Nitrogen isotope simulations show the importance of atmospheric iron deposition for nitrogen fixation across the Pacific Ocean

TitleNitrogen isotope simulations show the importance of atmospheric iron deposition for nitrogen fixation across the Pacific Ocean
Publication TypeJournal Article
Year of Publication2010
AuthorsSomes, C. J., A. Schmittner, and M. A. Altabet
JournalGeophysical Research Letters
Volume37
PaginationL23605
Date PublishedDec 3
ISBN Number0094-8276
Accession NumberISI:000285015100001
Keywordsatlantic-ocean, denitrification, diazotrophs, equatorial pacific, nitrate, north pacific, phosphorus, populations, trichodesmium cyanobacteria, western
Abstract

Nitrogen (N) fixation by specialized microorganisms (diazotrophs) influences global plankton productivity because it provides the ocean with most of its bio-available N. However, its global rate and large-scale spatial distribution is still regarded with considerable uncertainty. Here we use a global ocean nitrogen isotope model, in comparison with delta(NO3-)-N-15 observations, to constrain the pattern of N-2 fixation across the Pacific Ocean. N-2 fixation introduces isotopically light atmospheric N-2 from to the ocean (delta N-15 = parts per thousand) relative to the oceanic average near 5 parts per thousand, which makes nitrogen isotopes suitable to infer patterns of N-2 fixation. Including atmospheric iron limitation of diazotrophy in the model shifts the pattern of simulated N-2 fixation from the South Pacific to the North Pacific and from the East Pacific westward. These changes considerably improve the agreement with meridional transects of available delta(NO3-)-N-15 observations, as well as excess P (PO43- - NO3-/16), suggesting that atmospheric iron deposition is indeed important for N fixation in the Pacific Ocean. This study highlights the potential for using d15N observations and model simulations to constrain patterns and rates of N fixation in the ocean. Citation: Somes, C. J., A. Schmittner, and M. A. Altabet (2010), Nitrogen isotope simulations show the importance of atmospheric iron deposition for nitrogen fixation across the Pacific Ocean, Geophys. Res. Lett., 37, L23605, doi:10.1029/2010GL044537.

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