Abrupt Climate Change in the Atlantic Ocean During the Last 20,000 Years: Insights from Multi-Element Analyses of Benthic and Planktic Foraminifera and a Coupled OA-GCM

摘要

Minor and trace element records from planktic and benthic foraminifera from Atlantic sediment cores, as well as output from 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 OA-GCM 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 Al/Ca in foraminiferal samples using inductively- coupled plasma mass spectrometry. Paired records of planktic foraminiferal deltaO18 and Mg/Ca from the subpolar North Atlantic reveal trends of increasing temperatures (-3 deg C) and salinities over the course of the Holocene. The records provide the first evidence of open-ocean cooling (nearly 2 deg C) and freshening during the 8.2 kyr event, and suggest similar conditions at 9.3ka. Benthic foraminiferal Cd/Ca results from an intermediate depth, western South Atlantic core (1,268m) are consistent with reduced export into the S. Atlantic of N. Atlantic Intermediate Water during the Younger Dryas. Paired records of benthic foraminiferal Mg/Ca and deltaO18 from two intermediate depth low latitude western Atlantic sites-one from the Florida Current (751m) and one from the Little Bahama Bank (1,057m)-provide insights into the spatial distribution of intermediate depth temperature and salinity 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/amplifier of climate var.