HR: 16:00h
AN: PP44A-01 INVITED     [Abstracts]
TI: Deep Ocean Temperature and Salinity at the Last Glacial Maximum
AU: * Adkins, J F
EM: jess@gps.caltech.edu
AF: Caltech, MS 100-23 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Schrag, D P
EM: schrag@eps.harvard.edu
AF: Harvard U., Dept. of EPS 20 Oxford St., Cambridge, MA 02138 United States
AB: Sediment pore fluids from the deep ocean contain a record of the bottom water salinity and $\delta$$^{18}$O due to the last glaciation. Storage of water on land as glacial ice imparts a global signal of increased salinity and enriched oxygen isotopic values in the abyssal ocean and changes in deep circulation patterns can impart an additional local signal. In the mean this signal was about 3.5% in salinity and about 1.0\permil in $\delta$$^{18}$O, but has been diffusing and advecting away over the last 20,000 years. Today, high resolution sampling (every 1.5 meters) coupled with high precision geochemical analyses of pore fluids from a single core can be used, in conjunction with a 1-D pore fluid diffusion model, to reconstruct the Last Glacial Maximum (LGM) salinity and $\delta$$^{18}$O at that site. We have done this analysis for several globally distributed Ocean Drilling Program (ODP) holes including some new unpublished data from the equatorial Pacific. In addition, benthic foraminiferal measurements of modern and LGM CaCO$_{3}$ $\delta$$^{18}$O, coupled with the water $\delta$$^{18}$O reconstruction, can be used to constrain the deep-water temperature change from LGM to today. Plotted as a T/S diagram for the LGM, our data show that the entire deep ocean cooled to about $-$$1.0\deg$C potential temperature. This relative homogeneity in temperature is contrasted by much larger than modern salinity gradients in the deep. Due to increased sea ice export, the Southern Ocean was by far the saltiest water mass in the LGM, and as a result the modern salinity contrast between NADW and AABW was reversed. Stratification of the LGM deep ocean was largely controlled by salinity (as opposed to temperature today) and this feature has important implications for the stability of the LGM overturning circulation. With salty waters filling the deep LGM Ocean, it is difficult for fresh water changes at the surface of the North Atlantic to alter the abyssal circulation. Before freshwater forcing can trigger circulation changes, some other forcing must first increase the buoyancy of the deep Southern Source waters. In addition, the combination of our water $\delta$$^{18}$O data and a global database of benthic $\delta$$^{18}$O imply that the deep Pacific was warmer than the deep North Atlantic at the LGM.
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting