrically, De Geer moraine till does not differ significantly from tills of surrounding areas. Two-dimensional fabrics stress orientations at right angles to the ridge crest, and three-dimensional analyses reveal the slope-conformable character of pebble inclinations. Generally, spacings of the De Geer moraine ridges do not confirm annual deglaciation rates as conveyed by clay varve data. It is suggested the moraines were formed in basal crevasses of the ice, following active flow phases of a local surging nature. During the quiescent phase of the surge cycle, the ice subsided into a water-soaked till mattress, filling up basal cavities from the proximal or the distal side. Finnish De Geer moraines are thus neither annual nor end moraines. They are subglacial bedforms with no geochronological meaning, except that they formed during one single surge cycle. As the marginal zone of the ice sheet calved and thinned, it was lifted by proglacial water and the whole group of moraines became free of ice almost simultaneously.

Zilliacus, Harry

1989-05-01

53

Staggering through the ice ages  

SciTech Connect

Because the steady orbital cycles of earth, thought to control the ice ages, cannot easily account for the evidence of repeated rapid climatic shifts during the last ice age. Without knowing what made the iceage climate so in temperate, scientists cannot tell whether today's interglacial period is immune to the sudden swings. Information about climate instability has emerged from two drilling projects in the middle of Greenland where crews bored through the 3-kilometer think glacial cap. This paper describes the discoveries and the evidence for rapid climatic shifts, including conflicting results from different sites. The concerns about global warming are making questions about these shifts of increased interest. The possibility exists that modern climate harbors an inherently unstable element that could trigger wild wings in response to the atmospheric buildup of greenhouse gases. On the other hand sudden climatic shifts might have been unique to the ice-age Earth.

Monastersky, R.

1994-07-30

54

Little Ice Age glacial activity in Peter Lougheed and Elk Lakes provincial parks, Canadian Rocky Mountains  

Microsoft Academic Search

Dendrochronological, lichenometric, and I4C studies at 14 glacier sites in Peter Lougheed and Elk Lakes provincial parks were used to develop a chronology of Little Ice Age glacial events. The earliest indications of glacial activity are represented by moraines deposited prior to the 16th century. A major glacial expansion in the 17th century is recorded at three sites, where I4C

Daniel J. Smith; Daniel P. Mccarthy; Margaret E. Colenutt

1995-01-01

55

Little Ice Age glaciers in Britain: Glacier–climate modelling in the Cairngorm Mountains  

SciTech Connect

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 boulder 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.

Stephan Harrison; Ann V. Rowan; Neil F. Glasser; Jasper Knight; Mitchell A. Plummer; Stephanie C. Mills

2014-02-01

56

Mass loss of the Greenland Ice Sheet since the Little Ice Age, implications on sea level  

NASA Astrophysics Data System (ADS)

The impact of mass loss from the Greenland Ice Sheet (GrIS) on 20th Century sea level rise (SLR) has long been subject to intense discussions. While globally distributed tide gauges suggest a global mean SLR of 15-20 cm, quantifying the separate components is of great concern - in particular for modeling sea level projections into the 21st Century. Estimates of the past GrIS contribution to SLR have been derived using a number of different approaches, e.g. surface mass balance (SMB) calculations combined with estimates of ice discharge found by in correlating SMB anomalies and calving rates. Here, we adopt a novel geometric approach to determine the post-Little Ice Age (LIA) mass loss of the GrIS. We use high quality aerial stereo photogrammetric imagery recorded between 1978 and 1987 to map morphological features such as trim lines (boundary between freshly eroded and non-eroded bedrock) and end moraines marking the ice extent of the LIA, which thereby enables us to obtain vertical point-based differences associated with changes in ice extent. These point measurements are combined with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2002-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, and NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, to estimate mass loss throughout the 20th and early 21st Century. We present mass balance estimates of the GrIS since retreat commence from the maximum extent of the LIA to 2010 derived for three intervals, LIAmax (1900) - 1978/87, 1978/87 - 2002, and 2002 - 2010. Results suggest that despite highly spatially- and temporally variable post-LIA mass loss, the total mass loss and thus the contribution from the GrIS to global SLR has accelerated significantly during the 20th Century.

Kjeldsen, K. K.; Kjaer, K.; Bjork, A. A.; Khan, S. A.; Korsgaard, N. J.; Larsen, N. K.; Long, A. J.; Woodroffe, S.; Milne, G. A.; Wahr, J. M.; Geruo, A.; Bamber, J. L.; van den Broeke, M. R.

2013-12-01

57

Dating of Holocene lateral moraines in the western Southern Alps, New Zealand, applying Schmidt-hammer exposure-age dating (SHD)  

NASA Astrophysics Data System (ADS)

Research on Holocene mountain glacier chronologies has recently intensified due to the importance of mountain glaciers as key indicators for past and present climate change. This progress is closely connected with major improvements in modern dating techniques and the application of multi-proxy approaches adapted to specific local/regional conditions. Despite recent progress there is, however, still a need for better spatial differentiation and a lack of generally accepted concepts for global and inter-hemispheric correlation of Holocene glacier chronologies. Furthermore, the "geomorphological uncertainty" inevitably connected with numerical dating of moraines in neotectonic active mountain ranges characterised by highly dynamic geomorphological process systems requires careful consideration of any subsequent palaeoclimatic interpretation. During the past few years Schmidt-hammer exposure-age dating (SHD) has revealed its potential to successfully challenge those specific circumstances. The Southern Alps of New Zealand have provided one of only a few suitable study sites for investigating Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere. Recent years have seen a significant increase in terrestrial cosmogenic nuclide dating (TCND)-ages published for the Southern Alps, mainly for the last Glaciation, but also for the Holocene. The availability of a regional 10Be-production curve has improved the calibration of TCND-ages. These studies applying TCND alongside previous chronological studies using a variety of different dating techniques focus, however, primarily on a few selected glacier forelands east of the Main Divide in Aoraki/Mt Cook National Park. Bad accessibility and methodological problems account for comparatively few investigations on glacier forelands west of the Main Divide. Chronological studies applying Schmidt-hammer exposure-age dating (SHD) were performed on six glacier forelands in the western part of the Southern Alps/New Zealand. Although lithological heterogeneity prevented a regional age-calibration curve to be established, local age-calibration curves for La Perouse and Strauchon Glaciers could be derived. They show similar linear equations and trends/slopes, and enabled a preliminary assessment of the representativeness of individual 10Be TCND-ages obtained from the other forelands. No mid- and early-Holocene advance periods were detected. Clusters of moraine ages date around 2800, 1850 - 1450, and 1100 - 900 years ago, followed by the Little Ice Age (LIA) commencing c. 500 years ago. There is no good agreement with earlier radiocarbon-based studies in the western part of the Southern Alps, as well as with recently published TCND-chronologies from glacier forelands east of The Main Divide. This at least partly could be the result of different approaches to the palaeoclimatic interpretation of the dated samples rather than of spatial differentiation. The results obtained from this recent study do not support an elsewhere proposed general asynchronous glacier behaviour between the mid-latitudinal northern and southern hemispheres. They also show that due to the specific environmental conditions in the Southern Alps, more investigations are needed before a "regional" Holocene glacier chronology robust enough to allow reliable intra-hemispheric and global correlations can be undertaken.

Winkler, Stefan

2014-05-01

58

Submerged Tioga and Tahoe age Moraines at Meeks Bay, Lake Tahoe, Calif. Implications to Late Pleistocene Lake Levels  

Microsoft Academic Search

At Meeks Bay, a well-preserved right-lateral morainal complex is constructed of till from the Tioga (>20.4 +\\/- 0.7 ka B.P.) and Tahoe (>62.0 +\\/- 1.3 ka B.P.; Howle et al., 2005) glacial advances. High-resolution digital bathymetry merged with the terrestrial DEM reveals that the onshore Tioga and Tahoe moraines extend offshore below the modern lake level of 1,899m. Longitudinal profiles

J. F. Howle; R. A. Schweickert; R. C. Finkel; C. A. Kitts; J. Ota

2005-01-01

59

The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, MacAlpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data New Data for the Elephant Moraine, Ice Fields  

NASA Technical Reports Server (NTRS)

The natural TL survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to (1) identifying pairing, (2) providing an estimate of terrestrial age and residence time on the ice surface, (3) looking for differences in natural TL between ice fields, (4) looking for variations in natural TL level with location on the ice, (5) looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the @ost productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to (5) look for evidence for secular variation in the nature of the flux of meteorites to Earth, and (6) look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized in Table 1. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

Benoit, Paul H.; Sears, Derek W. G.

2000-01-01

60

The Natural Thermoluminescence Survey of Antarctic Meteorites: Ordinary Chondrites at the Grosvenor Mountains, Macalpine Hills, Pecora Escarpment and Queen Alexandra Range, and New Data for the Elephant Moraine, Ice Fields  

NASA Technical Reports Server (NTRS)

The natural TL (Thermoluminescence) survey of Antarctic meteorites was started in 1987 at the request of the Antarctic Meteorite Working Group in order to provide an initial description of radiation and thermal histories. It was intended to be a complement to the mineralogical and petrographic surveys performed at the Johnson Space Center and the Smithsonian Institution. All ANSMET (Antarctic Search for Meteorites) samples recovered since then, besides those that were heated throughout by atmospheric passage, have been measured. To date this amounts to about 1200 samples. As the data for each ice field reaches a significant level, we have been conducting a thorough examination of the data for that field with a view to identifying pairing, providing an estimate of terrestrial age and residence time on the ice surface, looking for differences in natural TL between ice fields, looking for variations in natural TL level with location on the ice, looking for meteorites with natural TL levels outside the normal range. Pairing is a necessary first step in ensuring the most productive use of the collection, while geographical variations could perhaps provide clues to concentration mechanisms. Samples with natural TL values outside the normal range are usually inferred to have had either small perihelia or recent changes in orbital elements. In addition, induced TL data have enabled us to look for evidence for secular variation in the nature of the flux of meteorites to Earth, and look for petrologically unusual meteorites, such as particularly primitive ordinary chondrites, heavily shocked meteorites, or otherwise anomalous meteorites. To date we have published studies of the TL properties of 167 ordinary chondrites from Allan Hills, 107 from Elephant Moraine and 302 from Lewis Cliff and we have discussed the TL properties of fifteen H chondrites collected at the Allan Hills by Euromet after a storm during the 1988 season. We now have additional databases for a reasonable number of ordinary chondrites from Grosvenor Mountains (39 meteorites), MacAlpine Hills (70 meteorites), Pecora Escarpment (60 meteorites), and Queen Alexandra Range (173 meteorites) and we have data for a further 101 samples from Elephant Moraine. The results are summarized. We also have fairly minimal databases (10-15 meteorites) for Dominion Range, Graves Nunataks, Reckling Peak and Wisconsin Range that will not be discussed here.

Benoit, Paul H.; Sears, Derek W. G.

1999-01-01

61

Mantle viscosity and ice-age ice sheet topography  

Microsoft Academic Search

Ice-age paleotopography and mantle viscosity can both be inferred from observations of Earth`s response to the most recent deglaciation event of the current ice age. This procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment. Results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from

W. R. Peltier

1996-01-01

62

A possible coseismic landslide origin of late Holocene moraines of the Southern Alps, New Zealand  

Microsoft Academic Search

Moraine deposits of the Southern Alps, New Zealand, have been used to infer past climatic regimes, such as the “Little Ice Age”. Recent work has identified four major movements of the Alpine Fault since AD 1200. These earthquakes are inferred to have produced numerous large rock avalanches, some of which must have fallen onto the valley glaciers, with this debris

S. H. Larsen; T. R. H. Davies; M. J. McSaveney

2005-01-01

63

Components of the ice age circulation  

NASA Technical Reports Server (NTRS)

The effects of ice age boundary conditions on atmospheric dynamics and regional climate patterns are investigated using four GCM simulations. Particular consideration is given to sea surface temperature-sea ice distribution, the appearance of land ice, and the increased elevation of land ice. It is observed that the ice-age sea surface temperature stabilizes the atmosphere over the oceans, increases the frequency of storm tracking through central North America, and amplifies transient eddy energy without increasing baroclinic generation. It is detected that low-elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases the transient and stationary eddy energy through increased baroclinicity.

Rind, D.

1987-01-01

64

Tree-Ring Dates for the Maximum Little Ice Age Advance of Kaskawulsh Glacier, St. Elias Mountains, Canada  

Microsoft Academic Search

A dendroglaciological study at Kaskawulsh Glacier provides the first calendar dating of a Little Ice Age glacier advance in the northeast St. Elias Mountains of Yukon Territory. Ring series from white spruce trees, Picea glauca (Moench) Voss, that had been sheared, tilted, and killed by deposition of till at the glacier's terminal moraine were cross-dated with a millennium-length ring-width chronology

ALBERTO V. REYES; BRIAN H. LUCKMAN; DAN J. SMITH; JOHN J. CLAGUE; RICHARD D. VAN DORP

65

Dynamics of ice ages on Mars.  

PubMed

Unlike Earth, where astronomical climate forcing is comparatively small, Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale. The geographic extent of the subsurface ice found poleward of approximately +/-60 degrees latitude on both hemispheres of Mars coincides with the areas where ice is stable. However, the tilt of Mars' rotation axis (obliquity) changed considerably in the past several million years. Earlier work has shown that regions of ice stability, which are defined by temperature and atmospheric humidity, differed in the recent past from today's, and subsurface ice is expected to retreat quickly when unstable. Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today. Simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of, from top to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements. PMID:17851518

Schorghofer, Norbert

2007-09-13

66

Debris flows from failures Neoglacial-age moraine dams in the Three Sisters and Mount Jefferson wilderness areas, Oregon  

USGS Publications Warehouse

The highest concentration of lakes dammed by Neoglacial moraines in the conterminous United States is in the Mount Jefferson and Three Sisters Wilderness Areas in central Oregon. Between 1930 and 1980, breakouts of these lakes have resulted in 11 debris flows. The settings and sequences of events leading to breaching and the downstream flow behavior of the resulting debris flows provide guidance on the likelihood and magnitude of future lake breakouts and debris flows.

O'Connor, J. E.; Hardison, J.H.; Costa, J.E.

2001-01-01

67

Geomorphology and the Little Ice Age extent of the Drangajökull ice cap, NW Iceland, with focus on its three surge-type outlets  

NASA Astrophysics Data System (ADS)

Detailed geomorphological maps from the forefields of three surging outlets of the Drangajökull ice cap, northwest Iceland, are presented. The maps are based on field studies in 2011-2013, high resolution orthorectified aerial photographs recorded in 2005-2006, and airborne LiDAR data from 2011. The maps cover an area of about 40-60 km2 each. Furthermore, we present an overview map that covers the area surrounding the Drangajökull ice cap. Landforms and sediments were manually registered in a geographic information system (ESRI ArcGIS 10). We mapped glacial landforms such as flutes, ice-sculpted bedrock, hummocky moraine, kame terraces, and moraines. Fluvial landforms include outwash plains/sandur, pitted sandur, and eskers. In addition raised beaches were mapped. The Little Ice Age (LIA) maximum extent of Drangajökull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock. Sediments distal to the LIA deposits were recorded and consist mainly of late Weichselian and early Holocene sediments and locally weathered bedrock. Periglacial activity is demonstrated by patterned ground, mainly occurring on the 500-700 m high plateaux, and three rock glaciers. At least 3-4 surge events are described from each of the outlet glaciers, occurring over the last three centuries. In contrast to most other surge-type outlets from Icelandic ice caps, the Drangajökull outlets are confined within valleys, which affect the forefield geomorphology. Glaciofluvial landforms, moraines, and a thin sheet of till with numerous boulders are characteristic for the forefields of the Drangajökull outlets.

Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur

2014-05-01

68

The natural thermoluminescence of meteorites. 7: Ordinary chondrites from the Elephant Moraine region, Antarctica  

NASA Technical Reports Server (NTRS)

We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76 deg 17 min S, 157 deg 20 min E) of Antarctica. We use our data to identify fragmented meteorites (i.e., 'pairings'); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (less than 12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H-chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.

Benoit, P. H.; Roth, J.; Sears, H.; Sears, D. W. G.

1994-01-01

69

Hummocky moraines of piedmont glaciers from Geyikda?, Central Tauride Mountains, Turkey; insights from cosmogenic 36Cl dating  

NASA Astrophysics Data System (ADS)

For the first time we report the presence of Late Quaternary piedmont glaciers represented by the largest hummocky moraine field in Turkey. The piedmont glaciers developed in the Central Taurides, 50 km north of the Mediterranean Sea. They were located on the north-facing hill-slopes of the Namaras Valley situated around 2000-2050 m above sea-level (a.s.l) in Geyikda?. The hummocky moraines resulted from in situ deposition of stagnant glacier ice (or dead-ice) where debris cover was heterogeneously distributed on the glacier surface. Twenty-six boulders from hummocky, lateral and terminal moraines from the Namaras Valley and the tributary Susam Valley were dated by cosmogenic 36Cl surface exposure dating. The moraine ages indicate three phases of glacial advances during the Late Quaternary. The oldest glacial advance occurred in the Namaras Valley at the end of the Last Glacial Maximum (18.0±0.4 ka, ka: thousands years ago) and is recorded entirely by the sequence of hummocky moraines in the mountain. Glaciers retreated towards the Susam Valley (2100-2200 m a.s.l.) and became stagnant during the Late Glacial (14.3±1.3 ka) as observed from hummocky and terminal moraines at the interior and outlet of the valley. Glaciers re-advanced at around 11.5±1.0 ka ago (Younger Dryas) which is represented by several lateral moraines that are at least 50 m higher than the surrounding hummocky moraines in both valleys. Comparable glacial chronologies were obtained from other Turkish mountains and from other Mediterranean mountains.

Ciner, Attila; Akif Sar?kaya, Mehmet; Y?ld?r?m, Cengiz

2014-05-01

70

How ice age climate got the shakes  

SciTech Connect

Records in Greenland ice, ocean mud, and ancient corals are revealing abrupt climate shifts during the last ice age. The climate at the end of the last ice age apparently jumped from cold to warmer conditions, jumped back to cold, and then jumped into the present warm weather conditions. The mechanism for this erratic behavior is unknown, but appears to be an interaction of North Atlantic ocean currents and the ice sheets themselves. Warm water from the tropics would evaporate and become more saline and dense as it moved north. The colder, denser water would then sink and flow back to the tropics. The melting of ice caused by the warm water would decrease the salinity of the North Atlantic current, the water would not sink, the return current would be shut down, and the waters surrounding the ice sheets would become colder, slowing melting of the sheets. The cycle could be started again by collapse of the ice sheets from their internal heat. There may be other switches that could cause sudden climate change, as may be evidenced by links between changes in the Pacific and a decade of erratic weather in North America. Researcher would like to identify these switches to prevent them from being activated by human activity.

Kerr, R.A.

1993-05-14

71

Volcano-ice age link discounted  

SciTech Connect

Speculation that huge volcanic eruptions may have caused an immediate `volcanic winter` that devastated early humans and accelerated a slide into the Ice Age. However, further information from the Greenland ice sheet about the Toba errumption on the island of Sumatra 70,000 years ago, seems to indicate that such volcanic actions wasn`t a major climatic catalyst. This article discusses the evidence and further possibilities.

Kerr, R.A.

1996-05-10

72

A review of topographic controls on moraine distribution  

NASA Astrophysics Data System (ADS)

Ice-marginal moraines are often used to reconstruct the dimensions of former ice masses, which are then used as proxies for palaeoclimate. This approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability. However, the validity of this assumption is open to question, as a number of additional, nonclimatic factors are known to influence moraine distribution. This review considers the role played by topography in this process, with specific focus on moraine formation, preservation, and ease of identification (topoclimatic controls are not considered). Published literature indicates that the importance of topography in regulating moraine distribution varies spatially, temporally, and as a function of the ice mass type responsible for moraine deposition. In particular, in the case of ice sheets and ice caps (> 1000 km2), one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback, whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles. For the marine-terminating outlets of such ice masses, fjord geometry also exerts a strong control on where moraines are deposited, promoting their deposition in proximity to valley narrowings, bends, bifurcations, where basins are shallow, and/or in the vicinity of topographic bumps. Moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape. In the case of icefields and valley glaciers (10-1000 km2), erosional feedback may well play some role in regulating where moraines are deposited, but other factors, including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points, are also likely to be important. This is particularly relevant where land-terminating glaciers extend into piedmont zones (unconfined plains, adjacent to mountain ranges) where large and readily identifiable moraines can be deposited. In the case of cirque glaciers (< 10 km2), erosional feedback is less important, but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris, regulate glacier dimensions and thereby determine where moraines are deposited. In such cases, moraines are likely to be small and particularly susceptible to post-depositional modification, sometimes making them difficult to identify in the modern landscape. Based on this review, we suggest that, despite often being difficult to identify, quantify, and mitigate, topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate (i.e., palaeoclimatic inferences should only be drawn from moraines when topographic controls on moraine distribution are considered insignificant).

Barr, Iestyn D.; Lovell, Harold

2014-12-01

73

Paraglacial response of steep, sediment-mantled slopes to post-Little Ice Age glacier recession in the central Swiss Alps  

Microsoft Academic Search

This research assesses the morphological consequences of recent (post-Little Ice Age) paraglacial reworking of valley-side sediment mantles in the European Alps. It aims to identify the extent and conditioning factors of slope adjustment at sites in the Swiss Alps, model the temporal pattern, and assess the rates of sediment reworking involved. Gully systems have cut into steep, high-level lateral moraines,

A. M. Curry; V. Cleasby; P. Zukowskyj

2006-01-01

74

Neoglaciation and an early 'Little Ice Age' in western Norway: lichenometric evidence from the Sandane area  

Microsoft Academic Search

Moraine sequences, protalus ramparts, rock glaciers and various slope deposits in seven separate glacier basins provide lichenometric ages for glacier retreat in an upland area of Sogn-og- Fjordane, southern Norway. Geomorphological mapping, relative dating based on section Rhizocarpon size-frequency distributions, observations on vegetation cover, and numeric dating based on a regional lichen dating curve for section Rhizocarpon, place moraines into

David J. A. Evans; Craig Butcher; Arjan V. Kirthisingha

1994-01-01

75

Ice Age Geomorphology of North America  

NASA Astrophysics Data System (ADS)

The Last Glacial Cycle in North America dramatically modified drainage patterns and geomorphology on a continental scale. As a consequence, the evolution of river systems holds information on the patterns of glaciation and isostatic response. This information can, in principle, be used to reconstruct the volumes of ice sheet sectors and eroded material by connecting the upstream ice sheets with stable isotope and other sedimentary records in offshore basins. Here we integrate this coupled geomorphic-hydrologic-glacial-sedimentary-paleoceanographic system to solve both the forward problem, how rivers evolve in response to Ice Age forcing, as well as the inverse problem, how fluvial systems record Quaternary history. The connections that define this system provide a link between climate and geomorphology that extends beyond the traditionally considered watershed-to-landscape scale by incorporating solid Earth deformations, large-scale shoreline migration, and the high amplitude changes in climate that drive the growth and decay of major ice sheets and water delivery to the bounding river systems. We address this continental scale problem using a valley-resolving drainage reconstruction that incorporates a realistic ice sheet history, a gravitationally self-consistent treatment of ice-age sea-level changes that includes shoreline migration, and precipitation and evapotranspiration retrodicted using general circulation model (GCM) runs. Drainage divides over the flat-lying North American interior migrate hundreds to thousands of kilometers in response to dynamic interactions between ice sheets and solid Earth response, and these changes coupled with post last glacial maximum (LGM) ice sheet melting drive high-amplitude variability in water and sediment discharge to the oceans. The Mackenzie River Delta records a sedimentary record produced by a highly non-eustatic sea level history and massive glacial sediment inputs routed along the axis that divided the Cordilleran and Laurentide Ice sheets. The upper Missouri River was re-routed northward during multiple deglacial periods due to isostatic depression of the Canadian interior; this re-routing is in addition to its known pre-Illinoian bedrock course to the Northeast. The Missouri River and many of its northerly tributaries hug the Laurentide ice margin, a sign that they were trapped between the ice sheet and its forebulge on the eastward-sloping High Plains. In contrast, the Upper Mississippi flows due south and contains a broad bedrock overdeepening along the Illinois border that records where this river must have sliced through one or more forebulges associated with Laurentide Ice Sheets. Offshore, sedimentary records coupled with these drainage reconstructions can be used as an independent geologic constraint on ice sheet volumes. Our drainage reconstructions provide a new paleogeographic backdrop to understand the North America's glacial past and a framework for tackling new problems at the interface of geomorphology, ice age geodynamics, and paleoclimate.

Wickert, A. D.; Anderson, R. S.; Mitrovica, J. X.; Picard, K.

2012-12-01

76

Age characteristics in a multidecadal Arctic sea ice simulation  

SciTech Connect

Results from adding a tracer for age of sea ice to a sophisticated sea ice model that is widely used for climate studies are presented. The consistent simulation of ice age, dynamics, and thermodynamics in the model shows explicitly that the loss of Arctic perennial ice has accelerated in the past three decades, as has been seen in satellite-derived observations. Our model shows that the September ice age average across the Northern Hemisphere varies from about 5 to 8 years, and the ice is much younger (about 2--3 years) in late winter because of the expansion of first-year ice. We find seasonal ice on average comprises about 5% of the total ice area in September, but as much as 1.34 x 10{sup 6} km{sup 2} survives in some years. Our simulated ice age in the late 1980s and early 1990s declined markedly in agreement with other studies. After this period of decline, the ice age began to recover, but in the final years of the simulation very little young ice remains after the melt season, a strong indication that the age of the pack will again decline in the future as older ice classes fail to be replenished. The Arctic ice pack has fluctuated between older and younger ice types over the past 30 years, while ice area, thickness, and volume all declined over the same period, with an apparent acceleration in the last decade.

Hunke, Elizabeth C [Los Alamos National Laboratory; Bitz, Cecllia M [UNIV. OF WASHINGTON

2008-01-01

77

Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages  

NASA Astrophysics Data System (ADS)

The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Preliminary dates from southern Finland, beginning at the Salpausselka Youngers Dryas moraine (11.5 ± 0.7 ka, n=2), inland southern Finland near Jyvaskyla (11.5 ± 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 ± 0.4ka, n=1) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.3 ± 0.5ka, n=2). Additional ages now being processed at PRIME Lab, Purdue University, which will establish a basis for SIS retreat from all sampled sites, will also be presented. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Pekka Lunka, J.; Wohlfarth, B.; Carlson, A. E.

2012-12-01

78

A glacial chronology for post Little Ice Age glacier changes based on proglacial geomorphology, tree rings, OSL- and 14C-dating at Mt. Pulongu, southeastern Tibet  

NASA Astrophysics Data System (ADS)

The remote eastern Nyainqêntanglha Range contains numerous temperate monsoonal glaciers which are highly sensitive to climate change. However, there is still a great lack of information on late Holocene glacier fluctuations and the factors driving these changes. We conducted field work at two large debris covered glaciers on the northern and southern slopes of Mt. Pulongu (~6,300 m a.s.l.). Detailed geomorphological mapping of the proglacial settings revealed similar patterns of two major and three minor/recessional glacial advances. At the northern glacier, tree ring dating for the moraines of the two major advances resulted in minimum ages of ~1670 AD and ~1745 AD, respectively. These Little Ice Age (LIA) ages are supported by geochemical measurements on glacial and glacio-fluvial sediments from these settings showing almost no signs of chemical weathering. Further evidence, including 14C-age and depositional characteristics of a buried tree, and moraine topography, suggest that the second advance was stronger but was hampered by a dead ice relict of the previous advance. At the northern glacier, this obstacle led to an ice tailback and subsequently to lateral moraine oversteepening and breaching, resulting in a large lateral glacier lobe. At the southern glacier, the valley is narrower and hence did not allow the formation of a lateral glacier lobe. However, the proglacial setting, i.e. pronounced push moraines, suggests a similar sequence of events. Furthermore, both settings contain two moraine-dammed lakes in similar positions. A combination of OSL-dating, tree ring based reconstruction of the local climate, and constraints from the proglacial geomorphological setting enabled the inclusion of the 3 minor moraine stages into the glacial chronology. This multiproxy-approach resulted in a well-established morphochronology with multiple direct and indirect dates that allow the reconstruction of the glacial fluctuations at Mt. Pulongu since the LIA. A regional remote sensing study revealed that these settings are no special cases, but that many large glaciers in the eastern Nyainqêntanglha range show similar proglacial sequences, including several examples of large lateral glacier lobes. We therefore assume that - despite great heterogeneity in this high-mountain environment - the emerging patterns were caused by climatic changes that affected the whole region.

Loibl, David; Hochreuther, Philipp; Hülle, Daniela; Zhu, Haifeng; Lehmkuhl, Frank

2014-05-01

79

Creswell Heritage Trust - Virtually the Ice Age  

NSDL National Science Digital Library

This website, produced by the Creswell Heritage Trust, discusses the characteristics of the climate and the environment of the Creswell Crags during the last Ice Age. By taking a survival test, users can discover the difficulties Stone Age people faced during this time period. The site offers a virtual tour of the Creswell Crags, which is one of the most northerly places on earth people visited between 50,000 and 10,000 years ago. Through a series of images, users can discover what Creswell and the Neanderthal's camp may have been like during this time period.

80

Airborne LiDAR detection of postglacial faults and Pulju moraine in Palojärvi, Finnish Lapland  

NASA Astrophysics Data System (ADS)

Postglacial faults (PGFs) are indicative of young tectonic activity providing crucial information for nuclear repository studies. Airborne LiDAR (Light Detection And Ranging) data revealed three previously unrecognized late- or postglacial faults in northernmost Finnish Lapland. Under the canopies of mountain birch (Betula pubescens ssp. czerepanovii) we also found clusters of the Pulju moraine, typically found on the ice-divide zone of the former Fennoscandian ice sheet (FIS), to be spatially associated with the fault-scarps. Tilt derivative (TDR) filtered LiDAR data revealed the previously unknown Palojärvi fault that, by the NE-SW orientation parallels with the well documented Lainio-Suijavaara PGF in northern Sweden. This suggests that PGFs are more extensive features than previously recognized. Two inclined diamond drill holes verified the fractured system of the Palojärvi fault and revealed clear signs of postglacial reactivation. Two other previously unrecognized PGFs, the W-E trending Paatsikkajoki fault and the SE-NW trending Kultima fault, differ from the Palojärvi faulting in orientation and possibly also with regard to age. The Pulju moraine, a morphological feature showing transitions from shallow (< 2-m-high) circular/arcuate ridges to sinusoidal/anastomosing esker networks was found to be concentrated within 6 km from the Kultima fault-scarp. We advocate that some of the past seismic events took place under the retreating wet-base ice sheet and the increased pore-water pressure triggered the sediment mass flows and formation of the Pulju moraine-esker landscape.

Sutinen, Raimo; Hyvönen, Eija; Middleton, Maarit; Ruskeeniemi, Timo

2014-04-01

81

ConcepTest: Ocean Salinity During an Ice Age  

NSDL National Science Digital Library

One million years ago ice sheets covered much of the Earth's land surface during an ice age. How did this affect the salinity of the oceans? a. Oceans were saltier than today. b. Oceans were less salty than ...

82

Why could ice ages be unpredictable?  

NASA Astrophysics Data System (ADS)

It is commonly accepted that the variations of Earth's orbit and obliquity control the timing of Pleistocene glacial-interglacial cycles. Evidence comes from power spectrum analysis of palaeoclimate records and from inspection of the timing of glacial and deglacial transitions. However, we do not know how tight this control is. Is it, for example, conceivable that random climatic fluctuations could cause a delay in deglaciation, bad enough to skip a full precession or obliquity cycle and subsequently modify the sequence of ice ages? To address this question, seven previously published conceptual models of ice ages are analysed by reference to the notion of generalised synchronisation. Insight is being gained by comparing the effects of the astronomical forcing with idealised forcings composed of only one or two periodic components. In general, the richness of the astronomical forcing allows for synchronisation over a wider range of parameters, compared to periodic forcing. Hence, glacial cycles may conceivably have remained paced by the astronomical forcing throughout the Pleistocene. However, all the models examined here show regimes of strong structural dependence on parameters. This means that small variations in parameters or random fluctuations may cause significant shifts in the succession of ice ages. Whether the actual system actually resides in such a regime depends on the amplitude of the effects associated with the astronomical forcing, which significantly differ across the different models studied here. The possibility of synchronisation on eccentricity is also discussed and it is shown that a high Rayleigh number on eccentricity, as recently found in observations, is no guarantee of reliable synchronisation.

Crucifix, M.

2013-10-01

83

Dendrogeomorphic reconstruction of Little Ice Age paraglacial activity in the vicinity of the Homathko Icefield, British Columbia Coast Mountains, Canada  

NASA Astrophysics Data System (ADS)

Moraine and glacier dams bordering the Homathko Icefield in the southern British Columbia Coast Mountains failed in the 1980s and 1990s, causing catastrophic downstream floods. The largest of the floods occurred in August 1997 and was caused by overtopping and rapid breaching of the moraine dam that impounds Queen Bess Lake. The floodwaters from Queen Bess Lake eroded Holocene-age sedimentary deposits along the west fork of Nostetuko River and caused a steep rise in the hydrograph of Homathko River at the head of Bute Inlet, ˜ 115 km downstream. A field investigation of the eroded valley fill in 2008, revealed multiple paraglacial valley-fill units, many of which are capped by in situ stumps and woody detritus. Dendrogeomorphological field techniques were employed to develop a chronology for the buried forests. A regional tree-ring chronology spanning the interval CE 1572-2007 was constructed from living subalpine fir ( Abies lasiocarpa) trees at seven sites in the southern Coast Mountains. In cases where subfossil stumps and boles predated the regional chronology, relative death dates constrained by radiocarbon ages were assigned to floating chronologies. By combining these dendrogeomorphological dating methods, we identified six floodplain aggradation episodes within the past 1200 years. Comparison to local and regional glacial histories suggests that these events reflect climate-induced Little Ice Age changes in local glacier cover.

Hart, Sarah J.; Clague, John J.; Smith, Dan J.

2010-09-01

84

Late-Wisconsinan submarine moraines along the north shore of the Estuary and Gulf of St. Lawrence (Eastern Canada)  

NASA Astrophysics Data System (ADS)

A series of ice-contact submarine fans and morainal banks along the Québec North-Shore of the Estuary and Gulf of St. Lawrence (Eastern Canada), between the Manicouagan River delta and the Mingan Islands, have been revealed with great detail by recent multibeam echosounder and high-resolution subbottom profiler surveys. These grounding-line landforms are observed between 65 and 190 m water depths and were constructed as the marine-based margin of the Laurentide Ice Sheet (LIS) stabilized or readvanced. Radiocarbon ages obtained from shells sampled in sediment cores collected in glaciomarine deposits 6 km south of a grounding line in the Sept-Iles area indicate a stabilisation that took place around 11 000 14C yr BP (12.5 ka cal BP with a ?R=120 ± 40 yr). In the Mingan Islands area, organic matter collected in distal deposits of an ice-contact fan is dated at 10 800 14C yr BP (11.6 ka cal BP). The position of the Sept-Iles and Mingan deposits, 20 km south of the ~9.7-9.5 14C kyr BP North-Shore Moraine, suggests that these ice marginal landforms were constructed during the Younger Dryas (YD) cold episode and that they might be the eastward submarine extent of the early YD St. Narcisse morainic system. Superimposed till sheets and morainal banks observed within grounding line deposits indicate that this stability phase was interrupted by local readvances that were marked in some cases by ice streaming. Segments of this morainic system are also visible along the shoreline in some sectors, where they have been generally washed out of fine fragments by waves. Another series of ice-contact deposits and landforms of similar nature observed farther offshore and at greater depths (100-190 m) were formed during a previous phase of stabilisation of the LIS margin. This older morainic system was probably deposited immediately after the opening of the Estuary and Gulf of the St. Lawrence.

Lajeunesse, Patrick; St-Onge, Guillaume

2013-04-01

85

Push moraines in the upper valley of Santa Cruz river, southwest Argentina. Structural analysis and relationship with Late Pleistocene paleoclimate  

NASA Astrophysics Data System (ADS)

The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments. The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.

Goyanes, Gabriel; Massabie, Armando

2015-01-01

86

The West Antarctic Ice Sheet: Instability, disintegration, and initiation of Ice Ages  

Microsoft Academic Search

An ice age model is proposed in which glacial-interglacial global climatic cycles are controlled by interactions between the cryosphere, hydrosphere, and atmosphere in the Atlantic environment. In the model, climatic change results from instabilities which develop in the snowfields or ice sheets of North America, Europe, and Antarctica. Disintegration of the West Antarctic ice sheet (that portion of the Antarctic

T. Hughes

1975-01-01

87

Cosmogenic 10Be and 26Al exposure ages of moraines in the Rakaia Valley, New Zealand and the nature of the last termination in New Zealand glacial systems  

Microsoft Academic Search

New Zealand glaciers reached their last glacial maximum position at or before ~25ka, and, as early as 23ka, commenced a slow and continual retreat. New cosmogenic exposure ages and field mapping from the Rakaia Valley in the South Island suggest that extensive ice survived well into the latter half of the Last Glacial–Interglacial Transition (18–11ka), with the post-15ka period inferred

James Shulmeister; David Fink; Olivia M. Hyatt; Glenn D. Thackray; Henrik Rother

2010-01-01

88

Abrupt onset and intensification of the Little Ice Age in Arctic Canada linked to explosive volcanism and sea-ice/ocean feedbacks  

NASA Astrophysics Data System (ADS)

At high northern latitudes the most reliable monitors of summer temperature are glaciers and ice caps. Small ice caps are multi-decadal integrators of climate. Precise 14C dates on rooted vegetation exposed by recent recession of more than 70 different ice caps that have remained perpetually frozen to their beds since their inception date ice-cap inception at that site. Unlike valley glacier moraines that are not formed until long after the initial climate shift, entombed plants date the moment of a persistent summer cooling. The composite probability density function of the 138 calibrated 14C ages indicates that ice caps expanded in four discrete intervals within the past 2 ka, with the most abrupt ice-cap growth ~1250 AD following three centuries of relative warmth, and intensified ice expansion ~1450 AD, with maximum ice cover ~1850 AD. These intervals of sudden and sustained ice expansion coincide with the three most volcanically perturbed half centuries of the past millennium. Separating the impacts of solar and volcanic forcings in the late Holocene has been vexing because decades of low solar irradiance largely coincide with decades of frequent explosive volcanism. Transient simulations with a fully coupled climate model show that the main features of our proxy data can be matched by decadally paced explosive volcanism alone, perpetuated by feedbacks related to consequent sea-ice expansion and export into the northern North Atlantic. Exported sea ice cools and freshens surface waters there, leading to a reduction in the AMOC and consequently perpetuation of an expanded sea ice state. The coincidence of low decadal solar irradiance with decades of explosive volcanism suggests that volcanic impacts may have been amplified by solar variability, but scaling the proxies of past solar irradiance remains uncertain. The persistence in the Eastern Canadian Arctic of some ice caps that formed 5000 years ago and remained intact until melting in the past decade, confirms that no subsequent century there was as warm as the most recent one, confirming the unusual character of present Arctic warming.

Miller, G. H.; Refsnider, K. A.; Zhong, Y.; Otto-Bliesner, B. L.; Lehman, S. J.; Southon, J. R.

2011-12-01

89

Ice Age Paleontology of Southeast Alaska  

NSDL National Science Digital Library

In 1990 vertebrate fossils were found in the caves of southeast Alaska, an area of impressive karst topography. Since then, large-scale paleontological and archaeological excavations have been conducted on northern Prince of Wales Island, and the research is now expanding to other islands and coastal mainland areas of southeast Alaska. The goal of this research is to establish a complete chronology of mammals, birds, and fish living in the region before, during, and following the Last Glacial Maximum, and up to the present day. This work is helping to establish the timing and extent of glaciation, the presence of Ice Age coastal refugia for land mammals, and the possibility that humans first entered North America by this coastal route. The results of this research are available at this site.

Timothy Heaton

2002-01-01

90

Self-potential investigation of moraine dam seepage  

NASA Astrophysics Data System (ADS)

Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m 3 of water at ~ 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events.

Moore, Jeffrey R.; Boleve, Alexandre; Sanders, Johnny W.; Glaser, Steven D.

2011-08-01

91

Geological Evidence for Recent Ice Ages on Mars  

NASA Astrophysics Data System (ADS)

A primary cause of ice ages on Earth is orbital forcing from variations in orbital parameters of the planet. On Mars such variations are known to be much more extreme. Recent exploration of Mars has revealed abundant water ice in the near-surface at high latitudes in both hemispheres. We outline evidence that these near-surface, water-ice rich mantling deposits represent a mixture of ice and dust that is layered, meters thick, and latitude dependent. These units were formed during a geologically recent major martian ice age, and were emplaced in response to the changing stability of water ice and dust on the surface during variations in orbital parameters. Evidence for these units include a smoothing of topography at subkilometer baselines from about 30o north and south latitudes to the poles, a distinctive dissected texture in MOC images in the +/-30o-60o latitude band, latitude-dependent sets of topographic characteristics and morphologic features (e.g., polygons, 'basketball' terrain texture, gullies, viscous flow features), and hydrogen concentrations consistent with the presence of abundant ice at shallow depths above 60o latitude. The most equatorward extent of these ice-rich deposits was emplaced down to latitudes equivalent to Saudi Arabia and the southern United States on Earth during the last major martian ice age, probably about 0.4-2.1 million years ago. Mars is currently in an inter-ice age period and the ice-rich deposits are presently undergoing reworking, degradation and retreat in response to the current stability relations of near-surface ice. Unlike Earth, martian ice ages are characterized by warmer climates in the polar regions and the enhanced role of atmospheric water ice and dust transport and deposition to produce widespread and relatively evenly distributed smooth deposits at mid-latitudes during obliquity maxima.

Head, J. W.; Mustard, J. F.; Kreslavsky, M. A.; Milliken, R. E.; Marchant, D. R.

2003-12-01

92

Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages  

NASA Astrophysics Data System (ADS)

The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Dates from southern Finland, beginning at the Salpausselka Younger Dryas moraine (11.5 × 0.7 ka, n=4), inland southern Finland near Jyvaskyla (11.5 × 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 × 0.4ka, n=4) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.8 × 0.5ka, n=4) and near Oulu (10.5 × 0.6 ka, n = 4) suggesting a later retreat in the north. Dates from southern Sweden, near Skovde (12.73 × 0.8ka, n=4) to Mora (10.41 × 0.6ka, n=5) suggest a slower retreat (over ~400km). Lastly, dates in Northwestern Sweden suggest a final termination of the SIS around 9.4 × 0.7ka (n = 3). Additional ages are now being processed at PRIME Lab, Purdue University, which will further strengthen our understanding of SIS retreat from all sampled sites. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Lunkka, J.; Wohlfarth, B.; Caffee, M. W.; Carlson, A. E.

2013-12-01

93

Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina  

NASA Astrophysics Data System (ADS)

We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages ( n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 14C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 14C yrs BP to 13,450 ± 150 14C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 14C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini had receded to just outboard of the outer Holocene moraines at Lago Frías and Lago Pearson (Anita) prior to 10,400 ± 40 14C yrs BP (12,270 ± 100 cal yrs BP) and 9040 ± 45 14C yrs BP (10,210 ± 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 ± 40 14C yrs BP (9300 ± 80 cal yrs BP). The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe.

Strelin, J. A.; Denton, G. H.; Vandergoes, M. J.; Ninnemann, U. S.; Putnam, A. E.

2011-09-01

94

ForPeerReview Ice age True Polar wander in a compressible and non  

E-print Network

ForPeerReview Ice age True Polar wander in a compressible and non hydrostatic Earth Journal Ice age (TPW), have continuously been debated, after the pioneering works of the sixties. We show ice age TPW

95

Ice Age terrestrial carbon changes revisited  

NASA Astrophysics Data System (ADS)

N. Shackleton (1977) first proposed that changes in the marine ?13C record (??13C) could be used to infer ice age changes in carbon storage on land. The previously published best estimate from the marine record is equivalent to about 490 Gt (0.32 ??13C). However, Adams et al. (1990) utilized a pollen database to estimate a 1350 Gt change in carbon storage, which would cause a ??13C of about 0.90‰. The nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land. To address the nature of this discrepancy, I have reexamined the terrestrial carbon record based on a new pollen database compiled by R. Webb and the Cooperative Holocene Mapping Project (COHMAP) group. I estimate about 750-1050 Gt glacial-interglacial change in terrestrial carbon storage, with the range reflecting uncertainties in carbon storage values for different biomes. Additional uncertainties apply to rainforest and wetland extent and presence of C4 plants, which have a significantly different isotopic signature than C3 plants. Although some scenarios overlap a new estimate of carbon storage based on the oceanic ??13C record (revised to 0.40‰ and 610 Gt), most estimates seem to fall outside the envelope of uncertainty in the marine record. Several possible explanations for this gap involve: (1) a missing sink may be involved in land-sea carbon exchange (e.g., continental slopes); (2) the geochemistry of the exchange process is not understood; (3) carbon storage by biome may have changed under ice age boundary conditions; or (4) the standard interpretation of whole ocean changes in the marine ?13C record requires reevaluation. This latter conclusion receives some support from comparison of the ?13C records for ?18O Stages 2 and 6. For the Stage 6 glacial, the ?13C changes are 50-60% larger than for the Stage 2 glacial. Yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading. To summarize, the above analysis implies that, despite the uncertainties remaining in estimates of terrestrial carbon storage changes, a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine ?13C record.

Crowley, Thomas J.

1995-09-01

96

Little ice age clearly recorded in northern Greenland ice cores  

Microsoft Academic Search

Four ice cores drilled in the little investigated area of northern and northeastern Greenland were evaluated for their isotopic (delta18O) and chemical content. From these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced, which reveals distinct climate cooling during the 17th and the first half of the 19th century. Timing of

H. Fischer; M. Werner; D. Wagenbach; M. Schwager; T. Thorsteinnson; F. Wilhelms; J. Kipfstuhl; S. Sommer

1998-01-01

97

Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains  

NASA Astrophysics Data System (ADS)

Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the ice sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and ice free mountains which archive limits of former ice advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the ice sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross Ice Shelf and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes glacially transported debris. Our glacial geomorphic survey from ice sheet contact edge (~850 masl) to mountain peak at 1600 masl together with a suite of 10Be and 26Al exposure ages, documents a pre-LGM ice volume at least 800 meters thicker than current ice levels which was established at least 2 million years ago. However a complex history of exposure and re-exposure of the ice free regions in this area is seen in accordance with advance and retreat of the ice sheets that feeds into the Darwin -Hatherton system. A cluster of mid-altitude boulders, located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, have exposure ages ranging from 30 to 40 ka. Exposure ages for boulders just above the ice contact range from 1to 19 ka and allow an estimate of inheritance. Hence, we conclude that LGM ice volume was not as large as previously estimated and actually little different from what is observed today. These results raise rather serious questions about the implications of a reduced WAIS at the LGM, its effect on the development of the Ross Ice Shelf, and how the Antarctic ice sheets respond to global warming. J. O. Stone et al., Science v299, 99 (2003). A. Mackintosh, D. White, D. Fink, D. Gore et al, Geology, v 35; 551-554 (2007).

Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James

2010-05-01

98

The Little Ice Age in Mesoamerica  

NASA Astrophysics Data System (ADS)

The spatial and seasonal distribution of rainfall is highly variable across the Yucatan Peninsula today, and is affected by climate variability of both Pacific (e.g., ENSO) and Atlantic (e.g., NAO) origin. The northwest coast is driest and is marked by a steep precipitation gradient from a low of 450 mm/yr near Progreso (21.3°N), increasing to 1000 mm/yr at Merida (21.0°N), and 1150 mm/yr at Abala (20.7°N), representing almost a 3-fold increase over a distance of only 65 km with negligible topographic relief. The region is highly attractive for paleoclimate study because of the steep rainfall gradient that is this sensitive to past changes in the position of the ITCZ. Consequently, we studied a 5.1-m sediment core from Aguada X'caamal (20.61°N, 89.72°W, max. depth = 12 m), a sinkhole lake located near the town of Abala, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of the gastropod Pyrgophorus coronatus (spinose) increased by ~3‰ and the benthic foraminifer Ammonia beccarii became abundant in the sediment profile, providing strong evidence for a pronounced increase in evaporation/precipitation ratio (E/P) and the salinity of Aguada X'caamal. This interpretation is supported by historical accounts of intense drought in the mid-1400s described in the Book of Chilam Balam of Mani (Gill, 2000), a town located only 45 km southeast of Aguada X'caamal. Oxygen isotope values in sediment cores from Lake Chichancanab (19.9°N) and Lake Salpeten (17°N) to the south also show an increase in the mid 15th century, although the magnitude is less than that recorded in northwest Yucatan. Increased E/P on the Yucatan Peninsula in the 15th century coincided with the start of the Little Ice Age (LIA), and is synchronous with increased aridity inferred from trace metals (Fe and Ti) in the Cariaco Basin off Venezuela, and with expressions of the LIA in tropical and polar ice cores. Colder temperatures during the LIA are well known to have had a societal impact in Greenland and Europe, and decreased precipitation in Mesoamerica may have contributed to cultural change such as the collapse of the Mayapan hegemony in the mid 15th century (Gill, 2000). Gill, R.B. (2000). The Great Maya Droughts, University of New Mexico Press, Albuquerque.

Hodell, D. A.; Brenner, M.; Curtis, J. H.; Medina Gonzalez, R. M.; Rosenmeier, M. F.; Guilderson, T. P.

2002-12-01

99

Potential improvement of Schmidt-hammer exposure-age dating (SHD) of moraines in the Southern Alps, New Zealand, by application of the new electronic Schmidt-hammer (SilverSchmidt)  

NASA Astrophysics Data System (ADS)

The Southern Alps of New Zealand are among the few key study sites for investigating Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere. Their characteristic highly dynamic geomorphological process systems prove, however, to be a considerable challenge for all attempts to date and palaeoclimatologically interpret the existing Holocene moraines record. As a multi-proxy approach combining 10Be terrestrial cosmogenic nuclide dating (TCND) with Schmidt-hammer testing, the recently developed Schmidt-hammer exposure-age dating (SHD) has already shown its potential in this study area (cf. Winkler 2005, 2009, 2013). An electronic Schmidt-hammer (named SilverSchmidt) was introduced by the manufacturer of the original mechanical Schmidt-hammer (Proceq SA) a few years ago. It offers, in particular, facilities for much easier data processing and constitutes a major improvement and potential replacement for the mechanical Schmidt-hammer. However, its different approach to the measurement of surface hardness - based on Q-(velocity) values instead of R-(rebound) values - is a potential drawback. This difference effectively means that measurements from the two instruments are not easily interconvertible and, hence, that the instruments cannot be used interchangeably without previous comparative tests of both instruments under field conditions. Both instruments used in this comparative study were N-type models with identical impact energy of 2.207 Nm for the plunger. To compare both instruments and explore interconvertibility, parallel measurements were performed on a selected number of boulders (10 boulders per site with 5 impacts each, at least 2 sites per moraine) on moraines of homogeneous lithology but different established ages covering the entire Holocene and the Late Glacial. All moraines are located east of the Main Divide of the Southern Alps at Mueller Glacier, Tasman Glacier, and in the outer Tasman River Valley. All paired samples (n = 50) were collected so that the plunger impacts of both instruments were set close together on the rock surface (to avoid any influence of modifications to the surface by consecutive impacts on the same spot). In order to test their performance at the higher and lower end of surface hardness, similar paired sample tests were also made on the full-metal test anvil. The results of paired samples for all sites/moraines reveal that Q-/R-value pairs are closely clustered for young surfaces but more scattered for the older ones with a corresponding moderate R2 for a calculated linear trend. The greater variability of the older, weathered surfaces with greater scatter and hence higher standard deviations and broader confidence intervals has been recognised in numerous previous Schmidt-hammer studies and is elated to the effects of micro-scale lithological variability, which becomes a more pronounced influence with time exposed to subaerial weathering. But most important, Q-values and R-values are closely related and Q-values are systematically higher than R-values by c. 10 - 12 units over most of the operational range of both instruments. Linear conversion equations indicate a conversion factor in the order of + 11 units is applicable when converting R-values to Q-values. These estimates agree well with data obtained on the standard test anvil. Given the apparent interconvertibility of the two instruments, the SilverSchmidt is regarded as a potential replacement for the mechanical Schmidt hammer. This enables, moreover, continuity in study areas with existing R-value data archives. However, when comparing data sets of different age, adjustments must be made for any changes to the instrumental calibration value over time. References: Winkler, S. (2005): The 'Schmidt hammer' as a relative-age dating technique: potential and limitations of its application on Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand. New Zealand Journal of Geology and Geophysics 48, 105 - 116. Winkler, S. (2009): First attempt to combine terrestrial cosmogenic nuclide (10Be) and Schmidt

Winkler, Stefan; Corbett, David

2014-05-01

100

Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.  

PubMed

The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20?m on Milankovitch timescales. The inception of colder climate since ?3?Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas. PMID:25908601

Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

2015-01-01

101

Glacier fluctuation and inferred climatology of Langjökull ice cap through the Little Ice Age  

Microsoft Academic Search

Emerging paleoclimate records from proglacial lake Hvítárvatn, central Iceland, suggest that Langjökull ice cap attained its maximum Holocene extent within the last 400 years. With the aim of constructing glaciological models and appropriate model inputs for Holocene simulations of Langjökull, we begin by simulating the evolution of Langjökull through the Little Ice Age to present, a period for which we

Gwenn E. Flowers; Helgi Björnsson; Áslaug Geirsdóttir; Gifford H. Miller; Garry K. C. Clarke

2007-01-01

102

Variations in the age of Arctic sea-ice and summer sea-ice extent  

Microsoft Academic Search

Three of the past six summers have exhibited record low sea-ice extent on the Arctic Ocean. These minima may have been dynamically induced by changes in the surface winds. Based on results of a simple model that keeps track of the age of ice as it moves about on the Arctic Ocean, we show that the areal coverage of thick

Ignatius G. Rigor; John M. Wallace

2004-01-01

103

500,000-year temperature record challenges ice age theory  

USGS Publications Warehouse

Just outside the searing heat of Death Valley lies Devils Hole (fig. 1), a fault-created cave that harbors two remnants of the Earth's great ice ages. The endangered desert pupfish (Cyprinodon diabolis) has long made its home in the cave. A 500,000-year record of the planet's climate that challenges a widely accepted theory explaining the ice ages also has been preserved in Devils Hole.

Snow, K. Mitchell

1994-01-01

104

Amplification of European Little Ice Age by sea ice-ocean-atmosphere feedbacks  

NASA Astrophysics Data System (ADS)

The transition from the Medieval Climate Anomaly (~950-1250 AD) to the Little Ice Age (~1400-1700 AD) is believed to have been driven by an interplay of external forcing and climate system-internal variability. While the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms shaping the climate on continental scale is less robust. Examining an ensemble of transient model simulations as well as a new type of sensitivity experiments with artificial sea ice growth, we identify a sea ice-ocean-atmosphere feedback mechanism that amplifies the Little Ice Age cooling in the North Atlantic-European region and produces the temperature pattern expected from reconstructions. Initiated by increasing negative forcing, the Arctic sea ice substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. As a consequence, northward ocean heat transport is reduced, reinforcing the expansion of the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea surface height anomalies cause the oceanic recirculation to strengthen at the expense of the warm Barents Sea inflow, thereby further reinforcing sea ice growth in the Barents Sea. The absent ocean-atmosphere heat flux in the Barents Sea results in an amplified cooling over Northern Europe. The positive nature of this feedback mechanism enables sea ice to remain in an expanded state for decades to centuries and explain sustained cold periods over Europe such as the Little Ice Age. Support for the feedback mechanism comes from recent proxy reconstructions around the Nordic Seas.

Lehner, Flavio; Born, Andreas; Raible, Christoph C.; Stocker, Thomas F.

2013-04-01

105

Radiostratigraphy and age structure of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.

MacGregor, Joseph A.; Fahnestock, Mark A.; Catania, Ginny A.; Paden, John D.; Prasad Gogineni, S.; Young, S. Keith; Rybarski, Susan C.; Mabrey, Alexandria N.; Wagman, Benjamin M.; Morlighem, Mathieu

2015-02-01

106

Constraints on ice volume changes of the East Antarctic Ice Sheet and Ross Ice Shelf since the LGM based on cosmogenic exposure ages from Darwin-Hatherton outlet glaciers.  

NASA Astrophysics Data System (ADS)

At the Last Glacial Maximum and during Termination-1 (~20-10 ka), marine evidence indicates that the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS), blocking drainage of the Darwin and Hatherton outlet glaciers through the Transantarctic Mountains (TM) resulting in significant downstream thickening of glacier profiles. These outlet glaciers provide geological and glaciological records of EAIS expansion through the TMs as well as WAIS fluctuations which together suggest an LGM thickness of ~800 m lager than today at their confluence with the Ross Embayment. About 80 cosmogenic 10Be and 26Al exposure ages of erratics from 3 locations flanking the Hatherton Glacier (Dubris Valley near the EAIS source region, from Lake Wellman at its midpoint and Diamond Hill at its terminus) taken along transects covering 800 m in differential elevation from ice-sheet contact to mountain peaks documents 2.5 Ma of ice volume evolution of the Hatherton allowing a reconstruction of its quaternary paleo-ice surface. Pleistocene ice thickness is some 800 to 400 meters thicker between 2.5 to 0.5 Ma years ago than today . However at all 3 locations, exposure ages of mapped glacial drifts younger than 0.5 Ma at lower elevations down to current ice margin did not show any evidence for a distinct LGM advance. At Lake Wellman a cluster of mid-elevation moraine boulders from the Britannia Drift, previously taken to demarcate the LGM advance, have exposure ages ranging from 30 to 40 ka. At Dubris Valley, the same drift returned ages of 120-125 ka. At Diamond Hill, the confluence of the Darwin Glacier and RIS, two transects were sampled that cover an altitude range of 1100 meters. Cosmogenic dates show a similar trend to that seen further upvalley - the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only minor advances in the last 10ka and an absence of any LGM ages. The absence of a LGM signal is perplexing. We suggest the idea that while WAIS expansion during the early Pleistocene was large, LGM ice volume in the Darwin-Hatherton Glaciers was not as large as previously estimated and perhaps little different from what is observed today (at most 50 m above current ice surface). These results raise serious questions about the implications of a reduced East Antarctic ice Sheet at the LGM, and how the Antarctic ice sheets respond to global warming. Similar conclusions from 10Be exposure ages from coastal sites of the East Antarctic Ice Sheet in the Lambert Glacier-Amery Ice Shelf and at the Framnes Mountains also indicate a far reduced LGM ice volume at ~15ka than previously assumed.

Fink, David; Joy, Kurt; Storey, Bryan

2013-04-01

107

Siple Dome ice reveals two modes of millennial CO2 change during the last ice age  

PubMed Central

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

Ahn, Jinho; Brook, Edward J.

2014-01-01

108

Siple Dome ice reveals two modes of millennial CO2 change during the last ice age.  

PubMed

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

Ahn, Jinho; Brook, Edward J

2014-01-01

109

The deglaciaton of the Pyreenes: from the Oldest Dryas to the Little Ice Age  

NASA Astrophysics Data System (ADS)

The main purpose of the paper is to study the deglaciation process, including the retreat of the glaciers and the occurrence of short advances with the deposition of new, relatively recent tills in two head valleys of the central-southern Pyrenees: The Upper Gállego Valley, with the main peak Balaitus (42°46'0' N, 0° 15'0'W, 3151 m), and the Marbore Cirque, at the head of the Cinca Valley, on the north face of the Monte Perdido Peak (42º400' N; 0.5º0'W; 3355 m). The deglaciation process was studied through geomorphological mapping and 36Cl cosmogenic exposure ages obtained from morainic and rock glacier boulders and polished bedrocks. Even though the exact position of the front glacier during the global Last Glacial Maximum is not known, there is evidence that the different ice tongues retreated until headwater positions, causing the subdivision of the main glaciers into various individual glaciers. Two clear climate reversals within the general trend to deglaciation have been detected: First of all, the Oldest Dryas, coinciding with the Heinrich Event 1 (ca 17-15 ka) and, secondly, the Younger Dryas (ca 13-11.7 ka). Between both stadials, the Bølling/Allerød Interstadial (ca 15-13 ka) represented an intense glacial retreat up to the cirque headwalls. During the Bølling/Allerød Interstadial the retreat was very rapid, although the occurrence of a short readvance of small glaciers during the Older Dryas must not be ruled out. The Younger Dryas is represented by a new glacial push with the deposition of distinct types of tills. During these late glacier advances, small glaciers and rock glaciers developed close to the cirque headwalls, and coexisted under the same climatic conditions. After the Younger Dryas, new glacial advances has not been detected until the Little Ice Age, except in the Marbore Cirque, where glacial expansion occurred during the Mid and Late Holocene (5.1 ± 0.1 ka), represented by a large push moraine. A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 ka (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. A melting period occurred during the Medieval Climate Anomaly following a glacial expansion during the Dark Age Cold Period (1.4-1.2 ka). The Little Ice Age represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and 1830 AD (Dalton Minimum).

Palacios, David; de Andrés, Nuria; López-Moreno, Juan I.; García-Ruiz, José M.

2014-05-01

110

Late Pleistocene ice-shelf, valley-glacier and ice-sheet interactions on Alexander Island, Antarctic Peninsula: implications for climatic and ice-volume changes  

NASA Astrophysics Data System (ADS)

Recent rapid warming across the Antarctic Peninsula has resulted in ice-sheet thinning, dramatic ice-shelf collapse, acceleration of ice-flow velocities and widespread glacier recession. Reconstructing past rates, volumes and magnitudes of cryospheric change, particularly with respect to the former configuration of ice sheets and ice shelves, and their response to changing oceanic and climatic regimes, is vital in providing a context for this change, in order to improve predictions of future ice-sheet behaviour, and to provide glacio-isostatic adjustment corrections for gravimetric measurements of contemporary ice loss. This research aimed to investigate valley glacier and ice-shelf interactions during the Last Glacial Maximum (LGM) and Holocene Epoch across George VI Sound and Alexander Island, western Antarctic Peninsula, an area with a well-preserved but poorly dated record. We identify four principal stratigraphic units: (1) a high-elevation drift with Alexander Island erratics only (interpreted as recording older advances of ice from the interior of the island), (2) a lower-elevation drift with exotic Palmer Land erratics (interpreted as ice-shelf moraine, representing incursions of George VI Ice Shelf onto Ablation Point Massif), (3) multiple overlapping sequences of valley glacier moraine and ice-shelf moraine, presumed to be Holocene in age, and (4) more recent processes and units, including frozen epishelf lakes, slope processes and alluvial fans. On-going cosmogenic nuclide dating on these sediments (in progress; 25 10Be exposure ages) has the potential to unlock the complex history and interactions of ice streams, valley glaciers and ice shelves in this area. This work will also provide the first long-term record of sea-level indicators, allowing the first estimates of glacial unloading, rates of uplift and ice-sheet thinning to be calculated. The Holocene record of the ice shelf, preserved in the younger ice-shelf moraines and in the overlapping sequence of ice-shelf and valley-glacier moraines in Erratic Valley, will assist not only in tying together limnological records from the epishelf lakes and the onshore geomorphological record, but will also allow inferences about Holocene ice-shelf collapse to be made. Dating these samples will provide a sensitive record of the geomorphological impact of Holocene climatic variations.

Davies, Bethan; Hambrey, Michael; Glasser, Neil; Smellie, John; Carrivick, Jonathan; Bentley, Michael

2014-05-01

111

Sea ice volume and age: Sensitivity to physical parameterizations and thickness resolution in the CICE sea ice model  

NASA Astrophysics Data System (ADS)

New dynamics parameterizations in Version 5 of the Los Alamos Sea Ice Model, CICE, feature an anisotropic rheology and variable drag coefficients. This study investigates their effect on Arctic sea ice volume and age simulations, along with the effects of several pre-existing model options: a parameter that represents the mean cumulative area of ice participating in ridging, the resolution of the ice thickness distribution, and the resolution of the vertical temperature and salinity profiles. By increasing shear stress between floes, the anisotropic rheology slows the ice motion, producing a thicker, older ice pack. The inclusion of variable drag coefficients, which depend on modeled roughness elements such as deformed ice and melt pond edges, leads to thinner ice and a more realistic simulation of sea ice age. Several feedback processes act to enhance differences among the runs. Notably, if less open water is produced mechanically through ice deformational processes, the simulated ice thins relative to runs with more mechanically produced open water. Thermodynamic processes can have opposing effects on ice age and volume; for instance, growth of new ice increases the volume while decreasing the age of the pack. Therefore, age data provides additional information useful for differentiating among process parameterization effects and sensitivities to other model parameters. Resolution of thicker ice types is crucial for proper modeling of sea ice volume, because the volume of ice in the thicker ice categories determines the total ice volume. Model thickness categories tend to focus resolution for thinner ice; this paper demonstrates that 5 ice thickness categories are not enough to accurately resolve the ice thickness distribution for simulations of ice volume.

Hunke, Elizabeth C.

2014-10-01

112

Ice ages and nuclear waste isolation  

Microsoft Academic Search

The greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800m are likely during rapid retreats of future ice sheets. The next major glacial retreat is expected at ca 70ka, well within the lifetime of high grade nuclear waste, but it is not yet clear how long

C. J Talbot

1999-01-01

113

Hydraulics of Ice-age Megafloods  

NASA Astrophysics Data System (ADS)

During the deglaciation of North America (ca. 12,000­8,000 BP), huge proglacial lakes formed along the southern margin of the Laurentide Ice Sheet. Depending on the location of the ice margin, overflow from these lakes was variably directed to the Mississippi, Hudson and St. Laurence drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events. On several occasions the ice dam formed by the Laurentide ice sheet was penetrated and massive outburst floods were routed to Hudson Bay and to the Arc- tic Ocean. In terms of released water volume the largest of these outburst floods was associated with the Kinojévis stage of Glacial Lake Agassiz. The impounded water volume has been estimated as 163, 000 km3 and the timing of the outburst coincides with the early Holocene cooling event at 8,200 BP. Although the total water discharge is reasonably well constrained by glacial geological observations, the magnitude and duration of the flood, which have a potential influence on the oceanic response, remain matters for speculation. To examine the range of possibilities we use the Spring-Hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and develop new theory to treat the case of outburst floods that occur by downcutting of a supraglacial drainage channel. Representative values for the peak flood magnitude and duration are 5 Sv and 1 yr.

Clarke, G. K. C.; Leverington, D. W.; Teller, J. T.

114

Timing of Expansions of the Quelccaya Ice Cap, Peru, and Implications for Cosmogenic Nuclide Production Rate Calibration  

NASA Astrophysics Data System (ADS)

We calibrate the production rate of the cosmogenic nuclide beryllium-10 (10Be) at a low-latitude, high-elevation site, using nuclide concentrations measured in moraine boulders and an independent chronology determined with bracketing radiocarbon dates. The measurement of terrestrial cosmogenic nuclide (TCN) concentrations in earth surface materials has been an important development for understanding a host of earth surface processes. Uncertainty in cosmogenic nuclide production rates has hampered application of this method. Here, we contribute to the estimation of 10Be production rates by reporting both preliminary 10Be concentrations and independent radiocarbon dates from a low latitude, high elevation site. Our study site in the southeastern Peruvian Andes (~13.9°S, 70.9°W, 4850 m asl) is centered on a moraine set, known as the Huancané II moraines, that represents a ~4 km expansion of Quelccaya Ice Cap during late glacial time. At this location, organic material situated both stratigraphically below and above moraines in two adjacent valleys provide material for radiocarbon dating. Based on geomorphic arguments, we correlate results from the two valleys. The timing of ice cap margin advance is bracketed by 13 radiocarbon ages on organic material within the outermost Huancané II moraines that range from 13.6 to 12.5 ka. Two stratigraphic sections upvalley from the moraines yield 6 radiocarbon ages from 11.3 to 12.4 ka, indicating the time of retreat . We computed the probability density function that lies between these two sets of dates, and assign an age of 12.4 ka (+/-???) for the formation of the Huancané II moraines. Calculating beryllium-10 exposure dates from the measured concentrations yield exposure dates that significantly underestimate the independently determined age of the moraine (~8-30%), if existing production rate estimates are used. We suggest that the radiocarbon age for the moraines can be used as a robust independent calibration for 10Be production rates at this site.

Lowell, T. V.; Kelly, M. A.; Applegate, P. J.; Smith, C. A.; Phillips, F. M.; Hudson, A. M.

2010-12-01

115

Measurements of Past Ice Sheet Elevations in Interior West Antarctica.  

PubMed

A lateral moraine band on Mount Waesche, a volcanic nunatak in Marie Byrd Land, provides estimates of past ice sheet surface elevations in West Antarctica. Helium-3 and chlorine-36 surface exposure ages indicate that the proximal part of the moraine, up to 45 meters above the present ice surface, was deposited about 10,000 years ago, substantially later than the maximum ice extent in the Ross Embayment. The upper distal part of the moraine may record multiple earlier ice sheet high stands. A nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at Mount Waesche relative to the maximum ice extent in the Ross Sea. The glacial geologic evidence, coupled with the ice sheet model, indicates that the contribution of the Ross Sea sector of the West Antarctic Ice Sheet to Holocene sea level rise was only about 3 meters. These results eliminate West Antarctic ice as the principle source of the large meltwater pulse during the early Holocene. PMID:10514368

Ackert; Barclay; Borns; Calkin; Kurz; Fastook; Steig

1999-10-01

116

The Little Ice Age in the Canadian Rockies  

Microsoft Academic Search

This paper reviews the evidence and history of glacier fluctuations during the Little Ice Age (LIA) in the Canadian Rockies. Episodes of synchronous glacier advance occurred in the 12th–13th, early 18th and throughout the 19th centuries. Regional ice cover was probably greatest in the mid-19th century, although in places the early 18th century advance was more extensive. Glaciers have lost

B. H. Luckman

2000-01-01

117

Little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap  

SciTech Connect

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical condutivity records confirms the worldwide character of this event.

Thompson, L.G.; Mosley-Thompson, E.; Dansgaard, W.; Grootes, P.M.

1986-10-17

118

Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.  

NASA Astrophysics Data System (ADS)

It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum occurred prior to the Antarctic LGM (18-22 ka). No evidence based on cosmogenic ages for post-LGM or Holocene advances were found. These results support an extensive exposure age data set from the nearby Darwin-Hatherton Glacier system that indicates an absence of EAIS expansion across the Transantarctic Mnts during the global LGM period.

Fink, David; Joy, Kurt; Storey, Bryan

2014-05-01

119

Ice-age rain forest found moist, cooler  

SciTech Connect

Climate researchers have argued for years about whether the tropics cooled a little or a lot during the height of the last ice age 18000 years ago. The answer will offer clues to the sensitivity of the Earth`s climate system to the strengthening greenhouse effect. On a different front, arguments have raged about how the Amazon flora and fauna became so divers. A single study of lake mud from deep in the Amazon rain forest sheds new light on both of these controveries by point toward a cool, but still wet ice age Amazon. This article goes on to discuss the background of the study, other view points, and the implications.

Kerr, R.A.

1996-10-04

120

Age vs depth of glacial ice at South Pole  

NASA Astrophysics Data System (ADS)

Knowledge of age as a function of depth in glacial ice is important for both glaciology and paleoclimatology. For sites near a ridge or dome, an ice flow model together with information on accumulation rate provides a first approximation. If the accumulation rate is high enough, annual layering of isotopes and dust measured in a solid core can provide a precise age vs depth relationship. For South Pole, the flow geometry is not simple and no deep core exists. Nevertheless, by remotely sensing peaks in scattering and absorption of light from pulsed sources buried at depths down to 2200 m, we have been able to determine age vs depth for ages up to 65,000 years. Analysis of radar isochrons by Siegert and Hodgkins provides a rough extension of the age vs depth model to ˜165,000 years near bedrock.

Price, P. B.; Woschnagg, K.; Chirkin, D.

2000-08-01

121

Airborne LiDAR DEMs as a tool for deriving information on past glacier extent and ice flow  

NASA Astrophysics Data System (ADS)

The quantification of ice volumes and the identification of ice flow regimes within historical glacier systems are important steps towards understanding historical phases of glacier advance and disintegration in the context of Holocene climate fluctuation. Topographic LiDAR DEMs provide an excellent tool for gaining various kinds of spatially distributed information. Several case studies have been performed in the Austrian Alps, where LiDAR DEMs are available for almost the entire glacier area. LiDAR DEMs achieve vertical accuracies of few decimetres and can be used to calculate hillshade images with flat incidence angles, so that the surface structures of moraines and other glacial deposits can be identified. These hillshade images were used together with aerial photographs to identify the LIA (Little Ice Age) moraines and the elevation of the lateral moraines, so that, together with information on today's ice volume, a lower limit for the LIA ice volume could be calculated. The resulting LIA glacier areas showed good coincidence with former reconstructions based on field mapping and airborne photogrammetry. In addition to that, historical ice flow directions could be derived from the structure of basal moraines. These data allow an interpretation of the changing contribution of specific tributary glaciers to a joint glacier tongue, which may result in an important switch in ice dynamics leading to fast glacier advances recorded by frontal moraines. The combination of terrestrial long-term observations and LiDAR data documents the genesis of specific geomorphological features in the periglacial area by recording the processes occurring during the disintegration of glacier tongues. For example, the deposition of the material from former medial moraines in the newly formed periglacial area can be identified and quantified from the LiDAR data as well as debris flows or rock falls from the LIA moraines.

Seiser, Bernd; Fischer, Andrea

2014-05-01

122

Combination of in situ cosmogenic nuclide (10Be) and Schmidt-hammer dating for the investigation of Late-Holocene lateral moraines in the Southern Alps of New Zealand  

NASA Astrophysics Data System (ADS)

The investigation of Holocene glacier chronologies in high mountain regions is important for use of glaciers as indicators for climate change. Only detailed Holocene glacier chronologies offer the opportunity to improve our knowledge on the relationship between glaciers and climate factors, and to verify models of the future glacier development. The Southern Alps of New Zealand represent the southern hemispheric study area within the complex comparative current research project "MaMoGla" (Holocene and recent dynamics of maritime mountain glaciers). Among other goals, new methodological attempts to date the dominating lateral moraines in the Southern Alps in order to revise existing glaciers chronologies have been integrated in this project. The need for improvement of the existing Holocene glacier chronology of the Southern Alps/New Zealand is mainly caused by methodological uncertainties and the focus on Tasman Glaciers as unreliable key locality. Previously, radiocarbon (14C) dating of organic material (plant remains, organic-rich soil layers etc.) buried beneath or within the complex lateral moraines was the predominating ‘absolute' dating technique applied. In addition to older studies using the measurement of weathering rind thickness on boulders, the potential of the Schmidt-hammer as relative-age dating technique has clearly been demonstrated by the successful application on several lateral and latero-frontal moraine sequences in the Mt Cook/Aoraki National Park. The relatively homogenous and weathering/erosion-resistant bedrock yielded comparatively small standard errors and, thus, a relatively high time resolution of up to 200 - 300 years. Supported by statistical treatment of the raw field data, the Schmidt-hammer provided sufficient information to group the individual moraine ridges into moraine sequences and relate them to separate Little Ice Age-type events. However, the final ‘absolute' age dating of the moraine sequences remained open. As an ‘absolute' age of the boulder surfaces was needed to allow the construction of a dating curve by reliable fixed points to, radiocarbon (14C) dating could not provide those information because of the lack of organic material indisputable be related to the glacier advance forming the moraine ridges. On base on these considerations, this study comprises the first attempt to combine in situ (terrestrial) cosmogenic nuclide (10Be) surface exposure dating with Schmidt-hammer measurements for the dating of Holocene moraines and the reconstruction of a regional glacier chronology. Cosmogenic 10Be dating has the important advantage of delivering an ‘absolute' age for the exposure of boulder or bedrock surfaces, i.e. the same surface tested with the Schmidt-hammer. One disadvantage of cosmogenic nuclide exposure dating is, however, the limited number of boulders sampled due to high costs. From this background, a combination with the Schmidt-hammer technique seems ideal as the latter could provide measurement of a large number of boulders. The Schmidt-hammer measurements can, on the other hand, help with the selection of representative boulders for cosmogenic nuclide (10Be) surface exposure dating avoiding boulders that have been exposed to post-depositional movement (e.g. rotation). Results from the application of this combined ‘multi-proxy-approach' at Strauchon Glacier in Westland/Tai Poutini National Park and Hooker Glacier in Mt Cook/Aoraki National Park on large lateral moraine complex with several individual moraine ridges proof its potential. Three pre-‘Little Ice Age' moraine sequences each related to an individual Late-Holocene Little Ice Age-type event unambiguously distinguished by Schmidt-hammer measurements provides cosmogenic (10Be) ages of 2,400/2,500 a BP, c. 1,700 a BP, and c. 1,000/1,100 a BP. The preliminary construction of a dating curve based on both Schmidt-hammer and cosmogenic (10Be) dating results shows high significance and confirms the successful application of this attempt. Although subsequent cosmogenic 10Be-dating is necessary

Winkler, S.

2009-04-01

123

ResearchHighlights The last Ice Age in Australia  

E-print Network

ResearchHighlights The last Ice Age in Australia Dr Timothy Barrows , Dr Keith Fifield, Accelerator of glaciation and climate change in Australia. By directly dating glacial debris and eroded bedrock, the timing of the glacial history of these regions, which were the only areas in Australia where glaciers existed

Chen, Ying

124

Milutin Milankovitch: Seeking the Cause of the Ice Ages  

NSDL National Science Digital Library

This online article, from Earth: Inside and Out, reports on how mathematician Milutin Milankovitch developed a complete astronomical theory of glaciers. It discusses his work charting the ice ages of the Pleistocene, which incorporated new information about how the gravitational tug of other planets causes small variations in the tilt of the Earth's axis.

125

Evaluating sun–climate relationships since the Little Ice Age  

Microsoft Academic Search

From the coldest period of the Little Ice Age to the present time, the surface temperature of the Earth increased by perhaps 0.8°C. Solar variability may account for part of this warming which, during the past 350 years, generally tracks fluctuating solar activity levels. While increases in greenhouse gas concentrations are widely assumed to be the primary cause of recent

Judith Lean; David Rind

1999-01-01

126

Global warming in the context of the Little Ice Age  

Microsoft Academic Search

Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond. The evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as

Melissa Free; Alan Robock

1999-01-01

127

Multiple ice-age refugia in Pacific cod, Gadus macrocephalus  

E-print Network

Anchorage, 3211 Providence Drive, Anchorage, AK 99508, USA, §Alaska Department of Fish and Game, 333 from the Sea of Japan to Washington State. Both microsatellite (mean H = 0.868) and mtDNA haplotype appeared between samples from the Sea of Japan and Okhotsk Sea that may reflect ice-age isolations

128

The genetic legacy of the Quaternary ice ages  

Microsoft Academic Search

Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable

Godfrey Hewitt

2000-01-01

129

PalaeobotanyIce-age steppe vegetation in east Beringia  

Microsoft Academic Search

The landmass known as Beringia is an extensive region that existed during the Pleistocene epoch and included the land bridge between present-day Siberia and Alaska, now submerged beneath the Bering Strait. It must have been covered with vegetation even during the coldest part of the most recent ice age (some 24,000 years ago) because it supported large populations of woolly

Grant D. Zazula; Duane G. Froese; Charles E. Schweger; Rolf W. Mathewes; Alwynne B. Beaudoin; Alice M. Telka; C. Richard Harington; John A. Westgate

2003-01-01

130

Glacier recession on Cerro Charquini (16° S), Bolivia, since the maximum of the Little Ice Age (17th century)  

NASA Astrophysics Data System (ADS)

Cerro Charquini, Bolivia (Cordillera Real, 5392 ma.s.l.) was selected as a site to reconstruct glacier recession since the maximum of the Little Ice Age (LIA) in the central Andes. Five glaciers, located on differently exposed slopes, present comprehensive and well-preserved morainic systems attributed to former centuries. The moraines were dated by lichenometry and show a consistent organization on the different slopes. The past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry. Lichenometric dating shows that the LIA maximum occurred in the second half of the 17th century, after which the glaciers have receded nearly continuously. Over the last decades of the 20th century (1983 97), recession rates increased by a factor of four. On the northern and western slopes, glaciers receded more than on the southern and eastern slopes (by 78% and 65% of their LIA maximum area, respectively). The mean equilibrium-line altitude (ELA) rose by about 160 m between the LIA maximum and 1997. Recession rates were analysed in terms of climatic signal, suggesting that glacier recession since the LIA maximum was mainly due to a change in precipitation and that the 19th century may have been drier. For the 20th century, a temperature rise of about 0.6°C appears to be the main cause of glacier recession. Recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1.36 mw.e.a-1. If such conditions persist, the small glaciers below 5300 ma.s.l. in the Cordillera Real should disappear completely in the near future.

Rabatel, Antoine; Machaca, Abraham; Francou, Bernard; Jomelli, Vincent

131

Recent Deglaciation of Darwin Mountains (Tierra de Fuego) after Little Ice Age: monitoring by photogrammetry, lichenometry, dendrochronology and field studies.  

NASA Astrophysics Data System (ADS)

Glaciers from the Darwin mountain range have been retreating since the Little Ice Age (LIA). However, the amount of retreat varies and is minimal for some glacial snouts and substantial for others. Possible explanations for this different behaviour include climatic and glacial dynamic causes. The aim of this work was to analyse the impact of climate change on these glaciers. The research site was the terminus of glacier Pia, which descends to the south of Mount Darwin (2488 m asl, 54°45'S, 69°29'W) and reaches the coastline at the Beagle Channel. The terminus is situated some hundreds of meters above the LIA moraine but, whereas one sector retreated rapidly and then stabilized, another sector has had several advances and retreats leaving a number of moraine arches. To better understand the origin of this dynamic behaviour, we undertook a study of the evolution of the terminus of glacier Pia over the last 60 years. We used aerial photographs and satellite images to determine the exact location of the glacial terminus in certain years (1943, 1963, 1987, 1990, 2001 and 2006). These results were completed in 2008 and 2009 through field work. We also carried out lichenometric studies of the two most abundant lichen species that rapidly colonize the moraine boulders abandoned by the glacier: Placopsis perrugosa and Rhizocarpon geographicum. By comparing results from field work carried out in 2008 and 2009, we were able to determine the growth rate of these two species (García-Sancho et al. 2011). In addition, we also carried out a dendrochronological study of Nothofagus antarctica and N. betuloides. The use of the four techniques involved in this study (photogrammetry, lichenometry, dendrochronology and multiyear field work) allowed us to establish the ecesis period of each species as well as their growth curves, from which we can deduce the movements of the glacial terminus from the end of the LIA to the present. From this study we can infer that the different behaviour detected at the Pia glacial terminus results from a combination of climatic factors and elements derived from the dynamics of the glacial flow. García-Sancho, L. Palacios, D., Green, T.G.A., Vivas, M., Pintado, A. (2011): Extreme lichen growth rates detected in recent deglaciated areas in Tierra del Fuego. Polar Biology, 34 (6): 813-822. DOI: 10.1007/s00300-010-0935-4. Research funded by POL20060840 & CGL2009-7343 projects, Government of Spain.

García-Sancho, L.; Palacios, D.; Zamorano, J. J.; Green, A.; Vivas, M.; Pintado, A.

2012-04-01

132

77 FR 14567 - Draft General Management Plan/Environmental Impact Statement for the Ice Age Complex at Cross...  

Federal Register 2010, 2011, 2012, 2013, 2014

...Statement for the Ice Age Complex at Cross Plains...SUMMARY: Under the National Environmental...Statement for the Ice Age Complex at Cross Plains...interpretive programming. Under this alternative, the Ice Age Complex would serve...

2012-03-12

133

The Little Ice Age and the emergence of influenza A.  

PubMed

Bayesian phylogenetic analysis of the haemagglutinin and neuraminidase proteins of influenza A virus demonstrates that their respective most recent common ancestors (MRCAs) both existed approximately 1000years ago. Most of the bifurcations within the haemagglutinin and neuraminidase phylogenetic trees occurred within a time window that can be dated with 95% confidence to the years 1411-1932 of the Common Era (AD) for haemagglutinin and 1366-1874 AD for neuraminidase. This subtype diversification episode is temporally congruent with the "Little Ice Age", a period of climatic cooling over the northern hemisphere. Furthermore, Bayesian probability mean ages for the bifurcation points within the haemagglutinin tree indicate two bursts of diversification from 1672 to 1715 AD and from 1825 to 1868 AD. The first of these follows in the wake of the coldest epoch in the Little Ice Age, and the second overlaps a later cooling episode. Since climate change is known to affect migration patterns in the reservoir host of influenza A, the aquatic wildfowl, and allopatric cladogenesis following population disruption is well supported in the evolutionary literature, a mechanism is proposed linking the Little Ice Age to influenza subtype diversification via ecological disruption of the wildfowl annual cycle. The suggestion that past climate change has impacted on influenza evolution implies that current global warming may cause a further burst of influenza subtype diversification with possible serious epidemiological consequences becoming apparent in the 22nd and 23rd centuries. PMID:20399567

Gatherer, Derek

2010-10-01

134

Moraine-dammed lake failures in Patagonia and assessment of outburst susceptibility in the Baker Basin  

NASA Astrophysics Data System (ADS)

Glacier retreat since the Little Ice Age has resulted in the development or expansion of hundreds of glacial lakes in Patagonia. Some of these lakes have produced large (?106 m3) Glacial Lake Outburst Floods (GLOFs) damaging inhabited areas. GLOF hazard studies in Patagonia have been mainly based on the analysis of short-term series (?50 years) of flood data and until now no attempt has been made to identify the relative susceptibility of lakes to failure. Power schemes and associated infrastructure are planned for Patagonian basins that have historically been affected by GLOFs, and we now require a thorough understanding of the characteristics of dangerous lakes in order to assist with hazard assessment and planning. In this paper, the conditioning factors of 16 outbursts from moraine dammed lakes in Patagonia were analysed. These data were used to develop a classification scheme designed to assess outburst susceptibility, based on image classification techniques, flow routine algorithms and the Analytical Hierarchy Process. This scheme was applied to the Baker Basin, Chile, where at least 7 moraine-dammed lakes have failed in historic time. We identified 386 moraine-dammed lakes in the Baker Basin of which 28 were classified with high or very high outburst susceptibility. Commonly, lakes with high outburst susceptibility are in contact with glaciers and have moderate (>8°) to steep (>15°) dam outlet slopes, akin to failed lakes in Patagonia. The proposed classification scheme is suitable for first-order GLOF hazard assessments in this region. However, rapidly changing glaciers in Patagonia make detailed analysis and monitoring of hazardous lakes and glaciated areas upstream from inhabited areas or critical infrastructure necessary, in order to better prepare for hazards emerging from an evolving cryosphere.

Iribarren Anacona, P.; Norton, K. P.; Mackintosh, A.

2014-07-01

135

The Last Glacial Maximum at 44°S documented by a 10Be moraine chronology at Lake Ohau, Southern Alps of New Zealand  

NASA Astrophysics Data System (ADS)

Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ˜26,500-˜19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the 'local LGM' (LLGM). We used 10Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr-1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ˜520 m and ˜3.6 °C, respectively, between ˜18,000 and ˜13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed southern LLGM is that southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.

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

2013-02-01

136

New Geomorphic map of SW Fraser Lowland, NW Washington, Shows Multiple Post-LGM Moraines, Fossil Shorelines, Outburst Flood and Glacial Outwash Features  

NASA Astrophysics Data System (ADS)

We have interpreted a ~1 pulse/m2 lidar survey (acquired in 2006 in leaf-on conditions under contract to the USGS) to construct a geomorphic map of western Whatcom County. The new lidar data reveal the existence of previously unrecognized landforms. Within this landscape, we see these features that reflect a rich post-LGM history: Glacial: Ice contact deposits interpreted as moraines reveal at least 8 successive moraines associated with the late Pleistocene Fraser Glaciation. At least two of the moraine crests were formed during ice re- advance; others may mark stillstands during ice retreat. All are older than about 10,250 14C yrs BP, based on basal peat from a kettle in outwash associated with the youngest moraine. Marine: Extensive and successive fossil shorelines, wave-cut notches, wave-washed surfaces, down- slope truncation of gullies, and deltas along the fringe of uplands surrounding the SW Fraser Lowland document former relative sea level and probable glacioisostatic tilting. The highest shorelines are at nearly 150 m above sea level. Some shorelines are cut into moraines, while others are truncated by them. Uplifted back-beach surfaces of likely mid-Holocene age at Birch Bay and Neptune Beach (elevations ~1 m and ~3 m higher than modern back-beach surfaces) suggest Holocene uplift. Glaciofluvial: Large, stepped, sediment wave bed-forms, with wavelengths of 430 to 850 m and heights from 1 to 3.5 m, record deposition associated with high discharge and rapid water release. Sub-parallel, narrow scour troughs are up to 4 km in length and 8 m in depth. These high energy geomorphic features record at least three large discharge events. Their apparent associations with former ice margins indicate that they are the result of outburst floods. Multiple outwash surfaces in the lowland are also related to former ice margins. Fluvial: At present the Nooksack River flows west from the town of Everson and reaches Bellingham Bay just south of Ferndale. Relatively low channel gradient, absence of incised valley walls west of Everson, and some archaeologic data suggests that the Nooksack formerly drained north from the town of Everson, via Sumas, into the Fraser River. Human activity: Modified land surfaces include river levees, highways, railways, and sea walls. Confinement of the modern Nooksack River has reduced depositional compensation for ongoing subsidence and led to net loss of surface elevation.

Easterbrook, D. J.; Kovanen, D. J.; Haugerud, R. A.

2008-12-01

137

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

USGS Publications Warehouse

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.

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

2013-01-01

138

Glimpses of the Ice Age from I-81  

NSDL National Science Digital Library

This United States Geological Survey (USGS) publication is part of a series entitled "Geologic Wonders of the George Washington and Jefferson National Forests". The article covers an area from Strasburg to Harrisonburg, Virginia along I-81 that shows evidence of glaciation. A description of the Ice Age, block fields and how they formed, and uses of block fields are discussed. Additional reading resources are also suggested.

139

The Little Ice Age: Understanding Climate and Climate Change  

NSDL National Science Digital Library

This is a classroom activity about the forcing mechanisms for the most recent cold period: the Little Ice Age (1350-1850). Students receive data about tree ring records, solar activity, and volcanic eruptions during this time period. By comparing and contrasting time intervals when tree growth was at a minimum, solar activity was low, and major volcanic eruptions occurred, they draw conclusions about possible natural causes of climate change and identify factors that may indicate climate change.

Lisa Gardiner

140

Radiocarbon in tropical tree rings during the Little Ice Age  

Microsoft Academic Search

Cross-dated tree-ring cores (Pinus merkusii) from north-central Thailand, spanning AD 1620–1780, were used to investigate atmospheric 14C for the tropics during the latter part of the Little Ice Age. In addition, a cross-dated section of Huon pine from western Tasmania, covering the same period of time, was investigated. A total of 16 pairs of decadal samples were extracted to alpha-cellulose

Q. Hua; M. Barbetti; U. Zoppi; D. Fink; M. Watanasak; G. E Jacobsen

2004-01-01

141

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

142

Recent Ice Ages on Mars: The Role of Radiatively Active Clouds and Cloud Microphysics  

E-print Network

-dependent sublimation of ice from the uppermost ice mantle, and forming a protective dust Copyright 2014 by the American] of these layered deposits. Assuming the same climate system and initial ice reser- voirs (polar caps) as on presentRecent Ice Ages on Mars: The Role of Radiatively Active Clouds and Cloud Microphysics J

Madeleine, Jean-Baptiste

143

The present flora and vegetation of the moraines of the Klutlan Glacier, Yukon Territory, Canada: A study in plant succession*1  

NASA Astrophysics Data System (ADS)

The flora and vegetation of six ice-cored moraines of the Klutlan Glacier were analyzed in 65 plots by European plant-sociological techniques. The age of each plot was estimated from annual growth rings of shrubs or trees in the plots. Nine major vegetation types are distinguished: Crepis nana, Dryas drummondii, Hedysarum mackenzii, Hedysarum-Salix, Salix-Shepherdia canadensis, Picea-Salix, Picea-Arctostaphylos, Picea-Ledum, and Picea-Rhytidium. These contain plants aged 2-6, 9-23, 10-20, 24-30, 32-58, 58-80, 96-178, 177-240, and >163- >339 yr, respectively. Six other vegetation types are described from windthrow areas, drainage channels, volcanic tephra slopes, lake margins, fens, and drained lakes. The major vegetation types reflect a vegetational succession related to moraine age and stability, with the Crepis nana type as the pioneer vegetation developing through the other vegetation types to the Picea-Rhytidium type on the oldest moraines. Changes in species diversity and soil development, particularly humus accumulation, parallel the vegetational succession. This succession differs from patterns of revegetation of deglaciated landscapes in Alaska and British Columbia today and in Minnesota in late-Wisconsin times because of differences in climate, plant migration, and local ecology.

Birks, H. J. B.

1980-07-01

144

Little Ice Age subsidence and post Little Ice Age uplift at Juneau, Alaska, inferred from dendrochronology and geomorphology  

Microsoft Academic Search

Application of dendrochronology and geomorphology to a recently emerged coastal area near Juneau, Alaska, has documented a Little Ice Age (LIA) sea-level transgression to 6.2 m above current sea level. The rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century, based on a sea-cliff eroded into late-Pleistocene glaciomarine sediments.

Roman J Motyka

2003-01-01

145

Spatial pattern of mass loss processes across the Greenland Ice Sheet from the Little Ice Age to 2010  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet loses mass through surface meltwater runoff and discharge from marine terminating outlet glaciers. The spatial variability and magnitude of these processes have been studied and described in detail for the past decades. Here, we combine the mass loss between the LIA to 2010 with a SMB model extending back to ~1900 in order to investigate the spatial distribution of mass loss processes. We use high quality aerial stereo photogrammetric imagery recorded between 1978 and 1987 to map morphological features such as trim lines and end moraines marking the maximum ice extent of the LIA, which enables us to obtain vertical point-based differences associated with former ice extent. These point measurements are combined with contemporary ice surface differences derived using NASA's Airborne Topographic Mapper (ATM) from 2003-2010, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) from 2003-2009, NASA's Land, Vegetation, and Ice Sensor (LVIS) from 2010, and ASTER (Silcast AST14DMO) co-registered to ICESat, to estimate mass loss throughout the 20th and early 21st Century. The mass balance estimates of the GrIS since retreat from maximum LIA is combined with a SMB model for the period for three intervals, LIAmax (~1900) - 1978/87, 1978/87 - 2003, and 2003 - 2010. Across the GrIS the total mass loss if found to be spatially- and temporally variable. However, when assessing the mass loss due to SMB and mass loss due to dynamic ice loss, we find that that the ratios between these components are variable between the different sectors of the GrIS, e.g. in the southeast sector of the GrIS we find substantial mass loss, possibly driven by high precipitation rates but also the presence of a large number of marine terminating glaciers. Furthermore many areas currently undergoing changes correspond to those that experienced considerable thinning throughout the 20th century. Consequently, comparing the 20th century thinning pattern to that of the last decade, and assuming a similar warming pattern, we argue that the present sensitivity distribution will hold also for future ice sheet mass loss until marine outlet glaciers become grounded.

Kjaer, K.; Korsgaard, N. J.; Kjeldsen, K. K.; Bjork, A. A.; Khan, S. A.; Funder, S.; Nuth, C.; Larsen, N. K.; Vinther, B.; Andresen, C. S.; Long, A. J.; Woodroffe, S.; Hansen, E. S.; Odgaard, B. V.; Olsen, J.; Bamber, J. L.; van den Broeke, M. R.; Box, J. E.; Willerslev, E.

2013-12-01

146

Spatial and temporal characteristics of the Little Ice Age: The Antarctic ice-core record  

SciTech Connect

Recently, ice core records from both hemispheres, in conjunction with other proxy records (e.g., tree rings, speleothems and corals), have shown that the Little Ice Age (LIA) was spatially extensive, extending to the Antarctic. This paper examines the temporal and spatial characteristics of the dust and delta 18O information from Antarctic ice cores. Substantial differences exist in the records. For example, a 550-year record of delta 18O and dust concentrations from Siple Station, Antarctica suggests that, less dusty conditions prevailed from A.D. 1600 to 1830. Alternately, dust and delta 18O data from South Pole Station indicate that opposite conditions (e.g., cooler and more dusty) were prevalent during the LIA. Three additional Antarctic delta 18O records are integrated with the Siple and South Pole histories for a more comprehensive picture of LIA conditions. The records provide additional support for the LIA temperature opposition between the Antarctic Peninsula region and East Antarctica. In addition, periods of strongest LIA cooling are not temporally synchronous over East Antarctica. These strong regional differences demonstrate that a suite of spatially distributed, high resolution ice core records will be necessary to characterize the LIA in Antarctica.

Mosley-Thompson, E.; Thompson, L.G.

1992-03-01

147

Ice Ages and the Asteroid Belt: A Surprising Connection  

SciTech Connect

Oxygen isotope records preserved in glacial ice, seafloor cores and lake beds, show that the climate for the past million years has been one of a nearly continuous ice age, with short 10-20 kyr interglacials that occur every 100 kyr. (All of civilization has developed during the current interglacial.) Spectral analysis shows narrow peaks that imply the cycles are astronomically driven, but the spectrum is incompatible with the climate 'standard model' -- otherwise known as Milankovitch theory. An alternative theory attributes the cycles to the Earth's orbital changes, and the resulting variations in the influx of extraterrestrial dust which originates in the asteroid belt. Recent measurements of dust influx verify a prediction of this new model.

Muller, Richard A. (Lawrence Berkeley Lab) [Lawrence Berkeley Lab

2001-05-23

148

Tree-ring-based reconstructions of North American glacier mass balance through the Little Ice Age — Contemporary warming transition  

NASA Astrophysics Data System (ADS)

Glacier mass-balance reconstructions provide a means of placing relatively short observational records into a longer-term context. In western North America, mass-balance records span four to five decades and capture a relatively narrow window of glacial behavior over an interval that was dominated by warming and ablation. We use temperature- and moisture-sensitive tree-ring series to reconstruct annual mass balance for six glaciers in the Pacific Northwest and Alaska. Mass-balance models rely on the climatic sensitivity of tree-ring chronologies and teleconnection patterns in the North Pacific. The reconstructions extend through the mid to latter portions of the Little Ice Age (LIA) and explore the role of climate variability in forcing mass balance across multiple environmental gradients. Synchronous positive mass-balance intervals coincide with regional moraine building and solar minima, whereas differences in LIA glacier behavior are related to synoptic climate forcing. Secular warming in the late 19th century to present corresponds with the only multi-decadal intervals of negative mass balance in all glacier reconstructions. This suggests that contemporary retreat in western North America is unique with respect to the last several centuries and that regional patterns of glacier variability are now dominated by global climate forcing.

Malcomb, Nathan L.; Wiles, Gregory C.

2013-03-01

149

Multiple ice-age refugia in Pacific cod, Gadus macrocephalus.  

PubMed

Pleistocene ice-ages greatly influenced the historical abundances of Pacific cod, Gadus macrocephalus, in the North Pacific and its marginal seas. We surveyed genetic variation at 11 microsatellite loci and mitochondrial (mt) DNA in samples from twelve locations from the Sea of Japan to Washington State. Both microsatellite (mean H = 0.868) and mtDNA haplotype (mean h = 0.958) diversities were large and did not show any geographical trends. Genetic differentiation between samples was significantly correlated with geographical distance between samples for both microsatellites (FST = 0.028, r(2) = 0.33) and mtDNA (FST = 0.027, r(2) = 0.18). Both marker classes showed a strong genetic discontinuity between northwestern and northeastern Pacific populations that likely represents groups previously isolated during glaciations that are now in secondary contact. Significant differences appeared between samples from the Sea of Japan and Okhotsk Sea that may reflect ice-age isolations in the northwest Pacific. In the northeast Pacific, a microsatellite and mtDNA partition was detected between coastal and Georgia Basin populations. The presence of two major coastal mtDNA lineages on either side of the Pacific Ocean basin implies at least two ice-age refugia and separate postglacial population expansions facilitated by different glacial histories. Northward expansions into the Gulf of Alaska were possible 14-15 kyr ago, but deglaciation and colonization of the Georgia Basin probably occurred somewhat later. Population expansions were evident in mtDNA mismatch distributions and in Bayesian skyline plots of the three major lineages, but the start of expansions appeared to pre-date the last glacial maximum. PMID:20819160

Canino, Michael F; Spies, Ingrid B; Cunningham, Kathryn M; Hauser, Lorenz; Grant, W Stewart

2010-10-01

150

High-precision 10Be chronology of moraines in the Southern Alps indicates synchronous cooling in Antarctica and New Zealand 42,000 years ago  

NASA Astrophysics Data System (ADS)

Millennial-scale temperature variations in Antarctica during the period 80,000 to 18,000 years ago are known to anti-correlate broadly with winter-centric cold-warm episodes revealed in Greenland ice cores. However, the extent to which climate fluctuations in the Southern Hemisphere beat in time with Antarctica, rather than with the Northern Hemisphere, has proved a controversial question. In this study we determine the ages of a prominent sequence of glacial moraines in New Zealand and use the results to assess the phasing of millennial climate change. Forty-four 10Be cosmogenic surface-exposure ages of boulders deposited by the Pukaki glacier in the Southern Alps document four moraine-building events from Marine Isotope Stage 3 (MIS 3) through to the end of the Last Glacial Maximum (?18,000 years ago; LGM). The earliest moraine-building event is defined by the ages of nine boulders on a belt of moraine that documents the culmination of a glacier advance 42,000 years ago. At the Pukaki locality this advance was of comparable scale to subsequent advances that, from the remaining exposure ages, occurred between 28,000 and 25,000, at 21,000, and at 18,000 years ago. Collectively, all four moraine-building events represent the LGM. The glacier advance 42,000 years ago in the Southern Alps coincides in Antarctica with a cold episode, shown by the isotopic record from the EPICA Dome C ice core, between the prominent A1 and A2 warming events. Therefore, the implication of the Pukaki glacier record is that as early as 42,000 years ago an episode of glacial cold similar to that of the LGM extended in the atmosphere from high on the East Antarctic plateau to at least as far north as the Southern Alps (?44°S). Such a cold episode is thought to reflect the translation through the atmosphere and/or the ocean of the anti-phased effects of Northern Hemisphere interstadial conditions to the southern half of the Southern Hemisphere. Regardless of the mechanism, any explanation for the cold episode at 42,000 years ago must account for its widespread atmospheric footprint not only in Antarctica but also within the westerly wind belt in southern mid-latitudes.

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

2014-11-01

151

A high glacier opens a view of the ice age tropics  

SciTech Connect

This article discusses new information about the ice age tropics as cores from a mountain glacier in the Peruvian Andes are analysed. Chemical markers in the ice of the two cores (160 and 166 meters long), covering 20,000 years, are starting to provide detailed support for understanding the ice age in the tropics. they show that climate in the tropics experience sharp oscillations at the end of the ice ages as it did in more northerly regions. Information about El Ninos and how the tropics respond to global climate changes is forthcoming. Comments on the actual expedition to obtain the ice cores are included.

Mlot, C.

1995-07-07

152

Geomorphic influences of the Little Ice Age glacial advance on selected hillslope systems in Nordfjord, Western Norway (Erdalen and Bødalen valleys)  

NASA Astrophysics Data System (ADS)

Hillslopes in glacially formed landscapes are typically characterized by talus cones developed beneath free rock faces. Studying hillslopes as sedimentary source, storage and transfer zones as well as surface processes acting on hillslopes since the end of the deglaciation is of importance in order to gain a better understanding of the complex sedimentary source-to-sink fluxes in cold climate environments. Hillslopes function as a key component within the geomorphic process response system. Large areas of the Norwegian fjord landscapes are covered by hillslopes and are characterized by the influences of the glacial inheritance. This PhD project is part of the NFR funded SedyMONT-Norway project within the ESF TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) programme. The focus of this study is on geomorphic influences of the Little Ice Age glacial advance on postglacial hillslope systems in four distinct headwater areas of the Erdalen and Bødalen valleys in the Nordfjord valley-fjord system (inner Nordfjord, Western Norway). Both valleys can be described as steep, U-shaped and glacier-fed, subarctic tributary valleys. Approximately 14% of the 49 km2 large headwater areas of Erdalen are occupied by hillslope deposits and 41% by rock surfaces; in Bødalen hillslope deposits occupy 12% and rock surfaces occupy 38% of the 42 km2 large headwater areas. The main aims of this study are (i) to analyze and compare the morphometric characteristics as well as the composition of hillslope systems inside and outside of the Little Ice Age glacial limit, (ii) to detect possible changes within the mass balances of these hillslope systems, (iii) to identify the type and intensity of currently acting hillslope processes as well as (iv) to determine possible sediment sources and delivery pathways within the headwater areas of the catchments. The process-based approach includes orthophoto- and topographical map interpretation, hillslope profile surveying, photo monitoring, geomorphological mapping as well as GIS and DEM computing. Two appropriate hillslope test sites within each headwater area are selected in order to follow the main aims of this study. The designed monitoring instrumentation of the slope test sites includes nets for collecting freshly accumulated rockfall debris, stone tracer lines for measuring surface movements, wooden sticks for monitoring of slow surface creep movements and peg lines for depth-integrated measurements of slow mass movements. In addition, remote site cameras for monitoring rapid mass movement events (avalanches, slush- and debris flows) and slope wash traps for analyzing slope wash denudation are installed and measurements of solute concentrations at small hillslope drainage creeks for investigating the role of chemical denudation are conducted. Measurements of morphometric characteristics and longitudinal profiles along the main axis of the talus cones are carried out at each test site. The manually obtained longitudinal profile data are combined with data derived from a DEM in order to generate complete longitudinal hillslope profiles reaching from the apex until the slope foot. Preliminary results show a steepening trend of the talus cones located inside the Little Ice Age glacier limit which is due to erosion during the Little Ice Age glacial advance. In addition, some of these talus cones are characterized by a recognizable more complex talus cone morphometry and composition, resulting from implementation of Little Ice Age glacier side moraines. The combination of (i) steepened talus cones and (ii) complex composition seems to increase currently acting hillslope processes which leads to a higher sediment delivery from these slopes as compared to hillslopes outside the Little Ice Age glacier limit. The implementation of moraine material but also the increased intensity of denudative processes has a recognizable influence on the mass balance of the hillslope systems inside the Little Ice Age glacier limit. Research on the complex developmen

Laute, Katja; Beylich, Achim A.

2010-05-01

153

Spatial and temporal variations in the age structure of Arctic sea ice  

USGS Publications Warehouse

Spatial and temporal variations in the age structure of Arctic sea ice are investigated using a new reverse chronology algorithm that tracks ice-covered pixels to their location and date of origin based on ice motion and concentration data. The Beaufort Gyre tends to harbor the oldest (>10 years old) sea ice in the western Arctic while direct ice advection pathways toward the Transpolar Drift Stream maintain relatively young (10 years old (10+ year age class) were observed during 1989-2003. Since the mid-1990s, losses to the 10+ year age class lacked compensation by recruitment due to a prior depletion of all mature (6-10 year) age classes. Survival of the 1994 and 1996-1998 sea ice generations reestablished most mature age classes, and thereby the potential to increase extent of the 10+ year age class during the mid-2000s.

Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

2005-01-01

154

Extremely eroded or incredibly young - 10Be depth profile dating of moraines in the Swiss Midlands  

NASA Astrophysics Data System (ADS)

During the Pleistocene, glaciers advanced repeatedly from the Alps into the Swiss Midlands. The exact extent and timing are still under debate, even for the last glacial advances. Decalcification depths, for example, increase from west to east in the western Swiss Midlands and have been interpreted to indicate that the Valais (Rhone) glacier may have been less extensive during the global Last Glacial Maximum (LGM) at 20 ka than assumed so far [1]. In an attempt to provide more quantitative age control, we applied 10Be depth profile dating [2] on moraines at two locations. Steinhof has previously been dated to the global LGM based on exposure ages from four boulders [3], and Niederbuchsiten presumably lies outside the last glacial ice extent [1]. The 10Be concentrations at both sites decrease consistently with depth, but are very similar. Assuming only a few decimeters of erosion since moraine deposition, we obtain apparent exposure ages of ~20 ka. Niederbuchsiten would thus be unexpectedly young, implying a much more extensive extent of the LGM glacier than assumed so far. Alternatively, if the till at Niederbuchsiten was deposited during or before the penultimate glaciation (>130 ka), the surprisingly low 10Be concentrations indicate several meters of erosion during the last glacial cycle and/or the Holocene, which seems to be at odds with the deep and intensive soil formation. References: [1] Bitterli et al. (2011) Geologischer Atlas der Schweiz, Blatt 1108. [2] Hidy et al. (2010) Geochem. Geophys. Geosyst. 11, doi:10.1029/2010GC003084. [3] Ivy- Ochs et al. (2004) Ecl. Geol. Helv. 97, 47-55.

Wüthrich, Lorenz; Zech, Roland; Haghipour, Negar; Gnägi, Christian; Christl, Markus; Ivy-Ochs, Susan; Veit, Heinz

2014-05-01

155

Paleoclimatology: Second clock supports orbital pacing of the ice ages  

SciTech Connect

For a while, it looked as if a water-filled crack in the Nevada desert might doom the accepted explanation of the ice ages. Twenty years ago, the so-called astronomical theory had carried the day. Oceanographers had found evidence implying that the march of ice ages over the last million years was paced by the cyclical stretching and squeezing of Earth`s orbit around the sun, which would have altered the way sunlight fell on the planet`s surface. But in 1988, researchers scuba diving in Nevada`s Devils Hole came up with a climate record--captured in carbonate deposits in the crack-that seemed to contradict this chronology. This article discusses the findings and the puzzles that still remain. The records of sea-level change in Barbados coral appear to be right and the astronomical theory is on solid ground using a new clock based on the radioactive decay of uranium-235 to protactinium-231. However, the Devils Hole record also seems to be correct.

Kerr, R.A.

1997-05-02

156

Distribution and trends in Arctic sea ice age through spring 2011  

NASA Astrophysics Data System (ADS)

Analysis of a satellite-derived record of sea ice age for 1980 through March 2011 shows continued net decrease in multiyear ice coverage in the Arctic Ocean, with particularly extensive loss of the oldest ice types. The fraction of total ice extent made up of multiyear sea ice in March decreased from about 75% in the mid 1980s to 45% in 2011, while the proportion of the oldest ice declined from 50% of the multiyear ice pack to 10%. These losses in the oldest ice now extend into the central Arctic Ocean and adjacent to the Canadian Archipelago; areas where the ice cover was relatively stable prior to 2007 and where long-term survival of sea ice through summer is considered to be most likely. Following record-minimum multiyear ice coverage in summer 2008, the total multiyear ice extent has increased to amounts consistent with the negative trend from 2001-2006, with an increasing proportion of older ice types. This implies some ability for the ice pack to recover from extreme conditions. This recovery has been weakest in the Beaufort Sea and Canada Basin though, with multiyear ice coverage decreasing by 83% from 2002 to 2009 in the Canada Basin, and with more multiyear ice extent now lost in the Pacific sector than elsewhere in the Arctic Ocean.

Maslanik, James; Stroeve, Julienne; Fowler, Charles; Emery, William

2011-07-01

157

Glacier retreat since the Little Ice Age in the eastern Nyainqêntanglha Range, southeastern Tibet  

NASA Astrophysics Data System (ADS)

The remote eastern Nyainqêntanglha Range in southeastern Tibet is situated in a transition zone between warm-wet subtropical and cold-dry plateau climate conditions. In this high mountain environment, intense summer monsoon rainfalls support numerous temperate glaciers despite the latitude of ~29° to ~31°N. Due to the outstanding importance of the monsoonal airmasses for the water cycle of the whole region, it is a key area to study climate and subsequent glacier change in High Asia. Here, we present the results of a study in which 1964 glaciers were mapped by remote sensing from a Landsat ETM+ scene and subsequently parameterized by DEM supported measurements. Geomorphological evidence, such as glacier trimlines and latero-frontal moraines, was used to delineate the Little Ice Age (LIA) maximum glacier advance terminus positions. Statistical analysis of glacier length change revealed an average retreat of ~40 % and a trend towards stronger retreat for smaller glaciers. Calculated ELAs show a southeast-northwest gradient ranging from 4,400 to 5,600 m a.s.l. and an average ELA rise of ~98 m since the LIA. Due to the large amount of measurements the ELA distribution reveals topographic effects down to the catchment scale, i.e. orographic rainfall and leeward shielding. This gives numerous hints on the relief-climate-glacier interactions and allows a simplified reconstruction of the flow patterns of the monsoonal air masses. Contrasting to the expectations for subtropical settings, glaciers on south facing slopes have not retreated strongest and ELAs on south facing slopes did not rise furthest. Instead, highly heterogeneous spatial patterns emerge that show a strong imprint of both, topography and monsoonal dynamics. Our results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings due to the coincidence of accumulation and ablation phases. First, monsoon intensity directly controls the amount of precipitation and additionally influences temperature through cloud cover. Second, many glaciers in the study area have steep upper accumulation areas. In these settings, temperature rise rapidly reduces the size of the accumulation areas. Additionally, the larger portion of precipitation that is falling as rain instead of snow results in increased melting through lowered albedos and the effects of liquid water in the glacier system.

Loibl, David; Grießinger, Jussi; Lehmkuhl, Frank

2014-05-01

158

Can a Little Ice Age Signal Be Found in the Southern Alps of New Zealand?  

Microsoft Academic Search

The Little Ice Age (LIA) was a late Holocene interval of climate cooling registered in the North Atlantic region by expansion of alpine glaciers and sea ice. Here the LIA includes an early phase from about AD 1280 to AD 1390, along with a main phase from about AD 1550 to AD 1860, followed by warming and ice retreat. It

J. L. Black; K. A. Maasch; B. A. Halteman

2001-01-01

159

The WAIS Divide deep ice core WD2014 chronology - Part 1: Methane synchronization (68-31 ka BP) and the gas age-ice age difference  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age-ice age difference (?age) using a combination of firn densification modeling, ice-flow modeling, and a data set of ?15N-N2, a proxy for past firn column thickness. The largest ?age at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu Cave speleothem record. The small ?age at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Buizert, C.; Cuffey, K. M.; Severinghaus, J. P.; Baggenstos, D.; Fudge, T. J.; Steig, E. J.; Markle, B. R.; Winstrup, M.; Rhodes, R. H.; Brook, E. J.; Sowers, T. A.; Clow, G. D.; Cheng, H.; Edwards, R. L.; Sigl, M.; McConnell, J. R.; Taylor, K. C.

2015-02-01

160

Crystal size variations in Eemian-age ice from the GRIP ice core, Central Greenland  

Microsoft Academic Search

Continuous measurements of ice crystal size have been carried out on an 80 m sequence between 2790 and 2870 m depth in the GRIP ice core from Central Greenland. The ice in this interval is at present considered to orginate from the Eemian interglacial period. The record reveals that the crystal size in ice older than 100,000 yr is highly

Thorsteinn Thorsteinsson; Josef Kipfstuhl; Hajo Eicken; Sigfus J. Johnsen; Katrin Fuhrer

1995-01-01

161

Ice Age Epochs and the Sun's Path Through the Galaxy  

E-print Network

We present a calculation of the Sun's motion through the Milky Way Galaxy over the last 500 million years. The integration is based upon estimates of the Sun's current position and speed from measurements with Hipparcos and upon a realistic model for the Galactic gravitational potential. We estimate the times of the Sun's past spiral arm crossings for a range in assumed values of the spiral pattern angular speed. We find that for a difference between the mean solar and pattern speed of Omega_Sun - Omega_p = 11.9 +/- 0.7 km/s/kpc the Sun has traversed four spiral arms at times that appear to correspond well with long duration cold periods on Earth. This supports the idea that extended exposure to the higher cosmic ray flux associated with spiral arms can lead to increased cloud cover and long ice age epochs on Earth.

Gies, D R

2005-01-01

162

Climate Discovery Teacher's Guide: The Little Ice Age Case Study  

NSDL National Science Digital Library

In this unit, students explore how scientists study climates of the past by modelling their methods through inquiry activities and investigating real data. The lessons address the difference between weather and climate, direct and indirect evidence of climate change, and natural indicators of climate such as tree rings. They will also examine what conditions were like in the 'Little Ice Age', a period of unusually cool conditions that occurred between 1300 and 1850 A.D. A lesson on glaciers uses imagery to show how they respond to climate change, and a lesson on sunspots uses real data to show the connection between sunspot activity and terrestrial climate. There is also a lesson on the effect of volcanism on climate and a summary activity that brings together all these concepts to draw conclusions about possible natural causes of climate change.

2007-12-12

163

Ice Age Epochs and the Sun's Path Through the Galaxy  

E-print Network

We present a calculation of the Sun's motion through the Milky Way Galaxy over the last 500 million years. The integration is based upon estimates of the Sun's current position and speed from measurements with Hipparcos and upon a realistic model for the Galactic gravitational potential. We estimate the times of the Sun's past spiral arm crossings for a range in assumed values of the spiral pattern angular speed. We find that for a difference between the mean solar and pattern speed of Omega_Sun - Omega_p = 11.9 +/- 0.7 km/s/kpc the Sun has traversed four spiral arms at times that appear to correspond well with long duration cold periods on Earth. This supports the idea that extended exposure to the higher cosmic ray flux associated with spiral arms can lead to increased cloud cover and long ice age epochs on Earth.

D. R. Gies; J. W. Helsel

2005-03-14

164

The possible role of Brazilian promontory in Little Ice Age  

NASA Astrophysics Data System (ADS)

The Gulf Stream, one of the strongest currents in the world, transports approximately 31 Sv of water (Kelly and Gille, 1990; Baringer and Larsen, 2001; Leaman et al., 1995) and 1.3 × 1015 W (Larsen, 1992) of heat into the Atlantic Ocean, and warms the vast European continent. Thus any change of the Gulf Stream could lead to the climate change in the European continent, and even worldwide (Bryden et al., 2005). Past studies have revealed a diminished Gulf Stream and oceanic heat transport that was possibly associated with a southward migration of intertropical convergence zone (ITCZ) and may have contributed to Little Ice Age (AD ?1200 to 1850) in the North Atlantic (Lund et al., 2006). However, the causations of the Gulf Stream weakening due to the southward migration of the ITCZ remain uncertain. Here we use satellite observation data and employ a model (oceanic general circulation model - OGCM) to demonstrate that the Brazilian promontory in the east coast of South America may have played a crucial role in allocating the equatorial currents, while the mean position of the equatorial currents migrates between northern and southern hemisphere in the Atlantic Ocean. Northward migrations of the equatorial currents in the Atlantic Ocean have little influence on the Gulf Stream. Nevertheless, southward migrations, especially abrupt large southward migrations of the equatorial currents, can lead to the increase of the Brazil Current and the significant decrease of the North Brazil Current, in turn the weakening of the Gulf Stream. The results from the model simulations suggest the mean position of the equatorial currents in the Atlantic Ocean shifted at least 180-260 km southwards of its present-day position during the Little Ice Age based on the calculations of simple linear equations and the OGCM simulations.

Zou, Youjia; Xi, Xiangying

2014-09-01

165

Seismic reflection study of recessional moraines beneath Lake Superior and their relationship to regional deglaciation  

USGS Publications Warehouse

Approximately 8000 km of continuous seismic reflection profiles throughout Lake Superior were examined for evidence of recessional moraines and other ice-margin deposits associated with the retreat of late Wisconsin ice. These features are correlated with the record of glacial-lake evolution in western Lake Superior. An offlapping sequence of glacial and glacial-lacustrine dediments overlying bedrock is recognized in west-central Lake Superior that is progressively younger to the northeast. The sequence underlies more recent glaical-lacustrine and postglacial sediments. Four facies are recognized on the basis of geomorphologic and acoustic properties and are interpreted to represent a southwest-to-northeast assemblage of: proglacial stratified drift (facies A), drift in major end moraines (facies B), till deposited as glacial retreat resumed, or possibly late-stage ablation till (facies C), and basal till (facies D). The prominent moraines of facies B are unusually thick and are believed to mark the ice-margin shorelines of successive major proglacial lakes that formerly occupied parts of western Lake Superior. The moraines are tentatively correlated with Glacial Lake Duluth (unit 1), Glacial Lake Washburn (unit 2), and Glacial Lake Beaver Bay (unit 3), the most prominent of lakes drained via the progressively lower outlets via the Moose Lake/ Brule-St. Croix Rivers, the Huron Mountains, and the Au Train-Whitefish regions, respectively. ?? 1982.

Landmesser, C.W.; Johnson, T.C.; Wold, R.J.

1982-01-01

166

Is the Charlottenthal fan (marginal zone of the Pomeranian phase, NE Germany) an end moraine?  

NASA Astrophysics Data System (ADS)

The maximum ice-sheet extent of a glaciation or glacial phase is in most cases indicated by the position of end moraines. In some cases, however, the maximum extent of the ice sheet is indicated by a fan which represents the transitional zone between the end moraine and the proximal outwash plain (sandur). Such a fan from the Pomeranian phase near Charlottenthal in NE Germany has been investigated for its lithofacies, and the depositional mechanisms of the two sedimentary environments (end moraine and outwash plain) are reconstructed. The Charlottenthal profle is not characteristic in a sedimentological sense of a typical marginal end moraine or a sandur. The deposits represent subaerial debris flows, sheet floods and channelized currents, which are typically processes for transitional fan. Gravel samples from the till complex show typical Weichselian till compositions. These till compositions indicate a general transport direction from North to South, which is consistent with the known movement of the ice sheet during the Pomeranian phase of the Weichselian.

Pisarska-Jamro?y, Ma?gorzata; Börner, Andreas

2011-04-01

167

Cosmogenic Be-10 Dating of Moraine in Tianshan, Central Asia  

NASA Astrophysics Data System (ADS)

The Tianshan mountain area is located towards the center of the Eurasian continent and is one of the driest regions in the world. Studies of glacial history in this region is especially important because it is far from the climatic key area of the North Atlantic, thus could better manifest interlink between ocean, atmosphere and terrestrial systems. Relating glacial advances in the extreme-continental environment to abrupt climatic changes initiated in the North Atlantic area which cannot be attributed directly to orbital forcing may especially improve the fundamental understanding of the interrelations of distinct elements of the earth climate system as well as the mechanisms underlying abrupt climate changes. Successions of well-preserved moraines are present in the Urumqi river head valley, Tianshan mountains. These moraines are relics of glacier advances and retreats during the late Quaternary. By using Be-10 surface-exposure dating of moraine boulders, we determined the timing of glacial advances in this area: ~17.7 ka, ~12.4 ka and ~8.3 ka. The first age is coincident with deglaciation after the Last Glacial Maximum (LGM) and the last two glacial advances are most likely associated with abrupt climate events after the LGM: the Younger Dryas and the 8200-year cooling event. Our results suggest a relation of glaciations in the Tianshan mountains with climate changes in the North Atlantic. The occurrence of glacial advances during abrupt climate cooling periods in the remote Eurasian continent suggests rapid linkages between ocean, atmosphere and terrestrial systems.

Kong, P.; Na, C.; Fink, D.; Huang, F.

2005-12-01

168

The whole world had a case of the ice age shivers  

SciTech Connect

There is now worldwide evidence of short-term increases in the earth's temperature during the last ice ages. This evidence comes from South American glaciers, Antarctic ice cores, and sediment cores from the tropical oceans, as well as Greenland ice cores. Researcher are unsure of the causes of these fluctuations. Some speculate a means for transmitting a climate signal from the North Atlantic to the rest of the world, while others look to some shorter-term version of the orbital variations that pace the cycle of the ice ages.

Kerr, R.A.

1993-12-24

169

Spatial and temporal variations in the age structure of Arctic sea ice  

USGS Publications Warehouse

Spatial and temporal variations in the age structure of Arctic sea ice are investigated using a new reversechronology algorithm that tracks ice-covered pixels to their location and date of origin based on ice motion and concentration data. The Beaufort Gyre tends to harbor the oldest (>10 years old) sea ice in the western Arctic while direct ice advection pathways toward the Transpolar Drift Stream maintain relatively young (???5 years) ice in the eastern Arctic. Persistent net losses (-4.2% yr-1) in extent of ice >10 years old (10+ year age class) were observed during 1989-2003. Since the mid-1990s, losses to the 10+ year age class lacked compensation by recruitment due to a prior depletion of all mature (6-10 year) age classes. Survival of the 1994 and 1996-1998 sea ice generations reestablished most mature age classes, and thereby the potential to increase extent of the 10+ year age class during the mid-2000s. Copyright 2005 by the American Geophysical Union.

Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

2005-01-01

170

The WAIS-Divide deep ice core WD2014 chronology - Part 2: Methane synchronization (68-31 ka BP) and the gas age-ice age difference  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet (WAIS)-Divide ice core (WAIS-D) is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WAIS-D gas age-ice age difference (?age) using a combination of firn densification modeling, ice flow modeling, and a dataset of ?15N-N2, a proxy for past firn column thickness. The largest ?age at WAIS-D occurs during the last glacial maximum, and is 525 ± 100 years. Internally consistent solutions can only be found when assuming little-to-no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WAIS-D chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu speleothem record. The small ?age at WAIS-D provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the bipolar "seesaw".

Buizert, C.; Cuffey, K. M.; Severinghaus, J. P.; Baggenstos, D.; Fudge, T. J.; Steig, E. J.; Markle, B. R.; Winstrup, M.; Rhodes, R. H.; Brook, E. J.; Sowers, T. A.; Clow, G. D.; Cheng, H.; Edwards, R. L.; Sigl, M.; McConnell, J. R.; Taylor, K. C.

2014-08-01

171

Timing of the East Antrim Coastal Readvance: phase relationships between lowland Irish and upland Scottish ice sheets during the Last Glacial Termination  

NASA Astrophysics Data System (ADS)

A submillennial ice readvance from upland centres of ice dispersal in west central Scotland into northeastern Ireland post-dates the retreat of lowland Irish ice immediately after the Killard Point Stadial (max. 16.5 cal ka BP). The dimensions of this southerly and westerly ice sheet readvance on the margins of the North Channel are reconstructed from subglacial bedform patterns, subglacial tectonic deformation of Tertiary lignite and glacigenic sediment, limiting moraines/outwash and glacial stratigraphy. Morainic ridges at Rams Island and Sandy Bay on the eastern margin of the Lough Neagh basin which mark this ice limit are perpendicular to a well-defined field of subglacial bedforms across east County Antrim. At the ice readvance limits glacial lakes impounded in the Lagan Valley were partially infilled with subaqueous outwash known as the Malone Sands. This water body drained south along the Dundonald/Comber Gap spillway providing sediment which formed extensive, late-glacial marine terraces at the northern end of Strangford Lough around 15-15.5 cal ka BP. The East Antrim Coastal Readvance is part of a much more extensive readvance southwards along the North Channel and adjacent lowlands associated with ice sheet reorganisation and ice sheet growth in west central Scotland. It is now termed the North Channel Readvance and may be similar in age to the Wester Ross Readvance moraines in northwestern Scotland.

McCabe, A. M.; Williams, G. D.

2012-12-01

172

The last ice sheet of the Kara Sea: Terrestrial constraints on its age  

Microsoft Academic Search

The ice dispersal features on the Siberian mainland unanimously indicate that the last ice domes were positioned on the Kara Sea shelf and adjacent coastal plains. The age of the last glacial maximum evokes much controversy. The problem may be solved by sorting out the available radiocarbon dates, both statistically and using geological common sense. Over 200 finite radiocarbon dates

Valery Astakhov

1998-01-01

173

Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks  

NASA Astrophysics Data System (ADS)

Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century-scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430-1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.

Miller, Gifford H.; Geirsdóttir, Áslaug; Zhong, Yafang; Larsen, Darren J.; Otto-Bliesner, Bette L.; Holland, Marika M.; Bailey, David A.; Refsnider, Kurt A.; Lehman, Scott J.; Southon, John R.; Anderson, Chance; Björnsson, Helgi; Thordarson, Thorvaldur

2012-01-01

174

Little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap  

Microsoft Academic Search

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that

L. G. Thompson; E. Mosley-Thompson; P. M. Grootes

1986-01-01

175

The Little Ice Age as Recorded in the Stratigraphy of the Tropical Quelccaya Ice Cap  

Microsoft Academic Search

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that

L. G. Thompson; E. Mosley-Thompson; W. Dansgaard; P. M. Grootes

1986-01-01

176

The last forests in Greenland, and the age of the ice sheet  

NASA Astrophysics Data System (ADS)

Recently ancient DNA (aDNA) studies of the basal ice in the Camp Century ice core, northern Greenland, have shown that mixed coniferous-deciduous forest grew here before the area was invaded and permanently covered by the ice sheet. The coring site is situated only 100 km from the present ice margin and more than 500 km from the ice divide, indicating that since this last inception the northern part of the ice sheet never receded more than 100 km from its present margin. Dating of the basal ice and obtaining an age for the forest and for the beginning of the ice sheet's permanency has been attempted by analyzing for optically stimulated luminescence (OSL), meteoric 10Be/36Cl cosmogenic nuclides, 234U/238U recoil. These methods all provide only minimum ages and show that the forest at Cap Century is older than 500 ka. Comparison with other Pleistocene "forest sites" in Greenland - the Kap København Formation in northernmost Greenland, the DYE-3 ice core in the south, the ODP boring 646 south of Greenland, as well as results from basal ice in the GRIP ice core - extends the minimum age to c. 1 ma. The maximum age is provided by the Kap København Formation, which must be older - or contemporaneous. The formation has recently been confirmed to date within the interval 2-2.5 ma, with a preferred age of 2.3-2.4 ma. Surprisingly, application of the molecular clock of insect COI sequences on the Camp Century aDNA now seem to push the minimum age just as far back - to 2.4 ma, suggesting that the timberline boreal forest at Kap København is contemporaneous with the mixed forest at Camp Century, 600 km to the south. From this we conclude that the northern ice sheet dome, which today contains 85% of the total ice sheet volume, has remained within 100 km of its present margin for at least 1 ma, and possibly may go back as far as 2.4 ma. The ice sheet has therefore survived both interglacials and "super interglacials" that were both warmer and longer than the present. This may give us some hope for the future.

Funder, Svend; Schmidt, Astrid M. Z.; Dahl-Jensen, Dorthe; Steffensen, Jørgen Peder; Willerslev, Eske

2014-05-01

177

El Nio's tropical climate and teleconnections as a blueprint for pre-Ice-Age Peter Molnar* and Mark A. Cane  

E-print Network

that of a typical El Niño event (1) (Fig. 1). Canada would be warmer. Ice on the Great Lakes would be thinner (21 El Niño's tropical climate and teleconnections as a blueprint for pre-Ice-Age climates Peter) were replaced by recurring ice ages. Most attempts to explain the change appeal either to changes in CO

Columbia University

178

Estimations of the age of the ice beneath Dome A, Antarctica  

NASA Astrophysics Data System (ADS)

The drilling of a deep ice core at the Chinese Kunlun station, Dome A, East Antarctica, is about to start with high expectations on obtaining the oldest possible ice so far. The Alpine type bedrock of the Gamburtsev mountains in combination with a largely undetermined geothermal heat flux distribution raises questions on the basal thermal conditions that via the melting rate have a strong feedback on the vertical flow velocity and in consequence on the age/depth horizons. Additionally, the undetermined ice fabric introducing anisotropic effects in rheology have to be taken into account. By deploying a full Stokes ice sheet model (http://elmerice.elmerfem.org) we investigate the influence of those parameters, namely anisotropy as well as geothermal heat flux values, on the spatial distribution of the age close to the bedrock. Results are compared with dated radar isochrones in the upper one third of the ice sheet. We find that a non-unique combination of parameters is able to closely reproduce those measured values, leading to the conclusion, that without additional information, the basal age beneath Kunlun station remains undetermined. However, our simulations suggest that vast spatial variation of basal melting rates and, in consequence, the age/depth distribution over a relative small domain exists, increasing the motivation for ice coring, obtaining both high resolution as well as possibly oldest ice from the same site.

Zwinger, Thomas; Sun, Bo; Liyun, Liyun; Moore, John C.; Steinhage, Daniel; Martin, Carlos

2014-05-01

179

The influence of continental ice sheets on the climate of an ice age  

Microsoft Academic Search

The climate influence of the land ice that existed 18,000 years before present (18K B.P.) is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean. Simulated climates are obtained from two versions of the model; one with the land ice distribution of the present and the other with that of 18K

S. Manabe; A. J. Broccoli

1985-01-01

180

Little Ice Age evidence from a south-central North American ice core, U.S.A.  

USGS Publications Warehouse

In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The ??18O (SMOW) profile from the core shows a -0.95??? shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the ??18O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

Naftz, D.L.; Klusman, R.W.; Michel, R.L.; Schuster, P.F.; Ready, M.M.; Taylor, H.E.; Yanosky, T.M.; McConnaughey, E.A.

1996-01-01

181

Moraine formation during an advance/retreat cycle at a temperate alpine glacier  

NASA Astrophysics Data System (ADS)

Mountain glaciers are highly sensitive to variations in temperature and precipitation, and so moraine records from such systems are strong indicators of climate change. Due to the prevailing trend of retreat of the majority of mountain glaciers globally over the last few decades, there are limited opportunities to observe moraine formation, especially at temperate alpine glaciers. In the Southern Alps of New Zealand, while glaciers have all experienced a major retreat since the late 19th century, within this loss of ice mass, there has been a distinct variance in individual glacier response. Indeed, while Tasman Glacier, the longest glacier in the Southern Alps has thinned and entered into the current phase of calving retreat in the early 1990s, the steeper, more responsive glaciers to the west of the Main Divide, such as Franz Josef and Fox Glacier have experienced more elaborate advance/retreat phases. We focus on moraine formation at Fox Glacier, a c. 12.5 km long valley glacier terminating at 300 m above sea level. Fox Glacier retreated substantially since the 1930s, before advancing 800 m between the mid-1980s and 1999. A minor retreat then followed until 2005, succeeded by a 300 m re-advance until 2007-8. Continued retreat and down-wasting has since followed. Superimposed on this alternating advance/retreat cycle, have been minor winter re-advances. Sedimentological and morphological information were combined with detailed observations, historical photos and recent time-lapse photography of the terminus. Characteristics of several modes of moraine formation have been observed: (1) the late 20th century advance culminated in a broad <5 m high terminal moraine, formed by an admixture of "bulldozed" proglacial sediments and dumping of supraglacial material; (2) the 21st century short-lived advances were characterized by 1-2 m high (often multi-crested) ridges with a "saw-tooth" plan-form controlled by longitudinal crevasses outcropping at the terminus; (3) time-lapse imagery identified thrusting and subsequent melt-out of fine-grained englacial material along reverse faults intersecting the terminal face as a significant contributor to the subdued terminal moraines forming during the most recent phase of recent recession; (4) collapse of lateral moraines due to post-2008 down-wasting is now proceeding. Overall, even short-term preservation of glacigenic sediment-landform associations on the Fox Glacier sandur is limited by the glacial meltwater regime, with lateral migration of the proglacial river continually reworking morainic material.

Brook, M.; Quincey, D.; Winkler, S.

2012-04-01

182

Ice-age Ice-sheet Rheology: Constraints from the Last Glacial Maximum Form of the Laurentide Ice Sheet  

NASA Technical Reports Server (NTRS)

State-ot-the-art thermomechanical models of the modern Greenland ice and the ancient Laurenticle ice sheet that covered Canada at the Last Glacial Maximum (LGM) are not able to explain simultaneously the observed forms of these cryospheric structures when the same, anisotropy-enhanced, version of the conventional Glen flow law is employed to describe their rheology. The LGM Laurenticle ice sheet. predicted to develop in response to orbital climate forcing, is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface-geomorphological and solid-earth-geophysical constraints. We show that if the Glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress-strain-rate relation, then the aspect ratios of both the modern Greenland ice sheet and the Laurenticle ice sheet, that existed at the LGM, are simultaneously explained with little or no retuning of the flow law.

Peltier, W. Richard; Goldsby, David L.; Kohlstedt, David L.; Tarasov, Lev

2000-01-01

183

An instability theory for the formation of ribbed moraine, drumlins and mega-scale glacial lineations.  

PubMed

We present a theory for the coupled flow of ice, subglacial water and subglacial sediment, which is designed to represent the processes which occur at the bed of an ice sheet. The ice is assumed to flow as a Newtonian viscous fluid, the water can flow between the till and the ice as a thin film, which may thicken to form streams or cavities, and the till is assumed to be transported, either through shearing by the ice, squeezing by pressure gradients in the till, or by fluvial sediment transport processes in streams or cavities. In previous studies, it was shown that the dependence of ice sliding velocity on effective pressure provided a mechanism for the generation of bedforms resembling ribbed moraine, while the dependence of fluvial sediment transport on water film depth provides a mechanism for the generation of bedforms resembling mega-scale glacial lineations. Here, we combine these two processes in a single model, and show that, depending largely on the granulometry of the till, instability can occur in a range of types which range from ribbed moraine through three-dimensional drumlins to mega-scale glacial lineations. PMID:25383019

Fowler, A C; Chapwanya, M

2014-11-01

184

94 GENE C. CARPENTER Vol. 65 A RADIOCARBON DATE FROM THE HARTWELL MORAINE,  

E-print Network

94 GENE C. CARPENTER Vol. 65 A RADIOCARBON DATE FROM THE HARTWELL MORAINE, WARREN COUNTY, OHIO on July 15, 1963. The sample was subsequently identified by Dr. George Burns and dated by Dr. J. Gordon age was determined to be 19,621±372 (OWU-102). From this date, it is obvious that "late" Wisconsin

Laughlin, Robert B.

185

Variations in the earth's orbit: pacemaker of the ice ages  

Microsoft Academic Search

Among the explanations for fluctuations in the Pleistocene ice sheets, only the orbital hypothesis has been formulated so as to predict the frequencies of major Pleistocene fluctuations. It is also the only explanation which can be tested geologically by determining what the frequencies are. All versions of the orbital hypothesis predict that the obliquity of the earth's axis and the

J. D. Hays; J. Imbrie; N. J. Shackleton

1976-01-01

186

Pre`Little Ice Age' glacier fluctuations in Garibaldi Provincial Park, Coast Mountains, British Columbia, Canada  

Microsoft Academic Search

Holocene glacier fluctuations prior to the `Little Ice Age' in Garibaldi Provincial Park in the British Columbia Coast Mountains were reconstructed from geomorphic mapping and radiocarbon ages on 37 samples of growth-position and detrital wood from glacier forefields. Glaciers in Garibaldi Park were smaller than at present in the early Holocene, although some evidence exists for minor, short-lived advances at

Johannes Koch; Gerald D. Osborn; John J. Clague

2007-01-01

187

Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice  

NASA Astrophysics Data System (ADS)

The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ?200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10-100 ky BP), despite subsequent fluctuations in climate, fire disturbance and vegetation. Radiocarbon (14C) analysis of dissolved organic carbon (DOC) in thaw waters supports ages greater than ?40 ky BP below 10 m. DOC concentrations in thaw waters increased with depth to maxima of >1000 ppm, despite little change in ice content or cryostructures. These relations suggest time-dependent production of old DOC that will be released upon permafrost thaw at a rate that is mediated by sediment transport, among other factors.

Ewing, S. A.; Paces, J. B.; O'Donnell, J. A.; Jorgenson, M. T.; Kanevskiy, M. Z.; Aiken, G. R.; Shur, Y.; Harden, J. W.; Striegl, R.

2015-03-01

188

Little Ice Age Glaciation in Alaska: A record of recent global climatic change  

SciTech Connect

General global cooling and temperature fluctuation accompanied by expansion of mountain glaciers characterized the Little Ice Age of about A.D. 1200 through A.D. 1900. The effects of such temperature changes appear first and are strongest at high latitudes. Therefore the Little Ice Age record of glacial fluctuation in Alaska may provide a good proxy for these events and a test for models of future climatic change. Holocene expansions began here as early as 7000 B.P. and locally show a periodicity of 350 years after about 4500 years B.P. The Little Ice Age followed a late Holocene interval of minor ice advance and a subsequent period of ice margin recession lasting one to seven centuries. The timing of expansions since about A.D. 1200 have often varied between glaciers, but these are the most pervasive glacial events of the Holocene in Alaska and frequently represent ice marginal maxima for this interval. At least two major expansions are, apparent in forefields of both land-terminating and fjord-calving glaciers, but the former display the most reliable and detailed climatic record. Major maxima occurred by the 16th century and into the mid-18th century. Culmination of advances occurred throughout Alaska during the 19th century followed within a few decades by general glacial retreat. Concurrently, equilibrium line altitudes have been raised 100-400 m, representing a rise of 2-3 deg C in mean summer temperature.

Calkin, P.E.; Wiles, G.C.

1992-03-01

189

Regional scale trends in the timing and magnitude of Little Ice Age glacial maxima in Europe and the North Atlantic  

NASA Astrophysics Data System (ADS)

Reconstructing the configuration of atmospheric/oceanic circulation during past climate perturbations is crucial for understanding how the climate system responds to changing forcing mechanisms. The most recent Holocene climatic perturbation, the Little Ice Age (LIA), covered the period ca AD 1200-1900 and has been widely recorded in a series of documented, early instrumental and palaeo-proxy data. Past research has used such data from the European/North Atlantic regions to elucidate the spatio-temporal distribution of heat and moisture related to possible changes in dominant modes of atmospheric/oceanic circulation such as the North Atlantic Oscillation. Despite this, interpretations of climate dynamics based on such reconstructions are often contradictory, for example in terms of constraining the prevailing position of the North Atlantic storm track. Until recently, glacial variability during the LIA has been considered somewhat separately from the large-scale climate dynamics which are thought to have characterised the period. Several recent studies have suggested that apparent asynchrony in the timing of the LIA glacial maximum between regions in Europe and the North Atlantic was controlled by shifts in large-scale oceanic/atmospheric circulation patterns. However, such interpretations have been based predominantly on single glacier comparisons and no understanding of regional-scale trends has been presented. This research aims to synthesise published data on the timing and maximum extent of glacier advances across Europe and the North Atlantic during the LIA. A standardised approach for estimating the glacier equilibrium line altitude (ELA) associated with the LIA maximum was systematically applied to digitised moraine outlines derived from the published literature. This involved using an equilibrium profile equation to reconstruct palaeo-glacier surface geometry and estimating ELA from appropriate balance ratios. ELA was reconstructed for over 150 glaciers and stored in a database alongside information relating to the timing of the LIA maximum, based on published dates using a variety of methods. An attempt was also made to correct for the lag time between glacier frontal response and the climatic drivers of glacier retreat. Trends in the timing and magnitude of the LIA glacial maximum were then mapped at a regional scale in order to analyse proposed changes to oceanic/atmospheric circulation patterns in the context of a more complete understanding of glacial variability than has been presented hitherto.

Frew, Craig R.; Rea, Brice R.; Spagnolo, Matteo; Edwards, Kevin J.; Schofield, J. Edward

2014-05-01

190

Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation  

NASA Astrophysics Data System (ADS)

Temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change and therefore of particular high interest for research on late Holocene changes of the monsoonal climate in High Asia. However, because of the remoteness of the area, the scarcity of empirical data, and the challenges to remote sensing work posed by cloud and snow cover, knowledge about the glacier dynamics and changes in this region is still very limited. In this study, we applied a remote sensing approach in which 1964 glaciers were mapped from a Landsat ETM+ scene and subsequently parameterized by DEM-supported measurements. Geomorphological evidence, i.e., trimlines and latero-frontal moraines, were used to obtain quantitative data on the glaciers' morphological characteristics and the changes since the Little Ice Age (LIA) maximum glacier advance. Statistical analysis of glacier length change revealed an average retreat of ~ 27% and a trend toward stronger retreat for smaller glaciers. An evaluation of different methods to calculate equilibrium line altitudes (ELAs) indicates that an optimized toe-to-ridge altitude method (TRAM) is more suitable than other methods in settings with complex topography and a lack of mass balance measurements. A large number of glacier measurements are crucial for high quality of TRAM results, and special attention has to be paid to different glacier characteristics. In order to determine the best-fitting TRAM ratio value and to test the quality of the calculated ELAs, a remote sensing approach was applied: for each investigated glacier, the altitudes of transient snowlines visible in the late summer Landsat scene were measured from the DEM and compared to TRAM results. The interpolated ELA results show a SE-NW gradient ranging from 4400 to 5600 m asl and an average ELA rise of ~ 136 m since the LIA. Because of the high spatial resolution of measurements, the ELA distribution reveals topographic effects down to the catchment scale, specifically orographic rainfall and leeward shielding. The interpretation of these patterns reveals that the eastern Nyainqêntanglha Range is influenced by both, the Indian (ISM) and East Asian summer monsoon (EASM). However, the EASM does not reach the western part of the study area. The results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases.

Loibl, David; Lehmkuhl, Frank; Grießinger, Jussi

2014-06-01

191

Controls on interior West Antarctic Ice Sheet Elevations: inferences from geologic constraints and ice sheet modeling  

NASA Astrophysics Data System (ADS)

Knowledge of the West Antarctic Ice Sheet (WAIS) response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future. The timing and extent of past interior WAIS elevation changes provides insight to WAIS behavior and constraints for ice sheet models. Constraints prior to the Last Glacial Maximum (LGM) however, are rare. Surface exposure ages of glacial erratics near the WAIS divide at Mt. Waesche in Marie Byrd Land, and at the Ohio Range in the Transantarctic Mountains, range from ˜10 ka to >500 ka without a dependence on elevation. The probability distribution functions (PDF) of the exposure ages at both locations, are remarkably similar. During the last glaciation, maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka. However, most exposure ages are older than the LGM and cluster around ˜40 ka and ˜80 ka. The peak in the exposure age distributions at ˜40 ka includes ages of alpine moraine boulders at Mercer Ridge in the Ohio Range. Comparison of the PDF of exposures ages from the Ohio Range and Mt. Waesche with the temperature record from the Fuji Dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the Last Glacial termination. A prominent peak in the Ohio Range PDF corresponds to the penultimate termination (stage 5e). During the intervening glacial period, there is not a consistent relationship between the peaks in the PDF at each location and temperature. A combined ice sheet/ice shelf model with forcing scaled to marine ?18O predicts that interior WAIS elevations near the ice divide have varied ˜300 m over the Last Glacial cycle. Peaks in the PDF correspond to model highstands over the last 200 ka. In the simulated elevation history, maximum ice elevations at Ohio Range (+100 m) and Mt. Waesche (+60 m) occur at ˜10 ka, in agreement with observations from these sites. During collapse of the marine portion of the WAIS, ice elevations at Ohio Range and Mt. Waesche are drawn down at least 200 m below the present ice elevation. The good correspondence between the model results and observations at both the Ohio Range and Mt. Waesche supports the conclusion that interior WAIS highstands do not occur during glacial maximums. Rather, the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials. Interior down-draw events follow highstands, resulting from the arrival of a wave of thinning triggered by retreat of the WAIS grounding line coupled with decreasing accumulation rates.

Ackert, Robert P.; Putnam, Aaron E.; Mukhopadhyay, Sujoy; Pollard, David; DeConto, Robert M.; Kurz, Mark D.; Borns, Harold W.

2013-04-01

192

Little ice age evidence from a south-central North American ice core, U.S.A.  

SciTech Connect

In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The {gamma}{sup 18}O (SMOW) profile from the core shows a -0.95{per_thousand} shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the {gamma}{sup 18}O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

Naftz, D.L. [Geological Survey, Salt Lake City, UT (United States); Klusman, R.W. [Colorado School of Mines, Golden, CO (United States); Michel, R.L. [Geological Survey, Menlo Park, CA (United States)] [and others

1996-02-01

193

Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model  

NASA Astrophysics Data System (ADS)

A new model of the last deglaciation event of the Late Quaternary ice age is here described and denoted as ICE-6G_C (VM5a). It differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available Global Positioning System (GPS) measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal. Additional space geodetic constraints have also been applied to specify the reference frame within which the GPS data are described. The focus of the paper is upon the three main regions of Last Glacial Maximum ice cover, namely, North America, Northwestern Europe/Eurasia, and Antarctica, although Greenland and the British Isles will also be included, if peripherally, in the discussion. In each of the three major regions, the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the Gravity Recovery and Climate Experiment satellites as an independent means of verifying the improvement of the model achieved by applying the GPS constraints. Several aspects of the global characteristics of this new model are also discussed, including the nature of relative sea level history predictions at far-field locations, in particular the Caribbean island of Barbados, from which especially high-quality records of postglacial sea level change are available but which records were not employed in the development of the model. Although ICE-6G_C (VM5a) is a significant improvement insofar as the most recently available GPS observations are concerned, comparison of model predictions with such far-field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration.

Peltier, W. R.; Argus, D. F.; Drummond, R.

2015-01-01

194

Cosmogenic {sup 36}Cl accumulation in unstable landforms 2. Simulations and measurements on eroding moraines  

SciTech Connect

Cosmogenic {sup 36}Cl ages of boulders from late Pleistocene moraines in Bishop Creek, Sierra Nevada, California, provided valuable details about {sup 36}Cl surface exposure dating and the nature of post depositional processes that modify glacial landforms. The natural variability of the apparent {sup 36}Cl ages among morainal boulders is due to soil erosion and gradual exposure of boulders at the surface. Two mechanisms are responsible for the resulting distributions of the apparent {sup 36}Cl ages. Variability of the initial burial depth among boulders and variability in the chemical composition of boulders from the same depth both result in different {sup 36}Cl ages due to the dependence of the depth production profile on the boulder chemistry. The authors measured cosmogenic {sup 36}Cl in boulders from a late Pleistocene moraine. The distribution of the calculated apparent ages allowed them to calculate the true age of 85 kyr and the erosion rate of 570 g cm{sup -2}. These results are in excellent agreement with independently estimated values of 87 kyr and 600 g cm{sup -2} for the age and erosion depth, respectively. These results indicate that the model satisfactorily simulates effects of erosion processes and can thus aid in surface exposure dating of eroding landforms.

Zreda, M.G.; Phillips, F.M. [New Mexico Tech., Socorro, NM (United States)] [New Mexico Tech., Socorro, NM (United States); Elmore, D. [Purdue Univ., West Lafayette, IN (United States)] [Purdue Univ., West Lafayette, IN (United States)

1994-11-01

195

Chronological framework for the deglaciation of the Lake Michigan lobe of the Laurentide ice sheet from ice-walled lake deposits  

USGS Publications Warehouse

A revised chronological framework for the deglaciation of the Lake Michigan lobe of the south-central Laurentide Ice Sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low-relief ice-walled lakes. We analyze the precision and accuracy of 15 AMS 14C ages of plant macrofossils obtained from a single ice-walled lake deposit. The semi-circular basin is about 0.72km wide and formed of a 4- to 16-m-thick succession of loess and lacustrine sediment inset into till. The assayed material was leaves, buds and stems of Salix herbacea (snowbed willow). The pooled mean of three ages from the basal lag facies was 18 270??50 14C a BP (21 810cal. a BP), an age that approximates the switch from active ice to stagnating conditions. The pooled mean of four ages for the youngest fossil-bearing horizon was 17 770??40 14C a BP (21 180cal. a BP). Material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform. Based on the estimated settling times of overlying barren, rhythmically bedded sand and silt, the lacustrine environment persisted for about 50 more years. At a 67% confidence level, the dated part of the ice-walled lake succession persisted for between 210 and 860cal. a (modal value: 610cal. a). The deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the Lake Michigan lobe have been assessed using this method. There is no overlap of time intervals documenting when ice-walled lakes persisted on these landforms. The rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice-walled lake sedimentation. ?? 2011 John Wiley & Sons, Ltd.

Curry, B.; Petras, J.

2011-01-01

196

Ice  

NSDL National Science Digital Library

When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

Harris, Kathryn Louise.

197

Sedimentology and architecture of De Geer moraines in the western Scottish Highlands, and implications for grounding-line glacier dynamics  

NASA Astrophysics Data System (ADS)

Sedimentary exposures in moraines in a Scottish Highland valley (Glen Chaorach), reveal stacked sequences of bedded and laminated silt, sand and gravel, interspersed or capped with diamicton units. In four examples, faults and folds indicate deformation by glaciotectonism and syndepositional loading. We propose that these sediments were laid down in an ice-dammed lake, close to the last ice margin to occupy this glen. Individual units within cross-valley De Geer moraine ridges are interpreted by comparison with examples from similar environments elsewhere: stratified diamictons containing laminated or bedded lenses are interpreted as subaqueous ice-marginal debris-flow deposits; massive fine-grained deposits as hyperconcentrated flow deposits, and massive gravel units as high-density debris-flow deposits. Using an allostratigraphic approach we argue that glaciotectonically deformed coarsening-upward sand and gravel sequences that culminate in deposition of subglacial diamicton represent glacier advances into the ice-marginal lake, whereas undisturbed cross-bedded sand and gravel reflects channel or fan deposits laid down during glacier retreat. A flat terrace of bedded sand and gravel at the northern end of Glen Chaorach is interpreted as subaerial glaciofluvial outwash. On the basis of these inferences we propose the following three stage deglacial event chronology for Glen Chaorach. During glacier recession, ice separation and intra-lobe ponding first led to subaquaeous deposition of sorted and unsorted facies. Subsequent glacier stabilisation and ice-marginal oscillation produced glaciotectonic structures in the ice-marginal sediment pile and formed De Geer moraines. Finally, drainage of the ice-dammed lake allowed a subaerial ice-marginal drainage system to become established. Throughout deglaciation, deposition within the lake was characterized by abrupt changes in grain size and in the architecture of individual sediment bodies, reflecting changing delivery paths and sediment supply, and by dynamic margin oscillations typical of water-terminating glaciers.

Golledge, Nicholas R.; Phillips, Emrys

2008-07-01

198

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach  

E-print Network

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers;Keywords Little Ice Age Á New Zealand Á Glaciers Á Equilibrium line altitude Á Synoptic types Á Southern the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA

Phipps, Steven J.

199

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach  

E-print Network

The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons:3039­3060 DOI 10.1007/s00382-013-1876-8 #12;Keywords Little Ice Age Á New Zealand Á Glaciers Á Equilibrium line

Phipps, Steven J.

200

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age  

E-print Network

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age Alfredo Martínez-García,1 of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern

Gilli, Adrian

201

Ice age climate, evolutionary constraints and diversity patterns of European dung beetles  

E-print Network

LETTER Ice age climate, evolutionary constraints and diversity patterns of European dung beetles patterns of diversity. We assess their associations with the European Scarabaeinae dung beetles, a group stationarity in climate variability since the last glacial maximum (LGM), we find that current scarab richness

Rodríguez, Miguel Ángel

202

Pacing, Forcing, or Chance? Milankovitch Plays Dice and Scores Ice Ages. (Invited)  

NASA Astrophysics Data System (ADS)

Understanding the role of orbital forcing in the ice ages has now occupied paleoclimatologists and paleoceanographers for many decades, and still we don’t really know how this works. Are ice ages directly forced by orbits, or are orbits a pacemaker that organize ice-age oscillations that would occur anyway (i.e., in the absence of orbital forcing)? Tuning of marine d18O (and other) records gives plausibly satisfying results in many contexts, but radiometric dates have led some to suggest that that glacial terminations can precede presumed forcing, and thus must be independent of, or at least only very weakly coupled to, Earth’s orbital variations. Several early efforts sought to separate the background variability and organized orbital pacing of ice ages, and concluded that a large fraction of climate change is stochastic. Simple models of various types imply that thresholds and limits must exist within the glacial system. Combining these ideas of stochasticity and thresholds implies that the timing of glacial-interglacial transition must be to some extent indeterminate, and if so the precise dating of any particular event is not important to defining the orbital controls of climate. Instead the overall pattern of variation in multiple parts of the climate system, if sufficiently constrained in a sequence, may provide better insights.

Mix, A. C.

2010-12-01

203

Foraminiferal faunal estimates of paleotemperature: Circumventing the no-analog problem yields cool ice age tropics  

USGS Publications Warehouse

The sensitivity of the tropics to climate change, particularly the amplitude of glacial-to-interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no-analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A new calibration strategy developed here, which uses past variability of species to define robust faunal assemblages, solves the no-analog problem and reveals ice age cooling of 5??to 6??C in the equatorial current systems of the Atlantic and eastern Pacific Oceans. Classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core-top assemblages misrepresented the ice age faunal assemblages. Our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981] and thus may help to resolve a long-standing controversy. Our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems, however, and supports CLIMAP's inference of stability of the subtropical gyre centers.

Mix, A.C.; Morey, A.E.; Pisias, N.G.; Hostetler, S.W.

1999-01-01

204

End of the Little Ice Age in the Alps forced by industrial black carbon  

E-print Network

the end of the 13th and the middle of the 19th centuries, glaciers in the European Alps were considerablyEnd of the Little Ice Age in the Alps forced by industrial black carbon Thomas H. Paintera,1 , Mark, Cambridge, MA, and approved July 19, 2013 (received for review February 19, 2013) Glaciers in the European

Marzeion, Ben

205

Saponaria Pumila (Caryophyllaceae) and the Ice Age in the European Alps  

Microsoft Academic Search

The polymerase chain reaction (PCR)-based amplified fragment length polymorphism (AFLP) technique was applied to elucidate the glacial history of the alpine cushion plant Saponaria pumilain the European Alps. Special emphasis was given to a dense sampling of populations. Our data support a survival of S. pumila during the last ice age in at least three refugia, which are characterized by

ANDREAS TRIBSCH; PETER SCHONSWETTER; T. F. Stuessy

2002-01-01

206

Tax records from western Norway, as an index of Little Ice Age environmental and economic deterioration  

Microsoft Academic Search

Data from general tax commissions held in Sunnfjord Fogderi, Norway, reveal a substantial decline in rural prosperity between\\u000a 1667 and 1723. Late seventeenth and eighteenth century incidence of serious physical damage to farmlands is documented in\\u000a tax relief proceedings. Environmental deterioration characterised the early years of the Little Ice Age in western Norway.

Jean M. Grove; Arthur Battagel

1983-01-01

207

Solving the paradox of the end of the Little Ice Age in the Alps  

Microsoft Academic Search

The causes and timing of the Little Ice Age (fifteenth to nineteenth centuries) are still unclear (Crowley, 2000; Bond et al., 2001; Shindell et al., 2001). During the last part of this event (1760-1830), the advance of glaciers in the Alps conflicts with the summer temperature signal (Intergovernmental Panel on Climate Change, 2001). This paper attempts to solve this paradox.

Christian Vincent; Emmanuel Le Meur; Delphine Six; Martin Funk

2005-01-01

208

The Medieval Warm Period, the Little Ice Age and simulated climatic variability  

Microsoft Academic Search

The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations

B. G. Hunt

2006-01-01

209

`Little Ice Age' glaciation and current glaciers in the Iberian Peninsula  

Microsoft Academic Search

`Little Ice Age' (LIA) glacier advance has been registered in three of the main Iberian high mountain areas: Pyrenees, Picos de Europa and Sierra Nevada. During the LIA, three different glacial environments have been differentiated in these three ranges. A high mountain glacial environment exists in the Pyrenees, where the altitude and northern latitude developed the most complex glacial environment

J. J. González Trueba; R. Martín Moreno; E. Martínez de Pisón; E. Serrano

2008-01-01

210

Little Ice Age glacial activity in the Mt. Waddington area, British Columbia Coast Mountains, Canada  

Microsoft Academic Search

The establishment of fourteen Little Ice Age (LIA) glacier chronologies in the Mt. Waddington area led to the development of an extended history of glacial activity in this portion of the southern British Columbia Coast Mountains, Canada. The glaciers were located within four different mountain ranges, and were of varying size and aspect. Dendrochronological and lichenometric techniques were used to

S. J. Larocque; D. J. Smith

2003-01-01

211

Integrating Teaching about the Little Ice Age with History, Art, and Literature.  

ERIC Educational Resources Information Center

Discusses climate change during the Little Ice Age as experienced during several historical events, including the settlement and demise of the Norse Greenland colonies, the landing of the Pilgrims at Plymouth, and both the Battle of Trenton and Washington's encampment at Valley Forge during the American Revolution. Associated artistic and literary…

Glenn, William Harold

1996-01-01

212

Rapid viscoelastic uplift in southeast Alaska caused by post-Little Ice Age glacial retreat  

Microsoft Academic Search

Our observations show that extreme uplift in southeast Alaska began about 1770 AD, with relative sea level (RSL) change to 5.7 m and current uplift rates to 32 mm\\/yr. This region experienced widespread glacial melting following the Little Ice Age (LIA), with the collapse of the Glacier Bay Icefield alone equivalent to 8 mm of global sea level rise. Geodynamic

Christopher F. Larsen; Roman J. Motyka; Jeffrey T. Freymueller; Keith A. Echelmeyer; Erik R. Ivins

2005-01-01

213

Climatic Change and Witchhunting: the Impact of the Little Ice Age on Mentalities  

Microsoft Academic Search

In addition to objective climatic data, subjective or social reactions can also serve as indicators in the assessment of climatic changes. Concerning the Little Ice Age the conception of witchcraft is of enormous importance. Weather-making counts among the traditional abilities of witches. During the late 14th and 15th centuries the traditional conception of witchcraft was transformed into the idea of

Wolfgang Behringer

1999-01-01

214

Some genetic consequences of ice ages, and their role in divergence and speciation  

Microsoft Academic Search

The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a

GODFREY M. HEWITT

1996-01-01

215

Intense storm activity during the Little Ice Age on the French Mediterranean coast L. Dezileau a,  

E-print Network

Oscillation Mediterranean Sea Risk assessments Understanding long-term variability in the frequency of intenseIntense storm activity during the Little Ice Age on the French Mediterranean coast L. Dezileau a and leading to a modification of the occurrence of extreme wind events along the French Mediterranean coast

Demouchy, Sylvie

216

Simulating Dust Cycling during the Late Paleozoic Ice Age  

NASA Astrophysics Data System (ADS)

Upper Carboniferous and Lower Permian strata preserve evidence for significant deposition of mineral dust, an aerosol with strong potential influence on the climate. Some equatorial marine carbonate records from this interval appear to record massive influxes of fine dust (diameter < 10 ?m) after rapid sea level fall, suggesting that the pacing of dust deposition was connected to the expansion and contraction of ice sheets during the important icehouse climate interval of Carboniferous and Permian time. Nearby continental strata record high accumulations of coarse dust (loess) during periods of increasing aridity (apparent glacial intervals) and of fine dust (paleosols) during periods of increasing humidity (apparent interglacial intervals), though the pacing of this deposition may be more strongly associated with orbital forcing than ice sheet dynamics. Significant dust deposition continued in many of these areas during the emergence of the Earth's climate from icehouse conditions during Middle Permian time. Understanding the dynamics of dust cycling during the depths of the icehouse is the first step to investigating dust records from the most recent icehouse termination of Earth's history. Here, we attempt to reconstruct the cycling and some of the potential climate impacts of mineral dust during this interval, using version 3 of the Community Climate System Model (CCSM3) and the best available records of dust deposition. Modeled sensitivity simulations suggest that climatic controls on dust cycling that act on relatively short timescales (primarily meteorological and vegetation-related) cannot explain the large variability in dust deposition rates inferred from marine carbonate records. Processes acting on longer timescales, particularly those that control the availability of wind-erodible sediment, likely are more important. We also consider whether exposure of sedimentary basins during sea level fall and glaciogenic dust production could modulate dust sources, but find that our modeling of these processes still cannot explain the full amplitude of variability in the marine records. By making some inferences from the provenance and grain size distribution of the dust deposition records, we reconstruct dust cycling during the termination of extreme glacial conditions in the Early Permian within observational uncertainty. This reconstruction allows a rough estimate of the sensitivity of Early Permian glacial climates to dust as well as radiative forcing. Moreover, the reconstruction highlights potential new areas to explore for non-equatorial marine records of dust deposition, which will improve future assessment of the impact of dust on late Paleozoic climate.

Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.; Shields, C. A.; Albani, S.

2012-12-01

217

Glacial age precipitation and temperature estimates for the tropical Guatemalan highlands  

NASA Astrophysics Data System (ADS)

The Sierra Cuchumatanes of Western Guatemala supported a large ice cap of approximately 44 square km area, and a group of 5-6 small valley glaciers during the local last glacial maximum (LLGM). We propose that a temperature reduction during the Guatemalan LLGM was between -4.5 degrees C and -6.0 degrees C from present accompanied by precipitation totals that fall between 80-100% of present day levels. Our new field work on moraine limits expands upon previous reconnaissance-level studies. Here we present a comprehensive reconstruction of the Guatemalan glacial geomorphology on a high limestone plateau; including delineations between morphologically different moraine sequences, boundaries of sub-glacial till deposits and locations of dry moraine dammed lakes. The glacial geologic map was produced via field mapping and GPS surveying, coupled with aerial photographic analysis. A 50m digital elevation model (DEM) created for the mapping portion was employed as input for a physically based GIS mass-balance model, developed by Plummer and Phillips (2003). The mass-balance model data was calculated for varying precipitation, temperature, environmental lapse rates, cloudiness, wind speed and humidity. A sensitivity analysis using variations in temperature and precipitation provided constraints on Guatemalan highland paleoclimate. Although the ages of the glaciations are unconstrained, a qualitative assessment of moraine morphology suggests correlation with the LLGM (20 - 17.5 ka) moraines of Mexico.

Roy, A. J.; Lachniet, M. S.

2007-12-01

218

A revised Little Ice Age chronology of the Franz Josef Glacier, Westland, New Zealand  

Microsoft Academic Search

A reassessed Little Ice Age chronology of the Franz Josef Glacier is presented. Diameter at breast height of 1340 southern rata (Metrosideros umbellata) and kamahi (Weinmannia racemosa) was measured within 50, 150?m quadrats in the Waiho Valley. Age?size relationships based on 60 tree?ring counts and associated diameter at breast height measurements were constructed, although the unknown shape of growth curves

Krista M. McKinzey; Wendy Lawson; Dave Kelly; Alun Hubbard

2004-01-01

219

Fire and ice in The Age of Innocence  

Microsoft Academic Search

This study will explore the dichotomy of culture and psychological landscape in Edith Wharton The Age of Innocence. To lay the foundation for this study, I first consider how Ms. Wharton often employed dichotomy in her own life: her role as socialite and author, woman of old New York and European maverick, and her life as spouse or beloved. Compartmentalizing

Alisa Mariva DeBorde

2005-01-01

220

Revised interpretation of Mueller Glacier moraines, Southern Alps, New Zealand  

NASA Astrophysics Data System (ADS)

A sequence of moraine ridges on the Mueller Glacier foreland, Southern Alps, New Zealand has previously formed part of a database used to develop a local/regional palaeoclimate chronology; however, it is possible that factors other than climate may have caused or influenced these moraine formations. Rock avalanches that deposit large volumes of rock debris on glacier ablation zones can affect glacier behaviour and cause moraine formation that does not necessarily reflect a climatically-driven advance (Reznichenko et al., 2011). Therefore, prior to the correlation of dated moraines with regional climate alterations, it is required to determine the genesis of these features. In previous studies the possible formation of some Mueller moraines by large-scale mass movements has been neglected that could have resulted in wrong assumptions of moraine positions having been entirely forced by climate change. The presence of modern rock avalanche deposits on glaciers in the Aoraki/Mt. Cook area indicates the probable contribution of supraglacial rock avalanches to the formation of these moraines in the past. This argument was recently supported by the presence of rock-avalanche-indicating agglomerates found in the sediment from two Mueller Glacier moraine ridges (Reznichenko et al., 2012). Previous interpretations of these ridges are inconsistent and are usually attributed to reflecting several glacial climatic-driven advances. In current research presented morphological and sedimentological analysis evidence that this feature is a single moraine (the "Mueller Memorial Moraine") formed following supraglacial transport of a large volume of rock avalanche debris to the glacier snout. Because a moraine formed by this process has no necessary association with a climate event, this finding raises concerns about the palaeoclimatic significance of this moraine; and, by implication, of other moraines in similar situations. References Reznichenko, N.V., Davies, T.R. and Alexander, D.J., 2011. Effects of rock avalanches on glacier behavior and moraine formation. Geomorphology 132: 327-338. Reznichenko, N.V., Davies, T.R., Shulmeister, J.P. and Larsen, S.H., 2012. A new technique for identifying rock avalanche-sourced sediment in moraines and some palaeoclimatic implications. Geology 40: 319-322.

Reznichenko, Natalya; Davies, Tim; Winkler, Stefan

2013-04-01

221

Sedimentology of latero-frontal moraines and fans on the west coast of South Island, New Zealand  

NASA Astrophysics Data System (ADS)

Exposures through the LGM latero-frontal moraine loops at sites along the west coast of South Island, New Zealand reveal a depositional environment that was dominated by the progradation of steep fronted, debris flow-fed fans, manifest in crudely stratified to massive diamictons, arranged in sub-horizontal to steeply dipping clinoforms and containing discontinuous bodies of variably sorted, stratified sediment (LFA 1). The fans were constructed by debris-covered glaciers advancing over outwash plains, as recorded by well stratified and horizontally bedded gravels, sands and diamicts (LFA 0). The ice-contact slopes of the fans are offlapped by retreat phase deposits in the form of glacilacustrine depo-centres (LFA 2), which record the existence of moraine-dammed lakes. Interdigitation of lake rhythmites and subaerial to subaqueous sediment gravity flow deposits documents intense debris-flow activity on unstable moraine/fan surfaces. Glacier readvances in all catchments are documented by glacitectonic disturbance and localized hydrofracturing of LFA 2, followed by the emplacement of schist-dominated debris flow-fed fans (LFA 3) inside and over the top of the earlier latero-frontal moraine/fan loops. Contorted and disturbed bedding in LFA 3 reflects its partial deposition in supraglacial positions. Clast lithologies in LFAs 1 and 3 reveal that two distinct transport pathways operated during moraine construction, with an early period of latero-frontal fan construction involving mixed lithologies and a later period of ice-contact/supraglacial fan construction dominated by schist lithologies from the mountains. These two periods of deposition were separated by a period of moraine abandonment and paraglacial reworking of ice-contact slopes to produce LFA 2. The occurrence of LFA 3 at all sites indicates that the glacier readvance phase responsible for its deposition was not localized or glacier-specific, and involved the transfer of large volumes of schist, possibly due to rock slope failures, onto glacier surfaces. The absence of any sediment that could be unequivocally classified as subglacial till reflects the dominance of debris flow and glacifluvial processes in latero-frontal moraine construction in this hyper-humid west coast setting.

Evans, David J. A.; Shulmeister, James; Hyatt, Olivia

2010-12-01

222

Middle and Late Pennsylvanian cyclothems, American Midcontinent: Ice-age environmental changes and terrestrial biotic dynamics  

NASA Astrophysics Data System (ADS)

The Pennsylvanian portion of the Late Paleozoic Ice Age was characterized by stratigraphic repetition of chemical and siliciclastic rocks in the equatorial regions of the Pangean interior. Known as “cyclothems”, these stratigraphic successions are a 105 yr-record of glacial waxing and waning, superimposed on longer term, 106 yr intervals of global warming and cooling and a still longer term trend of increasing equatorial aridity. During periods of maximum ice-minimum sea level, the interior craton was widely exposed. Epicontinental landscapes were initially subjected to dry subhumid climate when first exposed, as sea level fell, but transitioned to humid climates and widespread wetlands during maximum lowstands. During interglacials (ice-minima) seasonally dry vegetation predominated. The wetland and seasonally dry biomes were compositionally distinct and had different ecological and evolutionary dynamics.

Blaine Cecil, C.; DiMichele, William A.; Elrick, Scott D.

2014-07-01

223

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

SciTech Connect

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 cap 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.

Mann, D.H. (Univ. of Alaska, Fairbanks, AK (United States). Alaska Quaternary Center)

1992-01-01

224

Aging affects the ice-nucleating properties of volcanic ash aerosol  

NASA Astrophysics Data System (ADS)

The effectiveness of volcanic ash as ice nuclei (IN) has been debated in the past. While some reported enhanced IN concentrations in volcanic plumes, others found no evidence for that. Here we show that "aged" volcanic particles sampled from the atmosphere in central Germany when the ash cloud of the 2010 Eyjafjallajökull eruption was present are very effective IN, as compared to particles of aerosolized "fresh" volcanic sediment that had been collected close to the eruption site in Iceland. The number concentration of atmospheric IN was measured with the same method both at the Taunus Observatory in central Germany and at Tel Aviv University, Israel, as well as in laboratory-generated aerosol of volcanic ash. Aerosol was sampled by electrostatic precipitation of particles onto silicon substrates and was subsequently analyzed at - 8° to -18°C (deposition and condensation nucleation modes) in the isothermal static vapor diffusion chamber FRIDGE. The composition of individual atmospheric IN was analyzed by environmental scanning electron microscopy (ESEM) with EDX. Our daily measurements show a significant enhancement of atmospheric IN when the dispersed ash cloud reached central Europe in April 2010 and the eastern Mediterranean in May 2010. Pure volcanic ash accounts for at least 53-68% of the 239 individual ice nucleating particles that were analyzed by ESEM-EDX in aerosol samples collected at Taunus Observatory during the volcanic peak of April 2010. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at -18°C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected from ambient air during the volcanic peaks than in the aerosolized samples from the ash collected close to the eruption site. From this we conclude that the ice-nucleating properties of volcanic ash may be altered substantially by aging and processing during long-range transport in the atmosphere, and that global volcanism deserves further attention as a potential source of atmospheric ice nuclei.

Bingemer, H.; Klein, H.; Ebert, M.; Haunold, W.; Bundke, U.; Herrmann, T.; Kandler, K.; Müller-Ebert, D.; Weinbruch, S.; Judt, A.; Wéber, A.; Nillius, B.; Ardon-Dryer, K.; Levin, Z.; Curtius, J.

2012-04-01

225

The little ice age and medieval warm period in the Sargasso Sea  

SciTech Connect

Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbondated box core show that SST was {approximately} 1{degree}C cooler than today {approximately} 400 years ago (the Little Ice Age) and 1700 years ago, and {approximately} 1{degree}C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation. 39 refs., 4 figs., 1 tab.

Keigwin, L.D. [Woods Hole Oceanographic Institution, Woods Hole, MA (United States)

1996-11-29

226

Impact of Ice Ages on the genetic structure of trees and shrubs.  

PubMed Central

Data on the genetic structure of tree and shrub populations on the continental scale have accumulated dramatically over the past decade. However, our ability to make inferences on the impact of the last ice age still depends crucially on the availability of informative palaeoecological data. This is well illustrated by the results from a recent project, during which new pollen fossil maps were established and the variation in chloroplast DNA was studied in 22 European species of trees and shrubs. Species exhibit very different levels of genetic variation between and within populations, and obviously went through very different histories after Ice Ages. However, when palaeoecological data are non-informative, inferences on past history are difficult to draw from entirely genetic data. On the other hand, as illustrated by a study in ponderosa pine, when we can infer the species' history with some certainty, coalescent simulations can be used and new hypotheses can be tested. PMID:15101576

Lascoux, Martin; Palmé, Anna E; Cheddadi, Rachid; Latta, Robert G

2004-01-01

227

Marine ice sheets of Pleistocene age on the East Siberian Continental Margin (Invited)  

NASA Astrophysics Data System (ADS)

Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV "Polarstern' cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating that of the Last Glacial Maximum (LGM) also implies significantly different atmospheric circulation patterns, in particular availability and distribution of moisture during pre-LGM glaciations.

Niessen, F.; Hong, J.; Hegewald, A.; Matthiessen, J. J.; Stein, R. H.; Kim, H.; Kim, S.; Jensen, L.; Jokat, W.; Nam, S.; Kang, S.

2013-12-01

228

Sea-level responses to sediment transport over the last ice age cycle  

NASA Astrophysics Data System (ADS)

Sea-level changes over the last ice age cycle were instrumental in steering Earth's topographic evolution. These sea-level variations were driven by changes in surface mass loads, including not only ice and ocean mass variations but also the transfer of rock from eroding mountains to sedimentary deposits. Here we use an extended numerical model of ice age sea level (Dalca et al., 2013) to explore how sediment erosion and deposition affected global sea-level variations over the last ice age cycle. The model takes histories of ice and sediment loads as inputs, and it computes gravitationally self-consistent sea level responses by accounting for the deformational, gravitational, and rotational perturbations in the Earth's viscoelastic form. In these model simulations, we use published estimates of erosion rates, sedimentation rates, and ice sheet variations to constrain sediment and ice loading since the Last Interglacial. We explore sea-level responses to several erosional and depositional scenarios, and in each we quantify the relative contributions of crustal deformation and gravitational perturbation to the computed sea-level change. We also present a case study to illustrate the effects that sediment transfer can have on sea level at the regional scale. In particular, we focus on the region surrounding the Indus River, where fluvial sediment fluxes are among the highest on Earth. Preliminary model results suggest that sediment fluxes from Asia to the ocean are large enough to produce a significant response in sea level along the northeastern coast of the Arabian Sea. Moreover, they suggest that modeled sea-level histories are sensitive to the timing and spatial distribution of sediment erosion and deposition. For instance, sediment deposition along the continental shelf - which may have been the primary site of Indus River sediment deposition during the Holocene - produces a different sea-level response than sediment deposition on the deep-sea Indus Fan, where most of the Indus sediment may have been deposited during the glacial period preceding the Holocene. These simulations highlight the role that massive continent-to-ocean sediment fluxes can play in driving sea-level patterns over thousands of years. References: Dalca A.V., Ferrier K.L., Mitrovica J.X., Perron J.T., Milne G.A., Creveling J.R., 2013. On postglacial sea level - III: Incorporating sediment redistribution. Geophys. J. Int., doi: 10.1093/gji/ggt089.

Ferrier, K.; Mitrovica, J. X.

2013-12-01

229

The ‘Little Ice Age’ maximum in the Southern Alps, New Zealand: preliminary results at Mueller Glacier  

Microsoft Academic Search

Lichenometric-dating studies using the yellow-green Rhizocarpon subgenus at Mueller Glacier in the region of Mt Cook, Southern Alps, New Zealand, reveal a ‘Little Ice Age’ maximum about ad 1725\\/1730. Differences from previous studies are shown to result from different methods, especially the type of mathematical functions used for calculating the lichenometric dating curves. Previous work also used variable sample sizes,

Stefan Winkler

2000-01-01

230

An ice core perspective on the age of the Matuyama–Brunhes boundary  

Microsoft Academic Search

Two intervals of enhanced 10Be flux thought to be associated with periods of low dipole intensity and identified as the Matuyama–Brunhes transition and a precursor event have been observed in the bottom section of the EPICA Dome C ice core. The peaks span 764–776 ka and 788–798 ka on the new EDC3 chronology with a stated absolute age uncertainty of 6 ka (2?).

G. B. Dreyfus; G. M. Raisbeck; F. Parrenin; J. Jouzel; Y. Guyodo; S. Nomade; A. Mazaud

2008-01-01

231

Effects of sudden mixing in the solar core on solar neutrinos and ice ages.  

NASA Technical Reports Server (NTRS)

Some numerical experiments with a solar model have been conducted in connection with the hypothesis regarding the effects of mixing in the solar core. Questions concerning a plausible mechanism by which such a mixing could be produced are explored. The variation of solar luminosity throughout the numerical experiments is shown. In connection with a great change in luminosity after a second mixing, it is suggested that the earth is presently undergoing an ice age.

Ezer, D.; Cameron, A. G. W.

1972-01-01

232

Evidence for a little ice age and recent warming from a borehole temperature data inversion procedure  

SciTech Connect

In this article, we apply our analytical theory, published earlier in this journal, to obtain information on the earth surface temperature history from some borehole temperature data. Compared to the results of the five different methods applied to the same temperature data, our method seems to be easier, assumption-free, and yields internally consistent results. The results suggest a cooling a few centuries ago, followed by a continuing warming up to these days, in agreement with a little ice age scenario.

Fivez, J.; Thoen, J. [Laboratorium voor Akoestiek en Thermische Fysica, Department Natuurkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

2004-11-15

233

Weak chemical weathering during the Little Ice Age recorded by lake sediments  

Microsoft Academic Search

Low magnetic susceptibility, low Sr content and hence high Rb\\/Sr ratio in the lake sediment sequence indicate a weak chemical\\u000a weathering process under arid and cold climate of the Little Ice Age in a single closed lake watershed. According to different\\u000a geochemical behavior between rubidium and strontium in earth surface processes, variation of Rb\\/Sr ratios in the lake sediment\\u000a sequence

Zhangdong Jin; Sumin Wang; Ji Shen; Enlou Zhang; Junfeng Ji; Fuchun Li

2001-01-01

234

Little Ice Age sea surface temperature variability in the southwest tropical Pacific  

Microsoft Academic Search

We present a 60-year near-monthly record of tropical sea surface temperature (SST) during the Little Ice Age derived from coupled Sr\\/Ca and U\\/Ca analysis of a massive coral from New Caledonia (southwest tropical Pacific). The record indicates that, from 1701 to 1761, surface temperatures were on average 1.4°C cooler than during the past 30 years. This cooling was accompanied by

Thierry Corrège; Terry Quinn; Thierry Delcroix; Florence Le Cornec; Jacques Récy; Guy Cabioch

2001-01-01

235

Reconstruction of temperature conditions during the little ice age in Northern Eurasia, based on dendrochronological data  

Microsoft Academic Search

In this attempt at reconstructing temperatures during the Little Ice Age on the basis of dendrochronology, the author used ten?year running means for tree ring growth in the Ary?Mas forest island in the Khatanga Basin and also a generalized tree?ring series for the entire length of the treeline from the Kola Peninsula to Chukotka. These curves are keyed to temperature

M. M. Chernavskaya

1985-01-01

236

Calendar-dated, early 'Little Ice Age' glacier advance at Robson Glacier, British Columbia, Canada  

Microsoft Academic Search

Dendrochronological studies at Robson and Bennington Glaciers have provided the first calendar dating of an early 'Little Ice Age' glacier advance in North America. Dates derived from in-situ stumps indicate that Robson Glacier began over-riding forest between c. AD 1142 and 1150 and continued until at least AD 1350. The highest rates of glacier advance (c. 3.8 m yr-1 )

B. H. Luckman

1995-01-01

237

Little Ice Age glacial activity in Strathcona Provincial Park, Vancouver Island, British Columbia, Canada  

Microsoft Academic Search

Dendroglaciological and lichenometric techniques are used to establish the Little Ice Age (LIA) history of two glaciers (Colonel Foster and Septimus) in Strathcona Provincial Park, Vancouver Island, British Columbia. Our lichenometric investigations were preceded by the development of a locally calibrated Rhizocarpon geographicum growth curve (1708-1998 A.D.). Documentation of a 3-4-year ecesis interval for both trees and lichen greatly reduces

Dave H. Lewis; Dan J. Smith

2004-01-01

238

Impact of ice ages on circumpolar molecular diversity: insights from an ecological key species  

Microsoft Academic Search

We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum ) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium

I. G. ALSOS; T. ENGELSKJON; L. GIELLY; P. TABERLET; C. BROCHMANN

2005-01-01

239

Little Ice Age events (or not) in the middle to high latitudes of the Southern Hemisphere?  

NASA Astrophysics Data System (ADS)

The use of 'Little Ice Age' is prevalent in the literature on past Southern Hemisphere climates. We make a case that during the Little Ice Age period in Europe, terrestrial observations in the southern middle latitudes, specifically landform- and stratigraphic-based records, indicate that glaciers were typically not the most extensive of the Holocene. We summarize recently obtained findings from Patagonia and New Zealand. In both places, notable glacier advances did occur between ca. 1400 AD and 1850 AD and snowline depressions were about 100 m or more below present. Thus, Southern Hemisphere glaciers exhibited advances broadly at a similar time as during the European Little Ice Age. However, in contrast, glaciers in New Zealand and in at least some parts of Patagonia were consistently more extensive in the early or middle Holocene, respectively, when snowlines were 200 to 300 m below present-day. In addition, on both sides of the South Pacific region, we observe that glacier advances between ~1400 and 1600 AD were more extensive than those between 1600 and 1900 AD. We conclude that during the Holocene there were important differences in how glaciers behaved in the Northern and Southern hemispheres.

Kaplan, M. R.; Schaefer, J. M.; Denton, G. H.; Putnam, A. E.; Strelin, J.; García, J.; Sagredo, E. A.; Finkel, R. C.; Schwartz, R.

2013-12-01

240

A latest Pliocene age for the earliest and most extensive Cordilleran Ice Sheet in northwestern Canada  

NASA Astrophysics Data System (ADS)

The Klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive Cordilleran Ice Sheet (CIS) in NW North America. New terrestrial cosmogenic nuclide (TCN) burial ages indicate this gravel was emplaced 2.64+0.20/-0.18 Ma (1?). Coupled with previously interpreted paleomagnetic stratigraphy, this numerical age constrains the timing of the earliest CIS to the late Gauss Chron and provides a minimum age for the Upper White Channel gravel, a significant placer gold source in the Yukon. This implies the first CIS glacial maximum pre-dates the maximum extent of the Laurentide Ice Sheet, indicating that during the initial stages of northern hemisphere glaciation, the most extensive glaciers were present in the relatively cold and high elevation northern Cordillera. Our results verify the CIS as a likely source of persistent coeval ice-rafted debris in the northern Pacific, and suggest that the first CIS formed as a response to the establishment of the northern Pacific halocline and emergence of the 41 ka obliquity cycle during the Plio-Pliocene transition.

Hidy, Alan J.; Gosse, John C.; Froese, Duane G.; Bond, Jeffrey D.; Rood, Dylan H.

2013-02-01

241

A non-linear climate oscillator controlled by biogeochemical cycling in the ocean: an alternative model of Quaternary ice age cycles  

Microsoft Academic Search

A new, biogeochemical model of ice age cycles is developed and applied which explains major features of climate variations in the late Quaternary —rapid ice age terminations, large glacial-interglacial amplitudes and ~ 100-kyr cycles — in a way consistent with the paleorecord. Existing models which invoke non-linear, ice-sheet-earth-crust dynamics to explain ice age cycles are not consistent with simultaneous terminations

Gary Shaffer

1990-01-01

242

Holocene glacial history of the west Greenland Ice Sheet inferred from cosmogenic exposure ages and threshold lakes  

NASA Astrophysics Data System (ADS)

In this study, we use a combination of 10Be exposure ages and threshold lakes to constrain the ice sheet history in Godthåbs- and Buksefjorden, west Greenland (63-64°N) during the Holocene. The 10Be cosmogenic exposure ages have been used to quantify both the ice retreat and thinning of the west Greenland Ice Sheet in 3 transects from the coast to the present ice margin. Preliminary results (n=47) indicate initial deglaciation of coastal areas around 11 ka in concert with existing radiocarbon chronology, followed by a rapid retreat from the outer coast to the present ice margin around 10 ka. Boulder samples from the highest peaks demonstrate that the ice was warm-based whereas bedrock samples often contain an inherited signal. These results may have implications for other studies in Greenland, which have inferred thin LGM ice based on 10Be ages of bedrock samples. The threshold lakes are used to record episodes when the ice sheet was close-to-the present extent, represented by beds of clastic sediments whereas gyttja-deposition reflects periods when the glacier was behind the threshold, and no glacial meltwater input. Our results demonstrates that following the initial deglaciation the ice margin remained close to the present ice margin until around 7 cal. ka BP before it retreated behind the present extent during the Holocene Thermal Maximum (HTM). Here it remained until the Little Ice Age (LIA) where it readvanced to the present position around 0.5 cal. ka BP. Our results correspond to other recent findings from south and west Greenland that show that the ice sheet first began to retreat behind the present ice margin around 7 cal. ka BP. However, it differs from the other areas because the ice sheet first reappears at the present ice position during the LIA (i.e. no Neoglacial advance) and this suggest that the ice sheet in this area may have been more retracted and probably more sensitive to climate change than other areas in south and west Greenland.

Larsen, N. K.; Kjaer, K. H.; Colding, S.; Funder, S.; Kjeldsen, K. K.; Odgaard, B.; Olsen, J.; Linge, H. C.

2011-12-01

243

The complex behavior of the Cordilleran Ice Sheet and mountain glaciers to abrupt climate change during the latest Pleistocene  

NASA Astrophysics Data System (ADS)

Surficial mapping and more than 70 radiometric ages 10Be, 14C] constrain the evolution of the Cordilleran Ice Sheet (CIS) and associated mountain glaciers in western Canada during the latest Pleistocene. Our data suggest that: i) there is widespread evidence for the Younger Dryas (YD) throughout the mountains of western Canada; ii) late Pleistocene climate reconstructions based solely on alpine moraines may be misleading in regions with decaying ice sheets; iii) extensive interfluves in some mountain regions were ice-free between 16 ka and 13 ka (kilo calibrated yrs BP). Initial decay of the CIS from its maximum extent around 16 ka was likely due to a combination of climatic (surface melting) and dynamical factors. Climate amelioration during the Bølling-Allerød Warm Period [14.7-12.9 ka], likely the cause for the major phase of CIS decay, resulted in ice sheet equilibrium line altitudes (ELAs) ranging from 2500 m asl in southern BC to around 2000 m asl along the BC-Yukon border. Hence, before the onset of the Younger Dryas (YD) Cold Period [12.9-11.7 ka], the ice sheet shrank and became a labyrinth of individual and coalescing valley glaciers fed by major accumulation zones centered on the Coast Mountains and other high ranges of NW Canada. The response of remnant ice and cirque glaciers to the YD climate deterioration was highly variable. In some cases, small glaciers (0.5-2 km2) built YD moraines that were only hundreds of meters beyond those constructed during the Little Ice Age (LIA) [0.30-0.15 ka]. Our dating also reveals that much larger glaciers persisted in nearby valleys that lie hundreds of meters below the cirques. Hence, we infer that many cirques were completely deglaciated prior the YD, in contrast to low-lying valleys where ice sheet remnants persisted. Glaciers also advanced in north-central British Columbia during the YD, but here glaciers constructed large terminal and lateral moraines. In the Cassiar and northern Coast mountains, for example, 25 10Be [13.10-12.00 ka] and four minimum-limiting 14C ages from lakes impounded by moraines show that glaciers existed up to 10 km beyond LIA glacier limits during the YD. These glaciers thus had ELAs that were 300-500 m lower than contemporary glaciers. We are currently performing high-resolution (

Menounos, Brian; Goehring, Brent; Osborn, Gerald; Clarke, Garry K. C.; Ward, Brent; Margold, Martin; Bond, Jeff; Clague, John J.; Lakeman, Tom; Schaefer, Joerg; Koch, Joe; Gosse, John; Stroeven, Arjen P.; Seguinot, Julien; Heyman, Jakob; Fulton, Robert

2014-05-01

244

Author's personal copy Dendrogeomorphic reconstruction of Little Ice Age paraglacial activity in the vicinity  

E-print Network

-rings Moraine and glacier dams bordering the Homathko Icefield in the southern British Columbia Coast Mountains field techniques were employed to develop a chronology for the buried forests. A regional tree) trees at seven sites in the southern Coast Mountains. In cases where subfossil stumps and boles predated

Smith, Dan

245

Glacial geomorphology of terrestrial-terminating fast flow lobes/ice stream margins in the southwest Laurentide Ice Sheet  

NASA Astrophysics Data System (ADS)

Glacial geomorphological mapping of southern Alberta, Canada, reveals landform assemblages that are diagnostic of terrestrial-terminating ice streams/fast flowing outlet glaciers with lobate snouts. Spatial variability in features that comprise the landform assemblages reflects changes in (a) palaeo-ice stream activity (switch on/off); and (b) snout basal thermal regimes associated with climate sensitive, steady state flow. Palaeo-ice stream tracks reveal distinct inset sequences of fan-shaped flowsets indicative of receding lobate ice stream margins. Former ice lobe margins are demarcated by (a) major, often glacially overridden transverse moraine ridges, commonly comprising glacitectonically thrust bedrock; and (b) minor, closely spaced recessional push moraines and hummocky moraine arcs. Details of these landform types are well exhibited around the former southern margins of the Central Alberta Ice Stream, where larger scale, more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges (MTR types 1-3), hummocky terrain (HT types 1-3), flutings, and meltwater channels/spillways. The MTR type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined. The MTR type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts. The MTR type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain. The close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin, where the HT type 3 hummocks represent former ice-walled lake plains. The ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern Alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream/fast flow lobes of the southern Laurentide Ice Sheet, where alternate cold, polythermal, and temperate marginal conditions associated with climate sensitive, steady state flow sequentially gave way to more dynamic streaming and surging activity.

Evans, David J. A.; Young, Nathaniel J. P.; Ó Cofaigh, Colm

2014-01-01

246

Coral's chilling tale: Ancient reefs may resolve an ice-age paradox  

SciTech Connect

At the end of the Pleistocene epoch, the peak of the last ice age, the land that would become New York City lay hidden beneath a sheet of ice more than twice the height of the Empire State Building. However, researchers have found contradictory evidence about how the low latitudes fared during the ice age. Deep sea sediments seem to indicate that the tropical seas weathered the glacial epoch with remarkable stability while the continental record indicates evidence of marked cooling. This discrepancy is a problem for climate researchers because it raises the possibility that climate models may lack a critical element that will hinder their ability to accurately predict future changes. However, studies of an ancient coral species may help. The coral occasionally incorporates strontium into its shell, a situation which occurs more frequently in cold water. Looking at the ratio of strontium to calcium in coral, researchers have proposed that the surface waters off Barbados were 5[degree]C colder than today. The article discusses the scientific debate set off by this finding.

Monastersky, R.

1994-02-19

247

Past and future ice age initiation: the role of an intrinsic deep-ocean millennial oscillation  

NASA Astrophysics Data System (ADS)

This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. In the first contribution the millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA's observation of today's record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water production cited by Broecker (2000). The sinusoidal form of this conceptual model is therefore reinforced by both old and new data, and provides insights into world-wide climate change. The second contribution of this paper is a hypothesis for the initiation of Pleistocene ice ages, typified by the Last Ice Age that began 120 000 yr BP. Instead of the classical Northern high-latitude summer cooling caused by orbital precession and changes in Earth's axis inclination, this hypothesis proposes the sudden onset of year-round ice-free seas west of Greenland, with greatly increased precipitation in the ice sheet nucleation regions of Baffin Island, northern Quebec, and Labrador. Devon Island ice-core studies by Koerner at al. (1988) and deep-sea sediment data reported by Fillon (1985) support the concept of ice-free seas west of Greenland and imply the initial meteorological conditions that are proposed here. These conditions are consistent with the heavy precipitation inferred by Adkins et al. (1997) from deep-sea sediment data. The changes in northeastern Canada were accompanied by quite cold conditions in northern Europe, inferred by Field et al. (1994) from tree pollen data. The European cooling was probably caused by loss of the recurring Iceland low-pressure system due to the dominant effect of a frequent stronger low-pressure system over the Labrador Sea, as postulated in this paper. The key to ice-free seas west of Greenland is the loss of the near-surface stratification that normally enables sea ice to freeze. Using the high-resolution European Space Agency's ENVISAT system, I have monitored the flows through the Nares Strait and found that the dominant southward flow of lower density polar water into Baffin Bay correlated with the growing area of seasonal sea ice forming early in the winter in the Bay near the southern end of the Strait. This implies that low-salinity polar water was the cause of the stratification. A search for the cause of the stratification loss then became a search for the cause of the loss of the southward flow of polar water. The los

Johnson, R. G.

2014-05-01

248

Detailed Reconstructions of Fluctuations of Seven Glaciers during the "little Ice Age" in the Northern Caucasus, Russian Federation  

NASA Astrophysics Data System (ADS)

The main task of this work is the development of detailed reconstructions of mountain glaciers' fluctuations with precise spatial references in the Northern Caucasus, their analyses in terms of glacier length, area and volume changes and identification of climate role in these fluctuations. The studied glaciers (Alibek, Ullukam, Terskol, Kashkatash, Bezingi, Mijirgi, Tsey) are situated along the Bolshoy Caucasus Range from the very west (Teberda river basin) to the east (Tseydon river basin). These valley glaciers have different size, aspect and percent of debris-cover. Basing on instrumental data (since the middle of 20th century), remote sensing images (CORONA, Geoeye, Cartosat, IRS, ASTER, etc.), aerial photos of 1950s-1980s, maps (since 1887), old photographs, as well as proxy data (historical descriptions, lichenometry, dendrochronology, 14C, 10Be), we reconstructed 15-20 positions of the glaciers tongues for each glacier and produced maps showing variations of the glaciers with precise spatial reference since their maximum in the mid 17th or first half of 19th century. For example, for Alibek glacier seven former front positions and eleven moraines were photo-identified and dated. We obtained the carbon dating of intermorainal peat-bog (103%), moraine dating based on isotopes of 10Be (1900±12) and determined minimum age of most distant moraine according to dendrochronological analysis of trees (Abies nordmanniana), growing on its surface (more than 200 years). At that time (1895) the glacier was 290 m longer than today, its surface was 0.31 km2 larger (5.94 km2 in 1895, 5.63 km2 in 2008). We calculated glaciers' length and area changes, using different methods (GLIMS; Bhambri et al., 2012) and analyzed advantages and disadvantages of each method in case of their application for Caucasian glaciers. Based on our measurements we evaluated changes of equilibrium line altitude and volume. Volume changes have been reconstructed using the model offered by Lüthi et al. (2010). The obtained data can be used as the base for reconstructions of different climatic parameters, it is important contribution to the global paleoclimatic reconstructions (e.g. Leclercq and Oerlemans, 2011), where Caucasus is strongly underrepresented. The results of this study are also important for verification of other reconstructions with the lower spatial and temporal resolutions (Shahgedanova, 2009).

Bushueva, I.

2012-12-01

249

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

USGS Publications Warehouse

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.

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

2010-01-01

250

Glacier dynamics at Helheim and Kangerdlugssuaq glaciers, southeast Greenland, since the Little Ice Age  

NASA Astrophysics Data System (ADS)

Observations over the past decade show significant ice loss associated with the speed-up of glaciers in southeast Greenland from 2003, followed by a deceleration from 2006. These short-term, episodic, dynamic perturbations have a major impact on the mass balance on the decadal scale. To improve the projection of future sea level rise, a long-term data record that reveals the mass balance beyond such episodic events is required. Here, we extend the observational record of marginal thinning of Helheim and Kangerdlugssuaq glaciers from 10 to more than 80 years. We show that, although the frontal portion of Helheim Glacier thinned by more than 100 m between 2003 and 2006, it thickened by more than 50 m during the previous two decades. In contrast, Kangerdlugssuaq Glacier underwent minor thinning of 40-50 m from 1981 to 1998 and major thinning of more than 100 m after 2003. Extending the record back to the end of the Little Ice Age (prior to 1930) shows no thinning of Helheim Glacier from its maximum extent during the Little Ice Age to 1981, while Kangerdlugssuaq Glacier underwent substantial thinning of 230 to 265 m. Comparison of sub-surface water temperature anomalies and variations in air temperature to records of thickness and velocity change suggest that both glaciers are highly sensitive to short-term atmospheric and ocean forcing, and respond very quickly to small fluctuations. On century timescales, however, multiple external parameters (e.g. outlet glacier shape) may dominate the mass change. These findings suggest that special care must be taken in the projection of future dynamic ice loss.

Khan, S. A.; Kjeldsen, K. K.; Kjær, K. H.; Bevan, S.; Luckman, A.; Aschwanden, A.; Bjørk, A. A.; Korsgaard, N. J.; Box, J. E.; van den Broeke, M.; van Dam, T. M.; Fitzner, A.

2014-08-01

251

Modern pollen assemblages and vegetational history of the moraines of the Klutlan Glacier and its surroundings, Yukon Territory, Canada*1  

NASA Astrophysics Data System (ADS)

Modern pollen assemblages have been studied from surficial lake muds and moss polsters collected from five vegetated ice-cored moraines of the Klutlan Glacier. The youngest vegetated moraine (K-II) is characterized by high pollen values for Salix and Hedysarum, K-III by high Salix and Shepherdia canadensis and low Hedysarum and Picea, K-IV by high Betula, Salix, and Shepherdia, and K-V and the Harris Creek moraine (HCM) by high Picea. Variations are summarized by canonical variates analysis. A percentage pollen diagram from Gull Lake on the upland east of the glacier records vegetational development since the deposition of the White River volcanic ash 1220 14C yr ago. An initial species-rich treeless vegetation was replaced by birch-alder-willow shrub-tundra, and this by open Picea glauca forest similar to present vegetation around the lake. Sites on HCM show two basic stratigraphies. Triangle Lake reflects vegetational succession from Salix-Shepherdia canadensis scrub similar to that on K-III today, through open Picea woodland of K-IV type, to closed Picea forests of K-V and HCM. Heart Lake and Cotton Pond reflect vegetational development following melting of ice underlying the spruce forests of HCM. These two types are summarized by positioning the fossil spectra on the first two canonical variate axes of the modern surface spectra.

Birks, H. J. B.

1980-07-01

252

Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages.  

USGS Publications Warehouse

We produced a series of decimeter-sized impact craters in blocks of ice near 0oC and -70oC and in ice-saturated sand near -70oC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar satellites. Crater diameters in the ice-saturated sand were 2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were c.3 times larger. Martian impact crater energy versus diameter scaling may thus be a function of latitude. -from Authors

Croft, S.K.; Kieffer, S.W.; Ahrens, T.J.

1979-01-01

253

Soil-forming rates and processes on Quaternary moraines near Lago Buenos Aires, Argentina  

NASA Astrophysics Data System (ADS)

Thirty-four pedons on four moraine groups spanning the last 1 myr are used to investigate mechanisms and rates of soil development in Santa Cruz province, Argentina. All soils are coarse-loamy, mesic, Typic Haplocalcids or Calcic Haploxerolls occurring under short grass-shrub steppe, in a semi-arid climate. The dominant soil-forming processes are the accumulation of organic matter, carbonate, and clay-sized particles. Organic carbon accumulates rapidly in these soils, but significantly higher amounts in the oldest two moraine groups are likely the result of slight differences in soil-forming environment or grazing practices. Accumulation rates of carbonate and clay decrease with age, suggesting either decreased influx in the earliest part of the record or attainment of equilibrium between influx and loss. There are no changes in soil redness, and preservation of weatherable minerals in the oldest soils indicates there is little chemical weathering in this environment. Measured dust input explains the accumulation of both clay and carbonate. We present a carbonate cycling model that describes potential sources and calcium mobility in this environment. Calibration of rates of soil formation creates a powerful correlation tool for comparing other glacial deposits in Argentina to the well-dated moraines at Lago Buenos Aires.

Douglass, Daniel C.; Bockheim, James G.

2006-03-01

254

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments  

PubMed Central

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550–1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems. PMID:23716658

La Farge, Catherine; Williams, Krista H.; England, John H.

2013-01-01

255

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.  

PubMed

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550-1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems. PMID:23716658

La Farge, Catherine; Williams, Krista H; England, John H

2013-06-11

256

Soil development on recent end moraines of the Klutlan Glacier, Yukon Territory, Canada*1  

NASA Astrophysics Data System (ADS)

Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175-200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50-100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa ( Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.

Jacobson, G. L.; Birks, H. J. B.

1980-07-01

257

Exposure history of the lunar meteorite, Elephant Moraine 87521  

NASA Technical Reports Server (NTRS)

We report the noble gas concentrations and the Al-26, Be-10, Cl-36, and Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for about 1 Ma at a depth of 1-5 g/sq cm followed, not necessarily directly, by a second one for 26 Ma at about 565 g/sq cm; launch from the moon less than 0.1 Ma ago; and arrival on earth 15-50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent less than 1 Ma at a lunar depth less than 1 g/sq cm. EET 87521 has a K/Ar age in the range 3.0-3.4 Ga, which is typical for lunar mare basalts.

Vogt, S.; Herzog, G. F.; Eugster, O.; Michel, TH.; Niedermann, S.; Kraehenbuhl, U.; Middleton, R.; Dezfouly-Arjomandy, B.; Fink, D.; Klein, J.

1993-01-01

258

Where might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records?  

E-print Network

Mountain Range by dating glacial erratics and ice-cored moraines. They concluded that the elevationWhere might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records? S.L. Bradley a, , M. Siddall a , G.A. Milne b , V. Masson-Delmotte c , E. Wolff d

Siddall, Mark

259

Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska  

USGS Publications Warehouse

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems.

Carlson, P.R.; Cowan, E.A.; Powell, R.D.; Cai, J.

1999-01-01

260

On the age vs depth and optical clarity of deep ice at South Pole  

E-print Network

The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the South Pole. During the 1995-96 season an additional six strings will be deployed at greater depths. Provided absorption, scattering, and refraction of visible light are sufficiently small, the trajectory of a muon into which a neutrino converts can be determined by using the array of phototubes to measure the arrival times of \\v{C}erenkov light emitted by the muon. To help in deciding on the depth for implantation of the six new strings, we discuss models of age vs depth for South Pole ice, we estimate mean free paths for scattering from bubbles and dust as a function of depth, and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hydrate inclusions and normal ice. We conclude that the depth interval 1600 to 1800 m will be suitably transparent for the next six AMANDA strings and, moreover, that the interval 1600 to 2100 m will be suitably transparent for a future 1-km$^3$ observatory except possibly in a region a few tens of meters thick at a depth corresponding to a peak in the dust concentration at 60 kyr BP.

The AMANDA collaboration

1995-01-23

261

Depositional environments during the Late Palaeozoic ice age (LPIA) in northern Ethiopia, NE Africa  

NASA Astrophysics Data System (ADS)

The Late Palaeozoic sediments in northern Ethiopia record a series of depositional environments during and after the Late Paleozoic ice age (LPIA). These sediments are up to 200 m thick and exceptionally heterogeneous in lithofacies composition. A differentiation of numerous types of lithofacies associations forms the basis for the interpretation of a large range of depositional processes. Major glacigenic lithofacies associations include: (1) sheets of diamictite, either overlying glacially eroded basement surfaces or intercalated into the sediment successions, and representing subglacial tillites, (2) thick massive to weakly stratified muddy clast-poor diamictites to lonestone-bearing laminated mudstones originating from a combination of suspension settling of fines and iceberg rainout, (3) lensoidal or thin-bedded diamictites deposited from debris flows, (4) wedges of traction and gravity transported coarse-grained sediments deposited in outwash fans, (5) irregular wedges or sheets of mudstones deformed primarily by extension and incorporating deformed beds or rafts of other lithofacies formed by slumping, and (6) irregular bodies of sandstone, conglomerate and diamictite deformed by glacial pushing. The dominance of laminated or massive clast-bearing mudstones in most successions indicates ice-contact water bodies as the major depositional environment. Into this environment, coarse-grained sediments were transported by various gravity driven transport processes, including dropstone activity of ice-bergs, slumping, cohesive debris flow, hyperconcentrated to concentrated flow, hyperpycnal flow, and by turbidity flow. Close to glacier termini, wedge-shaped bodies of conglomerate, sandstone, diamictite and mudstone were deposited primarily in subaqueous outwash-fans. Soft-sediment deformation of these sediments either records ice push during glacier advance or re-sedimentation by slumping. Apart from an initial glacier advance when thick ice of temperate or polythermal glaciers covered the whole basin, many sections document at least a second major phase of ice advance and retreat, and some sections additional minor advance-retreat cycles. Whether most of the LPIA sediments in northern Ethiopia were deposited in lakes or in fjords is not yet clear. Although univocal evidence of marine conditions is missing, the presence of carbonate-rich beds and the trace fossil assemblage are compatible with a restricted marine environment such as broad palaeofjords affected by strong freshwater discharge during deglaciation. A restricted marine environment for most of the sediments in northern Ethiopia could challenge models of the LPIA sediments in Arabia as primarily glaciolacustrine and glaciofluviatile deposits.

Bussert, Robert

2014-11-01

262

Deposition ice nucleation on fresh, cloud processed, internally mixed and oxidatively aged ?-pinene secondary organic aerosol  

NASA Astrophysics Data System (ADS)

There are many uncertainties related to role of organic aerosol (OA) as ice nuclei (IN). To that end, the ice nucleating abilities of fresh, cloud processed, internally mixed, and oxidatively aged secondary organic aerosol (SOA) particles were investigated with the University of Toronto continuous flow diffusion chamber (UT-CFDC) at temperatures relevant for cirrus cloud formation. Our SOA particles were produced by ?-pinene ozonolysis which took place in a flow tube (FT) and a smog chamber (SC). The FT-SOA particles mimicked freshly formed particles while the water soluble organic compound (WSOC) experiments from both the flow tube (FT-WSOC-SOA) and the smog chamber (SC-WSOC-SOA) capture the character of aged and cloud processed SOA particles. The FT-SOA particles exhibited low ice nucleation efficiency, i.e. relative humidities with respect to ice (RHi) of 152×4% and 157×4% were required to activate 0.1% of the aerosol particles in deposition mode at 223K and 218K, respectively. Similarly, the IN efficiencies of the FT-WSOC-SOA and SC-WSOC-SOA particles were found to be comparably low between 233K and 214K. However, if both the FT-WSOC-SOA and the SC-WSOC-SOA particles were pre-cooled at 233K prior to entering the UT-CFDC they nucleate ice at between 6 to 9% lower relative humidities, probably due to decreased viscosity. We also observed that an increase in the oxygen to carbon ratio (from 0.39 to 0.78) of the SC-WSOC-SOA particles from aqueous oxidative processing did not modify IN abilities. Finally, given that SOA is commonly mixed with inorganic salts, especially when arising through cloud processing, it was found that internally mixed particles of SC-WSOC-SOA and ammonium sulfate (AS) had a significantly higher RHi (140×5% at 219K) than pure AS particles of the same size (125×4%). Overall conclusions are that SOA-containing particles may act as IN only in regions where more efficient are not present. The SOA component will serve to suppress the IN abilities of efficient IN when internally mixed.

Ladino Moreno, L.; Zhou, S.; Aljawhary, D.; Yakobi-Hancock, J.; Abbatt, J.

2013-12-01

263

Influence of the Little Ice Age on the biological structure of lakes in South West Greenland  

NASA Astrophysics Data System (ADS)

Arctic lakes are considered to be particularly sensitive to environmental change, with biological remains in lake sediment records being interpreted as reflecting climate forcing. However the influence that differences in catchment properties and lake morphometries have on the sedimentary record is rarely considered. We investigated sediment cores from three lakes located close to the inland ice sheet margin in the Kangerlussuaq area of South West Greenland but within a few kilometres of one another. This regional replication allowed for direct comparisons of biological change in lakes exposed to identical environmental pressures (cooling, increased wind speeds) over the past c.2000 years. Sedimentary pigments were used as a proxy for whole-lake production and to investigate differences in phytoplankton community structure whilst fossil diatom assemblages were studied to determine differences in ecological responses during this time. We noted several major effects of the Little Ice Age cooling (LIA, c. 1400-1850AD). The organic content of sediments in all three lakes declined, and this effect was most pronounced in lakes closest to the inland ice sheet margin, which suggests that aeolian inputs derived from the glacial outwash plains (sandurs), and wind-scouring of the thin catchment soils by strong katabatic winds associated with the regional cooling might have both contributed to this sedimentary change. During the LIA total algal production (as indicated by chlorophyll and carotenoid pigments) was lower in all three lakes, most likely because of extended ice-cover and shorter growing seasons, and the ratio of planktonic: benthic diatom taxa increased, possibly because of lower light availability or fertilization from loess material. Despite this coherence in lake response to the LIA, diatom community composition changes in individual lakes differed, reflecting individual lake morphometry and catchment characteristics. These findings highlight the importance of regionally-replicated palaeo-studies when interpreting ecological impacts of long-term climate variability, and in assessing likely future response to climate change.

McGowan, S.; Hogan, E. J.; Jones, V.; Anderson, N. J.; Simpson, G.

2013-12-01

264

Age of the crowfoot advance in the Canadian Rocky Mountains. A glacial event coeval with the Younger Dryas oscillation  

SciTech Connect

A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.

Reasoner, M.A.; Rutter, N.W. (Univ. of Alberta, Edmonton, Alberta (Canada)); Osborn, G. (Univ. of Calgary, Alberta (Canada))

1994-05-01

265

Deglaciation dynamics following the Little Ice Age on Svalbard: Implications for shaping of landscapes at high latitudes  

Microsoft Academic Search

The late culmination of the Little Ice Age (LIA) on Svalbard allows a detailed reconstruction of the landscape's response to the subsequent climatic warming. The study area comprises a small glacier (400–1000 m a.s.l.), on the south side of Adventfjorden (78°11?N) that was polythermal during the LIA and turned into a passively down-wasting cold-based ice-mass prior to 1936. Reconstruction of

Ida Lønne; Astrid Lyså

2005-01-01

266

Reassessment of ice-age cooling of the tropical ocean and atmosphere  

USGS Publications Warehouse

The CLIMAP project's reconstruction of past sea surface temperature inferred limited ice-age cooling in the tropical oceans. This conclusion has been controversial, however, because of the greater cooling indicated by other terrestrial and ocean proxy data. A new faunal sea surface temperature reconstruction, calibrated using the variation of foraminiferal species through time, better represents ice-age faunal assemblages and so reveals greater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans. Here we explore the climatic implications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model. Relative to model results obtained using CLIMAP sea surface temperatures, the cooler equatorial oceans modify seasonal air temperatures by 1-2??C or more across parts of South America, Africa and southeast Asia and cause attendant changes in regional moisture patterns. In our simulation of the Last Glacial Maximum, the Amazon lowlands, for example, are cooler and drier, whereas the Andean highlands are cooler and wetter than the control simulation. Our results may help to resolve some of the apparent disagreements between oceanic and continental proxy climate data. Moreover, they suggest a wind-related mechanism for enhancing the export of water vapour from the Atlantic to the Indo-Pacific oceans, which may link variations in deep-water production and high-latitude climate changes to equatorial sea surface temperatures.

Hostetler, S.W.; Mix, A.C.

1999-01-01

267

Holocene history of North Ice Cap, northwestern Greenland  

NASA Astrophysics Data System (ADS)

Although much research has focused on the past extents of the Greenland Ice Sheet, less is known about the smaller ice caps on Greenland and how they have evolved over time. These small ice caps respond sensitively to summer temperatures and, to a lesser extent, winter precipitation, and provide valuable information about climatic conditions along the Greenland Ice Sheet margins. Here, we investigate the Holocene history of North Ice Cap (76°55'N 68°00'W), located in the Nunatarssuaq region near Thule, northwest Greenland. Our results are based on glacial geomorphic mapping, 10Be dating, and analyses of sediment cores from a glacially fed lake. Fresh, unweathered and unvegetated boulders comprise moraines and drift that mark an extent of North Ice Cap ~25 m outboard of the present ice margin. It is likely that these deposits were formed during late Holocene time and we are currently employing 10Be surface exposure dating to examine this hypothesis. Just outboard of the fresh moraines and drift, boulders and bedrock show significant weathering and are covered with lichen. Based on glacial geomorphic mapping and detailed site investigations, including stone counts, we suggest that the weathered boulders and bedrock were once covered by erosive Greenland Ice Sheet flow from southeast to northwest over the Nunatarssuaq region. Five 10Be ages from the more weathered landscape only 100-200 m outboard of the modern North Ice Cap margin are 52 and 53 ka (bedrock) and 16, 23, and 31 ka (boulders). These ages indicate that recent ice cover has likely been cold-based and non-erosive, failing to remove inherited cosmogenic nuclides from previous periods of exposure, although the youngest boulder may provide a maximum limiting deglaciation age. Sediment cores collected from Delta Sø, a glacially-fed lake ~1.5 km outside of the modern North Ice Cap margin, contain 130 cm of finely laminated sediments overlying coarse sands and glacial till. Radiocarbon ages from just above the sands are 14,940 and 14,560 cal yr BP (medians of two-sigma ranges). Our results thus far suggest that the Nunatarssuaq region preserves a long and complex glacial history, including glaciation by the Greenland Ice Sheet and potentially North Ice Cap, as well as glaciation by both erosive and non-erosive ice. Based on the basal ages from Delta Sø and the youngest boulder 10Be age, recession at the end of the most recent glacial period likely occurred by ~15 ka. This is considerably earlier than most other terrestrial margins of Greenland that did not become ice free until ~10 ka. Our ongoing research is developing proxy and further chronological data from sediment cores from Delta Sø and nearby ice-marginal lakes to constrain the Holocene fluctuations of North Ice Cap.

Corbett, L. B.; Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Roy, E. P.; Thompson, J. T.

2013-12-01

268

Low-Velocity Impact Craters in Ice and Ice-Saturated Sand With Implications for Martian Crater Count Ages  

Microsoft Academic Search

We produced a series of decimeter-sized impact craters in blocks of ice near 0øC and -70øC and in ice-saturated sand near -70øC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar system satellites. The projectiles used were standard 0.22 and 0.30 caliber bullets fired at velocities between 0.3 and 1.5 km\\/s,

S. K. Croft; S. W. Kieffer; T. J. Ahrens

1979-01-01

269

Beacon Hill end moraine, Boston: new explanation of an important urban feature  

USGS Publications Warehouse

The usefulness of geology to engineers is in direct proportion to how well it helps us predict the subsurface; these predictions, in turn, depend on our knowledge of the geomorphic processes that molded the terrain. The uncertainties of interpretation are particularly great in glaciated terrain because our understanding of both glacial processes and history is so incomplete, a fact well illustrated in Beacon Hill. Recent construction activities in the eastern part of the hill, until now classified as a drumlin, have shown that it is better interpreted as an end moraine formed by a Wisconsonian glacial readvance. Instead of the firm till that was anticipated as foundation material, excavations exposed a complex of sand, gravel, and clay, with only minor zones of till. The structure of these deposits strongly suggests that originally they were plates of the glacial bed that froze to the glacier and were transported englacially. Thrust faulting and other deformations are glacial structures formed within the ice in the glacier's terminal zone. In spite of the complex englacial history, these deposits lost little of their original appearance and intergranular relationships. Upon deglaciation, the frozen moraine thawed, and slumping formed complex secondary structures on the ridge's lower flanks.

Kaye, Clifford A.

1976-01-01

270

Optically stimulated luminescence dating of sand-dune formed within the Little Ice Age  

NASA Astrophysics Data System (ADS)

Optically Stimulated Luminescence (OSL) dating has been intensively used to date the late Quaternary deposits. The Single-Aliquot Regenerative-dose (SAR) protocol was applied to measure coarse quartz grains extracted from Dali sand dunes, central China. It was found that this popular method could not accurately date sand dunes activities that recently happened. This is due to the low OSL sensitivity of quartz grains, leading to a failure in OSL dating that has also been met in other sediments before. To overcome this limitation, quartz grains were heated to 500 °C to increase the OSL output for one magnitude. Sensitivity changes could also be corrected by the following test dose OSL responses and has no influence on OSL ages. Thus it is suggested to carry out the SAR protocol for dim and young quartz OSL samples with additional annealing step (e.g. 500 °C) after the measurements of natural cycle. The resultant OSL ages proved that the last sand-dune activities happened during the Little Ice Age (?400 years ago), which was further supported by independent age control (?1600 AD) from historical documents.

Du, Jin-Hua; Wang, Xu-Long

2014-09-01

271

Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway  

NASA Astrophysics Data System (ADS)

In the Erdalen and Bødalen drainage basins located in the inner Nordfjord in western Norway the soils were formed after deglaciation. The climate in the uppermost valley areas is sub-arctic oceanic, and the lithology consists of Precambrian granitic orthogneisses on which Leptosols and Regosols are the most common soils. The Little Ice Age glacier advance affected parts of the valleys with the maximum glacier extent around AD 1750. In this study five sites on moraine and colluvium materials were selected to examine main soil properties, grain size distribution, soil organic carbon and pH to assess if soil profile characteristics and patterns of fallout radionuclides (FRNs) and environmental radionuclides (ERNs) are affected by different stages of ice retreat. The Leptosols on the moraines are shallow, poorly developed and vegetated with moss and small birches. The two selected profiles show different radionuclide activities and grain size distribution. The sampled soils on the colluviums outside the LIA glacier limit became ice-free during the Preboral. The Regosols present better-developed profiles, thicker organic horizons and are fully covered by grasses. Activity of 137Cs and 210Pbex concentrate at the topsoil and decrease sharply with depth. The grain size distribution of these soils also reflects the difference in geomorphic processes that have affected the colluvium sites. Significantly lower mass activities of FRNs were found in soils on the moraines than on colluviums. Variations of ERN activities in the valleys were related to characteristics of soil mineralogical composition. These results indicate differences in soil development that are consistent with the age of ice retreat. In addition, the pattern distribution of 137Cs and 210Pbex activities differs in the soils related to the LIA glacier limits in the drainage basins.

Navas, A.; Laute, K.; Beylich, A. A.; Gaspar, L.

2014-06-01

272

Revised Deglacial Chronology of the Laurentide Ice Sheet and Implications for Catastrophic Meltwater Discharge as Triggers for Abrupt Climate Change  

NASA Astrophysics Data System (ADS)

A current hypothesis suggests that the Younger Dryas climate change involves the sudden release of stored meltwater from glacial Lake Agassiz. However, such a trigger requires a specific flood chronology and volume. Because the retreat patterns of the Laurentide Ice Sheet control meltwater routing, timing, and volume, it is useful to assess whether the current retreat chronologies support meltwater release from Lake Agassiz immediately preceding the Younger Dryas. Specifically, we reexamine ice margin retreat from proposed outlet areas on the sub-continental divide through which Agassiz meltwater flowed. These outlet areas are the first gates any meltwater must have flowed through before reaching the ocean. In these two gate areas: Fort McMurray, Alberta (proposed northwest outlet), and Thunder Bay, Ontario (proposed eastern outlet), our geomorphic analysis of glacial landforms suggest a more complex deglaciation pattern than previously reconstructed. New radiocarbon analyses indicate that ice recession occurred up to 1000 14C yr later than previously thought. At least four distinct moraine sets around Fort McMurray record downslope ice margin recession that prevented ice-dammed meltwater from draining northward to the Arctic Ocean. These moraines are provisionally assigned ages of 10,460; 9,850; 9,660; and 9,510 14C yr, and the large Clearwater-lower Athabasca spillway cross-cuts the three oldest moraines. This relationship implies that the ice dam held until at least 9,660 14C yr, after which dam failure, lake drainage and any northwest drainage from Lake Agassiz across this divide occurred. Many long linear moraines southwest of Thunder Bay record deglaciation across the uplands of the Gunflint range from 12,000 until 10,550 14C yr. West of Thunder Bay in the lowlands north of the Gunflint range, along which the oldest eastern outlet into the Lake Superior basin is proposed, was not deglaciated until about 10,400 14C yr. Moreover, with continued ice recession, glaciolacustrine sediment records a widespread, ponded water body over the divide region until 10,100 14C yr. These new, younger deglacial chronologies from the proposed northwestern and eastern outlet regions do not support the hypothesis that meltwater from glacial Lake Agassiz triggered the Younger Dryas. Therefore as the evidence for a younger Lake Agassiz concomitant with a younger deglacial chronology continues to mount, it may be prudent to search elsewhere for a cause for the Younger Dryas.

Lowell, T. V.; Fisher, T. G.; Hajdas, I.

2005-12-01

273

The late Neoglacial ('Little Ice Age') glacier maximum in southern Norway : new 14C-dating evidence and climatic implications  

Microsoft Academic Search

Critical evidence is presented for the timing and extent of Holocene glacier variations in southern Norway based on end-moraine stratigraphy and 22 new 14C dates. Dates have been obtained from moss layers, other plant remains, peat and soil associated with outermost moraines delimiting the Neoglacial maximum extent of four glaciers in the Jotunheimen-Jostedalsbreen region. There is conclusive evidence for a

John A. Matthews

1991-01-01

274

Solving the paradox of the end of the Little Ice Age in the Alps  

NASA Astrophysics Data System (ADS)

The causes and timing of the Little Ice Age (fifteenth to nineteenth centuries) are still unclear (Crowley, 2000; Bond et al., 2001; Shindell et al., 2001). During the last part of this event (1760-1830), the advance of glaciers in the Alps conflicts with the summer temperature signal (Intergovernmental Panel on Climate Change, 2001). This paper attempts to solve this paradox. From glacier fluctuations and monthly temperature data, we show that mean winter precipitation was higher by at least 25% during this final phase compared to the twentieth century average and that glacier recession after 1830 clearly resulted from a winter precipitation decrease and not a temperature increase. Conversely, since the beginning of the twentieth century, glacier changes have been driven mainly by temperature change.

Vincent, Christian; Le Meur, Emmanuel; Six, Delphine; Funk, Martin

2005-05-01

275

Regionally coherent Little Ice Age cooling in the Atlantic Warm Pool  

USGS Publications Warehouse

We present 2 new decadal-resolution foraminiferal Mg/Ca-SST records covering the past 6-8 centuries from the northern Gulf of Mexico (GOM). These records provide evidence for a Little Ice Age (LIA) cooling of 2??C, consistent with a published Mg/Ca record from Pigmy Basin. Comparison of these 3 records with existing SST proxy records from the GOM-Caribbean region show that the magnitude of LIA cooling in the Atlantic Warm Pool (AWP) was significantly larger than the mean hemispheric cooling of <1??C. We propose that a reduction in the intensity and spatial extent of the AWP during the LIA, combined with associated changes in atmospheric circulation may account for the regional SST patterns observed in the GOM-Caribbean region during the LIA. Copyright 2009 by the American Geophysical Union.

Richey, J.N.; Poore, R.Z.; Flower, B.P.; Quinn, T.M.; Hollander, D.J.

2009-01-01

276

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.  

PubMed

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

277

Increase in penguin populations during the Little Ice Age in the Ross Sea, Antarctica.  

PubMed

Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes. Previous studies indicated that penguin populations increased when the climate became warmer and decreased when it became colder in the maritime Antarctic. Here we determined organic markers in a sediment profile collected at Cape Bird, Ross Island, high Antarctic, and reconstructed the history of Adélie penguin colonies at this location over the past 700 years. The region transformed from a seal to a penguin habitat when the Little Ice Age (LIA; 1500-1800 AD) began. Penguins then became the dominant species. Penguin populations were the highest during ca. 1490 to 1670 AD, a cold period, which is contrary to previous results in other regions much farther north. Different responses to climate change may occur at low latitudes and high latitudes in the Antarctic, even if for same species. PMID:23969993

Hu, Qi-Hou; Sun, Li-Guang; Xie, Zhou-Qing; Emslie, Steven D; Liu, Xiao-Dong

2013-01-01

278

Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly.  

PubMed

Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation. PMID:19965474

Mann, Michael E; Zhang, Zhihua; Rutherford, Scott; Bradley, Raymond S; Hughes, Malcolm K; Shindell, Drew; Ammann, Caspar; Faluvegi, Greg; Ni, Fenbiao

2009-11-27

279

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age  

PubMed Central

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

280

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

NASA Astrophysics Data System (ADS)

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.

Munroe, Jeffrey; Laabs, Benjamin

2013-04-01

281

Evolution of Glacier Snowline Since the End of the Last Ice Age in New Zealand  

NASA Astrophysics Data System (ADS)

An important problem in paleoclimatology is how Southern Hemisphere climate changed since the end of the last ice age. The terrestrial glacier record reflects past snowline (=equilibrium line altitude) variability and is one of the few direct proxies available, in the middle latitudes, of former atmospheric properties. We reconstruct changes in snowline since ~15 ka on the South Island of New Zealand using geomorphologic mapping, 10Be surface-exposure dating, accumulation-area ratio (AAR) methods and numerical modeling. The snowline data are a proxy for the 0°C atmospheric isotherm, which occurs above 1500 m asl in the central Southern Alps, and trends in temperature since ~15 ka. Our findings show that snowline was depressed during the Antarctic Cold Reversal. Subsequently, snowline rose ~100 m during the Younger Dryas stadial in Europe. These late glacial changes appear coherent across the southern middle latitudes. In the early Holocene, snowline was depressed >200 m relative to modern in the Southern Alps. Between 11 ka and 600 years ago, short-term oscillations punctuated a multi-millennia trend of decreasing glacier extent as snowline rose ~100 m. Since ~600 yrs ago, net snowline has continued progressively to rise. The record implies long-term warming in New Zealand since the Late Glacial period. During the Holocene, the lowest snowlines and most extensive glaciers occurred in the early part of the epoch. Snowline reconstruction and numerical modeling allow us to estimate that temperature depression during the Late Glacial was ~2.1±0.4°C (relative to modern) and increased about 0.6 to 1°C between the early and late Holocene. Our terrestrial glacier and snowline records show coherence and also they are consistent with marine records in the Australian sector, documenting a regional climate pattern. However, the climate of the southwest Pacific region was fundamentally different from that observed in the Northern Hemisphere, where the most extensive Holocene glaciers occurred during the European Little Ice Age period.

Kaplan, M. R.; Putnam, A. E.; Schaefer, J. M.; Denton, G. H.; Chinn, T. J.; Barrell, D.; Doughty, A. M.; Mackintosh, A. N.; Andersen, B. G.

2012-12-01

282

Lake carbonate-?18 records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns  

USGS Publications Warehouse

A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water ?18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water ?18O values decrease. Past lake-water ?18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate ?18O, supplemented by those in carbonate and organic ?13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ?AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ?AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake ?18O, a similarly small, stratified, alkaline lake located ?250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.

Anderson, Lesleigh; Finney, Bruce P.; Shapley, Mark D.

2011-01-01

283

Assessing the Response of Alaska's Glaciers to Post-Little Ice Age Climate Change  

NASA Astrophysics Data System (ADS)

A comprehensive survey of the eleven mountain ranges and three island areas in Alaska that presently support glaciers was conducted to determine how glaciers in each area have responded to post-Little Ice Age (LIA) climate change. Today, glaciers cover 5 percent of Alaska, about 75,000 sq. km., range in elevation from 6,000 m to below sea level, and span latitudes from south of 55 degrees N to north of 69 degrees N. During the LIA, Alaskan glaciers expanded significantly, covering 10 percent more area than today. Many different types of data were used to construct baselines and determine glacier change. These include: published descriptions of glaciers (1794 - 2000), historic and modern maps (1794 - 2000), aerial photography (1926 - 2001), ground photography (1884 - 2001), airborne radar (1981 - 1991), satellite radar (1978 - 1998), space photography (1984 - 1994), multi-spectral satellite imagery (1972 - 2001), aerial reconnaissance and field observations by the author (1968 - 2001), and various types of proxy data. Data available varied for each region and glacier. Every mountain range and island group investigated is characterized by significant glacier retreat, thinning, and/or stagnation, especially at lower elevations. At some locations, glaciers have completely disappeared during the twentieth century. In other areas, retreat that started as early as the early eighteenth century, has continued into the twenty-first century. Ironically, in several areas, retreat is resulting in the number of glaciers is actually increasing, but the volume and area of ice is decreasing. The key survey findings are: ALEXANDER ARCHIPELAGO, KODIAK ISLAND, ALEUTIAN ISLANDS: every glacier examined showed evidence of thinning and retreat. Some have disappeared since last being mapped in the mid-twentieth century; COAST MOUNTAINS, ST. ELIAS MOUNTAINS, CHUGACH MOUNTAINS, KENAI MOUNTAINS, WRANGELL MOUNTAINS, ALASKA RANGE, AND THE ALEUTIAN RANGE: more than 95 percent of glaciers ending below an elevation of 1,500 m are retreating, thinning, and/or stagnating. Some advancing glaciers have tidewater termini. The two largest glaciers, Bering and Malaspina Glaciers, are thinning and retreating, losing several cubic kilometers of ice each year to melting and calving; TALKEETNA MOUNTAINS, AHKLUN-WOOD RIVER MOUNTAINS, KIGLUAIK MOUNTAINS, AND THE BROOKS RANGE: every glacier examined is retreating. Some disappeared during the twentieth century. Glaciers at higher elevations show little or no change. Perhaps, at these locations, regional climate change has not resulted in temperatures being elevated to a level where they impact existing glacier ice. Increases in precipitation may also be compensating for increases in melting. Throughout Alaska, in response to post-Little Ice Age climate change, all but a few glaciers that descent below an elevation of 1,500 m have thinned, stagnated, and/or retreated. Of the nearly 700 named Alaskan glaciers, less than a dozen are currently advancing.

Molnia, B. F.

2001-12-01

284

Effect of vegetation on an ice-age climate model simulation  

NASA Astrophysics Data System (ADS)

A growing number of studies suggest that vegetation changes can significantly influence regional climate variations. Herein we utilize a climate model (GENESIS) with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum (LGM). In particular, we focus on the potential response to a significant reduction in the area of tropical rainforest. Simulations employed a global vegetation reconstruction for the LGM and Climate/Long-Range Investigation, Mapping and Prediction (CLIMAP) sea surface temperature (SST) estimates. Results indicate that expansion of dryland vegetation causes a 15-30% additional LGM cooling for Australia (0.4°C) and Africa (0.9°C), respectively. Turnover from conifer to tundra also causes cooling of 2°-4°C or more in western Europe and Siberia. However, for the largest rainforest area (Amazon Basin), inclusion of realistic vegetation increased modeled temperatures 2°-4°C and decreased precipitation by 10-35%. These latter results are similar to those obtained with sensitivity experiments of the effects of future Amazon deforestation. Initial assessment of the potential effect of decreased stomatal resistance due to lower ice age CO2 levels indicates little significant response to this effect. Comparison of model-predicted low-elevation LGM temperature changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the LGM results in slightly more than 50% agreement between models and data for low-elevation sites in low-mid latitudes. Data at variance with model predictions would appear to be explainable by considering additional changes in vegetation, ice age dust, or a 1°-2°C cooling below CLIMAP values. This conclusion is at variance with a 3°-4°C tropical cooling suggested by some studies for explaining estimated land temperature changes during the LGM. In some western European sites model temperatures are colder than proxy data by 2°-8°C. This model-data discrepancy may be explained by less sea ice in the subpolar North Atlantic than stipulated by CLIMAP, a conclusion consistent with new marine data from that region.

Crowley, Thomas J.; Baum, Steven K.

1997-07-01

285

Decreasing frequency of forest fires in the southern boreal zone of Québec and its relation to global warming since the end of the 'Little Ice Age'  

Microsoft Academic Search

Although an increasing frequency of forest fires has been suggested as a consequence of global warming, there are no empirical data that have shown a climatically driven change in fire frequency since the warming that has followed the end of the 'Little Ice Age'. We present here evidence from fire and tree-ring chronologies that the post-'Little Ice Age' climate change

Yves Bergeron; Sylvain Archambault

1993-01-01

286

Examining the relationship between relative age, competition level, and dropout rates in male youth ice-hockey players.  

PubMed

The relative age effect suggests that athletes born in the first two quartiles of a given selection year experience a selection advantage and therefore a greater opportunity for success. We describe two studies examining the relationship between relative age, competition level, and dropout rates of Ontario Minor Hockey Association male ice-hockey players from ages 10 to 15 years (n?=?14?325). In Study 1, dropout was highest among players born in quartiles three and four [?(2) (3)?=?16.32, P?age and dropout from ice-hockey and adds further depth to our understanding of this persistent phenomenon. PMID:24118622

Lemez, S; Baker, J; Horton, S; Wattie, N; Weir, P

2014-12-01

287

Steppe lion remains imported by Ice Age spotted hyenas into the Late Pleistocene Perick Caves hyena den in northern Germany  

Microsoft Academic Search

Upper Pleistocene remains of the Ice Age steppe lion Panthera leo spelaea (Goldfuss, 1810) have been found in the Perick Caves, Sauerland Karst, NW Germany. Bones from many hyenas and their imported prey dating from the Lower to Middle Weichselian have also been recovered from the Perick Cave hyena den. These are commonly cracked or exhibit deep chew marks. The

Cajus G. Diedrich

2009-01-01

288

Fluctuations in Tree Ring Cellulose d18O during the Little Ice Age Correlate with Solar Activity  

Microsoft Academic Search

The Maunder Minimum (AD1645-1715), when sunspots became exceedingly rare, is known to coincide with the coldest period during the Little Ice Age. This is a useful period to investigate possible linkage between solar activity and climate because variation in solar activity was different from that of today. The solar cycle length was longer (14 and 28 years) than that of

Y. T. Yamaguchi; Y. Yokoyama; H. Miyahara; T. Nakatsuka

2008-01-01

289

El Nin~o's tropical climate and teleconnections as a blueprint for pre-Ice Age climates  

E-print Network

El Nin~o's tropical climate and teleconnections as a blueprint for pre-Ice Age climates Peter Molnar Department of Geological Sciences, Cooperative Institute for Research in Environmental Science; published 21 May 2002. [1] At $2.7 million years ago the warm equable climates of early and ``middle

Mojzsis, Stephen J.

290

Glacial recession in the Tropical Andes from the Little Ice Age: the case of Ampato Volcanic Complex (Southern Peru  

Microsoft Academic Search

Data published over the last decade reveal substantial glacial recession in the tropical Andes since the Little Ice Age (LIA), (Ramirez, et al., 2001; Rabatel, et al., 2005; Rabatel, et al., 2008; Vuille, et al., 2008; Hastenrath, 2009; Jomelli, et al., 2009), and a growing rate of recession since the 1980's caused by global warming (Ramirez, et al., 2001; Vuille,

J. Alcalá; D. Palacios; J. J. Zamorano

2010-01-01

291

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia  

Microsoft Academic Search

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field

Kris Holm; Michael Bovis; Matthias Jakob

2004-01-01

292

Post–Little Ice Age record of coarse and fine clastic sedimentation in an Alaskan proglacial lake  

Microsoft Academic Search

Many assessments of glacial sediment yield rely solely on mea- surements of fine-grained suspended sediment. We show that sus- pended sediment contributes ,20% of the total clastic sediment discharge into Iceberg Lake, an Alaskan proglacial lake. Drainage of this lake in 1999 exposed outcrops of varved lacustrine sediment that record suspended sediment deposition. Since a Little Ice Age highstand two

Michael G. Loso; Robert S. Anderson; Suzanne P. Anderson

2004-01-01

293

Dominant ENSO frequencies during the Little Ice Age in Northern Patagonia: The varved record of proglacial Lago Frías, Argentina  

Microsoft Academic Search

The global character of the time interval known as the Little Ice Age (LIA) is at present relatively well established. However, the forcing mechanisms behind this cooling interval are still elusive. Investigations in annually laminated sediments have shown that varved sediments are among the best climate archives to tackle these questions. Proglacial Lago Frías in northern Patagonia is fed by

D. Ariztegui; P. Bosch; E. Davaud

2007-01-01

294

Cosmogenic exposure dating of boulders and bedrock in Denmark: wide range in ages reflect strong dependence of post-depositional stability related to specific glacial landforms  

NASA Astrophysics Data System (ADS)

The timing of ice-sheet fluctuations, as indicated by glacier advances and retreats, is detected from a wide range of geochronological techniques, including varve counting, and radiocarbon and luminescence dating of proglacial and inter till sediments. A robust Late Weichselian chronology of deglacial ice sheet fluctuations in southwestern Scandinavia indicates that the decline of the Scandinavian Ice Sheet from the Last Glacial Maximum position at c. 23-21 kyr (thousands of years) ago in central Denmark occurred through recessional stages and readvances. Active glaciers withdrew from eastern Denmark 17-16 kyr ago and left the southwestern Baltic basin ice free at the beginning of the Bølling interstade c. 14.5 kyr ago. The withdrawal left behind belts of elongate end moraines and streamlined ground moraine as large ice masses were successively isolated causing massive down wasting until c. 12 - 11 kyr ago. In Eastern Denmark and southernmost Sweden this lead to formation of complex superimposed glacial landscapes originally covered with a wealth of erratic boulders. Hitherto untried cosmogenic nuclide surface exposure dating was applied to sites in Eastern Denmark to test the method against independent chronologies. Samples collected from erratics, moraines and ice-sculpted bedrock were prepared at the Cosmogenic Nuclide Laboratory at the University of Glasgow and AMS measurements were carried out at the Scottish Universities Environmental Research Centre (SUERC) AMS facility. Procedural blank corrected 10Be concentrations were converted to in situ 10Be surface exposure ages using the online CRONUS-Earth 10Be-26Al exposure age calculator Version 2.2. Exposure ages from 35 samples range between 11.5 and 20 kyr, 18 of which lie within the expected age envelope. Two samples show overestimated ages apparently due to cosmogenic nuclide inheritance from previous exposure episodes. The remaining 17, two of which have suffered from exhumation, are younger than predicted. Dating of boulders and adjacent bedrock on the island of Bornholm in the western Baltic reveal almost similar ages and fit the independent chronology. This indicates that very little if any inherited nuclides are present in the boulders. Moreover, ages from Bornholm seem to become younger with descending height above sea level, suggesting that the island was progressively exposed as glaciers in the Baltic downwasted. In mainland Denmark ages that fit the age model are situated on top of end moraines or located on streamlined ground moraine. Boulders with underestimated ages were sampled in dead ice moraines and down wasting landscapes. These results are interpreted as providing landform stabilisation ages since these boulders appear to have first melted out of dead ice and came to rest after 15 until about 12 kyr ago. We conclude that cosmogenic nuclide surface exposure dating is very sensitive to landscape stability, and that when used for dating glacier fluctuations surface stability should be thoroughly evaluated before sampling.

Houmark-Nielsen, Michael; Linge, Henriette; Fabel, Derek; Xu, Sheng

2010-05-01

295

Asynchronous Little Ice Age glacier fluctuations in Iceland and European Alps linked to shifts in subpolar North Atlantic circulation  

NASA Astrophysics Data System (ADS)

Records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume. In the North Atlantic region, glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover. However, the majority of glacier records are discontinuous and temporally restricted, owing in part to the extensive advance of Northern Hemisphere glaciers during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Here, we combine an absolutely dated and continuous record of Langjökull ice marginal fluctuations with new reconstructions of sediment flux through the past 1.2 ka using varved sediments from Hvítárvatn, a proglacial lake in Iceland's central highlands. Large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles. Sediment data reveal two discrete phases of ice expansion occurring ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. These advances are separated by a persistent interval of ice retreat, suggesting that a substantial period of warming interrupted LIA cold. The pattern of Icelandic glacier activity contrasts with that of European glaciers but shows strong similarities to reconstructed changes in North Atlantic oceanographic conditions, indicating differing regional responses to coupled ocean-atmosphere-sea ice variations. Our data suggest that subpolar North Atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid LIA and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments.

Larsen, D. J.; Miller, G. H.; Geirsdottir, A.

2013-12-01

296

Asynchronous Little Ice Age glacier fluctuations in Iceland and European Alps linked to shifts in subpolar North Atlantic circulation  

NASA Astrophysics Data System (ADS)

Records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume. In the North Atlantic region, glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover. However, the majority of glacier records are discontinuous and temporally restricted, owing in part to the extensive advance of Northern Hemisphere glaciers during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Here, we combine an absolutely dated and continuous record of Langjökull ice marginal fluctuations with new reconstructions of sediment flux through the past 1.2 ka using varved sediments from Hvítárvatn, a proglacial lake in Iceland's central highlands. Large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles. Sediment data reveal two discrete phases of ice expansion occurring ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. These advances are separated by a persistent interval of ice retreat, suggesting that a substantial period of warming interrupted LIA cold. The pattern of Icelandic glacier activity contrasts with that of European glaciers but shows strong similarities to reconstructed changes in North Atlantic oceanographic conditions, indicating differing regional responses to coupled ocean-atmosphere-sea ice variations. Our data suggest that subpolar North Atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid LIA and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments.

Larsen, Darren J.; Miller, Gifford H.; Geirsdóttir, Áslaug

2013-10-01

297

Little Ice Age to modern climate transition of Meso-American climate derived from speleothems  

NASA Astrophysics Data System (ADS)

We present a high-resolution (annual) reconstruction of hydrological variability from a speleothem located in a cave under the Guatemala/Belize (G/B) border. Our age model is highly constrained by annual layering in the speleothem and nine U/Th MC ICPMS dates. Our ?18O record from 1640 to 2005 A.D. shows two large, abrupt decreases in inferred precipitation rates that appear to coincide with historical, large volcanic eruptions, superimposed on a general drying trend. The first abrupt increase in aridity occurred synchronously with the Tambora eruption in 1815, followed by another sharp decrease in Meso-American precipitation coincident with the eruption of Krakatau in 1883. Both drying events extend for thirty to forty years after the initial eruption, in good agreement with the 19th century drying and the "volcanic dust veil index" from Lamb (1970). Preliminary analysis indicates that the Meso-Americas may be highly sensitive to volcanic forcing because they receive considerable climate input from both Atlantic (primary) and Pacific (secondary) influences. Past volcanic aerosol model loading patterns from the Mt. Pinatubo eruption produced global and in particular, North Atlatic cooling. This could have moved the Atlantic ITCZ southwards and caused drying in Meso-America. Wavelet analysis of the speleothem data also shows ENSO scale variability. Our results highlight the need for better understanding of the consequences of volcanic eruptions and their patterns of climate variability, in particular during the transition from the Little Ice Age to the modern industrial era.

Winter, A.; Miller, T.; Kushnir, Y.; Black, D. E.; Estrella, J.; Burnett, A.; Haug, G. H.; Breitenbach, S.; Beaufort, L.; Edwards, R.

2011-12-01

298

End of the Little Ice Age in the Alps forced by industrial black carbon.  

PubMed

Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13-17 W?m(-2) between 1850 and 1880, and to 9-22 W?m(-2) in the early 1900s, with snowmelt season (April/May/June) forcings reaching greater than 35 W?m(-2) by the early 1900s. These snowmelt season radiative forcings would have resulted in additional annual snow melting of as much as 0.9 m water equivalent across the melt season. Simulations of glacier mass balances with radiative forcing-equivalent changes in atmospheric temperatures result in conservative estimates of accumulating negative mass balances of magnitude -15 m water equivalent by 1900 and -30 m water equivalent by 1930, magnitudes and timing consistent with the observed retreat. These results suggest a possible physical explanation for the abrupt retreat of glaciers in the Alps in the mid-19th century that is consistent with existing temperature and precipitation records and reconstructions. PMID:24003138

Painter, Thomas H; Flanner, Mark G; Kaser, Georg; Marzeion, Ben; VanCuren, Richard A; Abdalati, Waleed

2013-09-17

299

End of the Little Ice Age in the Alps forced by industrial black carbon  

PubMed Central

Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13–17 W?m?2 between 1850 and 1880, and to 9–22 W?m?2 in the early 1900s, with snowmelt season (April/May/June) forcings reaching greater than 35 W?m?2 by the early 1900s. These snowmelt season radiative forcings would have resulted in additional annual snow melting of as much as 0.9 m water equivalent across the melt season. Simulations of glacier mass balances with radiative forcing-equivalent changes in atmospheric temperatures result in conservative estimates of accumulating negative mass balances of magnitude ?15 m water equivalent by 1900 and ?30 m water equivalent by 1930, magnitudes and timing consistent with the observed retreat. These results suggest a possible physical explanation for the abrupt retreat of glaciers in the Alps in the mid-19th century that is consistent with existing temperature and precipitation records and reconstructions. PMID:24003138

Painter, Thomas H.; Flanner, Mark G.; Kaser, Georg; Marzeion, Ben; VanCuren, Richard A.; Abdalati, Waleed

2013-01-01

300

Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps)  

NASA Astrophysics Data System (ADS)

The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 14C ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 14C ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Würm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Würm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard-Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps.

Monegato, Giovanni; Ravazzi, Cesare; Donegana, Marta; Pini, Roberta; Calderoni, Gilberto; Wick, Lucia

2007-09-01

301

Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response  

NASA Technical Reports Server (NTRS)

A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.

Saltzman, Barry; Maasch, Kirk A.

1988-01-01

302

Geomorphic relations among glacial Lake Algonquin and the Munising and Grand Marais moraines in eastern Upper Michigan, USA  

NASA Astrophysics Data System (ADS)

Data obtained from ground-penetrating radar (GPR), optically stimulated luminescence (OSL) dating, and geostatistical reconstructions of Lake Algonquin water planes indicate that high-standing outwash aprons flanking the Munising moraine's southern margin in eastern Upper Michigan terminate as large, coalescing Gilbert-type ice-contact deltas graded to the Main level of Lake Algonquin. Nearly 30 km of GPR imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition. Landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation. In time, these deltas aggraded to the Main Lake Algonquin level as the ice margin stabilized. An OSL date of 12.5 ± 1.1 ka on a nearby beach ridge associated with the Main Algonquin shoreline is consistent with this interpretation. These new data, coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta, indicate that Lake Algonquin was falling as delta deposition waned, eventually reaching a level concordant with the Lower Orillia level before final abandonment. Large, regionally extensive heads of outwash marking the crest of the Munising moraine are graded to the upper margins of these deltas and, by inference, must also correlate with Main Lake Algonquin and the associated Two Rivers deglaciation ca. 13-12.5 ka. The deltas, in turn, are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group Lake Algonquin shoreline. Because these aforementioned heads of outwash, part of Drexler and others' Grand Marais moraine, correlate with the Marquette moraine farther west, they likely date to the Marquette advance ca. 11.5 ka. Thus, landforms related to Two Rivers and to Marquette glaciations appear to comingle across the study area. In the absence of extensive exposures and datable materials, our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of Michigan.

Blewett, William L.; Drzyzga, Scott A.; Sherrod, Laura; Wang, Hong

2014-08-01

303

Simple energy balance model resolving the seasons and the continents - Application to the astronomical theory of the ice ages  

NASA Technical Reports Server (NTRS)

An analysis is undertaken of the properties of a one-level seasonal energy balance climate model having explicit, two-dimensional land-sea geography, where land and sea surfaces are strictly distinguished by the local thermal inertia employed and transport is governed by a smooth, latitude-dependent diffusion mechanism. Solutions of the seasonal cycle for the cases of both ice feedback exclusion and inclusion yield good agreements with real data, using minimal turning of the adjustable parameters. Discontinuous icecap growth is noted for both a solar constant that is lower by a few percent and a change of orbital elements to favor cool Northern Hemisphere summers. This discontinuous sensitivity is discussed in the context of the Milankovitch theory of the ice ages, and the associated branch structure is shown to be analogous to the 'small ice cap' instability of simpler models.

North, G. R.; Short, D. A.; Mengel, J. G.

1983-01-01

304

Ice formation and development in aged, wintertime cumulus over the UK: observations and modelling  

NASA Astrophysics Data System (ADS)

In situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of a line of small cumulus clouds, using Radar and Lidar, as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than -8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed, near cloud top, temperatures (-7.5 °C). The role of mineral dust particles, consistent with concentrations observed near the surface, acting as high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by secondary ice particle production providing the observed small amount of primary ice (about 0.01 L-1) was present to initiate it. This emphasises the need to understand primary ice formation in slightly supercooled clouds. It is shown using simple calculations that the Hallett-Mossop process (HM) is the likely source of the secondary ice. Model simulations of the case study were performed with the Aerosol Cloud and Precipitation Interactions Model (ACPIM). These parcel model investigations confirmed the HM process to be a very important mechanism for producing the observed high ice concentrations. A key step in generating the high concentrations was the process of collision and coalescence of rain drops, which once formed fell rapidly through the cloud, collecting ice particles which caused them to freeze and form instant large riming particles. The broadening of the droplet size-distribution by collision-coalescence was, therefore, a vital step in this process as this was required to generate the large number of ice crystals observed in the time available. Simulations were also performed with the WRF (Weather, Research and Forecasting) model. The results showed that while HM does act to increase the mass and number concentration of ice particles in these model simulations it was not found to be critical for the formation of precipitation. However, the WRF simulations produced a cloud top that was too cold and this, combined with the assumption of continual replenishing of ice nuclei removed by ice crystal formation, resulted in too many ice crystals forming by primary nucleation compared to the observations and parcel modelling.

Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P. J.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

2012-06-01

305

Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations  

NASA Astrophysics Data System (ADS)

Acidity is an important chemical variable that impacts atmospheric and snowpack chemistry. Here we describe composite time series and the spatial pattern of acidity concentration (Acy = H+ - HCO3-) during the last 2000 years across the Dronning Maud Land region of the East Antarctic Plateau using measurements in seven ice cores. Coregistered measurements of the major ion species show that sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) determine greater than 98% of the acidity value. The latter, also described as excess chloride (ExCl-), is shown mostly to be derived from postdepositional diffusion of chloride with little net gain or loss from the snowpack. A strong inverse linear relationship between nitrate concentration and inverse accumulation rate provides evidence of spatially homogenous fresh snow concentrations and reemission rates of nitrate from the snowpack across the study area. A decline in acidity during the Little Ice Age (LIA, 1500-1900 Common Era) is observed and is linked to declines in HNO3 and ExCl- during that time. The nitrate decline is found to correlate well with published methane isotope data from Antarctica (?13CH4), indicating that it is caused by a decline in biomass burning. The decrease in ExCl- concentration during the LIA is well correlated to published sea surface temperature reconstructions in the Atlantic Ocean, which suggests increased sea salt aerosol production associated with greater sea ice extent.

Pasteris, Daniel; McConnell, Joseph R.; Edwards, Ross; Isaksson, Elizabeth; Albert, Mary R.

2014-05-01

306

The glacial sedimentology and geomorphological evolution of an outwash head/moraine-dammed lake, South Island, New Zealand  

NASA Astrophysics Data System (ADS)

Extensive exposures through the glacial landforms around southern Lake Pukaki, New Zealand, comprise seven lithofacies (LFs 1-7). LFs 1-3 are grouped together as LFA 1 (Pukaki Member) and record pulsed subaqueous grounding line fan progradation, cohesionless debris flows, underflow activity and rhythmite deposition by suspension settling, iceberg rafting of dropstones, and pulsed traction current activity. Localized disturbance of these deposits by glacitectonic deformation and multi-generational hydrofracture fills records minor readvances by the glacier snout and the emplacement of a glacitectonite (LF 4) derived from cannibalization of glacilacustrine sediments. LFs 4-6 are grouped together as LFA 2 (Twizel Member) and record direct glacigenic deposition of glacitectonite (LF 4), subglacial traction till (LF 5) and supraglacially dumped boulder rubble (LF 6). Stratigraphic relationships between LFA 1 with LFA 2 record the oscillatory behaviour of the former Tasman Glacier snout when it formed a calving margin in a proglacial and locally supraglacial lake dammed by a glacitectonically disturbed outwash head and lateral moraine ridges. This is entirely consistent with the landform-sediment record of its coeval terrestrial margins, where flutings and push moraines are diagnostic of active temperate glacier recession from a glacially overridden outwash head, the latter being recorded by the vertically stacked sub-horizontally bedded and coarse-grained gravels of LF 7 (Waitaki Member). Previous proposals that late Pleistocene lake damming was initiated by an ice-cored moraine arc appear unfounded, because the glacilacustrine deposits only lie above the altitude of the outwash head/lateral moraine arc in locations where they have been glacitectonically compressed. Alternatively, it is proposed that the overdeepened subglacial topography was produced by the construction of an outwash head, leading to a glacilacustrine sediment sink which operates at times when the expanded Tasman Glacier actively retreats from the outwash head apex. The changing landsystem imprint related to the shrinkage of the Tasman Glacier records spatio-temporal landsystem change, involving evolution from a coupled landsystem to a moraine-dammed to an uncoupled landsystem.

Evans, David J. A.; Rother, Henrik; Hyatt, Olivia M.; Shulmeister, James

2013-02-01

307

From Shakespeare to Defoe: malaria in England in the Little Ice Age.  

PubMed Central

Present global temperatures are in a warming phase that began 200 to 300 years ago. Some climate models suggest that human activities may have exacerbated this phase by raising the atmospheric concentration of carbon dioxide and other greenhouse gases. Discussions of the potential effects of the weather include predictions that malaria will emerge from the tropics and become established in Europe and North America. The complex ecology and transmission dynamics of the disease, as well as accounts of its early history, refute such predictions. Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s the coldest period of the Little Ice Age malaria was an important cause of illness and death in several parts of England. Transmission began to decline only in the 19th century, when the present warming trend was well under way. The history of the disease in England underscores the role of factors other than temperature in malaria transmission. PMID:10653562

Reiter, P.

2000-01-01

308

Conference Summary: First International Conference on Global Warming and the Next Ice Age  

NASA Technical Reports Server (NTRS)

The First International Conference on Global Warming and the Next Ice Age was convened in Halifax, Nova Scotia, August 19-24, 2001. The conference program began each day with a 30 minute live classical music performances of truly international quality before the beginning business. Ample time for panel discussions was also scheduled. The general public was invited to attend and participate in a special evening panel session on the last day of the conference. The unusual and somewhat provocative title of the conference was designed to attract diverse views on global climate change. This summary attempts to accurately reflect the tone and flavor of the lively discussions which resulted. Presentations ranged from factors forcing current climate to those in effect across the span of time from the Proterozoic "snowball Earth" epoch to 50,000 years in the future. Although, as should be expected, attendees at the conference arrived with opinions on some of the controversial issues regarding climate change, and no-one openly admitted to a 'conversion' from their initial point of view, the interdisciplinary nature of the formal presentations, poster discussions, panels, and abundant informal discourse helped to place the attendees' personal perspectives into a broader, more diversified context.

Wetzel, Peter J.; Chylek, Petr; Lesins, Glen; Starr, David OC. (Technical Monitor)

2002-01-01

309

Ecological Changes in Coyotes (Canis latrans) in Response to the Ice Age Megafaunal Extinctions  

PubMed Central

Coyotes (Canis latrans) are an important species in human-inhabited areas. They control pests and are the apex predators in many ecosystems. Because of their importance it is imperative to understand how environmental change will affect this species. The end of the Pleistocene Ice Age brought with it many ecological changes for coyotes and here we statistically determine the changes that occurred in coyotes, when these changes occurred, and what the ecological consequences were of these changes. We examined the mandibles of three coyote populations: Pleistocene Rancho La Brean (13–29 Ka), earliest Holocene Rancho La Brean (8–10 Ka), and Recent from North America, using 2D geometric morphometrics to determine the morphological differences among them. Our results show that these three populations were morphologically distinct. The Pleistocene coyotes had an overall robust mandible with an increased shearing arcade and a decreased grinding arcade, adapted for carnivory and killing larger prey; whereas the modern populations show a gracile morphology with a tendency toward omnivory or grinding. The earliest Holocene populations are intermediate in morphology and smallest in size. These findings indicate that a niche shift occurred in coyotes at the Pleistocene/Holocene boundary – from a hunter of large prey to a small prey/more omnivorous animal. Species interactions between Canis were the most likely cause of this transition. This study shows that the Pleistocene extinction event affected species that did not go extinct as well as those that did. PMID:25551387

Meachen, Julie A.; Janowicz, Adrianna C.; Avery, Jori E.; Sadleir, Rudyard W.

2014-01-01

310

The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean  

USGS Publications Warehouse

A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16-17. ??C between 600 and 950. CE (Common Era), centuries before the classic European Medieval Warm Period (950-1100. CE) and peak warming in the Nordic Seas (1000-1400. CE). A series of centennial warm/cool cycles began about 1000. CE with temperature minima of ~. 8 to 9. ??C about 1150, 1350, and 1650-1800. CE, and intervening warm periods (14-15. ??C) centered at 1200, 1400, 1500 and 1600. CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200. CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800. CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean-atmosphere processes. ?? 2010.

Cronin, T. M.; Hayo, K.; Thunell, R.C.; Dwyer, G.S.; Saenger, C.; Willard, D.A.

2010-01-01

311

Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica.  

PubMed

The causes of late-Holocene centennial to millennial scale climatic variability and the impact that such variability had on tropical ecosystems are still poorly understood. Here, we present a high-resolution, multiproxy record from lowland eastern Mesoamerica, studied to reconstruct climate and vegetation history during the last 2,000 years, in particular to evaluate the response of tropical vegetation to the cooling event of the Little Ice Age (LIA). Our data provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the LIA, with two deep lake phases that follow the Spörer and Maunder minima in solar activity. The high tropical pollen accumulation rates limit LIA's winter cooling to a maximum of 2 degrees C. Tropical vegetation expansion during the LIA is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation. These results highlight the importance of seasonal responses to climatic variability, a factor that could be of relevance when evaluating the impact of recent climate change. PMID:17913875

Lozano-García, Ma del Socorro; Caballero, Margarita; Ortega, Beatriz; Rodríguez, Alejandro; Sosa, Susana

2007-10-01

312

Ecological changes in Coyotes (Canis latrans) in response to the ice age megafaunal extinctions.  

PubMed

Coyotes (Canis latrans) are an important species in human-inhabited areas. They control pests and are the apex predators in many ecosystems. Because of their importance it is imperative to understand how environmental change will affect this species. The end of the Pleistocene Ice Age brought with it many ecological changes for coyotes and here we statistically determine the changes that occurred in coyotes, when these changes occurred, and what the ecological consequences were of these changes. We examined the mandibles of three coyote populations: Pleistocene Rancho La Brean (13-29 Ka), earliest Holocene Rancho La Brean (8-10 Ka), and Recent from North America, using 2D geometric morphometrics to determine the morphological differences among them. Our results show that these three populations were morphologically distinct. The Pleistocene coyotes had an overall robust mandible with an increased shearing arcade and a decreased grinding arcade, adapted for carnivory and killing larger prey; whereas the modern populations show a gracile morphology with a tendency toward omnivory or grinding. The earliest Holocene populations are intermediate in morphology and smallest in size. These findings indicate that a niche shift occurred in coyotes at the Pleistocene/Holocene boundary - from a hunter of large prey to a small prey/more omnivorous animal. Species interactions between Canis were the most likely cause of this transition. This study shows that the Pleistocene extinction event affected species that did not go extinct as well as those that did. PMID:25551387

Meachen, Julie A; Janowicz, Adrianna C; Avery, Jori E; Sadleir, Rudyard W

2014-01-01

313

Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.  

PubMed Central

Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

Hooghiemstra, Henry; Van der Hammen, Thomas

2004-01-01

314

Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.  

PubMed

Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

Hooghiemstra, Henry; Van der Hammen, Thomas

2004-02-29

315

Global warming and ice ages: I. prospects for physics based modulation of global change  

SciTech Connect

It has been suggested that large-scale climate changes, mostly due to atmospheric injection of greenhouse gases connected with fossil-fired energy production, should be forestalled by internationally-agreed reductions in, e.g., electricity generation. The potential economic impacts of such limitations are obviously large: greater than or equal to $10{sup 11}/year. We propose that for far smaller - less than 1% - the mean thermal effects of greenhouse gases may be obviated in any of several distinct ways, some of them novel. These suggestions are all based on scatterers that prevent a small fraction of solar radiation from reaching all or part of the Earth. We propose research directed to quite near-term realization of one or more of these inexpensive approaches to cancel the effects of the greenhouse gas injection. While the magnitude of the climatic impact of greenhouse gases is currently uncertain, the prospect of severe failure of the climate, for instance at the onset of the next Ice Age, is undeniable. The proposals in this paper may lead to quite practical methods to reduce or eliminate all climate failures.

Teller, E.; Wood, L.; Hyde, R.

1996-08-15

316

Ice formation and development in aged, wintertime cumulus over the UK : observations and modelling  

NASA Astrophysics Data System (ADS)

In-situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of Radar and Lidar as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than ~-8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed near cloud top temperatures (~-7 °C). The role of biological particles, consistent with concentrations observed near the surface, acting as potential efficient high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by powerful secondary ice particle production emphasising the importance of understanding primary ice formation in slightly supercooled clouds. Aircraft penetrations at -3.5 °C, showed peak ice crystal concentrations of up to 100 L-1 which together with the characteristic ice crystal habits observed (generally rimed ice particles and columns) suggested secondary ice production had occurred. To investigate whether the Hallett-Mossop (HM) secondary ice production process could account for these observations, ice splinter production rates were calculated. These calculated rates and observations could only be reconciled provided the constraint that only droplets >24 ?m in diameter could lead to splinter production, was relaxed slightly by 2 ?m. Model simulations of the case study were also performed with the WRF (Weather, Research and Forecasting) model and ACPIM (Aerosol Cloud and Precipitation Interactions Model) to investigate the likely origins of the ice phase in these slightly supercooled clouds and to assess the role played by the HM process in this and in controlling precipitation formation under these conditions. WRF results showed that while HM does act to increase the mass and number concentration of ice particles produced in the model simulations, in the absence of HM, the ice number concentration arising from primary ice nucleation alone (several L-1) was apparently sufficient to sustain precipitation although the distribution of the precipitation was changed. Thus in the WRF model the HM process was shown to be non-critical for the formation of precipitation in this particular case. However, this result is seen to be subject to an important caveat concerning the simulation of the cloud macrostructure. The model was unable to capture a sharp temperature inversion seen in the radiosonde profiles at 2 km, and consequently the cloud top temperature in the model was able to reach lower values than observed in-situ or obtained from satellite data. ACPIM simulations confirmed the HM process to be a very powerful mechanism for producing the observed high ice concentrations, provided that primary nucleation occured to initiate the ice formation, and large droplets were present which then fell collecting the primary ice particles to form instant rimer particles. However, the time to generate the observed peak ice concentrations was found to be dependant on the number of primary IN present (decreasing with increasing IN number). This became realistic (around 20 min) only when the temperature input to the existing IN parameterisation was 6 °C lower than observed at cloud top, highlighting the requirement to improve basic knowledge of the number and type of IN active at these high temperatures. In simulations where cloud droplet numbers were realistic the precipitation rate was found to be unaffected by HM, with warm rain processes dominating precipitation development in this instance.

Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

2011-11-01

317

Climatic warming, glacier recession and runoff from Alpine basins after the Little Ice Age maximum  

Microsoft Academic Search

Records of discharge of rivers draining Alpine basins with between 0 and ?? 70% ice cover, in the upper Aare and Rhone catchments, Switzerland, for the period 1894-2006 have been examined together with climatic data for 1866-2006, with a view to assessing the effects on runoff from glacierized basins of climatic warming coupled with glacier recession following the Little Ice

David N. Collins

2008-01-01

318

Caribbean sea surface temperatures: two-to-three degrees cooler than present during the Little Ice Age  

Microsoft Academic Search

We determined the seasonal environmental conditions during the Little Ice Age (LIA) by interpreting isotope proxies in the coral skeleton of Montastrea faveolata from the northeast Caribbean. The oxygen isotope composition was determined for three time intervals during the LIA (1700-1705, 1780-1785, 1810-1815), thought to correspond to the coldest intervals. The period 1984-1989 was used to represent modern calibration conditions.

Amos Winter; Hiroshi Ishioroshi; Tsuyoshi Watanabe; Tadamichi Oba; John Christy

2000-01-01

319

Social vulnerability to climate in the ``Little Ice Age?: an example from Central Europe in the early 1770s  

Microsoft Academic Search

The paper is oriented on social vulnerability to climate in Switzerland and in the Czech Lands during the early 1770s. Documentary sources of climate related to man-made archives are discussed. Methods of temperature and precipitation reconstruction based on this evidence as well as climate impact analyses are presented. Modelling of Little Ice Age-type Impacts (LIATIMP) is applied to highlight climate

C. Pfister; R. Brázdil

2006-01-01

320

'Little Ice Age' glaciation of Tröllaskagi peninsula, northern Iceland: climatic implications for reconstructed equilibrium line altitudes (ELAS)  

Microsoft Academic Search

Comparison of the equilibrium line altitudes (ELAS) for the present (1980s) and the maximum 'Little Ice Age' depression determined for glaciers in the Skíõadalur\\/Svarfaõardalur area of the Tröllaskagi peninsula, northern Iceland, shows a rise of c. 50 m over the last 100-150 years. Meteoro logical data suggest that over the same period the mean summer temperature at the equilibrium line

Chris Caseldine; Johann Stötter

1993-01-01

321

Middle to Late Amazonian tropical mountain glaciers on Mars: The ages of the Tharsis Montes fan-shaped deposits  

NASA Astrophysics Data System (ADS)

Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35°S, ~125 Ma for the Pavonis FSD at 1.48°N, and ~210 Ma for the Arsia FSD at 11.92°N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45-150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 105 km3) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined CSFD ages of three adjacent drop moraine units at Arsia Mons (725 Ma, 475 Ma and 345 Ma) and used these to calculate the average amount of time needed to form one of the approximately 185 drop moraines forming these deposits; we found that a typical drop moraine formation time in the Arsia FSD ridged facies to be on the order of ~106 years. These formation ages are considerably longer than that required for typical moraine systems alongside dynamic, wet-based glaciers on Earth, but are in approximate accord with recent geomorphological and geochemical data that document long-term, ice-margin stability for several cold-based glaciers in interior Antarctica. The difference in the ages of the ridged facies and non-ridged portion of the Arsia FSD suggests that the tropical mountain glaciers may have been emplaced over a period spanning many hundreds of millions of years. CSFD measurements for lava flows predating and postdating the Arsia Mons FSD suggest a maximum possible age of <750 Ma and a minimum age for the late stage, post FSD lava flows of ~105 Ma. Taken together, this evidence supports a scenario in which ice has been present and stable in substantial quantities (~105-106 km3) at tropical latitudes during extended periods of the Middle to Late Amazonian history of Mars. This implies that during this time, Mars sustained periods of spin-axis obliquity in the vicinity of 45°, during which time polar ice deposits were substantially reduced in volume or perhaps even absent.

Kadish, Seth J.; Head, James W.; Fastook, James L.; Marchant, David R.

2014-02-01

322

Glacier changes since Local Last Glacial Maximum in the South-West slope of Nevado Hualcán, Cordillera Blanca, Peru, deduced from moraine mapping and GIS-based analysis  

NASA Astrophysics Data System (ADS)

Anticipating and assessing hazards and risks associated with the shrinking of surface and subsurface ice in cold mountain chains is facilitated by empirical-quantitative data on present and past rates of change, as well as by a general understanding of related landforms and landscape evolution through time. Rock/ice avalanches and devastating outburst floods from glacial lakes indeed constitute a major cause of severe damage in populated mountain areas such as the Cordillera Blanca whose combination of tectonic, topographic and glaciological characteristics make it a threatened region. This study focuses on the Río Chucchún catchment above the city of Carhuaz, which was recently affected by a flood/debris flow from a rock/ice avalanche impacting a recently grown lake (Laguna 513). Traces left by past glaciations strongly affect the current geomorphodinamic behaviour of the catchment. For instance, a prominent sediment-filled glacial overdeepening behind Younger Dryas (YD) moraines (Pampa de Shonquil) with its retention function strongly influenced the chain of processes initiated by the outburst of Laguna 513. The aim of this study is to reconstruct earlier glacial phases in the SW slope of Nevado Hualcán (Río Chucchún catchment), in order to compile quantitative information on surface areas and Equilibrium Line Altitudes (ELAs). To do so, glacier stages were assigned to five different glacial phases, through photointerpretation and moraine cartography: 2003; 1962; Hualcán-I-LIA (15th to 18th centuries); Hualcán-II-YD (~12,5 ka BP); and Hualcán-III-LLGM (~34 to 21 ka BP). Glacial stages Hualcán-I-LIA, Hualcán-II-YD and Hualcán-III-LLGM present relative dating based on previous studies from different authors in the Peruvian Andes. Once glaciers were delimited, their surface areas and Equilibrium Line Altitudes (ELAs) were calculated. For ELA estimation three different methods were used: the mid-range elevation, the Accumulation Area Ratio (AAR), and the Area x Altitude Balance Ratio (AABR). The results show a decrease in surface area with respect to Hualcán-III-LLGM of 16% for Hualcán-II-YD; 50% for Hualcán-I-LIA; and 74% for 2003. With respect to 2003, ELAs shifted ~520 m since the Local Last Glacial Maximum (LLGM), ~470 m since a marked late-glacial stage (YD?), ~130 m since the Little Ice Age (LIA) and about ~100 m since 1962. If the changes are exclusively attributed to temperature effects, warming since LLGM can be estimated at some 3°C and since the maximum glacier extent of LIA at about 0.8°C. Such values are rather close to mean global temperature change during the corresponding intervals. Most of the ELA shift since LIA appears to have taken place during recent decades characterized by very rapid glacier shrinkage, although air temperature does not seem to have risen considerably during the last 30 years. These results along with other environmental and social approaches will contribute to a better understanding of impacts from climate change and glacier shrinkage in order to develop adaptation, mitigation and disaster risk reduction strategies in the Peruvian Andes.

Giráldez, Claudia; Palacios, David; Haeberli, Wilfried; Úbeda, Jose; Schauwecker, Simone; Torres, Judith

2014-05-01

323

The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes  

NASA Astrophysics Data System (ADS)

To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.

Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

2012-09-01

324

Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age.  

PubMed

The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific (15)N/(14)N isotopic ratios (?(15)N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, ?(15)N decreases between 1850 and the present. The total shift in ?(15)N of -2 per mil over this period is comparable to the total change in global mean sedimentary ?(15)N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age. PMID:24336216

Sherwood, Owen A; Guilderson, Thomas P; Batista, Fabian C; Schiff, John T; McCarthy, Matthew D

2014-01-01

325

Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios (?15N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, ?15N decreases between 1850 and the present. The total shift in ?15N of -2 per mil over this period is comparable to the total change in global mean sedimentary ?15N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

Sherwood, Owen A.; Guilderson, Thomas P.; Batista, Fabian C.; Schiff, John T.; McCarthy, Matthew D.

2014-01-01

326

Effects of a rule change that eliminates body-checking on the relative age effect in Ontario minor ice hockey.  

PubMed

Relative age effects in sport reflect an over-representation of athletes born early in a selection year that lead to selection and performance advantages. These effects might be enhanced by rules that increase physicality. An opportunity to investigate these influences arose when Hockey Canada altered its body-checking rules. Two studies are described that investigate the possible influence of this rule change. Study 1 used cross-sectional data to contrast relative age effects for 9-year-olds in games with and without body-checking (birth quartile 1 ranged from 27 to 39%; birth quartile 4 from 10 to 20%). Study 2 used quasi-longitudinal data to examine age effects when players transitioned from a season in which body-checking was permitted to one that prohibited such checking (birth quartile 1 ranged from 27 to 39%; birth quartile 4 from 11 to 20%). Chi-square statistics demonstrated relative age effects in both studies irrespective of body-checking. Post-hoc analyses indicated reductions in these effects that were limited to some second and third quartiles when body-checking was prohibited. Body-checking is not a critical mechanism of relative age effects. The physicality of ice hockey, regardless of body-checking, and increased experience in ice hockey are influential. PMID:21834643

Hancock, David J; Young, Bradley W; Ste-Marie, Diane M

2011-10-01

327

Area, volume and mass changes of southeast Vatnajökull ice cap, Iceland, from the Little Ice Age maximum in the late 19th century to 2010  

NASA Astrophysics Data System (ADS)

Area and volume changes and the average geodetic mass balance of the non-surging outlet glaciers of southeast Vatnajökull ice cap, Iceland, during different time periods between ~1890 and 2010, are derived from a multi-temporal glacier inventory. A series of digital elevation models (DEMs) (∼1890, 1904, 1936, 1945, 1989, 2002, 2010) have been compiled from glacial geomorphological features, historical photographs, maps, aerial images, DGPS measurements and a LiDAR survey. Given the mapped bedrock topography we estimate relative volume changes since the end of the Little Ice Age (LIA) ~1890. The variable dynamic response of the outlets, assumed to have experienced similar climate forcing, is related to their different hypsometry, bedrock topography, and the presence of proglacial lakes. In the post-LIA period the glacierized area decreased by 164 km2 and the glaciers had lost 10-30% of their ~1890 area by 2010. The glacier surface lowered by 150-270 m near the terminus and the outlet glaciers collectively lost 60 ± 8 km3 of ice, which is equivalent to 0.154 ± 0.02 mm of sea level rise. The relative volume loss of individual glaciers was in the range of 15-50%, corresponding to a geodetic mass balance between -0.70 and -0.32 m w.e. a-1. The rate of mass loss was most negative in the period 2002-2010, on average -1.34 ± 0.12 m w.e. a-1, which lists among the most negative mass balance values recorded worldwide in the early 21st century. From the data set of volume and area of the outlets, spanning the 120 years post-LIA period, we evaluate the parameters of a volume-area power law scaling relationship.

Hannesdóttir, H.; Björnsson, H.; Pálsson, F.; Aðalgeirsdóttir, G.; Guðmundsson, S.

2014-09-01

328

Coupled climate modelling of ocean circulation changes during ice age inception  

Microsoft Academic Search

Freshening of high latitude surface waters can change the large-scale oceanic transport of heat and salt. Consequently, atmospheric and sea ice perturbations over the deep water production sites excite a large-scale response establishing an oceanic \\

K. J. Meissner; R. Gerdes

2002-01-01

329

Reconstruction of late Wisconsinan Ice Sheet and sea-level implications  

NASA Technical Reports Server (NTRS)

The Ross Sea exhibits north-south oriented troughs associated with modern ice streams and outlet glaciers. Seismic reflection profiles across the troughs show evidence that they were glacially eroded. Seismic records show morphologic features interpreted as till tongues, morainal banks, and possibly glacial deltas formed near the grounding line of the former marine ice sheet. Piston cores from the continental shelf penetrated diamictons whose origin and age is problematic. Detailed petrographic analyses of the minerals and rocks comprising these diamictons were conducted to determine subglacial versus glacial marine origin, and to reconstruct the glacial setting of the Ross Sea during the most recent glacial maximum. The most detailed work, conducted in the western Ross Sea, shows that diamictons do occur in distinct petrologic provinces. This is consistent with deposition from the basal debris zone of either an ice sheet or an ice shelf. Overcompaction, in conjunction with the widespread nature of these deposits, favors deposition from marine ice sheets; ice shelves are believed to deposit their basal debris close to the grounding lines. Other results from the investigation are briefly discussed.

Anderson, John B.

1993-01-01

330

Terrestrial Kr-81-Kr ages of Antarctic meteorites  

NASA Technical Reports Server (NTRS)

The production rate of Ar-38 in meteorites P(38), has been determined, as a function of the sample's chemical composition, from Kr-81-Kr exposure ages of four eucrite falls. The cosmogenic Kr-78/Kr-83 ratio is used to estimate the shielding dependence of P(38). From the 'true' Ar-38 exposure ages and the apparent Kr-81-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 300,000 ages (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017, and A81009) have within the limits of error the same exposure age (15.2 x 10 to the 6th ages) and the same terrestrial age (110,000 ages). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case is the Elephant Moraine polymict eucrites A79005, A79006, and 82600 with an exposure age of 26 x 10 to the 6th ages and a terrestrial age of 180,000 ages. EETA 79004 may be different from this group because its exposure age and terrestrial age are 21 x 10 to the 6th ages and 250,000 ages, respectively. The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: directly deposited falls and meteorites transported to the Allen Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering 'half-life' is about 160,000 ages. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.

Freundel, M.; Schultz, L.; Reedy, R. C.

1986-01-01

331

Size, age and diet of polar cod, Boreogadus saida (Lepechin 1773), in ice covered waters  

Microsoft Academic Search

Polar cod (Boreogadus saida) associated with drifting sea-ice were collected in the western Barents sea and north of Svalbard with dip-nets while SCUBA-diving in 1986 and 1987. Length-frequency measurements and otolith-readings suggested that the specimens were either one or two years old. The diet of fish from the western Barents sea (first-year ice) consisted mainly of copepods (Calanus finmarchicus, Calanus

O. J. Lønne; B. Gulliksen

1989-01-01

332

Glacier change in Garibaldi Provincial Park, southern Coast Mountains, British Columbia, since the Little Ice Age  

Microsoft Academic Search

Fluctuations of glaciers during the 20th century in Garibaldi Provincial Park, in the southern Coast Mountains of British Columbia, were reconstructed from historical documents, aerial photographs, and fieldwork. Over 505 km2, or 26%, of the park, was covered by glacier ice at the beginning of the 18th century. Ice cover decreased to 297 km2 by 1987–1988 and to 245 km2 (49% of the

Johannes Koch; Brian Menounos; John J. Clague

2009-01-01

333

Radiocarbon ages of terrestrial gastropods extend duration of ice-free conditions at the Two Creeks forest bed, Wisconsin, USA  

USGS Publications Warehouse

Analysis of terrestrial gastropods that underlie the late Pleistocene Two Creeks forest bed (~ 13,800–13,500 cal yr BP) in eastern Wisconsin, USA provides evidence for a mixed tundra-taiga environment prior to formation of the taiga forest bed. Ten new AMS 14C analyses on terrestrial gastropod shells indicate the mixed tundra-taiga environment persisted from ~ 14,500 to 13,900 cal yr BP. The Twocreekan climatic substage, representing ice-free conditions on the shore of Lake Michigan, therefore began near the onset of peak warming conditions during the Bølling–Allerød interstadial and lasted ~ 1000 yr, nearly 600 yr longer than previously thought. These results provide important data for understanding the response of continental ice sheets to global climate forcing and demonstrate the potential of using terrestrial gastropod fossils for both environmental reconstruction and age control in late Quaternary sediments.

Rech, Jason A.; Nekola, Jeffrey C.; Pigati, Jeffrey S.

2012-01-01

334

Exploring controls on ice stream destabilisation during the LGM/Holocene transition in West Greenland  

NASA Astrophysics Data System (ADS)

Newly emerging onshore and offshore deglacial chronologies from West Greenland enable investigation of the role of both climate and topography in controlling ice stream dynamics The Uummannaq ice stream system (UIS) now has a comprehensive deglacial chronology (eg. Lane et al; 2013; Ó Cofaigh et al., 2013; Roberts et al., 2013) which includes four dimensional control i.e. location and geometry of the ice margin and ice stream trunk and rates of thinning and retreat. This provides a framework for interpreting the main drivers and controls on ice stream dynamics under changing climatic conditions. Deglaciation of the UIS began on the outer shelf at ~14.8 ka, with Ubekendt Ejland becoming ice free at ~12.4 ka. Staircases of lateral moraines on the southern flanks of Ubekendt point to step-wise thinning of the UIS as ice retreated from the shelf edge. This period of retreat coincided with a rise in air temperature between 16 -14.5 ka, increasing JJA solar radiation as well sea-level rise. The wide, mid-shelf trough (> 30km; which harboured the main UIS trunk zone) also had few constrictions which facilitated grounding line retreat. The UIS then withdrew rapidly with 80 - 100 km of retreat by ~11.4 ka - 10.8 ka as the northern and southern feeder zones unzipped. This coincided with increasing insolation and peak sea-level, but topography and bathymetry were also influential on margin retreat (i.e. reverse slope over-deepening and fjord widening). This retreat occurred despite Younger Dryas air temperature cooling. Along the southern arm of the UIS the grounding line retreated towards Store Gletscher becoming topographically pinned at ~11.4 - 11.0 ka, but from 9.3 ka onwards retreat rates increased with the ice reaching the present Store Gletscher margin by 8.7 ka. This coincided with increased air temperatures and peak summer insolation at the start of the Holocene. The northern arm of the UIS also deglaciated quickly from Ubekendt, calving northward into Karrat/Rinks and Ingia Fjords. Lateral moraines north of Karrat again point to step-wise thinning of the UIS as ice retreated. At ~11.3 ka the ice front in Karrat/Rinks Isfjord stabilised until ~6.5 ka and seemingly became unresponsive to both climate and marine forcing for 5000yrs due to topographic pinning. Ice sheet surface profile reconstructions based on two equilibrium models (perfectly plastic v Weertman-sliding profile; Roberts et al., 2013) combined with surface exposure ages have constrained likely minimum and maximum Last Glacial Maximum (LGM) ice surface geometries for the UIS.A 2D model, however, can simulate grounding line-retreat behaviour and surface thinning through time (e.g. Jamieson et al., 2012). Initial model results indicate that the non-linear retreat of the UIS is influenced by vertical and lateral constrictions in the marine trough system which partially regulates grounding line stability. It is apparent that during periods of rapid retreat the ice surface thins rapidly inland. Conversely, if the grounding line is pinned and relatively stable, surface thinning decelerates. This period of relatively slow ice surface thinning may be evidenced by the lateral moraine staircases which infer slow, incremental thinning along the margins of the UIS during different periods of retreat.

Roberts, David H.; Rea, Brice R.; Lane, Tim P.; Jamieson, Stewart S. R.; Cofaigh, Colm Ó.; Vieli, Andreas

2014-05-01

335

Beryllium-10 dating of Mount Everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the Himalaya  

NASA Astrophysics Data System (ADS)

Moraine successions in glaciated valleys south of Mount Everest provide evidence for at least eight glacial advances during the late Quaternary. Cosmogenic radionuclide (CRN) surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies. The CRN data show that glaciation was most extensive during the early part of the last glacial (marine oxygen isotype stage [MIS] 3 and earlier), but limited during MIS 2 (the global Last Glacial Maximum) and the Holocene. A previously assumed Neoglacial advance is dated to 3.6 ± 0.3 ka and the CRN dates confirm a glacial advance ca. 1 ka. These results show that glaciations on the south side of Everest were not synchronous with the advance of Northern Hemisphere ice sheets, yet glaciations within the Himalaya, the world's highest mountain belt, were synchronous during the late Quaternary. The existence of glacial advances during times of increased insolation suggests that enhanced moisture delivered by an active south Asian summer monsoon is largely responsible for glacial advances in this part of the Himalaya. These data allow us to quantify the importance of global climate change and monsoon influence on glaciation in the Himalaya.

Finkel, Robert C.; Owen, Lewis A.; Barnard, Patrick L.; Caffee, Marc W.

2003-06-01

336

The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories  

NASA Astrophysics Data System (ADS)

A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in viscous response to the early Holocene unloading of ice from the current locations of the ice shelf centers. ICE-6G_C (VM5A) fits the horizontal observations well (wrms residual speed of 0.7 mm yr-1), there being no need to invoke any influence of lateral variation in mantle viscosity. ICE-6G_C (VM5A) differs in several respects from the recently published W12A model of Whitehouse et al. First, the upper-mantle viscosity in VM5a is 5 × 1020 Pa s, half that in W12A. The VM5a profile, which is identical to that inferred on the basis of the Fennoscandian relaxation spectrum, North American relative sea level histories and Earth rotation constraints, when coupled with the revised ICE-6G_C deglaciation history, fits all of the available constraints. Secondly, the net contribution of Antarctica ice loss to global sea level rise is 13.6 m, 2/3 greater than the 8 m in W12A. Thirdly, ice loss occurs quickly from 12 to 5 ka, and the contribution to global sea level rise during Meltwater Pulse 1B (11.5 ka) is large (5 m), consistent with sedimentation constraints from cores from the Antarctica ice shelf. Fourthly, in ICE-6G_C there is no ice gain in the East Antarctica interior, as there is in W12A. Finally, the new model of Antarctic deglaciation reconciles the global constraint upon the global mass loss during deglaciation provided by the Barbados record of relative sea level history when coupled with the Northern Hemisphere counterpart of this new model.

Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

2014-07-01

337

Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age  

NASA Astrophysics Data System (ADS)

For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (?30Siopal) and nitrogen (?15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (ϵNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, ?15Nsed values of ~5‰ and intermediate ?30Siopal values of ~0.9‰. At the same time, the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were most likely caused by permanent El Niño-like conditions characterised by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, ? 30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by ?15Nsed of up to ~7‰, and by the highest degree of silicate utilisation with ?30Siopal reaching values of +1.1‰. At the same time, detrital ϵNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA, indicating significantly increased nutrient availability. Comparison between the ?30Siopal and ?15Nsed signatures suggests that during the past 650 years the ?15Nsed signature in the Peruvian upwelling area has to a large extent been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column, which only had a significant influence during modern times (i.e. since ~AD 1870).

Ehlert, C.; Grasse, P.; Gutiérrez, D.; Salvatteci, R.; Frank, M.

2015-02-01

338

The Medieval Climate Anomaly and the Little Ice Age in the eastern Ecuadorian Andes  

NASA Astrophysics Data System (ADS)

To better characterize the climate variability of the last millennium in the high Andes, we analyzed the pollen content of a 1150-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the Andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined. This index was used to distinguish changes in the atmospheric moisture from the soil moisture content of the páramo and their associated patterns of interdecadal El Niño-Southern Oscillation (ENSO) variability and South American summer monsoon (SASM) activity. Results show that between 850 and 1250 AD, the Medieval Climate Anomaly interval was warm and moist with a high transported pollen/Poaceae pollen (T/P) index linked to high ENSO variability and weak SASM activity. Between 1250 and 1550 AD, a dry climate prevailed, characterized by an abrupt decrease in the T/P index and therefore no upslope cloud convection, related to lower ENSO variability and with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed: first, a wet phase between 1550 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic sea surface temperatures (SSTs) favored the return of a wet páramo, and then a cold and dry phase between 1750 and 1800 AD associated with low ENSO variability and weak SASM activity resulted in drying of the páramo. The current warm period marks the beginning of a climate characterized by high convective activity - the highest in the last millennium - and weaker SASM activity modifying the water storage of the páramo. Our results show that the páramo is progressively losing its capacity for water storage and that the interdecadal variability of both tropical Pacific and Atlantic SSTs matter for Andean climate patterns, although many teleconnection mechanisms are still poorly understood.

Ledru, M.-P.; Jomelli, V.; Samaniego, P.; Vuille, M.; Hidalgo, S.; Herrera, M.; Ceron, C.

2013-02-01

339

Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age  

NASA Astrophysics Data System (ADS)

For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (?30Siopal) and nitrogen (?15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (?Nd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, ?15Nsed values of ~ +5‰ and intermediate ?30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, ?30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by ?15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with ?30Siopal reaching values of +1.1‰. At the same time detrital ?Nd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the ?30Siopal and ?15Nsed signatures suggests that during the past 650 years the ?15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column.

Ehlert, C.; Grasse, P.; Gutiérrez, D.; Salvatteci, R.; Frank, M.

2014-08-01

340

Accurate age scale of the Dome Fuji ice core, Antarctica from O2/N2 ratio of trapped air  

NASA Astrophysics Data System (ADS)

Chronology of the first Dome Fuji deep ice core (core length: 2,500 m, ice thickness: 3,035 m) for the age range from 80 kyr to 340 kyr ago was established by orbital tuning of measured O2/N2 ratios in trapped air to local summer insolation, with precision better than about 2,000 years (Kawamura et al., 2007). The O2/N2 ratios found in polar ice cores are slightly lower than the atmospheric ratio because of size-dependent molecular fractionation during bubble close-off. The magnitude of this gas fractionation is believed to be governed by the magnitude of snow metamorphism when the layer was originally at the surface, which in turn is controlled by local summer insolation (Fujita et al., 2009). A strong advantage of the O2/N2 chronology is that there is no need to assume a lag between climatic records in the ice core and orbital forcings, becacuse O2/N2 ratios record local insolation through physical processes. Accuracy of the chronology was validated by comparing the O2/N2 chronology with U-Th radiometric chronology of speleothem records (Cheng et al., 2009) for the ends of Terminations II, III and IV, as well as several large climatic events, for which both ice-core CH4 and speleothem ?18O (a proxy for precipitation) show abrupt shifts as seen in the last glacial period. All ages from O2/N2 and U-Th chronology agreed with each other within ~2,000 yr. The O2/N2 chronology permits comparisons between Antarctic climate, greenhouse gases, astronomically calculated orbital parameters, and radiometrically-dated sea level and monsoon records. Here, we completed the measurements of O2/N2 ratios of the second Dome Fuji ice core, which reached bedrock, for the range from 2,400 to 3,028 m (320 - 700 kyr ago) at approximately 2,000-year time resolution. We made significant improvements in ice core storage practices and mass spectrometry. In particular, the ice core samples were stored at about -50 ° C until the air extraction, except during short periods of transportation, in order to prevent size-dependent fractionation due to gas loss during storage. The precision of the new O2/N2 data set is improved by a factor of 3 over the previous data. Clear imprint of local insolation is recognizable in the O2/N2 data towards the deepest depths, even around 400 kyr ago when summer insolation wiggles are small due to small orbital eccentricity. A new chronology using this O2/N2 data set will be established by applying the inverse method for EDC3 age scale (Parrenin et al., 2007) for the entire 700 kyr, and climatic implications will also be discussed especially on Terminations and interglacial periods.

Kawamura, K.; Aoki, S.; Nakazawa, T.; Suzuki, K.; Parrenin, F.

2012-04-01

341

Larsen Ice Shelf Collapse (WMS)  

NSDL National Science Digital Library

The Larsen ice shelf at the northern end of the Antarctic Peninsula experienced a dramatic collapse between January 31 and March 7, 2002. First, melt ponds appeared on the ice shelf during these summer months (seen in blue on the shelf), then a minor collapse of about 800 square kilometers occurred. Finally, a 2600 square kilometer collapse took place, leaving thousands of sliver icebergs and berg fragments where the shelf formerly lay. Brownish streaks within the floating chunks mark areas where rocks and morainal debris are exposed from the former underside and interior of the shelf. These images were acquired by the MODIS instrument on the Terra satellite.

Stuart Snodgrass

2005-03-04

342

Late Holocene vegetation and climate change at Moraine Bog, Tiedemann Glacier, southern Coast Mountains, British Columbia  

Microsoft Academic Search

Moraine Bog lies just outside the outermost lateral moraine of Tiedemann Glacier in the southern Coast Mountains of British Columbia. A sediment core taken from the wetland was analyzed for pollen, magnetic susceptibility, and loss on ignition to reconstruct changes in vegetation and climate during the late Holocene. Vegetation changed little between about 3500 and 2400 14C years BP. A

T. A. Arsenault; John J. Clague; R. W. Mathewes

2007-01-01

343

Medial moraines of glaciers of the Copper River Basin, Alaska: Discrete landslides dominate over other sources  

Microsoft Academic Search

Medial moraines are visually dominant structures of most large valley glaciers in the Copper River Basin (CRB), Alaska. Areally extensive but thin (usually <20 cm) accumulations of debris pose challenges for glacier mapping based on multispectral imagery, as done, for instance, in the GLIMS project. The sources of this material include large discrete landslides from wallrocks and from lateral moraines;

J. S. Kargel; L. Fischer; R. Furfaro; C. Huggel; O. Korup; G. J. Leonard; M. Uhlmann; R. L. Wessels; D. F. Wolfe

2009-01-01

344

A volcanically triggered regime shift in the subpolar North Atlantic Ocean as a possible origin of the Little Ice Age  

NASA Astrophysics Data System (ADS)

Among the climatological events of the last millennium, the Northern Hemisphere Medieval Climate Anomaly succeeded by the Little Ice Age are of exceptional importance. The origin of these regional climate anomalies remains a subject of debate and besides external influences like solar and volcanic activity, internal dynamics of the climate system might have also played a dominant role. Here, we present transient last millennium simulations of the fully coupled model of intermediate complexity Climber 3? forced with stochastically reconstructed wind-stress fields. Our results indicate that short-lived volcanic eruptions might have triggered a cascade of sea ice-ocean feedbacks in the North Atlantic, ultimately leading to a persistent regime shift in the ocean circulation. We find that an increase in the Nordic Sea sea-ice extent on decadal timescales as a consequence of major volcanic eruptions in our model leads to a spin-up of the subpolar gyre and a weakened Atlantic meridional overturning circulation, eventually causing a persistent, basin-wide cooling. These results highlight the importance of regional climate feedbacks such as a regime shift in the subpolar gyre circulation for understanding the dynamics of past and future climate.

Schleussner, C. F.; Feulner, G.

2013-06-01

345

OSL ages on glaciofluvial sediment in northern Lower Michigan constrain expansion of the Laurentide ice sheet  

E-print Network

in the Great Lakes region, with the Fingers, an interlobate upland, remaining ice-free until ca. 27 ka. © 2008 University of Washington. All rights reserved. Keywords: Glaciation; Outwash; MIS 2; Great Lakes region; OSL work has been associated with sites near the edges of the peninsula, by the Great Lakes and the large

Schaetzl, Randall

346

Preservation of ancient ice at Pavonis and Arsia Mons: Tropical mountain glacier deposits on Mars  

NASA Astrophysics Data System (ADS)

Large tropical mountain glacier (TMG) deposits on the northwest flanks of the Tharsis Montes and Olympus Mons volcanoes are interpreted to be the record of ancient climates characteristic of Mars several hundred million years ago when planetary spin-axis obliquity was ~45°. During this era, polar volatiles (predominantly H2O) were mobilized and transferred equatorward, undergoing adiabatic cooling on the Tharsis volcano flanks, and precipitating snow and ice to form cold-based tropical mountain glaciers up to several kilometers in thickness. Subsequent climate change resulted in retreat, sublimation and collapse of the tropical mountain glaciers, leaving the three typical facies observed today: (1) concentric ridges, the ridged facies, interpreted as drop moraines; (2) knobby facies, interpreted as debris-dominated sublimation residue; and (3) the smooth facies, interpreted as remnant alpine glacial deposits. Ring-mold craters (RMCs) are distinctive features formed by impacts into debris-covered ice. We describe a set of relatively fresh ring-mold craters superposed on the Arsia and Pavonis Mons TMG deposits; we interpret these to indicate that the impact events penetrated a veneer of sublimation lag and excavated buried remnant glacial ice, despite the lack of detection of buried ice by orbital radar instruments. The diameter distribution of the RMCs suggest that the remnant ice lies at a depth of at least 16 m. The TMG deposit ages suggest that these ice deposits date from a period in the range of 125-220 million years before the present; the remnant ice may thus preserve records of the ancient atmospheric gas content and microbiota, as is common in terrestrial glacial ice. Preservation of this ice and the lack of any associated fluvial features suggest that the post-glacial climate has been cold, and related surface temperatures have not been sufficient to bring the buried deposits to the melting point of water.

Head, James W.; Weiss, David K.

2014-11-01

347

Valley-fill alluviation during the Little Ice Age (ca. A.D. 1400–1880), Paria River basin and southern Colorado Plateau, United States  

Microsoft Academic Search

Valley-fill alluvium deposited from ca. A.D. 1400 to 1880 is widespread in tribu- taries of the Paria River and is largely co- incident with the Little Ice Age epoch of global climate variability. Previous work showed that alluvium of this age is a map- pable stratigraphic unit in many of the larger alluvial valleys of the southern Col- orado Plateau.

Richard Hereford

2002-01-01

348

A continental shelf sedimentary record of Little Ice Age to modern glacial dynamics: Bering Glacier, Alaska  

NASA Astrophysics Data System (ADS)

The Bering Glacier System is the world's largest surging temperate glacier with seven events occurring over the past century under a range of north Pacific climatic conditions. Onshore records reveal changes in glacial termini positions and evidence of late Holocene glacial advances, but the Little Ice Age (LIA) record of potential glacial surging and associated flooding has not been examined. A 13.6 m-long jumbo core collected on the adjacent continental shelf reveals a 600-yr-long record of sedimentation associated with changing glacifluvial discharge. The chronology is based on 210Pb geochronology and five radiocarbon dates, and the core can be separated into three distinct lithologic units based on the examination of X-radiographs and physical properties: (1) an uppermost unit dating from ?125 cal yr BP to the present characterized by bioturbated mud interbedded with laminated, thick (5-20 cm) low-bulk density clay-rich beds; (2) a middle unit dating from ?120-400 cal yr BP that includes numerous interlaminated-to-interbedded low- and high-bulk density beds with infrequent evidence of bioturbation; thick laminated clay-rich beds are rare; (3) a lowermost unit that predates ?400 cal yr BP and is composed of rare laminated beds grading down into mottled to massive mud. In each of these units, the laminated lithofacies from this mid-shelf location indicates both flood deposition and likely sediment transport in the wave-current bottom-boundary layer. The thick low-density, clay-rich beds in the uppermost unit correlate with historic outburst floods associated with known surge events. Based on previous terrestrial studies, the terminus was at its Holocene Neoglacial maximum extent close to the modern coastline at some point in the middle to late stages of the LIA in southern Alaska (100-350 cal yr BP). During the LIA, preservation of bioturbated intervals is rare while laminated intervals are common. This style of interbedding indicates frequent (<10 yr recurrence interval) event-scale mud deposition, suggesting that frequent summer flooding and redistribution by winter storms were more prevalent during the LIA rather than the outburst flooding typical of the past century. Rare event-scale bedding indicative of outburst flooding and possible surge events is found within the middle unit, and may correspond to periods with similar climatic trends as in the 20th century. The infrequent deposition of event layers in the lowermost unit could be attributed to the less frequent flooding and/or enhanced diversion of glacial drainage to the eastern terminus instead of present day Seal River. The thickness and depositional frequency of event-scale bedding can be related to Gulf of Alaska tree-ring proxy temperature reconstructions, where more numerous event bed formation occurs when there are more frequent, higher-amplitude temperature excursions. These frequent fluctuations may have prevented the decadal-long periods of positive mass balance required to enable numerous surge events during this period.

Jaeger, John M.; Kramer, Branden

2014-09-01

349

Sedimentary processes on the NW Iberian Continental Shelf since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The OMEX core CD110 W90, retrieved from the Douro Mud Patch (DMP) off the River Douro in the north of Portugal, records the period since the beginning of Little Ice Age (LIA). The core chronology is based upon the data attributes for 210Pb, 137Cs and a 14C dating from a level near the core base. Geochemical, granulometric, microfaunal (benthic foraminifera) and compositional data suggest the occurrence of precipitation changes which may have been, at least partially, influenced by the North Atlantic Oscillation (NAO), that contributes to the regulation of the ocean-atmosphere dynamics in the North Atlantic. Southwesterly Atlantic storm track is associated with the negative phases of the NAO, when the Azores High is anomalously weak, higher oceanographic hydrodynamism, downwelling events and increased rainfall generally occurs. Prevalence of these characteristics during the LIA left a record that corresponds to phases of major floods. During these phases the DMP received a higher contribution of relatively coarse-grained terrigenous sediments, enriched in quartz particles, which diluted the contribution of other minerals, as indicated by reduced concentrations of several lithogenic chemical elements such as: Al, As, Ba, Ce, Co, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Rb, Sc, Sn, Th, V and Y. The presence of biogenic carbonate particles also underwent dilution, as revealed by the smaller abundance of foraminifera and correlative lower concentrations of Ca and Sr. During this period, the DMP also received an increased contribution of organic matter, indicated by higher values of lignin remains and a benthic foraminifera high productivity index, or BFHP, which gave rise to early diagenetic changes with pyrite formation. Since the beginning of the 20th century this contribution diminished, probably due to several drier periods and the impact of human activities in the river basins, e.g. construction of dams, or, on the littoral areas, construction of hard-engineering structures and sand extraction activities. During the first half of the 20th century mainly positive phases of the NAO prevailed, caused by the above normal strengthening of the subtropical high pressure centre of the Azores and the deepening of the low pressure centre in Iceland. These phases may have contributed to the reduction in the supply of both terrigenous sediments and organic matter from shallow water to the DMP. During the positive phases of the NAO, sedimentation became finer. The development of mining and industrial activities during the 20th century is marked, in this core, by higher concentrations of Pb. Furthermore, the erosion of heaps resulting from wolfram exploitation leaves its signature as a peak of W concentrations recorded in the sediments of the DMP deposited between the 1960s and the 1990s. Wolfram exploitation was an important activity in the middle part of the 20th century, particularly during the period of the Second World War.

Martins, Virgínia; Figueira, Rubens Cesar Lopes; França, Elvis Joacir; Ferreira, Paulo Alves de Lima; Martins, Paula; Santos, José Francisco; Dias, João Alveirinho; Laut, Lazaro L. M.; Monge Soares, António M.; Silva, Eduardo Ferreira da; Rocha, Fernando

2012-05-01

350

Rates of Deglaciation during the Last Glaciation and Holocene in the Cordillera Vilcanota-Quelccaya Ice Cap Region, Southeastern Perú  

NASA Astrophysics Data System (ADS)

Moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the Huancané Valley on the west side of the Quelccaya Ice Cap and the Upismayo Valley on the northwest side of the Cordillera Vilcanota. The fastest rates of deglaciation (39×10 -5 to 114×10 -5 km 3 yr -1 and 112×10 -5 to 247×10 -5 km 3 yr -1 for each valley, respectively) were calculated for the most recent paleoglaciers, corresponding to the last few centuries. These results are consistent with observations in the Venezuelan Andes showing high rates of deglaciation since the Little Ice Age. These rates also fall within the range of 20th century rates of deglaciation measured on the Quelccaya Ice Cap (29×10 -5 to 220×10 -5 km 3 yr -1, Brecher and Thompson, 1993; Thompson, 2000). These results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century. Equilibrium line altitude (ELA) depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the Quelccaya Ice Cap and 170 m for the Cordillera Vilcanota. Maximum ELA depressions are lower than previously published: <500 m for the Cordillera Vilcanota and <400 m for the Quelccaya Ice Cap. These lower values could imply a topographic control over paleoglacier extent.

Mark, Bryan G.; Seltzer, Geoffrey O.; Rodbell, Donald T.; Goodman, Adam Y.

2002-05-01

351

Rates of Holocene chemical weathering, `Little Ice Age' glacial erosion and implications for Schmidt-hammer dating at a glacier—foreland boundary, Fåbergstølsbreen, southern Norway  

Microsoft Academic Search

Average rates of Holocene chemical weathering and `Little Ice Age' glacial erosion of bedrock are estimated across the glacier—foreland boundary of an outlet glacier of the Jostedalsbreen ice-cap, southern Norway. Estimates are derived from two types of evidence: (1) the heights of quartz veins above adjacent surfaces of granitic or granodioritic gneiss; and (2) Schmidt-hammer R-values of rock hardness. Average

Geraint Owen; John A. Matthews; Paul G. Albert

2007-01-01

352

Volcanic ash layers in blue ice fields (Beardmore Glacier Area, Antarctica): Iridium enrichments  

NASA Technical Reports Server (NTRS)

Dust bands on blue ice fields in Antarctica have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the ice near moraines), and volcanic debris deposited on and incorporated in the ice by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. Ice core studies have revealed that most of the dust layers in the ice cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since ice cores usually incorporate younger ice. In contrast, dust bands on bare blue ice fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the ice and from dating the ice using the uranium series method. Also for the volcanic ash layers found on blue ice fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue ice fields at the Lewis Cliff Ice Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the Ice Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band samples, including Ir. Iridium determinations were made using INAA, with synthetical and natural (meteorite) standards. These findings are discussed.

Koeberl, Christian

1988-01-01

353

Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  

NASA Astrophysics Data System (ADS)

Glacially-deformed massive ice and icy sediments (MI-IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in Alaska, Greenland and Iceland; (2) ice crystal fabrics similar to those from basal ice in Antarctica and ice-cored moraines on Axel Heiberg Island, Canada; and (3) a thaw or erosional unconformity along the top of the MI-IS, buried by glacigenic or aeolian sediments. Intrasedimental ice consists of pore ice and segregated ice formed within Pleistocene sands deposited before glacial overriding. The co-existence of basal and intrasedimental ice within the MI-IS records their occurrence within the basal ice layer of the Laurentide Ice Sheet. Stagnation of the ice sheet and melt-out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale. The widespread occurrence of supraglacial melt-out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost.

Murton, J. B.; Whiteman, C. A.; Waller, R. I.; Pollard, W. H.; Clark, I. D.; Dallimore, S. R.

2005-03-01

354

Evidence for more extensive ice shelves along the Western Antarctic Peninsula during the Little Ice Age: observations from the LARISSA project in Barilari Bay, Graham Land  

Microsoft Academic Search

Barilari Bay, west Antarctic Peninsula, lies 12 nautical miles northwest from ice-core site Beta on the Bruce Plateau, which is an area of regionally high snow accumulation rates and ice velocity. This area has experienced recent rapid regional warming (Vaughan, 2003), and aerially-documented ice shelf disintegration since the 1940's . A 133cm Kasten core (KC54) was collected aboard the Nathaniel

A. E. Kirshner; A. Christ; T. Allinger; G. Armbruster; A. Crawford; N. Elking; J. Gao; M. Gunter; D. Kirievskaya; S. Jeong; C. Peers; P. Povea de Castro; D. Reardon; C. Sanchez Cervera; M. Talaia-Murray; W. Verreydt; M. Ward

2010-01-01

355

Substantial agreement on the timing and magnitude of Late Holocene ice cap expansion between East Greenland and the Eastern Canadian Arctic: a commentary on Lowell et al., 2013  

NASA Astrophysics Data System (ADS)

Lowell et al. (2013) present a large series of radiocarbon dates on tundra plants preserved beneath ice caps and cosmogenic nuclide exposure ages on moraine boulders and bedrock that document changes in the dimensions of Istorvet, an independent coastal ice cap on East Greenland. They argue that their reconstruction of Istorvet advances during the Late Holocene is inconsistent with the reconstructions of Miller et al. (2012) for Arctic Canada. Here we show that a careful interpretation of their data reveals a remarkable similarity with the compilation of radiocarbon dates on rooted tundra plants long-entombed beneath over 50 different ice masses in a 1000 km transect along Baffin Island, Arctic Canada and with the high-resolution record from an Icelandic ice cap (Miller et al., 2012). Collectively, these results suggest synchronous responses of ice masses across the northwestern sector of the North Atlantic Arctic during recent millennia. We also emphasize that the interpretation of radiocarbon ages of rooted plants exposed by receding ice depends to a large extent on the collection protocols employed. The sampling protocols outlined below maximize the value of these key new datasets to provide unambiguous constraints on past climates and changes in glacier dimensions. Examples of settings that meet these criteria are shown in Figs. 1 and 2.ice caps

Miller, Gifford H.; Briner, Jason P.; Refsnider, Kurt A.; Lehman, Scott J.; Geirsdóttir, Áslaug; Larsen, Darren J.; Southon, John R.

2013-10-01

356

Cosmogenic Ne-21 exposure ages of glacial boulders constrained by local bedrock erosion rates in Ong Valley, Antarctica  

NASA Astrophysics Data System (ADS)

In order to accurately determine the exposure age of glacial boulders with cosmogenic nuclides, we need to know something about the erosion rate of the rock and any previous exposure the boulder may have had. Commonly, the erosion rate is simply assumed, and inheritance is dealt with by both sampling strategy and removing outliers from the data. In this study, we determine the rock erosion rate by measuring the concentration of cosmogenic Ne-21 in granite bedrock samples. This is used to constrain the exposure age of glacial boulders of the same lithology from the same locale. Ong Valley, Antarctica, (157.5 East, 83.25 South) is an ice-free valley in the Miller Range of the Central Transantarctic Mountains. The valley contains three distinct glacial drifts, and the oldest of these is well defined by an end moraine. We collected samples from six boulders on this end moraine, and six additional samples from the surrounding bedrock that is composed of the same lithology, the Hope Granite. The bedrock samples were collected from the ridge bordering the valley, well above the glacial limit. Because the bedrock samples have not been shielded by ice and have been exposed for millions of years, the concentration of cosmogenic Ne-21 in these samples reflects only the erosion rate of the granite. We separated quartz from the granite samples following standard laboratory methods and measured the concentration of cosmogenic Ne-21 in the quartz at the BGC Noble Gas Thermochronometry Lab. The concentration of cosmogenic Ne-21 in the bedrock samples is interpreted as reflecting only the erosion rate. We can then assume that the erosion rate of the bedrock is equal to the erosion rate of the glacial boulders on the end moraine because they have the same lithology and have been subjected to the same climate conditions during their exposure. With this information, we can better constrain the exposure age of the glacial boulders in Ong Valley.

Morgan, D. J.; Balco, G.; Putkonen, J.; Bibby, T.; Giusti, C.; Ball, A. E.; Hedberg, C. P.; Diamond, M. S.; Ringger, K. C.

2013-12-01

357

Vostok Ice Core: Excel (Mac or PC)  

NSDL National Science Digital Library

Students use Excel to graph and analyze Vostok ice core data (160,000 years of Ice core data from Vostok Station). Data includes ice age, ice depth, carbon dioxide, methane, dust, and deuterium isotope relative abundance.

Professor Stephanie Pfirman, Barnard College. Based on data of J. Chapellaz, Laboratoire de Glaciologie et Geophysique de l'Environment, Grenoble. Archived at: Lamont-Dohert Earth Observatory (more info) . Starting Point page organized by R.M. MacKay.

358

Glacier change in Garibaldi Provincial Park, southern Coast Mountains, British Columbia, since the Little Ice Age  

NASA Astrophysics Data System (ADS)

Fluctuations of glaciers during the 20th century in Garibaldi Provincial Park, in the southern Coast Mountains of British Columbia, were reconstructed from historical documents, aerial photographs, and fieldwork. Over 505 km 2, or 26%, of the park, was covered by glacier ice at the beginning of the 18th century. Ice cover decreased to 297 km 2 by 1987-1988 and to 245 km 2 (49% of the early 18th century value) by 2005. Glacier recession was greatest between the 1920s and 1950s, with typical frontal retreat rates of 30 m/a. Many glaciers advanced between the 1960s and 1970s, but all glaciers retreated over the last 20 years. Times of glacier recession coincide with warm and relatively dry periods, whereas advances occurred during relatively cold periods. Rapid recession between 1925 and 1946, and since 1977, coincided with the positive phase of the Pacific Decadal Oscillation (PDO), whereas glaciers advanced during its negative phase (1890-1924 and 1947-1976). The record of 20th century glacier fluctuations in Garibaldi Park is similar to that in southern Europe, South America, and New Zealand, suggesting a common, global climatic cause. We conclude that global temperature change in the 20th century explains much of the behaviour of glaciers in Garibaldi Park and elsewhere.

Koch, Johannes; Menounos, Brian; Clague, John J.

2009-04-01

359

Palaeoclimatic interpretation of moraines: Identifying limitations and future tasks (the case study Southern Alps/New Zealand)  

NASA Astrophysics Data System (ADS)

During the past 20 years, the widespread deployment of terrestrial cosmogenic nuclide dating (TCND) alongside other substantial geochronological advances in laboratory precision and model calibration have seen an impressive increase in both number and claimed resolution of well-dated geomorphological reconstructions of mountain glacier fluctuations. Correlations at local, regional and hemispheric scales have frequently been performed on basis of those studies that partly include sophisticated probability analyses for reducing the statistical uncertainty of moraine ages, and analyses of glacier sensitivity to temperature and precipitation forcing. Although these recent advances especially with dating modern dating techniques are acknowledged, some basic conceptual issues still remain. It seems that in certain cases "technical" progress and improved modelling skills have encouraged us to over-reach our interpretive limits and overstate our optimism regarding "reliability" of glacier chronologies and their correlation. Critical evaluation of the interpretative limitations of chronological studies is not always recognised to the necessary extent. Interdisciplinary approaches - indispensable for the complex subject covering Geochronology, Glaciology, Glacial Geomorphology and Palaeoclimatology - are still not necessarily the norm. Based on a brief theoretical outline of the requirements for "reliable" palaeoclimatic interpretation of moraines (cf. Winkler & Matthews 2010, Kirkbride & Winkler 2012), one of the high-potential key sites for the investigation of Holocene glacier variation, the Southern Alps of New Zealand, are taken as case study to highlight a few of the practical limitations and outline future tasks that need improvement. Those tasks are - among others - identified as: (1) minimise the "geomorphological" uncertainty with the numerical dating of moraines, (2) identify possible non-glacial influence on the formation of moraines and address the potential misleading effect of large-scale mass movements on their subsequent palaeoclimatic interpretation, (3) improve the control on spatial coherence of existing data, and finally (4) include glaciological considerations and critical evaluation of the proposed resolution with any attempts of intra-hemispheric and global correlation. References: Kirkbride, M.P. & Winkler, S. (2012): Correlation of Late Quaternary glacier chronologies: impact of climate variability, glacier response, and chronological resolution. Quaternary Science Reviews 46, 1 - 29. Winkler, S. & Matthews, J.A. (2010): Holocene glacier chronologies: Are 'high-resolution' global and inter-hemispheric comparisons possible? The Holocene 20, 1137 - 1147.

Winkler, Stefan; Kirkbride, Martin

2013-04-01

360

An investigation into the use of color as a device to convey memes during the Little Ice Age  

NASA Astrophysics Data System (ADS)

Color is used as a tool in visual communication to express ideas in a symbolic fashion. It can also be used as a guide to assist the viewer in the visual narrative. Artwork created in the period of time between 1300 to 1850 in northern and central Europe provides a comprehensive perspective in the use of color as symbol and color as an elucidative devise. This period of time is known as the Little Ice Age, the duration of which spans European history between the Medieval period and the Romantic era. The extreme climatic conditions of this era caused profound changes in society on many levels and influenced the use of color in paintings throughout this chapter in history. The new paradigm of the science of ideas, called memetics, provides a framework to analyze the expression of ideas through the use of color within this span of time.

White, Peter A.

361

The Little Ice Age signature and subsequent warming seen in borehole temperature logs versus solar forcing model  

NASA Astrophysics Data System (ADS)

The `low' in the transient temperature versus depth borehole profiles around 120 m seen from deep temperature logs in the Canadian Prairies (southern Alberta-southern Saskatchewan), as well as in some of the European data, has been interpreted to be related to the Little Ice Age (LIA). Data point to the lowest ground surface and subsurface temperatures occurring in the very late eighteenth to nineteenth centuries. Inversion of these logs shows that surface temperature lows were followed by a recent warming period. Further, the synthetic profiles built on the basis of solar forcing history, stretching as far back as the beginning of the seventeenth century, suggest that the LIA signatures interpreted from the inversion of the borehole temperature logs would be difficult to be explained by known published models of past solar irradiation despite large range of assumed sensitivities for the couplings assumed, and that further forcing needs to be considered.

Majorowicz, Jacek; Šafanda, Jan; Przybylak, Rajmund

2014-06-01

362

Ice Age Methane Revisited: Oceans, Lightning, and the Steady Wetland Source  

NASA Astrophysics Data System (ADS)

The concentrations of reactive greenhouse gases in the atmosphere are a result of the interplay between sources on land and in the oceans and the atmospheric sink. Methane (CH4) is the most important of the major, long-lived reactive trace gases, and over the past 400,000 years it has more closely paralleled the higher-frequency component of polar temperature records than any other measured gas. Analyses of ice core CH4 concentrations and carbon isotope composition (? 13CH4) have suggested that changing CH4 emissions from wetlands drove prehistoric changes in ice-core CH4. As a reactive trace gas, the global CH4 budget is controlled not just by changes in source strength, but also by climate, changes in the flux of other reactive trace gases, and the nonlinear dynamics of atmospheric chemistry. To investigate the effect of long-term climate change on the atmospheric concentration of CH4 we coupled climate, vegetation, and atmospheric chemistry models to simulate the natural emissions and atmospheric chemistry of the major reactive trace gases. Climate was simulated by a coupled AGCM/mixed-layer ocean model with simulations at 1000-year intervals from the Last Glacial Maximum (LGM, ca. 21 ka) to present. Terrestrial CH4 and Biogenic Volatile Organic Compound (BVOC) emissions were simulated using the BIOME4-TG global vegetation model, with simple algorithms for determining wetland area based on topography and soil moisture, CH4 emissions based on ecosystem carbon turnover in wet soils, and BVOC emissions based on vegetation type and density. We simulated atmospheric chemistry and transport with the LMDz-INCA 3D chemistry-transport model, and included a full prognostic simulation of nitrogen oxide (NOx) emissions from lightning based on simulated convective precipitation. Global wetland area decreased by 1x106 km2 from the LGM to the present (nearly 15%). However, CH4 emissions - 110 Tg yr-1 - were nearly unchanged over this same period. During the Pleistocene-Holocene transition CH4 emissions reached a maximum of ca. 130 Tg. LGM CH4 emissions were ca. 2\\permil more depleted in ? 13CH4 compared to present because of the increase in tropical wetland activity relative to northern wetlands. Wetland CH4 emissions did not change drastically during the deglaciation because new wetland areas formed as ice sheets retreated, while other wetland areas were flooded by rising sea-level. Global emissions of BVOC increased significantly from the LGM to present, (350 Tg C yr-1 or 150%) because of increased vegetation density from warming climate and increased atmospheric CO2 concentrations. The simulated increase in sea surface temperatures (SST) from the LGM to present led to increased convective precipitation and a 10-30% increase in NOx emissions from lightning. Observed rapid changes in atmospheric CH4 concentrations over the last 21 ka cannot be completely attributed to climate change on millennial time-scales. However, the simulated changes in both the atmospheric BVOC and NOx burdens, which compete with CH4 as an OH sink, may have increased the lifetime of CH4 on the order of 30% at the present compared to LGM. This strong reduction in CH4 oxidation potential would have had long-term consequences for atmospheric CH4 concentrations and may explain much of the ice-core CH4 record without requiring major changes in the wetland CH4 source.

Kaplan, J. O.; Folberth, G.; Hauglustaine, D.

2004-05-01

363

Relative age and fast tracking of elite major junior ice hockey players.  

PubMed

Investigations in a variety of chronologically grouped team sports have reported that elite young athletes were more likely born in the early months of the selection year, a phenomenon known as the relative age effect. The present study investigated the birth dates and developmental paths of 238 (15 to 20 years old) Major Junior 'A' hockey players from the Ontario Hockey League to determine if a relative age effect still exists in elite junior hockey and if the path to elite sport was accelerated (i.e., fast tracked). The results identified a relative age effect in elite hockey although it is only apparent among individuals who fast track. PMID:17688123

Sherar, Lauren B; Bruner, Mark W; Munroe-Chandler, Krista J; Baxter-Jones, Adam D G

2007-06-01

364

CO2 Climate-Glaciation linkages During the Late Paleozoic Ice Age and the Earth's Penultimate Deglaciation  

NASA Astrophysics Data System (ADS)

The Late Paleozoic Ice Age (LPIA) was the longest-lived (330 to 260 Myr) and most intense glaciation of the past half-billion years. Emerging high-latitude Southern Hemisphere records document a much more dynamic ice age - one defined by multiple short-lived (1 to 7 myr duration) icehouse periods punctuated by warmer periods of glacial minima. These major climate shifts throughout the LPIA and its demise at the close of the Early Permian provide the only 'vegetated-Earth' analogues of major climate change in an icehouse. As our climate system departs from the well-studied Pleistocene glacial-interglacial cycles, a 'deep-time' perspective of pCO2-climate- glaciation linkages during past icehouse-to-greenhouse transitions provides a unique perspective into what may be the Earth's most epic deglaciation. Here we apply the carbon isotopic compositions of soil-formed carbonates and fossil plant material (cuticle, coals, charcoals) from several terrestrial basins in North America to a soil CO2-diffusion model and Monte Carlo modeling to estimate atmospheric pCO2 for the LPIA and its transition to the ensuing Mesozoic greenhouse state. Best estimates of Late Paleozoic pCO2 indicate repeated shifts from present-day levels to values of up to 2500 to 3000 ppmv during periods of glacial minima and possibly fully deglaciated greenhouse states. To evaluate the nature of the CO2-climate relationship during these major climate transitions, we developed a time-equivalent record of paleotropical sea-surface temperatures (SSTs) using ?18O values from a global compilation of well-preserved latest Permo-Carboniferous tropical shallow-water brachiopods. The observed covariance between shifts in inferred paleotropical SSTs, pCO2 and high- latitude Gondwanan glaciation implies a strong CO2-climate-glaciation linkage that is consistent with the range predicted by Permian climate simulations for a change in radiative CO2-forcing from 1 to 8 fold present-day levels. This apparent CO2-climate-glaciation link suggests that atmospheric CO2 levels may have been the primary driver for the repeated buildup and retreat of continental ice sheets during the Late Paleozoic. Integration of these climate proxy records with newly developed tropical paleobotanical records for paleotropical Euramerica reveals repeated major restructuring of flora in-step with climate and pCO2 shifts illustrating the impact on tropical floral ecosystems associated with past CO2-forced climate transitions.

Montanez, I. P.

2007-12-01

365

Relative importance of meridional and zonal sea surface temperature gradients for the onset of the ice ages and PliocenePleistocene climate  

E-print Network

midlatitudes and subpolar regions cooled, establishing a meridional sea surface temperature (SST) gradient of the changes in the meridional and zonal temperature gradients for the onset of glacial cycles and for Pliocene and zonal sea surface temperature gradients for the onset of the ice ages and PliocenePleistocene climate

366

Glacier changes since the Little Ice Age maximum in the western Qilian Shan, northwest China, and consequences of glacier runoff for water supply  

Microsoft Academic Search

Based on aerial photographs, topographical maps and the Landsat-5 image data, we have analyzed fluctuations of glaciers in the western Qilian Shan, northwest China, from the Little Ice Age (LIA) to 1990. The areas and volumes of glaciers in the whole considered region decreased 15% and 18%, respectively, from the LIA maximum to 1956.This trend of glacier shrinkage continued and

Liu Shiyin; Sun Wenxin; Shen Yongping; Li Gang

2003-01-01

367

The timing and nature of recession of outlet glaciers of Hielo Patagónico Norte, Chile, from their Neoglacial IV (Little Ice Age) maximum positions  

Microsoft Academic Search

The dates of recession of eleven outlet glaciers of the Hielo Patagónico Norte (Northern Patagonian Icefield) from their recent maximum positions have been inferred from dendrochronology, lichenometry, radiocarbon dating and historical sources. We have refined the dating for part of the Little Ice Age period in this area placing a glacial advance to between AD 1650 and 1766 with the

Stephan Harrison; Vanessa Winchester; Neil Glasser

2007-01-01

368

River channel changes in the Rhone Delta (France) since the end of the Little Ice Age: geomorphological adjustment to hydroclimatic change and natural resource management  

Microsoft Academic Search

This study provides a representative example of a river affected by artificial width contraction and consequent bed incision in a context of sea-level rise. Geomorphological adjustment in the Rhone catchment since the final stage of the Little Ice Age has been induced by hydroclimatic change and human disturbances. These adjustments are examined to highlight the response of two sand-bed distributary

G Arnaud-Fassetta

2003-01-01

369

'Little Ice Age' aridity in the North American Great Plains: a high-resolution reconstruction of salinity fluctuations from Devils Lake, North Dakota, USA  

Microsoft Academic Search

The 'Little Ice Age' was an interval between about AD 1500 and 1850, characterized by advancing glaciers in mountainous regions of Europe and western North America. However, it is unclear whether this cool moist period was truly global in extent, or how it was manifested in other regions with different climatic controls. A high-resolution reconstruction of salinity fluctuations in Devils

Sherilyn C. Fritz; Daniel R. Engstrom; Brian J. Haskell

1994-01-01

370

Little Ice Age fluctuations of small glaciers in the Monte Fitz Roy and Lago del Desierto areas, south Patagonian Andes, Argentina  

Microsoft Academic Search

Current knowledge about late Holocene glacier fluctuations in the south Patagonian Andes is mainly based on evidence from large outlet glaciers of the North and South Patagonian Icefields, and few data exist for the smaller glaciers elsewhere in the region. Here we provide dendrogeomorphological evidence for Little Ice Age (LIA) and post-LIA activity for five small glaciers near the northeast

M. H. Masiokas; B. H. Luckman; R. Villalba; S. Delgado; P. Skvarca; A. Ripalta

2009-01-01

371

Highly branched isoprenoid (HBI) biomarkers as an Antarctic sea-ice proxy in deep ocean glacial age sediments  

NASA Astrophysics Data System (ADS)

Antarctic sea-ice plays a primary role in the climate system, potentially modulating interhemispheric millennial-scale climate change and deglacial warming. Recently, microfossil proxy data have provided important insights into this potential forcing. However, additional proxies for glacial sea-ice reconstructions are required, to support the microfossil data and to control for potential preservation issues. We consider highly branched isoprenoids (HBIs) as a sea-ice proxy, building on earlier studies in the Arctic and Antarctic. This study focussed on measuring HBIs in glacial deposits in Southern Ocean deep ocean sediment cores. These deep-water sites provided a study location away from the local sea ice complexities associated with previously studied coastal and shallow water sites and, for the first time, allowed an evaluation of HBIs during several phases of glacial sea-ice variability inferred from microfossils. Down-core profiles of HBIs diene (II) and triene (III) were compared with diatom-based reconstructions of Antarctic sea-ice derived in three high-resolution sediment cores recovered from a transect across the Scotia Sea, Southwest Atlantic. High quality chronological control was achieved through a combination of abundance stratigraphy, relative geomagnetic palaeointensity data, and down-core magnetic susceptibility/ice core dust correlation. Positive correlations, observed between (II) and sea-ice presence, and a strong coupling between (III) and marginal ice zone conditions indicated that the two HBIs are both closely related to sea-ice edge dynamics. Strong down-core correlations between the HBIs indicate coeval sedimentation related to the summer breakdown of sea-ice melt-induced stratification. Combined, the two HBIs and diatoms demonstrated their potential as proxies for permanent sea-ice cover and sea-ice seasonality, two parameters poorly resolved in current climate models. The sea-ice reconstructions presented confirmed that HBIs are a viable proxy for glacial Antarctic sea-ice and sea ice dynamics back to at least 60 cal ka BP.

Collins, L. G.; Allen, C. S.; Pike, J.; Hodgson, D. A.; Weckström, K.; Massé, G.

2012-04-01

372

Geodiversity characterization and assessment of the Morainic Amphitheatre of Rivoli -Avigliana (NW-Italy)  

NASA Astrophysics Data System (ADS)

The concept of Geodiversity in its wide sense refers specifically to particular geosystems that are in themselves complex (e.g diverse) assemblages of bedrock, landform, and soil features. Therefore, geodiversity assessment is strictly related to landscape structure, whose studies are in the field of complex Physical Geography. Moreover, Geodiversity studies provide a fundamental base for geoconservation and environmental management in a holistic way. This is particularly true within complex geomorphological environments, where many intrinsic and extrinsic factors are interconnected. Various procedures has been already applied for the creation of geodiversity maps in different geomorphological context, but especially in wide areas with a large geodiversity of landforms. Pleistocene morainic amphitheatres of the Alpine piedmont regions are indeed particular and complex environments: not only for the geological and geomorphological points of view, but also for their relationships with biotic components and human life. The aim of this study is to carry out a geodiversity characterization of the Rivoli-Avigliana Morainic Amphitheatre (AMRA; NW Italy). The AMRA separates the lower Susa Valley from the middle course of the Sangone River; it is a set of low hills and depressions related to glacial pulsations aged between 750,000 and 12,000 years ago. Earth Sciences knowledge of the area has been compared to detailed field geomorphological and territorial data in order to determine qualitative and quantitative landscape parameters and to evaluate their validity for geodiversity assessment. A first qualitative characterization of the AMRA and an estimation of its geodiversity have been performed by means of geomorphological mapping and stratigraphic studies, including geomorphosites assessment for the same area. Then, geodiversity characterization and evaluation have been performed through the definition and application of quantitative parameters (landform energy, slope, land use, roughness, and other geomorphologic, hydrologic and geologic indexes). After acquisition of vector data, satellite and aerial images, GIS procedures allowed to manage and to process images and data: this allowed to interpret morphometric indexes and to obtain thematic maps with 3D views. Finally, results from the calculation of geodiversity and geomorphosites have been compared. Results turned out to be very effective for the study and for the reconstruction of the AMRA evolutionary stages, also for interpreting scenarios of future natural hazards, land occupation and risks posed to geodiversity for natural and anthropogenic causes. Geomatics devices and digital data demonstrated to be really suitable for improved analysis and representation of the observed phenomena. They can be easily integrated within GIS for decision support requirements. In this way, field and remote sensing data, together with indexes of biotic and abiotic aspects can generate synthetic information, to produce effective spatial interpolations and impressive 3D scenarios useful for Earth Science simulations and environmental/territorial advertising.

Giordano, Enrico; Lucchesi, Stefania; Perotti, Luigi; Giardino, Marco

2014-05-01

373

Coach Selections and the Relative Age Effect in Male Youth Ice Hockey  

ERIC Educational Resources Information Center

Relative age effects (RAEs; when relatively older children possess participation and performance advantages over relatively younger children) are frequent in male team sports. One possible explanation is that coaches select players based on physical attributes, which are more likely witnessed in relatively older athletes. Purpose: To determine if…

Hancock, David J.; Ste-Marie, Diane M.; Young, Bradley W.

2013-01-01

374

Regional drainage of meltwater beneath a Hesperian-aged south circumpolar ice sheet on Mars  

Microsoft Academic Search

Five sinuous valleys that begin near the margins of the Hesperian-aged Dorsa Argentea Formation (DAF) are examined using Mars Global Surveyor Mars Orbiter Laser Altimeter data. These valleys are carved into the surrounding Noachian cratered terrain and extend away from the DAF for lengths up to 1600 km before terminating in the Argyre basin 1–3 km below their starting elevations.

Gil J. Ghatan; James W. Head

2004-01-01

375

Lateglacial ice-cap dynamics in NW Scotland: evidence from the fjords of the Summer Isles region  

NASA Astrophysics Data System (ADS)

The seaboard of western Scotland is a classic fjord landscape formed by glaciation over at least the last 0.5 Ma. We examine the glacial geology preserved in the fjords (or sea lochs) of the Summer Isles region of NW Scotland using high-resolution seismic data, multibeam swath bathymetry, seabed sediment cores, digital terrain models, aerial photographs, and field investigations. Detailed analyses include seismic facies and lithofacies interpretations; sedimentological and palaeoenvironmental analyses; and radiocarbon dating of selected microfauna. Our results indicate that the Pleistocene sediments of the Summer Isles region, on- and offshore, can be subdivided into several lithostratigraphic formations on the basis of seismic character, geomorphology and sedimentology. These are: subglacial tills; ice-distal and glacimarine facies; ice-proximal and ice-contact facies; moraine assemblages; and Holocene basin fill. The submarine landscape is also notable for its large-scale mass-movement events - the result of glaciodynamic, paraglacial or seismotectonic processes. Radiocarbon dating of marine shells indicate that deglaciation of this part of NW Scotland was ongoing between 14 and 13 ka BP - during the Lateglacial Interstadial (Greenland Interstadial 1) - consistent with cosmogenic surface-exposure ages from previous studies. A sequence of numerous seafloor moraine ridges charts oscillatory retreat of the last ice sheet from a buoyant calving margin in The Minch to a firmly grounded margin amongst the Summer Isles in the early part of Lateglacial Interstadial (GI-1) (pre-14 ka BP). Subsequent, punctuated, frontal retreat of the ice mass occurred in the following ˜1000 years, during which time ice-cap outlet glaciers became topographically confined and restricted to the fjords. A late-stage readvance of glaciers into the inner fjords occurred soon after 13 ka BP, which calls into question the accepted limits of ice extent during the Younger Dryas Stadial (Greenland Stadial 1). We examine the wider implications of our chronostratigraphic model, discussing the implications for British Ice Sheet deglaciation, Lateglacial climate change, and the style and rates of fjord sedimentation.

Stoker, Martyn S.; Bradwell, Tom; Howe, John A.; Wilkinson, Ian P.; McIntyre, Kate

2009-12-01

376

A first-order global model of Late Cenozoic climatic change: Orbital forcing as a pacemaker of the ice ages  

NASA Technical Reports Server (NTRS)

The development of a theory of the evolution of the climate of the earth over millions of years can be subdivided into three fundamental, nested, problems: (1) to establish by equilibrium climate models (e.g., general circulation models) the diagnostic relations, valid at any time, between the fast-response climate variables (i.e., the 'weather statistics') and both the prescribed external radiative forcing and the prescribed distribution of the slow response variables (e.g., the ice sheets and shelves, the deep ocean state, and the atmospheric CO2 concentration); (2) to construct, by an essentially inductive process, a model of the time-dependent evolution of the slow-response climatic variables over time scales longer than the damping times of these variables but shorter than the time scale of tectonic changes in the boundary conditions (e.g., altered geography and elevation of the continents, slow outgassing, and weathering) and ultra-slow astronomical changes such as in the solar radiative output; and (3) to determine the nature of these ultra-slow processes and their effects on the evolution of the equilibrium state of the climatic system about which the above time-dependent variations occur. All