Seasonal variations of air-sea CO<sub>2</sub> fluxes in the largest tropical marginal sea (South China Sea) based on multiple-year underway measurements

Abstract

Based upon fourteen field surveys conducted between 2003 and 2008, we showed that the seasonal pattern of sea surface partial pressure of CO₂ (<i>p</i>CO₂) and air–sea CO₂ fluxes differed among four different physical-biogeochemical domains in the South China Sea (SCS) proper. The four domains were located between 4 and 23° N and 109 and 121° E, covering ~ 38% of the surface area of the entire SCS. In the area off the Pearl River Estuary, relatively low <i>p</i>CO₂ values of 320 to 390 μatm were observed in all four seasons and both the biological productivity and CO₂ uptake were enhanced in summer in the Pearl River plume waters. In the northern SCS slope/basin area, a typical seasonal cycle of relatively high <i>p</i>CO₂ in the warmer seasons and relatively low <i>p</i>CO₂ in the cold seasons was revealed. In the central/southern SCS area, moderately high sea surface <i>p</i>CO₂ values of 360 to 425 μatm were observed throughout the year. In the area west of the Luzon Strait, a major exchange pathway between the SCS and the Pacific Ocean, <i>p</i>CO₂ was particularly dynamic in winter, when northeast monsoon induced upwelling events and strong outgassing of CO₂. These episodic events might have dominated the annual air–sea CO₂ flux in this particular area. The estimate of annual sea–air CO₂ fluxes showed that, most areas of the SCS proper served as weak sources to the atmospheric CO₂, with sea–air CO₂ flux values of 0.46 ± 0.43 mol m⁻² yr⁻¹ in the northern SCS slope/basin, 1.37 ± 0.55 mol m⁻² yr⁻¹ in the central/southern SCS, and 1.21 ± 1.47 mol m⁻² yr⁻¹ in the area west of the Luzon Strait. However, the annual sea–air CO₂ exchange was nearly in equilibrium (−0.44 ± 0.65 mol m⁻² yr⁻¹) in the area off the Pearl River Estuary. Overall the four domains released (18 ± 10) × 10¹² g C yr⁻¹ into the atmosphere. The CO₂ release rate of the South China Sea essentially exceeded the average CO₂ emission level of most tropical oceans

Dynamics of the bacterial and archaeal communities in the Northern South China Sea revealed by 454 pyrosequencing of the 16S rRNA gene

“…The abundance and activity of prokaryotic cells are thought as one of the factors determining the carbon flux in estuarine and oceanic waters through the microbial carbon pump (Jiao et al, 2010a;Jiao et al, 2010b). Their seasonal and spatial variations could explain part of the spatio-temporal variation of carbon flux observed in the NSCS (Zhai et al, 2013).…”

Distributions and sea-to-air fluxes of nitrous oxide in the South China Sea and the West Philippines Sea

“…1a; Table 1 Samples were collected close to the south of the Taiwan Strait, which is located in the northeastern part of the SCS, during the cruises in August 2003 (ORIII-896) and July 2004 (ORIII-983). ORI-695 was conducted near the Pearl River estuary and was influenced by the summer estuarine plume (Gan et al, 2009;Cao et al, 2011;Han et al, 2012;Zhai et al, 2013;Bai et al, 2015). The Pearl River (Zhujiang) is the 13th largest river in the world (Yin et al, 2004) and the second largest river in China (after the Yangtze River) with a water discharge of 326 Â 10 9 m 3 annually; it is also the second largest river (after the Mekong River) that enters the SCS (Chen et al, 2008).…”

Air–sea CO&lt;sub&gt;2&lt;/sub&gt; fluxes in the East China Sea based on multiple-year underway observations

“…Having stated this, it remains, however, challenging to reliably assess the carbon fluxes in individual coastal systems that are often characterized by the greatest spatial and temporal variations (Cai and Dai, 2004;Dai et al, 2013;Dai et al, 2009;Zhai et al, 2013). Understanding regional fluxes and controls is important because it not only affects global flux estimation but also improves our capability of modelling the coastal ocean carbon cycle.…”