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Abstract Sediment geochemical characteristics were analyzed to assess how anthropogenic activities affected the Daya Bay, a subtropics bay adjacent to the most economically developed region of China. Vertical profiles of heavy metal contents and their enrichment factors indicated the development of Daya Bay environment in the past 100 years basically experienced three stages, which were closely consistent with the economic development. Before 1980s, the concentration of heavy metals was basically at the background level. Contamination of metals, particularly for Cr, Ni, Cu, Zn, Cd, and Pb, generally began in mid-1980s and became serious in 2000s. However, after late-2000s, the sediment quality had been radically improved. Heavy metals in nearshore sediment of Daya Bay were all closely related with import of anthropogenic and/or terrestrial material, whereas those in offshore were likely to be related with joint influence from the anthropogenic activities and the natural processes. Highlights • The evolution of Daya Bay environment in the past 100 years basically experienced three stages. • Before 1980s there was no record of heavy metals pollution. • Contamination of metals generally began in mid-1980s and became very serious in 2000s. • After late-2000s the sediment quality had been radically improved. • Contributions of anthropogenic and natural metals in sediment varied with heavy metal types and regional position. [ABSTRACT FROM AUTHOR]

To identify sources and evaluate ecological risks of heavy metals in sediments of Jiaozhou Bay, contents and chemical fractions of Cd, Cr, Cu, Pb, Zn, Ni, Sb and Sn were studied. Results suggested that higher metal contents appeared at inner bay and near marine dumping area. Labile fractions of heavy metals accounted for 0.5–77% (~36%) of total contents indicating their significant anthropogenic sources. The enrichment levels of Cd and Sb were relatively higher. Cu, Ni, Cd and Zn were at low to medium risks. Cr, Pb, Sn and Sb were at no or low risks. Total contents of heavy metals were mainly controlled by natural sources, while anthropogenic inputs were important sources of labile fractions of heavy metals in sediments of Jiaozhou Bay with industrial and domestic activities as main contributors for Cu, Pb, Zn, Cr, Ni and Sn, and agricultural activities for Cd and regional coal combustion for Sb. [ABSTRACT FROM AUTHOR]

Total contents and chemical speciation of Co, Ni, Cu, Ga, Mo, Cd, In, Sn, Sb, V, W, Tl, Bi and U in size-fractionated (< 32, 32–63 and > 63 μm) core sediments from Jiaozhou Bay were investigated to reveal their responses to anthropogenic activities. Metal contents showed a decreasing trend with increasing grain sizes. However, the loadings of metal fraction on < 32, 32–63 and > 63 μm grain sizes were 16%, 47% and 37%, respectively. Anthropogenic fluxes and enrichment factors of metals in > 63 μm fraction were closely linked to anthropogenic activities, with an obvious increase in upper 27 cm (1998–2015) and a slight decrease in 2009 year. Metals (especially for Cd, Co, Cu and Ni) in > 63 μm fraction were more easily released, with the highest percentage of acid soluble form and lowest residual form. Thus, the size fraction of > 63 μm cannot be ignored. [ABSTRACT FROM AUTHOR]

The behavior of heavy metals in contaminated sediment is of ecological significance considering the change of pH caused by ocean acidification. This study investigated the mobility of Cd, Cu, Ni, Pb, Fe, and Mn under experimental conditions for seawater acidification via enrichment of CO 2 gas at different reaction set-ups. The results indicated that the concerned metals behaved differently in the water compared to the sediment. The heavy metals were considerably transferred from sediment to seawater, and the resultant intensity was controlled by the degree of acidification and the chemical state of specific metals. Moreover, labile fractions of heavy metals in sediments were more susceptible to acidification than other fractions. These findings were observed and confirmed using real-time monitoring conducted via the diffusion gradient technique (DGT). Overall, the results of this study provided new insights into exploring the coupling risk of heavy metals with ocean acidification. • Long-term effects of acidification on heavy metal mobility • Variations in heavy metal distribution patterns in sediment–seawater systems • CO 2 enrichment acidified the pH of the system. • Changes in effective heavy metals were obtained by diffusion gradient technique. [ABSTRACT FROM AUTHOR]

Surface partial pressure of CO 2 ( p CO 2 ) and pertinent parameters (i.e., pH, total alkalinity, dissolved oxygen, chlorophyll a) were investigated in the southern Yellow Sea (SYS) and the East China Sea (ECS) basing on two surveys conducted in June and August of 2013. The results suggested carbonate chemistry dynamics and related controlling factors were provided with significant temporal and spatial variations in different subregions of these two continental shelf seas. The western of SYS (SYSW) was CO 2 -undersaturated both in June and August, with the average F CO 2 −1.88 mmol m −2 d −1 and −3.72 mmol m −2 d −1 , respectively. The phytoplankton initiated CO 2 -absorption and the suspended sediment induced CO 2 -emission jointly controlled the air–sea CO 2 exchange there. The center of SYS (SYSC) also behaved as an obvious CO 2 sink (−1.57 mmol m −2 d −1 and −3.99 mmol m −2 d −1 in June and August, respectively), probably due to elevated TA/DIC ratio and the subsequent effects of spring bloom. As for the Yangtze River estuary (YRE), it changed from an obvious CO 2 sink (−1.28 mmol m −2 d −1 ) in June into a very weak CO 2 source (0.04 mmol m −2 d −1 ) in August. This change was probably associated with the rising of seawater temperature and monthly variation of Yangtze River discharge. The inner shelf of ECS (ECSS) experienced obvious air–sea CO 2 flux changes during from June (−8.88 mmol m −2 d −1 ) to August (−0.36 mmol m −2 d −1 ) as well. Biological DIC consumption in the upper layer and DIC regenerated from respiration in the subsurface jointly controlled this p CO 2 variation. As a whole, the SYS and ECS acted as an obvious CO 2 sink during summer and could absorb atmospheric CO 2 with the average air–sea flux ( F CO 2 ) −2.68 mmol m −2 d −1 . The summary of air–sea CO 2 flux in the ECS and SYS during recent two decades indicated the ECS served as quite a stable CO 2 sink, whereas the SYS experienced obvious change. Discharge of Yangtze River and anthropogenic nutrients loading could profoundly affect the variations of p CO 2 and F CO 2 in future. [ABSTRACT FROM AUTHOR]

The partial pressure of CO2 (pCO2) and air-sea CO2 exchange flux (FCO2) in the southern Yellow Sea (SYS, 120–125°E, 31.5–37°N) were investigated basing on the field surveys conducted in April of 2011, and June, July, October of 2012. With significant spatial variations, surface pCO2 ranged from 243 to 574μatm, 206 to 620μatm, 102 to 655μatm and 328 to 557μatm in April, June, July and October, respectively. Nearshore area of Shandong Peninsula and Jiangsu Shallow (depth<50m) were pCO2-supersaturated (pCO2=400–600μatm), as the result of intensive water mixing which brought the bottom CO2-rich water to the surface layer. Conversely, offshore area of SYS center (depth>50m) was pCO2-undersaturated (pCO2<390μatm) in April, June and October, but supersaturated in July. Phytoplankton production sustained by abundant nutrient and suitable hydrodynamic conditions was of great importance for this undersaturated pCO2. Moreover, extreme low pCO2 (pCO2<300μatm) was observed in the Changjiang plume (32.5–33.5°N, 123–125°E) in July, which was also related with the biological uptake of CO2. Average air-sea CO2 exchange flux of the SYS in April, June, July and October was −3.16±0.40mmolm−2 d−1,−4.56±0.34mmolm−2 d−1, −0.36±0.51mmolm−2 d−1, and 6.67±0.57mmolm−2 d−1, respectively. As a whole, the SYS behaved as a weak CO2 sink during April to October, with an average flux for about −0.35mmolm−2 d−1. As for the controlling factors for pCO2 variation, temperature played the dominant role in October, whereas the non-temperature factors, such as vertical mixing, Changjiang plume and biological activity, were considered as the primary controlling factors in June and July. Spatially, the control of temperature on pCO2 was predominant in the offshore SYS; the non-temperature factors were predominant in the shallow nearshore area, especially in coast of Shandong Peninsula and the Jiangsu Shallow. [ABSTRACT FROM AUTHOR]

The TetraEther indeX of 86 carbon atoms (TEX 86) is widely used as a proxy to reconstruct past sea surface temperatures. Most current applications of TEX 86 are primarily based on analyzing the composition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) that comprise TEX 86 in sediments, with the assumption that the sedimentary isoGDGTs are mainly derived from the surface mixed layer. Here we report on the variations in the isoGDGT distribution, archaeal abundance and community through the water column of the Western Pacific Ocean, directly testing the export depth of isoGDGTs and constraining the temperature records of TEX 86. Our data show that maximum isoGDGT concentrations occurred in subsurface waters (150–200 m) with maximum archaeal abundances. The ratio between isoGDGTs bearing 2 vs. 3 cyclopentane moieties, i.e. [2/3] ratio, increased with depth, which is likely related to the shift of the archaeal community from Ca. Nitrosopelagicus-dominance to norank_f__Nitrosopumilaceae -dominance. Models based on the [2/3] ratios in the water column predicted an average export depth of isoGDGTs to sediments of around 150–200 m, consistent with the robust relationship between the compiled sedimentary TEX 86 and the annual mean subsurface temperature. Taken together, our findings support that TEX 86 records subsurface rather than surface temperatures in the open ocean. [ABSTRACT FROM AUTHOR]

Abstract The spatial and temporal dynamics of both dissolved and particulate nutrients were studied during 2015–2016 in the Jiaozhou Bay (JZB), a deeply anthropogenic impact ecosystem in China. The dissolved inorganic nutrients was mainly from the wastewater and riverine inputs which is demonstrated from the negative correlation between nutrients with salinity and their higher levels distribution observed in the northeastern and/or northwestern JZB, where mainly received industrial and agricultural source run-off, respectively. The high levels of dissolved and particulate organic pools were also observed in the same area but have autochthonous sources besides terrestrial input, which lead to their higher concentrations in autumn during phytoplankton bloom. The composition of DIN has been changed with the major component from NH 4 + to NO 3 -, which probably due to the controlling load of NH 4 + but no limitation of NO 3 - by human intervention. The average annual DIN/DIP ratio increased by one time but SiO 3 2-/DIN ratio has no obvious variation over the past decade, which indicated that the potential limiting nutrient for phytoplankton growth has been converted from silicon to phosphorus in JZB. Additional, more prone to partition into POC but not DOC pools of organic carbon were found during the phytoplankton bloom in autumn due to the nutrient-rich, diatom dominated condition and both DOP and POP may be the potential P source and can relieve P limitation to some extent during the same time. Nutrient budgets calculation also demonstrated that riverine input and wastewater discharge are major sources of dissolved nitrogen and phosphorus, while silicate were mainly came from submarine fresh groundwater discharge. The mixing flow transported large amounts of nutrients from JZB to the Yellow Sea. Meanwhile, the net ecosystem metabolism and nitrogen metabolism calculation showed the whole ecosystem was heterotrophic and a net nitrogen fixation in JZB. Highlights • The composition of DIN in JZB has been changed with the major component from NH 4 + to NO 3 -. • The proportions of DON and DOP to TDN and TDP has increased obviously over the past decade. • The potential limiting nutrient for phytoplankton growth has been converted from silicon to phosphorus in JZB. • An annual nutrients budget including submarine fresh groundwater discharge is proposed. • JZB is net heterotrophic (57 ×107 mol C/yr) and net nitrogen fixation (74 ×106 mol/yr) on annual basis. [ABSTRACT FROM AUTHOR]

To analyze the fluxes, seasonal variations, sources and potential ecological effects of dissolved trace elements (TEs) in atmospheric wet deposition (AWD), one-year wet precipitation samples were collected and determined for nine TEs in Jiaozhou Bay (JZB) between June 2015 and May 2016. Both the volume-weighted mean (VWM) concentration and flux sequence for the measured TEs was Al > Mn > Zn > Fe > Pb > Se > Cr > Cd > Co. Al was the most abundant TE with a VWM concentration and wet flux of 33.8 μg L −1 and 29.2 mg m −2 yr −1 , which were 2 and 3 orders of magnitude higher than those of Co, respectively. The emission intensities of pollutants, rainfall amount and wind speed were the dominating factors influencing seasonal variations of TEs in AWD. Based on enrichment factors, correlation analysis and principal component analysis, most of the TEs in AWD were primarily originated from anthropogenic activities except for Al and Fe, which are typically derived from re-suspended soil dusts. Although the TE inputs by AWD were significantly lower than those by rivers, the TE inputs via short-term heavy rains would distinctly increase surface seawater TE concentrations and then pollute the marine environment of JZB. AWD would have both profound impacts on the biogeochemical cycles of TEs and dual ecological effects (nutrient and toxicity) on aquatic organisms. [ABSTRACT FROM AUTHOR]