The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single-transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) -UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) - (UO−UOH2O) =AS (°/oo)+BS (°/oo)3/2 +CS (°/oo)2, where U and UH20 are the speeds of sound in seawater and pure water, respectively; superscripts P and O are used to denote applied pressure P and O (1 atm); A, B, and C are temperature- and pressure-dependent parameters; S (o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high-pressure pure-water sound-speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1-atm seawater sound-speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1 over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1 (maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1 (maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure-water data.

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.

The air–sea exchanges of CO₂ in the world's 165 estuaries and 87 continental shelves are evaluated. Generally and in all seasons, upper estuaries with salinities of less than two are strong sources of CO₂ (39 ± 56 mol C m⁻² yr⁻¹, positive flux indicates that the water is losing CO₂ to the atmosphere); mid-estuaries with salinities of between 2 and 25 are moderate sources (17.5 ± 34 mol C m⁻² yr⁻¹) and lower estuaries with salinities of more than 25 are weak sources (8.4 ± 14 mol C m⁻² yr⁻¹). With respect to latitude, estuaries between 23.5 and 50° N have the largest flux per unit area (63 ± 101 mmol C m⁻² d⁻¹); these are followed by lower-latitude estuaries (23.5–0° S: 44 ± 29 mmol C m⁻² d⁻¹; 0–23.5° N: 39 ± 55 mmol C m⁻² d⁻¹), and then regions north of 50° N (36 ± 91 mmol C m⁻² d⁻¹). Estuaries south of 50° S have the smallest flux per unit area (9.5 ± 12 mmol C m⁻² d⁻¹). Mixing with low-pCO₂ shelf waters, water temperature, residence time and the complexity of the biogeochemistry are major factors that govern the pCO₂ in estuaries, but wind speed, seldom discussed, is critical to controlling the air–water exchanges of CO₂. The total annual release of CO₂ from the world's estuaries is now estimated to be 0.10 Pg C yr⁻¹, which is much lower than published values mainly because of the contribution of a considerable amount of heretofore unpublished or new data from Asia and the Arctic. The Asian data, although indicating high pCO₂, are low in sea-to-air fluxes because of low wind speeds. Previously determined flux values rely heavily on data from Europe and North America, where pCO₂ is lower but wind speeds are much higher, such that the CO₂ fluxes are higher than in Asia. Newly emerged CO₂ flux data in the Arctic reveal that estuaries there mostly absorb rather than release CO₂. Most continental shelves, and especially those at high latitude, are undersaturated in terms of CO₂ and absorb CO₂ from the atmosphere in all seasons. Shelves between 0 and 23.5° S are on average a weak source and have a small flux per unit area of CO₂ to the atmosphere. Water temperature, the spreading of river plumes, upwelling, and biological production seem to be the main factors in determining pCO₂ in the shelves. Wind speed, again, is critical because at high latitudes, the winds tend to be strong. Since the surface water pCO₂ values are low, the air-to-sea fluxes are high in regions above 50° N and below 50° S. At low latitudes, the winds tend to be weak, so the sea-to-air CO₂ flux is small. Overall, the world's continental shelves absorb 0.4 Pg C yr⁻¹ from the atmosphere.