HR: 10:35h
AN: PP52C-02 INVITED     [Abstracts]
TI: Southern ocean controls on the extent of denitrification in the southeast Pacific (ODP Site 1234)
AU: * Robinson, R S
EM: rebeccar@princeton.edu
AF: Department of Geosciences Princeton University, Guyot Hall Washington Rd, Princeton, NJ 08544 United States
AU: Mix, A
EM: mix@coas.oregonstate.edu
AF: COAS-Oregon State University, COAS Admin. Bldg. 104 Oregon State University, Corvallis, OR 97331-5503 United States
AU: Martinez, P
EM: p.martinez@epoc.u-bordeaux1.fr
AF: D‚partement de G‚ologie et Oc‚anographie, Universit‚ Bordeaux I, UMR CNRS 5805 EPOC, avenue des facult‚, Talence cedex, 33405 France
AB: A mechanistic understanding of the observed temporal changes in oceanic denitrification, the bacterial reduction of nitrate under suboxic conditions, has been sought due to the potential importance of N inventory changes and the production of N₂O on the climate system. High-resolution oxygen isotope and bulk sediment δ¹⁵N records from ODP Site 1234 on the Chile Margin are presented as a record of denitrification changes within the Peru-Chile Upwelling system over the last 65ky. The character of the Site 1234 δ¹⁵N record is quite similar to that of its northern hemisphere counterparts with the exception of timing. Denitrification changes in the southeast Pacific show coherent variation with Antarctic climate, as indicated by the Byrd ice core δ¹⁸O record, rather than with northern hemisphere climate change. The high latitude polar oceans play a fundamental role in setting the physical and biological controls on subsurface oxygen supply and demand. The southern hemisphere character of the Chile margin record suggests that episodes of reduced denitrification in the SE Pacific likely represent times when more oxygen was supplied as the result of changes in the chemical composition of Subantarctic Mode Water (SAMW), which forms in the Subantarctic zone of the Southern Ocean and ventilates the low latitude thermocline. An increase in oxygen can be achieved through (1) lower temperatures/ higher ventilation rates and/or (2) reduced oxygen demand in the low latitude subsurface due to reduction in the preformed nutrient content of SAMW.
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005