Spatial distribution of riverine DOC inputs to the ocean: an updated global synthesis

Abstract

On the basis of most up-to-date literature data, this study evaluated the influxes of dissolved organic carbon (DOC) to the ocean. Using the DOC concentrations in 118 world rivers and long-term average river discharges, we estimated the river influxes of DOC to the coastal seas as 0.21 Pg C yr−1. This flux was reduced to 0.19 Pg C yr−1 when we took into account DOC removal during its transport into the Arctic. When we further adopted an average removal rate of 10% for the rest of the river DOC input into the coastal ocean, we obtained an estimate of the global river DOC flux of 0.17 Pg C yr−1, which is at the lower end of prior estimations. Considering the seasonal variation of the river end-member DOC concentration, our current estimate of the global river DOC discharge is subject to an uncertainty of ∼30%. DOC fluxes into the ocean have significant spatial variations in terms of their continents of origin, recipient coastal seas, ocean basins and latitudinal zones. The highest DOC flux was from South America into the western ocean boundaries and eventually into the Atlantic Ocean. The most abundant riverine DOC discharge was in the low latitudinal zones with 38.0 and 90.0 Tg C yr−1 in the 0–30° N and 0–30° S zones, respectively, the combination of which accounted for ∼62% of the global DOC input. On the basis of these updated fluxes, we estimated a global river mean DOC concentration of 5.29 mg L−1.