HR: 14:25h
AN: PP33C-04    [Abstracts]
TI: Evolution of Tropical Atlantic SST Gradients Since the LGM and Associated Shifts of the Marine Atlantic ITCZ: A New Look Using New Salinity and Temperature Calibrations
AU: * Arbuszewski, J A
EM: jarbo@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964,
AU: deMenocal, P B
EM: peter@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964,
AU: Kaplan, A
EM: alexeyk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964,
AB: Tropical Atlantic sea surface temperature (SST) and sea surface salinity (SSS) gradients are closely tied to the position of the modern marine Atlantic ITCZ. To reconstruct changes in tropical SST and SSS gradients since the LGM we measured paired G. ruber(w) Mg/Ca and d18O for six cores that form a transect with both a meridional and a zonal component across the tropical Atlantic. During the LGM, equatorial Atlantic SSTs were cooler by about 3°C and the modern zonal SST gradient was nearly absent, suggesting weaker trade winds on the equator. Following the conventional approach of solving for d18Osw using shell Mg/Ca and d18O measurements we find antiphase salinity histories north and south of the equator, documenting northward (southward) ITCZ shifts during the early Holocene (LGM). Using a larger Atlantic basin coretop calibration transect, we have recently discovered a significant salinity effect on shell Mg/Ca values that introduces significant d18Osw biases. Using new calibration equations relating paired shell Mg/Ca and d18O to estimate surface temperature and salinity (r2=0.8) we revisit our tropical Atlantic data and find that the principal conclusions regarding the temperature and salinity gradient changes are intact: we see comparable changes in the SST and SSS gradients and overall LGM cooling. These new data should represent a more accurate picture of the tropical Atlantic since the LGM as they correct for the observed "salinity effect" on Mg/Ca derived temperatures.
DE: 4835 Marine inorganic chemistry (1050)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting