Tropical Dominance of N2 Fixation in the North Atlantic Ocean
Overview
Research
Identity
Additional Document Info
View All
Overview
abstract
AbstractTo investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.14.3TgN/yr and 3.00.5TgN/yr are estimated north of 11S and 24N, respectively. That is, ~90% of the N2 fixation in the Atlantic north of 11S occurs south of 24N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern ironrich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to Pbearing, Npoor conditions. We estimate a N2 fixation rate of 30.54.9TgN/yr north of 30S, implying only 3TgN/yr between 30 and 11S, despite evidence of Pbearing, Npoor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in <2,500years, similar to the residence time of oceanic fixed N, Atlantic N2 fixation can stabilize the NtoP ratio of the global ocean. However, the calculated rate of Atlantic N2 fixation is a small fraction of global ocean estimates for either N2 fixation or fixed N loss. This suggests that, in the modern ocean, an approximate balance between N loss and N2 fixation is achieved within the combined Indian and Pacific basins.
Marconi, D., Sigman, D. M., Casciotti, K. L., Campbell, E. C., Weigand, M. A., Fawcett, S. E., ... Haug, G. H.
complete list of authors
Marconi, Dario||Sigman, Daniel M||Casciotti, Karen L||Campbell, Ethan C||Weigand, M Alexandra||Fawcett, Sarah E||Knapp, Angela N||Rafter, Patrick A||Ward, Bess B||Haug, Gerald H
