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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. [ABSTRACT FROM AUTHOR]

Trough mouth fans (TMF) situated at the mouths of formerly glaciated cross-shelf troughs are important paleoclimatic archives. Whereas the sedimentary processes of large, low-gradient TMFs have received considerable interest, little attention has been paid to the other end member of this landform class, i.e. TMFs with higher slope gradients. Detailed swath-bathymetric data and seismic profiles from the continental margin offshore Troms, northern Norway cover three high-gradient TMFs (the Andfjorden, Malangsdjupet and Rebbenesdjupet TMFs; slope gradients generally between 1° and 15°), as well as inter-fan areas, which include two submarine canyons (the Andøya and Senja Canyon) and the Malangsgrunnen inter-fan slope. The present-day morphologies of the Andfjorden and Malangsdjupet TMFs have evolved from sediment transport and distribution through gully-channel complexes. The Andfjorden TMF has later been affected by a large submarine landslide that remobilized much of these complexes. The Rebbenesdjupet TMF is dominated by a number of small and relatively shallow slide scars, which are inferred to be related to small-scale sediment failure of glaciomarine and/or contouritic sediments. The canyons cut into the adjacent TMFs, and turbidity currents originating on the fans widened and deepened the canyons during downslope flow. The Malangsgrunnen shelf break and inter-fan slope acted as a funnel for turbidity currents originating on the upper slope, forming a dendritic pattern of gullies. A conceptual model for the high-gradient TMFs on the Troms margin has been compiled. The main sediment input onto the TMFs has occurred during peak glacials when the Fennoscandian Ice Sheet reached the shelf edge. The overall convex fan form and progradational seismic facies show that these glacigenic deposits were repeatedly distributed onto the fan. On the Andfjorden and Malangsdjupet TMFs, gully-channel complexes occur within such deposits. It is thus inferred that the steep slope of these TMFs promoted rapid transformation from small-scale slumps and debris flows on the upper slope, into partly erosive turbidity currents. These flows continued into the deep sea, thus promoting efficient sediment by-pass across the TMFs. This model can be applied to other TMFs situated at the mouths of other glaciated cross-shelf troughs. In contrast, low-gradient TMFs are found to be dominated by glacigenic debris flow deposits. Furthermore, gully-channel complexes demonstrating the presence of erosive turbidity currents on high-gradient TMFs are rare on low-gradient TMFs. Large submarine landslides occur at both high- and low-gradient TMFs. [ABSTRACT FROM AUTHOR]

The interplay between the onshore and offshore areas during the Last Glacial Maximum and the deglaciation of the Scandinavian Ice Sheet is poorly known. In this paper we present new results on the glacial morphology, stratigraphy and chronology of Andøya, and the glacial morphology of the nearby continental shelf off Lofoten-Vesterålen. The results were used to develop a new model for the timing and extent of the Scandinavian Ice Sheet in the study area during the local last glacial maximum ( LLGM) (26 to 16 cal. ka BP). We subdivided the LLGM in this area into five glacial events: before 24, c. 23 to 22.2, 22.2 to c. 18.6, 18 to 17.5, and 16.9-16.3 cal. ka BP. The extent of the Scandinavian Ice Sheet during these various events was reconstructed for the shelf areas off Lofoten, Vesterålen and Troms. Icecaps survived in coastal areas of Vesterålen-Lofoten after the shelf was deglaciated and off Andøya ice flowed landwards from the shelf. During the LLGM the relative sea level was stable until 18.5 cal. ka BP, and thereafter there was a sea-level drop on Andøya. Thus, relative sea level (i.e. a sea level rise) does not seem to be a driving mechanism for ice-margin retreat in this area but the fall in sea level may have had some importance for the grounding episodes on the banks during deglaciation. The positions of the grounding zone wedges ( GZWs) in the troughs are related to the morphology as they are often located where the troughs narrow. [ABSTRACT FROM AUTHOR]

Today the Arctic is undergoing far-reaching changes with rising air and sea-water temperatures, and rapidly decreasing glaciers and ice sheets. In order to model future changes of the ice sheet-ocean-atmosphere climate system, it is urgent to obtain more knowledge on the glacier dynamics of the Greenland Ice Sheet. Very little is known about the past evolution of the eastern sector of this ice sheet, e.g. it has not been established where its maximum position was during the Last Glacial Maximum (LGM). Furthermore, neither ice dynamics, sediment production by subglacial erosion or timing and nature of ice recession from the shelf is established. In this study, we have investigated the outermost part of the northeastern Greenland continental shelf. This is the widest shelf surrounding Greenland, with a shelf edge located more than 200 km off the coastline. Here, the shelf morphology comprises two large troughs (Norske Trough and the Westwind Trough) separated by a shallow bank complex (Belgica Bank, Northwind Shoal and the AWI Bank). Previous studies differ strongly on where this sector of the Greenland Ice Sheet reached its maximum position during the LGM. The studies point to positions from the inner shelf, mid-shelf or the shelf edge with the largest uncertainty related to the area of the shallow bank complex. During favorable sea-ice conditions in 2017, a ~130 km2 area on the outermost part of the shelf was surveyed by multi-beam echo-sounder and a sub-bottom profiler (Chirp). Close to the shelf break, the data displays part of a shelf-break parallel ridge that is heavily scoured by icebergs. The ridge is c. 30 m high, up to 9 km wide and with a steep western (proximal) and a gentler eastern (distal) slope. Compared to the recessional moraines reported from elsewhere in this area (Arndt et al., 2017), this feature is wider and higher, and its shape resembles a grounding-zone wedge identified in the nearby Norske Trough. Thus, we tentatively suggest that the observed ridge is also a grounding zone wedge formed at the grounding line of an ice sheet or ice cap reaching the outermost shelf. Part of a second ridge is seen approx. 10 km west of (inside) this ridge, implying a dynamic ice front with several halts or readvances during the retreat from the outer shelf. The age of these features remains to be determined, and this will be part of the future analysis of the sediment cores obtained in the study area. [ABSTRACT FROM AUTHOR]

With the decay of marine-based ice sheets observed today, e.g. in Antarctica and Greenland, there is a pressing need also for an improved understanding of marine paleo-ice sheets and their decay, as they provide critical constraints for a better understanding of the dynamics of modern ice sheets and their future behavior.Here we present new multi-beam swath-bathymetry and high-resolution Topas seismic data from the NW Barents Sea acquired during the Nansen Legacy (https://arvenetternansen.com/) Paleo-cruise in 2018, which provide new insights on the deglaciation history of the marine based Svalbard-Barents Sea Ice Sheet. Previous multi-beam data from the straits and troughs east of the Svalbard archipelago provided unclear or even conflicting evidence of full-glacial flow; i) eastwards, through the Erik Eriksen Strait and its eastward continuation, terminating in the Franz Victoria Trough, and ii) northwards through the Kvitøya Trough (Dowdeswell et al., 2010; Hogan et al., 2010).The new data provide evidence of a dynamic ice-sheet retreat during the deglaciation of the Erik Eriksen Strait and its eastern extension. A succession of superposing transverse ridges with a zig-zag like morphology characterize the eastern part of the mapped area. These ridges are interpreted to be recessional push-moraines, resulting from several smaller re-advances of the ice front during overall retreat through this part of the strait. To the west, ridges are buried by a ~40 m high and 20 km long sedimentary wedge, characterized by a smooth surface. The internal seismic configuration of the wedge is transparent. This sediment accumulation is interpreted to be a grounding zone wedge that likely formed during a major eastward oriented re-advance of the Svalbard-Barents Sea Ice Sheet during the deglaciation, burying some of the older recessional push-moraines. Thus, the eastward flow previously identified may be due to a major re-advance during the deglaciation rather than formed during full-glacial conditions.A ~3 msec thick layer of acoustically transparent sediments covering the grounding zone wedge and the recessional push-moraines, has been ground-truthed by gravity cores, both in front (east) of, and on top of the wedge. Radiocarbon dating will provide a minimum age for the formation of the glacial landforms, and thus add to our knowledge on the timing and dynamics of the retreat of this marine-based sector of the Svalbard-Barents Sea Ice Sheet following the Last Glacial Maximum, and this will enable improved modelling of this marine-based ice sheet.References:Dowdeswell, J.A., Hogan, K.A., Evans, J., Noormets, R., Ó Cofaigh, C., and Ottesen, D. (2010). Past ice-sheet flow east of Svalbard inferred from streamlined subglacial landforms. Geology, 38(2), 163-166.Hogan, K.A., Dowdeswell, J.A., Noormets, R., Evans, J., Cofaigh, C.Ó., and Jakobsson, M. (2010). Submarine landforms and ice-sheet flow in the Kvitøya Trough, northwestern Barents Sea. Quaternary Science Reviews, 29(25), 3545-3562. [ABSTRACT FROM AUTHOR]