NOAA/WDS Paleoclimatology - Late glacial to Holocene sortable silt records from the southwestern Labrador Sea

The Labrador Sea is a vital region for the Atlantic Meridional Overturning Circulation (AMOC), where overflow waters from the Nordic Seas mix with locally produced Labrador Sea Water, before exiting to the interior of the Atlantic Ocean. The dynamical sedimentary proxy of mean sortable silt size (SS) can give information on past changes in deep water circulation speed and the strength of AMOC. We have produced (SS) records from two core sites at depths between 1500 and 2000 m on the continental slope east of Newfoundland, to reconstruct changes in intermediate depth water circulation speed, including Glacial North Atlantic Intermediate Water and Labrador Sea Water over the past 22,000 years. Increases in (SS) appear to coincide with much of the deglaciation as well as the mid-late Holocene. End-member modeling suggests that ice-rafted debris (IRD) is an important factor in interpreting (SS) during the deglaciation. We find that a robust increase in (SS) is likely unrelated to IRD during the past 5 ka, and probably reflects increased flow at intermediate depths due to local production of LSW strengthening as Nordic Seas overflows weakened at this depth. Our results highlight both the complications of producing (SS) records in IRD-rich, slope environments and the promise that this proxy nevertheless has for reconstructing dynamical changes in deep ocean currents.