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Abstract: We use an ice marginal "threshold lake", Lower Nordbosø, in southern Greenland to record episodes when the southern Greenland Ice Sheet (sGIS) 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. The results show that the sedimentation was initiated at c. 10.6 cal ka BP when the ice margin had reached the present extent following the deglaciation. After this the ice margin remained close to the present extent until c. 6.9 cal ka BP when it retreated behind the threshold and first reappeared with a clear glacial signal at c. 3.0–2.8 cal. ka BP and from c. 0.5 cal ka BP until the present. An overall good correlation between clastic input into Lower Nordbosø and IRD events from Narsaq Sound suggests that they represent a general glacial proximity signal of the sGIS. Our data demonstrates that the sGIS behaved less vigorously to Holocene climate changes compared to previous reconstructions. The ice sheet only retreated behind the present ice extent from c. 6.9 to 3.0 cal ka BP and c. 2.8 to 0.5 cal ka BP in the mountainous southern Greenland, whereas the more sensitive low-lying Qassimiut lobe was behind its present margin from c. 9 ka until the Little Ice Age. Accordingly, the ice marginal behavior in southern Greenland is not only governed by climate changes but also strongly influenced by the local topographic setting. [Copyright &y& Elsevier]

The deglaciation of the Svalbard-Barents Sea Ice Sheet was driven by relative sea-level rise, the incursion of North Atlantic waters around Spitsbergen, and increasing summer insolation. However, ice retreat was interrupted by asynchronous re-advances that occurred into high relative seas, during a period associated with warm regional waters and elevated summer temperatures. Better understanding of this complex style of deglaciation and the dynamic response to a warming climate can serve as an important analogue for modern warming and today's ice sheets. We present evidence from northern Svalbard of glacier re-advances during the Late Glacial-Early Holocene in hand with relative sea-level history and the occurrence of thermophilous molluscs. We argue that glacio-isostatic adjustment during the transition into the Holocene influenced ice marginal dynamics and as a result, the southern region of the Åsgardfonna ice cap persisted through the Holocene Thermal Maximum. • Asynchronous tributary glacier re-advances during the transition from Late Glacial to Early Holocene. • Tidewater glacier margin survives Holocene Thermal Maximum alongside thermophilous molluscs. • Glacier sustenance aided by glacio-isostatic adjustment. [ABSTRACT FROM AUTHOR]

The possible demise of the Greenland ice sheet and its effect on global sea level rank among the most serious climate threats to society. To improve our knowledge about the future behaviour of the ice margin, we studied the ice sheet's response to early Holocene warming in West Greenland using 47 cosmogenic 10Be exposure ages, 26 optically-stimulated luminescence ages as well as 15 new and 28 previously published radiocarbon ages. Paired bedrock and boulder ages show that the entire area was covered by warm-based ice during the Last Glacial Maximum (LGM), although glacial erosion was insufficient to completely remove the upper rock surface containing 10Be inherited from a previous period of exposure in bedrock samples above an elevation of 800 m. Our compilation of 10Be and 14C ages demonstrates that the ice sheet retreated from the outer-coast to the present ice margin between c. 11.4 and 10.4 cal. ka BP in the Godthåbsfjord system and between 10.7 ± 0.6 and 10.1 ± 0.4 ka ago in Buksefjord, whereas the coast at Sermilik became ice free at c. 10.5 cal. ka BP. We find no significant changes in the retreat rates between the deep Godthåbsfjord system and the Buksefjord-Sermilik region, which is characterized by only a few narrow and shallow fjords. However, deglaciation was initiated c. 700–900 years earlier in the Godthåbsfjord system indicating that the deep fjords probably triggered land-based deglaciation by dynamic ice loss leading to an overall rapid early Holocene ice retreat and drawdown of the ice sheet in West Greenland. These results demonstrate that even if there was a topographic control on the onset of deglaciation, fast ice retreat is not restricted to deep fjord systems but may occur independently of the topographic setting. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the glacial stratigraphy and palaeoenvironmental evolution around Constable Bugt, Johannes V. Jensen Land, located on the north coast of Greenland. This is a land of extreme climate: polar desert conditions and a coast bound by a permanent sea ice cover. Our data covers the period from the Last Glacial Maximum (LGM, 18–22 cal ka BP) into the Holocene. It records the history of a shelf-based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the Holocene. With ice on the coastal plain during the LGM, glaciolacustrine basins formed in marginal positions and in ice-dammed valleys to the south into the mountainous area of Peary Land. With the break-up of shelf-based ice there was a gradual marine inundation at which the marine limit formed at ∼45 m a.s.l. This initial early Holocene ice advance from the south formed prominent valley mouth moraines, especially in Sifs valley. Here, both glaciolacustrine and marine sediments were remoulded and/or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and >60 m in height. Radiocarbon ages of sediments incorporated in this moraine, as well as from on-lapping sediments, suggest that the moraine formed between 9.6 and 6.3 cal ka BP. Based on 14C dating results, the youngest ice advance phase can be narrowed down to 14C ages between ∼5.5–5.0 cal ka BP. The recorded ice advances took place during the Holocene Thermal Maximum (HTM) for North Greenland, the last one close to the beginning of the Neoglacial cooling. During the HTM we have recorded a period of ∼2500 years during which the north coast of Greenland – as opposed to today – experienced an absence to very restricted occurrence of land-fast or multi-year sea ice. This observation can be explained by the altitudinal and temporal distribution of beach-ridge complexes that must have formed by wave action and thus requiring at least partial open-water conditions. With a moisture source at hand, we propose that this lead to enhanced precipitation in the near-coastal areas which, coupled to documented HTM cold reversals, caused a lowered glaciation limit, and led to a positive mass balance and subsequent ice advance. [Copyright &y& Elsevier]

Abstract: Contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments. This study concerns the ice-marginal environment of the surge-type Brúarjökull in Iceland. The sediment distribution in the glacier forefield as well as the morphology, sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment/landform associations. As a result of substrate/bedrock decoupling during the 1890 surge, subglacial sediment was dislocated across the bedrock surface and deformed compressively, leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone. A drop in subglacial porewater pressure at the very end of the surge led to substrate/bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate. Simultaneously, the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine-ridge construction. Fine-grained and incompetent sediment deformed in ductile manner, resulting in a narrow moraine dominated by rooted folds, while coarse-grained and competent sediment deformed in brittle fashion, resulting in a wider moraine dominated by thrust blocks. A new sequential model of subglacial and ice-marginal processes operating during a glacier surge is proposed, illustrating the stepwise formation of a marginal sediment wedge and an end moraine—a twofold, inseparable marginal end-product that formed during the last days of the 1890 surge. [Copyright &y& Elsevier]

The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100–80 ka), (3) the Middle Weichselian (60–50 ka) and (4) the Late Weichselian (25–15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic- and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90–80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60–50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the Eurasian Arctic during the Early and Middle Weichselian. One reason for this is that the climate in the Eurasian Arctic was not as dry then as during the Late Weichselian glacial maximum. [Copyright &y& Elsevier]

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]

Knowledge about the future response of the Greenland Ice Sheet to global climate change, including ice sheet contributions to sea level rise, is important for understanding the impact of climate change on society. Such studies rely in ice sheet model predictions and improved chronological constraints of past ice sheet extents and paleoclimatic trends. Many regions in Greenland are well studied, but northwest Greenland and especially Melville Bay, being one of the most important regions in terms of dynamical ice mass loss, lack a firm chronology of Holocene ice marginal fluctuations. In this study, we present the first comprehensive chronology for Melville Bay spanning 73.1–75.7°N based on 36 new 10Be exposure ages of boulders and 39 new radiocarbon ages of marine molluscs in Little Ice Age moraines. From weighted mean 10Be exposure ages, excluding 6 outliers, we find that the outer coast in Melville Bay was deglaciated ∼11.6 ± 0.3 ka (n = 15) and the ice margin reached its present-day position 40 km farther inland ∼11.5 ± 0.3 ka (n = 15). Our results suggest an interval of rapid ice-marginal retreat (i.e. collapse) of the northwest GrIS in Melville Bay, most likely triggered by rapidly rising atmospheric temperatures in early Holocene. Additionally, combining the comprehensive dataset of new radiocarbon ages with 26 radiocarbon ages from previous studies shows a restricted ice sheet extent from 9.1 ± 0.2 to 0.4 ± 0.1 cal ka BP, which coincides with increased sea surface temperatures. Our results highlight past ice sheet sensitivity towards climate changes in one of the least explored and most vulnerable regions of Greenland. Furthermore, comparing our new results to already existing ice sheet models (Huy3 and Huy3b) emphasize the proximal relevance of the Agassiz ice core temperature reconstruction for Melville Bay, which indicates the possible sensitivity of the ice sheet to a warming climate and place improved constraints on ice sheet simulations. • The northwest Greenland Ice Sheet was very sensitive to past climate changes. • The marine-based part of the ice sheet collapsed in Early Holocene. • The ice sheet was smaller than present throughout middle and late Holocene. • Rising atmospheric and sea surface temperatures drove deglaciation. • Ice sheet models do not fully capture this behaviour and improvements are needed. [ABSTRACT FROM AUTHOR]