HR: 0800h
AN: PP11A-0539    [Abstracts]
TI: The `Antarctic signal' in Northeast Atlantic benthic $\delta^{18}$O during MIS 3 attributed primarily to deep-water temperature variations
AU: * Skinner, L C
EM: luke00@esc.cam.ac.uk
AU: Shackleton, N J
EM: njs5@cam.ac.uk
AB: A key, and unresolved though much theorised aspect of millennial climate variability during the last glacial period is the consistent asynchrony of planktonic and benthic foraminiferal $\delta^{18}$O recorded in the Northeast Atlantic (Shackleton et al., Paleoceanography 15, 565, 2000), and in particular the apparent coupling of such variations with an identical asynchrony between Greenland and Antarctic temperatures (Blunier et al., Nature 394, 739, 1998). These relationships result in an apparent coupling of Antarctic temperature and benthic $\delta^{18}$O variations throughout Marine Isotope Stage (MIS) 3. It was originally proposed that a climatic parameter with a long time-constant, such as global ice-volume, must account for the millennial benthic $\delta^{18}$O signal. Based on reconstructions of Red Sea salinity and coral terrace facies variations (Chappell, QSR 21, 1229, 2002; Siddall et al., Nature 423, 853, 2003) it has since been suggested that benthic $\delta^{18}$O has indeed responded to rapid glacioeustatic sea level fluctuations. Importantly, the sea level variations thus reconstructed could only account for approximately half of the observed amplitude of benthic $\delta^{18}$O; or if invoked as a complete explanation for the benthic $\delta^{18}$O signal would require a sensitivity of Atlantic deep-water $\delta^{18}$O to ice-volume change that was two times larger than on glacial - interglacial time-scales. Here, we present preliminary measurements of Mg/Ca ratios in benthic foraminifera from core MD01-2444 (recovered from 2,656m on the Iberian Margin) that indicate that most of the `Antarctic' benthic $\delta^{18}$O signal may be attributed to local deep-water temperature variations, and hence that sea-level fluctuations co-ordinated with Antarctic climate cannot account entirely for the benthic signal. Furthermore, it appears that sea-level change may not be in phase with the benthic $\delta^{18}$O, and that the timing of sea-level high-stands should not be inferred from the benthic $\delta^{18}$O record. The deep-water temperature variations reconstructed during MIS 3 are suggested to arise from local changes in deep-water circulation, including variations in deep-water sourcing and/or mode of formation in a manner similar to that proposed for the late glacial and across Termination I (Skinner et al., G$^{3}$ v.4 (12), 2003). The proven validity of these results would place important and much needed constraints on the mechanisms that may be invoked to explain the so-called `bi-polar see-saw' of Greenland and Antarctic temperatures, and their apparent links to other global phenomena, including sea level and atmospheric CO$_{2}$ fluctuations.
DE: 4267 Paleoceanography
DE: 4532 General circulation
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting