Synthesis & Modeling Project
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
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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