Revisiting the Seasonal Variations of Sea-Air CO2 Fluxes in the Northern East China Sea

Abstract

Temperature, salinity, chlorophyll a (Chl-a), nitrate, and sea-air differences of CO 2 partial pressure (ΔpCO 2 ) were extensively investigated in the northern East China Sea (ECS) during seven research cruises from 2003 to 2009. The ΔpCO 2 showed large intraseasonal variation in the spring and summer. In spring, the areal mean ΔpCO 2 in May 2004 was almost half of that in April 2008, probably associated with differences in sea surface temperature (SST). In summer, the areal mean ΔpCO 2 in August 2003 was also twice as large as that in July 2006. In addition, ΔpCO 2 exhibited large seasonal variation with positive values in autumn and negative values in other seasons. The positive ΔpCO 2 in autumn was ascribed to vertical mixing with CO 2 -enriched subsurface waters and relatively high SST in this season. The annually integrated sea-air CO 2 flux in the northern ECS was -2.2 ± 2.1 mol m -2 yr -1 , indicating CO 2 absorption from atmosphere to the sea, which was more than two times lower than the previous estimate (Shim et al. 2007) reported for the same region. This large difference was presumably responsible for the underestimation of winter CO 2 influx by Shim et al. (2007) and the large interannual variation of CO 2 flux. The CO 2 influx in the ECS was twice that estimated for continental shelves worldwide, suggesting that the ECS acts as a strong sink of atmospheric CO 2 compared to other continental shelves.

Seasonal Variations of Surface fCO2 and Sea-Air CO2 Fluxes in the Ulleung Basin of the East/Japan Sea

“…The annual CO 2 uptake rate in this study area was considerably larger than the estimate for worldwide continental shelves (-1.1 mol m -2 yr -1 ; Chen and Borges 2009) and the global mean (-0.51 mol m -2 yr -1 ; Takahashi et al 2009). Kim et al (2012) reported that the annual sea-air CO 2 flux in the northern East China Sea was -2.2 ± 2.1 mol m -2 yr -1 , which is comparable to our result. Therefore, the Ulleung Basin of the East Sea, like the East China Sea, acts as a strong sink of atmospheric CO 2 .…”

“…The Tsushima Warm Current branched from the Kuroshio Current and passed through the East China Sea before entering the study area. Kim et al (2012) measured the surface fCO 2 in the northern East China Sea during four seasons; the spatial mean fCO 2 values were 311 ± 31 μatm in spring, 309 ± 53 μatm in summer, 376 ± 37 μatm in autumn, and 335 ± 17 μatm in winter. To identify the effects of lateral advection on the surface fCO 2 , the spatial mean surface fCO 2 values measured in the study area were compared with those in the East China Sea during four seasons (Table 1).…”

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

“…Prior studies have already revealed that the ECS is overall an annual net sink of atmospheric CO 2 , with significant seasonal variations (Chou et al, 2009;Chou et al, 2011;Kim et al, 2013;Peng et al, 1999;Shim et al, 2007;Tsunogai et al, 1999;Wang et al, 2000;Zhai and Dai, 2009). The ranges of present estimates are −3.3 to −6.5 in spring, −2.4 to −4.8 in summer, 0.4 to 2.9 in autumn and −13.7 to −10.4 mmol m −2 d −1 in winter.…”

“…The ranges of present estimates are −3.3 to −6.5 in spring, −2.4 to −4.8 in summer, 0.4 to 2.9 in autumn and −13.7 to −10.4 mmol m −2 d −1 in winter. 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).…”

Estimating Remineralized Phosphate and Its Remineralization Rate in the Northern East China Sea During Summer 1997: A Snapshot Study Before Three-Gorges Dam Construction

“…The Yellow Sea Bottom Cold Water (YSBCW), which forms through winter cooling in the Yellow Sea, extends a considerable distance into the nECS (Lie 1984;Gong et al 1996). The atmospheric CO 2 sink (air to sea) during the summer in the nECS is significant (Wang et al 2000;Shim et al 2007;Kim et al 2013a). All of these processes suggest that the summer in this region is particularly dynamic due to both active physical mixing and biogeochemical processes.…”