Glacial Silicic Acid Concentrations in the Southern Ocean

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Science  21 Oct 2010:
DOI: 10.1126/science.1194614


Reconstruction of nutrient concentrations in the deep Southern Ocean has produced conflicting results. The cadmium/calcium (Cd/Ca) dataset suggest little change in nutrient concentrations during the last glacial period, whereas the carbon isotope (δ13C) dataset suggest nutrient concentrations were higher. We determined the silicon isotope (δ30Si) composition of sponge spicules from the Atlantic and Pacific sectors of the Southern Ocean and found higher silicic acid concentrations in the Pacific sector during the last glacial period. We propose that this increase results from changes in the stoichiometric uptake of silicic acid relative to nitrate and phosphate by diatoms, thus facilitating a redistribution of nutrients across the Pacific and Southern Ocean. Our results are consistent with the global Cd/Ca dataset and support the silicic acid leakage hypothesis.