Dataset: Model simulations of oxygen variability in the North Pacific, 2005 (U.S. JGOFS Synthesis & Modeling Phase project results)

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.