CO₂uptake in the East China Sea relying on Changjiang runoff is prone to change

Abstract

.[1] Limited knowledge exists concerning the unusually large CO 2 uptake capacity in the East China Sea (ECS), which is the eminent continental shelf pump for efficient transfer of atmospheric CO 2 to the deep ocean. Here we show evidence of strong control of river runoff on the CO 2 uptake capacity of the ECS. From 8-years of observations in the productive ECS shelf, we present the first dataset to show the complete seasonal cycle of CO 2 flux, which gives an annual flux of 2.3 AE 0.4 mol C m À2 y À1 as a net sink of atmospheric CO 2 . Further, we found biological sequestration of CO 2 taking place in the highly productive Changjiang river plume in warm seasons due to the riverine nutrient enrichment. Consequently, changes in the plume area due to changes in the Changjiang River Discharge (referred to as the Discharge hereafter) strongly affect the CO 2 uptake capacity. As the Discharge may decrease due to the Three Gorges Dam operation, the Changjiang plume will probably also decrease, resulting in reduction in CO 2 uptake capacity and even a shift from a CO 2 sink to a source.

Carbon dioxide dynamics and fluxes in coastal waters influenced by river plumes

“…Time and again, the East China Sea (ECS) has been found to be a sink of CO 2 (Chen and Wang 1999;Tsunogai et al 1999;Chou et al 2009a;Zhai and Dai 2009;Tseng et al 2011). This is in part because the Changjiang River not only exports a significant amount of nutrients to the ECS but also a large quantity of freshwater, which also helps to induce an estuarine type flow.…”

“…As a result, pCO 2 (or pH) in these river plumes are expected to be very low (or high) ( Fig. 7.2); such low pCO 2 and high pH values have been observed in the Mississippi (Guo et al 2012) and Changjiang River plumes (Chou et al 2009b;Zhai and Dai 2009;Tseng et al 2011). Consequently, we suggest that although ocean acidification, which has been linked with CO 2 uptake from the atmospheric (which has increased because of fossil fuel use), has become a major ocean environmental stressor, eutrophication-induced pH increases are a dominant feature in surface water pH in the nutrient-rich river plumes worldwide (Borges and Gypens 2010).…”

Air–sea CO<sub>2</sub> fluxes in the East China Sea based on multiple-year underway observations

“…However, these estimates are either based on limited (only one or a few) field surveys (Chou et al, 2009;Chou et al, 2011;Peng et al, 1999;Shim et al, 2007;Tsunogai et al, 1999;Wang et al, 2000) or suffer from spatial limitations (Kim et al, 2013;Shim et al, 2007;Tsunogai et al, 1999;Zhai and Dai, 2009). Tseng et al (2011) investigate the Changjiang diluted water induced CO 2 uptake in summer and obtain an empirical algorithm of surface water pCO 2 (partial pressure of CO 2 ) with the Changjiang discharge and sea surface temperature (SST). Subsequently, they extrapolate the empirical algorithm to the entire ECS shelf and the whole year to obtain a significant CO 2 sink of 6.3 ± 1.1 mmol m −2 d −1 .…”

Effects of a wind‐driven cross‐shelf large river plume on biological production and CO2 uptake on the Gulf of Mexico during spring

“…Large river plumes are known to influence air-sea exchange of carbon dioxide (CO 2 ) strongly with enhanced biological productivity contributing to a net uptake of CO 2 in river-influenced regions (Cooley and Yager 2006;Lohrenz et al 2010;Tseng et al 2011). Consequently, large river plumes can be expected to affect air-sea CO 2 exchange in their open ocean surroundings depending on their spatial variability.…”