HR: 1330h
AN: PP12A-0232    [PDF]
TI: Glacial-Interglacial Modulation of the Marine Nitrogen Cycle by Oxygen Supply to Intermediate Waters
AU: * Galbraith, E D
EM: egalbraith@eos.ubc.ca
AF: Department of Earth and Ocean Science, University of British Columbia, 6270 University Blvd, Vancouver, BC V6T 1Z4 Canada
AU: Kienast, M
EM: mkienast@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1050 United States
AU: Pedersen, T F
EM: tfp@uvic.ca
AF: School of Earth and Ocean Science, University of Victoria, P.O. Box 3055 Stn CSC, Victoria, BC V8W 3P6 Canada
AU: Calvert, S E
EM: calvert@eos.ubc.ca
AF: Department of Earth and Ocean Science, University of British Columbia, 6270 University Blvd, Vancouver, BC V6T 1Z4 Canada
AB: The marine inventory of bioavailable nitrogen has a turnover time of 2-5 ky and is therefore capable of large changes that could contribute to variations in {\it p}CO$_{2}$ over glacial-interglacial cycles. Bioavailable nitrogen is added to the oceans through nitrogen fixation and returned to the atmosphere as N$_{2}$ and radiatively-active N$_{2}$O through denitrification in suboxic environments. We present an analysis of sedimentary $\delta^{15}$N records that suggests a strong temporal coupling between these distant components of the global nitrogen cycle. This coupling can be parsimoniously explained by a simple physical control on the dissolved oxygen supply to suboxic zones, modulating the extent of denitrification, to which the marine biosphere responds by adjusting the rate of N fixation. Lower glacial-stage temperatures in regions of intermediate-water formation increased oxygen solubility, and the resultant colder, rapidly circulating intermediate waters thus decreased the extent of denitrification and, consequently, N fixation. During warm periods, sluggish circulation of warmer, less oxygen-rich intermediate waters caused expansion of denitrification zones and a concomitant increase in N fixation. This model suggests that the marine N cycle is biologically stabilized to some degree, but that anthropogenic warming at high latitudes could significantly enhance denitrification in the oceanic water column, potentially forcing additional warming.
DE: 0315 Biosphere/atmosphere interactions
DE: 1615 Biogeochemical processes (4805)
DE: 4267 Paleoceanography
DE: 4805 Biogeochemical cycles (1615)
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting