Sinking organic matter spreads the nitrogen isotope signal of pelagic denitrification in the North Pacific

Sigman, Daniel M., DiFiore, Peter J., Hain, Mathis P., Deutsch, Curtis and Karl, David M. (2009) Sinking organic matter spreads the nitrogen isotope signal of pelagic denitrification in the North Pacific. Geophysical Research Letters, 36 (8), L08605. (doi:10.1029/2008GL035784).

Abstract

Culture studies of denitrifying bacteria predict that denitrification will generate equivalent gradients in the ?15N and ?18O of deep ocean nitrate. A depth profile of nitrate isotopes from the Hawaii Ocean Time-series Station ALOHA shows less of an increase in ?18O than in ?15N as one ascends from abyssal waters into the denitrification-impacted mid-depth waters. A box model of the ocean nitrate N and O isotopes indicates that this is the effect of the low latitude nitrate assimilation/regeneration cycle: organic N sinking out of the surface spreads the high-?15N signal of pelagic denitrification into waters well below and beyond the suboxic zone, whereas the nitrate ?18O signal of denitrification can only be transmitted by circulation in the interior.

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