Asymmetrical turbid surface-plume deposition near ice-outlets of the Pleistocene Laurentide ice sheet in the Labrador Sea

Abstract

Ice-sheet drainage of glacial detritus into the sea involves size fractionation by ice-margin winnowing on a giant scale caused by the lower density of meltwater entering cold seawater. Despite its load of suspended sediment, the fresh water rises to or stays at the sea surface forming turbid surface plumes, whereas the coarsegrained sediment forms bed load. On the Labrador Slope south of the Hudson Strait turbid plumes were supplied by meltwater from the Pleistocene ice sheet (LIS). Sediments with the seismic characteristics of plume deposits occur in a 200-km-long slope sector up to 130 km seawards from the strait. The widespread distribution of these deposits is attributed to entrainment of the surface plumes by the south-flowing Labrador Current and suppressed flocculation due to the high detrital carbonatecontent of the suspended sediment. Deposits with typical characteristics of surface plume deposits have been recovered within 20 km from former ice margin south of or in front of outlets, but not north of outlets. They consist of 1 to 2-cm-thick alternations of fine sandy silt/coarse silt layers with finer-grained clayey silt/silty clay, and for brevity are called plumites.

Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years

“…This initial phase of ice retreat may not be detectable in trough cores as this area was still covered by the ice stream. Meltwater sedimentation at the slope decreased with time while the glacial front retreated, and finally stopped at the time the calving line reached a critical distance for meltwater distribution (Hesse et al, 1997;Lucchi et al, 2002;Lucchi and Rebesco, 2007;Lucchi et al, 2013). From that time on, meltwater derived sediments settled on the continental shelf only.…”

A Laurentide outburst flooding event during the last interglacial period

“…Deposition of the red layer from surface plumes of suspended sediment is also unlikely, as both sites are several hundred kilometres from the mouth of the Hudson Strait, a likely conduit for material from Hudson Bay, and, in the case of Site U1305, upstream of the present-day surface water currents in the region 18 . Thus, the two sites studied are out of the range of direct plume deposition 19 , although we cannot totally discount some transport of fine particulate material by sea ice. Nevertheless, we propose that the most likely mode of transport and deposition was through turbidity currents along the sea floor.…”

Late quaternary ice-rafted detritus events in the Chukchi Basin, western Arctic Ocean

“…Silt-and clay-fractions are transported mainly by sea ice and sand-and coarser fractions are carried predominantly by icebergs [35,38]. In addition, the fine-grained sediments can be also from turbid surface plume or nepheloid layers [39,40]. In polar and subpolar environments, the density difference between glacial meltwater and seawater is more pronounced (about 20% greater) than that for fresh river water entering warmer seawater in lower latitudes.…”

“…In polar and subpolar environments, the density difference between glacial meltwater and seawater is more pronounced (about 20% greater) than that for fresh river water entering warmer seawater in lower latitudes. Accordingly, the finegrained sediments carried by glacial rivers are entrained in jets buoyantly rising to the sea surface, where they form turbid surface plume [40]. This is due to clay-rich fine-grained sediments tend to flocculate and form larger aggregates when they come in contact with seawater, and thus settle rapidly [41].…”