Recent ice-core measurements have revealed that the atmospheric CO 2 level increased comparatively rapidly by about 70 p.p.m. at the end of the last ice age1. Here we present an ocean-atmosphere model in which changes in the productivity of high latitude surface waters (from which deep water is formed and circulated around the world's ocean) and/or in the thermo-haline overturning rate can lead to substantial changes in atmospheric partial pressure of carbon dioxide (PCO2), over a concentration range 163-425 p.p.m. A major contribution to the low PCO2 of the last ice may have been an increase in the net high latitude productivity, possibly coupled with a decrease in the thermohaline overturning.
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