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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Casciotti, Karen L. Prokopenko, Maria G. Capone, Douglas G. Berelson, William M. Knapp, Angela N. |
| Spatial Coverage | Pacific Ocean |
| Description | Author Affiliation: Knapp AN ( Earth, Ocean and Atmospheric Science Department, Florida State University, Tallahassee, FL 32306); Casciotti KL ( Department of Earth System Science, Stanford University, Stanford, CA 94305); Berelson WM ( Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089); Prokopenko MG ( Geology Department, Pomona College, Claremont, CA 91711); Capone DG ( Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089.); |
| Abstract | An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for $N_{2}$ fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of $N_{2}$ fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. $N_{2}$ fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N $m^{−2}$ $d^{−1}$ based on sediment trap fluxes. Whereas the fractional importance of $N_{2}$ fixation did not change, the $N_{2}-fixation$ rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these $N_{2}-fixation$ rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that $N_{2}$ fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term $N_{2}-fixation$ rates were higher, up to 100 µmol N $m^{−2}$ $d^{−1},$ and detected $N_{2}$ fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that $N_{2}$ fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit $N_{2}$ fixation in the ETSP. |
| ISSN | 00278424 |
| e-ISSN | 10916490 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Issue Number | 16 |
| Volume Number | 113 |
| Language | English |
| Publisher | National Academy of Sciences |
| Publisher Date | 2016-04-01 |
| Publisher Place | United States |
| Access Restriction | Open |
| Subject Keyword | Nitrogen Fixation Tropical Climate Pacific Ocean Research Support, U.S. Gov't, Non-P.H.S. Multidisciplinary |
| Content Type | Text |
| Resource Type | Article |
| Subject | Multidisciplinary |
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