In order to assess the role of submarine groundwater discharge (SGD) and its impact on the carbonate system on the northern South China Sea (NSCS) shelf, we measured seawater concentrations of four radium isotopes ^{223,224,226,228}Ra along with carbonate system parameters in June–July, 2008. Complementary groundwater sampling was conducted in coastal areas in December 2008 and October 2010 to constrain the groundwater end-members. The distribution of Ra isotopes in the NSCS was largely controlled by the Pearl River plume and coastal upwelling. Long-lived Ra isotopes (²²⁸Ra and ²²⁶Ra) were enriched in the river plume but low in the offshore surface water and subsurface water/upwelling zone. In contrast, short-lived Ra isotopes (²²⁴Ra and ²²³Ra) were elevated in the subsurface water/upwelling zone as well as in the river plume but depleted in the offshore surface water. In order to quantify SGD, we adopted two independent mathematical approaches. Using a three end-member mixing model with total alkalinity (TAlk) and Ra isotopes, we derived a SGD flux into the NSCS shelf of 2.3–3.7 × 10⁸ m³ day⁻¹. Our second approach involved a simple mass balance of ²²⁸Ra and ²²⁶Ra and resulted in a first order but consistent SGD flux estimate of 2.2–3.7 × 10⁸ m³ day⁻¹. These fluxes were equivalent to 12–21 % of the Pearl River discharge, but the source of the SGD was mostly recirculated seawater. Despite the relatively small SGD volume flow compared to the river, the associated material fluxes were substantial given their elevated concentrations of dissolved inorganic solutes. In this case, dissolved inorganic carbon (DIC) flux through SGD was 153–347 × 10⁹ mol yr⁻¹, or ~23–53 % of the riverine DIC export flux. Our estimates of the groundwater-derived phosphate flux ranged 3–68 × 10⁷ mol yr⁻¹, which may be responsible for new production on the shelf up to 0.3–6.3 mmol C m⁻² d⁻¹. This rate of new production would at most consume 11 % of the DIC contribution delivered by SGD. Hence, SGD may play an important role in the carbon balance over the NSCS shelf

Abstract. Based upon 14 field surveys conducted between 2003 and 2008, we showed that the seasonal pattern of sea surface partial pressure of CO 2 (pCO 2 ) and sea-air CO 2 fluxes differed among four different physicalbiogeochemical domains in the South China Sea (SCS) proper. The four domains were located between 7 and 23 • N and 110 and 121 • E, covering a surface area of 1344 × 10 3 km 2 and accounting for ∼ 54 % of the SCS proper. In the area off the Pearl River estuary, relatively low pCO 2 values of 320 to 390 µatm were observed in all four seasons and both the biological productivity and CO 2 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 pCO 2 in the warm seasons and relatively low pCO 2 in the cold seasons was revealed. In the central/southern SCS area, moderately high sea surface pCO 2 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, pCO 2 was particularly dynamic in winter, when northeast monsoon induced upwelling events and strong outgassing of CO 2 . These episodic events might have dominated the annual sea-air CO 2 flux in this particular area. The estimate of annual sea-air CO 2 fluxes showed that most areas of the SCS proper served as weak to moderate sources of the atmospheric CO 2 , with sea-air CO 2 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 ± 1.48 mol m −2 yr −1 in the area west of the Luzon Strait. However, the annual sea-air CO 2 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 contributed (18 ± 10) × 10 12 g C yr −1 to the atmospheric CO 2 .

Abstract. This study reports the most comprehensive data set thus far of surface seawater pCO 2 (partial pressure of CO 2 ) and the associated air-sea CO 2 fluxes in a major ocean margin, the East China Sea (ECS), based on 24 surveys conducted in 2006 to 2011. We showed highly dynamic spatial variability in sea surface pCO 2 in the ECS except in winter, when it ranged across a narrow band of 330 to 360 µatm. We categorized the ECS into five different domains featuring with different physics and biogeochemistry to better characterize the seasonality of the pCO 2 dynamics and to better constrain the CO 2 flux. The five domains are (I) the outer Changjiang estuary and Changjiang plume, (II) the Zhejiang-Fujian coast, (III) the northern ECS shelf, (IV) the middle ECS shelf, and (V) the southern ECS shelf. In spring and summer, pCO 2 off the Changjiang estuary was as low as < 100 µatm, while it was up to > 400 µatm in autumn. pCO 2 along the Zhejiang-Fujian coast was low in spring, summer and winter (300 to 350 µatm) but was relatively high in autumn (> 350 µatm). On the northern ECS shelf, pCO 2 in summer and autumn was > 340 µatm in most areas, higher than in winter and spring. On the middle and southern ECS shelf, pCO 2 in summer ranged from 380 to 400 µatm, which was higher than in other seasons (< 350 µatm). The areaweighted CO 2 flux on the entire ECS shelf was −10.0 ± 2.0 in winter, −11.7 ± 3.6 in spring, −3.5 ± 4.6 in summer and −2.3 ± 3.1 mmol m −2 d −1 in autumn. It is important to note that the standard deviations in these flux ranges mostly reflect the spatial variation in pCO 2 rather than the bulk uncertainty. Nevertheless, on an annual basis, the average CO 2 influx into the entire ECS shelf was 6.9 ± 4.0 mmol m −2 d −1 , about twice the global average in ocean margins.

Abstract. The causes for a productive upwelling region to be a source of CO2 are usually referred to the excess CO2 supplied via upwelling of high dissolved inorganic carbon (DIC) from deep water. Furthermore, we hypothesize that microbial activity plays a significant role on top of that. To test this hypothesis, multiple biogeochemical parameters were investigated at two cyclonic-eddy-induced upwelling sites, CE1 and CE2, in the western South China Sea. The data showed that upwelling can exert significant influences on biological activities in the euphotic zone and can also impact on particulate organic carbon (POC) export flux depending on upwelling conditions, such as the magnitude, timing, and duration of nutrient input and consequent microbial activities. At CE2, the increase of phytoplankton biomass caused by the upwelled nutrients resulted in increase of POC export flux compared to non-eddy reference sites, while at CE1 the microbial respiration of organic carbon stimulated by the upwelled nutrients significantly contributed to the attenuation of POC export flux. These results suggest that on top of upwelled DIC, microbial activities stimulated by upwelled nutrients and labile organic carbon produced by phytoplankton can play a critical role for an upwelling area to be outgassing or uptaking CO2. We point out that even though an upwelling region is outgassing CO2, carbon sequestration still takes place through the POC-based biological pump as well as the refractory dissolved organic carbon (RDOC)-based microbial carbon pump.

Central composite design using response surface methodology was employed to optimize soil/liquid ratio (S/L), pH, and incubation time for polycyclic aromatic hydrocarbons (PAHs) bioaccessibility from soil in a simulated gastrointestinal tract. The magnitude of PAHs bioaccessibility in intestinal tract was found higher than that in gastric tract. Results showed that S/L had significant negative effects on the bioaccessibility of PAHs in both the gastric and intestinal tracts. The effect of pH on the intestinal tract was significantly negative, while on the gastric tract, it was positive. The incubation time presented an insignificant effect in gastric tract despite its significant positive effect in intestinal tract. The worst-case bioaccessibility conditions for PAHs in the gastric tract were found to be S/L 0.004, pH 2, and incubation time 3 h, with the maximum bioaccessibility of PAHs at 6.0% compared with 41.8% in intestinal tract with S/L 0.004, pH 6.5, and incubation time 6 h.Doctoral Program of Higher Education of China [20060384007