Mixed-layer characteristics as related to the monsoon climate of New Delhi,India

Annual variations of mixed-layer characteristics at New Delhi, India have been studied for a weak monsoon (1987) and a strong monsoon (1988) year. In the weak monsoon year (1987), the maximum mixing depthh _max was found to have a value of around 3000 m during the pre-monsoon, less than 2000 m during the summer monsoon, around 2000 m during the post-monsoon, and less than 1000 m in the winter season. For the strong monsoon year (1988),h _max values were less than 1987 values for comparable periods throughout the year. The seasonal and yearly differences ofh _max were explained by the surface energy balance and potential temperature gradient at a time close to sunrise. According to the spatial patterns of obtained by an objective analysis of the 850 to 700 hPa layers. mixed-layer characteristics obtained at New Delhi are representative of the north and central regions of India.     

Thickness of the dry convection and large-scale subsidence above deserts

Thickness of dry convection above various deserts of the world is obtained from aerological data, and assimilated data from ECMWF. A mixed layer develops up to a height of about 1 km above the central Sahara, where strong subsidence occurs. However, above many other deserts in Africa and Asia, a deep mixed layer develops up to 4–6 km. These mixed layers develop to a high altitude because the daytime mixed layer links with an existing weakly stratified, near-neutral layer above. Large-scale subsidence does not reach the surface throughout the day, except in the winter season. Mixed-layer height is shallower in the Southern Hemisphere than in the Northern Hemisphere in the summer season.     

In-situ survey of nanomolar manganese in seawater using an autonomous underwater vehicle around a volcanic crater at Teishi Knoll,Sagami Bay,Japan

We present the results of a chemical survey at a submarine volcano, Teishi Knoll, obtained using a submersible in-situ Mn analyzer (GAMOS) mounted on an autonomous underwater vehicle (AUV) platform. During this survey, high-resolution data of dissolved Mn were obtained in three dimensions in nearly real time. The AUV enabled continuous detailed observations along a preprogrammed pathway, which could not have been performed with conventional CTD hydrocasts. During this observation, anomalously high dissolved Mn concentrations were obtained within the crater, corresponding to high water temperatures. The anomalies might be a hydrothermal signature due to volcanic activity from the crater.     

Silver in Tokyo Bay estuarine waters and Japanese rivers

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg⁻¹, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg⁻¹). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log K_d > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y⁻¹ and 15 kg y⁻¹, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.     

Long-term bottom water warming in the north Ross Sea

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.     

亚洲通量观测网建立的回顾与展望

1IntroductionTheelucidationofthebudgetsofcarbon,waterandothermassesatvariouslandecosystemshasbecomeanimportantsubjectintheglobalwarmingissue.Forthisstudy,thedatafrompreciseandlong-termobservationsofcarbondioxide,watervapor,andheatfluxtakeninvariouslandsur…     

Hydrothermal plumes in the eastern Manus Basin, Bismarck Sea: CH4, Mn, Al and pH anomalies

We present evidence for strong hydrothermal activity in the eastern Manus Basin (depth: 1700–2100 m), the existence of large scale triple-layered buoyant plumes at depths of 1100 m (“shallow plume”), 1700 m (“deep plume”), and 1400 m (“middle plume” with less extent than the other two plumes) that were revealed from water column anomalies of CH₄, Mn, Al and pH observed in November to December 1990. Judging from the horizontal distribution of these parameters, the deep plume seems to originate from two distinct hydrothermal sites (eastern and western sites) in the research area, the eastern site being visually ascertained with deep-tow observations at the same time. The CH₄/Mn ratio (mol mol⁻¹) of the deep plume (0.02–0.05) is the lowest yet observed in hydrothermal plumes. The order of magnitude difference of CH₄/Mn ratios between the shallow plume and the deep plume suggests that different kinds of fluid-rock interaction occurred to make the hydrothermal end members for the deep and shallow plumes. The shallow plume, which had an areal extent of more than 50 km, may be an episodic “megaplume”, because it was not recognized in the previous CH₄ profiles in 1986, and because it has a similar CH₄/Mn ratio as the megaplume observed in the North Fiji Basin. We found that the eastern deep plume is characterized by enormously high aluminium concentrations (0.6– 1.5 μmol kg⁻¹), pH anomalies (0.1) and high Al/Mn ratios (10–17). The endmember fluid for the eastern deep plume may have an unusually low pH value to dissolve this much aluminum during fluid-rock interaction, or this plume may originate from an eruption-influenced fluid.     

Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan

Secular variations in ¹³C/¹²C ratios and chemical compositions of gas samples from October 1986 to July 1992 are reported from a 92–95 °C steam well located about 3 km north of Mt. Mihara, an active volcano on Izu-Oshima Island, Japan. The δ¹³C value steeply increased from −2.97‰ (relative to PDB carbonate) in December 1986 to −1.15‰ in March 1988 and then gradually decreased to −1.75‰ in July 1992. Over the same period, the CO₂ content changed similarly with time, even though the experimental error is relatively large. These variations are consistent with helium isotope changes. Initially rapid and then slow enhancements of ³He/⁴He ratio, δ¹³C value and CO₂ content are invoked by violent eruptions of Izu-Oshima volcano from 15 November to 18 December 1986. After the eruptive activity, depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of ³He/⁴He ratio, δ¹³C value and CO₂ content. Taking into account the rates of these decreases, we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years.     

Origins of hydrocarbons in the Sagara oil field, central Japan

Abstract   We collected free-gas and in situ fluid samples up to a depth of 200.6 m from the Sagara oil field, central Japan (34°44'N, 138°15'E), during the Sagara Drilling Program (SDP) and measured the concentrations and stable carbon isotopic compositions of CH₄ and C₂H₆ in the samples. A combination of the CH₄/C₂H₆ ratios with the carbon isotope ratios of methane indicates that the hydrocarbon gases are predominantly of thermogenic origin at all depths. The isotope signature of hydrocarbon gases of δ¹³      < δ¹³     suggests that these gases in the Sagara oil field are not generated by polymerization, but by the decomposition of organic materials.