Synthesis & Modeling Project
Raymond Sambrotto
Mary-Lynn Dickson
Collaborative research:  Quantifying the relationship between nitrogen uptake and net community production using a synthesis of JGOFS data and 1-D modeling

NSF ('99), 36 months

PROJECT DESCRIPTION: Most models of ocean carbon flux are based on a limiting nutrient such as phosphorus or nitrogen from which an estimate of carbon export is computed.  The conversion among surface ocean nutrient cycles typically is based on the stoichiometric oxidative relationships found in ocean thermocline waters.  The measurement of Net Community Production (NCP) should be a robust estimate of net organic production.  This can be measured directly from the carbon system or by a conversion to carbon from the change in oxygen.  However, typical tracer rate measurements do not necessarily reflect changes in the entire ambient pool and usually ignore the production of dissolved organic matter.  Several lines of evidence from open ocean budgets, mesocosm experiments and tracer rate measurements suggest that the relationship between the consumption of limiting nutrients and the net production of organic carbon can be greater or less than the Redfield ratios.  This variation may be great enough to effect the predictive ability of biogeochemical models, particularly under changing environmental conditions.

Direct comparisons between NCP and nitrogen production are available from most of the JGOFS field studies that allow the assumptions about limiting nutrients and net production to be tested.  Based on an initial comparison from the Arabian Sea, the relative amount of net production is greater than would be expected from the nitrogen f-ratio at lower f-ratios.  It is not clear how much of this "extra" net production is actually exported.  However, it is possible that the biological pump of a warmer ocean may not decrease in proportion to the restriction of nutrients to the surface due to increased stability.


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Raymond Sambrotto
Lamont-Doherty Earth Observatory
Columbia University
P.O. Box 1000 Route 9W
Palisades, NY 10964-8000
tel: (914) 365-8402
fax: (914) 365-8150

Mary-Lynn Dickson
Marine and Atmospheric Chemistry
University of Rhode Island
Graduate School of Oceanography
Bay Campus
Narragansett, RI 02882
tel: (401) 874-6420
fax: (401) 874-6811