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The goal of this proposal is to quantify the physical mechanisms controlling
the rates of biological carbon export and the uptake of anthropogenic
CO2 in the North Pacific Ocean. We propose to use a
basin-wide, isopycnal general-circulation
model (GCM) as the basis of our analysis. The model is operational and
has been used to evaluate mechanisms of subduction and water mass formation
in the North Pacific and is currently being tested using CFCs.
Our strategy is to first, incorporate bomb 14C into the model
to validate its advective and diffusive fields. By adding this carbon-based
tracer we will have verified the model 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 NO3,
PO4 , (and their dissolved organic counterparts DON
and DOP), O2/Ar/N2 and the
13C/12C
of the dissolved inorganic carbon (DIC). We will then simulate the anthropogenic
CO2 perturbation and utilize independent reconstructions
of the anthropogenic DIC and 13C/12C changes in the
North Pacific to validate the model's predictions. Finally, we will examine
the model response to decadal variability in forcing.
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.
We will focus our 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,
3) diapycnal mixing and the influence of eddies in the upper thermocline, and
4) the impact of decadal variability on biological carbon export.
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