Seasonal Changes in Oceanic pCO2 in the Oyashio Region from Winter to Spring     

Takashi Midorikawa  Sonoki Iwano  Kazuhiro Saito  Hiroyuki Takano  Hitomi Kamiya  Masao Ishii  Hisayuki Y. Inoue 《Journal of Oceanography》2003,59(6):871-882

We observed the partial pressure of oceanic CO₂, pCO₂ ^sea, and related surface properties in the westernmost region of the subarctic North Pacific, seasonally from 1998 to 2001. The pCO₂ ^sea in the Oyashio region showed a large decrease from winter to spring. In winter, pCO₂ ^sea was higher than 400 μatm in the Oyashio region and this region was a source of atmospheric CO₂. In spring, pCO₂ ^sea decreased to extremely low values, less than 200 μatm (minimum, 139 μatm in 2001), around the Oyashio region with low surface salinity and this region turned out to be a strong sink. The spatial variations of pCO₂ ^sea were especially large in spring in this region. The typical Oyashio water with minimal mixing with subtropical warm water was extracted based on the criterion of potential alkalinity. The contribution of main oceanic processes to the changes in pCO₂ ^sea from winter to spring was estimated from the changes in the concentrations of dissolved inorganic carbon and nutrients, total alkalinity, temperature and salinity observed in surface waters in respective years. These quantifications indicated that photosynthesis made the largest contribution to the observed pCO₂ ^sea decreases in all years and its magnitude was variable year by year. These year-to-year differences in spring biological contribution could be linked to those in the development of the density stratification due to the decrease in surface salinity. Thus, the changes in the surface physical structure could induce those in pCO₂ ^sea in the Oyashio region in spring. Furthermore, it is suggested that the direction and magnitude of the air-sea CO₂ flux during this season could be controlled significantly by the onset time of the spring bloom. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios     

Toshihiro Usui  Seiya Nagao  Masanobu Yamamoto  Koji Suzuki  Isao Kudo  Shigeru Montani  Atsushi Noda  Masao Minagawa 《Marine Chemistry》2006,98(2-4):241-259

Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ¹³C, δ¹⁵N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ¹³C values of suspended POM in the surface seawater were higher in May and November than in August, while δ¹⁵N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ¹³C and δ¹⁵N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ¹³C and δ¹⁵N. Comparison of δ¹³C, δ¹⁵N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.  相似文献   

δ15N of PON and Nitrate as a Clue to the Origin and Transformation of Nitrogen in the Subarctic North Pacific and Its Marginal Sea     

Masao Minagawa  Mami Ohashi  Toshikatsu Kuramoto  Norihiro Noda 《Journal of Oceanography》2001,57(3):285-300

Nitrogen isotope compositions of particulate organic matter and nitrate were analyzed for seawater sampled at five stations at the Alaskan Gyre, Western Subarctic Gyre and East China Sea, focusing on the samples from the surface to 5000 m water to characterize the nitrogen cycling in the subarctic North Pacific Ocean and its marginal sea. The ¹⁵N of particulate organic matter showed little agreement with a conceptual closed model that interprets isotopic variation as being caused by isotope discrimination on nitrate utilization. The ¹⁵N and ¹³C of particulate organic matter varied with the water depth. A correlation between isotope compositions and C/N elemental ratio was found generally at all stations, although some irregular data were also found in deep layers. We developed a hypothetical nitrogen balance model based on N₂ fixation and denitrification in seawater and attempted to apply it to distinguish nutrient cycling using both ¹⁵N-NO₃ ^– and N* variation in seawater. This model was applied to the observed data set of ¹⁵N-NO₃ ^– and N* in the North Pacific water and estimated the ¹⁵N-NO₃ ^– of primordial nitrate in the North Pacific deep water as 4.8. The North Pacific intermediate water for all stations showed similar ¹⁵N-NO₃ ^– and N* values of 6 and –3 µmol/kg, respectively, suggesting a similar nitrogen biogeochemistry. In the East China Sea, analysis showed evidence of water exchange with the North Pacific intermediate water but a significant influence of nitrogen from the river runoff was found in depths shallower than 400 m.  相似文献   

Cooling history of pyroxene chondrules in the Yamato-74191 chondrite (L3)—an electron microscopic study     

Masao Kitamura  Masayo Yasuda  Seiko Watanabe  Nobuo Morimoto 《Earth and Planetary Science Letters》1983,63(2):189-201

Fine textures of clinopyroxene in an excentroradial pyroxene chondrule (EPC) and a comb-like pyroxene chondrule (CPC) in the Yamato-74191 chondrite (L3) have been studied by analytical electron microscopy. Both pyroxenes consist of three regions different in composition and texture; core, mantle and marginal regions, though the pyroxenes of the CPC are more Fe-rich than those of the EPC. The core region is the most Mg-rich with no Ca component and commonly shows polysynthetic (100) twins. The mantle region is slightly calcic, and the marginal region shows a rapid increase of Ca outward.The polysynthetic twins, cracks and subgrain boundaries in the core in the EPC and CPC must have formed during the transition from proto-type to clino-type pyroxenes. The exsolution textures in the mantle and marginal regions indicate initial crystallization of pigeonite-C followed by decomposition into pigeonite-P and augite. The decomposition must have taken place by nucleation growth in the mantle region and by spinodal decomposition in the marginal region. The periodicity of 15–20 nm in the spinodal decomposition textures indicates that the cooling rate of the pyroxenes, when passing through about 1000°C, was of the order of a few tens to several degrees centigrade per hour. The cooling history of the chondrules has been explained by a monotonous cooling controlled by the cooling rate of the surrounding medium.  相似文献   

Indialite from Unazuki Pelitic Schist,Japan, and its transition texture to cordierite     

Masao Kitamura  Yoshikuni Hiroi 《Contributions to Mineralogy and Petrology》1982,80(2):110-116

Indialite (hexagonal cordierite) has been found in a cordierite vein of polymetamorphosed pelitic rock, a member of the Unazuki schists in Hida terrane, central Japan. Most of the indialite grains show intergrowth textures with cordierite of orthorhombic symmetry. This is the second identification of indialite since the first one from a fused sediment in India. The intergrowth texture was formed by a nucleation-growth process accompanied with the first order transition from the hexagonal to the orthorhombic form. Characteristic pseudo-twin relation exists among the orthorhombic phases. Chemical compositions of both hexagonal and orthorhombic forms in the intergrowth have been deter-mined by analytical electron microscopy. The difference in Fe/(Mg+Fe) at the interfaces between the two forms indicates the existence of a transition loop in the (Mg, Fe)-cordierite. The transition of the present specimens is estimated to have initiated at about 700° C. A possible phase diagram of (Mg, Fe)-cordierite has been proposed, based on the result of this investigation.  相似文献   

Boron isotopic composition of fumarolic condensates from some volcanoes in Japanese island arcs     

Masao Nomura  Tadao Kanzaki  Takejiro Ozawa  Makoto Okamoto  Hidetake Kakihana 《Geochimica et cosmochimica acta》1982,46(11):2403-2406

Boron samples from 40 fumarolic condensates from volcanoes in the Ryukyu arc (Satsuma Iwo-jima and Shiratori Iwo-yama) and the North-east Japan arc (Usu-shinzan, Showa-shinzan, Esan and Issaikyo-yama) all have ${}^{11}\text{B}{}^{10}\text{B}$ ratios close to 4.07. Higher values, from 4.09 to 4.13, were only observed in condensates from volcanoes in the southernmost end of the North-east Japan arc (Nasu-dake), the northern part of the Izu-Bonin arc (Hakone), and the North Mariana arc (Ogasawara Iwo-jima). These higher values suggest geological interaction of the magmas with sea-water enriched in ¹¹B.  相似文献   

Removal of²³⁴Th from a coastal sea: Funka Bay,Japan     

Masao Minagawa  Shizuo Tsunogai 《Earth and Planetary Science Letters》1980,47(1):51-64

In Funka Bay of Hokkaido, Japan, seawater, suspended matter and settling matter were collected once every month in the summer of 1974. These samples were analyzed for²³⁴Th, a short-lived daughter of dissolved²³⁸U. A pronounced disequilibrium between²³⁴Th and²³⁸U, and a highly variable concentration of²³⁴Th were found. Positive correlation, however, exist among the deficiency of²³⁴Th relative to²³⁸U in seawater, the concentration of particulate²³⁴Th, the fraction of particulate²³⁴Th to total²³⁴Th in seawater, the total dry weight of suspended matter, and the primary productivity during the month previous to sampling. The specific activity of²³⁴Th for the settling particles (620 ± 170 dpm/g) was nearly equal to that for suspended particles (720 ± 600 dpm/g) but much greater than that for plankton (47 ± 24 dpm/g). These facts suggest that suspended particles are somehow closely related to the removal of heavy metals from seawater, in spite of the negligibly small settling flux of suspended matter. The residence time of thorium in Funka Bay (mean depth: 60 m) is found to be about 60 days, which is nearly equal to those of²¹⁰Pb and²¹⁰Po.  相似文献   

Pyroclastic flows in Japan     

Aramaki  Shigeo  Yamasaki  Masao 《Bulletin of Volcanology》1963,25(1):89-96

Bulletin of Volcanology -  相似文献   

The international at-sea intercomparison of fCO₂ systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean     

Arne Krtzinger  Ludger Mintrop  Douglas W. R. Wallace  Kenneth M. Johnson  Craig Neill  Bronte Tilbrook  Philip Towler  Hisayuki Y. Inoue  Masao Ishii  Gary Shaffer  Rodrigo F. Torres Saavedra  Eiji Ohtaki  Eiji Yamashita  Alain Poisson  Christian Brunet  Bernard Schauer  Catherine Goyet  Greg Eischeid 《Marine Chemistry》2000,72(2-4)

The ‘International Intercomparison Exercise of fCO₂ Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO₂) systems, one discrete fCO₂ system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO₂ measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO₂, temperature measurements) and a common procedure for calculation of final fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (C_T) and total alkalinity (A_T) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.  相似文献   

High organic carbon deposition in the northern margin of the Aleutian Basin (Bering Sea) before the last deglaciation   总被引：1，自引：0，他引：1  

Boo-Keun Khim  Sunghan Kim  Masao Uchida  Takuya Itaki 《Ocean Science Journal》2010,45(4):203-211

High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO₃ contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High C_org/N ratios and low δ¹³C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ¹⁵N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ¹⁵N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high C_org/N ratios and low δ¹³C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ¹⁵N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.  相似文献