HR: 08:30h
AN: H51E-02    [Abstracts]
TI: Nitrogen and oxygen isotope effects associated with nitrate assimilation and denitrification by laboratory cultures of marine plankton.
AU: * Granger, J
EM: jgranger@eos.ubc.ca
AF: University of British Columbia, Dept. Earth & Ocean Sciences 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada
AU: Sigman, D M
EM: sigman@princeton.edu
AF: Princeton University, Dept. Geosciences, Princeton, NJ 08544 United States
AU: Lehmann, M F
EM: lehmann.moritz@uquam.ca
AF: GEOTOP-UQUAM-McGill Research Centre, pc 8888 Succ. Centre-Ville, Montr‚al, Qu‚ H3C 3P8 Canada
AU: Tortell, P D
EM: tortell@eos.ubc.ca
AF: University of British Columbia, Dept. Earth & Ocean Sciences 6270 University Blvd., Vancouver, BC V6T 1Z4 Canada
AB: We report measurements of coupled nitrogen (N) and oxygen (O) isotopic variations in nitrate during a) its assimilation by laboratory cultures of marine phytoplankton, and b) during dissimilatory reduction by cultures of marine and fresh water denitrifiers. Nitrate N ($^{15}$N/$^{14}$N) and O ($^{18}$O/$^{16}$O) isotopic ratios were measured throughout growth using the denitrifier method (Sigman et al. 2001, Casciotti et al. 2002). In the case of denitrifier cultures, accumulated nitrite in the medium was removed to avoid interference with the measurement of N and O isotopic ratios in nitrate, using a new protocol which will be described. We observed large inter- and intra-species variations in the nitrate N and O isotope effects ($^{15}$$\epsilon$ and $^{18}$$\epsilon$, respectively) during its assimilation by marine microalgae. This stands in contrast to the ratio of respective N and O isotope effects (i.e., $^{15}$$\epsilon$:$^{18}$$\epsilon$), which remained remarkably close to unity regardless of the magnitude of $\epsilon$. Unlike nitrate assimilation, nitrate reduction by denitrifiers showed less variability in the magnitude of observed $^{15}$$\epsilon$ and $^{18}$$\epsilon$. Yet $^{15}$$\epsilon$ and $^{18}$$\epsilon$ were also strongly coupled in denitrification, for both marine and fresh water strains. The observed magnitudes of $^{15}$$\epsilon$ and $^{18}$$\epsilon$ and the respective coupling ($^{15}$$\epsilon$:$^{18}$$\epsilon$) will be discussed in the context of algal and bacterial physiology, as well as implications for the interpretation of nitrate N and O isotopes in marine and freshwater systems.
DE: 0330 Geochemical cycles
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting