Climate Science

Warming and Rising

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Science  24 Jan 2003:
Vol. 299, Issue 5606, pp. 477
DOI: 10.1126/science.299.5606.477b

During the midst of the last deglaciation, almost 15,000 years ago, sea level rose extremely rapidly during an episode of rapid glacial melting that is called meltwater pulse (MWP) 1a. At approximately the same time another dramatic event, an abrupt increase in Northern Hemisphere air temperature called the Bølling warming, occurred. The relative timing of these two episodes has been a point of active debate and must be resolved in order to develop a mechanistic understanding of the oceanographic, glaciological, and climatic changes that occurred during this period.

Kienast et al. provide a better picture of the phase relation between MWP 1a and the Bølling warming by examining a marine sediment core from the northern South China Sea. This core reveals that a rapid drop in the supply of terrestrial plant matter during the last deglaciation was paralleled by an equally rapid increase in sea surface temperatures corresponding with the Bølling warming 14,700 years ago. They interpret this sudden drop in terrigenous organic matter delivery as a short-term response of local rivers to rapid sea-level rise, implying that the Bølling warming and the onset of MWP 1a were synchronous. This result indicates that previous studies postulating a weakening of deep-water formation in the North Atlantic due to massive meltwater discharge during MWP 1a need to be reformulated. — HJS

Geology31, 67 (2003).

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