Mechanisms Controlling the Biological Pump and CO2 Uptake Rates in the North Pacific

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ABSTRACTOCE-0095106In this project, investigators at the University of Washington will quantify the physical mechanisms controlling the rates of biological carbon export and the uptake of anthropogenic carbon dioxide (CO2) in the North Pacific Ocean using a basin-wide general circulation model (GCM). The proposed model is operational and has already been used to evaluate mechanisms of subduction and water mass formation in the North Pacific and is currently being tested using chlorofluorocarbon tracers (CFCs).The approach will be first to incorporate bomb-produced 14C into the model to validate its advective and diffusive fields. By adding this carbon-based tracer the model will then have been verified with both CFCs and 14C -- two tracers with different boundary conditions and time histories. Next, the three-dimensional distribution of biological carbon export and remineralization rates will be determined by using the observed distributions of several biological productivity tracers, specifically nitrate and phosphate (and their dissolved organic counterparts DON and DOP), three dissolved atmospheric gases (oxygen, argon, and nitrogen), and the 13C/12C ratio of the dissolved inorganic carbon (DIC). The PIs would then simulate the anthropogenic CO2 perturbation and utilize independent reconstructions of the anthropogenic DIC and 13C/12C changes in the North Pacific to validate model predictions. Finally, the model response to decadal variability in forcing would be examined.There are several important reasons to choose the North Pacific Ocean as the site for a basin-scale modeling study. There are three JGOFS time-series sites that yield observed carbon fluxes and anthropogenic CO2 signals to compare to model predictions. The lack of deep-water formation at its poleward boundary simplifies the meridional circulation compared to the North Atlantic and southern oceans and justifies shorter model runs. Finally, the North Pacific has been the site of intensive chemical tracer measurements, specifically CFCs, 14C and 13C/12C, over the last 10 years. The investigators will focus their modeling efforts on quantifying physical processes that likely control tracer, nutrient and CO2 fluxes in the upper ocean: 1) equatorial-subtropical and subtropical-subpolar exchange, 2) thermocline ventilation and isopycnal transport both with and without eddies, and 3) diapycnal mixing and the influence of eddies in the upper thermocline, and 4) the impact of decadal variability on biological carbon export.