CO_2 exchange at air-sea interface in the Huanghai Sea

During the Huanghai Sea Circulation and Material Flux Expedition in Spring 1996, fco_2 in surface water and atmosphere was measured. The fco2 in surface water varied in a range from 220 to 360 uatm1) while atmospheric concentration was nearly constant at 360μatm, showing that the Huanghai Sea surface waters were undersaturated with respect to atmospheric Co during the time of investigation. A model was developed in this study in order to estimate the Co flux at the air-sea interface. The model incorporates the time-series variations of the distributions in SST (sea surface temperature), salinity, mixed-layer depth, atmospheric fco2, gas-transfer velocity, and CZCS chlorophyll concentration in the Huanghai Sea and was calibrated with the observed fco2 data. The primary parameter affecting fco2 in surface water is the variation of SST through time. The annual fluxes of Co are estimated as 0. 033 Gt C from the sea into the atmosphere and 0. 044 Gt C from the air into sea. The Huanghai Sea, thus behaves as a CO2 sink absorbing 0. 011 Gi C of CO2 a year. which.corresponds to about 0. 5 % of global oceanic absorption capacity.

Carbon sinks/sources in the Yellow and East China Seas Air-sea interface exchange, dissolution in seawater, and burial in sediments

The sinks/sources of carbon in the Yellow Sea(YS) and East China Sea(ECS), which are important continental shelf seas in China, could exert a great influence on coastal ecosystem dynamics and the regional climate change process. The CO_2 exchange process across the seawater-air interface, dissolved and particulate carbon in seawater, and carbon burial in sediments were studied to understand the sinks/sources of carbon in the continental shelf seas of China. The YS and the ECS generally have different patterns of seasonal air-sea CO_2 exchange. In the YS, regions west of 124°E can absorb CO_2 from the atmosphere during spring and winter, and release CO_2 to the atmosphere during summer and autumn. The entire YS is considered as a CO_2 source throughout the year with respect to the atmosphere, but there are still uncertainties regarding the exact air-sea CO_2 exchange flux. Surface temperature and phytoplankton production were the key controlling factors of the air-sea CO_2 exchange flux in the offshore region and nearshore region of the YS, respectively. The ECS can absorb CO_2 during spring, summer, and winter and release CO_2 to the atmosphere during autumn. The annual average exchange rate in the ECS was-4.2±3.2 mmol m^(-2) d^(-1) and it served as an obvious sink for atmospheric CO_2 with an air-sea exchange flux of 13.7×10~6 t. The controlling factors of the air-sea CO_2 exchange in the ECS varied significantly seasonally. Storage of dissolved inorganic carbon(DIC) and dissolved organic carbon(DOC) in the YS and the ECS were 425×10~6 t and 1364×10~6 t, and 28.2×10~6 t and 54.1×10~6 t,respectively. Long-term observation showed that the DOC content in the YS had a decreasing trend, indicating that the "practical carbon sink" in the YS was decreasing. The total amount of particulate organic carbon(POC) stored in the YS and ECS was10.6×10~6 t, which was comparable to the air-sea CO_2 flux in these two continental shelf seas. The amounts of carbon sequestered by phytoplankton in the YS and the ECS were 60.42×10~6 t and 153.41×10~6 t, respectively. Artificial breeding of macroalgae could effectively enhance blue carbon sequestration, which could fix 0.36×10~6–0.45×10~6 t of carbon annually. Organic carbon(OC) buried in the sediments of the YS was estimated to be 4.75×10~6 t, and OC of marine origin was 3.03×10~6 t, accounting for5.0% of the TOC fixed by phytoplankton primary production. In the ECS, the corresponding depositional flux of OC in the sediment was estimated to be 7.4×10~6 t yr^(-1), and the marine-origin OC was 5.5×10~6 t, accounting for 5.4% of the phytoplankton primary production. Due to the relatively high average depositional flux of OC in the sediment, the YS and ECS have considerable potential to store a vast amount of "blue carbon."