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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

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

E-print Network

advance exceeding the Little Ice Age maximum K. Winsor a,*, A.E. Carlson a,b , D.H. Rood c,d a Department of a historical Little Ice Age (LIA) moraine adjacent to the modern ice margin. Using 10 Be surface exposure summer insolation, culminating in the Little Ice Age (LIA) of the last several centuries (Kaufman et al

3

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

4

Do blue-ice moraines in the Heritage Range show the West Antarctic ice sheet survived the last interglacial?  

E-print Network

cosmogenic isotope data on blue-ice moraines in the Heritage Range, West Antarctica. The age of the moraines Hills are consistent with an alternative hypothesis, namely that the spread of ages on blue ice moraines to the moraine to build a deposit with a range of exposure ages. As the ice thickness fluctuates during glacial

5

Age of the Ørkendalen moraines, Kangerlussuaq, Greenland: constraints on the extent of the southwestern margin of the Greenland Ice Sheet during the Holocene  

NASA Astrophysics Data System (ADS)

Although Greenland ice core records register relatively stable Holocene climate conditions, the lower elevation margins of the Greenland Ice Sheet (GrIS) experienced significant Holocene fluctuations. These fluctuations include ice sheet recession during the Holocene Thermal Maximum (9-5 ka) and advance during the Little Ice Age (LIA; ˜A.D. 1350-1880). Determining the extent and timing of these fluctuations is important for understanding the response of the GrIS to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models. Sets of moraines marking past extents of the southwestern GrIS margin occur in the Kangerlussuaq region. We focus on the Ørkendalen moraines, a prominent moraine set located within 2 km of the modern ice margin and just outboard of the LIA moraines. We present the first 10Be ages of the Ørkendalen moraines indicating they were deposited at 6.8 ± 0.3 ka. The geomorphic relationship between the Ørkendalen and LIA moraines indicates that the ice sheet margin was inboard of its Ørkendalen extent between ˜6.8 ka and the culmination of the LIA. The age of the Ørkendalen moraines provides an important constraint on the extent of the southwestern GrIS during the middle Holocene.

Levy, Laura B.; Kelly, Meredith A.; Howley, Jennifer A.; Virginia, Ross A.

2012-10-01

6

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

7

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

8

Late-Glacial History of Lago Argentino, Argentina, and Age of the Puerto Bandera Moraines  

NASA Astrophysics Data System (ADS)

In the west-central part of Lago Argentino, the Puerto Bandera moraines are clearly detached from longer, more prominent moraines of the last glaciation and from shorter and smaller Neoglacial moraines. Scientists have long speculated about the age of the Puerto Bandera moraines. Detailed geomorphologic studies in the western area of Lago Argentino, including stratigraphic profiles at Bah?´a del Quemado in the northern branch (Brazo Norte), indicate that the Puerto Bandera moraines were deposited by three pulses of ice. Each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges. The timing of the three glacier advances was established by radiocarbon dating, including data published by John Mercer. The oldest moraine system, formed during the Puerto Bandera I substade, was deposited ca. 13,000 14C yr B.P. Moraines of the Puerto Bandera II substade were deposited ca. 11,000 14C yr B.P. The youngest moraine system was deposited during a minor readvance, shortly before 10,390 C14 yr B.P., and thus appears to have occurred some time during the European Younger Dryas interval. After this third substade, the ice tongues retreated into the interior branches of Lago Argentino and have remained there since. Evidence found at Bah?´a del Quemado, together with data provided by other authors, attests to a significant climatic change by the middle Holocene, which we believe occurred during the Herminita advance, the first Holocene glacial readvance recognized within the area.

Strelin, Jorge A.; Malagnino, Eduardo C.

2000-11-01

9

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

10

How can blue-ice moraines constrain elevation changes of the West Antarctic Ice Sheet in the southern Ellsworth Mountains?  

NASA Astrophysics Data System (ADS)

Observational data in the Weddell Sea sector of the Antarctic Ice Sheet has 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 first 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 boulders and finer debris in the glacier ice and that they are related to ice structures and to basal debris emerging at the glacier surface, (b) exposure ages of surface debris reveals boulders both recently exposed and those pre-dating the Last Glacial Maximum (LGM), (c) during the LGM the ice was thicker and the limit is marked by a zone of perched boulders and, in topographic hollows, by buried glacier ice, (d) weathered high elevation deposits with exposure ages in excess of 400 ka have been overridden by glacier ice and thus may represent deposits of much greater age, (e) the relationship between blue-ice moraines and deposits from local wind-drift glaciers makes it possible to constrain the date and duration of Holocene thinning. A forthcoming field season in 2013-2014 to re-measure 90 stakes for horizontal movement and ablation should help quantify the rate of blue-ice moraine formation. We will also obtain rock cores to establish rates of weathering of the older deposits and thus constrain their age more tightly.

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

2013-12-01

11

Changes in ice-margin processes and sediment routing during ice-sheet advance across a marginal moraine  

USGS Publications Warehouse

Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice-marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice-proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris-rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations. ?? 2007 Swedish Society for Anthropology and Geography.

Knight, P.G.; Jennings, C.E.; Waller, R.I.; Robinson, Z.P.

2007-01-01

12

Distribution of ice marginal moraines in NW Russia  

Microsoft Academic Search

Here we present results from a mapping project on the distribution of glacial end moraine zones in NW Russia, covering an area from the Baltics in the west (30°E) to Taymyr Peninsula and Byrranga mountains (120°E) in the East. Several previous studies have been made in the area, but none have mapped end moraine zones in a uniform way over

Ola Fredin; Lena Rubensdotter; Aurelien van Welden; Eiliv Larsen; Astrid Lyså

2012-01-01

13

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.

14

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

15

Be-10 Ages From Northern Alaska Range Moraines Help Constrain the Timing of the Penultimate Glaciation in Eastern Beringia  

NASA Astrophysics Data System (ADS)

Alaska and the adjoining Yukon Territory is currently the site of uncertainty concerning the timing of the penultimate glaciation. While the timing of the Last Glacial Maximum across this region is generally synchronous (~18-25 ka), several ages for the penultimate glaciation have been proposed, including 50-60 ka, 140 ka, and 250 ka, correlating with marine isotope stage (MIS) 4/early MIS 3, MIS 6, and MIS 8, respectively. Furthermore, an out-of-phase, late MIS 5 age has also been suggested in western Beringia. Here, 10 new 10Be ages are presented from a key reference locality in the Delta River valley, Alaska, situated in the north- central Alaska Range. Because boulders are absent at this moraine sequence, quartzose pebble collections from moraine crest surfaces are used. Five pebble samples taken from the Delta (penultimate glaciation) moraine range between 24.7 and 68.0 ka and average 53.5 ± 11.0 ka after excluding a young outlier (24.7 ± 0.6 ka). Because previous research has shown that exposure ages typically date moraine stabilization, emphasis should be placed on older ages within a suite of exposure ages where inheritance is of minimal concern. Five pebble samples taken from the up-valley, Donnelly moraine (late Wisconsin glaciation) range between 11.5 and 65.3 ka, and average 13.3 ± 2.0 ka after removing one sample due to obvious inheritance (65.3 ± 2.1 ka). A nearby site in the north-central Alaska Range also shows promise for exposure dating late Quaternary moraines. The Fish Lake valley, located approximately 70 km southeast of the Delta River valley, is host to an extensive sequence of moraines that spans between the Little Ice Age and the penultimate glaciation; 17 boulder samples from the penultimate and late Wisconsin moraines collected in the summer of 2006 will also be presented. 10Be ages from these boulders will serve as an important comparison to the pebble-based ages from the Delta River valley. Although 10Be dating of pebble collections is untested, the average ages are in broad agreement with recent exposure dating studies elsewhere in Alaska and the Yukon supporting a MIS 4/early MIS 3 age for the penultimate glaciation in eastern Beringia.

Young, N. E.; Briner, J. P.; Kaufman, D. S.; Finkel, R. C.

2007-12-01

16

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

17

Age of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka cooling events  

NASA Astrophysics Data System (ADS)

Retreat of the western Greenland Ice Sheet during the early Holocene was interrupted by deposition of the Fjord Stade moraine system. The Fjord Stade moraine system spans several hundred kilometers of western Greenland's ice-free fringe and represents an important period in the western Greenland Ice Sheet's deglaciation history, but the origin and timing of moraine deposition remain uncertain. Here, we combine new and previously published 10Be and 14C ages from Disko Bugt, western Greenland to constrain the timing of Fjord Stade moraine deposition at two locations ˜60 km apart. At Jakobshavn Isfjord, the northern of two study sites, we show that Jakobshavn Isbræ advanced to deposit moraines ca 9.2 and 8.2-8.0 ka. In southeastern Disko Bugt, the ice sheet deposited moraines ca 9.4-9.0 and 8.5-8.1 ka. Our ice-margin chronology indicates that the Greenland Ice Sheet in two distant regions responded in unison to early Holocene abrupt cooling 9.3 and 8.2 ka, as recorded in central Greenland ice cores. Although the timing of Fjord Stade moraine deposition was synchronous in Jakobshavn Isfjord and southeastern Disko Bugt, within uncertainties, we suggest that Jakobshavn Isbræ advanced while the southeastern Disko Bugt ice margin experienced stillstands during the 9.3 and 8.2 ka events based on regional geomorphology and the distribution of 10Be ages at each location. The contrasting style of ice-margin response was likely regulated by site-specific ice-flow characteristics. Jakobshavn Isbræ's high ice flux results in an amplified ice-margin response to a climate perturbation, both warming and cooling, whereas the comparatively low-flux sector of the ice sheet in southeastern Disko Bugt experiences a more subdued response to climate perturbations. Our chronology indicates that the western Greenland Ice Sheet advanced and retreated in concert with early Holocene temperature variations, and the 9.3 and 8.2 ka events, although brief, were of sufficient duration to elicit a significant response of the western Greenland Ice Sheet.

Young, Nicolás E.; Briner, Jason P.; Rood, Dylan H.; Finkel, Robert C.; Corbett, Lee B.; Bierman, Paul R.

2013-01-01

18

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

19

Thermoluminescence Measurements on Meteorites from the Elephant Moraine Region: L6 Showers and Regional Ice Movements  

NASA Astrophysics Data System (ADS)

As part of their initial characterization, we have completed natural and induced thermoluminescence (TL) measurements for over 800 Antarctic meteorites. We have previously discussed the implications of these data for pairing, terrestrial age, and meteorite concentration mechanism at the Lewis Cliff and Allan Hills sites (Benoit et al., 1992a,b). Here we report data for meteorites from the Elephant Moraine region (designated EET, see Huss, 1990, for description of region). Our present discussion is limited to meteorites collected in the 1986/87 and 1987/88 field seasons; measurement of samples from the 1990/91 field season are underway. The Elephant Moraine region encompasses at least five meteorite-bearing blue icefields, including Elephant Moraine proper (EM), Meteorite City (MC), Upper Meteorite City (UMC), Texas Bowl (TB), and the Northern Ice Patch (NIP). While MC, UMC, and TB are physically adjacent to each other, EM and NIP are separated from the others, the latter being approximately 40 km distant from UMC. We have previously identified numerous pairing groups within the EET database without regard for field location. While most pairing groups are found to be restricted to single fields, there are a significant number that span several fields. The howardite group EET87503 covers both TB and EM and several L6 groups either span TB and EM or span the physically adjacent TB, UMC, and MC icefields. Even the isolated NIP apparently shares a few pairing groups with UMC and TB, although the small number of samples from this field make comparison difficult. This result seems to indicate that, unlike the Allan Hills sites, the individual ice fields at EET are sampling the same meteorite population. Natural TL levels for EET meteorites (Fig. 1) are generally high, with a significant fraction having TL levels greater than 50 krad. This would suggest that, in general, these meteorites have small terrestrial ages, probably <100,000 years for most meteorites. In this sense, the region is comparable to the Yamato sites. The cumulative histogram and the data for TB show a large number of meteorites with low TL (<30 krad), which would suggest this field is older than the others. However, the low TL "hump" in the TB data is caused almost entirely by three large L6 pairing groups (EET87587, EET87596, and EET87601) that are probably paired with each other. This suggests that the TB data are dominated by a relatively old L6 shower, but that the meteorites at the site, in general, have short terrestrial ages similar to the other icefields. The short terrestrial ages of the EET meteorites might suggest a connection with the meteorites of the Farwestern icefield at Allan Hills. However, induced TL peak temperature and width data show that the unusual H5 group observed at the Allan Hills sites (including the Farwestern field, Benoit and Sears, 1992). is absent at all EET sites. This suggests that the meteorites at the EET sites have shorter terrestrial ages than those from the Farwestern field at Allan Hills, despite a possible link between these sites suggested by recent ice flow determinations (Schultz et al., 1990; Delisle and Sievers, 1991). Benoit P.H. and Sears D.W.G. (1992a) Science 255, 1685-1687. Benoit P.H., Sears H., and Sears D.W.G. (1992a) J. Geophys. Res. (in press). Benoit P.H., Sears H., and Sears D.W.G. (1992b) J. Geophys. Res. 97, 4629-4647. Delisle G. and Siever J. (1991) J. Geophys. Res. 96, 15577-15587. Huss G.R. (1990) Meteoritics 25, 41-56. Schultz L., Annexstad J.O., and Delisle G. (1990) Antarctic Journal the U.S. 25(5), 9495. Figure 1, which in the hard copy appears here shows the natural TL data for (A) EET ordinary chondrites, (B,C) broken down by icefield, and for ordinary chondrites from (D) Allan Hills Main and (E) Farwestern icefields.

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

1992-07-01

20

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

21

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.

22

New Constraints on the Ages of Old Moraines: The Impact of Erosion on Surface Exposure Age Distributions.  

E-print Network

New Constraints on the Ages of Old Moraines: The Impact of Erosion on Surface Exposure Age. However, old landforms typically yield exposure ages with large uncertainties because of the large reduce the age variance for old landforms. AGU, Fall 2000 Meeting, Session U03 #12;

Zreda, Marek

23

Modeling the Deposition of Deglaciation Moraines  

NASA Astrophysics Data System (ADS)

Moraine ages figure prominently in reconstructions of the history of the Greenland ice sheet and of other ice masses, and in testing of hypotheses such as that of Denton et al. (2005, QSR) that north Atlantic millennial oscillations including the Younger Dryas were primarily wintertime events. We present a fast, coupled ice- flow/moraine-deposition model to aid in such hypothesis-testing. We find that not only ages and positions of moraines, but also number of moraines and their volumes, can help in interpretation. The model allows for multiple sediment-transport mechanisms and climate forcings, in a simple but flexible flowline configuration fast enough that inversions may be practical in the future. The temperature forcing for the model was the GISP2 ice core record spanning the time period between LGM and modern. We decoupled the orbital deglacial signal and the millennial-scale signal using a band-pass filter with cut-off at 10,000 years. We applied the ice core records as the forcing to the glacier-sediment model while systematically varying the strength of the millennial scale signal. Our results are examples of moraines deposited with varying degree of strength of millennial-scale signals, some of which show similarity to moraine sets observed around Greenland and the northern hemisphere.

Vacco, D.; Alley, R.; Pollard, D.

2007-12-01

24

Age of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka cooling events  

E-print Network

dating Abrupt climate change a b s t r a c t Retreat of the western Greenland Ice Sheet during the early, and have also emphasized the dynamic nature in which the GrIS responds to climate change (Joughin et alAge of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka

Briner, Jason P.

25

Inferring moraine age and depth of glacial erosion from cosmogenic exposure dates using geomorphic process modeling  

NASA Astrophysics Data System (ADS)

Cosmogenic exposure dating provides insight into the timing of glacial fluctuations at high latitudes, but collections of exposure dates from isochronous surfaces often show unexpectedly large scatter. Here, we show that the structure of a recently published set of cosmogenic exposure dates from eastern Greenland (Kelly et al., 2008, Quaternary Science Reviews, v. 27, p. 2273) is distinctly different from the structures of selected data sets from the midlatitudes. Specifically, histograms of the eastern Greenland dates are right-skewed, whereas histograms of exposure dates from the mid-latitude sites are left-skewed. We infer that this difference in structure reflects a difference in the geomorphic processes active in eastern Greenland, as compared to the mid-latitude sites. Further, we fit the eastern Greenland data with a process model that relates moraine age, landscape age, and depth of glacial erosion to the observed distributions of cosmogenic exposure dates. Our model treats inherited nuclides in moraine boulders in a Monte Carlo framework. The unknown parameters for each boulder are 1) the amount of time it was exposed to cosmic rays before being incorporated into the moraine, and 2) the depth to which the sampled point on the boulder was buried during this predepositional exposure time. Neither of these parameters is known, so we assume that all values from zero up to some maximum are equally likely. We draw random values from these uniform distributions for a large number of synthetic boulders, calculate an apparent exposure time for each synthetic boulder, and histogram the apparent exposure times. The histograms produced by the inheritance model are right-skewed, consistent with the eastern Greenland data set. In contrast, the left-skewed structure of the other data sets is well reproduced by a model of moraine degradation. We present fits of the inheritance model to the eastern Greenland exposure dates, and discuss the implications of the resulting moraine age, landscape age, and glacial erosion depth estimates.

Applegate, P. J.; Kelly, M. A.; Urban, N. M.; Lowell, T. V.; Alley, R. B.

2009-04-01

26

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.

27

10Be chronology of the Drygalski Moraines, central western Greenland  

NASA Astrophysics Data System (ADS)

Ice sheet margin fluctuations throughout the Holocene are increasingly well documented in Greenland, but fundamental gaps still exist. The Drygalski Moraines on the Nuussuaq Peninsula, central western Greenland, represent one of the few locations on Greenland where potential early Neoglacial (~2-5 ka) moraines have been identified. We used cosmogenic 10Be exposure dating of moraine boulders to test the hypothesis that the Drygalski Moraines are early Neoglacial in age, as was previously estimated using cross-cutting relationships with relative sea level. Alternative hypotheses are that the Drygalski Moraines represent the northern extent of the Ørkendalen Moraine (6.8 × 0.3 ka) or the Fjord Stade Moraines (~9.3 and ~8.2 ka). Results from 10Be dating of perched erratics outboard of the Drygalski Moraines suggest that deglaciation of the area occurred between ~10.4 × 0.3 ka and 9.5 × 0.3 ka. We dated three different crests of the Drygalski Moraine complex, which have mean ages of 8.6 × 0.4 ka (n=2), 8.5 × 0.2 ka (n=3), and 7.6 × 0.1 ka (n=2) from outer to inner. Perched erratics between the younger two moraines average 7.8×0.1 ka (n=2) and are consistent with the nearby moraine ages. These results allow us to reject the early Neoglacial and Ørkendalen hypotheses and generally support the Fjord Stade Moraine hypothesis because the Drygalski and Fjord Stade moraines are both early Holocene in age. However, we propose that the Drygalski and Fjord Stade moraines represent a different ice sheet response to early Holocene climate history. This may be attributed to the fast-flowing, marine-terminating nature of Jakobshavn Isbræ (the outlet glacier that deposited the Fjord Stade Moraines) in contrast with the land-based and slower-flowing lobe that deposited the Drygalski Moraines. Evidence suggests that Jakobshavn Isbræ is extremely sensitive to changes in climate, even on the centennial to decadal scale. As a result, Jakobshavn Isbræ may create discrete moraines in response to short-lived climate events (i.e. the 9.3 and 8.2 ka climate events). In contrast, the Drygalski Moraines may archive the centennial- to millennial-scale climate variability during the early Holocene and do not seem to be associated with specific early Holocene climate events.

Cronauer, S. L.; Briner, J. P.; Kelley, S. E.; Zimmerman, S. R.

2013-12-01

28

The Ice Age  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 9-12. It explains what ice ages are, what causes ice ages to occur, plants and animals that lived during the last Ice Age, and why some Ice Age animals went extinct. It includes objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order that complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

29

Ice age paleotopography  

SciTech Connect

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 to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.

Peltier, W.R. (Univ. of Toronto, Ontario (Canada))

1994-07-08

30

Ice age paleotopography.  

PubMed

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 to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set. PMID:17750657

Peltier, W R

1994-07-01

31

Boulder Recycling, Moraine Degradation, and Their Effects on Cosmogenic Exposure Dating of Moraines  

NASA Astrophysics Data System (ADS)

Recent exposure dates from the Gurreholm valley in Greenland suggest that the ice sheet advanced several times during late glacial to early Holocene time and during the Little Ice Age. Here, we demonstrate that this data set has a distinctly different structure from a recent set of exposure dates from the Waiho Loop moraine in New Zealand. Using geomorphic process modeling, we explain this difference in terms of the dominant geomorphic process at each field site. Our model treats two processes, boulder recycling and moraine degradation. In boulder recycling, previously exposed boulders are incorporated into new moraines. The degree to which any given boulder reflects the true age of a new moraine depends on both the predepositional exposure time of the boulder and how much the boulder was rotated from its original orientation by glacial transport. Where moraine degradation is the dominant process, previously shielded boulders are exposed to cosmic rays by the diffusive removal of material from the moraine's crest. In the model, these two processes yield distinctly different cumulative probability distributions of exposure ages. The cumulative density function for a set of exposure dates biased by boulder recycling rises rapidly, then levels off; the cumulative density function for exposure dates biased by moraine degradation rises more slowly at first, then increases. There is good agreement between model curves assuming moraine degradation and the observed distribution of exposure dates from the Waiho Loop. Similarly, the observed cumulative density functions for moraines in the Gurreholm valley resemble curves generated by the model for boulder recycling. Some mismatch remains between the observed and modeled cumulative density functions for the Gurreholm data sets. We expect this mismatch to be reduced as we improve the realism of the cosmic ray flux dependence on the angle from vertical in the model. In addition, preliminary fits of the model to the Gurreholm data set suggest that the prevalence of inheritance is correlated with the stratigraphic order of the moraines; the boulders on the youngest group of moraines contain the smallest amount of inherited nuclides, and the boulders on the oldest group of moraines contain the largest amount of inherited nuclides. This observation suggests that older advances removed preexposed boulders from the valley, leaving fewer boulders for subsequent advances to incorporate into their moraines.

Applegate, P. J.; Kelly, M. A.; Lowell, T. V.; Alley, R. B.

2008-12-01

32

The Great Ice Age  

NSDL National Science Digital Library

The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. Mountain glaciers formed on all continents, the ice caps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across North America and Eurasia. This ice age, the most recent in the history of the Earth, took place from 20 million years to 6 thousand years ago (Quaternary Period). The development of our understanding and the evidence for this worldwide event are covered in this United States Geological Survey (USGS) publication.

Ray, Louis

33

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

34

The Great Ice Age  

USGS Publications Warehouse

The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. During the Pleistocene Epoch of the geologic time scale, which began about a million or more years ago, mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across northern North America and Eurasia. So extensive were these glaciers that almost a third of the present land surface of the Earth was intermittently covered by ice. Even today remnants of the great glaciers cover almost a tenth of the land, indicating that conditions somewhat similar to those which produced the Great Ice Age are still operating in polar and subpolar climates.

Ray, Louis L.

1992-01-01

35

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

36

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

37

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

38

Simulating the climatic response of Hardangerjøkulen ice cap since the Little Ice Age with ISSM  

NASA Astrophysics Data System (ADS)

Glaciers and small ice caps respond considerably faster to climate change than the large ice sheets Greenland and Antarctica. We use the Ice Sheet System Model (ISSM) to model the dynamics and evolution of the maritime-continental Hardangerjøkulen ice cap (73 km^2, 60.55°N, 7.43°E) from the Little Ice Age (LIA) until today. ISSM is a finite element model with anisotropic mesh capabilities (resolution can be refined in regions of interest) and includes different approximations for the dynamics of ice flow, including the Shallow Ice Approximation (SIA) and Full-Stokes. The SIA neglects important stresses when topography is complex; however it has proved accurate in representing glacier volume fluctuations on decadal and longer timescales. As Hardangerjøkulen has relatively gentle slopes and lacks areas of very fast flow, we choose to use the SIA to study this ice cap on climatic time scales. As initial forcing for the ice flow model, we use a dynamically calibrated mass balance history corresponding to moraine evidence from the Little Ice Age maximum in 1750 AD, as well as later outlet glacier front positions from moraines, direct measurements and aerial photographs. For the 1900s, we use surface mass balance from a spatially distributed energy-balance model using data from meteorological stations as forcing. Glaciological mass balance records and front positions for the two main outlet glaciers, along with surface DEMs, are used for calibration. We investigate total ice volume and outlet glacier responses since the LIA. The sensitivity to surface mass balance as well as the applicability of the SIA to small ice caps is also discussed. Finally, our findings are compared and contrasted with previous model results for Hardangerjøkulen.

Åkesson, Henning; Nisancioglu, Kerim H.; Giesen, Rianne H.; Morlighem, Mathieu

2014-05-01

39

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.

40

Cracking the Ice Age  

NSDL National Science Digital Library

This web site is part of NOVA online from the Public Broadcasting System (PBS). It examines earth and atmospheric topics with a focus on historical and present climates, ice ages, glaciers, climactic change, Wilson cycles, the greenhouse effect, carbon dioxide, chlorofluorocarbons, plate tectonics, and Alfred Wegener. Tutorials are entitled: Big Chill, Greenhouse - Green Planet, Hot Science: Continents on the Move, and Related Links. Each topic has a brief report and includes scientific illustrations.

41

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

42

Mars Ice Age, Simulated  

NASA Technical Reports Server (NTRS)

December 17, 2003

This simulated view shows Mars as it might have appeared during the height of a possible ice age in geologically recent time.

Of all Solar System planets, Mars has the climate most like that of Earth. Both are sensitive to small changes in orbit and tilt. During a period about 2.1 million to 400,000 years ago, increased tilt of Mars' rotational axis caused increased solar heating at the poles. A new study using observations from NASA's Mars Global Surveyor and Mars Odyssey orbiters concludes that this polar warming caused mobilization of water vapor and dust into the atmosphere, and buildup of a surface deposit of ice and dust down to about 30 degrees latitude in both hemispheres. That is the equivalent of the southern Unites States or Saudi Arabia on Earth. Mars has been in an interglacial period characterized by less axial tilt for about the last 300,000 years. The ice-rich surface deposit has been degrading in the latitude zone of 30 degrees to 60 degrees as water-ice returns to the poles.

In this illustration prepared for the December 18, 2003, cover of the journal Nature, the simulated surface deposit is superposed on a topography map based on altitude measurements by Global Surveyor and images from NASA's Viking orbiters of the 1970s.

Mars Global Surveyor and Mars Odyssey are managed by NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, for the NASA Office of Space Science, Washington.

2003-01-01

43

Melt-out till and ribbed moraine formation, a case study from south Sweden  

NASA Astrophysics Data System (ADS)

Hummocky moraine with dispersed agglomerations of ribbed moraine - here named 'Åsnen-type ribbed moraine' - forms a 20-40 km wide zone over Småland, south Sweden, terminated to the north by a sharp boundary to streamlined terrain. The hummocky/ribbed moraine zone can be geomorphologically linked to the subaqueous Göteborg Moraine, formed at an oscillation/stand-still phase during the deglaciation of the Swedish west coast. Based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt-out from stagnant, debris-rich ice with synsedimentary deposition of sorted sediments, preferentially at a melting ice/bed interface. To accommodate for the geomorphological expression, such an interpretation further implies that debris-rich ice formed in an intermediate adfreezing zone between ice at the pressure-melting point and a frontal frozen zone at deglaciation. Basal debris-rich ice was stacked into transversally arranged zones (controlled moraine), forming ribbed moraine 'embryos', the active phase of ridge formation. The stacked sequences of debris-rich ice eventually melted out beneath a stable and melt-retarding supraglacial ablation complex to form the final moraine ridges, the passive phase of ridge formation. In areas with no stable supraglacial ablation complex, the resulting landform after final de-icing was a hummocky moraine landscape. Internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments, intercalated with stream-deposited sediments, all resting on a platform of subglacial melt-out till. De-icing of the zone now occupied by hummocky and ribbed moraine took a considerable time; deglacial 14C age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary, and that it took another 200-300 yr for the stagnant ice zone to melt during the final formation of present-day landforms.

Möller, Per

2010-12-01

44

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

45

Components of the ice age circulation  

Microsoft Academic Search

Four general climate model (GCM) simulations are compared to investigate te the influence of ice age boundary conditions on atmospheric dynamics and regional climate patterns. Starting with a simulation of the current climate, the ice age distributions of (1) sea surface temperatures; (2) 10-m-thick land ice in locations of ice age ice sheets; and (3) ice sheets elevated to their

D. Rind

1987-01-01

46

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

47

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

48

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

49

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

50

Milankovitch solar radiation variations and ice age ice sheet sizes  

Microsoft Academic Search

The fluctuations in the size of ice age ice sheets are calculated using glacier mechanics and the Milankovitch solar radiation variations. The calculations are greatly simplified by considering only two-dimensional ice sheets with profiles that would be appropriate if ice obeyed the flow law of a perfectly plastic solid. The solar radiation variations seem to be large enough to account

Johannes Weertman

1976-01-01

51

Glaciology and the Ice Age.  

ERIC Educational Resources Information Center

Discusses: (1) the beginning of glaciology; (2) origin of erratic boulders, meteorites, volcanic explosions, floods, and drift; (3) ice age hypothesis in Europe and the United States; (4) development of glacial theory; (5) and a unified explanation of glacial events. A bibliography of classical research on glaciology is included. (BC)

Carozzi, Albert V.

1984-01-01

52

3, 435467, 2007 Gas age-ice age  

E-print Network

CPD 3, 435­467, 2007 Gas age-ice age differences along the EPICA cores L. Loulergue et al. Title of the Past New constraints on the gas age-ice age difference along the EPICA ice cores, 0­50 kyr L. Loulergue­467, 2007 Gas age-ice age differences along the EPICA cores L. Loulergue et al. Title Page Abstract

Paris-Sud XI, Université de

53

Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada  

Microsoft Academic Search

Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of

Thomas R. Lakeman; John J. Clague; Brian Menounos

2008-01-01

54

AN INTRODUCTION TO THE ICE AGES  

E-print Network

ASTRO 101A AN INTRODUCTION TO THE ICE AGES The Authors: Group 77* National University of Singapore courtesy of http://www.magicaweb.com #12;ASTRO 101A AN INTRODUCTION TO THE ICE AGES Notes from the authors This course is designed to introduce students to the basic idea of the astronomical aspects of the ice ages

Aslaksen, Helmer

55

Submarine end moraines on the continental shelf off NE Greenland - Implications for Lateglacial dynamics  

NASA Astrophysics Data System (ADS)

Favourable sea-ice conditions gave way to an acoustic survey offshore NE Greenland during RV Polarstern ARK-XXIV/3 leg in 2009. The acquired data set clearly depicts sediment ridges in an area of app. 18 × 9 km. The ridges are found in water depths between 270 and 350 m. The sediment ridges are 2.5-9 km long, 50-250 m wide and 5-25 m high. In profile, most of these ridges are characterized by steep slopes towards Northwest and gentle slopes towards Southeast. Their internal structure, imaged by parametric echo-sounding data, shows that they are positive sedimentation features rather than erosive remnant structures. Arcuate shape, joint orientation and position on a basal till are indicative for end moraines. Because they are positioned within the Westwind Trough on a basal till that extends further east, we consider these ridges end moraines of the Westwind ice stream reported by Evans et al. (2009), Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the north-east Greenland continental shelf. Journal of Quaternary Science (2008), doi: 10.1002/jqs.1231.). Based on our hydro-acoustic data, we interpret these end moraines to be formed by short-lived re-advances during an overall recession of the ice margin. However, they could also be deposited during halts of the grounding line (comparable to De Geer moraines) though their morphological characteristics are slightly different from most published De Geer moraines. The ages for the moraine deposition can be inferred from a thin sedimentary drape indicating timing between Lateglacial and early Holocene. This set of end moraines is direct evidence for a dynamic behaviour of the marine-based ice stream during the last deglaciation on the NE Greenland shelf.

Winkelmann, Daniel; Jokat, Wilfried; Jensen, Laura; Schenke, Hans-Werner

2010-05-01

56

Evolution of crystal fabric: Ice-Age ice versus Holocene ice  

Microsoft Academic Search

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric

J. H. Kennedy; E. C. Pettit

2009-01-01

57

LGM Snow-Line Elevations In The Western Tropical Pacific Exposure Ages On Moraines From Mt. Giluwe, Papua New Guinea  

Microsoft Academic Search

Snow-line elevations of former glaciers around the tropical Pacific Ocean during the Last Glacial Maximum (LGM) provide critical constraints on the state of the lower tropical troposphere. We present new moraine chronological information that pins down LGM snow-line elevations adjacent to the western Pacific warm-pool. We mapped several major sequences of glacier moraines on Mt. Giluwe, an extinct massive stratovolcano

M. L. Prentice; M. D. Kurz; G. Hope; T. Barrows

2010-01-01

58

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

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

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

61

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

62

Mass loss from the southern half of the Greenland Ice Sheet since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The impact of mass loss from the Greenland Ice sheet (GrIS) on the 20th Century sea level rise (SLR) has long been subject to immense discussions. While globally distributed tide gauges suggest SLR of 15-20 cm computing the input constituents is of great concern - in particular for modeling sea level projections into the 21st Century. Estimates of the 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 founded in correlating SMB anomalies and calving rates. Here, we show a novel geometric approach to determine the post-Little Ice Age (LIA) mass loss of the southern GrIS. We present mass balance estimates of the GrIS south of 71N since retreat commence from the maximum extent of the LIA to 2010. The mass loss estimates are derived for three intervals, LIAmax (1900) - 1981/85 (1), 1981/85 - 2002 (2), and 2002 - 2010 (3). We use high quality aerial stereo photogrammetric imagery recorded in 1981 and 1985 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 difference associated with former ice extent. We combine these 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. Using our novel approach we find mass loss rates for the above periods (1) to (3) of 53 Gt/yr, 46 Gt/yr, and 109 Gt/yr, respectively. In southeast GrIS we find substantial and extensive mass loss reaching the ice divide while in southwestern GrIS mass loss is less and mainly associated with marine outlet glaciers. Furthermore, post-LIA mass loss is found to be highly variable, even within relative close proximity to other outlet glaciers and within comparable terminal environments.

Kjeldsen, Kristian K.; Kjær, Kurt H.; Bjørk, Anders A.; Khan, Shfaqat A.; Korsgaard, Niels J.; Funder, Svend; Larsen, Nicolaj K.; Vinther, Bo; Andresen, Camilla S.; Long, Antony J.; Woodroffe, Sarah A.; Steen Hansen, Eric; Olsen, Jesper

2013-04-01

63

Modeling the ice-age climate  

Microsoft Academic Search

The last great (Wisconsin) ice age has long held the interest of climatologists, geologists, and geographers as the best documented of the several ice ages of the last million years. Although local glaciation maximums varied by several thousand years, the time 18,000 B.P. (years before present) is globally representative of this event. The changes of flora and fauna that accompanied

W. Lawrence Gates

1976-01-01

64

Evolution of crystal fabric: Ice-Age ice versus Holocene ice  

NASA Astrophysics Data System (ADS)

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007, Pages 303-313, ISSN 0033-5894, DOI: 10.1016/j.yqres.2007.07.013. DiPrinzio, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract C11C-0834, 2003

Kennedy, J. H.; Pettit, E. C.

2009-12-01

65

Geological Evidence for Recent Martian Ice Ages  

Microsoft Academic Search

Multiple lines of evidence for surface deposits formed as a result of quasi- periodic climate change on Mars are presented which are remarkably consistent with models of ground-ice stability and climate. These results are used to present a new model for martian ice ages.

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

2003-01-01

66

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

67

Modeling the ice-age climate.  

PubMed

Using the boundary conditions of seasurface temperature, ice sheet topography, and surface albedo assembled by CLIMAP for 18,000 B.P., the global ice-age July climate has been simulated with a two-level dynamical atmospheric model. Compared with the simulation for present July climate, the ice age is substantially cooler and drier over the unglaciated continental areas, with the maximum zonal westerlies in the Northern Hemisphere displaced southward in the vicinity of the ice sheets. The simulated changes of surface air temperature agree reasonably well with the estimates available from the analysis of fossil pollen and periglacial data, and are consistent with the simulated changes of other climatic variables. These results are generally supported by independent investigations with simpler models. In spite of this qualified success, further analysis of both simulated and verification data is needed to establish the details of ice-age climate, especially the precipitation regimes, and to document the role of eddy fluxes in maintaining the heat, momentum, and moisture balances of the ice-age general circulation. New paleoclimatic data bases for both July and January of 18,000 B.P. are being assembled by CLIMAP and will be used in new simulations of the seasonal ice-age climate. PMID:17781631

Gates, W L

1976-03-19

68

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

69

Stationary Waves of the Ice Age Climate.  

NASA Astrophysics Data System (ADS)

A linearized, steady state, primitive equation model is used to simulate the climatological zonal asymmetries (stationary eddies) in the wind and temperature fields of the 18 000 YBP climate during winter. We compare these results with the eddies simulated in the ice age experiments of Broccoli and Manabe, who used CLIMAP boundary conditions and reduced atmospheric CO2 in an atmospheric general circulation model (GCM) coupled with a static mixed layer ocean model. The agreement between the models is good, indicating that the linear model can be used to evaluate the relative influences of orography, diabatic heating, and transient eddy heat and momentum transports in generating stationary waves. We find that orographic forcing dominates in the ice age climate. The mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies. This concept of the ice age climate is complicated by the sensitivity of the stationary eddies to the large increase in the magnitude of the zonal mean meridional temperature gradient simulated in the ice age GCM.

Cook, Kerry H.; Held, Isaac M.

1988-08-01

70

Mantle viscosity and ice-age ice sheet topography  

SciTech Connect

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 the ICE-4G model. The accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process, thus resolving a fundamental issue concerning mantle rheology. The combined model also explains postglacial sea level histories for the east cost of the United States. 28 refs., 9 figs.

Peltier, W.R. [Univ. of Toronto, Ontario (Canada)

1996-09-06

71

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

72

Terminating the 100 kyr ice age cycle  

Microsoft Academic Search

We report a simulation of the most recent 100,000-year glaciation-deglaciation cycle of the late Pleistocene ice age, a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record. Our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing

Lev Tarasov; W. Richard Peltier

1997-01-01

73

Monday, November 29, 2010 Chapters 12 and 14 "Ice Ages"  

E-print Network

Monday, November 29, 2010 Chapters 12 and 14 ­ "Ice Ages" #12;Chapter 12 - Earth has had five six the earth cool. #12;The second ice age was ~2500 mya (Huronian) ­ removal of methane from the atmosphere due. These were followed by 1 billion years of ice-free conditions! #12;Third Ice Age - 800-600 mya (Late

Toohey, Darin W.

74

Beringia as an Ice Age genetic museum  

Microsoft Academic Search

Thousands of Late Pleistocene remains are found in sites throughout Beringia. These specimens comprise an Ice Age genetic museum, and the DNA contained within them provide a means to observe evolutionary processes within populations over geologically significant time scales. Phylogenetic analyses can identify the taxonomic positions of extinct species and provide estimates of speciation dates. Geographic and temporal divisions apparent

Beth Shapiro; Alan Cooper

2003-01-01

75

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

76

The Astronomical Theory of Ice Ages on Mars  

E-print Network

The Astronomical Theory of Ice Ages on Mars Norbert Sch¨orghofer University of Hawaii October 2007 #12;History of Terrestrial Ice Ages 19th century Jean de Charpentier (1786­1855) and others: glaciers distribution quickly adjusts to atmo- spheric humidity. Subsurface-atmosphere exchange is crucial for ice ages

Schörghofer, Norbert

77

Dynamics of ice ages on Mars Norbert Schorghofer1  

E-print Network

LETTERS Dynamics of ice ages on Mars Norbert Schorghofer1 Unlike Earth, where astronomical climate loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise. Such aver- aging methods have been applied to the retreat of an ice table11,16 and can be extended

Schörghofer, Norbert

78

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 the last Ice Age, particularly in the Snowy Mountains and Tasmania have led to a complete revision is the greatest in recent geological history. Using the altitude of the ice age landforms we have calculated

Chen, Ying

79

Friday April 19, 2013 Chapters 12 and 14 "Ice Ages"  

E-print Network

Friday April 19, 2013 Chapters 12 and 14 ­ "Ice Ages" #12;Friday April 19, 2013 Chapters 12 and 14 ­ "Ice Ages" Note ­ because campus was closed due to snow on Monday and Exam 3 was postponed until back to space, keeping the earth cool. #12;The second ice age was ~2500 mya (Huronian) ­ removal

Toohey, Darin W.

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

Why could ice ages be unpredictable?  

E-print Network

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 conceivabl...

Crucifix, Michel

2013-01-01

82

Why could ice ages be unpredictable?  

E-print Network

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 also show a range of parameters for which the structural stability of the ice age dynamics is weak. This means that small variations in parameters or random fluctuations may cause significant shifts in the succession of ice ages if the system were effectively in that parameter range. Whether or not the system has strong structural stability 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.

Michel Crucifix

2013-02-06

83

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.

84

Coherence resonance and ice ages Jon D. Pelletier  

E-print Network

Coherence resonance and ice ages Jon D. Pelletier Department of Geosciences, University of Arizona, stochastic, energy balance Citation: Pelletier, J. D., Coherence resonance and ice ages, J. Geophys. Res-wavelength outgoing radiation, (2) the ice-albedo feedback, and (3) lithospheric deflection within the simple

Rácz, Zoltán

85

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 ...

86

Intermittent thinning of Jakobshavn Isbræ, West Greenland, since the Little Ice Age  

NASA Astrophysics Data System (ADS)

Rapid thinning and velocity increase on major Greenland outlet glaciers during the last two decades may indicate that these glaciers became unstable as a consequence of the Jakobshavn effect (Hughes, 1986), with terminus retreat leading to increased discharge from the interior and consequent further thinning and retreat. To assess whether recent trends deviate from longer-term behavior, we measured glacier surface elevations and terminus positions for Jakobshavn Isbræ, West Greenland, using historical photographs acquired in 1944, 1953, 1959, 1964 and 1985. These results were combined with data from historical records, aerial photographs, ground surveys, airborne laser altimetry and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the Little Ice Age (LIA). We identified three periods of rapid thinning since the LIA: 1902-13, 1930-59 and 1999-present. During the first half of the 20th century, the calving front appears to have been grounded and it started to float during the late 1940s. The south and north tributaries exhibit different behavior. For example, the north tributary was thinning between 1959 and 1985 during a period when the calving front was stationary and the south tributary was in balance. The record of intermittent thinning, combined with changes in ice-marginal extent and position of the calving front, together with changes in velocity, imply that the behavior of the lower parts of this glacier represents a complex ice-dynamical response to local climate forcings and interactions with drainage from the interior.

Csatho, Bea; Schenk, Toni; van der Veen, C. J.; Krabill, William B.

87

Determination of the age distribution of sea ice from Lagrangian observations of ice motion  

SciTech Connect

A procedure for monitoring the local age distribution of the Arctic sea ice cover is presented. The age distribution specifies the area covered by ice in different age classes. In the authors` approach, a regular array of grid points is defined initially on the first image of a long time series, and an ice tracker finds the positions of those points in all subsequent images of the series. These Lagrangian points mark the corners of a set of cells that move and deform with the ice cover. The area of each cell changes with each new image or time step. A positive change indicates that ice in a new age class was formed in the cell. A negative change is assumed to have ridged the youngest ice in the cell, reducing its area. The ice in each cell ages as it progresses through the time series. The area of multiyear ice in each cell is computed using an ice classification algorithm. Any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first-year ice. They thus have a fine age resolution in the young end of the age distribution, and coarse resolution for older ice. The age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing-degree days and ice thickness, or using a more complicated thermodynamic model. They describe a general scheme for implementing this procedure for the Arctic Ocean from fall freeze-up until the onset of melt in the spring. The concept is illustrated with a time series of five ERS-1 SAR images spanning a period of 12 days. Such a scheme could be implemented with RADARSAT SAR imagery to provide basin-wide ice age and thickness information.

Kwok, R.; Cunningham, G.F. [California Inst. of Tech., Pasadena, CA (United States). Jet Propulsion Lab.] [California Inst. of Tech., Pasadena, CA (United States). Jet Propulsion Lab.; Rothrock, D.A.; Stern, H.L. [Univ. of Washington, Seattle, WA (United States)] [Univ. of Washington, Seattle, WA (United States)

1995-03-01

88

A revisionist timetable for the ice ages  

SciTech Connect

In terms of sheer mass, there's no contest. In one corner, there's a land-based record of ice age climates that takes the form of a single carbonate cylinder about the size of the cardboard tube in a roll of paper towels. In the other corner, there's the marine record, which draws on the tons of deep-sea mud cored around the world during the past 20 years. But a group of researchers argues that the lone continental record, drilled from a wall of calcite in Devil's Hole, Nevada, is enough to unseat the conventional wisdom about the causes of the ice ages. The reason a single stick of carbonate has received all this attention is the unique resource it contains: a precisely dated continental climate record of the past 600,000 years. The record was deposited from ground water, which carried a measure of air temperature in the form of the water's oxygen isotope composition. As the water seeped into Devil's Hole - an open, water-filled fault zone - carbonate crystallized out, locking up some of the water's oxygen and building up a climate record layer by layer. Drilling into the walls of the fault, a core was retrieved spanning layers formed between 60,000 and 560,000 years ago, as measured by high-precision uranium thorium dating.

Kerr, R.A.

1992-10-09

89

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

90

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

91

Moraine chronosequence of the Donnelly Dome region, Alaska  

NASA Astrophysics Data System (ADS)

We present 10Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. 10Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ˜ 17 ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing 10Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12 ka.

Matmon, A.; Briner, J. P.; Carver, G.; Bierman, P.; Finkel, R. C.

2010-07-01

92

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.

Heaton, Timothy

2002-01-01

93

Gas ageice age differences and the chronology of the Vostok ice core, M. L. Bender,1  

E-print Network

Gas age­ice age differences and the chronology of the Vostok ice core, 0­100 ka M. L. Bender,1 G the ice in which it is embedded. The age difference is not well constrained for slowly accumulating ice chronologies that use different assumptions to calculate gas age­ice age differences. We then evaluate

Chappellaz, Jérôme

94

Simulation of the tropical climate of an ice age  

Microsoft Academic Search

Numerical time integrations of a general circulation model of the atmosphere are performed with both modern and ice age boundary conditions. It is shown that the climate of continental portions of the tropics in the ice age simulation is much drier than that of the modern climate simulation. According to comparisons of results from the two experiments, tropical continental aridity

Syukuro Manabe; Douglas G. Hahn

1977-01-01

95

Carbon-14 ages of Allan Hills meteorites and ice  

NASA Technical Reports Server (NTRS)

Allan Hills is a blue ice region of approximately 100 sq km area in Antarctica where many meteorites have been found exposed on the ice. The terrestrial ages of the Allan Hills meteorites, which are obtained from their cosmogenic nuclide abundances are important time markers which can reflect the history of ice movement to the site. The principal purpose in studying the terrestrial ages of ALHA meteorites is to locate samples of ancient ice and analyze their trapped gas contents. Attention is given to the C-14 and Ar-39 terrestrial ages of ALHA meteorites, and C-14 ages and trapped gas compositions in ice samples. On the basis of the obtained C-14 terrestrial ages, and Cl-36 and Al-26 results reported by others, it is concluded that most ALHA meteorites fell between 20,000 and 200,000 years ago.

Fireman, E. L.; Norris, T.

1982-01-01

96

Dynamics of Ice Ages Norbert Schorghofer  

E-print Network

K to 310 K #12;ice-free surface Phoenix on Mars May­November 2008 latitude: 68N ice buried by 5cm.5 2 2.5 3 3.5 4 pressure (Pa) 0 1 2 0 0.5 1 1.5 2 2.5 3 3.5 4 ice filling fraction (ppm) Movie of Ice Growth [online] [local] #12;Two Modes of Ice Growth 0 20 40 60 80 100 120 0 0.2 0.4 0.6 0.8 1 equilibrium

Schörghofer, Norbert

97

An 'Older Little Ice Age' ~3 kyr ago? Evidence from mountain glaciers in northern mid-latitudes  

NASA Astrophysics Data System (ADS)

The 'Little Ice Age' (LIA, CE 1300-1860) has been identified in many climate records in the Northern Hemisphere and is widely seen as the culmination of a multi-millennia cooling trend throughout the middle and late Holocene. This cooling trend is commonly related to the astronomical forcing represented by decreasing northern summer insolation. Less is known about the extent and duration of LIA-type cold-excursions earlier in the Holocene, mostly due to missing historical evidence and low-resolution climate records. Based on precise cosmogenic Be-10 surface exposure dating, we here present surveys of Holocene fluctuations of glaciers in the Swiss Alps (46°N), which are highly sensitive to regional climate changes and in particular, to summer temperature variations. Our results show that the most extensive Holocene glacier culminations in the Alps occurred during the earliest Holocene. No moraines are preserved from the mid-Holocene, consistent with the scenario of small glaciers during this time. However, we dated moraine fragments close to the LIA moraines to the period between ~3.2 to 2.8 kyr ago, indicating LIA-type climate conditions as early as 3 kyr ago. This finding from the Alps is in agreement with our glacier records from the Western US as well as with existing glacier studies in Alaska, British Columbia and Greenland. Beyond, north Atlantic bottom water temperature records indicate an abrupt, 'LIA' level cold excursion around this time. Taken together, we will discuss this 'older LIA' phenomenon in a hemispheric climate context, challenging the view that Holocene climate was quasi-continuously cooling over several millennia prior to the LIA cold peak.

Schimmelpfennig, I.; Schaefer, J. M.; Putnam, A. E.; Akçar, N.; Ivy-Ochs, S.; Finkel, R. C.; Schlüchter, C.

2012-12-01

98

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

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

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

101

Geological Evidence for Recent Ice Ages on Mars  

Microsoft Academic Search

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

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

2003-01-01

102

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

103

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

104

The deglaciation of Iztaccíhuatl volcano (Mexico) from the Little Ice Age maximum to the present, determined by photogrametry and lichenometry  

NASA Astrophysics Data System (ADS)

Iztaccíhualt Volcano (19°10'20''N, 98°38'30''W, 5230 m asl) preserves an important moraine complex from the Little Ice Age (LIA), which stretches to 4300 m asl. These moraines are different from former ones because they are not covered by ash fall from the last plinian explosive phases of the nearby Popocatépetl volcano. In fact, the last emission of those pyroclasts took place during the XI century (Vázquez-Selem, 2000). The summit area of the Iztaccíhualt volcano still has glaciers whose terminus are located around 5000 m asl. From the end of the LIA until present the glacier terminus have ascended 700 m. To study the deglaciation process in Iztaccíhualt volcano from the LIA maximum to present, the Ayoloco valley was selected as it is the most important valley of the western slope of the volcano. Taking this valley as a reference, we determined the limits of glaciers in different dates by georeferencing the aerial and panoramic photographs (from 1897 to 2000) and analysing the 1958 field cartography of the glacial limits (Lorenzo, 1964). On the one hand, we carried out a statistical analysis of the size of the Rhizocarpon geographicum thallus and, on the other hand, we undertook a statistical study of the biodiversity of the lichen species through a number of cross-sections from the lowest LIA moraines to the current glacier snouts. This methodology allowed dating the exact moment in which the glacier retreated over certain points of the analysed cross-sections and determining the ecesis and the growth curve of the Rhizocarpon geographicum specie. In the Ayoloco valley the average growth rate is of 0.23 mm per year. From this information, we could deduce the evolution of the glacier from the LIA maximum to present. The results indicate that two main advances took place during the XVII and the XIX centuries. At the beginning of the XX century the glacier terminus were very close to the moraines of the maximum advance. An intense glacial retreat took place during the 40s and 50s, which was however interrupted during the 60s and 70s by a period of stabilization and re-advance. Since the mid-80s, we obreved an accelerated glacial retreat, that increased during the first decade of the XXI century. If this rate of retreat remains, the glaciers from Iztaccíhualt could disappear in 20 years. Research funded by POL2006-08405 & CGL2009-7343 project, Government of Spain.

Palacios, D.; García-Sancho, L.; Zamorano, J. J.; Andrés, N.; Pintado, A.

2012-04-01

105

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

106

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

107

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

108

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

109

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

110

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

111

Reconstructing the history of major Greenland glaciers since the Little Ice Age  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and ice shelf break-up, including thinning episodes that occurred when the calving front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate glacier changes likely associated with changes in glacier dynamics. We also examined the potential influence of geologic control, including the effect of increased heat flux and high rates of subglacial melt suggested by geophysical data.

Csatho, B. M.; Schenk, A. F.; van der Veen, C. J.; Stearns, L.; Babonis, G. S.

2008-12-01

112

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

113

The deglacial history of the Lake Michigan lobe in Illinois, USA, fleshed out by chronologies associated with ice-walled lakes  

NASA Astrophysics Data System (ADS)

The onset of deglaciation of the Lake Michigan lobe (LML) in the western Great Lakes region of North America is well-defined by radiocarbon ages from terrestrial plant material that was buried by proglacial lake sediment and till. A small portion of the lobe began its final retreat during the Marengo Phase at about 24,780 C-14 yr BP (29,630 cal yr BP) [CalPal]; most of the lobe began its final retreat during the Shelby Phase starting at about 19,350 C-14 yr BP (23,010 cal yr BP)[Calib 5.02]. New radiocarbon ages from tundra plant fossils encased in the deposits of ice-walled lakes allow estimation periods of ice stagnation vs. margin advance as well as constraining the age of important events during the late Wisconsin Episode. For example, radiocarbon ages from fossils in ice-walled deposits indicate the LML margin began its final retreat from Illinois at the onset of the Mackinaw lake phase by about 13,650 C-14 yr BP (16,250 cal yr BP). Located on the Marseilles Morainic System, the oldest dated ice-walled lake deposit known in Illinois began to form at 18,210 C-14 yr BP (21,680 cal yr BP). From its end moraine located near Peoria to Chicago on the shores of southern Lake Michigan, the LML extended about 230 km. Collectively, the ages indicate that the outer 100 km of the LML margin retreated about three times faster than the inner 130 km (7.5 x 10-2 km/yr vs. 2.4 x 10-2 km/yr). Changes in ice thickness and dynamics, debris concentration, climate, and regional drainage are some of the likely factors that affected the difference in rate. The existing data provide conservative estimates for the formation of two moraines, the lake-border Deerfield Moraine (720 cal yrs) and the Tinley Moraine (850 cal yrs). Periods of stagnations, marked by radiocarbon ages from fossils in the ice-walled lake sediments, include about 320 years (Deerfield Moraine), 520 cal yrs (Tinley Moraine), 500 cal yrs (Woodstock Moraine), and 710 years (Ransom Moraine). These and other ages indicate that ice stagnation occurred during at least 45% of the 5,430 year period when these and intervening moraines formed.

Curry, B.

2009-12-01

114

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

115

Little Ice Age glaciers in the Mediterranean mountains  

NASA Astrophysics Data System (ADS)

Only a few small glaciers survive today in the Mountains of the Mediterranean. Notable examples are found in the Pyrenees, Maritime Alps, Italian Apennines, the Dinaric and Albanian Alps and the mountains of Turkey. Many glaciers disappeared during the 20th Century. Glaciers were much larger and more numerous during the Little Ice Age (Hughes, 2014). Small glaciers even existed as far south as the High Atlas of Morocco and the Sierra Nevada of southern Spain. In more northerly areas, such as the western Balkans, glaciers and permanent snow patches occupied hundreds of cirques on relatively low-lying mountains. In the High Atlas and the Sierra Nevada no glaciers exist today, whilst in the Balkans only a few modern glaciers have been reported. A similar situation is apparent throughout the mountains of the Mediterranean region. New evidence for glacier change since the Little Ice Age will be published soon in Hughes (2014) and this paper reviews the extent, timing and climatic significance of Little Ice Age glaciation in the Mediterranean region. Reference: Hughes, P.D. (2014) Little Ice Age glaciers in the Mediterranean mountains. In: Carozza, J.-M., Devillers, B., Morhange, C. (eds) Little Ice Age in the Mediterranean, Méditerranée, volume 123.

Hughes, Philip

2014-05-01

116

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

117

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

E-print Network

Recent Ice Ages on Mars: The Role of Radiatively Active Clouds and Cloud Microphysics J Mantle (LDM), a dust-ice mantling deposit that is thought to represent a re- cent "Ice Age", remains. These observations were interpreted to represent ice ages [Head et al., 2003], during which deposition and removal

Madeleine, Jean-Baptiste

118

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

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

Climate models and the astronomical theory of the ice ages  

NASA Astrophysics Data System (ADS)

The relationship between equilibrium and nonequilibrium responses of climate to perturbations in the earth's orbital parameters, and its implications for climatic sensitivity, are discussed in the context of an empirical model due to Imbrie and Imbrie (1980). Counterintuitive features of the linear equilibrium response to the perihelion cycle in a simple energy balance model are described, and the results of North and Coakley (1979) and of Pollard et al. (1976) are examined as examples of, respectively, discouraging and encouraging results for proponents of the astronomical theory of the ice ages. Calculations of Manabe (1977, 1980), which are of relevance to the ice age problem, based on an atmospheric general circulation model, are noted.

Held, I. M.

1982-05-01

121

Title: Oak Ridges Moraine Data Creator /  

E-print Network

Title: Oak Ridges Moraine Data Creator / Copyright Owner: Ontario Ministry of Natural Resources: NAD83 /UTM Resolution: N/A Coordinates: N/A Index Map: N/A Keywords (Place): Oak Rides Moraine. Ministry of Natural Resources. "Oak Ridges Moraine" [electronic resource: vector]. Peterborough, Ontario

122

The Medieval Warm/Little Ice Age Transition as Recorded by Ice Caps in East Greenland  

NASA Astrophysics Data System (ADS)

The spatial-temporal distribution of late Holocene temperature changes over the last 2000 yr is still being defined. The high Arctic is often represented by the borehole tem-perature records from GISP and Dye 3. These both show a distinct, but different magni-tude, Medieval warm interval from ~500 to ~1200 AD, with two cold intervals after 1500 AD. However small glaciers in the high Arctic appear reflect a more complex late Holo-cene pattern. On the eastern coast of Greenland two ice caps record a warm interval from 400 AD to 600 AD but cooling after that. These ice caps, Istorvet ,on the coast beside the cold East Greenland Current, and Bregne ice cap, ~ 100 km inland, have yielded organic remains from > 50 sites. A preliminary interpretation is that the organic remains record the last time these ice caps were as small or smaller than the present configuration. Exposure ages show these ice caps reached their post glacial maximum extent within the last 1000 yr. The Istorvet ice cap is thought to show initial cooling at ~AD 884 and an advance to within 500 m of the Little Ice Age extent at AD 1022 and its fullest extent at 1125 AD. Core sediments suggest that extent was maintained until 1750 AD. Results from the inland site indicate a retracted ice cap from AD 1054 to 1393, followed by expansion. Although some of these events appear to have correlative events recorded in SST or sea ice near Iceland. Taken together they appear to have a different signature than lo-cations further south. This may indicate that temperature patterns at high latitudes are only partly coupled with those at lower latitudes.

Lowell, T. V.; Kelly, M. A.; Hall, B. L.; Bennike, O.; Honsaker, W. M.; Levy, L.; Lusas, A.

2011-12-01

123

Ice-Age Rain Forest Found Moist, Cooler  

Microsoft Academic Search

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

Richard A. Kerr

1996-01-01

124

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

125

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

126

Isotopes, ice ages, and terminal Proterozoic earth history  

Microsoft Academic Search

ABSTRACT Detailed correlations of ancient glacial de- posits, based on temporal records of carbon and strontium isotopes in seawater, indicate four (and perhaps five) discrete ice ages in the terminal Proterozoic Eon. The close and repeated stratigraphic relationship between C-isotopic excur- sions and glaciogenic rocks suggests that unusually high rates of organic carbon burial facilitated glaciation by reducing atmospheric greenhouse

Alan J. Kaufman; Andrew H. Knoll; Guy M. Narbonne

1997-01-01

127

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.

128

The coldness of `Little Ice Age' Bjerknes' hypothesis revisited  

E-print Network

atmospheric circulation assimilate large scale patterns no `ordinary' data-assimilation excercise The coldness-assimilation excercise `observation' of atmosphere: 30 yr average The coldness of `Little Ice Age' climate ­ p.8 #12 circulation assimilate large scale patterns no `ordinary' data-assimilation excercise `observation

Schrier, Gerard van der

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

Late pleistocene ice age scenarios based on observational evidence  

SciTech Connect

Ice age scenarios for the last glacial interglacial cycle, based on observations of Boyle and Keigwin concerning the North Atlantic thermohaline circulation and of Barnola et al. concerning atmospheric CO[sub 2] variations derived from the Vostok ice cores, are herein analyzed. Northern Hemisphere continental ice sheets are simulated with an energy balance model (EBM) that is asynchronously coupled to vertically integrated ice sheets models based on the Glen flow law. The EBM includes both a realistic land-sea distribution and temperature-albedo feedback and is driven with orbital variations of effective solar insolation. With the addition of atmospheric CO[sub 2] and ocean heat flux variations, but not in their absence, a complete collapse is obtained for the Eurasian ice sheet but not for the North American ice sheet. We therefore suggest that further feedback mechanisms, perhaps involving more accurate modeling of the dynamics of the mostly marine-based Laurentide complex appears necessary to explain termination I. 96 refs., 12 figs., 2 tabs.

DeBlonde, G. (Canada Center for Remote Sensing, Ottawa, Ontario (Canada)); Peltier, W.R. (Univ. of Toronto, Ontario (Canada))

1993-04-01

131

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

132

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 seven 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.

2014-12-01

133

The cause of the ice ages  

Microsoft Academic Search

A composite deep-sea core, normalized on the basis of sedimentary averages from seven cores from the Caribbean and one from the Pacific, reveals the occurrence of ten major glaciations during the past 730,000 years and affords a close estimate of their ages. Spacing of glaciation through time ranges from 50,000 to > 100,000 years. Obliquity minima caused significant lowering of

Cesare Emiliani

1978-01-01

134

A survey of age group ice hockey goal keepers.  

PubMed

How large are age group ice hockey goal keepers who defend goals in the Canadian amateur hockey system? This and similar questions regarding physical size were the subject of a survey of age group ice hockey goal keepers from six age categories recognized by the Canadian Amateur Hockey Association. Of these six categories, only four, namely Mite, Pee Wee, Bantam, and Midget were sampled with sufficient frequency to be reported here. A non-amateur seventh category entitled Professional was also examined using the same survey instruments. The goalers participating in the survey provided anecdotal information, were weighed, height measured, and then photographed while in their goal keepers' 'crouch', both with and without their full goal keeping equipment. Non-inferential statistics of central tendency and dispersion were used to examine normalcies of anthropometric measures, proportionality of growth process, and distribution of apparent body size as determined from the blocking area of the body (frontal perspective). PMID:3219671

Wilberg, R B

1988-12-01

135

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

136

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

E-print Network

Intense storm activity during the Little Ice Age on the French Mediterranean coast L. Dezileau a November 2010 Available online 13 November 2010 Keywords: Lagoon Storm Little Ice Age North Atlantic increase in intense storms around 250 years ago occurs during the latter half of the Little Ice Age, a time

Demouchy, Sylvie

137

Varve and radiocarbon dating support the rapid advance of Jakobshavn Isbr during the Little Ice Age  

E-print Network

Keywords: Jakobshavn Isbræ Varve Radiocarbon dating Lake sediments Little Ice Age a b s t r a c t Large in uenced by the recent advance of Jakobshavn Isbræ, which took place during the Little Ice Age interval. The GIS, like many glaciers across the globe, most recently advanced during the Little Ice Age

Briner, Jason P.

138

Modeling dependence of moraine deposition on climate history: the effect of seasonality  

NASA Astrophysics Data System (ADS)

A simple shallow-ice flowline glacier model coupled to a model of sediment transport and deposition is used to simulate formation and preservation of moraines. The number, positions, and volume of moraines formed all are sensitive to the climate history assumed. We drive the model with the GISP2 central-Greenland temperature record, and with reduced-millennial-amplitude versions of that record, to test the hypothesis that the Younger Dryas and other millennial oscillations were primarily wintertime events and thus had less influence on glacier behavior than did the Last Glacial Maximum with its strong summertime as well as wintertime signal. We find that forcing the model by GISP2, with dampened strength of the millennial-scale signal, provides modeled moraine configurations that reflect observed moraine records in the Northern Hemisphere.

Vacco, David A.; Alley, Richard B.; Pollard, David

2009-04-01

139

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

140

On the Origins of the Ice Ages: Insolation Forcing, Age Models, and Nonlinear Climate Change  

E-print Network

On the Origins of the Ice Ages: Insolation Forcing, Age Models, and Nonlinear Climate Change by Peter Huybers Submitted to the Department of Earth, Atmospheric and Planetary Sciences in partial .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Department of Earth, Atmospheric and Planetary Sciences May, 2004 Certified by

Huybers, Peter

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

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.

143

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

144

Ice Ages on the Earth and their astronomical implications  

Microsoft Academic Search

It is pointed out that while the long-periodic variations of the elements of the terrestrial orbit around the Sun are probably sufficient to account for the frequency-spectrum of recurrent ice-ages established from the geological record of climatic changes experiences by the Earth in the course of the past half a million years, such kinematic phenomena cannot account naturally for the

Zdenek Kopal

1980-01-01

145

Variations in the age of Arctic sea-ice and summer sea-ice extent Ignatius G. Rigor1,2  

E-print Network

Variations in the age of Arctic sea-ice and summer sea-ice extent Ignatius G. Rigor1,2 and John M that keeps track of the age of ice as it moves about on the Arctic Ocean, we show that the areal coverage, even though temperatures were locally colder than normal. The age of sea-ice explains more than half

Rigor, Ignatius G.

146

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

147

The Uummannaq Ice Stream System, West Greenland  

NASA Astrophysics Data System (ADS)

The offshore and coastal geomorphology of the Uummannaq region of West Greenland records evidence for the advance and decay of the Uummannaq Ice Stream system (UISS) during the Last Glacial Maximum (LGM). Regional ice flow patterns across this region show evidence for a large coalescent onset zone formed of smaller ice streams and fjord outlet glaciers which converged into the Uummannaq trough to form a single ice stream which flowed to the continental shelf break at the LGM. Ice stream surface elevation throughout the onset zone is constrained to a minimum of 1000m asl based on striae, bedform and moraine data, and is further supported by cosmogenic exposure ages on erratics that show warm based ice operating up to 975m asl in both ice stream and inter-stream areas. 14C and surface exposure ages along a transect from the mid-shelf to the present ice margin record initial ice surface down-wasting between 25 to 10.5 ka BP, though some ice stream marginal moraines show late stage ice re-thickening prior to extremely rapid ice stream collapse through the Uummannaq trough between 10.5 and 10.1 ka BP. We suggest this pattern of deglaciation reflects strong surface ablation associated with increased air temperatures running up to the Bolling Interstadial (GIS1e) at c. 14 ka BP, followed by ice re-thickening during the Younger Dryas, and late stage rapid marine calving driven by peak sea-level and bathymetric over-deepening at the start of the Holocene.

Roberts, D. H.; Rea, B.; Lane, T.; Schnabel, C.; Rodes, A.

2012-04-01

148

A comparison of Holocene fluctuations of the eastern and western margins of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Determining how the Greenland Ice Sheet (GrIS) responded to past temperature fluctuations is important for assessing its future stability in a changing climate. We present a record of the Holocene extents of the western GrIS margin near Kangerlussuaq (67.0°N, 50.7°W) and compare this with the past fluctuations of Bregne ice cap (71°N, 25.6° W), a small ice cap in the Scoresby Sund region 90 km from the eastern GrIS margin, to examine the mechanisms that influenced past ice margin fluctuations. The past extents of the Bregne ice cap are a proxy for the climatic conditions that influenced the nearby GrIS margin. We used glacial geomorphic mapping, 10Be dating of boulders and bedrock, and sediment cores from proglacial and non-glacial lakes. In western Greenland, 10Be ages on the Keglen moraines, 13 km west of the current GrIS margin and the Ørkendalen moraines, ?2 km west of the current ice margin date to 7.3 × 0.1 ka (n=6) and 6.8 × 0.3 ka (n=9), respectively. Fresh moraines, ?50 m from the current ice margin date to AD 1830-1950 and are likely associated with advances during the Little Ice Age (LIA). In some areas, the LIA moraines lie stratigraphically above the Ørkendalen moraines, indicating the GrIS was inboard of the Ørkendalen limit from 6.8 ka to the 20th century. In eastern Greenland, 10Be ages show that Bregne ice cap retreated within its late Holocene limit by 10.7 ka. A lack of clastic sediment in a proglacial lake suggests the ice cap was smaller or completely absent from ~10-2.6 ka. A snowline analysis indicates that temperatures ~0.5°C warmer than present would render the entire ice cap into an ablation zone. Glacial silts in the proglacial lake at ~2.6 and ~1.9 cal kyr BP to present indicate advances of Bregne ice cap. Fresh moraines ?200 m of Bregne ice cap were deposited ?2.6 cal kyr BP and mark the largest advance of the Holocene. Both the western GrIS margin and Bregne ice cap were influenced by Northern Hemisphere summer insolation during the Holocene. The western GrIS margin retreated significantly and Bregne ice cap likely disappeared during the warm early to middle Holocene. 10Be ages (10.7 ka) outboard of the late Holocene moraines at Bregne ice cap compared to those outside of the LIA moraines near Kangerlussuaq (6.8 ka) differ by ~4 kyr. This disparity in ages may have been caused by a large late Holocene advance in eastern Greenland, or perhaps the western GrIS margin retreated farther inland during the middle Holocene. Decreasing Northern Hemisphere summer insolation during the late Holocene, combined with a strong, cold East Greenland Current near Scoresby Sund may have influenced a significant ice cap advance. The temporal pattern of the responses of the eastern and western ice margins to Holocene climate changes may be indicative of how the GrIS will respond to future changes.

Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.; Applegate, P. J.; Howley, J.; Axford, Y.

2013-12-01

149

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

150

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

151

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

152

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model  

NASA Technical Reports Server (NTRS)

The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

Pollard, D.

1978-01-01

153

Acting Out History from the Ice Age to the Modern Age.  

ERIC Educational Resources Information Center

Addresses the teaching methods of Michael Welch, a seventh grade teacher, who incorporates the humanities, such as drama and literature, into his history classroom in order to help students learn to question, think analytically, solve problems, and make decisions. Summarizes a particular unit on the Ice Age. (CMK)

Mattioli, Denee J.; Drake, Frederick

1999-01-01

154

Return to the Ice Age: The La Brea Exploration Guide  

NSDL National Science Digital Library

This study guide explores the tar pits and fossil sites of Rancho La Brea. Located in the heart of Los Angeles, the La Brea Tar Pits have yielded over three million fossils from the last Ice Age. It was here that huge mammoths, fierce sabertoothed cats, and giant ground sloths became trapped and entombed in the asphalt that has been seeping out of the ground for the past 40,000 years. Visitors can discover and explore how these tar pits formed, what types of plants and animals became trapped, and how scientists have used these fossil deposits to open a window into the world of prehistoric Los Angeles.

Peterson, Chris

155

Isotopes, ice ages, and terminal Proterozoic earth?history  

PubMed Central

Detailed correlations of ancient glacial deposits, based on temporal records of carbon and strontium isotopes in seawater, indicate four (and perhaps five) discrete ice ages in the terminal Proterozoic Eon. The close and repeated stratigraphic relationship between C-isotopic excursions and glaciogenic rocks suggests that unusually high rates of organic carbon burial facilitated glaciation by reducing atmospheric greenhouse capacity. The emerging framework of time and environmental change contributes to the improved resolution of stratigraphic and evolutionary pattern in the early fossil record of animals. PMID:11038552

Kaufman, Alan J.; Knoll, Andrew H.; Narbonne, Guy M.

1997-01-01

156

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

157

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

158

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

159

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

NASA Technical Reports Server (NTRS)

The paper reports on a series of low-velocity impact experiments performed in ice and ice-saturated sand. It is found that crater diameters in ice-saturated sand were about 2 times larger than in the same energy and velocity range in competent blocks of granite, basalt and cement, while craters in ice were 3 times larger. It is shown that if this dependence of crater size on strength persists to large hypervelocity impact craters, then surface of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. Among the conclusions are that Martian impact crater energy versus diameter scaling may also be a function of latitude.

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

1979-01-01

160

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Age Characteristics in a Multidecadal Arctic Sea Ice1  

E-print Network

T November 3, 2008, 12:14pm D R A F T #12;X - 2 HUNKE AND BITZ: SEA ICE AGE CHARACTERISTICS Abstract. Results from adding a tracer for age of sea ice to a sophisti-6 cated sea ice model that is widely used for climate studies are presented. The7 consistent simulation of ice age, dynamics, and thermodynamics

Bitz, Cecilia

161

Timing of the Little Ice Age in southern Greenland  

NASA Astrophysics Data System (ADS)

Northern hemisphere temperatures reached their Holocene minimum and most glaciers reached their maximum during The Little Ice Age (LIA), but the timing of specific cold intervals is site-specific. In southern Greenland, we have compiled data from organic matter incorporated in LIA sediments, used as a signal for ice-free terrain being overridden by LIA glacier advances, and data from threshold lakes showing the onset of glacier-fed lakes, thus revealing the advance-maximum phase initiating the LIA. Finally, we have compiled lichenometry results indicating the onset of bedrock vegetation succeeding ice retreat. Our results show that the advance of glaciers during the LIA occurs early after the Medieval Warm Period terminating soon after 1200 AD and culminates c. 1500-1600 AD. Historical maps also show that many glaciers on the western coast occupy a still-stand near the LIA maximum until 1900 AD before retreat commence. Thus in southern Greenland, we define LIA as the period between the first signs of Late Holocene glacier readvance and the latest onset of retreat - i.e. from ca. 1200 to c. 1900. During this period northern hemisphere annual mean temperatures, although fluctuating, were generally below the 1961-1990 average, with the coldest interval between c. 1600 and 1800. Even though winter temperatures may have dominated the cooling, also the summer temperatures which are most closely correlated with glacier mass balances, dropped, to c. 0.6° below the average in the northern hemisphere including the Arctic. Furthermore, the glacier response seems to be mirrored by a oceanic cooling between 500-1000 AD, followed by onset of the LIA at 1150-1250 AD as seen in the relative strength of warm subsurface water and the influence of the East Greenland Current.

Kjær, Kurt H.; Kjeldsen, Kristian K.; Bjørk, Anders A.; Khan, Shfaqat A.; Korsgaard, Niels J.; Funder, Svend; Larsen, Nicolaj K.; Vinther, Bo; Andresen, Camilla S.; Long, Antony J.; Woodroffe, Sarah A.; Steen Hansen, Eric; Olsen, Jesper

2013-04-01

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

Environmental processes of the ice age: land, oceans, glaciers (EPILOG)  

NASA Astrophysics Data System (ADS)

Knowledge of the state of the earth at the Last Glacial Maximum (LGM, an interval around 21,000 years ago) is an important benchmark for understanding the sensitivity of global environmental systems to change. Much progress in understanding climates of the LGM has occurred in the ˜20 years since the end of the CLIMAP project of the 1970s (Climate Long-range Investigation, Mapping and Prediction). Here we review this progress, based on presentations and discussion at a first open science meeting of the EPILOG project (Environmental Processes of the Ice age: Land, Oceans, Glaciers) held in Delmenhorst, Germany, May 1999. We outline key controversies and document protocols for EPILOG contributions, so that a new synthesis of the LGM Earth can emerge as an open project of the world's community of scientists.

Mix, Alan C.; Bard, Edouard; Schneider, Ralph

2001-02-01

165

Readvance of the last British-Irish Ice Sheet during Greenland Interstade 1 (GI-1): the Wester Ross Readvance, NW Scotland  

NASA Astrophysics Data System (ADS)

Fourteen samples obtained from Torridon sandstone boulders on four moraines marking the limit of the Wester Ross Readvance (WRR) in NW Scotland yielded tightly clustered 10Be exposure ages confirming contemporaneous or penecontemporaneous moraine deposition. Collectively, the 14 samples yield mean ages of 13.5 ± 1.2 ka to 14.0 ± 1.7 ka, depending on choice of geomagnetic scaling and sampling surface erosion rates. All fourteen moraine ages are significantly younger than an age of ca 16.3 ka previously proposed for the WRR, and also younger than most samples obtained from rock outcrops within the WRR limits. The ages obtained for the WRR moraines appear to confirm that a substantial cover of glacier ice persisted over low ground in NW Scotland during at least the early part of the Lateglacial Interstade (?Greenland Interstade 1). We infer that the WRR probably occurred in response to rapid short-lived cooling during the Older Dryas climatic reversal (?Greenland Interstade 1d), though the possibilities that the WRR represents ice-margin response to a later climatic reversal during the Lateglacial Interstade or stabilization and readvance of the ice margin following rapid offshore calving cannot be discounted.

Ballantyne, Colin K.; Schnabel, Christoph; Xu, Sheng

2009-05-01

166

Morainal bank progradation and sediment accumulation in Disenchantment Bay, Alaska: Response to advancing Hubbard Glacier  

NASA Astrophysics Data System (ADS)

Morainal banks are primary features at the margins of advancing and stable to quasi-stable temperate tidewater glaciers, yet their roles in glacier dynamics and terminus stability are poorly defined by submarine observations. Analysis of new and archival multibeam data and Landsat images of the advancing Hubbard Glacier, southeast Alaska, reveal that between 1978 and 2010 the ice face and morainal bank advanced together at an average rate of ˜34 m/yr, varying spatially and temporally between 14 and 80 m/yr. Morphological features including gullies and a boulder lag suggest cyclical deposition and gravitational erosion on the proximal slope of the morainal bank (15-18°), and possible ice pushing in an area without recent sedimentation. In contrast, the morainal bank of the nearby, quasi-stable (surging) Turner Glacier advanced steadily since 1978 by proximal sedimentation on the steep fjord wall below its hanging valley. Sedimentation in the deep (>220 m) basin of Disenchantment Bay increased from 0.88 m/yr spanning 1978 to 1999, to 1.22 m/yr thereafter. This change appears to be a combined response to glacier advance and sediment dispersal farther down-fjord, and to an increase in sediment yield from other glacial and non-glacial sources. Analysis of Hubbard Glacier illustrates the direct correlation between movement of the terminus and morainal bank in advancing the grounding line of a marine-terminating glacier, and that morainal banks provide a fundamental stabilizing role for advance into a deep-water fjord, compensating for changes in water depth at the grounding line.

Goff, John A.; Lawson, Daniel E.; Willems, Bryce A.; Davis, Marcy; Gulick, Sean P. S.

2012-06-01

167

ICES/GLOBEC Newsletter Number 10, September 2003 Reaction norms for age and size at  

E-print Network

ICES/GLOBEC Newsletter Number 10, September 2003 Reaction norms for age and size at maturation morhua). Reaction norms for age and size at maturation, describing the age and size dependence, however, fully determined by age and size alone. The residual effects not captured by age and size

Dieckmann, Ulf

168

Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles  

NASA Astrophysics Data System (ADS)

A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where ?-pinene was added for the ageing process, showed an ice nucleation enhancement at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C whereas no ice nucleation was observed at -30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

Chou, C.; Kanji, Z. A.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

2013-01-01

169

Effect of photochemical aging on the ice nucleation properties of diesel and wood burning particles  

NASA Astrophysics Data System (ADS)

A measurement campaign (IMBALANCE) was conducted in 2009 and aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro with no emission after-treatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical aging did not play a role in modifying their ice nucleation behavior. Only one diesel experiment where ?-pinene was added, showed an ice nucleation enhancement after the aging at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical aging did also not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C with no ice nucleation observed at -30 °C for wood burning particles. Photochemical aging did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -30 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical aging on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

Chou, C.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Kanji, Z. A.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

2012-06-01

170

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

NASA Astrophysics Data System (ADS)

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 mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin. The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines. Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment.

Holm, Kris; Bovis, Michael; Jakob, Matthias

2004-02-01

171

Body Size Trends in Ice Age (Pleistocene) Horses from the Great Plains Nathan Lilienthal & Dr. Ross Secord  

E-print Network

Body Size Trends in Ice Age (Pleistocene) Horses from the Great Plains Nathan Lilienthal & Dr. Ross at the end of the last Ice Age (Pleistocene epoch). HYPOTHESIS Metacarpal Data · Suggests two species

Farritor, Shane

172

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

173

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

174

Several caves in high elevated alpine regions host massive ice fillings and underground glaciers. The age of the ice may exceed several hundred or thousand years and the ice bodies possibly have recorded paleoclimatic information. Despite  

E-print Network

. The age of the ice may exceed several hundred or thousand years and the ice bodies possibly have recordedSeveral caves in high elevated alpine regions host massive ice fillings and underground glaciers paleoclimatic information. Despite their scientific value, the knowledge on ice caves is relatively sparse

Brückl, Ewald

175

Age of Allan Hills 82102, a meteorite found inside the ice  

NASA Technical Reports Server (NTRS)

The terrestrial age of a meteorite that was recovered from below the surface of Antarctic ice is reported, and it is argued that this represents a measurement of the age of the ice itself. The cosmogenic radionuclides Be-10, C-14, Al-26, Cl-36, and Mn-53 are measured in the meteorite and Be-10 and Cl-36 in the ice. A terrestrial age of 11,000 yr is obtained for the meteorite, which suggests that the snow accumulation area where it fell was only a few tens of km away.

Nishiizumi, K.; Jull, A. J. T.; Bonani, G.; Suter, M.; Woelfli, W.

1989-01-01

176

Atlantic forcing of Amazonian climates in the last ice age  

NASA Astrophysics Data System (ADS)

An absence of study sites means that the relative influence of orbitally driven presession cycles and millenial scale variability upon ice-age Amazonian precipitation is unknown. Here we present a continuous isotopic (?O18 and C13) record spanning the period from ~93-8 ka, from the aseasonal forests of Amazonian Ecuador. The variability in ?O18 depletion is probably related to the relative strength of evapotranspired moisture (less depleted) and tropical Atlantic moisture carried across the basin by the South American Low Level Jet (more depleted). Times of strengthened South American Low Level Jet probably correspond to increased overall moisture availability and hence elevated precipitation. The occurrence of markedly depleted ?O18 signatures during Heinrich events suggests a strong influence of the Atlantic Ocean on this system, and that these northern hemispheric stadials induced wet episodes in western Amazonia. Weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been suggested to strengthen the South American Low Level Jet. The isotopic records reveal strong cohesion with previously published records from southern Brazil. A precessional influence amplifies the north Atlantic signal between c. 93 ka and 50 ka. However, after c. 50 ka the precessional signal weakens, perhaps sugesting that at a critical size the Laurentide ice mass exerted a strong influence on Neotropical climates suppressing the weaker forcing associated with precession. Contrary to long-standing expectation, the Last Glacial Maximum (21 ± 2 ka) does not stand out as time of aridity in this record. However, between c. 35 ka and 18 ka there is a drift toward less depleted rainfall. One hypothesis to account for this observation is that the climate was becoming more seasonal as the Intertropical Convergence Zone (ITCZ) formed further south than its modern location. The resulting weakened influence of the South American Summer Monsoon (SASM) would probably reduce wet season precipitation to this region of Amazonia. About 18 ka a marked shift toward less isotopically depleted moisture is consistent with a strengthening influence of SASM as the ITCZ migrated northward. The southerly movement and northerly return of the SASM influence between c. 35 and 18 ka has the temporal asymmetry common to many glacial events. In the deglacial period, the dominance of precession appears to be re-asserted, but the signal of Heinrich events is lost.

Bush, M. B.; Mosblech, N.; Valencia, B. G.; Hodell, D. A.; Gosling, W. D.; Van Calsteren, P. W.; Thomas, L. E.; Curtis, J. H.

2011-12-01

177

'Little Ice Age' summer temperature variations: their nature and relevance to recent global warming trends  

Microsoft Academic Search

Climatic changes resulting from greenhouse gases will be superimposed on natural climatic variations. High-resolution proxy records of past climate can be used to extend our perspective on regional and hemispheric changes of climate back in time by several hundred years. Using historical, tree-ring and ice core data, we examine climatic variations during the period commonly called the 'Little Ice Age'.

Raymond S. Bradley; Philip D. Jonest

1993-01-01

178

Neoglacial fluctuations of terrestrial, tidewater, and calving lacustrine glaciers, Blackstone-Spencer Ice Complex, Kenai Mountains, Alaska  

NASA Astrophysics Data System (ADS)

The glaciers surrounding the Blackstone-Spencer Ice Complex display a variety of termini types: Tebenkov, Spencer, Bartlett, Skookum, Trail, Burns, Shakespeare, Marquette, Lawrence, and Ripon glaciers end in terrestrial margins; Blackstone and Beloit glaciers have tidewater termini; and Portage Glacier has a calving lacustrine margin. In addition, steep temperature and precipitation gradients exist across the ice complex from the maritime environment of Prince William Sound to the colder, drier interior. The Neoglacial history of Tebenkov Glacier, as based on overrun trees near the terminus, shows advances ca. 250- 430 AD (calibrated date), ca. 1215-1275 AD (calibrated date), and ca. 1320-1430 AD (tree ring evidence), all intervals of glacier advance around the Gulf of Alaska. However, two tidewater glaciers in Blackstone Bay retreated from their outermost moraines by 1350 AD, apparently asynchronously with respect to the regional climate signal. The most extensive Kenai Mountain glacier expansions during Neoglaciation occurred in the late Little Ice Age. The outermost moraines are adjacent to mature forest stands and bog peats that yield dates as old as 5,600 BP. Prince William Sound glaciers advanced during two Little Ice Age cold periods, 1380-1680 and 1830-1900 AD. The terrestrial glaciers around the Blackstone-Spencer Ice Complex all built moraines during the 19th century and began retreating between 1875 and 1900 AD. Portage and Burns glaciers began retreating between 1790 and 1810 AD, but their margins remained close to the outermost moraines during the 19th century. Regional glacier fluctuations are broadly synchronous in the Gulf of Alaska region. With the exception of the two tidewater glaciers in Blackstone Bay, all glaciers in the Kenai Mountains, no matter their sizes, altitudes, orientations, or types of margins, retreated at the end of the Little Ice Age. The climate signal, especially temperature, appears to be the strongest control on glacier behavior during the last millennium.

Crossen, Kristine June

1997-12-01

179

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

180

Borax in the supraglacial moraine of the Lewis Cliff, Buckley Island quadrangle--first Antarctic occurrence  

USGS Publications Warehouse

During the 1987-1988 austral summer field season, membersof the south party of the antarctic search for meteorites south-ern team* working in the Lewis Cliff/Colbert Hills region dis-covered several areas of unusual mineralization within theLewis Cliff ice tongue and its associated moraine field (figure1). The Lewis Cliff ice tongue (84°15'S 161°25'E) is a meteorite-stranding surface of ablating blue ice, about 2.3 by 7.0 kilo-meters, bounded on the west by the Lewis Cliff, on the northand northeast by a large supraglacial moraine, and on the eastby the Colbert Hills. To the south it opens to the Walcott Névé.Because it is a meteorite-stranding surface, the major component of ice motion in the area is believed to be vertical(Whillans and Cassidy 1983). The presence of Thule-Baffinmoraines at the northern terminus of the blue ice tends tosupport the hypothesis that the area underlying the moraineis essentially stagnant and that ice arriving from the south ispiling up against it. Areas containing mineral deposits werefound within the moraine field to the north and east of theblue ice margin and also along the east margins of the blue iceitself. Subsequent X-ray diffraction analyses of these depositshave shown that they are composed predominantly of nah-colite (NaHCO3), trona [Na3(CO3)(HCO3) · 2H20], borax[Na2B405(OH)4 · 8H20], and a new hexagonal hydrous sulfatespecies. This paper reports the details of the borax occurrence,because it is the first known on the continent.

Fitzpatrick, J.J.; Muhs, D.R.

1989-01-01

181

Tropical North Atlantic Hydrologic Cycle Variability in the Florida Straits During the Last Ice Age  

E-print Network

Abrupt, millennial-scale climate oscillations, known as Dansgaard-Oeschger (D-O) cycles, characterized the climate system during the last ice age. Proxy evidence suggests these climate oscillations resulted in global-scale reorganizations...

Them, Theodore

2012-10-19

182

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

183

Records of past ice sheet fluctuations in interior East Antarctica  

USGS Publications Warehouse

The results of a land-based multi-disciplinary study of the past ice surface elevation in the Grove Mountains of interior East Antarctica support a dynamic evolution of the East Antarctic Ice Sheet (EAIS). Moraine boulders of sedimentary rocks and spore pollen assemblage imply a significant shrinkage of the EAIS, with its margin retreating south of the Grove Mountains (~450 km south of recent coast line) before the middle Pliocene. The exposure ages indicate that the ice sheet subsequently re-advanced, with the ice surface rising locally at least 450 m higher than today. It then went back down constantly from before 2.3 Ma to 1.6 Ma. The glacial topography and existence of soil show that the ice surface fluctuation continued since the early Quaternary, but with highest levels never exceeding ~100 m higher than today.

Liu, Xiaohan; Huang, Feixin; Kong, Ping; Fang, Aimin; Li, Xiaoli

2007-01-01

184

QUATERNARY RESEARCH 27, 1-29 (1987) Age Dating and the Orbital Theory of the Ice Ages: Development of a  

E-print Network

QUATERNARY RESEARCH 27, 1-29 (1987) Age Dating and the Orbital Theory of the Ice Ages: Development School Lane, Cambridge, England CB2 3RS Using the concept of "orbital tuning," a continuous, high is developed using a stacked oxygen-isotope stratigraphy and four different orbital tuning approaches, each

185

Much attention has been focused on the extinction of Ice Age giants such as woolly mammoths, woolly rhinos,  

E-print Network

Much attention has been focused on the extinction of Ice Age giants such as woolly mammoths, woolly.7 million years old (middle Pliocene), is much older and more primitive than its Ice Age (Pleistocene of the late Pleistocene mammoth fauna. Out of Tibet: Pliocene Woolly Rhino Suggests High-Plateau Origin of Ice

186

A rapidly growing moraine-dammed glacial lake on Ngozumpa Glacier, Nepal  

NASA Astrophysics Data System (ADS)

Moraine-dammed glacial lakes are becoming increasingly common in the Himalaya as a result of glacier mass loss, causing concern about glacier lake outburst flood risk. In addition to extant lakes, the potential exists for many more to form, as more glaciers ablate down to the level of potential moraine dams. In this paper, we document the recent rapid growth of, a moraine-dammed lake on Ngozumpa Glacier, Nepal. Using a combination of ground-based mapping and sonar surveys, aerial photographs (< 1 m resolution), and ASTER imagery (15 m resolution), processes and rates of lake expansion have been determined. The lake first formed between 1984 and 1992 when collapse of an englacial conduit allowed water to accumulate at the level of a gap in the lateral moraine, ~km from the glacier terminus. Lake growth was initially slow, but since 2001 it has undergone exponential growth at an average rate of 10% y-1. In 2009, the lake area was 300,000 m2, and its volume was at least 2.2 million m3. Calving, subaqueous melting, and melting of subaerial ice faces all contribute to the expansion of the lake; but large-scale, full-height slab calving is now the dominant contributor to growth. Comparison with other lakes in the region indicate that lake growth will likely continue unchecked whilst the spillway remains at its current level and may attain a volume of hundreds of millions of cubic metres within the next few decades.

Thompson, Sarah S.; Benn, Douglas I.; Dennis, Kathryn; Luckman, Adrian

2012-04-01

187

Out of Tibet: Pliocene woolly rhino suggests high-plateau origin of Ice Age megaherbivores.  

PubMed

Ice Age megafauna have long been known to be associated with global cooling during the Pleistocene, and their adaptations to cold environments, such as large body size, long hair, and snow-sweeping structures, are best exemplified by the woolly mammoths and woolly rhinos. These traits were assumed to have evolved as a response to the ice sheet expansion. We report a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive woolly rhino. These new Tibetan fossils suggest that some megaherbivores first evolved in Tibet before the beginning of the Ice Age. The cold winters in high Tibet served as a habituation ground for the megaherbivores, which became preadapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe. PMID:21885780

Deng, Tao; Wang, Xiaoming; Fortelius, Mikael; Li, Qiang; Wang, Yang; Tseng, Zhijie J; Takeuchi, Gary T; Saylor, Joel E; Säilä, Laura K; Xie, Guangpu

2011-09-01

188

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

189

The surface of the ice-age Earth.  

PubMed

In the Northern Hemisphere the 18,000 B.P. world differed strikingly from the present in the huge land-based ice sheets, reaching approximately 3 km in thickness, and in a dramatic increase in the extent of pack ice and marine-based ice sheets. In the Southern Hemisphere the most striking contrast was the greater extent of sea ice. On land, grasslands, steppes, and deserts spread at the expense of forests. This change in vegetation, together with extensive areas of permanent ice and sandy outwash plains, caused an increase in global surface albedo over modern values. Sea level was lower by at least 85 m. The 18,000 B.P. oceans were characterized by: (i) marked steepening of thermal gradients along polar frontal systems, particularly in the North Atlantic and Antarctic; (ii) an equatorward displacement of polar frontal systems; (iii) general cooling of most surface waters, with a global average of -2.3 degrees C; (iv) increased cooling and up-welling along equatorial divergences in the Pacific and Atlantic; (v) low temperatures extending equatorward along the western coast of Africa, Australia, and South America, indicating increased upwelling and advection of cool waters; and (vi) nearly stable positions and temperatures of the central gyres in the subtropical Atlantic, Pacific, and Indian oceans. PMID:17781630

1976-03-19

190

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

191

Ice age True Polar Wander in a compressible and non-hydrostatic Earth  

NASA Astrophysics Data System (ADS)

Issues related to long timescale instability in the Earth's rotation, named True Polar Wander (TPW), have continuously been debated, after the pioneering works of the sixties. We show ice age TPW results from a newly developed compressible model, based on the numerical integration in the radial variable of the momentum and Poisson equations and on the contour integration in the Laplace domain which allows us to deal with the non-modal contribution from continuous radial rheological variations. We thus fully exploit the long term behaviour of the Earth's rotation and we quantify the effects of the compressible rheology, compared to the widely used incompressible one. We discuss the so-called `traditional approach' to the Earth's rotation developed during the eighties and nineties, both for ice age and mantle convection TPW and we explain within this approach the sensitivity of TWP predictions to the elastic and viscoelastic rheologies of the lithosphere. We agree on the necessity to include the effects of the non-hydrostatic bulge from mantle convection to obtain realistic ice age TPW rates in the lower mantle viscosity range [1021,1022] Pa s, as first indicated by Mitrovica et al. Their analysis represents a first attempt to couple the effects on TPW from mantle convection and glacial forcing, by including the non-hydrostatic bulge due to mantle convection but not the other time-dependent driving terms. This partial coupling freezes in space the non-hydrostatic contribution due to mantle convection, thus damping the present-day ice age TPW and forcing the axis of instantaneous rotation to come back to its initial position when ice ages started as discussed in Mitrovica et al. We also describe a peculiar behavior of the new ice age TPW predictions exhibiting a dampened pendulum motion, with the axis of instantaneous rotation overcrossing the position it had before ice ages started. We argue that a viscoelastic rather than elastic lithosphere should be adopted in the modelling of TPW although, on the time of ice ages, it is difficult to disentangle the effects of lithospheric rheology and of mantle convection. We discuss the implication of self-consistent convection calculations of the non-hydrostatic contribution and its impact on the long term Earth's rotation stability during ice ages. The ice age TPW cannot account for more than 70 per cent of the observed one, at least for lower mantle viscosities lower than 1022 Pa s: mantle convection must therefore contribute to the observed TPW.

Cambiotti, Gabriele; Ricard, Yanick; Sabadini, Roberto

2010-12-01

192

Off-ice fitness of elite female ice hockey players by team success, age, and player position.  

PubMed

This study examined off-ice fitness profiles of 204 elite female ice hockey players from 13 countries who attended a high-performance camp organized by the International Ice Hockey Federation (IIHF) in Bratislava, Slovakia, in July of 2011. Athletes were tested using standardized protocols for vertical jump (centimeters), long jump (centimeters), 4-jump average (centimeters), elasticity ratio (4-vertical jump average/vertical jump), pull-up or inverted row (n), aerobic fitness (V[Combining Dot Above]O2max), body mass (kilograms), and body composition (% fat). These variables were examined relative to team success in major international hockey competition (group 1: Canada and USA, group 2: Sweden and Finland, group 3: All other participating countries), age group (Under 18 and Senior/Open Levels), and player position (forwards, defenders, and goalies). The athletes from countries with the best international records weighed more, yet had less body fat, had greater lower body muscular power and upper body strength, and higher aerobic capacity compared with their less successful counterparts. Compared with the younger athletes, athletes from the senior-level age group weighed more and had higher scores for lower body power, pull-ups, and aerobic capacity. There were no significant differences in anthropometric or fitness data based on player position. This study is the first to report the physical characteristics of a worldwide sample of elite female ice hockey players relative to team performance, age, and player position. Coaches should use these data to identify talent, test for strengths and weaknesses in conditioning programs, and design off-ice programs that will help athletes match the fitness profiles of the most successful teams in the world. PMID:22739329

Ransdell, Lynda B; Murray, Teena M; Gao, Yong

2013-04-01

193

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

194

Evidence for multiple glacier advances in Svalbard recorded by push moraine complex-meltwater channel relationships: the case studies of Finsterwalderbreen and Grønfjordbreen  

NASA Astrophysics Data System (ADS)

Large ice-marginal push moraine complexes, also known as composite ridge systems, have a restricted distribution at active glacier margins, and are thought to be associated with a combination of specific glaciological conditions and the availability of deformable material in the glacier foreland. In Svalbard, it has been recognised that they are often found at the margins of glaciers thought to be of surge-type, and therefore may be a useful indicator of palaeo-surging when found in a Quaternary context elsewhere, although specific case studies are needed to confirm this. We describe geomorphological evidence from large push moraine complexes in front of Finsterwalderbreen and Grønfjordbreen, both of which have been described as surge-type glaciers but have never been observed to surge. A combination of fieldwork, aerial photographs and a digital elevation model were used to assess the relationship between individual ridges within the moraine complexes and meltwater channels, from which it is possible to identify multiple advances of both glaciers. Specifically, there is clear evidence for relict channels and associated outwash fans which breach outer ridges but have been blocked off by a ridge or ridges formed during a subsequent advance. Using this approach, it is possible to identify four separate advances of Finsterwalderbreen and two of Grønfjordbreen, which is consistent with their classification as surge-type glaciers. Further support is provided by both quantitative and qualitative relative-age indicators for the different ridges, including lichenometry, vegetation cover, frost-shattered lithologies and overall ridge morphology and composition. It is anticipated that this relatively simple way to detect multiple advances within composite ridge systems has a wider application across Svalbard as a method for identifying possible surge-type glaciers and, if used in conjunction with dating techniques, could provide important information on the frequency and magnitude of glacier advances and/or surges in Svalbard during the Holocene.

Lovell, Harold; Lukas, Sven; Benn, Douglas; Swift, Darrel; Spagnolo, Matteo; Clark, Chris; Yde, Jacob

2013-04-01

195

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

196

Ice ages and the thermal equilibrium of the earth, II  

USGS Publications Warehouse

The energy required to sustain midlatitude continental glaciations comes from solar radiation absorbed by the oceans. It is made available through changes in relative amounts of energy lost from the sea surface as net outgoing infrared radiation, sensible heat loss, and latent heat loss. Ice sheets form in response to the initial occurrence of a large perennial snowfield in the subarctic. When such a snowfield forms, it undergoes a drastic reduction in absorbed solar energy because of its high albedo. When the absorbed solar energy cannot supply local infrared radiation losses, the snowfield cools, thus increasing the energy gradient between itself and external, warmer areas that can act as energy sources. Cooling of the snowfield progresses until the energy gradients between the snowfield and external heat sources are sufficient to bring in enough (latent plus sensible) energy to balance the energy budget over the snowfield. Much of the energy is imported as latent heat. The snow that falls and nourishes the ice sheet is a by-product of the process used to satisfy the energy balance requirements of the snowfield. The oceans are the primary energy source for the ice sheet because only the ocean can supply large amounts of latent heat. At first, some of the energy extracted by the ice sheet from the ocean is stored heat, so the ocean cools. As it cools, less energy is lost as net outgoing infrared radiation, and the energy thus saved is then available to augment evaporation. The ratio between sensible and latent heat lost by the ocean is the Bowen ratio; it depends in part on the sea surface temperature. As the sea surface temperature falls during a glaciation, the Bowen ratio increases, until most of the available energy leaves the oceans as sensible, rather than latent heat. The ice sheet starves, and an interglacial period begins. The oscillations between stadial and interstadial intervals within a glaciation are caused by the effects of varying amounts of glacial meltwater entering the oceans as a surface layer that acts to reduce the amount of energy available for glacial nourishment. This causes the ice sheet to melt back, which continues the supply of meltwater until the ice sheet diminishes to a size consistent with the reduced rate of nourishment. The meltwater supply then decreases, the rate of nourishment increases, and a new stadial begins. ?? 1975.

Adam, D.P.

1975-01-01

197

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model  

Microsoft Academic Search

THE astronomical (or Milankovitch) theory of the Quaternary ice ages has been the subject of several recent studies using simple climate models1-3 this approach is potentially more complete than earlier `insolation curve' investigations4. The external forcing of this theory, that is, variations in incident sunlight due to secular earth orbit perturbations, is well known5, and deep-sea sediment core records6,7 provide

David Pollard

1978-01-01

198

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

199

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

200

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

201

PNAS: May 28, 2013 URL: http://www.pnas.org/content/early/2013/05/22/1304199110 Regeneration of Little Ice Age bryophytes  

E-print Network

of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme radiocarbon dates demonstrate entombment during the Little Ice Age (1550­1850 AD). The exhumed bryophyte regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were

Machel, Hans

202

www.sciencemag.org SCIENCE VOL 302 14 NOVEMBER 2003 1111 Algal Clues to Antarctic Ice Shelf Ages  

E-print Network

www.sciencemag.org SCIENCE VOL 302 14 NOVEMBER 2003 1111 Algal Clues to Antarctic Ice Shelf Ages The naturally high variability of sea ice extent in Antarctica and the short duration of instrumental records have combined to obscure any clear record of sea ice coverage change. Curran et al. (p. 1203; see

Nori, Franco

203

Ice-age atmospheric concentration of nitrous oxide from an Antarctic ice core  

Microsoft Academic Search

Results from Antarctic ice cores are reported which show that the atmospheric N2O concentration was about 30 percent lower during the Last Glacial Maximum than during the Holocene epoch. The data also show that present-day N2O concentrations are unprecedented in the past 45 kyr and hence provide evidence that recent increases in atmospheric N2O are of anthropogenic origin.

Markus Leuenberger; Ulrich Siegenthaler

1992-01-01

204

Nonlinear and chaotic ice ages: data vs speculations  

E-print Network

It is shown that, the wavelet regression detrended fluctuations of the reconstructed temperature for the past 400,000 years (Antarctic ice cores data) are completely dominated by one-third subharmonic resonance, presumably related to Earth precession effect on the energy that the intertropical regions receive from the Sun. Effects of Galactic turbulence on the temperature fluctuations are also discussed. Direct evidence of chaotic response of the atmospheric CO_2 dynamics to obliquity periodic forcing has been found in a reconstruction of atmospheric CO_2 data (deep sea proxies), for the past 650,000 years.

Bershadskii, A

2010-01-01

205

Nonlinear and chaotic ice ages: data vs speculations  

E-print Network

It is shown that, the wavelet regression detrended fluctuations of the reconstructed temperature for the past 400,000 years (Antarctic ice cores data) are completely dominated by one-third subharmonic resonance, presumably related to Earth precession effect on the energy that the intertropical regions receive from the Sun. Effects of Galactic turbulence on the temperature fluctuations are also discussed. Direct evidence of chaotic response of the atmospheric CO_2 dynamics to obliquity periodic forcing has been found in a reconstruction of atmospheric CO_2 data (deep sea proxies), for the past 650,000 years.

A. Bershadskii

2010-03-15

206

Ice sheet extent and early deglacial history of the southwestern sector of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

The offshore and coastal geomorphology of southwest Greenland records evidence for the advance and decay of the Greenland Ice Sheet during the Last Glacial Maximum. Regional ice flow patterns in the vicinity of Sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf, with an ice stream centred over Holsteinsborg dyb. High level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using 26Al and 10Be cosmogenic exposure ages. These limit the maximum surface elevation of the Last Glacial Maximum ice sheet in this part of southwest Greenland to ca 750-810 m asl, and demonstrate that terrain above this level has been ice free since MIS 6. Last Glacial Maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the Outer Hellefisk moraines. Exposure dates record ice surface thinning from 21.0 to 9.8 ka, with downwasting rates varying from 0.06 to 0.12 m yr -1. This reflects strong surface ablation associated with increased air temperatures running up to the Bølling Interstadial (GIS1e) at ca 14 ka, and later marine calving under high sea levels. The relatively late retreat of the Itilleq ice stream inland of the present coastline is similar to the pattern observed at Jakobshavn Isbræ, located 250 km north in Disko Bugt, which also retreated from the continental shelf after ca 10 ka. We hypothesise that the ice streams of West Greenland persisted on the inner shelf until the early Holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet.

Roberts, David H.; Long, Antony J.; Schnabel, Christoph; Davies, Bethan J.; Xu, Sheng; Simpson, Matthew J. R.; Huybrechts, Philipe

2009-12-01

207

Ice sheet extent and early deglacial history of the southwestern sector of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

The offshore and coastal geomorphology of southwest Greenland records evidence for the advance and decay of the Greenland Ice Sheet during the Last Glacial Maximum. Regional ice flow patterns in the vicinity of Sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf, with an ice stream centred over Holsteinsborg dyb. High level periglacial terrain composed of blockfield and tors is dated to between 101 - 142 ka using 26Al and 10Be cosmogenic exposure ages. These limit the maximum surface elevation of the Last Glacial Maximum ice sheet in this part of southwest Greenland to ca 750 - 810 m asl, and demonstrate that terrain above this level has been ice free since MIS 6. Last Glacial Maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the Outer Hellefisk moraines. Exposure dates record ice surface thinning from 21.0 to 9.8 ka, with downwasting rates varying from 0.06 to 0.12m yr-1. This reflects strong surface ablation associated with increased air temperatures running up to the Bølling Interstadial (GIS1e) at ca 14 ka, and later marine calving under high sea levels. The relatively late retreat of the Itilleq ice stream inland of the present coastline is similar to the pattern observed at Jakobshavn Isbræ, located 250 km north in Disko Bugt, which also retreated from the continental shelf after ca 10 ka. We hypothesise that the ice streams of West Greenland persisted on the inner shelf until the early Holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet.

Roberts, D. H.; Long, A. J.; Schnabel, C.; Simpson, M. J.

2009-12-01

208

Last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western Uinta ice field, Uinta Mountains, Utah  

NASA Astrophysics Data System (ADS)

During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic 10Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired 26Al and 10Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages suggest that ice reached its maximum extent by 17.4 ± 0.5 ka (± 2?). 10Be and 26Al measurements on striated bedrock from Bald Mountain Pass, situated near the former center of the ice field, yield a mean 26Al/ 10Be ratio of 5.7 ± 0.8 and a mean exposure age of 14.0 ± 0.5 ka, which places a minimum-limiting age on when the ice field melted completely. We also applied a mass/energy-balance and ice-flow model to investigate the LGM climate of the western Uinta Mountains. Results suggest that temperatures were likely 5 to 7°C cooler than present and precipitation was 2 to 3.5 times greater than modern, and the western-most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east. This scenario is consistent with the hypothesis that precipitation in the western Uintas was enhanced by pluvial Lake Bonneville during the last glaciation.

Refsnider, Kurt A.; Laabs, Benjamin J. C.; Plummer, Mitchell A.; Mickelson, David M.; Singer, Bradley S.; Caffee, Marc W.

2008-01-01

209

Recent Ice Ages on Mars: The role of radiatively active clouds and cloud microphysics  

NASA Astrophysics Data System (ADS)

Global climate models (GCMs) have been successfully employed to explain the origin of many glacial deposits on Mars. However, the latitude-dependent mantle (LDM), a dust-ice mantling deposit that is thought to represent a recent "Ice Age," remains poorly explained by GCMs. We reexamine this question by considering the effect of radiatively active water-ice clouds (RACs) and cloud microphysics. We find that when obliquity is set to 35°, as often occurred in the past 2 million years, warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter-thick ice mantle poleward of 30° in each hemisphere during winter. This mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low-altitude clouds. We outline a scenario for its deposition and preservation that compares favorably with the characteristics of the LDM.

Madeleine, J.-B.; Head, J. W.; Forget, F.; Navarro, T.; Millour, E.; Spiga, A.; Colaïtis, A.; Määttänen, A.; Montmessin, F.; Dickson, J. L.

2014-07-01

210

Paired bedrock and boulder 10Be concentrations resulting from early Holocene ice retreat near Jakobshavn Isfjord, western Greenland  

NASA Astrophysics Data System (ADS)

We measured in situ cosmogenic 10Be in 16 bedrock and 14 boulder samples collected along a 40-km transect outside of and normal to the modern ice margin near Sikuijuitsoq Fjord in central-west Greenland (69°N). We use these data to understand better the efficiency of glacial erosion and to infer the timing, pattern, and rate of ice loss after the last glaciation. In general, the ages of paired bedrock and boulder samples are in close agreement ( r2 = 0.72). Eleven of the fourteen paired bedrock and boulder samples are indistinguishable at 1 ?; this concordance indicates that subglacial erosion rates are sufficient to remove most or all 10Be accumulated during previous periods of exposure, and that few, if any, nuclides are inherited from pre-Holocene interglaciations. The new data agree well with previously-published landscape chronologies from this area, and suggest that two chronologically-distinct land surfaces exist: one outside the Fjord Stade moraine complex (˜10.3 ± 0.4 ka; n = 7) and another inside (˜8.0 ± 0.7 ka; n = 21). Six 10Be ages from directly outside the historic (Little Ice Age) moraine show that the ice margin first reached its present-day position ˜7.6 ± 0.4 ka. Early Holocene ice margin retreat rates after the deposition of the Fjord Stade moraine complex were ˜100-110 m yr -1. Sikuijuitsoq Fjord is a tributary to the much larger Jakobshavn Isfjord and the deglaciation chronologies of these two fjords are similar. This synchronicity suggests that the ice stream in Jakobshavn Isfjord set the timing and pace of early Holocene deglaciation of the surrounding ice margin.

Corbett, Lee B.; Young, Nicolás E.; Bierman, Paul R.; Briner, Jason P.; Neumann, Thomas A.; Rood, Dylan H.; Graly, Joseph A.

2011-06-01

211

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 L.

212

Deep water formation in the North Atlantic Ocean during the last ice age  

Microsoft Academic Search

Oxygen-18 records of benthic foraminifera from northeastern Atlantic and Southern Ocean cores are significantly different. This difference indicates that the deep water in the northeastern Atlantic Ocean during the last Ice Age was at least 1.3 °C cooler than in modern times. We show here that the occurrence of such a cold deep water mass implies that the North Atlantic

Jean-Claude Duplessy; J. Moyes; C. Pujol

1980-01-01

213

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

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

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. Jaccard,6 Timothy I. Eglinton,1 Gerald H. Haug1 John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused

Gilli, Adrian

216

Foraminiferal faunal estimates of paleotemperature: Circumventing the No-analog problem yields cool Ice Age tropics  

NASA Astrophysics Data System (ADS)

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, Alan C.; Morey, Ann E.; Pisias, Nicklas G.; Hostetler, Steven W.

1999-06-01

217

Ice-age endurance: DNA evidence of a white spruce refugium in Alaska  

E-print Network

Ice-age endurance: DNA evidence of a white spruce refugium in Alaska Lynn L. Anderson*, Feng Sheng-standing controversy. We sequenced chloroplast DNA (cpDNA) of white spruce (Picea glauca), a dominant boreal tree glaciation. Thus, white spruce apparently survived long glacial episodes under climatic extremes in a heter

Hu, Feng Sheng

218

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

219

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

220

The Sugetbrak basaltsfrom northwestern TarimBlock ofnorthwest China: Geochronology, geochemistry and implications for Rodiniabreakupand ice age inthe Late Neoproterozoic  

E-print Network

and implications for Rodiniabreakupand ice age inthe Late Neoproterozoic BeiXua, , Haibo Zoub , Yan Chenc , Jinyou.07.009 #12;2 Abstract Zircons from two samples of the Sugetbrak basalts (SB) yieldweighted mean ages of 615.24.8Ma and 614.49.1Ma. These ages,interpreted as the eruption age of the SB, providean age constraint

Boyer, Edmond

221

Age and thickness distribution of polynya sea ice in the Laptev Sea determined by satellite SAR imagery and airborne EM  

NASA Astrophysics Data System (ADS)

The importance and annual amount of sea ice volume produced during polyna opening events in the Siberian Laptev Sea is still controversially discussed. So far, published information about sea ice volume production are purely based on indirect thickness measurements of thin ice using remote sensing techniques or on computer simulations of sea ice growth based on reanalysis climate data. We recorded a sea ice thickness transect of approximately 160 km length using helicopter electromagnetics (HEM) in the region of the so called West New Siberian (WNS) Polynya located directly north of the Lena delta in April 2008. In addition, a time series of synthetic aperture radar (SAR) images covering the complete polynya region was analyzed and ice area fragments were tracked from their origin to the moment when we recorded their thickness. Both data sets together, HEM and SAR, provide the opportunity to classify overflown ice areas in terms of age, area and thickness and therefore in terms of volume. From December 2007 to April 2008 approximately 50.000 km2 of sea-ice area was produced in the WNS polynya, which is more than the size of Switzerland. The youngest surveyed sea-ice was 6 days old and had a mean total and a mean level-ice thickness of 0.2 m. The oldest surveyed ice floe had an age of 104 days and a mean total thickness of 2.4 +/- 0.3 m and a mean level ice thickness of 1.8 +/- 0.3 m. The error is based on the HEM instrument accuracy and a lag of snow thickness data. Assuming that ice thickness along the HEM transect was representative for entire overflown ice areas, our calculations result that the produced sea ice area contained a volume of approximately 86 km3. This is about 1.8 % of the Arctic wide ice production between October 2007 and March 2008, as it was published by Kwok et al. 2009 on the basis of ICE-Sat ice thickness data. The combined HEM and SAR study enabled us furthermore to analyze thickness vs. age relations of first year ice floes. Mean thickness showed to be a bad indicator for ice age determination and vice versa, due to the dynamic component of sea-ice growth. The most surprising result was a 16 days old ice floe which was piled up to deformed sea ice with a mean thickness of 2.4 m. Mean level-ice thickness is a far better indicator for ice age, although we found mean thickness variations for level ice of the same age of about 0.5 m. Reference: Kwok, R., Cunningham, G.F., Wensnahan, M., Rigor, I., Zwally, H.J., Yi,D., Thinning and volume loss of the Arctic Ocean sea ice cover: 2003-2008, Journal of Geophysical Research, 114, 2009

Rabenstein, L.; Krumpen, T.; Hendricks, S.; Hoelemann, J.

2012-04-01

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

Last Glacial Maximum extent and timing of ice retreat in the Lambert Glacier-Amery Ice Shelf region  

NASA Astrophysics Data System (ADS)

The response of the East Antarctic Ice Sheet (EAIS) to global climatic and sea level changes that occurred during the last glacial cycle provide important clues to the dynamics of the ice sheet, and it's potential response to future global change. While it is possible to estimate many parameters of the EAIS using methods such as isostatic rebound, marine d180, numerical models and ice core gas content, none provide direct evidence of former ice volumes and geometries that are critical in assessing how the EAIS responded to forcing parameters. We present an overview of the recent program of 26Al and 10Be exposure age dating of the last local Glacial Maximum (lGM) moraines and erratics in the Lambert Glacier-Amery Ice Shelf drainage system (LG-AIS), that presently drains up to one fifth of the entire East Antarctic Ice Sheet. We contrast these results with existing data from the surrounding area to examine how the convergent ice flow and strong ice streaming of the LG-AIS affected the response of this system to global changes during this time. The lGM moraine heights in the LG-AIS indicate a relatively moderate advance of the ice sheet in this region and can account for no more than ~0.5 m of eustatic sea level rise since 20 ka BP, and are consistent with the both the most recent glacio-hydro-isostatic models that predict former ice heights based on post lGM sea level changes in the LG-AIS, and marine records that indicate that ice did not reach the continental shelf break in this region at the lGM. The small amount of ice thickening precludes this area as a significant source of sea level rise since 20 ka BP, including during MWP-1a. The low ice profiles also suggest that ice streaming occurred in the LG-AIS at the lGM. The pattern of deglaciation following the lGM in and around the LG-AIS was complex. Slow ice downwasting in the middle reaches of the system (near Loewe Massif) began at ~16-15 ka BP and had reached the modern glacial margin by ~11 ka BP. The initial drawdown in this area was coincident with the decoupling of ice from the bed under the modern Amery Ice shelf at AM02. However, ice remained grounded on the shallower banks of Prydz Bay until ~13 ka, confirming a relatively slow ice drawdown, and no large scale ice sheet collapse in this area MWP-1a. Also, while downwasting in the southern Prince Charles Mountains probably began at a similar time as the coastal reaches of the LG-AIS, most of the ice retreat occurred between 10-8 ka BP. This pattern suggests that while deglaciation of the coastal regions of the ice sheet were controlled by both sea level rise and subglacial topography, snow accumulation and ice dynamics may be more important in the inland reaches of large ice drainage systems. The cosmogenic isotope ages provide robust evidence that the LG-AIS deglaciated between 3-6 ka earlier than the surrounding coastal oases and ranges. This early deglaciation suggests that areas of strong ice streaming, with their relatively low ice profiles are more sensitive to changes in external forcing parameters such as eustatic sea level and increased temperatures than the higher, and thus more heavily grounded regions of the ice sheet.

White, D. A.; Gore, D. B.; Fink, D.; Ferguson, R.

2005-12-01

224

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

225

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

226

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

227

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

228

Atmospheric response to Ice Age conditions: Climatology near the Earth's surface  

Microsoft Academic Search

We present a 6-year simulation of the ice age atmosphere using the T21 Atmospheric General Circulation Model (AGCM) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The lower boundary conditions (18 kyr B.P.) were taken from CLIMAP Project Members (1981). The analysis is restricted to the surface climatology for two reasons: The surface fields are the test data derived

M. Lautenschlager; K. Herterich

1990-01-01

229

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

230

Ice-age cycles: Earth's rotation instabilities and sea-level changes  

Microsoft Academic Search

A new class of multilayered, viscoelastic Earth models based on PREM is applied to the modeling of Earths's rotation instabilities and associated sea-level changes, induced by the occurrence of Pleistocene ice-age cycles that match the oxygen isotope records over the last 0.8 Myr. The novelty of our approach stands on the usage, for the first time in post-glacial rebound induced

R. Sabadini; L. L. A. Vermeersen

1997-01-01

231

The ‘Little Ice Age’ glacial expansion in western Scandinavia: summer temperature or winter precipitation?  

Microsoft Academic Search

Reconstructing the temporal and spatial climate development on a seasonal basis during the last few centuries, including the\\u000a ‘Little Ice Age’, may help us better understand modern-day interplay between natural and anthropogenic climate variability.\\u000a The conventional view of the climate development during the last millennium has been that it followed a sequence of a Medieval\\u000a Warm Period, a cool ‘Little

A. Nesje; S. O. Dahl; T. Thun; Ø. Nordli

2008-01-01

232

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

233

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

234

The pleistocene glaciation of Tibet and the onset of ice ages — An autocycle hypothesis  

Microsoft Academic Search

During seven expeditions new data were obtained on the maximum extent of glaciation in Tibet and the surrounding mountains. Evidence was found of moraines at altitudes as low as 980 m on the S flank of the Himalayas and 2300 m on the N slope of the Tibetan Plateau, in the Qilian Shan. On the N slopes of the Karakoram,

Matthias Kuhle

1988-01-01

235

On the interpretation of paleomagnetic data on moraines  

NASA Astrophysics Data System (ADS)

Some methods of the interpretation and application of paleomagnetic data for the stratigraphic separation and correlation of Neopleistocene moraines, as well as the factors affecting the degree of ordering of magnetic moments of ferromagnetic particles in a moraine, are considered. A refined interpretation of the well-known Ryabushkin-Pevzner model of moraine magnetization is proposed. It is shown that the way of using an occasional coincidence of the direction of long axes of fragments with the direction of magnetization vectors, which is stated in some publications, has no grounds for its application for the stratigraphic separation of moraines related to the Dnieper and Moscow glaciations. However, it cannot be ruled out that this phenomenon may be used for the investigation of processes of glacial lithogenesis.

Bol'Shakov, V. A.

2011-09-01

236

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

237

Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland  

NASA Astrophysics Data System (ADS)

The Arctic cryosphere is responding rapidly to modern global warming. Documenting past changes in the Arctic cryosphere, particularly during times of warmer than present conditions such as the Holocene Thermal Maximum (HTM; 9,000-5,000 yr BP) provides an important background against which the present response and potential for future changes can be compared. Small ice caps located adjacent to the Greenland Ice Sheet respond sensitively to climate change and their past extents provide a proxy for the climatic conditions that have influenced the ice sheet margin. In order to document cryosphere and climatic changes during warmer conditions, we are constructing records of Holocene fluctuations of small ice caps in the Scoresby Sund region of eastern Greenland (71° N, 25.6° W). We use geomorphic mapping, lake sediment records, radiocarbon, and surface exposure (10Be) dating to reconstruct past ice extents. Lake sediment records are from both glacially fed (i.e., threshold) lakes and lakes with no glacial input during the time of interest (i.e., control). Here we present a record of the Holocene extents of Bregne ice cap, Milne Land, western Scoresby Sund, ~50 km southeast of Renland ice cap. Sediments from Two Move Lake (TML), a threshold lake, register the entire Holocene in a thickness of ~70 cm. Radiocarbon dates of lake sediments indicate that the onset of organic accumulation in the lake following the Last Glacial Maximum occurred 8,890±120 cal yr BP. The mid-Holocene is characterized by organic rich mud that is finely laminated in some sections. The onset of Neoglaciation (cooling after HTM) occurs at 2,810±50 cal yr BP and finely laminated sediments during Neoglaciation may register annual deposition. The sediment record from Last Chance Lake, a control lake located 0.5 km from TML, indicates that there has been no glacial input since deglaciation from the Last Glacial Maximum. Unweathered moraines occur <0.5 km from the modern ice cap margin, inboard from TML. 10Be ages of boulders and bedrock just outside these moraines indicate that deglaciation occurred at 10.4±0.5 ka and that the moraines mark the maximum ice extent during the Holocene. Beginning in the early Holocene, the ice cap then had either entirely retreated from the TML basin or contributed minimal sediment input until ~2,800 cal yr BP when clay-rich, finely laminated sediments begin to occur. This chronology is in contrast to small ice caps located in Liverpool Land, 130 km east of Milne Land. In Liverpool Land, lake sediment records indicate that the onset of Neoglaciation occurred at ~800 cal yr BP. The difference between the onset of Neoglaciation in western and eastern Scoresby Sund may be due to differences in basin position relative to the ice cap or may represent a temperature gradient between the inland, high elevation of Bregne ice cap and the coastal, low elevation Liverpool Land ice caps. Other records, such as GRIP borehole temperatures and the ?18O record from the Renland ice cap show cooling from ~4,500-2,000 yr BP suggesting that the terrestrial advances of ice caps in Scoresby Sund lagged behind temperatures registered in ice cores or ice core records are not good proxies for changes at the ice margins.

Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

2011-12-01

238

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

239

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

240

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

241

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

242

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

243

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

244

A recent ice age on Mars: Evidence for climate oscillations from regional layering in mid-latitude mantling deposits  

NASA Astrophysics Data System (ADS)

Two end-member hypotheses have been proposed to account for the emplacement and distribution of ice in the near-subsurface of Mars at mid to high latitudes during recent spin-axis/orbital variation-induced climate change. In the first, diffusion of atmospheric water vapor into and out of a porous regolith forms ice-cemented soils whose latitudinal stability migrates as a function of orbitally controlled climatic conditions. In the alternative hypothesis, atmospheric deposition of ice, snow, and dust produces dusty ice-rich layers during periods of higher obliquity. New image data reveal meters-thick layered deposits exposed on mid-latitude pole-facing slopes supporting the latter hypothesis. These observations suggest that the near surface ice detected by the GRS instrument suite and the Phoenix lander at high latitudes is linked to thick, buried ice that was atmospherically deposited during recent ice ages and that significant amounts of subsurface ice may remain today in the 30-50° mid-latitude regions where fresh craters, imaged by HiRISE, expose abundant ice.

Schon, Samuel C.; Head, James W.; Milliken, Ralph E.

2009-08-01

245

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

246

Ice sheet extent and deglacial history of the central western sector of the Greenland Ice sheet during the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

The offshore and coastal geomorphology of central west Greenland record evidence for the advance and decay of the Greenland ice sheet during the Last Glacial Maximum (LGM). Regional ice flow patterns to the south of Sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf along topographically constrained basal flow pathways, probably forming an ‘isbrae' flowing into Holsteinsborg Dyb. This is further supported by striae and roche moutonnée long axes orientations along the coast at Itvidleq which show a southwesterly flowing ice stream that deflected east to west flowing locally sourced valley glaciers. Neighbouring periglacial terrain composed of blockfield and tors is dated to between 111 - 161 ka using Al 26 and Be 10 cosmogenic exposure ages. These limit the maximum surface elevation of the LGM ice sheet to c. 750 - 810 m asl, and demonstrate that terrain above this level has been ice free since MIS 6. Ice thickness of this magnitude means that the ice sheet likely reached the outer shelf edge and implies that the Outer Hellefiske moraines in this area are of LGM age. Exposure dates record down wasting of ice from 21.3 to 9.9 ka in the Itvidleq/Nagtoralinguaq area. In Nagtoralinguaq, rates of surface downwasting vary from 0.06 to 0.11m yr and were accelerated by the buoyant lift off of the Nagtoralinguaq valley glacier between 16.5 and 9.9 ka, when active marginal calving lead to the formation of a De Geer moraine train on the Nagtoralinguaq valley floor. The regional orientation of this moraine train suggests that the Itvidleq ice stream persisted on the coast and controlled the position of the Nagtoalinguaq glacier calving front between 16.5 and 9.9 ka. This is supported by cosmogenic ages that show the Itvidleq ice stream lingered over the outer coast until c. 10 ka, due to greater ice thickness and larger ice flux from the main ice sheet. The early downwasting of the Nagortoralinguaq and Itvidleq glaciers coincides with increased air temperatures over Greenland running up to the Bolling (GIS1e) temperature maximum at c. 14 ka and was predominantly driven by surface ablation, although the early deglaciation of local valley glaciers was also influenced by buoyant lift off and marine calving under high sea levels. As the Itvidleq ice stream remained along the coast until c. 10 ka, it operated on the inner shelf throughout the Younger Dryas. This pattern of delayed ice stream retreat is directly comparable to evidence from the Jakobshavns ice stream in Disko Bugt, located to the north of the study area, which too only retreated from the outer coast after c. 11 ka BP. Evidence from these two areas suggest rapid ice stream collapse post the onset of the early Holocene, in contrast to previous models of deglaciaion, that favour initial retreat of the marine-based ice sheet from the continental shelf between c. 16 - 11 ka BP.

Roberts, D. H.; Long, A. J.; Schnabel, C.

2009-04-01

247

Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet  

USGS Publications Warehouse

The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

Brigham-Grette, J.; Gualtieri, L.M.; Glushkova, O.Y.; Hamilton, T.D.; Mostoller, D.; Kotov, A.

2003-01-01

248

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

PubMed

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 and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal 'Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal 'Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The 'Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions. PMID:16029475

Alsos, I G; Engelskjøn, T; Gielly, L; Taberlet, P; Brochmann, C

2005-08-01

249

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

250

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

251

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

252

Changes in Attitude on Equatorial Latitudes: Tropical Climate Evolution During the Ice Ages  

NASA Astrophysics Data System (ADS)

Some 50 years ago, Cesare Emiliani published the first oxygen isotope records from marine sediment cores taken in the Caribbean Sea. He interpreted the observed oscillations as a consequence of 6 deg cooler tropical sea surface temperatures (SSTs) during the Ice Ages. In the following decades, this interpretation was discarded in favor of the dominant role of high latitude ice volume on oxygen isotope variability. Consequently, and as bolstered by a lack of faunal evidence for significant tropical changes, the Ice Ages were regarded as largely high and mid latitude phenomenon, with minimal involvement of the tropics. This view began to change when evidence emerged from terrestrial archives, from new proxies of tropical SST, and from tropical sites with rapidly accumulating sediments such as the Cariaco Basin, for an active climate role for the tropics on both orbital and millennial timescales. Today it is largely accepted that tropical SSTs cooled by about 3 deg during glacial episodes, and that at least some parts of the tropics played a dynamical role in the abrupt millennial scale events first identified in high latitude ice cores. What is still controversial is: 1) the timing of tropical changes, with some records strongly suggesting that tropical changes pre-dated northern hemisphere high latitude changes, including ice volume changes; 2) the climate forcing that drove tropical changes, with greenhouse gas forcing and high latitude shifts the most likely sources; and 3) the role of the tropics in triggering, amplifying or even driving large scale climate evolution. This talk will address these three critical questions and survey the most recent evidence. In particular, I will present new evidence that supports an early deglacial warming of the tropics in response to greenhouse gas forcing. If this interpretation is correct, it suggests that tropical warming might have played a key role in driving deglaciation. It also suggests that past tropical changes under known forcing can be used to gauge climate sensitivity, both in the narrow sense of temperature response, and in the broad sense of how tropical climate and circulation evolved. Ultimately, I will argue that tropical paleoclimate records inform predictions of how both the tropics and the global climate system will respond to rising greenhouse gases in the atmosphere.

Lea, D. W.

2007-12-01

253

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

254

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

255

A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages  

NASA Astrophysics Data System (ADS)

Ice cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing dating of any such ice core at arbitrary depth for the age range between ˜500 years B.P. and the late Pleistocene. This new, complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies. Using small to ultrasmall sample size (100 ?g > carbon content > 5 ?g) accelerator mass spectrometry, we take advantage of the ice-included, water-insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon (14C) dating. Analysis and dating of the bottom ice of the Colle Gnifetti glacier (Swiss-Italian Alps, 45°55'50?N, 7°52'33?E, 4455 m asl) has been successful in a first application, and the results revealed the core to cover most of the Holocene at the least with indication for late Pleistocene ice present at the very bottom.

Jenk, Theo M.; Szidat, SöNke; Bolius, David; Sigl, Michael; GäGgeler, Heinz W.; Wacker, Lukas; Ruff, Matthias; Barbante, Carlo; Boutron, Claude F.; Schwikowski, Margit

2009-07-01

256

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

257

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

NASA Astrophysics Data System (ADS)

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.

1999-06-01

258

Ice age as a trigger of active Quaternary volcanism and tectonism  

NASA Astrophysics Data System (ADS)

The stress accumulation within the crust, caused by the surface mass redistribution associated with the glaciation-deglaciation cycle during the Quaternary, was numerically evaluated in order to examine the relationship between active Quaternary volcanism and tectonism in island-arc areas and ice age. The vertical gradient of horizontal stress difference in the lithosphere for a meltwater of 130 m in equivalent sea-level reaches a maximum value of 0.8 MPa/km, which is corresponding to the equivalent buoyancy of about 100 kg/m 3 for magma-filled cracks, for an earth model with a lithospheric layer of 20-30 km thickness and with a viscosity greater than 10 23 Pa s. The changes in stress difference during the stages of deglaciation of 10,000 years amount to 13 MPa for both the top and bottom of the thin lithosphere. Thus, the additional stress difference within the crust may be effective for island-arc areas with thin lithospheric thickness. We, therefore, speculate that the stress accumulation associated with ice age may be an important trigger and/or accelerator on the active Quaternary volcanism and tectonism for the areas along the circum-Pacific.

Nakada, Masao; Yokose, Hisayoshi

1992-10-01

259

CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada  

E-print Network

CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting zone from 50 to 60 m depth. A firn-ice age profile was produced from density measurements of 54.9 (+6.0/Ã?12.0) years for firn air at 60 m depth in 140-year-old ice. Thus CO2 has a mean age 85

Chappellaz, Jérôme

260

On the effects of anisotropic rheology on ice flow, internal structure, and the age-depth relationship at ice divides  

Microsoft Academic Search

We use numerical modeling with a full-system Stokes solver to elucidate the effects of nonlinear rheology and strain-induced anisotropy on ice flow at ice divides. We find that anisotropic rheology profoundly affects the shape of both isochrone layering and surface topography. Anisotropic effects cause the formation of a downward curving fold, i.e., a syncline, in isochrones in the lower central

Carlos Martín; G. Hilmar Gudmundsson; Hamish D. Pritchard; Olivier Gagliardini

2009-01-01

261

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

262

The Medieval Climate Anomaly and the Little Ice Age: testing the NAO hypothesis  

NASA Astrophysics Data System (ADS)

Medieval Climate Anomaly (MCA) terrestrial proxy records (speleothem, NW Scotland; tree rings, Morocco) from close to the centres of action of the winter North Atlantic Oscillation (NAO) indicate that the MCA was characterized by a pervasive positive phase of the NAO(1). Spatial gradients across Europe in this MCA synoptic climatological interpretation were analyzed using the Proxy Surrogate Reconstruction approach based on general circulation model simulations. Changes in pervasive NAO phase result in synoptic shifts in surface pressure, wind fields and precipitation. It is hypothesized that these NAO changes are associated with oceanic responses/feedbacks including upwelling intensity and heat transport via the Atlantic Meridional Overturning Circulation (AMOC). Positive (negative) phases of the NAO are associated with enhanced (reduced) AMOC. We review high quality palaeoceanographic data from the North Atlantic covering the last 1000 years to test this hypothesis. These data include proxies for sea surface temperature, bottom water temperature, sea ice cover, upwelling intensity and reconstructions of ocean hydrographic variability, including Gulf Stream outflow, North Atlantic Deep Water return flow and the position of the oceanic Polar Front. Palaeoceanographic data are consistent with the hypothesis that the MCA (Little Ice Age, LIA) was characterized by more (less) intense AMOC. However, there are multiple datasets, including the Na ion ice core proxy from the Greenland Ice Sheet(2), that indicate enhanced storminess across the North Atlantic during the LIA. These data conflict with the hypothesis in that enhanced winter storminess (cyclone frequency) should correspond to the NAO positive rather than negative phase. A possible explanation of this problem has been provided by ensemble simulations of the cyclone-resolving Climate Community System Model (CCSM) coupled ocean-atmosphere general circulation model for the Maunder Minimum (LIA)(3). These indicate major mid-latitude blocking anticyclones and reduced cyclone frequency constructions for the LIA consistent with NAO negative phase. But the intensity of cyclones during the LIA is found to be increased when anticyclones break down. The enhanced storminess during the LIA indicated by the ice core and coastal proxies and archival data may therefore be a product of more intense, rather than more frequent, storms during the LIA. (1)Trouet, V.et al. 2009. Persistent positive North Atlantic Oscillation mode dominated the Medieval Climate Anomaly. Science 324, 78-80. (2)Meeker, L.D. & Mayewski, P.A. 2002. A 1400-year high-resolution record of atmospheric circulation over the North Atlantic and Asia. The Holocene 12, 257-266. (3)Raible, C.C. et al. 2007. Extreme midlatitide cyclones and their implications for precipitation and wind speed extremes in simulations of the Maunder Minimum versus present day conditions. Climate Dynamics 28, 409-423.

Scourse, James; Trouet, Valerie; Raible, Christoph

2010-05-01

263

A comparison of late glacial to early Holocene fluctuations of Greenland Ice Sheet outlet glaciers with nearby mountain glaciers in central east Greenland  

NASA Astrophysics Data System (ADS)

Recent rapid fluctuations of Greenland Ice Sheet outlet glaciers have alarmed scientists and the public alike. These outlet glacier fluctuations may result from the internal mechanics of tidewater glaciers or the influence of ocean-water temperatures on glacial melting. In contrast, it is generally assumed that fluctuations of temperate mountain glaciers are influenced mainly by summer temperatures and, to a lesser amount, winter precipitation. Here we show that during late glacial and early Holocene time Greenland Ice Sheet outlet glacier fluctuations occurred at the same time as mountain glacier fluctuations in central east Greenland. Our recent work in the Scoresby Sund region of central east Greenland used equilibrium line altitudes determined from past mountain glacier extents to estimate summer temperatures during late glacial and early Holocene time. A chronology of these past mountain glacier extents is based on surface exposure (10Be) dating of moraines and a radiocarbon-dated relative sea level curve. In this same area, we applied 10Be dating to determine a chronology of past extents of Greenland Ice Sheet outlet glaciers. We present thirty new 10Be ages of moraines deposited by outlet glaciers located adjacent to mountain glaciers in the Scoresby Sund region. A comparison of the outlet glacier moraine ages with the previously determined chronology of mountain glacier extents shows that, during late glacial and early Holocene time, Greenland Ice Sheet outlet glaciers and mountain glaciers fluctuated on similar time scales. These results suggest that the ice sheet margin was sensitive to local climatic conditions, most likely summer temperatures. If so, the magnitude of summer cooling that drove the mountain glacier advances, estimated at 3.6 to 6.6°C, also influenced significant advances of outlet glaciers.

Kelly, M. A.; Lowell, T. V.; Hall, B. L.; Schaefer, J. M.

2010-12-01

264

Several million years of stability among insect species because of, or in spite of, Ice Age climatic instability?  

PubMed Central

There is a curious paradox in the evolutionary legacy of Ice Ages. Studies of modern species suggest that they are currently evolving in response to changing environments. If extrapolated into the context of Quaternary Ice Ages, this evidence would suggest that the frequent climatic changes should have stimulated the evolutionary process and thus increased the rates of change within species and the number of speciation events. Extinction rates would, similarly, be high. Quaternary insect studies call into question these interpretations. They indicate that insect species show a remarkable degree of stability throughout the Ice Age climatic oscillations. The paradox arises from the apparent contradiction between abundant evidence of incipient speciation in insect populations at the present day and the evidence that, in the geological past, this apparently did not lead to sustained evolution. PMID:15101577

Coope, G R

2004-01-01

265

Cosmogenic exposure-age chronologies of Pinedale and Bull Lake glaciations in greater Yellowstone and the Teton Range, USA  

USGS Publications Warehouse

We have obtained 69 new cosmogenic 10Be surface exposure ages from boulders on moraines deposited by glaciers of the greater Yellowstone glacial system and Teton Range during the middle and late Pleistocene. These new data, combined with 43 previously obtained 3He and 10Be ages from deposits of the northern Yellowstone outlet glacier, establish a high-resolution chronology for the Yellowstone-Teton mountain glacier complexes. Boulders deposited at the southern limit of the penultimate ice advance of the Yellowstone glacial system yield a mean age of 136??13 10Be ka and oldest ages of ???151-157 10Be ka. These ages support a correlation with the Bull Lake of West Yellowstone, with the type Bull Lake of the Wind River Range, and with Marine Isotope Stage (MIS) 6. End moraines marking the maximum Pinedale positions of outlet glaciers around the periphery of the Yellowstone glacial system range in age from 18.8??0.9 to 16.5??1.4 10Be ka, and possibly as young as 14.6??0.7 10Be ka, suggesting differences in response times of the various ice-cap source regions. Moreover, all dated Pinedale terminal moraines in the greater Yellowstone glacial system post-date the Pinedale maximum in the Wind River Range by ???4-6 kyr, indicating a significant phase relationship between glacial maxima in these adjacent ranges. Boulders on the outermost set and an inner set of Pinedale end moraines enclosing Jenny Lake on the eastern Teton front yield mean ages of 14.6??0.7 and 13.5??1.1 10Be ka, respectively. The outer Jenny Lake moraines are partially buried by outwash from ice on the Yellowstone Plateau, hence their age indicates a major standstill of an expanded valley glacier in the Teton Range prior to the Younger Dryas, followed closely by deglaciation of the Yellowstone Plateau. These new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the Rocky Mountains during the Pleistocene. ?? 2008 Elsevier Ltd. All rights reserved.

Licciardi, J.M.; Pierce, K.L.

2008-01-01

266

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

267

Future ice ages and the challenges related to final disposal of nuclear waste: The Greenland Ice Sheet Hydrology Project  

NASA Astrophysics Data System (ADS)

A deep geological repository for nuclear waste is designed to keep radiotoxic material separated from mankind and the environment for several hundreds of thousands of years. Within this time perspective glacial conditions are expected in high latitudes/Canada and North Europe. Climate induced changes such as the growth of ice sheets and permafrost will influence and alter the ground surface and subsurface environment, which may impact repository safety. In order to understand how climate change, particularly cooling and glaciation, might affect a repository in the long term, the use of present-day analogues helps to reduce the uncertainties and support the assumptions made in safety assessments. There are major uncertainties concerning hydrological processes related to glacial conditions. The impact of glaciations on any planned repository is a key consideration when performing safety assessments as it is one of the strongest perturbations related to climate change in the long term. The main aspects that need to be further investigated include: 1) to what extent does the meltwater produced by an ice sheet penetrates into the bedrock; 2) what is the pressure situation under an ice sheet, driving ground water flow; 3) how much oxygenated water will reach repository depth; 4) to what depth does glacial meltwater penetrate into the bedrock ; 5)what chemical composition does such water has when and if it reaches repository depth; and 6) can taliks (unfrozen ground in a permafrost area) act as concentrated discharge points of deep groundwater potentially transporting radionuclides in case of repository failure? Field data is needed in order to achieve a better and integrated understanding of the problems discussed above. Thus, research in a natural analogue site in Greenland has been planned and initiated by the Finnish (Posiva), Swedish (SKB) and Canadian (NWMO) nuclear waste management companies. The Greenland ice sheet and the Kangerlussuaq area (west Greenland) provides a good analogue for this purpose due to similarities in geology (in the selected study area), and the climate conditions and ice sheet size in Kangerlussuaq resemble the expected conditions in Fennoscandia during future glaciations. In 2005 and 2008 reconnaissance field trips were made to Kangerlussuaq, which confirmed the suitability of the area for the planned studies. According to the present Work Programme the investigations will be carried out in 2009-2012. The project is divided into four subprojects (SPA, SPB, SPC and SPD) addressing specific and different topics at or in relation to the ice margin: SPA (ice sheet hydrology and glacial groundwater formation); SPB (subglacial ice sheet hydrology), SPC (hydrogeochemistry and hydrogeology) and SPD (periglacial environment: biosphere and permafrost). The main objectives of SPA and SPB are to gain a better process understanding of supra- and subglacial hydrology. Qualitative and quantitative knowledge of the mechanisms, rates and distribution of the melt water recharge through the ice down to the bed, location and extension of warm-based areas and hydraulic pressure conditions at the base are the key issues to be studied. This will be made by meteorological observations, GPS measurements, radar surveys, drilling through the ice sheet and by ice sheet modelling. SPC will further study the fate of melt water by extending the investigations into the bedrock. It is assumed that the high hydraulic pressures at the ice sheet bed force water into the fracture network prevailing in the bedrock. However, it is not known how the fracture network behaves under loading, what is the proportion of recharging water compared to the drainage through the bed sediments, what is the intrusion depth, how long the meltwater can sustain its oxic nature and what chemical composition the recharging water has when and if it reaches repository depth (400-700 m). SPC seeks to answer these questions by drilling and instrumenting boreholes drilled into the bedrock and below the ice sheet. SPD is aiming at describing and studying proce

Lehtinen, A.; Claesson-Liljedahl, L.; Näslund, J.-O.; Ruskeeniemi, T.

2009-04-01

268

Relative sea-level change in Greenland during the last 700 yrs and ice sheet response to the Little Ice Age  

Microsoft Academic Search

This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. ?0.80±0.20m at c. 1300A.D. to c.

Antony J. Long; Sarah A. Woodroffe; Glenn A. Milne; Charlotte L. Bryant; Matthew J. R. Simpson; Leanne M. Wake

269

Surface changes in the eastern Labrador Sea around the onset of the Little Ice Age  

NASA Astrophysics Data System (ADS)

the relative climate stability of the present interglacial, it has been punctuated by several centennial-scale climatic oscillations; the latest of which are often colloquially referred to as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA). The most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and/or volcanic activity and amplified by ocean-atmosphere-sea ice feedbacks. As such, changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) are widely believed to have been involved in the amplification of such climatic oscillations. The Labrador Sea is a key area of deep water formation. The waters produced here contribute approximately one third of the volume transport of the deep limb of the AMOC and drive changes in the North Atlantic surface hydrography and subpolar gyre circulation. In this study, we present multiproxy reconstructions from a high-resolution marine sediment core located south of Greenland that suggest an increase in the influence of polar waters reaching the Labrador Sea close to MCA-LIA transition. Changes in freshwater forcing may have reduced the formation of Labrador Sea Water and contributed toward the onset of the LIA cooling.

Moffa-Sánchez, Paola; Hall, Ian R.; Barker, Stephen; Thornalley, David J. R.; Yashayaev, Igor

2014-03-01

270

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

PubMed Central

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

271

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

272

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

273

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

274

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

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

275

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

276

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

277

The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth  

E-print Network

The short term variability of the Galactic cosmic ray flux (CRF) reaching Earth has been previously associated with variations in the global low altitude cloud cover. This CRF variability arises from changes in the solar wind strength. However, cosmic ray variability also arises intrinsically from variable activity of and motion through the Milky Way. Thus, if indeed the CRF climate connection is real, the increased CRF witnessed while crossing the spiral arms could be responsible for a larger global cloud cover and a reduced temperature, thereby facilitating the occurrences of ice ages. This picture has been recently shown to be supported by various data (Shaviv, 2001). In particular, the variable CRF recorded in Iron meteorites appears to vary synchronously with the appearance ice ages. Here we expand upon the original treatment with a more thorough analysis and more supporting evidence. In particular, we discuss the cosmic ray diffusion model which considers the motion of the Galactic spiral arms. We also elaborate on the structure and dynamics of the Milky Way's spiral arms. In particular, we bring forth new argumentation using HI observations which imply that the galactic spiral arm pattern speed appears to be that which fits the glaciation period and the cosmic-ray flux record extracted from Iron meteorites. In addition, we show that apparent peaks in the star formation rate history, as deduced by several authors, coincides with particularly icy epochs, while the long period of 1 to 2 Gyr before present, during which no glaciations are known to have occurred, coincides with a significant paucity in the past star formation rate.

Nir J. Shaviv

2002-09-12

278

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

279

Contribution of Icelandic ice caps to sea level rise: Trends and variability since the Little Ice Age  

NASA Astrophysics Data System (ADS)

In total, Icelandic ice caps contain ˜3600 km3 of ice, which if melted would raise sea level by ˜1 cm. Here, we present an overview of mass changes of Icelandic ice masses since the end of the 19th century. They have both gained and lost mass during this period. Changes in ice volume have been estimated both through surface mass balance measurements (performed annually since ˜1990) and differencing of digital elevation models derived from various satellite and airborne observations. While the glaciers showed little mass loss as the 20th century began, losses increased rapidly after 1925, peaked in the 1930s and 1940s, and remained significant until the 1960s. After being near-zero or even positive during the 1980s and early 1990s, glacier mass budgets declined considerably, and have since the mid-1990s shown an average annual loss of 9.5±1.5 Gt a-1, contributing ˜0.03 mm a-1 to sea level rise. Since 1995 interannual variability in mass loss is high, ranging from 2.7 to 25.3±1.5 Gt a-1, corresponding to surface mass balances of -0.2 to -2.2 ± 0.15 m we a-1. This variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions.

Björnsson, Helgi; Pálsson, Finnur; Gudmundsson, Sverrir; Magnússon, Eyjólfur; Adalgeirsdóttir, Gudfinna; Jóhannesson, Tómas; Berthier, Etienne; Sigurdsson, Oddur; Thorsteinsson, Thorsteinn

2013-04-01

280

Reconstructing the late Holocene expansion of mountain ice caps in west-central Greenland  

NASA Astrophysics Data System (ADS)

The retreat of glaciers is one of the most profound visual manifestations of global warming. Yet without the longer-term context of glacier history, the magnitude of retreat observed today is less meaningful. We are reconstructing the late Holocene history of mountain ice caps in west-central Greenland to determine: 1) the precedence of their current size, 2) the pattern of Neoglaciation across the northwestern North Atlantic, and 3) how their record of Neoglaciation compares with that of the adjacent Greenland Ice Sheet. Our chronology is built on radiocarbon ages from in situ surface moss emerging from receding ice cap margins. We assert that the moss died during ice cap expansion across tundra surfaces, and has since been entombed beneath non-erosive ice cap sectors that we strategically target. Although this project is in its beginning stages, two initial radiocarbon ages from in situ moss that recently were exposed in front of Lyngmarksbræen, a plateau ice cap on southern Disko island, are 3580-3700 and 3450-3570 cal yr BP. The moss became ice free sometime during the summer in which they were collected, and historical imagery shows the sites are tens of meters behind the ice margin in August 23, 2004. The radiocarbon ages indicate that Lyngmarksbræen has not been as small as it is today since ~3500 yr ago. Other age constraints on Neoglaciation from the Disko Bugt region are similar to the ages we obtained here: reworked marine fauna in Greenland Ice Sheet moraines indicate ice sheet growth at this time, and relative sea level records indicate that landscape submergence (due to ice sheet growth) initiated around this time. Furthermore, ice cap melt records demonstrate that ice caps in this sector of the Arctic are melting more today than they have in the past 4000 years. Additional ages from multiple ice cap margins on Disko island, the Nuussuaq peninsula and various locations in the Uummannaq region will be presented. This dataset of ice cap expansion in western Greenland will be compared to similar constraints on late Holocene ice cap expansion on Baffin Island and in Liverpool Land, eastern Greenland.

Briner, J. P.; Schweinsberg, A.; Miller, G. H.; Bennike, O.; Lifton, N. A.

2013-12-01

281

Organic Remains from the Istorvet Ice Cap, Liverpool Land, East Greenland: A Record of Late Holocene Climate Change  

NASA Astrophysics Data System (ADS)

Radiocarbon dates of emergent organic remains along the western margin of Istorvet ice cap (70.8°N, 22.2°W) indicate a time when the ice cap was smaller than at present. This ice cap, similar to others in east Greenland, exhibits "historic" moraines ~1-2 km in front of the presently retreating ice margins. At Istorvet, ice margin retreat has exposed a thin (~8 cm) organic horizon and in situ plant remains in bedrock cracks lie less than 10 m away from the present ice margin (453 m asl in 2006). Clusters of multi-species vegetation also were found on two nuntaks (to 719 m asl) located ~3 km from the historic drift limit. All organic remains were located in protected bedrock lees. On the west side of the ice-cap, vegetation is sparse but present at elevations near the ice margin. Both the ice cap geometry and the presence of overrun organic remains indicate past temperatures at least as warm as those at present. At Istorvet plant remains yielded 12 number of radiocarbon dates. These ages, when converted to calendar years, range from A.D. 400 to 1014, with the largest concentration from A.D. 800 to 1014. This work hones the conclusion of Funder (1978) who reported general climate deterioration since 800 BC. Moreover, it indicates warm conditons at this latitude at the time of Norse colonization of Greenland.

Lowell, T. V.; Kelly, M. A.; Hall, B.; Smith, C. A.; Garhart, K.; Travis, S.; Denton, G. H.

2007-12-01

282

Comparing ice margin response to early Holocene warmth, Disko Bugt region, west Greenland  

NASA Astrophysics Data System (ADS)

The response of the Greenland Ice Sheet (GrIS) margin to climate change is spatially variable. Understanding the mechanisms that control ice margin variability is important for future predictions of changes in the mass balance and configuration of the GrIS. One factor that appears to play a role in driving varying response of the GrIS is the setting in which the ice margin terminates. We hypothesize that marine terminating glaciers react to changing climate faster than their land-based counterparts. We believe this disparity is due at least in part to differences surface velocities. Marine terminating glaciers in west Greenland have velocities one to two orders higher than that of land based glaciers, as well as additional heat transport to the glacier's terminus via ocean currents. Here we present a 10Be chronology of Holocene deglaciation for two outlet glacier systems, one primarily land-base (Nordenskiöld Gletscher) and one marine terminating (Torrssukátak Fjord; an extension of NE Disko Bugt), in central west Greenland. To test our hypothesis we compare the timing and rate of retreat of the two systems during the ameliorating climate of the early Holocene. Transects of 10Be ages at each site, extending eastward from the ice margin, detail the timing and rate of retreat during the early Holocene. Our 10Be chronology indicates that Disko Bugt deglaciation began at 10.8×0.5 ka. Deglaciation continued northeast to Torrssukátak Fjord, with ice receding from the western mouth of the fjord at 10.9×0.5 ka. A moraine at the eastern end of the fjord, ~500 m west of the present ice margin, is evidence of a pause or re-advanced of the GrIS during early Holocene deglaciation. 10Be ages bracketing the moraine indicated that the moraine was formed between 9.5×0.4 and 8.6×0.8 ka. The Torrssukátak Fjord deglacial chronology is supported by radiocarbon evidence, which suggests ice had receded within ~5 km of the present location by 8,600×100 cal yr BP. Results from the nearly 100 km-wide swath of land between the Baffin Bay and Nodenskiöld Gletscher are pending at the time of this abstract submission. The combined 10Be and radiocarbon chronology will allow for comparison of the two glaciers systems during retreat in the early Holocene. This comparison will provide insight into the mechanisms that control glacier fluctuations, as well as provide constraints on the reaction of the GrIS to warming climate for a time period prior to the historical record.

Kelley, S. E.; Briner, J. P.; Cronauer, S. L.; Zimmerman, S. R.

2013-12-01

283

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

284

Evidence for long-lasting landform surface instability on hummocky moraines in the Pamir Mountains (Tajikistan) from 10Be surface exposure dating  

Microsoft Academic Search

Surface exposure dating is a new, but already widely used tool in geomorphological studies, aiming, e.g. at the establishment of glacial chronologies. Sometimes, however, results from samples taken from one and the same moraine scatter widely and thus interpretation turns out to be difficult. Here we assess sample-specific effects (topographic shielding, sample geometry and erosion) on 17 surface exposure ages

Roland Zech; Bruno Glaser; Pjotr Sosin; Peter W. Kubik; Wolfgang Zech

2005-01-01

285

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

286

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

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

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

289

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

290

Palynology as an age-control tool for ice cores. First results of PAMOGIS - Pollen Analyses of the Mt. Ortles Glacier Ice Samples  

NASA Astrophysics Data System (ADS)

Glacier ice cores from the mid latitude are capable of retaining essential information on past climate, environmental and human activities on a seasonal/annual time resolution. However, for a correct interpretation of the ice record a good chronological control is essential. Absolute time markers such as 3H peaks and Sahara dust horizons, together with radiometric methods such as 210Pb, radiocarbon from carbonaceous aerosol particles and AMS-dating are commonly used to obtain the age depth model of ice cores. In this frame we present the first pollen-based chronology from the Eastern Alps. Results of pollen analyses performed on a 10 m firn core taken on the top of Alto dell'Ortles Glacier (3905 m a.s.l.) will be discussed. Palynological data are compared and complemented with stable isotopes, major ions and trace elements analyses. Based on the single species flowering periods, our results show that the pollen spectrum presents seasonal and inter-annual variability that enables to distinguish snow accumulated in the three different flowering seasons and winter snow. According to these four components a seasonal and annual chronology was established, proving that the 10 m firn core encompasses four years of snow accumulation and presents a clear seasonal palynological signal. These first results reveal the potential of pollen content of glacier snow and ice as a chronological tool that can contribute to the construction of a robust chronological model with a seasonal to annual resolution. This study is the first step and the base for future research on deeper ice cores on the Alto dell'Ortles Glacier (Ortles project: www.ortles.org).

Festi, Daniela; Kofler, Werner; Gabrielli, Paolo; Oeggl, Klaus

2014-05-01

291

Relative sea-level change in Greenland during the last 700 yrs and ice sheet response to the Little Ice Age  

NASA Astrophysics Data System (ADS)

This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300 A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. - 0.80 ± 0.20 m at c. 1300 A.D. to c. - 0.20 m ± 0.25 m at c. 1600 A.D., after which RSL slowed and then stabilised. At a third site in south Greenland, we observe RSL rise from c. - 1.40 ± 0.20 m at c. 1400 A.D. until c. 1750 A.D., after which RSL slowed and was stable during at least the latter part of the 20th century. The c. 1600 A.D. RSL slow-down seen at the two former sites is surprising because it occurs during the LIA when one might expect the ice sheet to be gaining mass and causing RSL to rise. We interpret this RSL slowdown to indicate a period of enhanced regional mass loss from central west Greenland since c. 1600 A.D. and propose two hypotheses for this loss: first, a reduction in precipitation during cold and dry conditions and second, higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards. The latter hypothesis is compatible with a well-established temperature seesaw between western Greenland and northern Europe and, potentially, a previously identified shift from a positive to generally more negative NAO conditions around 1400 to 1600 A.D. Our study shows how RSL data from Greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern Europe the ice sheet in west Greenland gained mass.

Long, Antony J.; Woodroffe, Sarah A.; Milne, Glenn A.; Bryant, Charlotte L.; Simpson, Matthew J. R.; Wake, Leanne M.

2012-01-01

292

Solar Cycle Variations in Ice Acidity at the End of the Last Ice Age: Possible Marker of a Climatically Significant Interstellar Dust Incursion  

E-print Network

Hammer et al. [1997] report the presence of regularly spaced acidity peaks (H+, F-, Cl-) in the Byrd Station, Antarctica ice core. The event has a duration of about one century and falls at the beginning of the deglacial warming. Volcanism appears to be an unlikely cause since the total acid deposition of this event was about 18 fold greater than the largest known volcanic eruption, and since volcanic eruptions are not known to recur with such regularity. We show that the recurrence period of these peaks averages to 11.5 +/- 2.4 years, which approximates the solar cycle period, and suggest that this feature may have an extraterrestrial origin. We propose that this material may mark a period of enhanced interstellar dust and gas influx modulated by the solar cycle. The presence of this material could have made the Sun more active and have been responsible for initiating the warming that ended the last ice age.

Paul LaViolette

2005-02-04

293

Stable isotope and sea-level data from New Guinea supports Antarctic ice-surge theory of ice ages  

Microsoft Academic Search

Two theories of glaciation have received considerable attention, the Milankovitch orbital theory1,2 in which climatic change is ascribed to latitude-dependent variations in solar radiation that accompany changes in the Earth's orbital parameters, and the Antarctic surge hypothesis3-6, in which a large Antarctic ice sheet `surges' into the Southern Ocean thereby increasing the Earth's albedo, and the resultant cooling triggers the

Paul Aharon; John Chappell; William Compston

1980-01-01

294

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

295

Variability in the timing of the late Holocene maximum extent of the southwest Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Boreal summer climate generally cooled across the mid to late Holocene, driving growth of the Greenland Ice Sheet. The timing of maximum late Holocene Greenland Ice Sheet extent is usually assigned to the Little Ice Age (LIA), although earlier more extensive Neoglacial advances may have occurred. Here we present new 10-Be surface exposure ages from erratic boulders on bedrock just outside of historical moraines deposited during the LIA near Kangerlussuaq, Paamiut and Narsarsuaq in southwest Greenland to date when ice was more extensive than during the LIA. A more extensive Neoglacial advance at ~2 ka was previously proposed near Kangerlussuaq. Our cosmogenic dates just outside the historical moraine at Kangerlussuaq indicate, however, that ice has been within its historical limit since 6.8±0.1 ka (n=6, 1 std. error), which is similar to recently published age constraints further north in the Disko Bugt region of west Greenland. Near Narsarsuaq in south Greenland, cosmogenic boulder dates indicate that at 1.2±0.2 ka (n=4, 1 std. error), the outlet glacier Kiagtût sermiat was ~200 m thicker than its historical limit. The timing of thicker ice near Narsarsuaq is likely concurrent with an ~8 km advance the same outlet glacier relative to the modern ice margin previously inferred from one minimum limiting radiocarbon date of 1.2±0.1 ka (1?). Cosmogenic dates from near Paamiut in southwest Greenland and additional Narsarsuaq dates are forthcoming. The timing of ice thinning and retreat near Narsarsuaq beginning at ~1.2 ka is concurrent with a switch from the dominance of Arctic- to Atlantic-sourced water masses within southern Greenland fjords, inferred from changes in fjord faunal assemblages. Modern switches in the source of fjord waters are related to variations in the North Atlantic Oscillation (NAO), with a switch from a positive to a negative phase causing the incursion of relatively warm Irminger Current waters around southern Greenland. We hypothesize that similar variations in North Atlantic atmospheric-oceanic circulation at centennial time-scales could have resulted in relatively cold southern Greenland fjord waters prior to ~1.2 ka during a positive NAO-like state, which forced a more extensive Neoglacial advance in southern Greenland than during the LIA. Conversely, during the LIA, warmer Atlantic waters may have dominated southern Greenland fjords, resulting in less extensive ice. The importance of this effect may have diminished northward up the coast, such that at Kangerlussuaq and further north, temperatures reached Holocene minima and the ice sheet margin its Holocene maximum extent during the LIA.

Carlson, A. E.; Winsor, K.; Ullman, D. J.; Murray, D. S.; Rood, D. H.; Axford, Y.

2011-12-01

296

Possible effects of anthropogenically-increased CO2 on the dynamics of climate - Implications for ice age cycles  

NASA Technical Reports Server (NTRS)

A dynamical model, developed to account for the observed major variations of global ice mass and atmospheric CO2 during the late Cenozoic, is used to provide a quantitative demonstration of the possibility that the anthropogenically-forced increase of atmospheric CO2, if maintained over a long period of time (perhaps by tectonic forcing), could displace the climatic system from an unstable regime of oscillating ice ages into a more stable regime representative of the pre-Pleistocene. This stable regime is characterized by orbitally-forced oscillations that are of much weaker amplitude than prevailed during the Pleistocene.

Saltzman, Barry; Maasch, Kirk A.; Verbitsky, Mikhail YA.

1993-01-01

297

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

298

Little Ice Age and Medieval Warm Periods in Eastern China as Read from the Speleothem Records  

NASA Astrophysics Data System (ADS)

The long-term climatic pace has often been interrupted by short-term abrupt changes. The Little Ice Age and Medieval Warm Period represent the two most important such changes over the last two millennia. Largely due to a dearth of high-resolution climatic records, our knowledge on the spatial extent, duration, and moisture characteristics of these two events is incomplete, and this has hampered our understanding of the driving force causing them as well as the recent global warming trend. Here we present high-resolution climatic records reflected by the ? 18O and ? 13C in three stalagmites from limestone caves in China: S312 from Shihua Cave (about 50 km southwest of Beijing), SF from Buddha Cave (about 80 km south of Xian), and F4 from Fengyu Cave (about 100 km south of Guilin). The chronologies of the stalagmites were determined by lamination counting and by the 210Pb and 230Th (TIMS) methods. S312 (3,600 years old) and F4 (600 years old) have mean growth rates of 0.035 and 0.24 mm/yr, respectively; whereas SF (10,000 years old) has a growth rate of 0.087 mm/yr for the top 1.6 cm and a rate of 0.0163 mm/yr below. We measured ? 18O and ? 13C at a resolution of 1-10 years for the last 1,000 years or so in all three stalagmites. These measurements were extended to the past 4,000 years at lower resolutions in S312 and SF. A total of 1052 pairs of ? 18O and ? 13C data thus obtained forms the basis for our reconstruction of the temperature (using ? 18O as proxy) and moisture (using ? 13C as proxy) variability in eastern China over the last four millennia. From the measured cave-water ? 18O and cave temperature at each location, we calculated the ? 18O values for calcites precipitated under isotopic equilibrium and found them to be similar to the observed ? 18O values in modern stalagmite layers. Measured ? 18O values in S312 and SF average -8.8\\permil and -9.1\\permil, respectively, reflecting a similar mean temperature of about14°C. The average ? 18O value of F4 is 2.2\\permil heavier than those of S312 and SF, indicating an annual mean temperature in Fengyu Cave that is about 5°C warmer than those of the two northern caves. Although the three caves are more than 1000 km apart, their long-term ? 18O records show patterns that are remarkably similar. The records show that in eastern China, the Medieval Warm Period started around 1000 AD and lasted until 1500 AD. A brief cooling during this warm interval occurred around 1150 AD. The Little Ice Age in China started at around 1500 AD and ended in the mid-1800s. Since then, all three locations show a warming trend that has been observed elsewhere in the world. The records of S312 and SF show that for the past 4,000 years, the two locations has had similar temperature variations with five distinct warming trends, but a different moisture variability which is probably more sensitive to local atmospheric circulation changes than temperature. In general, it was relatively dry during the Medieval Warm Period and wet during the Little Ice Age in eastern China. Of the five warming trends, the most recent one is the strongest.

Li, H.; Ku, T.

2002-12-01

299

Beryllium-10 exposure ages of erratic boulders in southern Norway and implications for the history of the Fennoscandian Ice Sheet  

NASA Astrophysics Data System (ADS)

The margins of the Fennoscandian Ice Sheet (FIS) during the Last Glacial Maximum (LGM) are fairly well constrained, yet the thickness of the FIS and its temporal evolution are poorly known. Here, we use beryllium-10 ( 10Be) exposure ages of glacially transported boulders along three vertical transects in southern Norway to determine past ice-sheet elevations. The ice surface elevation during the LGM at our westernmost site, Skåla, was likely at approximately 1440 m, coinciding with a previously mapped trimline. At our central site, Blåhø, the ice surface elevation at the LGM was at least at ˜1620 m, likely closer to 1800 m. At Elgåhogna, our easternmost site, LGM ice was above the summit elevation of 1460 m. Rapid deglaciation began at Skåla and Blåhø at approximately 13.5-14.5 10Be ka and at approximately 12 10Be ka at Elgåhogna. By approximately 9 10Be ka, the FIS had thinned to below our lowest sample at each location. Periods of rapid thinning correlate with an exposure dated ice-margin history, as well as the glaciation curve for western Scandinavia. Our data, when combined with previous bedrock and blockfield (highly weathered bedrock on summits) exposure ages, resolve a long-standing debate over the age and geomorphic interpretation of blockfields and weathering zones in southern Norway. Frozen-bed, low-erosive ice clearly covered the summit blockfields at Blåhø, and especially at Elgåhogna, where we find a large and progressive divergence between boulder and bedrock exposure ages with elevation. We conclude that the lower limit of blockfields in these areas should be interpreted as an englacial thermal boundary, rather than the upper limit of the LGM FIS, and that blockfields have survived multiple glacial cycles. We also compare our deglaciation record with several models of the FIS. Models that predict how the FIS changed during deglaciation, either through inversion of crustal rebound or through climate-dependent forward modeling, generally match our exposure ages reasonably well during deglaciation, but predict larger LGM surface elevations than our data indicate. On the other hand, the CLIMAP maximum model, which provides LGM elevations only, agrees with our results fairly well.

Goehring, Brent M.; Brook, Edward J.; Linge, Henriette; Raisbeck, Grant M.; Yiou, Francoise

2008-02-01

300

10Be surface exposure ages on the late-Pleistocene and Holocene history of Linnébreen on Svalbard  

NASA Astrophysics Data System (ADS)

Arctic glaciers were sensitive to past changes in high-latitude winter precipitation and summer temperature. Here we develop a late-Pleistocene to Holocene history for Linnébreen (Linné Glacier) in western Svalbard using 10Be surface exposure ages on isolated erratic and moraine boulders. We show that Linnébreen had separated from the larger ice sheet over Svalbard and was retreating up valley around the start of the Younger Dryas cold period. We attribute this retreat during a cold period on Svalbard to moisture starvation of Linnébreen from advanced sea ice and/or elevated shortwave boreal summer insolation that overwhelmed any reduction in sensible heat. After an ice-free period during the early to middle Holocene, Linnébreen reformed sometime after 4.6 ± 0.2 ka, and was at a position roughly equivalent to its Little Ice Age (LIA) maximum extent before it began to retreat at 1.6 ± 0.2 ka. Comparison with calibrated 14C dates from three other glaciers could suggest that this period of ice retreat at ˜1.6 ka could be regional in extent. Linnébreen occupied the pre-LIA moraine when there was an increased ratio of cold Arctic-sourced relative to warm Atlantic-sourced waters around Svalbard and advanced sea ice. The retreat of Linnébreen at ˜1.6 ka was concurrent with the increased presence of warm Atlantic waters around Svalbard and attendant sea-ice retreat. These coincident changes in ocean temperatures, sea-ice extent, and Linnébreen moraine age could imply a climatic forcing of the pre-LIA advance and retreat of Linnébreen. Summer temperatures, rather than changes in precipitation, would then be dominant in driving ice retreat, although the possibility of stochastic glacier-margin variability cannot be excluded. Our data therefore suggest that Linnébreen may have responded differently to past changes in sea-ice extent that could depend on the background climate state (deglacial climate vs. late-Holocene climate), which highlights the complexity in climatic controls on Arctic glaciers.

Reusche, Melissa; Winsor, Kelsey; Carlson, Anders E.; Marcott, Shaun A.; Rood, Dylan H.; Novak, Anthony; Roof, Steven; Retelle, Michael; Werner, Alan; Caffee, Marc; Clark, Peter U.

2014-04-01

301

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

302

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)

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

303

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

304

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

305

Ice-age survival of Atlantic cod: agreement between palaeoecology models and genetics  

PubMed Central

Scant scientific attention has been given to the abundance and distribution of marine biota in the face of the lower sea level, and steeper latitudinal gradient in climate, during the ice-age conditions that have dominated the past million years. Here we examine the glacial persistence of Atlantic cod (Gadus morhua) populations using two ecological-niche-models (ENM) and the first broad synthesis of multi-locus gene sequence data for this species. One ENM uses a maximum entropy approach (Maxent); the other is a new ENM for Atlantic cod, using ecophysiological parameters based on observed reproductive events rather than adult distribution. Both the ENMs were tested for present-day conditions, then used to hindcast ranges at the last glacial maximum (LGM) ca 21?kyr ago, employing climate model data. Although the LGM range of Atlantic cod was much smaller, and fragmented, both the ENMs agreed that populations should have been able to persist in suitable habitat on both sides of the Atlantic. The genetic results showed a degree of trans-Atlantic divergence consistent with genealogically continuous populations on both sides of the North Atlantic since long before the LGM, confirming the ENM results. In contrast, both the ENMs and the genetic data suggest that the Greenland G. morhua population post-dates the LGM. PMID:17999951

Bigg, Grant R; Cunningham, Clifford W; Ottersen, Geir; Pogson, Grant H; Wadley, Martin R; Williamson, Phillip

2007-01-01

306

Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay  

USGS Publications Warehouse

We present paleoclimate evidence for rapid (< 100 years) shifts of ??? 2-4??C in Chesapeake Bay (CB) temperature ???2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (???1400-1900 AD) and the Medieval Warm Period (???800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between ???450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average ???70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450-1000 AD, by 2-3??C, suggesting anomalous recent behavior of the climate system. ?? 2002 Elsevier Science B.V. All rights reserved.

Cronin, T. M.; Dwyer, G.S.; Kamiya, T.; Schwede, S.; Willard, D.A.

2003-01-01

307

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

308

Little Ice Age climate in the tropical Pacific from sediment, mollusks and corals  

NASA Astrophysics Data System (ADS)

The Little Ice Age (LIA, 1400-1800 A.D.) was a time of harsh winters and glacier advances in the Northern Hemisphere that coincided with three extended sunspot minima and active volcanism. While some evidence exists for contemporaneous climate extremes in the tropics and the Southern Hemisphere there is no consensus yet on whether the LIA was global in extent. We will present data from lake sediments on islands across the tropical Pacific, mollusks from the coast of Peru, and corals from the Society Islands and the Great Barrier Reef that indicate (1) the Intertropical Convergence Zone (ITCZ) was closer to the equator by about 5° of latitude, (2) the South Pacific Convergence Zone (SPCZ) was weaker and/or located closer to the equator, (3) ENSO variability was diminished, and (4) the mean annual SST and seasonal SST range were diminished along the coast of Peru during the LIA relative to today. What caused the LIA remains unknown but our data make clear that it involved the primary modes of tropical climate variability.

Sachs, J. P.; Carre, M.; Tudhope, A. W.; Mügler, I.; Lough, J.; Richey, J. N.

2011-12-01

309

Earth's orbital eccentricity and the rhythm of the Pleistocene ice ages: the concealed pacemaker  

NASA Astrophysics Data System (ADS)

Most paleoclimate researchers would probably agree that variations in Earth's axial tilt and precession parameters have influenced past climate change. However, claims of connections between orbital eccentricity and ice age climate are more difficult to demonstrate or accept, especially since the amplitude of the strongest component of eccentricity-induced insolation, the 413-ky signal, is conspicuously small or absent from the power spectra of the last million years of paleoclimate data, and climate models without external forcing can easily reproduce the main ˜100-ky cycles of the late Pleistocene and Holocene. Here I show that it is possible to tease out the 413-ky component of eccentricity directly from orbitally untuned deep-sea ? 18O time series, and that the signal is strong, albeit buried deep in the ? 18O time series, concealed by frequency modulation (FM). To extract the 413-ky signal, the data is frequency and phase demodulated numerically, while synthetic surrogate time series with properties believed similar to the actual data are used to test the nature of the modulator and the accuracy of each step in the inversion.

Rial, J. A.

2004-04-01

310

On the choice of ingredients for a theory of the Ice Ages  

E-print Network

"With five parameters one can fit an elephant". This provocative statement expresses the fact that when a theory has several adjustable parameters, an agreement with empirical data can be of modest value. What about a theory which contains unobserved objects? This is the subject of this paper. It is motivated by a model of the Ice Ages of the Pleistocene, which postulates a hot planet in an extremely eccentric orbit. This object has many consequences. It is rather well defined by the requirements, that it must not be in conflict with laws of nature, nor with empirical data. It must have sufficient mass to produce a rapid geographic pole shift on Earth after a close flyby at the end of the Pleistocene, and also be small enough to disintegrate at this occasion and to evaporate during the Holocene. These requirements leave hardly any adaptable parameters. In this situation, the agreement with further data, in particular the reverse Dansgaard-Oeschger events of the Holocene, represents a significant support of th...

Baltensperger, Walter

2013-01-01

311

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

312

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

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

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

315

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

316

Response of Jakobshavn Isbræ, west Greenland, to Little Ice Age climate change  

Microsoft Academic Search

The Greenland Ice Sheet (GIS) plays a critical role in the cryosphere's link with climate change. The recent fluctuations of thickness and velocity of Jakobshavn Isbræ, one of the largest outlet glaciers draining the GIS, indicates that Greenland's outlet glaciers have the potential to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing changes in ice

H. A. Stewart; B. M. Csatho; J. P. Briner

2009-01-01

317

On the dynamics of the ice ages: Stage-11 Paradox, mid-brunhes climate shift, and 100-ky cycle  

NASA Astrophysics Data System (ADS)

The Stage-11 Paradox consists in the fact that the stage sequence 12-11-10 has the greatest range of climatic variation in the Pleistocene, but only very modest forcing. The fundamental difference between the sequences 15-14-13 and 12-11-10 shows that the climate rules changed about 450,000 years ago. Basically, the world became more orderly and predictable. It marks the time when internal oscillation in the climate system became co-equal with Milankovitch forcing as a governing factor of ice-age dynamics. Thus, Stage 11 was so warm because Stage 12 was so cold. The maximum amplitude of climate variation around Stage 11 results from two opposing trends. One is an overall cooling trend, which when combined with changes in feedback mechanisms (NADW, albedo, carbon dioxide, marine-based ice) generates a propensity for ever-increasing glacial-interglacial amplitudes. The other is an overall negative feedback on glaciation, resulting from wearing down the base areas for ice-sheet buildup, which makes it more difficult to restart growing ice sheets after removal of ice, and makes it more difficult to build successive ice sheets to the same limit as previous ones. The combination of these factors is such that the system reached an opportunity for maximum contrast when forcing was at a minimum during mid-Brunhes time. On the whole, Stage 11 belongs with the succeeding interglacials, rather than the preceding ones. The new regime is characterized by strong terminations. An overall warming trend since 12-11-10 is nicely documented in the warm-water pool expansion in the western equatorial Pacific (which in turn stimulated reef growth).

Berger, W. H.; Wefer, G.

318

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

319

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

320

Caribbean Mixed Layer And Thermocline Temperatures During The Little Ice Age: Reconstructions With Sclerosponges  

NASA Astrophysics Data System (ADS)

The warming of the tropical ocean mixed layer since the Last Glacial Maximum has been estimated to be less than 2K according to CLIMAP data and possibly up to 5K in some regions. From this point of view the deduction of a warming of the Caribbean on the order of 2-3K from the Little Ice Age to present times from coral SST proxy records (Winter et al. 2000, GRL 27, 3365-3368) appears quite challenging. We present independent evidence from temperature proxy records of sclerosponge skele- tons that confirm the strong warming and additionally show that it was not restricted to the sea surface but prevailed to a water depth of at least 125 m. We investigated Sr/Ca ratios of sclerosponge skeletons, collected at two sites in the central Caribbean: A shallow water Jamaican reef (20 m water depth) and a deeper water site at Pedro Bank (125 m). The U/Th-dated sponge skeletons provide temperature proxy records back to the late 14th century with a temporal resolution of 3-5 years per sample. The Sr/Ca records from both the shallow and the deeper water show a strong warming from the early 19th century until the late 20th century. With a preliminary calibration of the sclerosponge Sr/Ca thermometer we estimate this warming to be on the order of 4K. The older parts of our temperature proxy records show a period of almost con- stant temperature from 1400 to 1550 A.D. During this time the temperature gradient between shallow and deeper water was slightly steeper than in the late 20th century. This period was followed by a 100 year interval of shallow water cooling (2K), while the deeper waters cooled only slightly (0.5K). This led to a thermal homogenization of the water column to at least a depth of 125m around 1700 A.D. During the 18th century shallow and deeper water temperature curves diverged again with a warming that was more pronounced in shallow waters and a subsequent cooling that was more pronounced in the deep. This second cool spell around 1800 A.D. was followed by the parallel 4K warming of both shallow and deeper water until recent times. Our results show that in addition to a significant cooling of the Caribbean surface and shallow sub- surface waters during the Little Ice Age, there was a period around 1700 A.D. when the thermal structure of the upper water column was significantly different from today with an at least 125 m thick isothermal surface layer. After that period the Caribbean thermocline reached its shallow position above 125 m around 1800 A.D. with a maxi- mum temperature difference between shallow and deep around the middle of the 19th century.

Haase-Schramm, A.; Böhm, F.; Eisenhauer, A.; Dullo, W.-Chr.

321

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

322

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

323

Using proglacial-threshold lakes to constrain fluctuations of the Jakobshavn Isbræ ice margin, western Greenland, during the Holocene  

NASA Astrophysics Data System (ADS)

The future response of the Greenland Ice Sheet (GIS) and its potential contribution to sea level rise are uncertain. Rapid changes of Greenland's outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future. This significant short-term variability highlights the need for longer-term, geologic (e.g., Holocene) records of ice margin fluctuations. However, a major challenge with reconstructing the GIS during the Holocene stems from it having been smaller than it is at present, thus traditional glacial geologic approaches are not suitable. We use radiocarbon-dated sediment sequences from seven proglacial-threshold lakes spanning ˜50 km of the western GIS margin near Jakobshavn Isbræ to constrain the timing of early Holocene deglaciation, the duration that this sector of the western GIS was smaller than its present configuration, and the timing of its advance during Neoglaciation. Our reconstructions suggest deglaciation ˜7300 cal yr BP, minimum ice extent ˜6000-5000 cal yr BP and smaller-than-present ice configuration until at least ˜2300 cal yr BP for the ice margin south of Jakobshavn Isbræ, and until ˜400 cal yr BP for the ice margin north of Jakobshavn Isbræ. One relatively large proglacial lake that became briefly ice-free during the middle Holocene lies in a catchment that likely extends 10s of km inland beneath the GIS, suggesting significant middle Holocene retreat of this portion of the GIS. The overall pattern of ice sheet change is inconsistent with existing ice sheet model reconstructions for this region, but is consistent with numerous paleoclimate proxy and relative sea level data. These continuous lacustrine records corroborate, but provide closer age control than, existing non-continuous records of radiocarbon-dated reworked bivalves from historical moraines in the region. Reconstructing ice margin change from proglacial-threshold lakes is one of few approaches with the potential to constrain smaller-than-present ice sheet extent.

Briner, J. P.; Stewart, H. A. M.; Young, N. E.; Philipps, W.; Losee, S.

2010-12-01

324

Tropical cooling and the isotopic composition of precipitation in general circulation model simulations of the ice age climate  

NASA Astrophysics Data System (ADS)

We test the climate effects of changes in the tropical ocean by imposing three different patterns of tropical SSTs in ice age general circulation model simulations that include water source tracers and water isotope tracers. The continental air temperature and hydrological cycle response in these simulations is substantial and should be directly comparable to the paleoclimatic record. With tropical cooling imposed, there is a strong temperature response in mid- to high-latitudes resulting from changes in sea ice and disturbance of the planetary waves; the results suggest that tropical/subtropical ocean cooling leads to significant dynamical and radiative feedbacks that might amplify ice age cycles. The isotopes in precipitation generally follow the temperature response at higher latitudes, but regional ?18O/air temperature scaling factors differ greatly among the experiments. In low-latitudes, continental surface temperatures decrease congruently with the adjacent SSTs in the cooling experiments. Assuming CLIMAP SSTs, 18O/16O ratios in low-latitude precipitation show no change from modern values. However, the experiments with additional cooling of SSTs produce much lower tropical continental ?18O values, and these low values result primarily from an enhanced recycling of continental moisture (as marine evaporation is reduced). The water isotopes are especially sensitive to continental aridity, suggesting that they represent an effective tracer of the extent of tropical cooling and drying. Only one of the tropical cooling simulations produces generalized low-latitude aridity. These results demonstrate that the geographic pattern of cooling is most critical for promoting much drier continents, and they underscore the need for accurate reconstructions of SST gradients in the ice age ocean.

Charles, C. D.; Rind, D.; Healy, R.; Webb, R.

325

Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages  

USGS Publications Warehouse

The extent of the last British-Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23-19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright ?? 2008 John Wiley & Sons, Ltd.

Phillips, W.M.; Hall, A.M.; Ballantyne, C.K.; Binnie, S.; Kubik, P.W.; Freeman, S.

2008-01-01

326

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

327

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

328

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

NASA Astrophysics Data System (ADS)

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.

2012-03-01

329

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

330

Designing for effective stationkeeping in ice  

E-print Network

, etc. · Ice geometry, ice age, density, salinity, etc. · Sea ice tracking (drift speed and directionDesigning for effective stationkeeping in ice CeSOS Highlights and AMOS Visions Conference DP Ice loads Ice #12;Effective stationkeeping in ice 1. Effective ship design. 2. An effective Ice

Nørvåg, Kjetil

331

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

332

Groundwater prospects in the Oak Ridges Moraine area southern Ontario: application of regional geological models  

Microsoft Academic Search

Abstract: Ageological model ,is presented for the glacial deposits of the Oak Ridges Moraine area of southern ,Ontario. The model contains four units as well as incised channels dissecting the strata. Channels eroded through the Newmarket Till, a regional aquitard, provide hydraulic connection between the aquifers of the overlying Oak Ridges Moraine and those of the underlying lower drift. Buried

D. r. Sharpe; L. d. Dyke; M. j. Hinton; S. e. Pullan; H. a. j. Russell; T. a. Brennand

333

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

334

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

335

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

336

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

337

European floods during the winter 1783/1784: scenarios of an extreme event during the `Little Ice Age'  

NASA Astrophysics Data System (ADS)

The Lakagígar eruption in Iceland during 1783 was followed by the severe winter of 1783/1784, which was characterised by low temperatures, frozen soils, ice-bound watercourses and high rates of snow accumulation across much of Europe. Sudden warming coupled with rainfall led to rapid snowmelt, resulting in a series of flooding phases across much of Europe. The first phase of flooding occurred in late December 1783-early January 1784 in England, France, the Low Countries and historical Hungary. The second phase at the turn of February-March 1784 was of greater extent, generated by the melting of an unusually large accumulation of snow and river ice, affecting catchments across France and Central Europe (where it is still considered as one of the most disastrous known floods), throughout the Danube catchment and in southeast Central Europe. The third and final phase of flooding occurred mainly in historical Hungary during late March and early April 1784. The different impacts and consequences of the above floods on both local and regional scales were reflected in the economic and societal responses, material damage and human losses. The winter of 1783/1784 can be considered as typical, if severe, for the Little Ice Age period across much of Europe.

Brázdil, Rudolf; Demarée, Gaston R.; Deutsch, Mathias; Garnier, Emmanuel; Kiss, Andrea; Luterbacher, Jürg; MacDonald, Neil; Rohr, Christian; Dobrovolný, Petr; Kolá?, Petr; Chromá, Kate?ina

2010-03-01

338

Abrupt change in atmospheric CO2 during the last ice age Jinho Ahn,1  

E-print Network

than, a rapid increase of Antarctic temperature inferred from stable isotopes. Citation: Ahn, J., E. J that these changes were gradual. In a detailed analysis of one event we now find that approximately half of the CO2 of previously published ice core records. 2. Methods [3] Details of CO2 analysis at Oregon State University (OSU

Schmittner, Andreas

339

Late glacial and Early Holocene climatic conditions along the margin of the Greenland Ice Sheet, registered by glacial extents in Milne Land, east Greenland  

NASA Astrophysics Data System (ADS)

Determining the mechanisms that caused past abrupt climate changes is important for understanding today’s rapidly warming climate and, in particular, whether we may be faced with abrupt climate change in the future. Scientists, policy makers and the public are concerned about ongoing warming because it is sending our climate into unprecedented territory at a rapid pace. The Younger Dryas cold event (~12,850-11,650 cal yr B.P.) was an abrupt climate event that occurred during the last transition from glacial to interglacial conditions. Due to its abrupt nature and the magnitude of temperature change that occurred, the Younger Dryas has been the focus of extensive research, however, the mechanisms that caused this cold event are still not well understood. Wide belts (up to 5 km) of moraines, known as the Milne Land stade moraines, are present in the Scoresby Sund region of central east Greenland. Previous work in the region using a combination of equilibrium line altitudes, surface exposure dating of moraines, and relative sea level changes indicates that mountain glacier advances during Younger Dryas time represent only moderate summer temperature cooling (~3-4C colder than at present). In contrast, Greenland ice cores, which register mean annual temperatures, indicate that Younger Dryas temperatures over the ice sheet were ~15C colder than at present. This mismatch between the two nearby paleoclimate records is interpreted to result from strong seasonality (very cold winters and only moderately cold summers) during Younger Dryas time. We are examining seasonality during Younger Dryas time by developing records of summer temperatures from local glaciers in Milne Land (71.0°N, 25.6°W). These mountain glaciers are located adjacent to the Greenland Ice Sheet, less than 50 km from the location of Renland Ice core and only ~250 km from the locations of the GISP2 and GRIP cores. We present new 10Be ages of local glacial extents in Milne Land. Ages range from 11,880 yr to 10,410 yr, indicating that glacial advances occurred during the late Younger Dryas and early Holocene time. The ELA depression of 3-4°C associated with these advances indicates strong seasonality during this time period. These new ages do not show an influence of 10Be inherited from prior periods of exposure, an issue that has hindered applications of 10Be dating in the region in the past. Thus, these ages demonstrate clear evidence for advances of late glacial and early Holocene cooling that must have also influenced the margin of the Greenland Ice Sheet.

Levy, L.; Kelly, M. A.; Lowell, T. V.

2010-12-01

340

The northern Uummannaq Ice Stream System, West Greenland: ice dynamics and and controls upon deglaciation  

NASA Astrophysics Data System (ADS)

At the Last Glacial Maximum (LGM), the Uummannaq Ice Stream System comprised a series coalescent outlet glaciers which extended along the trough to the shelf edge, draining a large proportion of the West Greenland Ice Sheet. Geomorphological mapping, terrestrial cosmogenic nuclide (TCN) exposure dating, and radiocarbon dating constrain warm-based ice stream activity in the north of the system to 1400 m a.s.l. during the LGM. Intervening plateaux areas (~ 2000 m a.s.l.) either remained ice free, or were covered by cold-based icefields, preventing diffluent or confluent flow throughout the inner to outer fjord region. Beyond the fjords, a topographic sill north of Ubekendt Ejland prevented the majority of westward ice flow, forcing it south through Igdlorssuit Sund, and into the Uummannaq Trough. Here it coalesced with ice from the south, forming the trunk zone of the UISS. Deglaciation of the UISS began at 14.9 cal. ka BP, rapidly retreating through the overdeepened Uummannaq Trough. Once beyond Ubekendt Ejland, the northern UISS retreated northwards, separating from the south. Retreat continued, and ice reached the present fjord confines in northern Uummannaq by 11.6 kyr. Both geomorphological (termino-lateral moraines) and geochronological (14C and TCN) data provide evidence for an ice marginal stabilisation at within Karrat-Rink Fjord, at Karrat Island, from 11.6-6.9 kyr. The Karrat moraines appear similar in both fjord position and form to 'Fjord Stade' moraines identified throughout West Greenland. Though chronologies constraining moraine formation are overlapping (Fjord Stade moraines - 9.3-8.2 kyr, Karrat moraines - 11.6-6.9 kyr), these moraines have not been correlated. This ice margin stabilisation was able to persist during the Holocene Thermal Maximum (~7.2 - 5 kyr). It overrode climatic and oceanic forcings, remaining on Karrat Island throughout peaks of air temperature and relative sea-level, and during the influx of the warm West Greenland Current into the Uummannaq region. Based upon analysis of fjord bathymetry and width, this ice marginal stabilisation has been shown to have been caused by increases in topographic constriction at Karrat Island. The location of the marginal stillstand is coincident with a dramatic narrowing of fjord width and bed shallowing. These increases in local lateral resistance reduces the ice flux necessary to maintain a stable grounding line, leading to ice margin stabilisation. This acted to negate the effects of the Holocene Thermal Maximum. Following this stabilisation, retreat within Rink-Karrat Fjord continued, driven by calving into the overdeepened Rink Fjord. Rink Isbræ reached its present ice margin or beyond after 5 kyr, during the Neoglacial. In contrast, the southern UISS reached its present margin at 8.7 kyr and Jakobshavn Isbræ reached its margin by 7 kyr. This work therefore provides compelling evidence for topographically forced asynchronous, non-linear ice stream retreat between outlet glaciers in West Greenland. In addition, it has major implications for our understanding and reconstruction of mid-Holocene ice sheet extent, and ice sheet dynamics during the Holocene Thermal Maximum to Neoglacial switch.

Lane, Timothy; Roberts, David; Rea, Brice; Cofaigh, Colm Ó.; Vieli, Andreas

2013-04-01

341

Growth and age estimation of greater fork-beard ( Phycis blennoides Brünnich, 1768) in the north and northwest of the Iberian Peninsula (ICES Division VIIIc and IXa)  

Microsoft Academic Search

In 1996 and 1997, a wide size range of greater fork-beard (Phycis blennoides Brünnich, 1768) was sampled from experimental and research surveys, trawlers and commercial landings from ICES Divisions VIIIc and IXa. Otoliths were collected and aged. Sectioned otoliths displayed numerous weakly marked rings that make ageing difficult. In the central part of the otolith, close to the nucleus, a

José Miguel Casas; Carmen Piñeiro

2000-01-01

342

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

343

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

344

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

345

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

346

Using ice cores from the East Antarctic Ice Sheet, scientists have been able to study  

E-print Network

in the bubbles is about the same age as the ice, so scientists use bubbles to learn about the ancient atmosphereUsing ice cores from the East Antarctic Ice Sheet, scientists have been able to study ice's ice sheets. Ice sheets are huge areas of permanent ice. There are only three ice sheets on Earth

347

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

348

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

349

Characteristics of dams constructed with moraine soils at the hydroelectric developments of the Kovda cascade  

Microsoft Academic Search

Conclusions  The construction of 19 reservoirs with moraine soil under different geological conditions and with soils having different\\u000a compositions has contributed to knowledge in hydraulic engineering practice, by making possible the development of the following\\u000a design and construction techniques.\\u000a \\u000a \\u000a 1. \\u000a \\u000a Moraine soil low in fine particles (30–35%) was successfully used as underlying material for stone protections.\\u000a \\u000a \\u000a \\u000a \\u000a 2. \\u000a \\u000a Moraine soil high in

P. A. Bukin

1968-01-01

350

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

351

Cosmogenic 10Be Exposure Age Limits on the Angel Lake Glaciation, Ruby Mountains, Northeastern Nevada  

NASA Astrophysics Data System (ADS)

Evidence of Pleistocene glaciations in the northern Great Basin of the interior western U.S. has been known for decades. Nonetheless, this area has received considerably less attention than the eastern and western extremes of the Great Basin, despite being centrally located among numerous well-dated Pleistocene glacial chronologies and in a setting where such chronologies can provide clues to the influence of North American ice sheets, Great Basin paleolakes, and atmospheric circulation changes on climate change. Among the most extensively glaciated mountains in the Great Basin are the Ruby and East Humboldt Mountains in northeastern Nevada, where the type localities for the last two Pleistocene glaciations in the region, the Lamoille and Angel Lake Glaciations, are found. The glacial record in these two ranges includes sequences of moraines deposited during the Angel Lake Glaciation, displaying abundant material suitable for terrestrial cosmogenic 10Be surface-exposure dating. Exposure ages of boulders from atop a sequence of well-preserved moraines in Seitz Canyon in the western Ruby Mountains limit the end of the Angel Lake Glaciation to 19.3 ± 1.0 ka. This preliminary age limit verifies that the Angel Lake Glaciation coincided with marine oxygen-isotope stage 2 and the global Last Glacial Maximum, and suggests that mountain glaciers in northeastern Nevada began retreating in step with the Laurentide Ice Sheet. When compared to glacial chronologies from elsewhere in the region, this age limit indicates an early start of the last deglaciation relative to the Sierra Nevada and the Wasatch Mountains, at the western and eastern extremes of the Great Basin respectively. Furthermore, this age limit suggests that ice retreat began before the highstands of the largest Great Basin paleolakes, Lakes Bonneville and Lahontan. Further development of the glacial chronology of the northern Great Basin is needed to evaluate the significance of these apparent age differences, and will provide a useful framework for resolving the pattern of climate change during the last glacial-interglacial transition.

Laabs, B. J.; Munroe, J. S.; Best, L. C.; Caffee, M. W.

2011-12-01

352

Chronology of glacial and periglacial deposits in front of the 1850 moraine of the Goldberg-Glacier, Sonnblick area (Salzburg/Austria)  

NASA Astrophysics Data System (ADS)

Since the Sonnblick-Observatory (3705 m) was founded in 1887, the nearby situated Goldberg Glacier (also termed Goldbergkees) was subject to numerous glaciological investigations. During the Würm glaciation the Goldberg Glacier covered the Rauris Valley and flew to the north. A giant landslide occurred in the upper Rauris Valley partly overlying moraines at an altitude of 1700 m. Based on morphostratigraphic relationships relative age sequences were established in the 1960ies. The 1850 moraine of the Goldberg Glacier was mapped at an altitude of 2200 m, and scarce remnants of older and younger moraines are preserved. Applying several new methods we want to date moraine stages in front of the 1850 moraine. Based on a detailed geological and geomorphological mapping using LIDAR topography we selected boulders on glacial stadials and on landslides for dating their surface exposure using the cosmogenic nuclide Be-10. The lithology of boulders on stadials is mostly gneiss whereas boulders of landslides are mostly biotite schist, garnet-mica schist and quartzite. We also applied the Schmidt-Hammer method as a proxy for estimating the degree of weathering of exposed boulders in order to establish a relative chronology of their deposition. In addition C-14 dating of peat deposits bordering the landslide will be used for establishing a robust time frame of glacier retreat and events of mass movements. The field work revealed temporal relationships of cross-cutting landscape elements due to the fact that the dominant glacial stadial overlies the giant landslide of the upper Rauris Valley, and the supposed Egesen stadial moraine itself is topped by a younger landslide of smaller dimension. Our goal is to decipher the chronologic evolution of the Goldberg Glacier as well as the landscape development of the Rauris Valley from the Alpine Lateglacial to the Holocene. Especially the effects of the cold spells of the Younger Dryas (12.7-11.6 ka BP) and of the "8,2 ka event" in this inner-Alpine mountain range, both linked to circulation changes in the North Atlantic, are of the essence for Quaternary stratigraphy and paleo-climatological reconstructions.

Bichler, M.; Reindl, M.; Häusler, H.; Reitner, J. M.

2012-04-01

353

Was the Little Ice Age the result of a volcanically-triggered regime shift in the North Atlantic ocean circulation?  

NASA Astrophysics Data System (ADS)

One of the most important events in the climate history of the North Atlantic region during the last millennium is the transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), a transition that had substantial impact on societies in medieval Europe. The origin of this shift in regional climate, however, is not fully understood. Volcanic eruptions and changes in the total solar irradiance (TSI) as well as internal climate variability on multi-centennial time-scales might have contributed, and it is likely that an interplay of a variety of forcings in combination with regional climate feedbacks is needed to understand the MCA-LIA transition. Here, we present transient last millennium simulations of the fully-coupled model Climber 3?. Based on reconstructions for the North Atlantic Oscillation (NAO), the dominant mode of North Atlantic atmospheric climate variability, as well as on observational data, we stochastically generated wind field ensembles over the last millennium. We performed ensemble simulations prescribing atmospheric and natural forcings and also separated the individual forcings. We find good agreement with paleo reconstructions of Nordic Sea sea-ice cover and AMOC strength over the last millennium. The ensemble spread for different stochastic wind fields reconstructions is substantial, thus highlighting the importance of atmospheric dynamics for North-Atlantic oceanic climate variability. However, when separating individual forcings, pure atmospheric forcing alone as well as in combination with TSI forcing are found to be insufficient to reproduce key features of the MCA-LIA transition as apparent in paleo reconstructions, whereas volcanic forcing can generate a transition in agreement with the reconstructions. Our results indicate a coupled sea-ice ocean feedback mechanism behind the MCA-LIA transition and decadally-paced volcanic eruptions as a potential trigger. The latter will lead to a substantial sea-ice increase in the Nordic Seas, hindering convection and subsequently weakening the overflows over the Greenland-Scotland Ridge. This in turn leads to a strengthening of the subpolar gyre circulation and eventually a weakening of the Atlantic Meridional Overturning Circulation (AMOC). The subsequent basin-wide cooling helps to maintain a greater sea-ice cover in absence of external forcing and thereby stabilises the new circulation regime. Our results demonstrate the possibility of a persistent regime shift in the North Atlantic oceanic circulation regime in response to a short-lived external forcing in a fully coupled climate model and highlight the importance of regional climate feedbacks in order to advance the understanding of past and future climate. References: C. F. Schleussner, G. Feulner: A volcanically triggered regime shift in the subpolar North Atlantic ocean as a possible origin of the Little Ice Age, Clim. Past Discuss. 8 (2012), 6199-6219, doi:10.5194/cpd-8-6199-2012.

Schleussner, Carl-Friedrich; Feulner, Georg

2013-04-01

354

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.

355

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

356

Y-Chromosome Evidence for a Northward Migration of Modern Humans into Eastern Asia during the Last Ice Age  

PubMed Central

Summary The timing and nature of the arrival and the subsequent expansion of modern humans into eastern Asia remains controversial. Using Y-chromosome biallelic markers, we investigated the ancient human-migration patterns in eastern Asia. Our data indicate that southern populations in eastern Asia are much more polymorphic than northern populations, which have only a subset of the southern haplotypes. This pattern indicates that the first settlement of modern humans in eastern Asia occurred in mainland Southeast Asia during the last Ice Age, coinciding with the absence of human fossils in eastern Asia, 50,000–100,000 years ago. After the initial peopling, a great northward migration extended into northern China and Siberia. PMID:10577926

Su, Bing; Xiao, Junhua; Underhill, Peter; Deka, Ranjan; Zhang, Weiling; Akey, Joshua; Huang, Wei; Shen, Di; Lu, Daru; Luo, Jingchun; Chu, Jiayou; Tan, Jiazhen; Shen, Peidong; Davis, Ron; Cavalli-Sforza, Luca; Chakraborty, Ranajit; Xiong, Momiao; Du, Ruofu; Oefner, Peter; Chen, Zhu; Jin, Li

1999-01-01

357

Multiproxy Evidence for a Positive Hydrological Budget during the Little Ice Age in the East African Rift, Kenya  

NASA Astrophysics Data System (ADS)

Hominin evolution took place in Africa during the Plio-Pleistocene and climate change is thought to be a factor, with Africa experiencing a general cooling and increasing aridification over the last several million years. Today, the climate of the East African Rift Valley of Kenya is characterized as semi-arid with evapotranspiration four times precipitation. Water resources are a valuable commodity for the many millions of inhabitants of the Valley. The short instrumental record shows precipitation fluctuates at sub-decadal timeframes as a result of the ENSO cycle; while during prehistory variations in monsoonal precipitation occurred on Milankovitch timescales (i.e. African Humid Period). Both timescales exhibit significant impacts on the distribution of surface water. However, little is known regarding precipitation variability over sub-millennial timescales. Emerging paleoclimate data indicates that the near surface presence of water has also varied over century length timescales. We present paleoclimate data from multiple sites along a north-south 600 km transect of the Gregory Rift Valley (Kenya) that indicate the region experienced wetter conditions during the Little Ice Age (A.D. 1400-1850). Our reconstructions of landscape and climate during this time frame rely upon a multiproxy and interdisciplinary approach. We discuss data from a variety of environmental settings (e.g. lakes, wetlands, and springs) that indicate an overall increase in hydrologic balance. Evidence is derived from biologic microfossils such as pollen, diatom and testate amoebae assemblages as well as inorganic components of the sedimentary record and geomorphic changes. The data differs significantly from studies undertaken to the west in Uganda and the Congo, where negative hydrologic balances occurred during the Little Ice Age. While the atmospheric dynamics causing this disparity are not yet recognized, interactions between the Intertropical Convergence Zone and the Congo Air Boundary are a likely causal agent.

Goman, M.; Ashley, G. M.; Hover, V. C.; Owen, R.

2011-12-01

358

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

359

'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

360

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

361

Ice-age endurance: DNA evidence of a white spruce refugium in Alaska  

PubMed Central

Paleorecords offer key information for evaluating model simulations of species migration in response to forecast climatic change. However, their utility can be greatly compromised by the existence of glacial refugia that are undetectable in fossil records (cryptic refugia). Despite several decades of investigation, it remains controversial whether Beringia, the largely unglaciated area extending from northeastern Siberia to the Yukon Territory, harbored small populations of certain boreal tree species during the last glaciation. Here, we present genetic evidence for the existence of a glacial refuge in Alaska that helps to resolve this long-standing controversy. We sequenced chloroplast DNA (cpDNA) of white spruce (Picea glauca), a dominant boreal tree species, in 24 forest stands across northwestern North America. The majority of cpDNA haplotypes are unique, and haplotype diversity is relatively high in Alaska, arguing against the possibility that this species migrated into the region from areas south of the Laurentide Ice Sheet after the end of the last glaciation. Thus, white spruce apparently survived long glacial episodes under climatic extremes in a heterogeneous landscape matrix. These results suggest that estimated rates of tree migration from fossil records may be too high and that the ability of trees to track anthropogenic warming may be more limited than previously thought. PMID:16894151

Anderson, Lynn L.; Hu, Feng Sheng; Nelson, David M.; Petit, Rémy J.; Paige, Ken N.

2006-01-01

362

A mechanism for freshening the Caribbean Sea in pre-Ice Age time  

NASA Astrophysics Data System (ADS)

believe that the Central American Seaway closed near 4 Ma and that that closure led to increased salinity in the Caribbean Sea and stronger Meridional Overturning Circulation in the Atlantic, which facilitated the waxing and waning of ice sheets in the Northern Hemisphere. We offer an alternative explanation for Caribbean salinification. The atmosphere transports approximately 0.23 Sv (1 Sv = 106 m3s-1) of fresh water (moisture) from the Caribbean to the Pacific today, but that amount varies by >20% during El Niño-Southern Oscillation events. Regressions of moisture transport against the Niño-3 index, a measure of the sea surface temperature in the eastern tropical Pacific, show less moisture transport from the Caribbean during El Niño events than average. Abundant evidence indicates that at 3-4 Ma the eastern tropical Pacific was 3.5-4°C warmer than today, and if so, an extrapolation of such regressions suggests that smaller moisture transport across Central America might account for paleoceanographic inferences of a smaller salinity difference between the Caribbean and Pacific at that time. Accordingly, that decreased salinity difference at ~3-4 Ma would not require blockage of relatively fresh Pacific water at ~2-4 Ma by the closure of the Central American Seaway, but rather would be consistent with a transition from El Niño to La Niña-like conditions in the eastern tropical Pacific around that time.

Mestas-Nuñez, Alberto M.; Molnar, Peter

2014-06-01

363

Ice front configuration and torrential flow features of the Late Wisconsinan interlobate region of southcentral Michigan  

SciTech Connect

A large re-entrant, bordered on three sides by ice of the Michigan, Saginaw and Huron-Erie lobes, developed over a five-county area in southcentral Michigan during ice retreat of the Port Bruce Stade of the Woodfordian Substage. At this time, ice occupied positions marked by the Sturgies, Tekonsha, and Kalamazoo Moraines. The presence of numerous boulder beds within outwash deposits attests to frequent episodes of torrential flow. A major source of the discharge was the draining of short-lived proglacial and subglacial lakes identified by lacustrine deposits which occur at different altitudes within moraine belts. Tunnel valleys, meltwater channels, and narrow chutes carried the high discharges of water that were partly responsible for the Kankakee torrent of northeastern Illinois. The configuration of abandoned meltwater channels in eastern Calhoun and western jackson counties, between the Kalamazoo Moraine on the northeast and the Tekonsha Moraine to the southwest, indicates that a large ice-collapsed depression, 30 km long and 8 km to 16 km wide, developed within the Saginaw lobe just behind its margin. For a short period of time it contained intermittent glacial lakes one of which drained through the Kesler Lakes sluiceway. A large outwash plain, the Union City-Mendon sluiceway, heads at the Tekonsha Moraine in southcentral Calhoun County and extends southwest through northeastern Branch County to the Sturgis Moraine. Several abandoned narrow chutes, up to 1.6 km long and 60 m to 300 m wide, are incised in the outwash plain in the vicinity of Union City. Channel geometry indicates that flow exceeded 850 cms (30,000 cfs) during bankfull discharge and came from the overflow of a lake dammed by ice blocks in the ancient St. Joseph River floodplain.

Taylor, L.D. (Albion Coll., MI (United States). Dept. of Geological Sciences)

1994-04-01

364

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

365

Cosmogenic age constraints on the last deglaciation in Southern Patagonia (49 - 50°S)  

NASA Astrophysics Data System (ADS)

The glacial-to-interglacial transition since the Last Glacial Maximum (LGM) reflects climate system dynamics and the mechanisms that force climate change. Numerous studies of glacier behavior, mainly in the Northern Hemisphere, have sought to delineate the LGM termination as well as post-LGM climate reversals. We know far less about the Southern Hemisphere, where the extent and timing of climate shifts, and the degree of linkage to changes in the Northern Hemisphere, remain uncertain. Quantifying the temperature and precipitation changes across southern South America can help assess the migration of precipitation patterns tied to the position of the Southern Westerlies and the Antarctic Polar Front. This data can also be used to detect the extent of temperature reversals across and between continents, such as the Antarctic Cold Reversal, if present. The testing of hypotheses regarding changes in global atmospheric and oceanic circulation since the LGM is partly dependent on the deconvolution of these two parameters. Glacial activity in the Southern Patagonian Icefield is highly sensitive to changes in temperature and precipitation, while the adjacent Andean rainshadow desert preserves a remarkably complete set of glacial deposits that span a wide transect of the southern mid-latitudes. These deposits are ideal for surface exposure dating, which in turn can provide a proxy for glacial activity and for changes in the factors that govern glacial mass balance. We use a new beryllium-10 production rate calibrated to the southern mid-latitudes to recalculate published surface exposure chronologies from Patagonia (46 to 53°S). The revised temporal framework indicates the presence of expansive ice from ~30 ka until regional retreat 17-18 ka, with a significant late-glacial re-advance or still-stand ending ~13 ka. This latitudinal transect is notable for a gap in glacial records between 49 and 50°S. New surface exposure age determinations from the Santa Teresita moraine along the western shores of the large outlet valley of Lago Viedma, and from several moraines within the narrow pre-Cordilleran Rio Guanaco mountain valley begin to fill this gap. Initial results from a moraine in Rio Guanaco valley indicate ice retreat at ~18 ka, correlative with final LGM moraines at Lago Buenos Aires and Lago Pueyrredon to the north (46 - 47°S) and to the south near Torres del Paine and the Straits of Magellan (51 - 53°S). Exposure ages for the Santa Teresita moraine indicate ice retreat at ~13 ka, coincident with the well-dated Puerto Banderas moraine (Ackert et al., 2008, Science) in the Lago Argentino outlet valley to the south. These surface exposure chronologies are consistent with other regional records. Moreover, the emerging chronology is consistent with results of a fully-coupled transient general circulation model that predicts minimal deglacial precipitation change with significant temperature and equilibrium line altitude lowering during the last deglaciation at 50°S near 14 ka, followed by resumed warming from ~13.5 ka into the Holocene. These findings suggest that unlike more northerly portions of Patagonia, the Antarctic Cold Reversal impacted the Andes as far north as 50°S.

Murray, D. S.; Singer, B. S.; Carlson, A. E.; Caffee, M. W.

2010-12-01

366

Ice Sheet Deglaciation, Younger Dryas Readvance and Palaeoclimatic Implications in the Cairngorm Mountains, Scotland.  

NASA Astrophysics Data System (ADS)

The Cairngorm Mountains contain an outstanding assemblage of glacial landforms from both the deglaciation of the last British-Irish Ice Sheet and the Younger Dryas Readvance; these can provide a wealth of information about palaeoclimate and glacier-climate interaction. Previous interpretations have left doubt over the extent and style of the Younger Dryas readvance. In addition, although the ice sheet deglaciation of the northern margin of the Cairngorms is relatively well understood, the pattern and timing of deglaciation on the southern margin and particularly how local and external ice masses interacted is unclear. New geomorphological mapping from aerial images and fieldwork has been compiled in a GIS for a 600km² area of the Cairngorm Mountains. This systematic mapping covers all previously reconstructed Younger Dryas glaciers and the landform assemblages associated with ice sheet deglaciation. For the first time, Cairngorm-wide patterns of deglaciation have been mapped and comparisons between the northern and southern margins made. Interpretations suggest that during ice sheet deglaciation, outlet glaciers were fed by locally-sourced plateau ice caps. On both the northern and southern margin of the Cairngorms, large ice-dammed lakes formed between locally sourced ice and neighbouring ice masses. The presence of these lakes indicates that ice masses in the Cairngorms began to recede early in deglaciation, most likely as a result of precipitation starvation. Detailed mapping, combined with new surface exposure ages taken from areas of 'hummocky moraine' previously subject to differing interpretation, will assist in determining the extent of Younger Dryas glaciation. The new ages will also guide new modelling of snow delivery to the surface of Younger Dryas glaciers. Preliminary results suggest snow blow factors cannot account for the low ELAs of some previously reconstructed valley glaciers. As a result, either very strong precipitation gradients existed within the Cairngorms during the Younger Dryas or previously reconstructed glaciers did not occur simultaneously. The geomorphological evidence and palaeoclimatic inferences are important alongside a growing number of palaeoglaciological studies in acting as evaluation areas for current numerical models of ice sheet growth and decay.

Standell, Matthew; Graham, David; Hodgkins, Richard; Rodés, Ángel

2013-04-01

367

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 three problems are discussed in the context of the theory of the Quaternary climate, which will be incomplete unless it is embedded in a more general theory for the fuller Cenozoic that can accommodate the onset of the ice-age fluctuations. We construct a simple mathematical model for the Late Cenozoic climatic changes based on the hypothesis that forced and free variations of the concentration of atmospheric greenhouse gases (notably CO2), coupled with changes in the deep ocean state and ice mass, under the additional 'pacemaking' influence of earth-orbital forcing, are primary determinants of the climate state over this period. Our goal is to illustrate how a single model governing both very long term variations and higher frequency oscillatory variations in the Pleistocene can be formulated with relatively few adjustable parameters.

Saltzman, Barry

1992-01-01

368

The Medieval Warm Period-Little Ice Age Relative Sea Level Slowdown in Western Greenland: A response of the Greenland Ice Sheet to a phase shift of the North Atlantic Oscillation?  

NASA Astrophysics Data System (ADS)

Changes in mass balance can force spatially variable sea-level changes in both the near- and far-field of an ice sheet (Farrell and Clark, 1976; Mitrovica et al. 2001). During the period spanning the Medieval Warm Period and the Little Ice Age (LIA), reconstructions of century-scale relative sea-level (RSL) extracted from salt marsh deposits in Greenland (Long et al. 2011, Woodroffe and Long, 2009) reveal that the century-scale RSL trends differ significantly to millennial-scale trends inferred from isolation basin data in their respective areas. At sites in west Greenland (Sisimiut: 68.6oN, 52.6oW; Aasiaat: 68.6oN, 52.6oW), RSL rise slows from ~3 mm/yr to ~0 mm/yr at ~1600AD and is stable thereafter. In south Greenland (Nanortalik, 60oN, 44.7oW), a similar trend is observed, but the slowdown occurs 200 years later. Sensitivity tests show that substantial contributions from oceanographic changes can be ruled out as drivers of RSL slowdown at Aasiaat and Sisimiut but could be more important at Nanortalik. Dynamic ice loss from Jakobshavn Isbrae is predicted to produce an extremely localised RSL signal and is likely to be only a secondary contributor to RSL changes at Aasiaat. For Sisimiut and Aasiaat, regional-scale changes in ice load are the most likely candidate to explain the observed RSL signals. Marginal ice loss in western Greenland beginning around 1600AD is required to initiate local sea-level fall to counteract the background viscous sea-level rise associated with GIA from non-Greenland sources. However, ice loss is deemed an unlikely scenario since this is incompatible with widely-perceived climatic conditions associated with the Little Ice Age. Recently it has been shown that the North Atlantic Oscillation (NAO) was predominantly in a positive phase prior to the LIA (Trouet et al., 2009), switching to a variable positive/negative phase since ~1600AD. This offers a mechanism to explain the RSL changes at Sisimiut and Aasiaat at 1600AD. We present the results of a sensitivity study which support the hypothesis first proposed in Long et al. (2011) that the western part of the Greenland Ice Sheet may have been losing mass as a result of warmer conditions associated with NAO-, during a time when the many glaciers around the world were expanding.

Wake, L. M.; Milne, G. A.; Long, A. J.; Woodroffe, S. A.

2012-04-01

369

Greenland Ice Sheet Retreat from the Central West Greenland Shelf during the Last Deglaciation and the early Holocene (Invited)  

NASA Astrophysics Data System (ADS)

Geophysical and sediment core data collected in 2007, 2008 and 2009 provide evidence for the extent of the Greenland Ice Sheet on the central West Greenland shelf seaward of Jakobshavns Isbrae, and the history and style of ice sheet retreat since the LGM. Sediment gravity flows delivered to the trough mouth fan document an active glacier margin at or near the shelf edge until at least 13.5 and possibly as late as 12.5 cal kyr BP. Outer shelf cores have thin sediment sequences and fairly young basal ages between 11 and 12 cal kyr BP that do not tightly constrain the timing of deglaciation of the outer shelf. The oldest ages obtained thus far on the outer shelf are c. 12.5 cal kyr BP from a site 60 km from the shelf edge. These dates come from mollusk shells immediately below and within a diamicton whose origin is still under investigation. No ice-proximal glacial marine sediments overlie the diamicton suggesting that if it does represent till, then glacier ice must have retreated rapidly from the site. Ice distal glacial marine sediments with arctic fauna were deposited on the outer shelf between 12 and 10.2 indicating ice distal conditions dominated by ice-berg rafting. Stratified pebbly mud reflecting ice proximal glacial marine sedimentation outside the mouth of Disko Bay reflects ice margin retreat to the inner shelf by processes involving both calving and release of turbid meltwater plumes. Farther east, rapid sedimentation rates and high IRD fluxes documented in a core at the mouth of Disko Bay suggest this site was deglaciated as early as 12 cal kyr BP, but no later than 11.1 cal kyr BP. At this site, two periods of rapid sedimentation associated with high IRD flux document phases of ice retreat within Disko Bay from 10.7 to 10.2 cal kyr BP and from 9.7 to 9.3 cal kyr BP. Ice proximal sediments in inner Disko Bay date to 9.4 cal kyr BP, consistent with the age of the rapid sedimentation rate and high IRD flux in outer Disko Bay and with the age of the earlier set of Fjord Stade moraines on land.

Jennings, A. E.; Walton, M. E.; O'Cofaigh, C.; Kilfeather, A. A.; Moros, M.; Andrews, J. T.

2010-12-01

370

Reconstruction of Wisconsinan-age ice dynamics and compositions of southern Ontario glacial diamictons, glaciofluvial/lacustrine, and deltaic sediment  

NASA Astrophysics Data System (ADS)

Macrofabric analysis of till sections in south-central Ontario confirms that clast orientation yields information related to changing ice dynamics during the Wisconsinan glaciation. Test stations in six sections yield unimodal to multimodal macrofabrics that indicate ice flow direction, ranging from SE-NW vectors when ice was thin and flowing radially to variable NE-SW, NNE-SSW, and N-S vectors when ice thickened. Ice loci appear to range from the Lake Ontario basin and southern Quebec (thin ice), Labrador Ungava (thicker ice), and Hudson Bay (thickest ice). The north-south fabric may identify the intergrowth of Keewatin-Labrador ice, presumably the maximum ice thickness of the Last Glacial Maximum (LGM). The preliminary data support the theory that topography directed ice movement during preliminary and closing stages of glaciation in southern Ontario, while thick ice generated flow vectors largely unaffected by underlying topography; hence, leading to clast azimuthal variations reflecting changing ice loci with glacier growth. The fabrics analyzed suggest that inferring difference between ductile and brittle lodgement tills is possible as well as to identifying possible glacial tectonic action/overburden loading that disturbs the least friction-fit position of clasts in till. The changing dynamics within till sheets are supported, in part, by variations in glacial crushing seen in SEM imagery that depict a range of microtextures from full-scale fractures under brittle conditions to those indicating less viscous transport under ductile regimes. To some degree, changes in flow direction are further supported by geochemical variations that relate to bedrock/regolith up-glacier controlling Ca-dilution and variable concentrations of Rare Earth Elements (REEs).

Mahaney, W. C.; Hancock, R. G. V.; Milan, Alison; Pulleyblank, Coren; Costa, Pedro J. M.; Milner, M. W.

2014-02-01

371

Dynamic ancient ice caps in the sub-Antarctic suggested by new mapping of submarine ice-formed landscapes  

NASA Astrophysics Data System (ADS)

Recent bathymetric investigations have provided hints of significant past glaciations on several Southern Ocean sub-polar islands. The extent and behaviour of ice cover in these regions is important because it provides critical limits on the evolution of refugia and marine benthic organisms, as well as unique far-field constraints for improving polar ice-sheet model sensitivity. However, despite improvements in regional mapping, sea-floor acoustic data from key shelf areas have still not been of sufficient quality, or broad enough in their coverage, to resolve the number, form or flow of past glacial episodes. Hence the history and style of sub-Antarctic glaciation remains poorly known. Here we use a compilation of multibeam bathymetry and fisheries echo-sounding data to provide evidence for dynamic, widespread ice caps on sub-Antarctic South Georgia during past glacial periods. We present a hitherto unmapped record of sea-bed glacigenic structures, including end moraines and subglacial landforms, from which the flow and form of at least three major, entirely marine-terminating configurations is resolved. The largest glaciation covered the majority of the continental shelf, and included fast-flowing outlets, possible switching of internal flow, meltwater activity, warm-based ice erosion, and substantial marginal deposition during retreat: all features of dynamic ice-cap behaviour. Existing biological evidence suggests the largest glaciation likely pre-dated the Last Glacial Maximum, which may have been restricted in extent reaching to the island's fjord mouths, while a third mid-shelf limit appears partially recorded. Work on dating the relict landscape of ancient ice cap advance and retreat is ongoing, but our preliminary age model suggests that South Georgia's history is unique from the Antarctic polar glacial record, and may be more similar to that of past ice caps on Patagonia. The glacial configurations revealed by these data will provide the basis of new boundary conditions for polar ice sheet models, and must have been significant for the evolution of Antarctic benthic habitat.

Graham, Alastair; Hodgson, Dominic; Cofaigh, Colm Ó.; Hillenbrand, Claus-Dieter; Kuhn, Gerhard

2014-05-01

372

SCIENCE BRIEFING Ice cores and climate change  

E-print Network

seen during Earth's emergence from the last ice age around 12,000 years ago). CO2 concentration-known from other records, and the coldest periods in Antarctica are the times when we had ice ages.Ice sheetsSCIENCE BRIEFING Ice cores and climate change Slices of ice core, drilled from the depths

Little, John B.

373

Oxygen isotope evidence of Little Ice Age aridity on the Caribbean slope of the Cordillera Central, Dominican Republic  

NASA Astrophysics Data System (ADS)

Climate change during the so-called Little Ice Age (LIA) of the 15th to 19th centuries was once thought to be limited to the high northern latitudes, but increasing evidence reflects significant climate change in the tropics. One of the hypothesized features of LIA climate in the low latitudes is a more southerly mean annual position of the Intertropical Convergence Zone (ITCZ), which produced more arid conditions through much of the northern tropics. High-resolution stable oxygen isotope data and other sedimentary evidence from Laguna de Felipe, located on the Caribbean slope of the Cordillera Central of the Dominican Republic, support the hypothesis that the mean annual position of the ITCZ was displaced significantly southward during much of the LIA. Placed within the context of regional paleoclimate and paleoceanographic records, and reconstructions of global LIA climate, this shift in mean annual ITCZ position appears to have been induced by lower solar insolation and internal dynamical responses of the global climate system. Our results from Hispaniola further emphasize the global nature of LIA climate change and the sensitivity of circum-Caribbean climate conditions to what are hypothesized to be relatively small variations in global energy budgets.

Lane, Chad S.; Horn, Sally P.; Orvis, Kenneth H.; Thomason, John M.

2011-05-01

374

Proxy records of Late Holocene climate events in the eastern United States: Medieval Warm Period and Little Ice Age  

NASA Astrophysics Data System (ADS)

We are conducting a multiproxy, regional reconstruction of climate variability during the last two millennia including the Medieval Warm Period (MWP) and Little Ice Age (LIA) in eastern North America. Pollen, benthic foraminifers, ostracodes, and other proxies were analyzed from high-resolution sampling of continuous sedimentary records from lakes, wetlands, and estuaries in Florida, North Carolina, Chesapeake Bay, and Lake Champlain. These records document multi-decadal changes in vegetation, temperature, precipitation, and estuarine salinity across a latitudinal transect. During both the MWP and LIA, decreased precipitation altered plant community composition and distribution in the southeastern United States, and the LIA triggered threshold changes in vegetation that persisted until anthropogenic land-cover change overwhelmed the climate signature. In the mid-Atlantic region, progressively cooler and wetter late Holocene springs culminated in a cool, wet LIA; this trend correlates with observed oceanic changes. Trend analysis of the data suggest that inter-regional correlation of multi-decadal and centennial-scale Holocene climate events will be forthcoming.

Willard, D. A.; Cronin, T. M.; Hayo, K. M.

2006-12-01

375

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

NASA Astrophysics Data System (ADS)

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 absence of lion cub bones, in contrast to hyena and cave bear cub remains in the Perick Caves, and other caves of northern Germany, excludes the possibility that P. leo spelaea used the cave for raising cubs. Only in the Wilhelms Cave was a single skeleton of a cub found in a hyena den. Evidence of the chewing, nibbling and cracking of lion bones and crania must have resulted from the importation and destruction of lion carcasses (4% of the prey fauna). Similar evidence was preserved at other hyena den caves and open air sites in Germany. The bone material from the Perick and other Central European caves points to antagonistic hyena and lion conflicts, similar to clashes of their modern African relatives.

Diedrich, Cajus G.

2009-05-01

376

Phylogeographic Analysis Elucidates the Influence of the Ice Ages on the Disjunct Distribution of Relict Dragonflies in Asia  

PubMed Central

Unusual biogeographic patterns of closely related groups reflect events in the past, and molecular analyses can help to elucidate these events. While ample research on the origin of disjunct distributions of different organism groups in the Western Paleartic has been conducted, such studies are rare for Eastern Palearctic organisms. In this paper we present a phylogeographic analysis of the disjunct distribution pattern of the extant species of the strongly cool-adapted Epiophlebia dragonflies from Asia. We investigated sequences of the usually more conserved 18 S rDNA and 28 S rDNA genes and the more variable sequences of ITS1, ITS2 and CO2 of all three currently recognised Epiophlebia species and of a sample of other odonatan species. In all genes investigated the degrees of similarity between species of Epiophlebia are very high and resemble those otherwise found between different populations of the same species in Odonata. This indicates that substantial gene transfer between these populations occurred in the comparatively recent past. Our analyses imply a wide distribution of the ancestor of extant Epiophlebia in Southeast Asia during the last ice age, when suitable habitats were more common. During the following warming phase, its range contracted, resulting in the current disjunct distribution. Given the strong sensitivity of these species to climatic parameters, the current trend to increasing global temperatures will further reduce acceptable habitats and seriously threaten the existences of these last representatives of an ancient group of Odonata. PMID:22666462

Büsse, Sebastian; von Grumbkow, Philipp; Hummel, Susanne; Shah, Deep Narayan; Tachamo Shah, Ram Devi; Li, Jingke; Zhang, Xueping; Yoshizawa, Kazunori; Wedmann, Sonja; Hörnschemeyer, Thomas

2012-01-01

377

Late Holocene Environment in the Lower Hudson Valley, New York: Medieval Warming, Little Ice Age, and European Impact  

NASA Astrophysics Data System (ADS)

Two sediment cores from Piermont Marsh, located in the southern Hudson River Valley, provide a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from A.D.800-1350, paralleling records southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. Increases in Picea and Tsuga with corresponding decreases in Liquidambar, coupled with increasing organic percentages due to cooler, moister conditions indicate the presence of the Little Ice Age. European impact is manifested by increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), decline in arboreal pollen due to land clearance, and increase in inorganic particles to the watershed. Radionuclide dating using Cs-137 and Pb-210 from the southern end of the marsh shows that little disturbance of sediments has occurred, adding validity to the high resolution results and supporting the sedimentation rates obtained using radiocarbon dating. Comparison with other marsh records in the Hudson River estuary shows general agreement in chronology with interesting differences in species changes and sedimentation rates.

Pederson, D. C.; Peteet, D. M.; Kurdyla, D.; Guilderson, T.

2004-05-01

378

Little Ice Age and recent treeline fluctuations at the Columbia Icefield, Alberta  

SciTech Connect

Vegetation dynamics at two treeline sites (north- and south-facing) were reconstructed using tree-ring and age-structure studies. Trees, seedlings and snags were mapped in two, 30m x 275m plots running upslope from continuous forest to alpine tundra. The Athabasca Glacier advanced against the base of the south-facing slope ca. 1714 and in the 1840`s. Snags on this slope indicate that treeline was higher than present prior to ca. 1200 A.D. and between 1400-1700 A.D. Many trees died between 1650-1700 A.D. during the advance of the Athabasca Glacier. Tree establishment took place in the late 1700`s and the 1800`s as well as during periods of warmer climate in the 1940`s and 1960`s. Both Picea engelmannii and Abies lasiocarpa form treeline at this site. On the north-facing slope (8 km south) treeline dynamics are different. A. lasiocarpa dominates the vegetation and P. engelmannii is rare. There is no strong evidence of historical fluctuations of treeline at the north-facing site. Tree establishment is primarily due to expansion of tree clumps by layering at the north-facing site, whereas treeline expansion at the south-facing site is due to seedling establishment. At both sites tree establishment by seed appears to be limited to periods of warmer climate, whereas population expansion by layering occurs continuously.

Kavanagh, T.A.; Luckman, B.H. [Univ. of Western Ontario, London (Canada)

1995-06-01

379

Was the 19th Century end of the Little Ice Age in the Alps forced by industrial black carbon?  

NASA Astrophysics Data System (ADS)

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. Our current knowledge of the Alpine climate, climatologists consider the climatic end of the LIA to have come markedly later than the glaciological end, resulting in a paradox. Simulations of glacier length variations using glacier flow and mass balance models forced with instrumental and proxy temperature and precipitation fail to match the timing and magnitude of the observed late 19th century retreat. Matches between simulations and observations have only been achieved when additional glacier mass loss is imposed after 1865 or when precipitation signals are generated that would fit the glacier retreat rather than using actual precipitation records. A known transition however did occur across that half century and into the 20th century that may have held powerful potential consequences for absorption of solar radiation, earlier melt of snow cover, and, in turn, the retreat of glaciers. That transition was the dramatic rise in a byproduct of industrialization: black carbon. Ice cores indicate that BC concentrations increased abruptly at mid 19th century and largely continued to increase into the 20th century, consistent with known increases in BC emissions from the industrialization of Western Europe. We estimate the radiative forcings by these changes in BC loading and whether they were of sufficient magnitude to produce the pronounced negative glacier mass balance that began mid 19th century. 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. Fig. 3 Atmospheric structure in the Swiss Alps, photo courtesy of Dano Olivieri (www.onyrix.com).

Painter, T. H.; Flanner, M.; Marzeion, B.; Kaser, G.; VanCuren, R. A.; Abdalati, W.

2013-12-01

380

Modern and Little Ice Age equilibrium-line altitudes on Outlet Valley glaciers from Jostedalsbreen, western Norway: An evaluation of different approaches to their calculation  

SciTech Connect

The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glacier from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 [+-] 0.05 gave a mean little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account gave a mean ELA depression of 35-255 m, the median elevation of glaciers 115 m, and the toe-to-headwall altitude ration 140 m. Differences in the ELA estimates can be attributed to the differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results. This will aid in determining mean global temperatures during the LIA. 34 refs., 9 figs., 5 tabs.

Torsnes, I.; Rye, N. (Univ. of Bergen (Norway)); Nesje, A. (Univ. of Bergen, Bergen-Sandviken (Norway))

1993-05-01

381

Ice stratigraphy at the Pa^kitsoq ice margin, West Greenland, derived from gas records  

E-print Network

than deep ice-coring projects, but they also pose specific challenges. The first challenge is