In:
Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 106, No. D23 ( 2001-12-16), p. 31893-31901
Abstract:
Air trapped in ice core bubbles provides our primary source of information about past atmospheres. Air isotopic composition ( 15 N/ 14 N and 40 Ar/ 36 Ar) permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets. A rapid surface temperature change modifies temporarily the firn temperature gradient, which causes a detectable anomaly in the isotopic composition of nitrogen and argon. The location of this anomaly in depth characterizes the gas age‐ice age difference (Δage) during an abrupt event by correlation with the δD (or δ 18 O) anomaly in the ice. We focus this study on the marine isotope stage 5d/5c transition (108 kyr B.P.), a climate warming which was one of the most abrupt events in the Vostok (Antarctica) ice isotopic record [ Petit et al. , 1999]. A steplike decrease in δ 15 N and δ 40 Ar/4 from 0.49 to 0.47‰ (possibly a gravitational signal due to a change in firn thickness) is preceded by a small but detectable δ 15 N peak (possibly a thermal diffusion signal). We obtain an estimate of 5350±300 yr for Δage, close to the model estimate of 5000 years obtained using the Vostok glaciological timescale. Our results also suggest that the use of the present‐day spatial isotope‐temperature relationship slightly underestimates (but by no more than 20±15%) the Vostok temperature change from present day at that time, which is in contrast to the temperature estimate based on borehole temperature measurements in Vostok which suggests that Antarctic temperature changes are underestimated by up to 50% [Salamatin et al, 1998].
Type of Medium:
Online Resource
ISSN:
0148-0227
DOI:
10.1029/2001JD900145
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
2001
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