HR: 1340h
AN: PP33C-1589    [Abstracts]
TI: Using Kr/Ar and Xe/Ar Ratios to Identify Melt Layers in ice Cores
AU: * Headly, M A
EM: mheadly@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail Code 0208 9500 Gilman Drive , La Jolla, CA 92093-0208
AU: Ahn, J
EM: jiahn@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail Code 0208 9500 Gilman Drive , La Jolla, CA 92093-0208
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail Code 0208 9500 Gilman Drive , La Jolla, CA 92093-0208
AB: Melt layers in ice cores form during exceptionally warm conditions. Frequency of melt layers can be used as a climate proxy to estimate summer temperatures. Shallow melt layers are visible as horizontal bands of ice with few air bubbles. In deeper ice, melt layers are harder to identify due to thinning of the layers with depth and air clathrate formation. We have measured Kr/Ar and Xe/Ar ratios in visible melt layers in shallow ice from the Dye 3 ice core in Greenland. These ratios have a distinct signature in melt layers, as compared to ice that has not melted and refrozen. Because krypton and xenon are highly soluble in liquid water, they are present in higher concentrations in melted and refrozen ice than argon, which is less soluble. These noble gas ratios may be used as an additional, independent indicator of melt layers in ice cores. We have modeled the effects of melted ice, as well as gravitational settling and gas loss, on Kr/Ar, Xe/Ar, and ⁴⁰Ar/³⁶Ar in ice. For simplicity this model assumes that all the dissolved gas is retained during the refreezing process. Using this model, we are able to invert the three measured parameters for the firn diffusive column depth, gas loss, and the volume ratio of refrozen liquid water to bubble air at ambient pressure. We have also used Kr/Ar and Xe/Ar to identify melted and subsequently refrozen ice in the Siple Dome ice core at depths with high CO₂ values. The high Kr/Ar and Xe/Ar values are used to constrain the extent of melting/refreezing that may have caused the elevated CO₂ concentrations.
DE: 0724 Ice cores (4932)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005