-Tung Arthur Chen

Heavy metal pollution status in surface sediments of the coastal Bohai Bay

Bohai Bay, the second largest bay of Bohai Sea, largely due to the huge amount of pollutants discharged into it annually and its geohydrologic condition, is considered to be one of the most polluted marine areas in China. To slow down, halt and finally reverse the environmental deterioration of Bohai Sea, some researchers have proposed to connect it with Jiaozhou Bay in the western coast of Southern Yellow Sea by digging an interbasin canal through Shandong Peninsula. In order to assess the heavy metal pollution and provide background information for such a large geoengineering scheme, surface sediments from 42 stations covering both riverine and marine regions of the northwestern coast of Bohai Bay were analyzed for heavy metal content and fractionation (Cd, Cr, Cu, Ni, Pb and Zn). Three empirically derived sediment quality guidelines were used to assess the pollution extent of these metals. The studied metals had low mobility except for Cd at all stations and Zn at some riverine stations. Although a high mobility of Cd was observed, it could hardly cause a bad effect on the environment owing to its low total concentrations. Anthropogenic influence on the accumulation of studied heavy metals in sediments of Bohai Bay was obvious, but their contents were relatively lower to date comparing with some other marine coastal areas that receive important anthropogenic inputs. Taking as a whole, surface sediments of northwestern Bohai Bay had a 21% probability of toxicity based on the mean effects range-median quotient.

Carbon dioxide and related parameters in the East China Sea

A low-temperature, low-salinity water mass lying on the bottom of the shelf area in the northern area of the East China Sea (ECS) in summertime is regarded as remnant winter water. Carbonate and related parameters suggest that it may originate from the Yellow Sea Cold Water which is formed farther north. There are no apparent annual variations in the carbonate parameters in the Kuroshio east of the shelf break. The partial pressure of CO2 calculated from the pH, TA or TCO2 data in this study show that the surface water in the shelf area is undersaturated with CO2 in spring and summer. When combined with other data collected in different seasons, the results show that the shelf area of the ECS is indeed a net sink for atmospheric CO2. The shelf area of the ECS may absorb as much as 0.013–0.030 Gt C per year. The carbonate data also suggest that the Tsushima Warm Current is a branch of the Kuroshio.

Exchange of water masses between the East China Sea and the Kuroshio off northeastern Taiwan

Abstract At least six water masses take part in the mixing processes between the East China Sea and the Kuroshio off northeastern Taiwan: the Kuroshio Surface Water (SW), Kuroshio Tropical Water (TW), Kuroshio Intermediate Water (IW), East China Sea Water (ECSW), Coastal Water (CW) and the Taiwan Strait Water (TSW). SW is depleted in nutrients and normalized alkalinity but has the highest temperature and pH of all these waters. TW has relatively high temperature, and the highest salinity of all waters. The salinity maximum in the Kuroshio is usually between 100 and 300 m deep, with large interannual and seasonal variability. IW is characterized by a salinity minimum, high nutrient content and alkalinity, but low pH and oxygen. ECSW is low in salinity, temperature and nutrients, but high in oxygen and normalized calcium and alkalinity. CW has low salinity and nutrient content but is high in normalized alkalinity. TSW is generally depleted in nutrients. The characteristics of the above mentioned waters are discussed. The mixing percentages of SW, TW, IW, and the composite Shelf Surface Water (composed of ECSW, CW and TSW) off the northeast corner of Taiwan in September 1988 and December 1989 are calculated.

The Dry Holocene Megathermal in Inner Mongolia

The paleoclimate since 14 kyr BP (14C age) was reconstructed based on a 16.22-m-long sediment core collected from Lake Yanhaizi, a saline lake located near the northern limit of the East Asian summer monsoon in Inner Mongolia. Coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated. These sediments have low organic carbon contents but high maturity indices, indicating that they were deposited in an arid environment. By contrast, based on high organic contents and low maturity indices, fine sediments were deposited during periods of high lake stand in a humid environment. It was in general dry between 8.0 and 4.3 kyr BP. The above dry and wet phases are consistent with those recovered from the arid–semiarid transition zone elsewhere, but are unlike the widely perceived humid Holocene Megathermal reported in east China and the newly reconstructed record in the alpine Retreat Lake in Taiwan. The discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon. On the other hand, much enhanced evaporation over higher monsoon precipitation at Lake Yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon. This also accounts for the fact the high-temperature Holocene Megathermal, as revealed in the Okinawa Trough and the northern South China Sea, is correlated to the dry phases at Lake Yanhaizi. Conversely, the 4–2-kyr BP coldest period in the Holocene corresponds to a wet phase at Lake Yanhaizi.

Nutrient budgets for the South China Sea basin

Abstract Varying atmospheric forcing and an elaborate geography make for a complex flow in the South China Sea (SCS). Throughout the year, the surface waters of the Kuroshio flow into the SCS, while the surface waters of the SCS flow out through the Bashi Channel. Cumulatively, there is a small (∼1 Sv) net outflow of surface water (0–350-m depth) from the SCS in the wet season, but a net inflow (∼3 Sv) in the dry season through the Bashi Channel. The differences are mainly made up by inflow and outflow of Sunda Shelf Water in the wet and dry seasons, respectively. Seawater, phosphorus, nitrogen and silicate budgets were calculated based on a box model. The results point out an intermediate water outflow (350–1350-m depth) into the West Philippine Sea (WPS) through the Bashi Channel in both the wet and dry seasons, though this, along with the nutrients it carries, is slightly larger in the dry season (2 Sv) than in the wet (1.8 Sv). More importantly, the export of nutrient-laden SCS intermediate water through the Bashi Channel subsequently upwells onto the East China Sea (ECS) shelf. The denitrification rate for shelves in the SCS is 0.11 mol N m−2 year−1, calculated by balancing the nitrogen budget. The oxygen consumption and the nutrient regeneration rates, based on the mass-balance and the one-dimensional advection–diffusion models, stand between those for the Bering Sea and the Sea of Japan.

Pollution status of the Bohai Sea: an overview of the environmental quality assessment related trace metals.

It is well recognized that the ecosystem of the Bohai Sea is being rapidly degraded and the Sea has basically lost its function as a fishing ground. Billions of funds have been spent in slowing down, halting and finally reversing the environmental deterioration of the Bohai Sea. Although trace metals are routinely monitored, the data with high temporal resolution for a clear understanding of biogeochemical processes in the ecosystem of the Bohai Sea are insufficient, especially in the western literature. In this review, status of trace metal contamination in the Bohai Sea is assessed based on a comprehensive review of their concentrations recorded in the waters, sediments and organisms over the past decades. Studies show that metal contamination in the Bohai Sea is closely associated with the fast economic growth in the past decades. Concentrations of trace metals are high in coastal areas especially in the estuaries. Alarmingly high metal concentrations are observed in the waters, sediments and organisms from the western Bohai Bay and the northern Liaodong Bay, especially the coasts near Huludao in the northernmost area of the Bohai Sea, which is being polluted by industrial sewage from the surrounding areas. The knowledge of the speciation and fractionation of trace metals and the influence of submarine groundwater discharge on the biogeochemistry of trace metals in the Bohai Sea is far from enough and related work needs to be done urgently to get a better understanding of the influence of trace metals on the ecosystem of the Bohai Sea. A clear understanding of the trace metal pollution status of the Bohai Sea could not be achieved presently for lack of systematic cooperation in different research fields. It is quite necessary to apply the environmental and ecological modeling to the investigation of trace metals in the Bohai Sea and then provide foundations for the protection of the environment and ecosystem of the Bohai Sea.

Continental Margin Exchanges

Biogeochemical processes principally occur in the upper 200 metres of the sea and are often associated with continental margins. Although the continental margins, with waters shallower than 200 m, occupy a mere 7% of the ocean surface and even less than 0.5% of the ocean volume, they still play a major role in oceanic biogeochemical cycling. Significantly higher rates of organic productivity occur, in fact, in the coastal oceans than in the open oceans because of rapid turnover and the higher supply of nutrients from upwelling and riverine inputs. Also, 8 to 30 times more organic carbon and 4 to 15 times more calcium carbonate per unit area accumulate in the coastal oceans than in the open oceans. Similarly, gas exchange fluxes of carbon and nitrogen are considerably higher in coastal waters than in the open oceans per unit area. As a result, it has been reported that around 14% of total global ocean production, along with 80–90% of new production and as much as up to 50% of denitrification takes place in the coastal oceans. The burial sites of 80% of the organic carbon derived from both oceanic processes and terrestrial sources, in excess of 50% of present day global carbonate deposition, are also located in the coastal oceans. The unburied portion of organic carbon may be respired on the shelf, thus forming a potential natural source of atmospheric carbon dioxide. However, how much is actually respired is unknown since much of this carbon is highly inert and only mixes conservatively with seawater (Smith and Mackenzie 1987; Mantoura et al. 1991; Wollast 1998).

A Mid-Depth Front Separating the South China Sea Water and the Philippine Sea Water

In order to understand the influence of the South China Sea (SCS) water on the Kuroshio, and to study the dissolved carbonate system, we participated in six WOCE cruises aboard R/V Ocean Researcher 1. The areas studied were the northeast South China Sea and the West Philippine Sea near the Luzon Strait. Temperature, salinity, pH, alkalinity and total CO2 were measured. Our data indicate that, although the Kuroshio and the SCS waters flow in and out of the Luzon Strait near surface, the SCS water seems mainly to flow out of the SCS at mid-depth. There exists a “mid-depth front” near 122°E between 350 and 1350 m in all seasons and years that we studied. The water mass between 350 and 1350 m east of the front belongs to the West Philippine Sea proper water, while on the west is the mixed water of the South China Sea and the West Philippine Sea.

Amorphous silica solubilities IV. Behavior in pure water and aqueous sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate solutions up to 350°C

Abstract Solubilities of amorphous silica were determined in separate aqueous solutions of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate at temperatures up to 350°C. These salts, of strong interest in hydrothermal oceanography and geothermal energy, generally ranged in concentration from zero to saturation. Solubilities in the sodium chloride solutions followed closely earlier observed decreases in sodium nitrate solutions at high temperatures. Amorphous silica solubilities were depressed most by magnesium chloride, followed by magnesium sulfate, and less by sodium chloride. As the temperature rose the relative decrease in solubility caused by added salt became smaller. Surprisingly, sodium sulfate solutions, showing little effect at 25°C, sharply raised the solubility as the temperature increased to 350°C. Plots of the logarithms of derived activity coefficients against molalities of added salt gave approximately straight lines. These plots allow simple predictions of amorphous silica solubility in single salt solutions.

Variability of the chemical hydrography at the frontal region between the East China Sea and the Kuroshio north-east of Taiwan

Abstract The hydrography across the frontal region between the East China Sea and the Okinawa Trough north-east of Taiwan, observed during the summer of 1985 and 1988 and the early spring of 1987, was governed mainly by mixing across the front and the topographically induced upwelling of the modified Kuroshio water in the Okinawa Trough during the periodic shelfward migration of the Kuroshio. The location of the front relative to the shelf break seemed to be temporally variable. Topographically induced upwelling was evident during the summer of 1988 and the early spring of 1987 when the front was located close to the shelf break. It might not have occurred in the summer of 1985 when the front was further offshore. The end-member composition of the upwelling water was similar in both seasons. It originated from about 300 m with a temperature and salinity of 13 °C and 34·4 psu. It was rich in nutrients and poor in oxygen with concentrations of nitrate, phosphate, silicate and oxygen of 16, 1, 18 and 160 μM respectively. This upwelling water is potentially a major source of nutrients to the East China Sea. The deep water in the Okinawa Trough at temperatures below 15 C did not participate in cross-shelf mixing. Its chemical characteristics did not change significantly from year to year.