Rapid oxygen utilization in the ocean twilight zone assessed with the cosmogenic isotope ~7Be

摘要

The rate of oxygen utilization beneath the sunlit surface ocean provides a measure of the export rate of biologically produced carbon to the deep sea, and its variation with. depth suggests where remineralization of that carbon occurs. The latter consideration is relevant to the efficiency of carbon sequestration in deep water. However, accurate characterization of this process, particularly within 200 m of the euphotic zone where carbon utilization is most intense, has been difficult owing to limitations of techniques applied to these shallow depths. Here, a novel approach utilizing the cosmogenic isotope ~7Be indicates that at a site in the subtropical North Atlantic, 65% of sinking carbon is remineralized within 200 m of the ocean's surface and is thus readily available for return to the atmosphere. The corresponding oxygen utilization rates are greater than would be suggested by the attenuation with depth of organic matter measured by shallow sediment traps.