HR: 10:20h
AN: B42A-01 INVITED    [Abstracts]
TI: The Modern Polar Antarctic Zone: Insight From the Stable Isotopes of Nitrate
AU: * DiFiore, P J
EM: pdifiore@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08544, United States
AU: Sigman, D M
EM: sigman@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08544, United States
AU: Dunbar, R
EM: dunbar@stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, United States
AU: Wang, F
EM: yw@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08544, United States
AB: We report nitrate N and O isotope measurements from the seasonally sea ice covered Polar Antarctic Zone (AZ). We estimate equivalent N and O isotope effects of 5 ‰ for nitrate assimilation in the upper water column. The amplitude of the N isotope effect is less than previously observed in the Subantarctic Zone (SAZ), > 7 ‰. The difference in isotope effects suggests the potential use of the expressed isotope effect of nitrate assimilation as an indicator of the physiological state of algae growing in the Southern Ocean. We previously hypothesized that the high SAZ isotope effect results from unbalanced growth due to light-limitation (DiFiore et al., 2006). The lower isotope effect in the AZ, which has shallower summer time mixed layer depths, is consistent with that hypothesis. The O isotopes of nitrate can be decoupled from the N isotopes during nitrification and therefore provide a tool for quantifying this additional source of mixed layer nitrate. Wankel et al. (2007) used this approach to identify a significant fraction (up to 30%) of nitrate that may result from mixed layer nitrification off Monterey Bay, California. Our data from the AZ indicates little decoupling of the dual isotopes of nitrate suggesting that nitrification is not a major source of nitrate in the AZ mixed layer, establishing a baseline to which other regions may be compared.
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4870 Stable isotopes (0454, 1041)
DE: 5462 Polar regions
SC: Biogeosciences [B]
MN: 2007 Fall Meeting