Modeling the Seasonal and Interannual Variability of Nutrients, Biomass, and Carbon Species in the Subtropical North Atlantic and North Pacific

A one dimensional, coupled ecosystem/carbon cycle model is used to analyze the biogeochemical-physical interactions and carbon fluxes at two time-series study sites: the Bermuda Atlantic Time-series Study (BATS) site, and the Hawaii Ocean Time-series (HOT) site. Physical forcing and biogeochemical boundary conditions are derived from the comprehensive BATS and HOT data sets. The observed parameters not used for model forcing and boundary conditions are used to verify model performance. The seasonal and interannual variability of biomass, nutrients, and carbon species of these two sites are investigated and compared, and the long-term (decadal) trends of carbon stocks (DIC, DOC, and CO₂) are analyzed in the context of climate variability. The two sites have very distinct physical forcing characteristics. At BATS, the winter mixed layer can reach 300 meters, while at HOT it rarely exceeds 100 meters. Also, the BATS region is affected by a pervasive translation of strong mesoscale eddies that promote large vertical excursions of the thermocline/nutricline. In the HOT region the mesoscale variability is more episodical such that the vertical transport of nutrients is achieved predominantly by vertical mixing. These differences in physical forcing have an impact on the nutrient and carbon balances of the two regions, which is clearly demonstrated by the model results.