HR: 0800h
AN: U31A-0011    [Abstracts]
TI: Warmer tropics during stage 11 - evidence from the Cariaco Basin
AU: * Lea, D W
EM: lea@geol.ucsb.edu
AF: University of California, Department of Geological Sciences, Santa Barbara, CA 93106 United States
AU: Peterson, L C
EM: peterson@rsmas.miami.edu
AF: RSMAS - University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AB: Marine Isotope Stage (MIS) 11 stands out as the most extreme interglacial episode of the last million years. But evidence for unusual warmth in the tropics at this time remains equivocal. A proxy SST record from the equatorial western Pacific (ODP 806B - Lea et al., 2000; Medina et al., this meeting) suggests that MIS 11 was the warmest time interval of the last million years. A key question that directly addresses the hypotheses proposed to explain MIS 11 is whether anomalously warm SSTs were a common feature of the tropics at this time. The Cariaco Basin, an anoxic marine basin on the northern shelf of Venezuela, preserves a unique high resolution climate record of the southeastern Caribbean/tropical Atlantic. This record is continuous through the last 580,000 years and includes multiple varved intervals. Records from this basin have been instrumental in establishing ties between tropical climate records and high latitude ice core and oceanic records. Paleothermometry based on planktic foraminiferal Mg/Ca works well in the Cariaco Basin because of the presence of a wide range of planktic species and superb preservation of carbonates, including pteropods. We have analyzed Mg/Ca in samples from ODP Hole 1002C (10ø42.73'N, 65ø10.18'W, 893ÿm water depth) that span MIS 11. Our preliminary results, covering the interval 402-409 ky BP, from surface dwelling Globigerinoides ruber yield Mg/Ca values of 4-5 mmol/mol, equivalent to SSTs of 26.5-28 degrees C. For comparison, Mg/Ca values in the Holocene range from 4-4.5 mmol/mol, equivalent to SSTs of 26-27.5. We are in the process of adding further results to evaluate how systematic this difference is. Poore and Dowsett (2001) reported oxygen isotope results from the same sequence and species and found that MIS 11 values were 0.3 permil more depleted than the Holocene. Our preliminary Mg/Ca-SST results suggest that most of this difference is not due to higher SST, suggesting either lower Cariaco salinity at this time and/or a negative shift in mean ocean O18 related to higher sea level during MIS 11. These findings will be considered in light of the unusual climate state that prevailed during MIS 11.
UR: http://www.geol.ucsb.edu/faculty/lea/
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1600 GLOBAL CHANGE (New category)
SC: Union [U]
MN: 2004 AGU Fall Meeting