Temporal Trends in Deep Ocean RedÞeld Ratios

The RedÞeld ratio [carbon:nitrogen:phosphorus (C:N:P)] of particle ßux to the deep ocean is a key factor in marine biogeochemical cycling. Changes in oceanic carbon sequestration have been linked to variations in the RedÞeld ratio on geological time scales, but this ratio generally is assumed to be constant with time in the modern ocean. However, deep-water RedÞeld ratios in the northern hemisphere show evidence for temporal trends over the past Þve decades. The North Atlantic Ocean exhibits a rising N:P ratio, which may be related to increased deposition of atmospheric nitrous oxides from anthropogenic N emissions. In the North PaciÞc Ocean, increasing C:N and C:P ratios are ac-companied by rising remineralization rates, which suggests intensiÞed export production. Stronger export of carbon in this region may be due to enhanced bioavailability of aeolian iron. These Þndings imply that the biological part of the marine carbon cycle currently is not in steady state. The nutrient composition of marine surface wa-ters affects the C:N:P elemental compositio