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The Laurentide Ice Sheet (LIS) was the largest ice sheet during the last glacial period. An accurate representation of its behavior during the last deglaciation is critical to understanding its influence on and response to a changing climate. We use 10Be dating and Bayesian modeling to track the recession of the southwest sector of the Labrador Dome of the LIS along an ~500-km-long transect west of Lake Superior during the last deglaciation. This transect reflects terrestrial ice-margin retreat and crosses multiple moraine sets, with the southwestern part of the transect deglaciated by ca. 19 ka and the northeastern part deglaciated by ca. 10 ka. The predominant behavior of the ice margin during this interval is near-constant retreat with retreat rates varying between ~59 m/a and 38 m/a. The moraine sets mark standstills and/or readvances that in total constitute only ~17% of the retreat interval. The spatial and temporal pattern of ice-margin retreat tracked here differs from existing reconstructions that are based on using isochrons to define ice-margin positions. Acknowledging the uncertainties associated with the modeled ages of ice-margin retreat, we suggest that the overall retreat pattern is consistent with forcing by a gradual increase in Northern Hemisphere, high-latitude summer insolation. The pattern of ice-margin retreat is inconsistent with Greenland ice-core temperature records, and thus these records may not be suitable to drive models of the LIS. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records. Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ∼250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ∼2.6 cal ka BP and ∼1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6 cal ka BP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: This paper is the first to summarize research on fluctuations of local glaciers in Greenland (e.g. ice caps and mountain glaciers independent of the Greenland Ice Sheet) during latest Pleistocene and Holocene time. In contrast to the extensive data available for fluctuations of the Greenland Ice Sheet, surprisingly little data exist to constrain local glacier extents. Much of the available research was conducted prior to wide-spread use of AMS radiocarbon dating and the advent of surface-exposure and luminescence dating. Although there is a paucity of data, generally similar patterns of local glacier fluctuations are observed in all regions of Greenland and likely reflect changes in paleoclimate, which must have influenced at least the margins of the Inland Ice. Absolute-age data for late-glacial and early Holocene advances of local glaciers are reported from only two locations: Disko (island) and the Scoresby Sund region. Subsequent to late-glacial or early Holocene time, most local glaciers were smaller than at present or may have disappeared completely during the Holocene Thermal Maximum. In general, local glacier advances that occurred during Historical time (1200–1940 AD) are the most extensive since late-glacial or early Holocene time. Historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last ∼100 yrs. In all but one area (North Greenland), local glaciers are currently receding from Historical extents. [Copyright &y& Elsevier]

Abstract: Thirty-eight new cosmogenic (10Be) exposure ages from the Scoresby Sund region of east Greenland indicate that prominent moraine sets deposited by mountain glaciers date from 780 to 310yr, approximately during the Little Ice Age, from 11 660 to 10 630yr, at the end of the Younger Dryas cold interval or during Preboreal time, and from 13 010 to 11 630yr, during lateglacial time. Equilibrium line altitudes (ELAs) interpreted from lateglacial to Early Holocene moraines indicate summertime cooling between ∼3.9 and 6.6°C relative to today''s value, much less than the extreme Younger Dryas cooling registered by Greenland ice cores (mean-annual temperatures of ∼15°C colder than today''s value). This apparent discrepancy between paleotemperature records supports the contention that Younger Dryas cooling was primarily a wintertime phenomenon. 10Be ages of lateglacial and Holocene moraines show that mountain glaciers during the Little Ice Age were more extensive than at any other time since the Early Holocene Epoch. In addition, 10Be ages of lateglacial moraines show extensive reworking of boulders with cosmogenic nuclides inherited from prior periods of exposure, consistent with our geomorphic observations and cosmogenic-exposure dating studies in other Arctic regions. [Copyright &y& Elsevier]

Much of Greenland experienced summers warmer than present in parts of the early to middle Holocene, during a precession-driven positive anomaly in summer insolation. However, the magnitude of that warmth remains poorly known, and its timing and spatial pattern are uncertain. Here we describe the first quantitative Holocene palaeotemperature reconstruction from central East Greenland based upon insect (chironomid) assemblages preserved in lake sediments. We postulate that landscapes like our study site, characterized by minimal soil and vegetation development through the Holocene and thus little influenced by some important secondary gradients, are especially well suited to the use of chironomids to reconstruct Holocene temperatures. The inferred timing of warmth at our study site near Scoresby Sund agrees well with other nearby evidence, including glacial geological reconstructions and temperatures inferred from precipitation isotopes at Renland ice cap, supporting the use of chironomids to reconstruct temperatures at this site. We infer highest temperatures from c. 10 to 5.5 ka, followed by gradual cooling after 5.5 ka and progressively colder and less productive conditions after 3.5 ka. Models based upon two independent training sets yield similar inferred temperature trends, and suggest an average summer temperature anomaly from c. 10 to 5.5 ka of 3 to 4 °C relative to the preindustrial last millennium. The estimated overall rate of Neoglacial cooling averaged over the period from 5.5 to 0.5 ka was 0.6 to 0.8 °C per thousand years, more than twice the rate previously estimated for the Arctic as a whole. Given strong apparent spatial variability in Holocene climate around the Arctic, and the utility of palaeoclimate data for improving climate and ice-sheet models, it should be a priority to further quantify past temperature changes around the margins of the Greenland Ice Sheet, where few quantitative reconstructions exist and future warming will affect global sea level. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called “local ice caps”) are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ∼11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ∼AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two polar hemispheres. [Copyright &y& Elsevier]

Shrinking glaciers, melting permafrost, and reduced sea ice all indicate rapid contraction of the Arctic cryosphere in response to present-day climate warming, a trajectory that is expected to continue, if not accelerate. The reaction of the Arctic cryosphere to past periods of climate variation can afford insight into its present and future behavior. Here, we examine a ∼12,000 year record of glacier fluctuations and meltwater variation associated with the Renland Ice Cap, East Greenland, that extends from the early Holocene thermal optimum through the cooling of the Little Ice Age to present. Sediment records from glacially fed lakes indicate rapid early Holocene deglaciation, with ice extent likely slightly smaller than at present by ∼9500 yr BP. Glacial activity resulted in occasional deposition of rock flour in the studied lakes in the early Holocene until at least ∼7500 yr BP. Rock flour is absent for much of the period ∼7000-4000 yr BP, suggesting ice extent generally was smaller than at present. However, thin layers of blue-gray clay throughout this period may indicate millennial-scale ice expansions, with Renland Ice Cap briefly reaching extents during cold phases that may have been similar to today. Glacial sediment deposition occurred again in the late Holocene at ∼3200–3400 yr BP and was followed by a brief glacial episode at ∼1340 yr BP and then a major event beginning shortly after ∼1050 yr BP. We infer that rock flour deposition in the lakes in the last millennium corresponds with advance of Renland glaciers to their Little Ice Age positions, marked by a fresh, gray drift limit. Radiocarbon dates of in situ plant remains adjacent to the present ice cap indicate a short relatively warm period ∼500 yr ago, when ice was within its AD 2011 limit, followed by glacier readvance. The general pattern of ice fluctuations in Renland is similar to that at other ice caps in the region, but also has important differences, including the preservation of a possible mid-Holocene record at times when lower-elevation ice caps in the Scoresby Sund region may have been absent. This finding reinforces the concept that examination of multiple geographic and geomorphologic settings is necessary for a full understanding of ice variations in a region. • Sediments from glacially fed lakes constrain the Holocene history of Renland Ice Cap. • Ice extent was similar to or smaller than at present by ∼10,000 yr BP. • Millennial-scale glacier fluctuations occurred throughout the Holocene. • Examination of multiple geographic settings is necessary for a full understanding of ice variations in a region. [ABSTRACT FROM AUTHOR]

To put recent Greenland Ice Sheet (GrIS) ice loss into a longer-term context, we must understand its behavior during late-glacial and Early Holocene warming. Previous results seem to suggest that there is a large contrast in the timing of deglaciation between South and Southeast Greenland. However, because of lack of available data, in particular in Southeast Greenland, it is difficult to assess how the ice sheet responded to major late-glacial and Early Holocene climate changes. In this study, we use 41 new 10Be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in South and Southeast Greenland. We find that South Greenland (south of 61.5°N) deglaciated between ∼14.8 and 11.9 ka, whereas Southeast Greenland (61.5°N to 68.2°N) deglaciated between ∼11.4 and 11.3 ka. The deglaciation of the coastal, low-intermediate topography in South Greenland coincides with increased air surface temperatures during the Bølling-Allerød with fjords continuing to deglaciate into the Early Holocene. In contrast, the ice sheet persisted at the coast until the late-glacial and Early Holocene in Southeast Greenland, likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry (e.g. width of fjords and presence of sills). This multi-phased deglaciation demonstrates a contrasting response of the southern GrIS to changes in climate and variations in topographic setting, and that the spatial deglaciation of the GrIS was complex and likely did not respond to a single external climate forcing. • Deglaciation began in South Greenland by 14.8 ka coeval with rising air temperature. • Warm Atlantic water likely drove deglaciation during the Younger Dryas. • Ice retreated from Southeast Greenland coast by 11.3 ka when air temperatures rose. • Evidence of a Neoglacial advance occurs in Southeast Greenland by ∼1.9 ka. • Local climate, topography and fjord geometry/bathymetry likely mediated ice retreat. [ABSTRACT FROM AUTHOR]