HR: 10:35h
AN: PP21D-02    [PDF]
TI: Caribbean Salinity Variation During the Last Glacial Cycle
AU: * Schmidt, M W
EM: schmidt@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Spero, H J
EM: spero@gelogy.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Lea, D W
EM: lea@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106 United States
AB: Evaporation exceeds precipitation in the tropical Atlantic, resulting in a net freshwater removal across the Central American Isthmus. Because most of the north Atlantic's subtropical gyre water circulates through the Caribbean before flowing north to sub-polar regions via the Gulf Stream, changes in tropical atmospheric circulation have the potential to affect the salinity and density structure of the entire north Atlantic, thereby influencing glacial-interglacial oscillations in North Atlantic Deep Water (NADW) formation. Here, we combine Mg/Ca measurements (a proxy for the temperature of calcification) and $\delta$$^{18}$O analyses of shells from the surface-dwelling foraminifera {\it Globigerinoides ruber s.s.} (white var.) from the western Caribbean Colombian Basin at ODP Site 999A (2827m; 4cm/ka sed. rate) and VM28-122 (3623m; 4-10cm/ka sed. rate) to produce the first continuous record of western tropical Atlantic $\delta$$^{18}$O$_{SEAWATER}$ ($\delta$$^{18}$O$_{SW}$) during the last 130ka. In order to generate a record for sea surface salinity (SSS) due to regional hydrological change, we removed the $\delta$$^{18}$O$_{SW}$ signal due to glacial ice volume variation and normalized the residual to the modern $\delta$$^{18}$O$_{SW}$ value for the Colombian Basin (0.8$\permil$ ). The resulting ice volume-free ($\Delta$$\delta$$^{18}$O$_{IVF-SW}$) record shows that Caribbean $\Delta$$\delta$$^{18}$O$_{IVF-SW}$ increased by $\sim$0.5$\permil$ during the Last Glacial Maximum and Marine Isotope Stage 4. Using a modern western Caribbean $\delta$$^{18}$O$_{SW}$:SSS relationship, these enriched $\delta$$^{18}$O$_{SW}$ values suggest glacial Caribbean salinities were 2.3 - 2.8$\permil$ higher than modern after removing the influence of ice-volume. Our data supports the hypothesis that the tropics might have been in a state more similar to the modern El Nino mode, characterized by a more southerly position of the ITCZ, during cold phases of the last glacial cycle. Within the resolution of our $\Delta$$\delta$$^{18}$O$_{IVF-SW}$ record from VM28-122, elevated glacial Caribbean salinity decreased to modern levels at the onset of the Bolling-Allerod (B/A) interstadial event (14.6 cal ka) as NADW formation reinitiated and the ITCZ migrated northward. We hypothesize that the transport of salty tropical waters into the North Atlantic during the early deglaciation, in combination with a reorganization of ocean circulation, may have served to increase subpolar surface water density and amplify the overturning circulation that produced the warm B/A. The B/A salinity reduction occurs simultaneously with previous evidence for wetter conditions in the Cariaco Basin, suggesting a northward shift in the ITCZ to a wetter, more La Nina-like state in the tropics.
DE: 4231 Equatorial oceanography
DE: 4267 Paleoceanography
DE: 4283 Water masses
DE: 4522 El Ni¤o
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting