HR: 1340h
AN: PP13B-1265    [Abstracts]
TI: The Evolution of Surface and Deep Water Circulation in the Northern North Atlantic Over the Last 21,000 Years.
AU: * Thornalley, D J
EM: djrt2@cam.ac.uk
AF: The Godwin Laboratory for Palaeoclimate Research Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: McCave, N
EM: mccave@esc.cam.ac.uk
AF: The Godwin Laboratory for Palaeoclimate Research Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Elderfield, H
EM: he101@esc.cam.ac.uk
AF: The Godwin Laboratory for Palaeoclimate Research Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AB: The northern North Atlantic is a critical location in the Atlantic Meridional Overturning Circulation (AMOC) where inflowing surface waters are converted into a deep water return flow. Foraminiferal stable isotope and Mg/Ca measuremnents from four sediment cores between 1237 m and 2303 m water depth on the South Iceland Rise document the changes in these water-masses through the deglaciation and Holocene. The evolution from the glacial mode of circulation to the present regime is punctuated by two periods with low benthic δ¹³C and δ¹⁸O values which do not lie on glacial or Holocene mixing lines. These periods correlate to the Younger Dryas (11.5-12.7 ka) and Heinrich Event 1 (16.8-14.5 ka) during which time meltwater input to the Nordic Seas and sea-ice formation led to brine rejection and export as an overflow into the northern North Atlantic. Planktonic paired δ¹⁸O – Mg/Ca measurements indicate that these periods of brine export are also accompanied by an increased influence of the inflowing, warm and saline, surface North Atlantic Current. Holocene circulation shows considerable variability, most notably periods of surface stratification and Polar Front advance, which show a 1500 year cyclicity and correlate to published records of drift ice and deepwater flow speed. The data presented provide evidence for the role of deepwater brine export and consequent surface inflow to the Nordic Seas in resuming overturning following meltwater inputs. The illustrated export of brine with low δ¹³C values from the Nordic Seas complicates traditional interpretations of low δ¹³C values during the deglaciation as incursions of Southern Source Water although the spatial extent of this brine is uncertain.
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting