Phosphate availability and the ultimate control of new nitrogen input by nitrogen fixation in the tropical Pacific Ocean
Karl, David M.
Van Mooy, Benjamin A. S.
MetadataShow full item record
Due to the low atmospheric input of phosphate into the open ocean, it is one of the key nutrients that could ultimately control primary production and carbon export into the deep ocean. The observed trend over the last 20 years has shown a decrease in the dissolved inorganic phosphate (DIP) pool in the North Pacific gyre, which has been correlated to the increase in di-nitrogen (N2) fixation rates. Following a NW-SE transect, in the Southeast Pacific during the early austral summer (BIOSOPE cruise), we present data on DIP, dissolved organic phosphate (DOP) and particulate phosphate (PP) pools along with DIP turnover times (TDIP) and N2 fixation rates. We observed a decrease in DIP concentration from the edges to the centre of the gyre. Nevertheless the DIP concentrations remained above 100 nmol L−1 and T DIP was more than 6 months in the centre of the gyre; DIP availability remained largely above the level required for phosphate limitation to occur and the absence of Trichodesmium spp and low nitrogen fixation rates were likely to be controlled by other factors such as temperature or iron availability. This contrasts with recent observations in the North Pacific Ocean at the ALOHA station and in the western Pacific Ocean at the same latitude (DIAPALIS cruises) where lower DIP concentrations (<20 nmol L−1) and T DIP <50 h were measured during the summer season in the upper layer. The South Pacific gyre can be considered a High Phosphate Low Chlorophyll (HPLC) oligotrophic area, which could potentially support high N2 fixation rates and possibly carbon dioxide sequestration, if the primary ecophysiological controls, temperature and/or iron availability, were alleviated.
© 2008 Author(s). This work is distributed under the Creative Commons Attribution License. The definitive version was published in Biogeosciences 5 (2008): 95-109, doi:10.5194/bg-5-95-2008
Suggested CitationBiogeosciences 5 (2008): 95-109
The following license files are associated with this item:
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 2.5 Generic
Showing items related by title, author, creator and subject.
Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation Moore, J. Keith; Doney, Scott C. (American Geophysical Union, 2007-04-04)Recent upward revisions in key sink/source terms for fixed nitrogen (N) in the oceans imply a short residence time and strong negative feedbacks involving denitrification and N fixation to prevent large swings in the ocean ...
Cole, Marci L.; Kroeger, Kevin D.; McClelland, James W.; Valiela, Ivan (2005-07-18)Eutrophication is a major agent of change affecting freshwater, estuarine, and marine systems. It is largely driven by transportation of nitrogen from natural and anthropogenic sources. Research is needed to quantify ...
Sachs, Julian P. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-02)The goals of this thesis were: (1) to establish methods for the determination of nitrogen and carbon isotope ratios in marine particulate and sedimentary chlorophyll derivatives; (2) to establish chlorophyll δ15N and ...