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Understanding the CO₂cycle in the North Pacific Ocean using inverse box models Matear, Richard J.

Abstract

Tracer transports across 35°N were computed using the hydrographic data from a synoptic section (INDOPAC) and from the Levitus annual mean section. The tracer transports calculated from the INDOPAC section were better able to close the tracer budgets in the North Pacific than the Levitus section. The transport calculations showed that highly resolved hydrographic data are necessary to accurately determine the tracer transports, and pointed out the sensitivity of the calculation to errors in the Ekman transports and air-sea exchanges of fresh water. The inverse box model was applied to data generated from the Hamburg LSGOC-biogeochemical model. For this data, the mixing transports of the tracers were important for closing the tracer budgets. Applying the inverse box model to the temperature, salinity, total CO2, alkalinity, phosphate, oxygen, POC, calcite, and 14C fields produced poor results. With the addition of velocity shear information, the inverse box model extracted the correct velocity fields and produced air-sea exchanges and detrital rain rates consistent with the known values from the Hamburg model. A model of the nutrient and carbon cycles in the North Pacific north of 24°N is formulated, and water flow rates, eddy mixing coefficients, particle fluxes and air-sea exchange rates of fresh water, heat, CO2 and 02 are calculated. The model incorporates geostrophy, wind-driven Ekman transports and budget equations for a suite of seven tracers. Geostrophic transports are based on two highly resolved synoptic sections across the North Pacific at 24°N (Roemmich et al., 1991) and 47°N (Talley et al., 1991). Tracer distributions are obtained from historical station data. Budgets of mass, heat, salt, oxygen, phosphate, silicate, CO2 and alkalinity are satisfied simultaneously in the North Pacific. The water transports in the model are in agreement with other transport calculations for the Pacific. The calculated heat transport showed that the subtropical North Pacific transfers heat into the atmosphere while the subarctic ocean gains heat. The net heat lost by the North Pacific ocean was 0.12 ± 0.08 PW. The North Pacific Ocean was calculated to be a sink of 0.1 ± 0.1 Gt C yr-1 of atmospheric carbon. The calculated maximum values of new production for the subarctic and subtropical regions are 42 g C m-2 yr-1 and 12 g C m-2 yr-1respectively. The influence of the dissolved organic matter on the nutrient and carbon cycles is investigated using the data reported by Suzuki et al., (1985). The model showed that the dissolved organic matter had little influence on the carbon and nutrient cycles. More data for the dissolved organic matter should be collected to verify this result.

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