HR: 14:55h
AN: PP33C-06    [Abstracts]
TI: Linking Atmospheric and Ocean Circulation Change Across the Last Glacial Termination
AU: * Schmidt, M W
EM: mschmidt@eas.gatech.edu
AF: Texas A&M University, Department of Oceanography 3146 TAMU, College Station, TX 77843-3146, United States
AU: Lynch-Stieglitz, J
EM: jean@eas.gatech.edu
AF: Georgia Institute of Technology, School of Earth and Atmospheric Sciences 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AB: In order to determine the relative timing between atmospheric vs. ocean circulation changes in the North Atlantic across last glacial termination, we generated proxy records for sea surface salinity (SSS) and ocean circulation change in the same low latitude North Atlantic sediment cores for the last 20 kyr. By combining Mg/Ca- paleothermometry with δ¹⁸O analyses of shells from the surface-dwelling foraminifera Globigerinoides ruber in Florida Straits cores KNR166-2-JPC29 (24°17'N, 83°16'W; 648 m; 9-19 cm/kyr sed. rate) and JPC26 (24°19.61'N, 83°15.14'W; 546 m depth; 18-240 cm/kyr sed. rate) we generated a record of δ¹⁸O_SEAWATER (δ¹⁸O_SW) change. After removing the δ¹⁸O_SW signal due to continental ice volume variation (Fairbanks et al., 1992), the resulting ice volume-free δ¹⁸O_SW record (a proxy for SSS variability due to regional hydrological change) shows that regional δ¹⁸O_SW values increased by more than 0.6‰ during Heinrich Event 1 (H1) and the Younger Dryas (YD) and returned to modern values (about 1.0‰) during the Bolling Allerod and at the end of the YD. Based on the modern tropical Atlantic δ¹⁸O_SW:SSS relationship, δ¹⁸O_SW=0.26*SSS-8.44, a 0.6‰ enrichment in δ¹⁸O_SW equates to a 2.3 increase in SSS. In comparison, benthic Cibicidoides pachyderma δ¹⁸O values in the same cores decrease during the YD and H1, suggesting an intermediate-depth warming on the western margin of the Florida Straits. Benthic δ¹⁸O values on the eastern margin of the Florida Straits do not show a coeval warming, indicating that the cross-current density gradient was relaxed in response to reduced geostrophic transport through the Florida Straits. The abrupt benthic δ¹⁸O decrease at the start of the YD is synchronous with an increase in ice volume-free G. ruber δ¹⁸O values and with calculated ice volume-free δ¹⁸O_SW values, suggesting the rapid development of increased regional SSS in less than 100 years. Such a rapid change suggests that an atmospheric, rather than an oceanic mechanism is responsible for the increase in regional SSS at the start of the YD. On the transition out of the YD, benthic δ¹⁸O values in JPC 26 suggest a somewhat gradual increase in Florida Current transport from 12 to 11.4 kyr. In comparison, the corresponding ice volume-free G. ruber δ¹⁸O values also begin to return to pre- YD values around 12 kyr, but complete the transition before benthic δ¹⁸O values, suggesting atmospheric circulation returned to a pattern characteristic of the early Holocene before meridional overturning circulation fully recovered.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1655 Water cycles (1836)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting