Ocean Science

Mysterious Rise

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Science  31 May 2013:
Vol. 340, Issue 6136, pp. 1016-1017
DOI: 10.1126/science.340.6136.1016-e

The concentration of atmospheric carbon dioxide (CO2) rose from about 180 parts per million by volume (ppmv) to 280 ppmv between the end of the Last Glacial Maximum and the Holocene. It is widely believed, largely based on measurements of the 14C in the CO2 of air trapped in polar ice and of forams from marine sediments, that the atmospheric CO2 rise was caused in large part by ventilation of old, CO2-rich water from the deep Southern Ocean. Tessin and Lund analyzed another isotope of carbon, 13C, to show that the mid-depth waters along the Brazil Margin underwent an abrupt change in their inventories of 13C during the initial 30-ppmv increase in CO2 between about 17,000 and 16,000 years ago. These data, collected from analyses of planktonic forams in marine sediments, in conjunction with data on the oxygen isotopic composition of these waters, suggest that two distinct water masses must have influenced the mid-depth Atlantic Ocean during that interval and that a previously unrecognized source of carbon outside of the ocean-atmosphere system may have been involved. The authors also inferred that the release of carbon into the atmosphere from a reservoir depleted in 13C must have been a key trigger of the last deglaciation.

Paleoceanography 10.1002/palo.20026 (2013).

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