American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 375454 bytes)    Cited by

GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 12, 1564, doi:10.1029/2001GL014349, 2002

A switch from Si(OH)4 to NO3− depletion in the glacial Southern Ocean

Mark A. Brzezinski

Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA


Carol J. Pride

Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA


Valerie M. Franck

Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA


Daniel M. Sigman

Department of Geosciences, Princeton University, Princeton, New Jersey, USA


Jorge L. Sarmiento

Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA


Katsumi Matsumoto

Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA


Nicolas Gruber

Institute of Geophysics and Planetary Physics and Department of Atmospheric Sciences, University of California Los Angeles, California, USA


Greg H. Rau

Institute of Marine Sciences, University of California, Santa Cruz, California, USA


Kenneth H. Coale

Moss Landing Marine Laboratory, Moss Landing, California, USA


Abstract

Phytoplankton in the Antarctic deplete silicic acid (Si(OH)4) to a far greater extent than they do nitrate (NO3−). This pattern can be reversed by the addition of iron which dramatically lowers diatom Si(OH)4:NO3− uptake ratios. Higher iron supply during glacial times would thus drive the Antarctic towards NO3− depletion with excess Si(OH)4 remaining in surface waters. New δ30Si and δ15N records from Antarctic sediments confirm diminished Si(OH)4 use and enhanced NO3− depletion during the last three glaciations. The present low-Si(OH)4 water is transported northward to at least the subtropics. We postulate that the glacial high-Si(OH)4 water similarly may have been transported to the subtropics and beyond. This input of Si(OH)4 may have caused diatoms to displace coccolithophores at low latitudes, weakening the carbonate pump and increasing the depth of organic matter remineralization. These effects may have lowered glacial atmospheric pCO2 by as much as 60 ppm.

Published 18 June 2002.

Index Terms: 4267 Oceanography: General: Paleoceanography; 4215 Oceanography: General: Climate and interannual variability (3309); 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4870 Oceanography: Biological and Chemical: Stable isotopes.

Read Full Article (file size: 375454 bytes)    Cited by

Citation: Brzezinski, M. A., C. J. Pride, V. M. Franck, D. M. Sigman, J. L. Sarmiento, K. Matsumoto, N. Gruber, G. H. Rau, and K. H. Coale (2002), A switch from Si(OH)4 to NO3− depletion in the glacial Southern Ocean, Geophys. Res. Lett., 29(12), 1564, doi:10.1029/2001GL014349.