Geology

Moving in Synchrony

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Science  23 Apr 2004:
Vol. 304, Issue 5670, pp. 491
DOI: 10.1126/science.304.5670.491a

Mountain glaciers in the Northern Hemisphere—in the Alps of Europe and in the Rocky Mountains and Sierra Nevada of North America—generally kept pace with the advance and retreat of the large continental ice sheets at the end of the last glaciation; they advanced until about 22,000 years ago and retreated after about 16,000 years ago. Because glacial cycles are largely thought to reflect changes of incident solar energy in the Northern Hemisphere and because mountain glaciers can respond in a complicated fashion to fluctuations in precipitation and temperature, it has not been clear whether glaciers throughout the Southern Hemisphere would have waxed and waned in lockstep.

Kaplan et al. used cosmogenic nuclides in glacial deposits and moraines to date the retreat of a major glacier in Patagonia, Argentina. This kind of isotope record is produced when cosmic rays strike exposed bedrock as a glacier recedes and the protective cover of ice and snow is lost. The data reveal a similar chronology as seen for the Northern Hemisphere mountain glaciers, implying that atmospheric processes synchronized climate in the two hemispheres. — BH

Geol. Soc. Am. Bull. 116, 308 (2004).

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