HR: 1340h
AN: PP23B-1409    [Abstracts]
TI: Reconstructing Deep Ocean Temperature During the Last Glacial Maximum Based on Kr/N$_{2}$ and Xe/N$_{2}$ Ratios in air Trapped in Glacial ice
AU: * Headly, M A
EM: mheadly@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail code 0244, 9500 Gilman Drive, La Jolla, CA 92093-0244 United States
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail code 0244, 9500 Gilman Drive, La Jolla, CA 92093-0244 United States
AB: Deep ocean temperature is a fundamental parameter of the climate system, but its past variations remain poorly known. This is mainly due to the inherent ambiguity of oxygen isotope records from benthic foraminifera, which are affected by both temperature and ice volume. Sediment pore water studies have provided a single estimate of deep ocean cooling at the last glacial maximum, but do not resolve a time series of temperature. We discuss the development of a new technique to reconstruct average ocean temperature by using noble gas measurements of the past atmosphere from ice cores. This reconstruction should place constraints on the timing and magnitude of deep ocean temperature variations. Using noble gas and nitrogen inventories and solubilities, as well as the Levitus ocean temperature database, a box model of the ocean and atmosphere indicates that atmospheric Kr/N$_{2}$ and Xe/N$_{2}$ concentrations should have been lower during the last glacial maximum (LGM), approximately 20,000 years ago. This is due to the greater temperature dependence of the solubilities of the heavy noble gases relative to nitrogen. Assuming an average ocean cooling of $4\deg$C, we calculate the change in Kr/N$_{2}$ relative to today$'$s atmosphere to be $-$1.69$\permil$. A similar calculation for Xe/N$_{2}$ yields a result of $-$3.93$\permil$. For a comparison between present and glacial conditions, we have measured these ratios in trapped air bubbles in Greenland ice cores from both the late Holocene and the LGM. The $\delta$Kr/N$_{2}$ and $\delta$Xe/N$_{2}$ in the GISP 2 ice core during the late Holocene ($\sim$ 1,500 years ago) are $-$0.07$\permil$ $\pm$ 0.40$\permil$ and $-$0.29$\permil$ $\pm$ 2.27$\permil$, respectively. We also present preliminary measurements of $\delta$Kr/N$_{2}$ and $\delta$Xe/N$_{2}$ from the LGM in the Dye 3 and GISP2 ice cores, as well as in air bubbles in ice from Pakitsoq, Greenland.
DE: 1694 Instruments and techniques
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting