Seismic stratigraphy records the deglacial history of Jakobshavn Isbræ, West Greenland

Abstract

Jakobshavn Isbrae is one of the largest ice streams in the Greenland Ice Sheet, presently draining c. 6.5% of the Inland Ice. Here we present high-resolution Chirp and Sparker sub-bottom profiles from a seismic survey conducted just outside of the Jakobshavn Isfjord, which provides detailed insight into the glacimarine sedimentary history of the Jakobshavn ice stream during the Holocene. We observe acoustically stratified and homogeneous sediments that drape an irregular substratum and were deposited between $10 and c. 7.6k cal a BP. The stratified lower units are interpreted as the product of ice-proximal glacimarine sedimentation deposited rapidly when the grounded ice margin was located close to depositional basins on topographic highs. The upper acoustically homogenous units reflect suspension settling of fine-grained material and gravitational flows that were extruded from an increasingly unstable ice margin as the ice retreated into the fjord. Proximity to the ice margin and bedrock topography were the dominant controls on sediment accumulation during deglaciation although the 8.2-ka cooling event probably influenced the position of the ice margin at the fjord mouth. The post-glacial sedimentary record is characterized by glacimarine and hemipelagic rainout with an increased ice-rafted detritus fraction that records sedimentation following ice stream retreat into Jakobshavn Isfjord sometime after c. 7.8k cal a BP.

The role of the cryosphere in source-to-sink systems

“…In contrast, in West Greenland, marine records of LGM-Holocene glacigenic sediment fluxes in the fjords and on the shelf are relatively few, but recent field data have added substantial information about ice dynamics in this region (Roksandic, 1979;Kuijpers et al, 2007;Hogan et al, 2011;Schumann et al, 2012;Dowdeswell et al, 2014;Hogan et al, 2012;Cofaigh et al, 2013). During the LGM, ice streams from western Greenland extended to the shelf edge through Uummannaq and Disko troughs, and retreated episodically after 14.8 kya (Cofaigh et al, 2013;Dowdeswell et al, 2014).…”

Sedimentary evidence for a mid-Holocene iceberg-generated tsunami in a coastal lake, west Greenland

“…2). But icebergs are not the only source of tsunami that may impact Greenland and other polar regions, where two other processes can also be important: those associated with terrestrial landslides that terminate in the sea, and far-field tsunamis that are generated by an earthquake or submarine landslide, for instance the early-Holocene Storegga slide tsunami that originated from offshore of Norway and which impacted Norway, Scotland, northeast England, as well as east Greenland [16,28,58].…”

“…These icebergs travel 45 km along the Isfjord and must then cross into Disko Bugt via the Isfjeldsbanken (Fig. 1), a shallow bank (50-300 m water depth) that forms a significant topographical barrier to the large icebergs [28]. The depth of the wider Disko Bugt varies between 200 and 400 m ( [9,13], defining an upper limit to iceberg size in coastal water of Disko Bugt.…”

Seafloor geomorphology and glacimarine sedimentation associated with fast-flowing ice sheet outlet glaciers in Disko Bay, West Greenland

“…Ottesen & Dowdeswell, 2006;Ottesen 243 et al, 2008;Hogan et al, 2011;Flink et al, 2015;Streuff et al, 2015), and the 244 sub-bottom profiler data show that the majority of the topographically distinct 245 highs are formed in bedrock (e.g. Fig.…”

“…Bay, and (2) the sill traps larger icebergs inside the fjord due to the shallow 469 water depth (Echelmeyer et al, 1991;Hogan et al, 2011 1982; Boulton, 1990;Sexton et al, 1992). Indeed, the ice margin is thought to The stratified fine-grained mud in lithofacies LD3 is interpreted as glacima-564 rine mud from meltwater, with the sand laminae deposited from down-slope 565 gravity flows, e.g.…”