A SWITCH FROM Si(OH)4 TO NO3 DEPLETION IN THE GLACIAL SOUTHERN OCEAN

Reference

Brzezinaki, M.A. C.J. Pride, V.M. Franck, D.M.Sigman, J.L. Sarmiento, K. Matsumoto, N. Gruber, G.H. Rau, K.H. Coale,
A switch from Si(OH)4 to NO3 depletion in the glacial Southern Ocean,
Geophysical Research Letters, 29(12), 10.1029/2001GL014349, 2002.

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 d 30 Si and d 15 N 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.

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