The Ocean's Biological Pump: In Situ Oxygen Measurements in the Subtropical Oceans

Abstract

The magnitude and distribution of the ocean's biological pump (the downward flux of organic carbon (OC) from the ocean surface) influences the pCO2 of the atmosphere and the O2 content of the deep sea, but has not been well quantified. We determine this flux in the ocean's five subtropical gyres using upper-ocean oxygen mass balance and measurements of T, S, and pO2 by autonomous profiling floats. Our results suggest that the biological OC pump is not globally uniform among the subtropical gyres: values in the North Pacific and Atlantic indicate distinct autotrophy (1–2 mol C m−2 yr−1) while near zero values in the S. Indian Ocean suggest the possibility of net heterotrophy. There is a correlation between the surface water iron/nitrate ratio and the magnitude of the biological pump suggesting an important role for nitrogen fixation in controlling the global distribution.