Role of eddy pumping in enhancing primary production in the ocean

Abstract

IN steady-state models of primary production in the open ocean, the upward fluxes of nutrients are balanced by the export of particulate production to the ocean depths. Export production represents the biological effect of carbon production on the net exchange of carbon dioxide between the atmosphere and the ocean. Geochemical estimates of exported production, based on calculations of rates of oxygen usage¹ or heat fluxes² are two to three times as high as those determined from biological measurements^3–5. One possible explanation for the differing estimates is that export production, calculated from independent geochemical signals, is too high. Another is that biological measurements severely undersample episodic nutrient injections into the photic zone^1,4. Eddy pumping represents one of the possible mechanisms of nutrient injection¹. Here we examine the enhancement of production by a cyclonic eddy in the subtropical Pacific with instrumentation that allows us to overcome the sampling problem. Our results reveal that eddy pumping markedly stimulates primary production, and that phytoplankton in the upper oligotrophic ocean outside the eddy are not growing near their maximum relative specific growth rates. But if the relative enhancement of production is typical, our results suggest that eddy pumping would enhance total primary production by only ˜20%.