Carbon, alkalinity and nutrient budgets on the East China Sea continental shelf

Abstract

The western part of the Kuroshio Intermediate Water originates from the nutrient-rich South China Sea intermediate water which upwells onto the East China Sea (ECS) continental shelf and contributes a large amount of nutrients to the ECS. This contribution, especially for phosphorus, is far more than the inputs from the phosphorus-deficient Yangtze and Yellow Rivers. Mass balance calculations reveal that the net denitrification rate in the ECS shelf is 95 ± 50 × 109 mol N yr-1, which is more than the total riverine supply of nitrogen. The nutrient supply allows the ECS to produce 1030 ± 310 × 109 moles dissolved organic carbon and 709 ± 280 × 109 mol particulate organic carbon for a total of 1739 ± 870 × 109 mol organic carbon per year, which translates to a new production rate of phytoplankton as 64 ± 32 mg C m-2 d-1 or 15% of the average primary production rate. The downslope transport of modern particulate carbon is 2547 ± 1250 × 109 mol yr-1, of which 695 ± 350 × 1019 mol yr-1 is organic. This value is only 12% of the offshore dissolved organic carbon transport of 5563 ± 1700 × 109 mol yr-1. The alkalinity budget, never attempted before, indicates that there is a substantial amount of alkalinity generation in the sediments (3.9 ± 3.9 mmol m-2 d-1) due to anaerobic respiration such as by iron and sulfate reductions. Copyright 1999 by the American Geophysical Union.