Denitrification and N2 fixation in the Pacific Ocean

We establish the fixed nitrogen budget of the Pacific Ocean based on nutrient fields from the recently completed World Ocean Circulation Experiment (WOCE). The budget includes denitrification in the water column and sediments, nitrogen fixation, atmospheric and riverine inputs, and nitrogen divergence due to the large-scale circulation. A water column denitrification rate of 48±5 Tg N yr −1 is calculated for the Eastern Tropical Pacific using N* [Gruber and Sarmiento, 1997] and water mass age tracers. On the basis of rates in the literature, we estimate sedimentary denitrification to remove an additional 15±3 Tg N yr−1. We then calculate the total nitrogen divergence due to the large scale circulation through the basin, composed of flows through a zonal transect at 32°S, and through the Indonesian and Bering straits. Adding atmospheric deposition and riverine fluxes results in a net divergence of nitrogen from the basin of −4±12 Tg N yr−1. Pacific nitrogen fixation can be extracted as a residual component of the total budget, assuming steady state. We find that nitrogen fixation would have to contribute 59±14 Tg N yr−1 in order to balance the Pacific nitrogen budget. This result is consistent with the tentative global extrapolations of Gruber and Sarmiento [1997], based on nitrogen fixation rates estimated for the North Atlantic. Our estimated mean areal fixation rate is within the range of direct and geochemical rate estimates from a single location near Hawaii [Karl et al., 1997]. Pacific nitrogen fixation occurs primarily in the western part of the subtropical gyres where elevated N* signals are found. These regions are also supplied with significant amounts of iron via atmospheric dust deposition, lending qualitative support to the hypothesis that nitrogen fixation is regulated in part by iron suppy.

[1]  S. Doney,et al.  Iron supply and demand in the upper ocean , 2000 .

[2]  S. Seitzinger,et al.  Global distribution of nitrous oxide production and N inputs in freshwater and coastal marine ecosystems , 1998 .

[3]  Laurence A. Anderson,et al.  On the hydrogen and oxygen content of marine phytoplankton , 1995 .

[4]  Paul G. Falkowski,et al.  Evolution of the nitrogen cycle and its influence on the biological sequestration of CO2 in the ocean , 1997, Nature.

[5]  I. Fung,et al.  Modeling of mineral dust in the atmosphere: Sources, transport, and optical thickness , 1994 .

[6]  R. Y. Morita,et al.  Denitrification and Nitrogen Fixation in Alaskan Continental Shelf Sediments , 1981, Applied and environmental microbiology.

[7]  Carl Wunsch,et al.  Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data , 2000, Nature.

[8]  L. Codispoti,et al.  Denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget , 1987 .

[9]  R. Weiss,et al.  Basin-wide distributions of chlorofluorocarbons CFC-11 and CFC-12 in the North Pacific: 1985–1989 , 1996 .

[10]  T. Saino,et al.  Geographical variation of the water column distrubution of suspended particulate organic nitrogen and its 15N natural abundance in the Pacific and its marginal seas , 1987 .

[11]  Nicolas Gruber,et al.  Global patterns of marine nitrogen fixation and denitrification , 1997 .

[12]  Wallace S. Broecker,et al.  The sequence of events surrounding Termination II and their implications for the cause of glacial‐interglacial CO2 changes , 1998 .

[13]  F. A. Richards,et al.  An analysis of the horizontal regime of denitrification in the eastern tropical North Pacific1 , 1976 .

[14]  Ricardo M Letelier,et al.  Tricho-desmium blooms and new nitrogen in the North Pacific gyre , 1992 .

[15]  R. Barnes,et al.  N2 : Ar, nitrification and denitrification in southern California borderland basin sediments1 , 1975 .

[16]  B. Hicks,et al.  The atmospheric input of trace species to the world ocean , 1991 .

[17]  Toby Tyrrell,et al.  The relative influences of nitrogen and phosphorus on oceanic primary production , 1999, Nature.

[18]  M. McElroy,et al.  Marine biological controls on atmospheric CO2 and climate , 1983, Nature.

[19]  Kon‐Kee Liu,et al.  Denitrification rates and availability of organic matter in marine environments , 1984 .

[20]  S. Tsunogai.  Ammonia in the oceanic atmosphere and the cycle of nitrogen compounds through the atmosphere and the hydrosphere , 1971 .

[21]  D. Hutchins,et al.  Iron nutrition of Trichodesmium , 1992 .

[22]  I. Koike,et al.  Hydrographic features of the deep water of the Bering Sea—the sea of Silica , 1979 .

[23]  W L Gates,et al.  A New (Revised) Tabulation of the Scripps Topography on a 1 Degree Global Grid , 1975 .

[24]  R. Fine.  Tracers, time scales, and the thermohaline circulation: The lower limb in the North Atlantic Ocean , 1995 .

[25]  Ricardo M Letelier,et al.  The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean , 1997, Nature.

[26]  M. Pahlow,et al.  Temporal trends in deep ocean Redfield ratios. , 2000, Science.

[27]  P. Crutzen,et al.  A three-dimensional model of the global ammonia cycle , 1994 .

[28]  W. A. Kaplan,et al.  Aquatic sources and sinks for nitrous oxide , 1978, Nature.

[29]  E. Carpenter.  Chapter 3 – NITROGEN FIXATION BY MARINE OSCILLATORIA (TRICHODESMIUM) IN THE WORLD's OCEANS , 1983 .

[30]  R. Ganeshram,et al.  Large changes in oceanic nutrient inventories from glacial to interglacial periods , 1995, Nature.

[31]  Edward J. Carpenter,et al.  Trichodesmium, a Globally Significant Marine Cyanobacterium , 1997 .

[32]  I. Koike,et al.  Estimates of denitrification in sediments of the Bering Sea shelf , 1979 .

[33]  A. Hattori.  Chapter 6 – DENITRIFICATION AND DISSIMILATORY NITRATE REDUCTION , 1983 .

[34]  G. Gong,et al.  The nitrogen isotopic composition of nitrate in the Kuroshio Water northeast of Taiwan: evidence for nitrogen fixation as a source of isotopically light nitrate , 1996 .

[35]  Jorge L. Sarmiento,et al.  Redfield ratios of remineralization determined by nutrient data analysis , 1994 .

[36]  C. Wunsch,et al.  Oceanic nutrient and oxygen transports and bounds on export production during the World Ocean Circulation Experiment , 2002 .

[37]  P. Quay,et al.  WOCE AMS Radiocarbon I: Pacific Ocean Results (P6, P16 and P17) , 1996, Radiocarbon.

[38]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[39]  William J. Jenkins,et al.  A comparison of ocean tracer dating techniques on a meridional section in the eastern North Atlantic , 1997 .

[40]  W. Prell,et al.  Climate-related variations in denitrification in the Arabian Sea from sediment 15N/14N ratios , 1995, Nature.

[41]  P. Kasibhatla,et al.  Simulated tropospheric NOx : Its evaluation, global distribution and individual source contributions , 1999 .

[42]  P. L. Traon,et al.  A method for optimal analysis of fields with spatially variable mean , 1990 .

[43]  C. Reimers,et al.  Intensification of recycling of organic matter at the sea floor near ocean margins , 1990, Nature.

[44]  K. Wyrtki.  Circulation and water masses in the eastern equatorial Pacific Ocean , 1967 .

[45]  W. Brandhorst.  Nitrification and Denitrification in the Eastern Tropical North Pacific , 1959 .