Sortable silt records of intermediate-depth circulation and sedimentation in the Southwest Labrador Sea since the Last Glacial Maximum

• Published in: Quaternary science reviews Vol. 206; pp. 99 - 110
• Main Authors: Hoffmann, Sharon S., Dalsing, Risa E., Murphy, Sarah C.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-02-2019
• Subjects: Holocene; Labrador Sea; Paleoceanography; Sedimentology-marine cores; Paleoceanography; Sedimentology-marine cores; Holocene; Labrador Sea
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/j.quascirev.2018.12.028

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 (LSW), 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.
•Robust increase in silt size at 5 ka reflects increased flow of Labrador Sea Water.•Ice-rafted debris likely affects SS¯ on the Labrador Slope during the last deglacial.•End member modeling and corrections provide insight into deglacial sediments.