Katsuhiko Fushimi

Seasonal variation in total inorganic carbon and its controlling processes in surface waters of the western North Pacific subtropical gyre

Abstract Seasonal variation in total inorganic carbon (TCO 2 ) in surface waters of the western North Pacific (137°–152°E) subtropical gyre was analyzed on the basis of measurements of TCO 2 and partial pressure of CO 2 ( p CO 2 sw). The controlling processes including vertical mixing, horizontal advection, and net air–sea CO 2 transport, as well as biological activity, were quantified. The seasonal increase in normalized TCO 2 (NTCO 2 ) from autumn to winter, ranging from 19 to 37 μmol kg −1 in the northern part of the subtropical gyre between 24°N and 30°N, was predominantly accounted for by the upward supply of TCO 2 due to enhanced vertical mixing. The contribution of horizontal advection, estimated from monthly meridional NTCO 2 distributions and the monthly advection field of the Meteorological Research Institute (MRI)s 3D-ocean general circulation model, was insignificant. Analyses of the mixed-layer NTCO 2 budget revealed that biological activity was playing an important role in the decrease in surface NTCO 2 from winter to summer. Annual net community production reached 48±19 gC m −2 between 24°N and 30°N, and 19±16 gC m −2 between 15°N and 23°N.

85Kr measurement system for continuous monitoring at the Meteorological Research Institute, Japan

A 85Kr measurement system for continuous monitoring based principally on the BfS-IAR method (activity measurement of 85Kr by gas counting coupled with gas chromatographic separation, using pure CH4 as carrier and Counting gas) was implemented for the first time in Japan. In this paper, a detailed description of the system and procedures is given and the inter-comparison results of our system with the BfS-IAR system are presented. A consistent temporal concentration change with high accuracy and consistency of the respective data with the BfS-IAR data (maximum difference of 5%) were achieved with the Meteorological Research Institute (MRI) system, which shows that the system is valid and reliable for the purpose of background monitoring for 85Kr in air. Also, the 85Kr monitoring record at the MRI during 1995-2001 is described. The record distinctively shows the Northern Hemispheric background 85Kr concentrations at the mid-latitude and the elevated concentrations affected by the operation of a nuclear fuel reprocessing plant in Tokai-mura, Ibaraki. Japan.

Spatial and temporal variations of surface seawater fCO2 in the Kuroshio off Japan

To examine the annual growth rate of CO2 in the ocean, spatial and temporal variations of the fugacity of CO2 (fCO2) in surface seawater in the Kuroshio off Japan were surveyed, using the data obtained by the Japan Meteorological Agency in the period 1989–1995. Winter surface seawater fCO2 decreased distinctly in the south of the Kuroshio front, where sea surface temperature increased sharply. In other seasons, such a large spatial variability at the Kuroshio front was rarely found. The temporal variation in surface seawater fCO2 at the selected area could be expressed by a rather simple function consisting of annual and bi-annual harmonics and a linear trend. The seasonal variation has a sharp maximum peak in summer, but an indistinct minimum peak in the period from winter to spring. The annual growth rate was 1.5 μatm/yr, significant at the 95% level. The seasonal variation reproduced assuming a thermodynamic dependence of surface seawater fCO2 on water temperature and salinity explains only about ∼24% of the observed seasonal variation.

Deposition of Sulfate, Chloride and Sodium at Japanese Meteorological Observatories and on the Western North Pacific

Abstract A simple plastic sampler was tested to get the information on the deposition amount of chemical components throughout Japan and the neighbouring regions. Polypropylene cylinders of diameter 117 mm which contained 300ml pure water were set in the observation fields and kept open for one month. At the end of the month the samplers were covered with caps and sent to Meteorological College, Kashiwa, Chiba. The sample solutions were filtered through Millipore filter (0.45μm pore size) and used for the determination by ion chromatography, atomic absorption and flame emission analyses. Monthly deposition amounts of sulfate, chloride and sodium ions were determined simultaneously at 21 Japanese meteorological observatories in June and October 1987. Similar samples were also set on the upper deck of RV Ryofu-maru for 4–7 days during cruises across the western North Pacific in 1987 and 1988. The deposition amount of SO4(excess) (SO4–Na × SO4(seasalt)/Na(seasalt)) was calculated. The strongest source region...

Determination of chemical elements in deposition on the Western North Pacific

Abstract Shipboard sampling was performed for the evaluation of the deposition amount of chemical species on the southwestern section of the North Pacific, utilizing simple plastic samplers fixed on the upper decks of research vessels of the Japan Meteorological Agency on their routine meteorological and oceanographical cruises from 1988 to 1990. The deposition of nss-sulfate (non-seasalt sulfate, calculated from the concentration of sodium) was found to be high in the western Japan Sea, East China Sea and southern sea adjacent to the Japanese Islands. In the Mariana Sea and the equatorial area, the lowest values were constantly observed in the summer of those 3 years. Values a little higher, but much lower than in the Japan Sea or East China Sea, were measured off the Philippine Islands. The deposition amounts of crustal elements such as silicon, aluminum and iron showed similar tendencies but with some difference in detail.