Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 4 4 2007 10.5194/bg-4-455-2007 http://www.biogeosciences.net/4/455/2007/ http://www.biogeosciences.net/4/455/2007/bg-4-455-2007.html http://www.biogeosciences.net/4/455/2007/bg-4-455-2007.pdf 455 479 2007-07-06 Modeling the impact of iron and phosphorus limitations on nitrogen fixation in the Atlantic Ocean V. J. Coles vcoles@hpl.umces.edu R. R. Hood Horn Point Laboratory, University of Maryland Center for Environmental Science, P.O. Box 775, 2020 Horns Point Road, Cambridge, MD, 21613 USA The overarching goal of this study is to simulate subsurface N* (sensu, Gruber and Sarmiento, 1997; GS97) anomaly patterns in the North Atlantic Ocean and determine the basin wide rates of N₂-fixation that are required to do so. We present results from a new Atlantic implementation of a coupled physical-biogeochemical model that includes an explicit, dynamic representation of N₂-fixation with light, nitrogen, phosphorus and iron limitations, and variable stoichiometric ratios. The model is able to reproduce nitrogen, phosphorus and iron concentration variability to first order. The latter is achieved by incorporating iron deposition directly into the model's detrital iron compartment which allows the model to reproduce sharp near surface gradients in dissolved iron concentration off the west coast of Africa and deep dissolved iron concentrations that have been observed in recent observational studies. The model can reproduce the large scale N* anomaly patterns but requires relatively high rates of surface nitrogen fixation to do so (1.8×10¹² moles N yr^−1 from 10° N–30° N, 3.4×10¹² moles N yr^−1 from 25° S–65° N). In the model the surface nitrogen fixation rate patterns are not co-located with subsurface gradients in N*. Rather, the fixed nitrogen is advected away from its source prior to generating a subsurface N* anomaly. Changes in the phosphorus remineralization rate (relative to nitrogen) linearly determine the surface nitrogen fixation rate because they change the degree of phosphorus limitation, which is the dominant limitation in the Atlantic in the model. Phosphorus remineralization rate must be increased by about a factor of 2 (relative to nitrogen) in order to generate subsurface N* anomalies that are comparable to the observations. We conclude that N₂-fixation rate estimates for the Atlantic (and globally) may need to be revised upward, which will help resolve imbalances in the global nitrogen budget suggested by Codispoti et al. (2001) and Codispoti (2007). Ammerman, J. W., Hood, R. R., Case, D. A., and Cotner, J. B.: Phosphorus deficiency in the Atlantic: An emerging paradigm in Oceanography, EOS 84, 165–170, 2003. Anderson, R. F. and Henderson, G. M.: GEOTRACES A global study of the marine biogeochemical cycles of trace elements and their isotopes, Oceanography, 18, 76–79, 2005. Bates, N. R. and Hansell, D. A.: Temporal variability of excess nitrate in the Subtropical Mode Water of the North Atlantic Ocean, Mar. Chem., 84, 225–241, 2004. Bergquist, B. A. and Boyle, E. A.: Dissolved iron in the tropical and subtropical Atlantic Ocean, Global Biogeochem. Cy., 20, GB1015, doi:10.1029/2004GB0025405, 2006. Bleck, R.: An oceanic general circulation model framed in hybrid isopycnic-cartesian coordinates, Ocean Model., 4, 55–88, 2002. Bowie, A. R., Whitworth, D. J., Achterberg, E. P., Mantoura, R. F. C., and Worsfold, P. J.: Biogeochemistry of Fe and other trace elements (Al, Co, Ni) in the upper Atlantic Ocean, Deep-Sea Res. I, 49, 605–636, 2002. Broecker, W. S.: Keeping global change honest, Global Biogeochem. Cy., 5, 191–192, 1991. Capone, D. G., Burns, J. A., Montoya, J. P., Michaels, A. F., Subramaniam, A., Carpenter, E. J.: Nitrogen fixation by \textitTrichodesmium spp.: An important source of new nitrogen to the tropical North Atlantic Ocean, Global Biogeochem. Cy., 19, GB2024, doi:10.1029/2004GB002331, 2005. Capone, D. G., Zehr, J. P., Paerl, H. W., Bergman, B., and Carpenter, E. J.: \textitTrichodesmium: a globally significant marine cyanobacterium, Science, 276, 1221–1229, 1997. Carpenter, E. J. and Romans, K.: Major role of the cyanobacterium \textitTrichodesmium in nutrient cycling in the North Atlantic Ocean, Science, 254, 1356–1358, 1991. Chassignet, E. P., Smith, L. T., Halliwell, G. R., and Bleck, R.: North Atlantic simulation with the HYbrid Coordinate Ocean Model (HYCOM): Impact of the vertical coordinate choice, reference density, and thermobaricity, J. Phys. Oceanogr., 33, 2504–2526, 2003. Christian, J. R., Verschell, M. A., Murtugudde, R., Busalacchi, A. J., and McClain, C. R.: Biogeochemical modeling of the tropical Pacific Ocean. II: Iron biogeochemistry, Deep-Sea Res. II, 49, 545–565, 2002b. Codispoti, L., Brandes, J. A., Christensen, J., Devol, A., Naqvi, S., Paerl, H. W., and Yoshinari, T.: The oceanic fixed nitrogen and nitrous oxide budgets: Moving targets as we enter the anthropocene?, Scientia Marina (Barcelona), 65, suppl. 2, 85–105, 2001. Codispoti, L.: An oceanic fixed nitrogen sink exceeding 400 Tg N a_1 vs the concept of homeostasis in the fixed-nitrogen inventory, Biogeosciences, 4, 233–253, 2007. Coles, V. J., Hood, R. R., Pascual, M., and Capone, D. G.: Modeling the effects of \textitTrichodesmium and nitrogen fixation in the Atlantic Ocean, J. Geophys. Res., 109, C06007, doi:06010.01029/02002JC001754, 2004. Conkright, M. E., Levitus, S., and Boyer, T. P.: World Ocean Atlas 1994, Volume 1: Nutrients. NOAA Atlas NESDIS 1. U.S. Department of Commerce, NOAA, NESDIS, Silver Spring, MD, 1994. Croot, P. L., Streu, P., and Baker, A. R.: Short residence time for iron in surface seawater impacted by atmospheric dry deposition from Saharan dust events, Geophys. Res. Lett., 31, doi:10.1029/2004GL020153, 2004. da Silva, A., Young, A. C., and Levitus, S.: Atlas of Surface Marine Data, Vol 1, Algorithms and Procedures, National Oceanic and Atmospheric Administration, Silver Spring, MD, 1994. Davis, C. S. and McGillicuddy, D. J.: Transatlantic abundance of the N₂-fixing colonial cyanobacterium \textitTrichodesmium, Science, 312, 1517–1520, 2006. Del Vecchio, R. and Subramaniam, A.: Influence of the Amazon River on the surface optical properties of the western tropical North Atlantic Ocean, J. Geophys. Res., 109, C11001, doi:10.1029/2004JC002503, 2004. Deutsch, C., Sarmiento, J. L., Sigman, D. M., Gruber, N., and Dunne, J. P.: Spatial coupling of nitrogen inputs and losses in the ocean, Nature, 455, doi:10.1038 163–167, 2007. Doney, S. C.: Ocean Carbon and Climate Change (OCCC): An Implementation Strategy for U.S. Carbon Science Scientific Steering Group (CCSSG) and Inter-agency Working Group (CCIWG), Washington D.C., 108~pp., 2004. Duce, R. A. and Tindale, N. W.: Atmospheric transport of iron and its deposition in the ocean, Limnol. Oceanogr., 36, 1715–1726, 1991. Dutkiewicz, S., Follows, M. J., and Parekh, P.: Interactions of the iron and phosphorus cycles: A three-dimensional model study, Global Biogeochem. Cy., 19(1), GB1021, doi:10.1029/2004GB002342, 2005. Dyhrman, S. T., Chappell, P. D., Haley, S. T., Moffett, J. W., Orchard, E. D., Waterbury, J. B., and Webb, E. A.: Phosphonate utilization by the globally important marine diazotroph \textitTrichodesmium, Nature, 439, 68–71, 2006. Fennel, K., Spitz, Y. H., Letelier, R. M., Abbott, M. R., and Karl, D. M.: A deterministic model for N₂-fixation at stn. ALOHA in the subtropical North Pacific Ocean, Deep-Sea Res. II, 49, 149–174, 2002. Fung, I. Y., Meyn, S. K., Tegen, I., Doney, S. C., John, J. G., Bishop, J. K. B.: Iron supply and demand in the upper ocean, Global Biogeochem. Cyc., 14, 281–295, 2000. Gruber, N. and Sarmiento, J. L.: Global patterns of marine nitrogen fixation and denitrification, Global Biogeochem. Cy., 11, 235–266, 1997. Gruber, N. and Sarmiento, J. L.: Large scale biogeochemical-physical interactions in elemental cycles, in: The Sea, edited by: Robinson, A. R., McCarthy, J. J., Rothschild, B. J., John Wiley, New York, 337–399, 2002. Gruber, N.: The marine nitrogen cycle: Overview of distributions and processes, in: Nitrogen in the Marine Environment, 2nd Edition, edited by: Carpenter, E. J., Capone, D. G., Bronk, D. A., and Mulholland, M. R., Elsevier, 2007, in press. Halliwell, G. R.: Evaluation of vertical coordinate and vertical mixing algorithms in the HYbrid Coordinate Ocean Model (HYCOM), Ocean Model., 7, 285–322, 2004. Hansell, D. A., Bates, N. R., and Olson, D. B.: Excess nitrate and nitrogen fixation in the Subtropical North Atlantic, Mar. Chem., 84, 243–265, 2004. Her\~nandez-León, S., Postel, L., Arístegui, J., Gómez, M., Frenanda Montero, M., Torres, S., Almeida, C., Kuhner, E., Brenning, U., and Hagen, E.: Large-scale and mesoscale distribution of plankton biomass and metabolic activity in the northeastern central Atlantic, J. Oceanogr., 55, 471–482, 1999. Hood, R. R., Bates, N. R., Capone, D. G., and Olson, D. B.: Modeling the effect of nitrogen fixation on carbon and nitrogen fluxes at BATS, Deep-Sea Res. II, 48, 1609–1648, 2001. Hood, R. R., Coles, V. J., and Capone, D. G.: Modeling the distribution of \textitTrichodesmium and nitrogen fixation in the Atlantic Ocean, J. Geophys. Res., 109, C06006, doi:10.1029/2002JC001753, 2004. Hood, R. R., Laws, E. A., Armstrong R. A., Bates N. R., Brown C. W., Carlson C. A., Chai F., Doney S. C., Falkowski P.G., Feely R.A., Friedrichs M.A.M., Landry M.R., Moore J.K., Nelson D.M., Richardson T.L., Salihoglu B., Schartau M., Toole D.A., Wiggert J.D.: Pelagic functional group modeling: Progress, challenges and prospects, Deep-Sea Res. II, 53, 459-512, 2006. Hood, R. R., Michaels, A. F., and Capone, D. G.: Answers sought to the enigma of marine nitrogen fixation, EOS, 81, 133, 138–139, 2000. Karl, D. M., Letelier, R., Hebel, D. V., Bird, D. F., and Winn, C. D.: Trichodesmium blooms and new nitrogen in the North Pacific gyre, in: Marine Pelagic Cyanobacteria: Trichodesmium and other Diazotrophs, edited by: Carpenter, E. J., Capone, D. G., and Reuter, J. G., Kluwer Academic Publishers, Boston, 219–237, 1992. Karl, D. M., Letelier, R., Tupas, L., Dore, J., Christian, J., and Hebel, D.: The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean, Nature, 388, 533–538, 1997. Key, R. M., Kozyr, A., Sabine, C. L., Lee, K., Wanninkhof, R., Bullister, J., Feely, R. A., Millero, F., Mordy, C., and Peng, T. H.: A global ocean carbon climatology: Results from GLODAP, Global Biogeochem. Cy., 18, BG4031, doi:10.1029/2004GB002247, 2004. Langlois, R. J., LaRoche, J., and Raab, P. A.: Diazotrophic diversity and distribution in the tropical and subtropical Atlantic ocean, Appl. Environ. Microbiol., 71, 7910–7919, 2005. Laws, E. A., Falkowski, P. G., Smith, W. O., Ducklow, H., and McCarthy, J. J.: Temperature effects on export production in the open ocean, Global Biogeochem. Cy., 14, 1231–1246, 2000. Lee, K.: Global net community production estimated from the annual cycle of surface water total dissolved inorganic carbon, Limnol. Oceanogr., 46, 1287–1297, 2001. Lee, K., Karl, D. M., Waninkhof, R., and Zhang, J.-Z.: Global estimates of net carbon production in the nitrate-depleted tropical and subtropical oceans, Geophys. Res. Lett., 29, 1907, doi:1910.1029/2001GL014198, 2002. Levitus, S. and Boyer, T. P.: World Ocean Atlas 1994, Vol 4, Temperature, NOAA Atlas NESDIS 4, U.S. Department of Commerce, NOAA, NESDIS, Silver Spring, MD, 1994. Levitus, S., Burgett, R., and Boyer, T. P.: World Ocean Atlas 1994, Vol 3, Salinity, NOAA Atlas NESDIS 3, U.S. Department of Commerce, NOAA, NESDIS, Silver Spring, MD, 1994. Louanchi, F. and Najjar, R. G.: A global climatology of phosphate, nitrate and silicate in the upper ocean: Spring-summer production and shallow remineralization, Global Biogeochem. Cy., 14, 957–978, 2000. Louanchi, F. and Najjar, R. G.: Annual cycles of nutrients and oxygen in the upper layers of the North Atlantic Ocean, Deep-Sea Res. II, 48, 2155–2171, 2001. Luo, C., Mahowald, N., and del Corral, J.: Sensitivity study of meteorological parameters on mineral aerosol mobilization, transport and distribution, J. Geophys. Res., 108(D12), 4447, doi:10.1029/2003JD0003483, 2003. Mahowald, N. and Luo, C.: A less dusty future?, Geophys. Res. Lett., 30, 1903, doi:10.1029/2003GL017880, 2003. Mahowald, N., Luo, C., del Corral, J., and Zender, C.: Interannual variability in atmospheric mineral aerosols from a 22-year model simulations and observational data, J. Geophys. Res., 108(D12), 4352, doi:10.1029/2002JD002821, 2003. Martin, J. H., Knauer, G. A., Karl, D. M., and Broenkow, W. W.: VERTEX: Carbon cycling in the Northeast Pacific, Deep-Sea Res., 34, 267–285, 1987. Michaels, A. F., Olson, D., Sarmiento, J. L., Ammerman, J. W., Fanning, K., Jahnke, R., Knap, A. H., Lipschultz, F., and Prospero, J. M.: Inputs, losses and transformations of nitrogen and phosphorus in the pelagic North Atlantic Ocean, Biogeochemistry, 35, 181–226, 1996. Mills, M. M., Ridame, C., Davey, M., La Roche, J., and Geider, R. J.: Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic, Nature, 429, 292–294, 2004. Moore, C. M., Mills, M. M., Milne, A., Langlois, R., Achterberg, E. P., Lochte, K., Geider, R. J., and La Roche, J.: Iron limits primary productivity during spring bloom development in the central North Atlantic, Global Change Biol., 12, 626–634, 2006a. Moore, J. K., Doney, S. C., Glover, D. M., and Fung, I. Y.: Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean, Deep-Sea Res. II, 49, 463–507, 2002b. Moore, J. K., Doney, S. C., Kleypas, J. A., Glover, D. M., and Fung, I. Y.: An intermediate complexity marine ecosystem model for the global domain, Deep-Sea Res. II, 49, 403–462, 2002a. Moore, J. K., Doney, S. C., and Lindsay, K.: Upper ocean ecosystem dynamics and iron cycling in a global three-dimensional model, Global Biogeochem. Cy., 18, GB4028, doi:4010.1029/2004GB002220, 2004. Moore, J. K., Doney, S. C., Lindsay, K., Mahowald, N., and Michaels, A. F.: Nitrogen fixation amplifies the ocean biogeochemical response to decadal timescale variations in mineral dust deposition, Tellus Series B, 58(5), 560–572, 2006b. Moore, J. K. and Doney, S. C.: Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation, Global Biogeochem. Cy., 21, GB2001, doi:10.1029/2006GB002762, 2007. Neumann, T.: Towards a 3D-ecosystem model of the Baltic Sea, J. Mar. Syst., 25, 405–419, 2000. Orcutt, K. M., Lipschultz, F., Gundersen, K., Anrimoto, R., Gallon, J. R., Michaels, A. F., and Knap, A. H.: A Seasonal study of the significance of N₂ fixation by \textitTrichodesmium spp. at the Bermuda Atlantic Time-Series Study (BATS), Deep-Sea Res., 48, 1583–1608, 2001. Paerl, H. W., Prufert-Bebout, L. E., Guo, and C. Z.: Iron-stimulated N-2 fixation and growth in natural and cultured populations of the planktonic marine cyanobacteria \textitTrichodesmium spp., Appl. Environ. Microbiol., 60, 1044–1047, 1994. Parekh, P., Follows, M. J., and Boyle, E. A.: Decoupling of iron and phosphate in the global ocean, Global Biogeochem. Cy., 19, GB2020, doi:10.1029/2004GB002280, 2005. Redfield, A. C. , Ketchum, B. H., and Richard, F. A.: The influence of organisms on the composition of seawater, in: The Sea, edited by: Hill, M. N., Interscience, New York, 27–77, 1963. Rueter, J. G.: Theoretical Fe limitations of microbial N₂ fixation in the oceans, EOS, 63, 945, 1982. Rueter, J. G., Hutchins, D. A., Smith, R. W., and Unsworth, N. L.: Iron nutrition of Trichodesmium, in: Marine Pelagic Cyanobacteria: Trichodesmium and other Diazotrophs, edited by: Carpenter, E. J., Capone, D. G., and Rueter, J. G., Kluwer Academic Publishers, Dordrecht, The Netherlands, 289–306, 1992. Sanudo-Wilhelmy, S. A., Kustka, A. B., Gobler, C. J., Hutchins, D. A., Yang, M., Lwiza, K., Burns, J., Capone, D. G., Raven, J. A., and Carpenter, E. J.: Phosphorus limitation of nitrogen fixation by Trichodesmium in the central Atlantic Ocean, Nature, 411, 66–69, 2001. Sarmiento, J. L. and Bender, M. L.: Carbon biogeochemistry and climate change, Photosynth. Res., 39, 209–234, 1994. Siegel, D. A. and Deuser, W. G.: Trajectories of sinking particles in the Sargasso Sea: modeling of statistical funnels above deep-ocean sediment traps, Deep-Sea Res., 44, 1519–1541, 1997. Tortell, P. D., Maldonado, M. M., Granger, J., and Price, N. M.: Marine bacteria and biogeochemical cycling of iron in the oceans, FEMS Microbiol. Ecol., 29, 1–11, 1999. Tyrrell, T.: The relative influences of nitrogen and phosphorus on oceanic primary production, Nature, 400, 525–531, 1999. Tyrrell, T., Marañón, E., Poulton, A., Bowie, A. R., Harbour, D. S., and Woodward, E. M. S.: Large-scale latitudinal distribution of \textitTrichodesmium spp. in the Atlantic Ocean, J. Plankton Res., 25, 405–416, 2003. Voss, M., Croot, P., Lochte, K., Mills, M. and Peeken, I.: Patterns of nitrogen fixation along 10N in the tropical Atlantic, Geophys. Res. Let., 31, L23S09, doi:10.1029/2004GL020127, 2004. Vrede, K., Heldal, M., Norland, S., and Bratbak, G.: Elemental composition (C, N, P) and cell volume of exponentially growing and nutrient-limited bacterioplankton, Applied and Environmental Microbiology, 68(6), 2965–2971, doi:10.1128/AEM.68.6.2965-2971.2002, 2002. Walsh, J. J. and Steidinger, K. A.: Saharan dust and Florida red tides: The cyanophyte connection, J. Geophys. Res., 106, 11 597–11 612, 2001. Wu, J., Sunda, W., Boyle, E. A., and Karl, D. M.: Phosphate depletion in the Western North Atlantic Ocean, Science, 289, 759–762, 2000. Yamamoto-Kawai, M., Carmack, E., and McLaughlin, F.: Nitrogen balance and Arctic throughflow, Nature, 443(7107), 43–43, 2006.