BOTH increased biological productivity and more efficient uptake of upwelled nutrients in high-latitude oceans have been proposed 1-5 as mechanisms responsible for the glacial reduction in atmospheric concentrations of carbon dioxide deduced from ice-core measurements 6-8. These glacial models invoke more efficient 'biological pumping' of carbon into the deep sea by increasing the uptake of 'excess' biolimiting nutrients in the Antarctic surface ocean 9 or by reorganizing chemical circulation patterns within the ocean 10,11. Here we challenge this conventional view with new evidence from tracers of palaeoproductivity preserved in Antarctic sediments. Records of the accumulation rates of diatom shells, the ratio of germanium to silicon in diatomaceous opal and the carbon isotope ratio in foraminiferal carbonate all suggest lower glacial productivity and less efficient uptake of nutrients. Although alternative interpretations are possible, our results support previous studies that indicate lower glacial productivity in the Southern Ocean 12,13 and raise new questions about the role of ocean productivity in models of the causes (or remedies) for changes in atmospheric concentrations of carbon dioxide.
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