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PALEOCEANOGRAPHY,
VOL. 20,
PA3003,
doi:10.1029/2004PA001114,
2005
Diatom-bound 15N/14N: New support for enhanced nutrient consumption in the ice age subantarctic
Rebecca S. Robinson
Department of Geosciences, Princeton University, Princeton, New Jersey, USA
Daniel M. Sigman
Department of Geosciences, Princeton University, Princeton, New Jersey, USA
Peter J. DiFiore
Department of Geosciences, Princeton University, Princeton, New Jersey, USA
Melissa M. Rohde
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada
Tracy A. Mashiotta
Byrd Polar Research Center, Columbus, Ohio, USA
David W. Lea
Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, California, USA
Abstract
Diatom-bound 15N/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from
both the Pacific and Indian sectors show δ15N of 5 to 6‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as
2‰. The effect of either diatom assemblage or physiological change on the diatom-bound 15N/14N is unknown and cannot yet be ruled out as a possible explanation for the observed change. However, the consistency between
Indian and Pacific sector records and with other paleoceanographic data suggests that the glacial-interglacial difference
in diatom-bound 15N/14N was driven by higher consumption of nitrate in the subantarctic surface during the last ice age. Such a change in nutrient
consumption may have resulted from atmospheric iron fertilization and/or decreased glacial mixed layer depths associated with
sea ice melting. Enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of
CO2 in the ice age atmosphere. It also would have reduced the preformed nutrient content of the low-latitude thermocline, leading
to decreases in low-latitude productivity, suboxia, and denitrification.
Received 9
November
2004;
accepted 28
March
2005;
published 22
July
2005.
Keywords: subantarctic;
diatom-bound 15N/14N;
glacial-interglacial CO2.
Index Terms: 4912 Paleoceanography: Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805); 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling (0470, 1050); 4870 Oceanography: Biological and Chemical: Stable isotopes (0454, 1041); 4806 Oceanography: Biological and Chemical: Carbon cycling (0428).
Read Full Article (file size: 510078 bytes) Cited by
Citation: Robinson, R. S., D. M. Sigman, P. J. DiFiore, M. M. Rohde, T. A. Mashiotta, and D. W. Lea
(2005),
Diatom-bound 15N/14N: New support for enhanced nutrient consumption in the ice age subantarctic,
Paleoceanography,
20,
PA3003,
doi:10.1029/2004PA001114.
Copyright 2005 by the American Geophysical Union.
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