Antarctic and Greenland Climate Changes

Abstract

CLIMATE To investigate the temporal relationship between climate changes in the Northern and Southern Hemispheres, the ages of climate events recorded in ice cores from near the two poles are often compared. However, there is a large inherent uncertainty in this technique because it is difficult to date ice cores absolutely. Caillon et al . describe a possible way around this problem by measuring the isotopic compositions of Ar and N2 and the concentration of methane trapped in the bubbles of ice cores from Antarctica. When the local temperature change is fast and large enough, the resulting thermal gradient in the developing ice causes measurable isotopic fractionation of Ar and N2, thereby recording the temperature change event at the site. Methane is well mixed in the atmosphere on a global scale, and atmospheric methane levels increased when wetlands expanded because of Northern Hemispheric warming. Thus, by comparing the two signals, a robust estimate of the relative timing of warming in the Northern and Southern Hemispheres can be made. This technique, applied to 108,000-year-old ice from Vostok in Antarctica, indicates that the South warmed approximately 2000 years before the North, consistent with the popular idea of a climatological “bipolar seesaw.” — HJS Geophys. Res. Lett. 30 , 1899 (2003).