A numerical model of seasonal primary production within the Chukchi/Beaufort Seas

A coupled three-dimensional circulation and ecological model provided numerical analysis of daily carbon/nitrogen cycling by the planktonic and benthic components of western Arctic shelf/basin ecosystems during 2002, when extensive field data were obtained by American and Canadian ice-breakers. Seasonal model budgets of April-May, July-August, and September-October 2002 allowed both interpolation and extrapolation of these validation data, suggesting that the most productive shelf regime of the Chukchi/Beaufort Seas was that of summer. Yet, during this period of July-August, a combination of light-limitation and nutrient-limitation limited shelf-wide mean simulated net photosynthesis to only ∼709 mg C m^-2 day^-1 for shelf waters of <220 m depth. This modeled seasonal carbon fixation then accounted for ∼45% of the annual shelf primary production of 97.4 g C m^-2 yr^-1 Identification of the relative importance of natural control factors of light and nutrients by the coupled model provided insight into possible consequences of future global climatic changes at these high latitudes. The model's seasonal penetration of relatively saline, nutrient-rich Anadyr Water of Pacific origin into the eastern Chukchi Sea replicated the time series of observed salinity fields. A similar fidelity of the simulated nitrate, silicate and dissolved inorganic carbon fields with the observed ones yielded an assessment of nutrient uptake and photosynthesis during a natural fertilization experiment. The simulated chlorophyll, dissolved organic carbon (DOC), and NH₄ stocks also mimicked these shipboard observations. We found that the spring 2002 stocks of new nutrients were stripped by the end of summer, with little fall nutrient resupply by physical and biotic factors, when incident light waned. However, because of extensive ice cover and nutrient-poor upper waters within the Canadian Basin, the slope regions remained oligotrophic throughout the year, yielding a simulated annual net photosynthesis of ∼50 g C m^-2 yr^-1. We conclude that future ice cover retreat, without eutrophication, may have little impact on increased carbon sequestration within these high-latitude ecosystems.