HR: 1340h
AN: OS13B-0536    [Abstracts]
TI: Modeling the Distribution and $\delta$$^{15}$N of Nitrogen Gas and Nitrogen Species in the Black Sea
AU: Konovalov, S K
EM: sergey@alpha.mhi.iuf.net
AF: Marine Hydrophysical Institute, Kapitanskaya St. 2A, Sevsatopol, 99000 Ukraine
AU: Fuchsman, C A
EM: cafuchsman@yahoo.com
AF: University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351
AU: * Murray, J W
EM: jmurray@u.washington.edu
AF: University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351
AB: We have measured the distributions of NO$_{3}$, NO$_{2}$, NH$_{4}$, N$_{2}$ and PON and their $\delta$$^{15}$N values in the Black Sea in order to unravel the cycling of nitrogen, especially the role of anammox (NO$_{2}$$^{-}$ + NH$_{4}$$^{+}$ = N$_{2}$). In conjunction with these measurements we have constructed a coupled physical-biogeochemical model of the water column. The physical model is a vertical transport model that includes simulation of entrainment and intrusions from the Bosporus Plume. This model has been calibrated using the historical record of Cs-137 measurements. The biogeochemical model includes mass balance equations for $^{14}$N and $^{15}$N. The main features and possible explanations from the model runs include: 1. Values of $\delta$$^{15}$N-N$_{2}$ are low ($\sim$0.5 per mil) compared with $\delta$$^{15}$N for NO$_{3}$, NH$_{4}$ and PON ($\sim$8 per mil) because a significant fraction of NO#_{3}$ must be reduced to NH$_{4}$ rather than N$_{2}$. 2. $\delta$$^{15}$N-NO$_{3}$ is constant (and unusually high) in the oxic layer ($\sim$8 per mil) then increases sharply towards the onset of sulfide. This must result from the anammox reaction that takes place in the suboxic layer. 3. $\delta$$^{15}$N-NH$_{4}$ is low in the deep water ($\sim$2 per mil) and increases toward the onset of H$_{2}$S. This must be the result of reduction of NO$_{3}$ to NH$_{4}$ when NO$_{3}$ in the Bosporus Plume intrusions reacts with H$_{2}$S. 4. $\delta$$^{15}$N-PON remains constant ($\sim$7 per mil) in the oxic layer, increases to a small maximum ($\sim$9 per mil) at the top of the suboxic zone and then decreases to 3 per mil in the sulfide layer. These distributions reflect oxidation of NH $_{4}$ and bacterial production from DON and NH$_{4}$.
DE: 4820 Gases
DE: 4834 Hypoxic environments
DE: 4851 Oxidation/reduction reactions
DE: 4870 Stable isotopes
DE: 4802 Anoxic environments
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting