Insolation and gacial meltwater influence on sea‐ice and circulation variability in the Northeastern Labrador Sea during the last glacial period

The variable amounts of ice rafted debris (IRD) and foraminifers in North Atlantic sediments are related to the abrupt, millennial-scale alteration from Greenland stadials to interstadials during the last glacial period and indicate past ice sheet instabilities, changes in sea-ice cover and productivity. In the Norwegian Sea, Greenland stadials were likely characterized by an extensive, near-perennial sea-ice cover whereas Greenland interstadials were seasonally ice-free. The variability in other areas, such as the Labrador Sea, remains, however, obscure. We therefore investigated deep-sea sediment core GS16-204-22CC retrieved south of Greenland. Using a multiproxy approach, we distinguish two sediment regimes and hence different environmental conditions between ca. 65 and 25 ka b2k. Regime 1 (similar to 65-49 ka b2k) is characterized by the dominance of planktic foraminifers in the sediments. During late MIS4 and early MIS3, the site was covered by near-perennial sea-ice with occasional periods of iceberg discharge. During the younger part of regime 1 the northeastern Labrador Sea was seasonally ice-free with hardly any icebergs melting near the site and long-term environmental conditions were less variable. Regime 2 (similar to 49-25 ka b2k) is characterized by pronounced stadial-interstadial variability of foraminifer and IRD fluxes, suggesting an extensive sea-ice cover during most Greenland stadials and seasonally ice-free conditions during most Greenland interstadials. During MIS2 environmental conditions were very similar to those of the younger part of regime 1. While all Heinrich (H) related Greenland stadials are marked by depleted oxygen isotope values at our core site, only H4 and H3 are associated with pronounced IRD peaks. Plain Language Summary North Atlantic sediments contain variable amounts of sand-sized mineral grains and microorganism shells. Mineral grains indicate iceberg transport from continental ice sheets, like the Greenland ice sheet (more icebergs/melting sea-ice, more grains). If the sea-ice cover is too thick, no light can penetrate and fewer microorganisms live in the water beneath the ice. Using these indicators, we investigated ocean sediments from south of Greenland covering the time period between ca. 65 and 25 thousand years ago. This time period was characterized by several abrupt changes between cold and warm climates on millennial timescales. We find that the ocean south of Greenland was sea-ice covered for most of the year with occasional time periods of iceberg discharge between 65 to 56 thousand years ago. From 56 to 49 thousand years ago the ice-free season was extended and hardly any icebergs melted near the site. From 49 thousand years ago our study area was covered by sea-ice year-round during cold time intervals whereas warm time intervals were only seasonally sea-ice covered. Continental ice sheets were growing during this time interval and we observed two major calving events related to two of the four very cold climate intervals recorded in the analyzed sediment.Fundacao de a Ciencia e a Tecnologia IF/01500/2014 UID/Multi/04326/2019