HR: 16:45h
AN: PP54A-04 INVITED     [Abstracts]
TI: Rapid North Atlantic Salinity Oscillations Across Dansgaard-Oeschger Transitions
AU: * Schmidt, M W
EM: schmidt@geology.ucdavis.edu
AF: University of California Davis, Department of Geology One Shields Avenue, Davis, CA 95616 United States
AU: Spero, H J
EM: spero@geology.ucdavis.edu
AF: University of California Davis, Department of Geology One Shields Avenue, Davis, CA 95616 United States
AU: Vautravers, M J
EM: mv217@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Godwin Institute for Quaternary Research Department of Earth Sciences, Cambridge, CB3 2SA United Kingdom
AB: Paleoclimate archives indicate that Marine Isotope Stage 3 (MIS 3) was characterized by a highly variable climate, expressed in the Greenland ice cores by Dansgaard-Oeschger (D-O) cycles associated with large atmospheric and oceanic temperature changes. However, the question remains as to the trigger for these abrupt Northern Hemisphere climate swings. A popular theory implicates North Atlantic meridional overturning circulation (MOC) instability as a driver for D-O cycles, suggesting that changes in North Atlantic surface water salinity played a significant role in triggering and driving millennial-scale oscillations in glacial MOC (Broecker et al., 1990; Zaucker and Broecker, 1992). In order to investigate the relationship between subtropical North Atlantic gyre surface salinity variation and D-O cycles, we combine Mg/Ca measurements (a proxy for the temperature of calcification) with δ¹⁸O analyses of shells from the surface-dwelling foraminifera Globigerinoides ruber (white var.) from ODP site 1060 located beneath the Gulf Stream on the Blake Outer Ridge (36.77°N, 74.47°W; 3480 m; 20-53 cm/kyr sed. rate) to produce a sub-millennial scale record of δ¹⁸O_SEAWATER (a proxy for surface salinity) during MIS 3 (45.9 - 59.2 kyr, Interstadials 12 through 16 on the SSO9sea time scale). The calculated δ¹⁸O_SW record co-varies with the Greenland ice core δ¹⁸O record (Johnsen et al., 2001), suggesting abrupt salinity increases at the initiation of each cold stadial event followed by rapid returns to fresher interstadial conditions. Enriched stadial δ¹⁸O_SW values average 2.3‰ and interstadial δ¹⁸O_SW values average between 1.7 and 1.9‰. These punctuated centennial-scale salinity shifts are followed by relatively stable δ¹⁸O_SW, suggesting gyre salinity may have remained relatively constant during interstadials and stadials rather than gradually decreasing (or increasing) prior to climatic transitions as was previously proposed. We hypothesize that rather than serving as a trigger, elevated gyre stadial salinities played a critical role in maintaining elevated North Atlantic surface-water density by offsetting the influence of increased freshwater flux from melting ice during interstadial transitions. If correct, the trigger for D-O transitions remains to be determined.
DE: 4271 Physical and chemical properties of seawater
DE: 4825 Geochemistry
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4904 Atmospheric transport and circulation
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005