Synthesis of observed air–sea CO<sub>2</sub> exchange fluxes in the river-dominated East China Sea and improved estimates of annual and seasonal net mean fluxes

Abstract

Abstract. Limited observations exist for a reliable assessment of annual CO2 uptake that takes into consideration the strong seasonal variation in the river-dominated East China Sea (ECS). Here we explore seasonally representative CO2 uptakes by the whole East China Sea derived from observations over a 14-year period. We firstly identified the biological sequestration of CO2 taking place in the highly productive, nutrient-enriched Changjiang River plume, dictated by the Changjiang River discharge in warm seasons. We have therefore established an empirical algorithm as a function of sea surface temperature (SST) and Changjiang River discharge (CRD) for predicting sea surface pCO2. Syntheses based on both observations and models show that the annually averaged CO2 uptake from atmosphere during the period 1998–2011 was constrained to about 1.8 ± 0.5 mol C m−2 yr−1. This assessment of annual CO2 uptake is more reliable and representative, compared to previous estimates, in terms of temporal and spatial coverage. Additionally, the CO2 time series, exhibiting distinct seasonal pattern, gives mean fluxes of −3.7 ± 0.5, −1.1 ± 1.3, −0.3 ± 0.8 and −2.5 ± 0.7 mol C m−2 yr−1 in spring, summer, fall and winter, respectively, and also reveals apparent interannual variations. The flux seasonality shows a strong sink in spring and a weak source in late summer–mid-fall. The weak sink status during warm periods in summer–fall is fairly sensitive to changes of pCO2 and may easily shift from a sink to a source altered by environmental changes under climate change and anthropogenic forcing.

Carbon dioxide and methane dynamics in a human-dominated lowland coastal river network (Shanghai, China)

“…On the other hand, given that the Shanghai river network covers only about 20% of the surface water area of the Taihu Lake basin (i.e., 2800 km 2 , excluding the Taihu Lake), the total CO 2 emission from the Shanghai river network indicates that a minimum of 10% of the estimated NEP may be offset at the basin scale (Table ), reinforcing the need to accurately account for aquatic C fluxes in watershed C budgets [ Raymond et al , ; Butman et al , ]. Furthermore, there is growing evidence that nutrient exports via the Yangtze River fuel GPP of the river‐dominated East China Sea, creating a net C sink of −47.5 Tg CO 2 ‐eq yr −1 [ Tseng et al , ]. In this context, CO 2 evasion from the Shanghai river network offsets about 10% of this C sink, although the Shanghai river network is only less than 0.1% of the river‐dominated East China Sea by area (Table ).…”

Export Flux, Biogeochemical Effects, and the Fate of a Terrestrial Carbonate System: From Changjiang (Yangtze River) Estuary to the East China Sea

“…In the 1990s, the lowest springtime and/or summertime sea surface pCO 2 was recorded off Changjiang Estuary at 200 μatm (Peng et al, 1999;Tsunogai et al, 1999;Wang et al, 2000;Zhang et al, 1997;Zhang et al, 1999). In the early 2000s, quite low pCO 2 of 110-140 μatm was detected in this region (Chen et al, 2006;Tan et al, 2004;Tseng et al, 2014). In the recent decade, however, extremely low sea surface pCO 2 values of 30-80 μatm were frequently observed in the CDW area (Figure S7), which was only 10-20% of the air-equilibrated level.…”

Regionalized global budget of the CO2 exchange at the air‐water interface in continental shelf seas

“…Our calculations suggest, however, that these emissions could contribute only marginally to the global CO 2 budget. Tseng et al, 2014. v Shim et al, 2007.…”