Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 6 2009 10.5194/bg-6-1105-2009 http://www.biogeosciences.net/6/1105/2009/ http://www.biogeosciences.net/6/1105/2009/bg-6-1105-2009.html http://www.biogeosciences.net/6/1105/2009/bg-6-1105-2009.pdf 1105 1114 2009-06-25 Evidence for surface organic matter modulation of air-sea CO₂ gas exchange M. Ll. Calleja mcalleja@ucsc.edu C. M. Duarte Y. T. Prairie S. Agustí G. J. Herndl IMEDEA (CSIC-UIB), Grup d' Oceanografía Interdisciplinar, C/ Miquel Marquès 21, 07190 Esporles, Mallorca, Spain Department of Ocean Sciences, University of California, 1156 High Street, Santa Cruz, CA 95064, USA Département des Sciences Biologiques, Université du Québec à Montréal. Box 8888, succ. Centre-Ville, Montreal, Qc, H3C 3P8 Canada Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, The Netherlands Air-sea CO₂ exchange depends on the air-sea CO₂ gradient and the gas transfer velocity (<i>k</i>), computed as a function of wind speed. Large discrepancies among relationships predicting <i>k</i> from wind suggest that other processes also contribute significantly to modulate CO₂ exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean, confirming previous observations. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (<i>k</i>) was evaluated by direct measurements of air-sea CO₂ fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO₂ fluxes, for a given air-sea CO₂ partial pressure gradient and wind speed below 5 m s^&minus;1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These results support previous evidences that consideration of the role of organic matter in modulating air-sea CO₂ exchange may improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean. Belanger, T. V., and Korzun E. A.: Critique of floating dome technique for estimating reaeration rates, J. Environ. Eng. 117, 144–150, 1991. Borges, A. V., Delille, B., Schiettecatte, L.-S., Gazeau, F., Abril G., and Frankignoulle, M.: Gas transfer velocities of CO₂ in three European estuaries (Randers Fjord, Scheldt and Thames), Limnol. Oceanogr., 49, 1630–1641, 2004a. Borges, A. V., Vanderborght, J. P., Schiettecatte, L.-S., Gazeau, F., Ferron-Smith, S., Delille, B., and Frankignoulle, M.: Variability of the gas transfer velocity of CO₂ in a Macrotidal Estuary (the Scheldt), Estuaries, 27, 593–603, 2004b. Broecker, H. C., and Siems, W.: The role of bubbles for gas transfer from water to air at higher wind speeds. Experiments in the wind-wave facility in Hamburg, in: Gas Transfer at Water Surfaces, edited by: Brutsaert, W. and Jirka, G. H., pp. 229-236. Dordrecht, Reidel, 1984. Calleja, M. Ll., Duarte, C. M., Navarro, N., and Agustí, S.: Control of air-sea CO₂ disequilibria in the subtropical NE Atlantic by planktonic metabolism under the ocean skin, Geophys. Res. Lett., 32, L08606, doi:10.1029/2004GL022120, 2005. Dachs, J., Calleja, M., Ll., Duarte, C. M., delVento, S., Turpin, B., Polidori, A., Herndl, G. J., and Agustí, S.: High atmosphere-ocean exchange of organic carbon in the NE subtropical Atlantic, Geophys. Res. Lett., 32, L21807, doi:10.1029/2005GL023799, 2005. Donelan, M. A. Air-sea interaction, in: The Sea, 9, edited by: Le Mehaute, B. and D. M., 239–292, Ocean Eng. Sci., Wiley-Interscience, Hoboken, New Jersey, USA, 1990. Duarte, C. M. and Prairie, Y. T.: Prevalence of heterotrophy and atmospheric CO₂ emissions from aquatic ecosystems, Ecosystems, 8, 862–870, 2005. Frankignoulle, M.: Field-measurements of air sea CO₂ exchange, Limnol. Oceanogr., 33, 313–322, 1988. Frew, N. M.: The role of organic films in air-sea gas exchange, in: The Sea Surface and Global Change, edited by: Liss, P. S. and Duce, R. A., 121–171. Camb. Univ. Press, Cambridge, New York, USA, 1997. Frew, N. M., Goldman, J. C., Dennett, M. R., and Johnson, A. S.: Impact of phytoplankton-generated surfactants on air-sea gas-exchange, J. Geophys. Res.-Ocean., 95, 3337–3352, 1990. Frew, N. M., Nelson, R. K., McGillis, W. R., Edson, J. B., Bock, E. J., and Hara, T.: Spatial variations in surface microlayer surfactants and their role in modulating air-sea exchange, in: Gas Transfer at Water Surfaces, edited by: Donelan, M. A., Drennan, W. M., Saltzman, E. S., and Wanninkhof, R., 153–159, Washington DC, USA, 2002. Gašparovi&#x0107;, B. and \'Cosovi&#x0107;, B.: Distribution of surface-active substances in the Northern Adriatic Sea, Estuar. Mar. Chem. 75, 301–313, 2001. Gašparovi&#x0107;, B., and \'Cosovi&#x0107;, B.: Surface active properties of organic matter in the north Adriatic Sea, Estuar. Coast. Shelf Sci. 58, 555–566, 2003. Gašparovi&#x0107;, B., Plavši&#x0107;, M., \'Cosovi&#x0107;, B., and Reigstad, M. Organic matter characterization and fate in the subarctic Norwegian fjords during late spring/summer period, Estuar. Coast. Shelf Sci., 62, 95–107, 2005. Gašparovi&#x0107;, B., Plavši&#x0107;, M., \'Cosovi&#x0107;, B., and Saliot, A.: Organic matter characterization in the sea surface microlayers in the subarctic Norwegian fjords region, Mar. Chem. 105, 1–14, 2007. Goldman, J. C., Dennet, M. R., and Frew, N. M.: Surfactants effects on air-sea gas exchange under turbulent conditions, Deep-Sea Res., 35, 1953–1970, 1988. Guérin, F., Gwena\"el, A., Serça, D., Delon, C., Richard, S., Delmas, R., Tremblay, A., and Varfalvy, L.: Gas transfer velocities of CO₂ and CH₄ in a tropical reservoir and its river downstream, J. Mar. Syst., 66, 161–172, 2007. Hartman, B., and Hammond D. E.: Gas exchange in San Francisco Bay, Hydrobiologia, 129, 59–68, 1985. Hunter, K. A. and Liss P. S.: Organic sea surface films, in: Marine Organic Chemistry, edited by: Duursma, E. K. and Dawson, R., Elsevier, Amsterdam, 259–298, 1982. Jähne, B. and Haußecker, H.: Air-water gas exchange, Annu. Rev. Fluid. Mech., 30, 443–468, 1998. Jähne, B., Munnich, K. O., Bosinger, R., Dutzi, A., Huber, W., and Libner, P.: On parameters influencing air–water exchange, J. Geophys. Res., 92, 1937–1949, 1987. Keeling, R. F.: On the role of large bubbles in air-sea gas exchange and supersaturation in the ocean, J. Mar. Res., 51, 237–271, 1993. Kremer, J. N., Nixon, S. W., Buckley, B., and Roques, P.: Technical Note: Conditions for using the floating chamber method to estimate air-water gas exchange, Estuaries, 26, 985–990, 2003. Kuss, J., Nagel, K., and Schneider, B.: Evidence from the Baltic Sea for an enhanced CO₂ air-sea transfer velocity, Tellus 56B, 175–182, 2004. Kuss, J. and Schneider, B.: Chemical enhancement of the CO₂ gas exchange at a smooth seawater surface, Mar. Chem., 91, 165–174, 2004. Kuznetsova, M., Lee, C., Aller, J., and Frew, N.: Enrichment of amino acids in the sea surface microlayer at coastal and open ocean sites in the North Atlantic Ocean, Limnol. Oceanogr., 49, 1605–1619, 2004. Liss, P. S. and Merlivat, L.: Air-sea gas exchange rates: Introduction and synthesis, in: The Role of Air-Sea Exchange in Geochemical Cycling, edited by: Buat-Ménard, 113–127, D. Reidel Publishing Company, Boston, Massachusetts, USA, 1986. Marino, R. and Howarth, R. W.: Atmospheric oxygen-exchange in the Hudson River- dome measurements and comparison with other natural waters, Estuaries, 16, 433–445, 1993. Matthews, C. J. D., St. Louis, V. L., and Hesslein, R. H.: Comparison of three techniques used to measure diffusive gas exchange from sheltered aquatic surfaces, Environ. Sci. Technol., 37, 772–780, 2003. McGillis, W. R., Edson, J. B., Ware, J. D., Dacey, J. W. H., Hare, J. E., Fairall, C. W., and Wanninkhof, R., Carbon dioxide flux techniques performed during GasEx-98, Mar. Chem., 75, 267–280, 2001. McGillis, W. R., Edson, J. B., Zappa, C. J., Ware, J. D., McKenna, S. P., Terray, E. A., Hare, J. E., Fairall, C. W., Drennan, W., Donelan, M., DeGrandpre, M. D., Wanninkhof, R., and Feely, R. A.: Air-sea CO₂ exchange in the equatorial Pacific, J. Geophys. Res., 109, C08S02, doi:10.1029/2003JC002256, 2004. McKenna, S. P. and McGillis, W. R.: The role of free-surface turbulence and surfactants in air-water gas transfer, Int. J. Heat Mass Transfer, 47, 539–553, 2004. Nightingale, P. D., Liss, P. S., and Schlosser, P.: Measurements of air-sea gas transfer during an open ocean algal bloom, Geophys. Res. Lett., 27, 2117–2120, 2000a. Nightingale, P. D., Malin, G., Law, C. S., Watson, A. J., Liss, P. S., Liddicoat, M. I., Boutin, J., and Upstill-Goddard, R. C.: In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers, Global Biogeochem. Cy., 14, 373–387, 2000b. Smedman, A., Högström, U., Bergström, H., Rutgersson, A., Kahma, K. K., and Pettersson, H.: A case study of air-sea interaction during swell conditions, J. Geophys. Res., 104, 25833–25851, 1999. Takahashi, T., Feely, R. A., Weiss, R., Wanninkhof, R. H., Chipman, D. W., Sutherland, S. C., and Takahashi, T. T.: Global air-sea flux of CO₂: an estimate based on measurements of sea–air pCO₂ difference, Proc. Natl. Acad. Sci., 94, 8292–8299, 1997. Takahashi, T., Sutherland, S. C., Sweeney, C., Poisson, A., Metzl, N., Tilbrook, B., Bates, N., Wanninkhof, R., Feely, R. A., Sabine, C., Olafsson, J., and Nojiri, Y.: Global sea-air CO₂ flux based on climatological surface ocean $p$CO₂, and seasonal biological and temperature effects, Deep-Sea Res. Part II-Topical Studies in Oceanogr., 49, 1601–1622, 2002. Tseng, R. S., Viechnicki, J. T., Skop, R. A., and Brown, J. W.: Sea-to-air transfer of surface-active organic-compounds by bursting bubbles, J. Geophys. Res.-Oceans., 97, 5201–5206, 1992. Wanninkhof, R.: Relationship between wind-speed and gas-exchange over the ocean, J. Geophys. Res.-Oceans., 97, 7373–7382, 1992. Wanninkhof, R. and Knox, M.: Chemical enhancement of CO₂ exchange in natural waters, Limnol Oceanogr. 41, 689–698, 1996. Wanninkhof, R., Ledwell, J. R., and Broecker, W. S.: Gas-exchange wind-speed relation measured with sulfur-hexafluoride on a lake, Science, 227, 1224–1226, 1985. Wanninkhof, R. and McGillis, W. R.: A cubic relationship between air-sea CO₂ exchange and wind speed, Geophys. Res. Lett., 26, 1889–1892, 1999. Weiss, R. F.: Carbon dioxide in water and seawater: The solubility of a non ideal gas, Mar. Chem., 2, 203–215, 1974. Zappa, C. J., Asher, W. E., Jessup, A. T., Klinke, J. and Long, S. R.: Microbreaking and the enhancement of air-water transfer velocity, J. Geophys. Res., 109, C08S16, doi:10.1029/2003JC001897, 2004. Zappa, C. J., McGillis, W. R., Raymond, P. A., Edson, J. B. Hintsa, E. J., Zemmelink, H. J. Dacey, J. W. H., and Ho, D. T.: Environmental turbulent mixing controls on air-water gas exchange in marine and aquatic systems, Geophys. Res. Lett., 34, L10601, doi:10.1029/2006GL028790, 2007. Zemmelink, H. J., Houghton, L., Sievert, S. M., Frew, N. M., and Dacey, J. W. H.: Gradients in dimethylsulfide, dimethylsulfoniopropionate, dimethylsulfoxide, and bacteria near the sea surface, Mar. Ecol. Prog. Ser., 295, 33–42, 2005. Zutic, V., \'Cosovi&#x0107;, B., Marcenko, E., Bihari, N., and Krsinic, F.: Surfactant production by marine-phytoplankton, Mar. Chem., 10, 505–520, 1981.