Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 8 2009 10.5194/bg-6-1405-2009 http://www.biogeosciences.net/6/1405/2009/ http://www.biogeosciences.net/6/1405/2009/bg-6-1405-2009.html http://www.biogeosciences.net/6/1405/2009/bg-6-1405-2009.pdf 1405 1421 2009-08-05 Estimating the monthly <i>p</i>CO₂ distribution in the North Atlantic using a self-organizing neural network M. Telszewski m.telszewski@uea.ac.uk A. Chazottes U. Schuster A. J. Watson C. Moulin D. C. E. Bakker M. González-Dávila T. Johannessen A. Körtzinger H. Lüger A. Olsen A. Omar X. A. Padin A. F. Ríos T. Steinhoff M. Santana-Casiano D. W. R. Wallace R. Wanninkhof School of Environmental Sciences, University of East Anglia, Norwich, UK L'Institut Pierre-Simon Laplace/Laboratoire des Sciences du Climat et de l'Environnement, Centre National de la Recherche Scientifique – Commissariat à l'Énergie Atomique, Gif-sur-Yvette, France Department of Marine Chemistry, Universidad de Las Palmas de Gran Canaria, Las Palmas, Gran Canaria, Spain Geophysical Institute, University of Bergen, Bergen, Norway Leibniz Institute of Marine Sciences, Kiel, Germany Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, Florida, USA Instituto de Investigaciones Marinas, Consejo Superior de Investigaciones Científicas (CSIC), Vigo, Spain Bjerknes Centre for Climate Research, UNIFOB AS, Bergen, Norway Marine Chemistry, Departement of Chemistry, University of Göterborg, Göteborg, Sweden Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (<i>p</i>CO₂) for the North Atlantic on a 1&deg; latitude by 1&deg; longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine <i>p</i>CO₂. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFS-MODIS chlorophyll-<i>a</i> concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway <i>p</i>CO₂ measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437 &mu;atm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 &mu;atm, which equals to just above 3 per cent of an average <i>p</i>CO₂ value in the in situ dataset. The seasonal <i>p</i>CO₂ cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO₂ fluxes or improvement of seasonal and interannual marine CO₂ cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences. Ali, M. M., Kishtawal, C. M., and Jain, S.: Predicting cyclone tracks in the North Indian Ocean: An artificial neural network approach, Geophys. Res. Lett., 34, L04603, doi:10.1029/2006GL028353, 2007. Bates, N. R., Takahashi, T., Chipman, D. W., and Knap, H.: Variability of $p$CO₂ on diel to seasonal timescales in the Sargasso Sea, J. Geophys. Res., 103, 15567–15585, 1998. Bates, N. R.: Interannual variability of oceanic CO₂ and biogeochemical properties in the western North Atlantic subtropical gyre, Deep-Sea Res. Pt. II, 48, 1507–1528, 2002. Bates, N. R., Pequignet, A. C., Johnson, R. J., and Gruber, N.: A short term sink for atmospheric CO₂ in subtropical mode water of the North Atlantic Ocean, Nature, 420, 489–493, 2002. Canadell, J. G. Le Quéré, C., Raupach, M. R., Field, C. B., Buitenhuis, E. T., Ciais, P., Conway, T. J., Gillett, N. P., Houghton, R. A., and Marland, G.: Contributions to accelerating atmospheric CO₂ growth from economic activity, carbon intensity, and efficiency of natural sinks, P. Natl. Acad. Sci. USA, 104(24), 10288–10293, 2007. Cavazos, T.: Using Self-Organizing Maps to Investigate Extreme Climate Events: An Application to the Wintertime Precipitation in the Balkans, J. Climate, 13, 1718–1732, 1999. Chierici, M., Olsen, A., Johannessen, T., Trinanes, J., and Wanninkhof, R.: Algorithms to estimate the carbon dioxide uptake in the northern North Atlantic using ship-observations, satellite and ocean analysis data, Deep-Sea Res. Pt. II, 56(8–10), 630–639, 2009. Cooper, D. J., Watson, A. J., and Ling, R. D.: Variation of $p$CO₂ along a North Atlantic shipping route (UK to the Caribbean): A year of automated observations, Mar. Chem., 60, 147–164, 1998. Corbière, A., Metzl, N., Reverdin, G., Brunet, C., and Takahashi, T.: Interannual and decadal variability of the oceanic carbon sink in the North Atlantic subpolar gyre, Tellus, 59B(2), 168–178, 2007. Dreyfus, G.: Neural Networks: Methodology and Applications, Springer-Verlag, Berlin Heidelberg, New York, Germany, 2005. Friedrich, T. and Oschlies, A.: Neural network-based estimates of North Atlantic surface pCO₂ from satellite data: A methodological study, J. Geophys. Res., 114, C03020, doi:10.1029/2007JC004646, 2009. Hagen, E.: Northwest African upwelling scenario, Oceanol. Acta, 24, S113–S128, 2001. Hewitson, B. C. and Crane, R. G.: Self-organizing maps: applications to synoptic climatology, Climate Res., 22, 13–26, 2002. Jamet, C., Moulin, C., and Lefèvre, N.: Estimation of the oceanic $p$CO₂ in the North Atlantic from VOS lines in situ measurements: Parameters needed to generate seasonally mean maps, Ann. Geophys., 25, 2247–2257, 2007. Kalnay, E. Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Redell, M., Saha, S., White, G., Woollen, J., Zhu, Y., Chelliah, M., Ebisuzaki, W., Higgins, W., Janowiak, J., Mo, K. C., Ropelewski, C., Leetmaa, A., Reynolds, R., and Jenne, R.: The NCEP/NCAR Reanalysis Project, B. Am. Meteorol. Soc., 77, 437–471, 1996. Kaufman, Y. J.: The atmospheric effect on remote sensing and its correction, pages 336–428, in: Theory and applications of optical remote sensing, edited by: Asrar, G., 752 pp., Wiley-Interscience, 1989. Kohonen, T.: Self-Organizing Maps, Third ed., Springer-Verlag, Berlin Heidelberg New York, 501 pp., 2001. Lefèvre, N., Watson, A. J., Cooper, D. J., Weiss, R. F., Takahashi, T., andSutherland, S. C.: Assessing the seasonality of the oceanic sink for CO₂ in the northern hemisphere, Global Biogeochem. Cy., 13(2), 273–286, 1999. Lefèvre, N., Watson, A. J., Olsen, A., Ríos, A. F., Pérez, F. F., and Johannessen, T.: A decrease in the sink for atmospheric CO₂ in the North Atlantic, Geophys. Res. Lett., 31, L07306, doi:10.1029/2003GL018957, 2004. Lefèvre, N., Watson, A. J., and Watson, A. R.: A comparison of multiple regression and neural network techniques for mapping in situ $p$CO₂ data, Tellus, 57, 375–384, 2005. Liu, Y. and Weisberg, R. H.: Patterns of ocean current variability on the West Florida Shelf using self-organizing map, J. Geophys. Res, 110, C06003, doi:10.1029/2004JC002786, 2005. Liu, Y., Weisberg, R. H., and He, R.: Sea Surface Temperature Patterns on the West Florida Shelf Using Growing Hierarchical Self-Organizing Maps, J. Atmos. Ocean. Tech., 23, 325–338, 2006a. Liu, Y., Weisberg, R. H., and Mooers, C. N. K.: Performance evaluation of the self-organizing map for feature extraction, J. Geophys. Res., 111, C05018, doi:10.1029/2005JC003117, 2006b. Longhurst, A. R.: Ecological Geography of the Sea, Second Ed., Academic, Boston, Mass., 542 pp., 2007. Lüger, H., Wallace, D. W. R ., Körtzinger, A., and Nojiri, Y.: The pCO₂variability in the midlatitude North Atlantic Ocean during a full annual cycle, Global Biogeochem. Cy., 18, GB3023, doi:10.1029/2003GB002200, 2004. Lüger, H., Wanninkhof, R., Wallace, D. W. R., and Körtzinger, A.: CO₂ fluxes in the subtropical and subarctic North Atlantic based on measurements from a volunteer observing ship, J. Geophys. Res, 111, C06024, doi:10.1029/2005JC003101, 2006. Moulin, C., Gordon, H. R., Chomko, R. M., Banzon, V. F., and Evans, R. H.: Atmosphereic correction of ocean color imagery through thick layers of Saharan dust, Geophys. Res. Lett., 28, 5–8, 2001. Niang, A., Thiria, S., Badran, F., and Moulin, C.: Automatic neural classification of ocean colour reflectance spectra at the top of the atmosphere with introduction of expert knowledge, Remote Sens. Environ., 86, 257–271, 2003. Niang, A., Badran, F., Moulin, C., Crepon, M., and Thiria, S.: Retrieval of aerosol type and optical thickness over the Mediterranean from SeaWiFS images using an automatic neural classification method, Remote Sens. Environ., 100, 82–94, 2006. Olsen, A., Bellerby, R. G. J., Johannessen, T., Omar, A. M., and Skjelvan, I.: Interannual variability of the wintertime air-sea flux of carbon dioxide in the northern North Atlantic, 1981–2001, Deep-Sea Res. Pt. I, 50, 1323–1338, 2003. Olsen, A., Triñanes, J. A., and Wanninkhof, R.: Sea-air flux of CO₂ in the Caribbean Sea estimated using in situ and remote sensing data, Remote Sens. Environ., 89, 309–325, 2004. Olsen, A., Brown, K. R., Chierici, M., Johannessen, T., and Neill, C.: Sea-surface CO₂ fugacity in the subpolar North Atlantic, Biogeosciences, 5, 535–547, 2008. Omar, A. M. and Olsen, A.: Reconstructing the time history of the air-sea CO₂ disequilibrium and its rate of change in the eastern subpolar North Atlantic, 1972–1989, Geophys. Res. Lett., 33, L04602, doi:10.1029/2005GL025425, 2006. Pelegri, J. L., Aristegui, J., Cana, L., Gonzalez-Davila, M., Hernandez-Guerra, A., Hernandez-Leon, S., Marrero-Diaz, A., Montero, M. F., Sangra, P., and Santana-Casiano, J. M.: Coupling between open ocean and the coastal upwelling region off northwet Africa:water circulation and offshore pumping of organic matter, J. Marine Syst., 54, 3–37, 2005. Phillips, H. E. and Joyce, T. M.: Bermuda's tale of two time series: Hydrostation S and BATS, J. Phys. Oceanogr., 37, 554–571, 2007. Reusch, D. B., Alley, R. B., Hewitson, B. C.: North Atlantic climate variability from a self-organizing map perspective, J. Geophys. Res., 112, D02104, doi:10.1029/2006JD007460, 2007. Richardson, A. J., Risien, C., and Shillington, F. A.: Using self-organizing maps to identify patterns in satellite imagery, Prog. Oceanogr., 59, 223–239, 2003. Sabine, C. L., Feely, R. A., Gruber, N., Key, R. M., Lee, K., Bullister, J. L., Wanninkhof, R., Wong, C. S., Wallace, D. W. R., Tilbrook, B., Millero, F. J., Peng, T. H., Kozyr, A., Ono, T., and Rios, A. F.: The oceanic sink for anthropogenic CO₂, Science, 305(5682), 367–371, 2004. Santana-Casiano, J. M., Gonzalez-Davila, M., Rueda, M. J., Llinas, O., and Gonzalez-Davila, E. F.: The interannual variability of oceanic CO₂ parameters in the northeast Atlantic subtropical gyre at the ESTOC site, Global Biogeochem. Cy, 21, GB1015, doi:10.1029/2006GB002788, 2007. Sarmiento, J. L. and Gruber, N.: Sinks for anthropogenic carbon, Phys. Today, 55, 30–36, 2002. Schuster, U. and Watson, A. J. W.: A variable and decreasing sink for atmospheric CO₂ in the North Atlantic, J. Geophys. Res., 112, C11006, doi:10.1029/2006JC003941, 2007. Schuster, U., Watson, A. J., Bates, N., Corbière, A., Gonzalez-Davila, M., Metzl, N., Pierrot, D., and Santana-Casiano, M.: Trends in North Atlantic sea surface fCO₂ from 1990 to 2006, Deep-Sea Res. Pt. II, 56(8–10), 620–629, 2009. Takahashi, T. Feely, R. A., Weiss, R. F., Wanninkhof, R. H., Chipman, D. W., Sutherland, S. C., and Takahashi, T. T.: Global sea-air CO₂ flux based on climatological surface ocean pCO₂, and seasonal biological and temperature effects, Deep-Sea Res. Pt. II, 49(9–10), 1601–1622, 2002. Takahashi, T., Sutherland, S. C., Wanninkhof, R., Sweeney, C., Feely, R. A., Chipman, D. W., Hales, B., Friederich, G., Chavez, F., Sabine, C., Watson, A. J., Bakker, D. C., Schuster, U., Metzl, N., Yoshikawa-Inoue, H., Ishii, M., Midorikawa, T., Nojiri, Y., Körtzinger, A., Steinhoff, T., Hoppema, M., Olafsson, J., Arnarson, T. S., Tilbrook, B., Johannessen, T., Olsen, A., Bellerby, R., Wong, C. S., Delille, B., Bates, N. R., and de Baar, H. J. W.: Climatological mean and decadal change in surface ocean $p$CO₂, and net sea-air CO₂ flux over the global oceans, Deep-Sea Res. Pt. II, 56(8–10), 554–577, 2009. Vesanto, J., Himberg, J., Alhoniemi, E., and Parhankagas, J.: SOM Toolbox for Matlab 5., Libella Oy, Espoo, 59 pp., 2000. Watson, A. J., Schuster, U., Bakker, D .C. E., Bates, N., Corbière, A., Friedrich, T., González-Dávila, M., Hauck, J., Heinze, C., Johannessen, T., Körtzinger, A., Metzl, N., Olafsson, J., Olsen, A., Oschlies, A., Padin, X. A., Pfeil, B., Santana-Casiano, M., Steinhoff, T., Telszewski, M., Ríos, A., and Wallace, D. W. R., Wanninkhof, R.: Accurately tracking the variation in the North Atlantic sink for atmospheric CO₂, Science, in review, 2009.