Geology

Sea Ice Amplification

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Science  21 Oct 2005:
Vol. 310, Issue 5747, pp. 409
DOI: 10.1126/science.310.5747.409a

Numerous, millennial-scale warming episodes, called Dansgaard-Oeschger (D-O) events, punctuated the last glacial period. These events, first discovered in deep ice cores from Greenland, are visible in climate records extending from pole to pole, and in Pacific as well as Atlantic marine sediments. One popular hypothesis about the cause of these abrupt climate warmings invokes changes in the strength of the ocean's thermohaline circulation, which affect ocean heat transport. Such a model, however, cannot explain the size of the temperature swings in Greenland, which were as large as 5° to10°C. Li et al. use an atmospheric general circulation model to show that warming and cooling of the magnitude observed in Greenland can be caused by only small changes in the amount of sea ice around it. Furthermore, the sea ice changes that they suggest would also account for variations in snow accumulation and oxygen isotope composition similar to those measured in ice cores from Greenland. Finally, the amount of sea ice retreat proposed is consistent with forcing either by ocean thermohaline circulation variations, or by changes in surface wind stress in the North Atlantic. Thus, sea ice can provide a positive feedback strong enough to cause warming like that which occurred during D-O events. — HJS

Geophys. Res. Lett. 32, L19702 (2005).

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