HR: 16:45h
AN: OS54A-04    [Abstracts]
TI: Decoupling of Export From New Production: The Role of Lateral Transport
AU: * Plattner, G
EM: plattner@igpp.ucla.edu
AF: IGPP & Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, 5839 Slichter Hall, Los Angeles, CA 90095 United States
AU: Gruber, N
EM: ngruber@igpp.ucla.edu
AF: IGPP & Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, 5839 Slichter Hall, Los Angeles, CA 90095 United States
AU: Frenzel, H
EM: hfrenzel@igpp.ucla.edu
AF: IGPP & Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, 5839 Slichter Hall, Los Angeles, CA 90095 United States
AU: McWilliams, J C
EM: jcm@atmos.ucla.edu
AF: IGPP & Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, 5839 Slichter Hall, Los Angeles, CA 90095 United States
AB: Since the work of Eppley and Peterson in the late 1970s, it has been a widely applied concept in ocean biogeochemical studies to numerically equate export production with new production in equilibrium situations. This concept allows the use of estimates of new production as a substitute for the often more difficult measurements of export production. The underlying assumption is that horizontal transport of organic matter is negligible compared to vertical export. We investigate the validity of this assumption using an eddy-resolving coupled physical-biogeochemical model of the central Californian coast forced with climatological winds as discussed by Frenzel et al. The central Californian coast is dominated by intense coastal upwelling, highly turbulent flow, and high biological production. Meso- and submesoscale phenomena such as eddies and filaments are common features in this environment and are key processes controlling the input of nutrients into the euphotic zone as well as the vertical and lateral export of organic matter. We find that transport associated with such circulation structures leads to a substantial local decoupling of export from new production, which is largest in the very dynamic near-shore region. The distribution of new production is primarily determined by the vertical supply of nitrate and shows a relatively smooth on-offshore gradient caused by the near-shore upwelling and the ensuing lateral supply of nitrate. By contrast, export production shows a complicated pattern with both negative and positive values, even in the annual mean, determined primarily by the convergence and divergence of the flow and the associated vertical transport of organic matter in and out of the euphotic zone. These annual mean divergences and convergences are associated with the fact that eddies and other meso-scale phenomena along the central Californian coast tend to be organized into standing features primarily related to undulations in topography and shoreline. In summary, our results indicate that the concept of numerically equal new and export production has to be used with great care, particularly in dynamic oceanic environments.
DE: 4806 Carbon cycling
DE: 4815 Ecosystems, structure and dynamics
DE: 4842 Modeling
DE: 4845 Nutrients and nutrient cycling
DE: 4520 Eddies and mesoscale processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting