Seasonal variation of water temperature in the Seto Inland Sea

The seasonal variation of water temperature in the Seto Inland Sea, Japan is examined using data analysis and numerical experiments and is shown to be controlled by heat exchange through the sea surface and horizontal heat dispersion from the Pacific Ocean. The average water temperature goes down from the Pacific Ocean to the center of the Seto Inland Sea indicating that 4.0 to 6.0×10¹⁵ cal day^?1 (1.6 to 2.5×10¹⁶ joule day^?1) of heat is transported from the Pacific Ocean to the Seto Inland Sea and is lost through the sea surface. The amplitude of seasonal variation of water temperature is large at the center of the Seto Inland Sea and the maximum water temperature is reached first at Bisan Straits and last at Iyo-Nada.     

Mercury concentration in the ocean

Seventy percent of 342 seawater samples collected in the Bering Sea, North and South Pacific, Japan Sea, East and South China Seas, and Indian Ocean had concentrations of “total” mercury ranging from 3 to 6 ng Hg l^?1 with an arithmetic mean of 5.3 ng l^?1 and a geometric mean of 5.0 ng l^?1. In some cases, a higher concentration was observed at the surface, at the halocline or thermocline, or in the bottom water. But in general, there was no consistent correlation between mercury concentration and depth, except for a statistical tendency for mercury concentration to be slightly higher in the surface water. This tendency suggests that mercury in the ocean is supplied from the atmosphere by rain washout. The latitudinal variation of surface mercury concentrations showed that the maximum concentration at each latitude decreased from 40°N to 30°S. This variation provides evidence that atmospheric mercury is emitted mainly from continental areas naturally or anthropogenically.     

Distribution of nitrogen-fixing bacteria in the Central Pacific Ocean

The plate culture method using the two formulae for non-nitrogenous media was adopted in this investigation for the purpose of counting and isolating nitrogen-fixing bacteria distributed in the open sea. Sea water samples were collected at eighteen different stations in the region of Lat. 50°N–15°S along Long. 155°W and two other stations in the Pacific Ocean. In order to compare with those samples from the open sea, water samples were also obtained at four stations in Suruga and Sagami Bays. Nitrogen-fixing bacteria appear to be widely but very unevenly distributed at all depths in sea water, in numbers approximately ranging from nil to 10⁴ per 100 ml of sea water, and denser vertical populations have been found in the area of Lat. 40°N and 5°N along Long. 155°W, even at depths from 2,000 to 3,000m. A conparatively denser population of bacteria was found in sea water from Suruga Bay and Sagami Bay. The bacteria associated with plankton were abundantly demonstrated, in numbers ranging from 10⁶ to 10⁸ per 1 ml settling volume of plankton, in many plankton samples collected at four stations in the southern parts of the Pacific Ocean. Almost all the bacteria isolated from the samples of blue green algal colonies,Trichodesmium, sp., were able to grow on nonnitrogeneous media.     

Ventilation time and anthropogenic CO<Subscript>2</Subscript> in the Bering Sea and the Arctic Ocean based on carbon tetrachloride measurements

The Arctic Ocean is connected to the Pacific by the Bering Sea and the Bering Strait. During the 4th Chinese National Arctic Research Expedition, measurements of carbon tetrachloride (CCl₄) were used to estimate ventilation time-scales and anthropogenic CO₂ (C_ant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution method. The profile distribution showed that there was a high-CCl₄ tongue entering through the Canada Basin in the intermediate layer (27.6?<?σ_θ?<?28), at latitudes between 78 and 85°N, which may be related to the inflow of Atlantic water. Between stations B09 and B10, upwelling appeared to occur near the continental slope in the Bering Sea. The ventilation time scales (mean ages) for deep and bottom water in the Arctic Ocean (~?230–380 years) were shorter than in the Bering Sea (~?430–970 years). Higher mean ages show that ventilation processes are weaker in the intermediate water of the Bering Sea than in the Arctic Ocean. The mean C_ant column inventory in the upper 4000 m was higher (60–82 mol m^?2) in the Arctic Ocean compared to the Bering Sea (35–48 mol m^?2).     

Cadmium and zinc concentrations in zooplankton in the subarctic region of the North Pacific

Cadmium and zinc concentrations were determined in 10 species of pelagic zooplankton collected in the northern North Pacific, the Bering Sea, the Okhotsk Sea and off Hokkaid?, during the summers of 1974–1976. The mean cadmium contents in euphausiids, copepods, and amphipods were 1.16μg/g dry wt (range: 0.36–2.17μg/g), 6.63μg/g (1.66–14.55μg/g), and 8.28μg/g (2.83–14.50μg/g), respectively. Cadmium in euphausiids was significantly lower in concentration than in the other two crustacean groups. The difference in cadmium levels among the crustacean groups is discussed on the basis of feeding habits and physiological characteristics of the zooplankton. Zinc levels in the crustaceans were similar, with values around 100μg/g (range: 59–195μg/g). Both cadmium and zinc concentrations in euphausiids taken from coastal waters off Hokkaid? were significantly higher than those from the Bering Sea and the northern North Pacific. This trend may reflect coastal pollution rather than characteristics of the species. Contribution No. 117 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University     

Thorium concentration and the activity ratios230Th/232Th and228Th/232Th in sea water in the western North Pacific

The concentration of thorium isotopes and the activity ratios of²³⁰Th/²³²Th and²²⁸Th/²³²Th in sea water collected in the Kuroshio region, the mixing area of Oyashio and Kuroshio, the Japan Sea and the East China Sea in the western North Pacific were determined. Thorium isotopes were analyzed by α-ray spectrometry after separating them with an anion exchange resin. The average content of thorium (²³²Th) of 2.2×10⁻⁹ g/l was obtained in the open Pacific waters. The ratio of²³⁰Th/²³²Th is in accord with that of the top layer of the sediment in the same area. The high values of²²⁸Th/²³²Th ratio up to 36 were observed in sea water. The excess²²⁸Th in sea water may be due to the migration of²²⁸Ra through the water-sediment interface. Thorium content in suspended matter was 10 to 20% of the total thorium content in the Pacific water.     

Spatial and temporal variability of the ratios between the nitrate and phosphate concentrations in the Sea of Okhotsk

The relation between the nitrate and phosphate concentrations in the Sea of Okhotsk and the bordering waters of the Pacific Ocean were studied. The surveys were carried out in the autumn, spring, and summer of 2001–2002. For the deepwater part of the sea, the relation [NO^? ₃] = ((14.88 ± 0.07) × [PO^3? ₄] ? 5.46 ± 0.17) was found. The coefficients in the equation given are statistically different from those in the similar equation for the Pacific waters: [NO^? ₃] = (16.05 ± 0.15) × [PO^3? ₄]-(7.23 ± 0.36). In the northern part of the sea; on the shelf; in the slope area; and, especially, in the deep waters of the TINRO Depression, the linear dependence between the phosphate and nitrate concentrations was distorted. This feature was described in terms of nitrate deficiency. The maximum values of this deficiency were found in the near-bottom waters. The principal processes that might cause the nitrate deficiency were considered: the difference in the oxidation rates of the nitrogen and phosphorus organic compounds, the matter transfer between the continent and the sea, the different efficiency of the biogenic burial of nitrogen and phosphorus in the bottom sediments, and the denitrification in the upper layer of the bottom sediments. It was shown that the most probable cause of the nitrate deficiency was the denitrification. The loss of inorganic nitrogen owing to the supply of the waters of the Sea of Okhotsk to the Pacific Ocean was estimated as ～2.5 × 10¹¹ mol N/year.     

Radium-228 in the Japan Sea

The distribution of²²⁸Ra in surface and subsurface waters in the Japan Sea was studied. The concentrations of²²⁸Ra in surface waters were around 100 dpm/1000l which were much higher than those reported for Pacific surface waters. The concentrations of²²⁸Ra decreased with increasing depth to less than 10 dpm/1000l in the Japan Sea Proper Water. Based on the comparison between observed values of²²⁸Ra and calculated profile through the near-surface water mass and the underlying main water mass in the Japan Sea, the apparent vertical eddy diffusion coefficient was estimated to be about 2 cm² s^–1.     

Numerical experiment for strontium-90 and cesium-137 in the Japan Sea

A numerical experiment is carried out to reproduce distribution of concentration of ⁹⁰Sr and ¹³⁷Cs, estimate their total amount and verify their source in the Japan Sea. Model results are in good agreement with observational findings in the Japan Sea expeditions between 1997 and 2002 by the Japan Atomic Energy Agency. Vertical profiles of the concentration of ⁹⁰Sr and ¹³⁷Cs show exponential decreases with depth from the sea surface to the sea bottom. From the model and observational results, it is suggested that the concentration of ⁹⁰Sr and ¹³⁷Cs in the surface layer is approximately in the range of 1.0–1.5 Bq/m³ and 2.0–2.5 Bq/m3, respectively. On the other hand, it is found that the concentration in the intermediate and deep layer is higher than that observed in the northwestern Pacific Ocean, suggesting active winter convection in the Japan Sea. The total amount of ⁹⁰Sr and ¹³⁷Cs in the seawater is evaluated to be 1.34 × 10¹⁵ Bq and 2.02 × 10¹⁵ Bq, respectively, in the numerical experiment, which demonstrates an estimation by observational data obtained in the Japan Sea expeditions. The total amount of ⁹⁰Sr and ¹³⁷Cs changed during the second half of 20th century corresponding to deposition at the sea surface with the maximums of 4.86 × 10¹⁵ Bq for ⁹⁰Sr and 7.33 × 10¹⁵ Bq for ¹³⁷Cs, respectively, in the mid-1960s. The numerical experiment suggests that the main source of ⁹⁰Sr and ¹³⁷Cs has been global fallout, although there have been some potential sources in the Japan Sea.     

The continental shelf pump for CO2 in the North Sea—evidence from summer observation

Data on the distribution of dissolved inorganic carbon (DIC) and partial pressure of CO₂ (pCO₂) were obtained during a cruise in the North Sea during late summer 2001. A 1° by 1° grid of 97 stations was sampled for DIC while the pCO₂ was measured continuously between the stations. The surface distributions of these two parameters show a clear boundary located around 54°N. South of this boundary the DIC and pCO₂ range from 2070 to 2130 μmol kg⁻¹ and 290 to 490 ppm, respectively, whereas in the northern North Sea, values range between 1970 and 2070 μmol kg⁻¹ and 190 to 350 ppm, respectively. The vertical profiles measured in the two different areas show that the mixing regime of the water column is the major factor determining the surface distributions. The entirely mixed water column of the southern North Sea is heterotrophic, whereas the surface layer of the stratified water column in the northern North Sea is autotrophic. The application of different formulations for the calculation of the CO₂ air–sea fluxes shows that the southern North Sea acts as a source of CO₂ for the atmosphere within a range of +0.8 to +1.7 mmol m⁻² day⁻¹, whereas the northern North Sea absorbs CO₂ within a range of −2.4 to −3.8 mmol m⁻² day⁻¹ in late summer. The North Sea as a whole acts as a sink of atmospheric CO₂ of −1.5 to −2.2 mmol m⁻² day⁻¹ during late summer. Compared to the Baltic and the East China Seas at the same period of the year, the North Sea acts a weak sink of atmospheric CO₂. The anticlockwise circulation and the short residence time of the water in the North Sea lead to a rapid transport of the atmospheric CO₂ to the deeper layer of the North Atlantic Ocean. Thus, in late summer, the North Sea exports 2.2×10¹² g C month⁻¹ to the North Atlantic Ocean via the Norwegian trench, and, at the same period, absorbs from the atmosphere a quantity of CO₂ (0.4 10¹² g C month⁻¹) equal to 15% of that export, which makes the North Sea a continental shelf pump of CO₂.     

Distribution and seasonal variation of vitamin B12, thiamine and biotin in the sea

The distributions and seasonal variations of vitamin B₁₂, thiamine and biotin were investigated in waters of the North Pacific Ocean, the East China Sea, and the bays and inlets along the Pacific coast of Japan, by use of microbiological assay methods. A marine diatom Cyclotella nana clone 3H for vitamin B₁₂, and marine yeast Cryptococcus albidus for thiamine, and a marine bacterium Achromobacter sp. strain yH-51 for biotin were used as assay organisms. In the surface water of Sagami Bay, monthly changes in the amounts of the three dissolved vitamins followed closely that of chlorophyll a, being highest in July and lowest during late autumn and winter. The geographical and vertical distributions of thiamine and biotin in the sea generally showed similar patterns to that of chlorophyll a, whereas vitamin B₁₂ did not always follow the trend. Amounts of particulate thiamine and biotin corresponded to about 1 % of that of the dissolved form in the surface water of the North Pacific Ocean. In the coastal waters, however, they were at times found to be 144.0 % and 53.9 % respectively.     

Content of plutonium,thorium and protactinium in sea water and recent coral in the North Pacific

The contents of plutonium isotopes (²³⁹Pu and²³⁸Pu), thorium isotopes (²³²Th,²³⁰Th and²²⁸Th) and protactinium-231 in sea water collected in the North Pacific, the East China Sea and the Japan Sea were determined. These nuclides were sequentially analyzed byα-ray spectrometry after separating them mainly with solvent extraction technique. The contents of²³⁹Pu in surface sea water ranged from 0.6 to 1.6 pCi/10001,²³⁸Pu/²³⁹Pu activity ratios being 0.2～0.7. The²²⁸Th/²³²Th activity ratios for the North Pacific waters varied between 7.6 and 30, whereas the sample from the East China Sea showed the very high value, 65. The contents of²³¹Pa are less than 6 percent of that in equilibrium with its parent²³⁵U. Furthermore, the analysis of plutonium isotopes in recent coral from Yoron Island was carried out and it was confirmed that plutonium isotopes have concentrated in recent coral with the concentration factor of about 1～2×10³.     

Specific absorption coefficient and phytoplankton community structure in the southern region of the California Current during January 2002

Measurements of the specific absorption coefficients of phytoplankton (a*_ph) are currently required to estimate primary productivity at regional to global scales using satellite imagery. The variability in a*_ph and phytoplankton size fraction was determined during January 2002 in the southern region of the California Current. Median values of a*_ph at 440 nm and 674 nm were 0.061 and 0.028 m² (mg Chl-a)^?1 and significant variability was found between inshore and offshore stations. A decrease of a*_ph is associated with increased phytoplankton abundance and larger species. The a*_ph tends to be high when the photoprotector zeaxanthin is present in elevated concentrations and phytoplankton abundance lower. The nano-microphytoplankton (>5 µm) community consisted of 28 diatom and 15 dinoflagellate genera with mean abundance values of 2.8 and 1.6 × 10³ cells l^?1, respectively. The picophytoplankton (<5 µm) community consisted of Prochlorococcus sp. (mean 8.2 × 10⁶ cells l^?1) and Synechococcus sp. (mean 19.5 × 10⁶ cells l^?1), as well as a mixture of picoeukaryotes (mean 8.6 × 10⁶ cells l^?1). The contributions of nano-microphytoplankton and picophytoplankton to the total biomass (µg C l^?1) were 46% and 54%, respectively. This study showed that picophytoplankton cells increased 2.5 times up during January 2002 compared with the previous year. It was concluded that the waning of La Niña conditions had a clear effect on the pelagic ecosystem in January 2002 and that the higher microphytoplankton abundance in the California Current was dominated by local and regional seasonal processes.     

Vertical heat transfer based on direct microstructure measurements in the ice-free Pacific-side Arctic Ocean: the role and impact of the Pacific water intrusion

This study quantifies diapycnal mixing and vertical heat transfer in the Pacific side of the Arctic Ocean, where sea-ice cover has disappeared between July and September in the last few decades. We conducted microstructure measurements in the open water region around the Canada Basin from late summer to fall in 2009 and 2010 using R/V Mirai. In the study domain, the dissipation rate of turbulent kinetic energy, ε, is typically as low level as O(10^?10) W kg^?1, resulting in vertical heat diffusivity of O(10^?7) m² s^?1, which is close to the molecular diffusivity of heat, suggesting comparatively little predominance of mechanical turbulent mixing. An exception is the case at the Barrow Canyon, where the strong baroclinic throughflow generates substantial vertical mixing, producing ε > O(10^?7) W kg^?1, because of the shear flow instability. Meanwhile, in the confluence region, where the warm/salty Pacific water and the cold/fresh Arctic basin water encounter, the micro-temperature profiles revealed a localized enhancement in vertical diffusivity of heat, reaching O(10^?5) m² s^?1 or greater. In this region, an intrusion of warm Pacific water creates a horizontally interleaved structure, where the double-diffusive mixing facilitates vertical heat transfer between the intruding Pacific water and the surrounding basin waters.     

Sinking fluxes of particulate U-Th radionuclides in the East Sea (Sea of Japan)

A record of radionuclide fluxes at a deep marginal sea of the Northwest Pacific Ocean (39°40′N 132°24′ E, Japan Basin, East Sea/Sea of Japan) was obtained from analysis of a 1-year continuous collection of sediment-trap samples. The trap was placed at a depth of 2800 m, 500 m above the sea floor, and the samples were recovered at the end of one year. Concentrations of ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th and ²²⁸Th were measured in the trapped material. All of the radionuclide fluxes showed seasonal variations that were in phase with the variations in total particle flux, which were shown in earlier work to be closely tied to the primary production in the surface water. The formation of authigenic ²³⁸U appears to be less than in other open ocean regimes. The residence time of particulate thorium isotopes were of the order of a year, resulting in an average settling rate of a meter per day. Comparison of the measured ²³⁰Th_ex flux with that of the theoretical production in the overlying water column yielded about 40% surplus of ²³⁰Th, indicating that lateral advection contributes ²³⁰Th to this sampling site.     

Sources and distribution of fresh water in the East Greenland Current

Fresh water flowing from the Arctic Ocean via the East Greenland Current influences deep water formation in the Nordic Seas as well as the salinity of the surface and deep waters flowing from there. This fresh water has three sources: Pacific water (relatively fresh cf. Atlantic water), river runoff, and sea ice meltwater. To determine the relative amounts of the three sources of fresh water, in May 2002 we collected water samples across the East Greenland Current in sections from 81.5°N to the Irminger Sea south of Denmark Strait. We used nitrate-phosphate relationships to distinguish Pacific waters from Atlantic waters, salinity to obtain the sum of sea ice melt water and river runoff water, and total alkalinity to distinguish the latter. River runoff contributed the largest part of the total fresh water component, in some regions with some inventories exceeding 12 m. Pacific fresh water (Pacific source water S ∼ 32 cf. Atlantic source water S ∼ 34.9) typically provided about 1/3 of the river runoff contribution. Sea ice meltwater was very nearly non-existent in the surface waters of all sections, likely at least in part as a result of the samples being collected before the onset of the melt season. The fresh water from the Arctic Ocean was strongly confined to near the Greenland coast. We thus conjecture that the main source of fresh water from the Arctic Ocean most strongly impacting deep convection in the Nordic Seas would be sea ice as opposed to fresh water in the liquid phase, i.e., river runoff, Pacific fresh water, and sea ice meltwater.     

Distribution of particulate organic carbon and nitrogen in the Bering Sea and northern North Pacific Ocean

Particulate matter was collected in the Bering Sea and the northern North Pacific Ocean during the cruise of R. V. Hakuho-maru, Ocean Research Institute of Tokyo University in summer of 1975. The particulate matter was analyzed for organic carbon and nitrogen, chlorophylla and amino acids.The concentrations of particulate organic carbon and nitrogen were measured with the range of 16–422gC l^–1 and 1–85gN l^–1, 19–186gC l^–1 and 1–26gN l^–1, 46–1,038gC l^–1 and 6–79gN l^–1 and 19–246gC l^–1 and 2–25gN l^–1 in the Oyashio, the Deep Bering Sea, the continental shelf of Bering Sea and the northern North Pacific, respectively. Particulate organic carbon and nitrogen decreased with depth throughout the areas. The average concentrations of organic carbon and nitrogen in the entire water column tended to decrease in the following order; the continental shelf > Oyashio > northern North Pacific > Deep Bering Sea.C/N of particulate matter varied in the range of 3–15 (7 on average) in surface waters throughout the areas and these values tended to increase with depth to 5–20 (11 on average) in deep waters without significant regional variability.Linear regressions between chlorophylla and particulate organic carbon in the euphotic layers indicate that detrital organic carbon accounted for 34.2, 44.9, 49.1 and 25.2 % of particulate organic carbon in the Oyashio, the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively.Particulate amino acid was determined in the range of 10.3–78.0g l^–1, 104–156g l^–1 and 10.4–96.4g l^–1 in the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively. Aspartic acid, glutamic acid, serine, glycine and alanine were found as dominant species of amino acid of particulate matter.     

Assimilation of sea surface temperature in the Northwest Pacific Ocean and its marginal seas using the ensemble Kalman filter

Satellite-borne sea surface temperature (SST) data were assimilated with the ensemble Kalman filter (EnKF) in a Northwest Pacific Ocean circulation model to examine the effect of data assimilation. The model domain included the northwestern part of the Pacific Ocean and its marginal seas, such as the Yellow Sea and East/Japan Sea. The performance of the data assimilation was evaluated by comparing the simulated ocean state with that observed. Spatially averaged root-mean-squared errors in the SST and sea surface height (SSH) decreased by 0.44 °C and 4 cm, respectively, by the assimilation. The results of the numerical experiments substantiated the effectiveness of the SST assimilation via the EnKF for all marginal seas, as well as the Kuroshio region. The benefit of the data assimilation depended on the characteristics of each marginal sea. The variation of the SST in the East/Japan Sea and the Kuroshio extension (KE) region were improved 34% and those in the Yellow Sea 12.5%. The variation of the SSH was improved approximately 36% in the KE region. This large improvement was achieved in the deep-water regions because assimilation of SST data corrected the separation point of the western boundary currents, such as the Kuroshio and the East Korea Warm Current, and the associated horizontal surface currents. The SST assimilation via the EnKF also improved the subsurface temperature profiles. The effectiveness of SST assimilation was seasonally dependent, with the improvement being relatively larger in winter than in summer, which was related to the seasonal variation of the vertical mixing and stratification in the ocean surface layer.     

Spreading and salinity change of North Pacific Tropical Water in the Philippine Sea

Newly formed North Pacific Tropical Water (NPTW) is carried to the Philippine Sea (PS) by the North Equatorial Current (NEC) as a subsurface salinity maximum. In this study its spreading and salinity change processes are explored using existing hydrographic data of the World Ocean Database 2009 and Argo floats. Spreading of NPTW is closely associated with the transports of the NEC, Mindanao Current (MC), and Kuroshio. Estimated for subsurface water with salinity S greater than 34.8?psu, the southward (northward) geostrophic transport of NPTW by the MC (Kuroshio) at 8°N (18°N) is about 4.4 (5.7)?Sv (1?Sv?=?10⁶?m³?s^?1), which is not sensitive to reference level choice. Fields of salinity maximum, geostrophic current, sea level variation, and potential vorticity suggest that the equatorward spreading of NPTW to the tropics is primarily afforded by the MC, whereas its poleward spreading is achieved by both the Kuroshio transport along the coast and open-ocean mesoscale eddy fluxes in the northern PS. The NPTW also undergoes a prominent freshening in the PS. Lying beneath fresh surface water, salinity decreases quicker in the upper part of the NPTW, which gradually lowers the salinity maximum of NPTW to denser isopycnals. Salinity decrease is especially fast in the MC, with along-path decreasing rate reaching O (10^?7?psu?s^?1). Both diapycnal and isopycnal mixing effects are shown to be elevated in the MC owing to enhanced salinity gradient near the Mindanao Eddy. These results suggest intensive dispersion of thermal anomalies along the subtropical-to-tropical thermocline water pathway near the western boundary.     

Chemical modification of sea water by submarine volcanism at Nishinoshima-Shintô Island

Sea water samples, still hot from volcanic emanations were taken in a bay of Nishinoshima-Shintô Island just after volcanic activity had ceased and were analysed for borate-B, fluoride-F and bromide-Br. The hot water is considered to be formed by the conservative mixing of volcanic emanations with sea water, and the emanations containedCl, B, F andBr in the ratio of 1∶1.84×10^?3∶0.474×10^?3∶6.47×10^?3 by weight. RatiosB/Cl andF/Cl can be used as effective measures of the contribution of volcanic emanations to sea water.