Abstract
Abstract. The presence of a grounded Greenland Ice Sheet on the northeastern part of the Greenland continental shelf during the Last Glacial Maximum is supported by new swath bathymetry and high-resolution seismic data, supplemented with multi-proxy analyses of sediment gravity cores from Store Koldewey Trough. Subglacial till fills the trough, with an overlying drape of maximum 2.5 m thick glacier-proximal and glacier-distal sediment. The presence of mega-scale glacial lineations and a grounding zone wedge in the outer part of the trough, comprising subglacial till, provides evidence of the expansion of fast-flowing, grounded ice, probably originating from the area presently covered with the Storstrømmen ice stream and thereby previously flowing across Store Koldewey Island and Germania Land. Grounding zone wedges and recessional moraines provide evidence that multiple halts and/or readvances interrupted the deglaciation. The formation of the grounding zone wedges is estimated to be at least 130 years, while distances between the recessional moraines indicate that the grounding line locally retreated between 80 and 400 m yr−1 during the deglaciation, assuming that the moraines formed annually. The complex geomorphology in Store Koldewey Trough is attributed to the trough shallowing and narrowing towards the coast. At a late stage of the deglaciation, the ice stream flowed around the topography on Store Koldewey Island and Germania Land, terminating the sediment input from this sector of the Greenland Ice Sheet to Store Koldewey Trough.
Highlights
The Greenland Ice Sheet (GrIS) is the second largest ice sheet on Earth storing 2.9 million cubic kilometers of ice (AMAP, 2009)
Based on the diamictic composition of these deposits, the high amounts of clasts, absence of bioturbation and a considerable consolidation of the sediments, we suggest that the facies represents diamictic subglacial debris/basal till deposited at the base of an ice stream from the GrIS
Gether with subglacial debris/basal till in sediment cores from the middle trough, suggest that a grounded, fast-flowing ice stream draining the northeastern sector of the GrIS extended to the shelf break in Store Koldewey Trough at maximum ice extent during the last glacial (Fig. 8a)
Summary
The Greenland Ice Sheet (GrIS) is the second largest ice sheet on Earth storing 2.9 million cubic kilometers (km3) of ice (AMAP, 2009). A future warming global climate, which will be strong in the Arctic (Serreze and Francis, 2006), will possibly lead to a reduced seaice cover adjacent to the glacier termini and subsequent accelerated melting of the ice sheet in NE Greenland (Bendtsen et al, 2017). This could cause an instability and possibly irreversible loss of the GrIS, which has – together with the West Antarctic Ice Sheet (WAIS) – been identified as a tipping element in the Earth’s climate system (Lenton et al, 2008). A better understanding of the development of glaciers in response to past climate changes, e.g., from the Last Glacial Maximum (LGM; ca. 26.5–19 ka, Clark et al, 2009) towards the present, is needed to validate and improve numerical models focusing on present processes, as well as the future development of glaciers and ice sheets
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