An estimate of the vertical diffusivity of the deep water

A simple advection-diffusion model is applied to the deep water of the North Pacific Ocean. The physical mixing parameter, i.e., the ratio of vertical advection velocity (W) to vertical eddy diffusivity (D), is obtained from the vertical distribution of a conservative property such as salinity. The rate of decomposition of organic matter is estimated from the oxygen consumption rate which is obtained from dissolved oxygen content. The calcium carbonate flux in the deep water is obtained from alkalinity. Using these values and the vertical distribution of a radioisotope,¹⁴C or²²⁶Ra, the vertical eddy diffusivity and the upwelling velocity are found to be 1.2 cm²/sec and 1.4 ×10^–5 cm/sec, respectively, at the Geosecs 1969 station. The oxygen consumption rate at 3 km depth of the station is found to be 1.4×10^–3ml/l/yr.     

Role of dissolved silicate in the occurrence of a phytoplankton bloom

The spring bloom of phytoplankton was studied in March in Funka Bay, Japan, to test the Tsunogai (1979)'s hypothesis regarding the role of silicate in the bloom. The hypothesis comprises two parts. 1) Diatoms are predominant when all the physical and chemical conditions are adequate for plankton growth. 2) Since the Si:P ratio of the diatom body is usually much larger than that of sea water, flagellates (non-siliceous phytoplankton) replace diatoms after dissolved silicate in the sea water has been almost completely consumed by diatoms. At the end of the bloom in late March phosphate still remained in the water but silicate was exhausted and the main species of phytoplankton changed from diatoms to flagellates. Grazing pressure by zooplankton at this time was not so great. A model using the data on assimilation rates of silicate showed a dramatic change of silicate uptake in late March. Poison in scallops caused byProtogonyaulux sp. (dinoflagellates) rapidly increased from mid-April at all stations along the coast of Funka Bay. All of these findings support Tsunogai's hypothesis.     

Methane in the East China Sea water

Methane in the East China Sea water was determined four times at a fixed vertical section along PN line consisting of 11–14 stations, in February 1993, October 1993, June 1994 and August 1994. The mean concentration of methane in the surface water was not significantly higher than that in the open ocean. The methane concentration below the pycnocline increased during the stratified period in summer to autumn and reached to 15 nmoles/l at most in October. The concentration of methane was fairly well correlated with AOU in the layer below the pycnocline in the stratified season. This means that methane in the bottom water has only a single source, which is expected to be anoxic sediments near the coast, and that the oxidation rate of methane in the water is extremely slow in the oxic water. The high methane observed in October completely disappeared in February, indicating that the methane was escaped to the atmosphere or transported to the pelagic ocean by the Kuroshio current. The East China Sea, therefore, is not a large direct and stationary source for the atmospheric methane, but may have some role as a source by supplying it sporadically to the atmosphere in early winter or indirectly from the surface of the pelagic ocean.     

A simple indirect method for the determination of organic-carbon in marine particles

A simple indirect method for the determination of organic carbon in marine particulate matter is proposed. The recommended procedure is as follows: The dried sample is ashed at 450°C for about 24 hr. The ashed sample is put into a Teflon vessel followed by a mixed solution of nitric acid, perchloric acid and hydrofluoric acid. The vessel is sealed and allowed to stand at 150°C for 5 hr. The concentrations of Si and Al in the digested solution are determined. The organic carbon content (Cal-C, %) is calculated by the following equation: Cal-C=0.52 ([CF]–0.10 [Opal]–0.03 [A-Si]), where [CF] is the combustible fraction (%), [Opal] is the biogenic-SiO₂(%), and [A-Si] is the content of aluminosilicate mineral (%).     

Evidence for predominance of internal tidal currents in Sagami and Suruga bays

Tidal currents observed in a surface layer overlying deep water in Sagami and Suruga Bays frequently have large amplitude in summer and fall. Numerical experiments show that the current amplitude due to the surface tides is below 1.0 cm sec^–1 for the semidiurnal and diurnal constituents in the inner region of the two bays. The observed current amplitudes are larger than the calculated ones due to the surface tides. Therefore, the observed tidal currents are indicated to be due mainly to the internal tides. In addition, the semidiurnal currents dominate the diurnal currents in Sagami Bay, while the opposite occurs in Suruga Bay. These results suggest that the prevailing periods of the internal tides differ between the two bays,i.e., the internal tide has a semidiurnal period in Sagami Bay and a diurnal period in Suruga Bay.     

Annual variation of methane in seawater in Funka bay,Japan

The concentration of methane in seawater was determined approximately once a month for one year from August 1990 to July 1991 at a station close to the center of Funka bay (92 m depth) and some supplementary observations were also carried out. The concentration of methane was usually increased with increasing depth, suggesting that methane was emitted from the bottom of the bay. While highly variable both spatially and temporally, the emission was intense in March and April, a period immediately after the spring bloom of phytoplankton. The maximum of methane found in the intermediate water suggests its source from the slope of the bay. The concentration of methane in the surface water changed seasonally and also interannually. The annually averaged flux of methane transferred to the atmosphere in the bay was estimated to be 6×10^–3 gCH₄m²/day. The coastal zone in the world may be a significant source of the atmospheric methane, although its source strength has yet to be accurately estimated from more data in different coastal seas.     

河口Si输运过程研究

基于拉格朗日余流及其输运过程的一种三维空间弱非线性理论，进一步假定Ｓｉ在河口的无因次化学转移项量级为ｋ＾２，给出了Ｓｉ的长期输运方程。对于一种二维模型河口，数值求解了零阶天文潮，欧拉余流、斯托克斯漂移、拉格朗日余流和盐度的分布；分别计算了平均逼留时间为１３，３０，６０，１８０ｄ等所对应的Ｓｉ浓度分布；给出了Ｓｉ－ｓ相关图，讨论了河口中Ｓｉ的保守性问题。     

Regeneration of chemical elements from settling particles collected by sediment trap in Funka Bay,Japan

Sediment trap experiments were carried out 39 times during the years from 1977 to 1981 in Funka Bay, Hokkaido, Japan. The observed total particulate flux varies seasonally, that is, the particulate fluxes in winter and spring are larger than those in summer. The fluxes in all seasons increased with depth. Major components of settling particles are aluminosilicate in winter, biogenic silicate in spring and organic matter and terrestrial material in summer, respectively. The fluxes of each chemical component observed with sediment traps are normalized to that of Al by assuming that the actual flux of Al is equal to the accumulation rate onto the sediment surface. Vertical changes of the normalized flux of each chemical component indicate the following: Fe was not regenerated from the settling particles in the water column. Mn was regenerated from the settling particles in the lower layer exclusively between 80 m depth and the sediment surface. Cd was actively regenerated in the upper layer above 80 m depth. Phosphate was regenerated in the upper layer, while biogenic silicate was in the lower layer. The silicate regeneration, therefore, occurs after phosphate regeneration. The material decomposing in the water column below 40 m has an atomic ratio of P ∶ Si ∶ C = 1 ∶ 52 ∶ 128.     

Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf

In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C₂, homogenous ¹³C₁ values and a large difference (19.7 on average) between ¹³C₁ (–55.2 to –53.6 PDB) and ¹³C₂ (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C₁ at the early thermal cracking stage of labile source materials, after which the C₂ gas is enriched in ¹³C by diffusion or biological alternation at the generation or accumulation site. The homogenous ¹³C₁ values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.     

Increase in total carbonate in the western North Pacific water and a hypothesis on the missing sink of anthropogenic carbon

Sea water samples were collected from various depths in the North Pacific (40–21°N) along 165°E in 1991. Their total carbonate (total dissolved carbonate species) contents were determined with random errors less than 0.2% by a coulometric method. The preformed carbonate contents defined by Chen (1982) were calculated from the obtained data and other observed data including potential temperature, salinity, dissolved oxygen and total alkalinity. The same calculation was done for the GEOSECS data obtained in nearly the same region in 1973. The difference between the two data sets reveals that the preformed carbonate has increased by 180±41 gC/m² during the last 18 years. This value is comparable or somewhat larger than 150 gC/m² obtained in the case that the ocean uptakes 3 GtC/yr for 18 years and distributes it equally among the world oceans. Based on the results, a hypothesis on the missing sink for the anthropogenic carbon dioxide is presented, in that the missing sink is the intermediate waters formed in the northern North Pacific and the Southern Ocean besides the deep waters formed in the North Atlantic and the Southern Ocean.