HR: 16:15h
AN: PP44B-02    [Abstracts]
TI: Deepening of the mixed layer during ice-rafting events: implication for the Meridional Overturning Circulation
AU: Boyle, E A
EM: eaboyle@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139,
AU: * Rashid, H
EM: hrashid@marine.usf.edu
AF: University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701,
AU: * Rashid, H
EM: hrashid@marine.usf.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139,
AU: Goddard, E
EM: egoddard@marine.usf.edu
AF: University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701,
AU: Rodgers, B
EM: sregdorb@tampabay.rr.com
AF: University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701,
AB: Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated abrupt climate swings of a few decades to millennia, including Heinrich massive ice-rafting and Dansgaard-Oeschger ice- rafting events, which disrupted ocean circulation, resulting in severe cooling. In this study, we used sediment samples from cores CHN82-20 (43.31°N, 29.52°W; 3020 m wd) and Integrated Ocean Drilling Program Expedition 306 Site U1313 (41°N, 32.95°W; 3426 m wd) from the subtropical North Atlantic Ocean to document the impact of these events in the upper water masses. We have measured δ ¹⁸O in four planktonic foraminiferal taxa Globigerinoides ruber (white), Globigerina bulloides, and Neogloboquadrina pachyderma (dextral and sinistral) which dwell in the mixed-layer and thermocline waters. We found similar δ ¹⁸O values from mixed-layer and thermocline-dwelling planktonic foraminifera during Heinrich events and large amplitude ice-rafted detritus (IRD)-events in Marine Isotope Stage 12 suggesting the deepening of the mixed-layer. These data further suggest that the planktonic foraminiferal taxa calcified their shells at similar temperatures in a homogenized water column. Similar deepening of the upper water masses can be seen from the northern margin of the IRD-belt, implying that this homogenization of water masses was widespread in the North Atlantic. We suggest that an increase in storminess during Heinrich ice-rafting and large IRD-events intensify vertical mixing of meltwater from ice-rafting in the upper ocean.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting