Abrupt climate change in the Atlantic Ocean during the last 20,000 years : insights from multi-element analysis of benthic and planktic foraminifera and a coupled OA-GCM
Came, Rosemarie E.
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Little Bahama Bank
Minor and trace element records from planktic and benthic foraminifera from Atlantic sediment cores, as well as outputfrom a coupled OA·GCM, were used to investigate the magnitude and distribution of the oceanic response to abrupt Climate events.of the past 20,000 years. The study addressed three major questions: 1) What is the magnitude of high-latitude sea surface temperature and salinity variability during abrupt climate events? 2) Does intermediate depth ventilation change in conjunction with high-latitude climate variability? 3) Are the paleoclimate data consistent with the response of a coupled OAGCM to a freshwater perturbation? To address these questions, analytical methods were implemented for the simultaneous measurement of Mg/Ca, Zn/Ca, Cd/Ca, Mn/Ca and All Ca in foraminiferal samples using inductively-coupled plasma mass spectrometry. Paired records of planktic foraminiferal ()IRO and Mg/Ca from the subpolar North Atlantic reveal trends of increasing temperatures (-3°C) and salinities over the course of the Holocene. The records provide the first evidence of open':'ocean cooling (nearly 2°C) and freshening during the 8.2 kyr event, and suggest similar conditions at 9.3 ka. Benthic foraminiferal Cd/Ca results from an intermediate depth, western South Atlantic core (l,268 ni) are consistent with reduced export into the South Atlantic of North Atlantic Intermediate Water during the Younger Dryas. Paired records. of benthic foraminiferal Mg/Ca and bIRO from two intermediate depth low latitude western Atlantic sites - one from the Florida Current (751 m) and one from the Little Bahama Bank (l,057 m) - provicie insights into the spatial distribution of intermediate depth temperature and sii!.inity variability during" the Younger Dryas. The intermediate depth paleoceanographic temperature and salinity data are consistent with the results of a GFDL R30 freshwater forced model simulation, suggesting that freshwater forcing is a possible driver or amplifier for B011ing-Aller0d to Younger Dryas climate variability. Benthic foraminiferal Cd/Ca results from an intermediate depth Florida Current core (751 m) are consistent with a decrease in the northward penetration of southern source waters within the return flow of the Atlantic meridional overturning circulation (MOC) and an increase in the influence of intermediate depth northern source waters during the Younger Dryas.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 2005
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