PP42B-07
Pronounced Weakening of Deep Components of the AMOC During the Late Holocene Caused by Export of Arctic Sea-Ice and Freshwater

Thursday, 17 December 2015: 11:50
2012 (Moscone West)
David J Thornalley1,2, Delia Oppo2, Paola Moffa-Sanchez3, Ian R Hall4, Lloyd D Keigwin2 and I.N. Nicholas McCave5, (1)University College London, London, United Kingdom, (2)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)Rutgers University, Department of Marine and Coastal Sciences, Piscataway, NJ, United States, (4)Cardiff University, Cardiff, United Kingdom, (5)University of Cambridge, Cambridge, United Kingdom
Abstract:
Several proxy and modelling studies suggest that there may have been considerable change in the operation of the Atlantic Meridional Overturning Circulation (AMOC) during the last millennium. Yet despite its importance for regional and global climate, the recent history of the AMOC is poorly constrained, and comprehensive observational records only extend back a few decades at most. Observational data suggest that the export of large volumes of sea-ice and freshwater from the Arctic during the Great Salinity Anomaly of the late 1960s to early 1970s impacted North Atlantic circulation, and perhaps the strength of the AMOC, thus raising the possibility that more extreme events may have affected the AMOC during the pre-instrumental era.

Firstly, we place the last millennium in a longer-term context by presenting Holocene grain-size records in depth transects from Blake Outer Ridge and Cape Hatteras, sampling the full-depth range of the Deep Western Boundary Current (DWBC), part of the lower limb of the AMOC. These records complement a depth-transect of grain-size records sampling the Iceland-Scotland (I-S) overflow, and together enable us to provide a synthesis of Holocene changes in the deep components of the AMOC and the impact on the AMOC of long-term variability in the export of Arctic sea-ice and freshwater.

We then present detailed grain-size records for the last 1,000 years, both in a depth transect of cores off Cape Hatteras, and from cores in the Iceland Basin, sampling the I-S overflow. Initial results suggest a pronounced reduction over the last ~100-200 years in the inferred flow strength at sites bathed by Labrador Sea Water (LSW), while sites south of Iceland show an exceptional weakening of the I-S overflow over the last ~300 years. We explore the possibility that these events are linked to the export of large volumes of sea-ice and freshwater from the Arctic during the end of the Little Ice Age.

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