Biological CO2 Uptake and Upwelling Regulate the Air-Sea CO2 Flux in the Changjiang Plume Under South Winds in Summer

Abstract

The partial pressure of CO2 (pCO2) in the sea and the air-sea CO2 flux in plume waters are subject to interactions among biological production, horizontal advection, and upwelling under wind events. In this study, time series of pCO2 and other biogeochemical parameters in the dynamic Changjiang plume were presented to illuminate the controlling factors of pCO2 and the air-sea CO2 flux after a strong south wind event (July 23–24, maximum of 11.2 ms–1). The surface pCO2 decreased by 310 μatm (to 184 μatm) from July 24 to 26. Low-pCO2 waters (<200 μatm) were observed in the following 2 days. Corresponding chlorophyll a and dissolved oxygen (DO) increase, and a significant relationship between DO and npCO2 indicated that biological uptake drove the pCO2 decrease. The salinity of undersaturated-CO2 waters decreased by 3.57 (from 25.03 to 21.46) within 2 days (July 27–28), suggesting the offshore advection of plume waters in which CO2 had been biologically reduced. Four days after the wind event, the upwelling of high-CO2 waters was observed, which increased the pCO2 by 428 μatm (up to 584 μatm) within 6 days. Eight days after the onset of upwelling, the surface pCO2 started to decrease (from 661 to 346 μatm within 3 days), which was probably associated with biological production. Regarding the air-sea CO2 flux, the carbon sink of the plume was enhanced as the low-pCO2 plume waters were pushed offshore under the south winds. In its initial stage, the subsequent upwelling made the surface waters act as a carbon source to the atmosphere. However, the surface waters became a carbon sink again after a week of upwelling. Such short-term air-sea carbon fluxes driven by wind have likely occurred in other dynamic coastal waters and have probably induced significant uncertainties in flux estimations.

Riverine Influences and Seasonal Dynamics: Exploring Carbonate System Variations and Air‐Sea CO2 Fluxes in the Southern Yellow Sea and East China Sea

“…During their rapid growth phase, these U . prolifera spores absorb a significant amount of DIC from the seawater, leading to a notable decrease in DIC concentration and subsequent pH elevation (Li, Liu, et al., 2021; Li, Ni, et al., 2021). Consistent with our findings, Deng et al.…”

“…The SYS‐ECS has a complex circulation system with significant seasonal variations, consisting of the main following water masses: (a) the southeast‐flowing Yellow Sea Coastal Waters; (b) the Changjiang River Plume; (c) the ECS Coastal Waters, which flows southward during winter and northward during summer under the action of monsoons; (d) the Taiwan Warm Current derived from the Taiwan Strait (or onshore Kuroshio intrusion northeast of Taiwan Island), and the Kuroshio Current originating from the northern branch of the North Equatorial Current (Figure 1a). The Changjiang River Plume extends hundreds of kilometers into the sea and carries a substantial amount of freshwater, nutrients, and sediment loadings that significantly affect biogeochemical processes in the inner ECS (Li, Liu, et al., 2021; Li, Ni, et al., 2021). The dispersal direction of the river plume varies between seasons, heading southwest from December to early March and branching northeast and southwest from June to early September (Chen, 2009).…”

“…As P. yezoensis are harvested, substantial quantities of attached U. prolifera spores are released into the seawater (Keesing et al, 2011). During their rapid growth phase, these U. prolifera spores absorb a significant amount of DIC from the seawater, leading to a notable decrease in DIC concentration and subsequent pH elevation (Li, Liu, et al, 2021;Li, Ni, et al, 2021). Consistent with our findings, Deng et al ( 2021) also observed a similar phenomenon during their investigation of the spring SYS, reporting a pH value of approximately ∼8.60.…”

Persistent Continental Shelf Carbon Sink at the Ieodo Ocean Research Station in the Northern East China Sea

“…With regard to the status of net air-sea CO 2 flux across the entire ECS, mixed conclusions have been reported in literature, in part because the datasets that led to differing conclusions did not cover time and space extensively (Deng et al, 2021 and references therein). Specifically, the datasets were skewed to either the Chinese coastal waters under the direct influence of the nutrient-rich CDW (Li et al, 2021;Wu et al, 2021) or the offshore waters distant from the CDW influence (Shim et al, 2007;Kim et al, 2013). Overall, the entire ECS appeared to be a slight C sink on an annual scale (Wang et al, 2000;Zhai and Dai, 2009;Guo et al, 2015;, although it can be a weak C source when seasonal dynamics of river input and physical mixing occasionally induce C release in summer and fall in the inner shelves of the ECS (the Changjiang freshwater plume).…”

Distribution characteristics of pCO2 at the air-sea in the East China Sea and changes over the last 20 years

“…As the largest carbon pool on earth, the blue carbon sink has become the focus of research at home and abroad [3][4][5][6][7][8]. The study of CO 2 partial pressure and ux at the sea-air interface is of great signi cance for understanding and utilizing marine negative emissions to achieve carbon neutrality, as well as predicting the future trend of atmospheric CO 2 content level [9][10][11][12][13][14][15][16]. The continental marginal sea is located between the land and the vast ocean, and the terrigenous sources and pollutants enter the ocean through the continental marginal sea, which plays an important role in the global carbon dioxide biogeochemical cycle [17].…”