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Midorikawa T.,Meteorological Research Institute | Inoue H.Y.,Hokkaido University | Ishii M.,Meteorological Research Institute | Sasano D.,Meteorological Research Institute | And 4 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2012

The Southern Ocean is an important region for investigation because it has a major effect on global air-to-sea CO 2 fluxes and because of the ocean acidification resulting from the uptake of anthropogenic carbon, leading to serious consequences for marine ecosystems in the near future. We estimated long-term trends of ocean acidification in surface waters of the Pacific sector of the Southern Ocean, based on the summer observational records of oceanic CO 2 partial pressure and related surface properties during 1969-2003. The computed pH time series exhibited substantial decreasing trends in the extensive region from the subtropical to polar zones. The mean rates of pH decrease over the 35-year period were 0.0011 to 0.0013yr -1 in the zones north of the Polar Front and were larger in the polar zone (0.0020yr -1). The contribution of trends in sea surface temperature to the trends of pH decrease was small in all zones. The high rate of pH decrease in the polar zone was attributed to the supply of dissolved inorganic carbon from lower layers, enhanced by intensified wind stress and superimposed onto the accumulation of anthropogenic CO 2. A preliminary evaluation of thermodynamic changes in the upper carbonate system, using observational results, projected that the polar zone south of the Polar Front would be undersaturated with respect to aragonite in summer after 80 years. © 2011 Elsevier Ltd. Source


Midorikawa T.,Meteorological Research Institute | Ishii M.,Meteorological Research Institute | Sasano D.,Meteorological Research Institute | Kosugi N.,Meteorological Research Institute | And 6 more authors.
Papers in Meteorology and Geophysics | Year: 2011

The recent uptake of anthropogenic carbon by the ocean brings about changes in the surface-ocean carbon cycle that could result in ocean acidification with subsequent serious effects on marine ecosystems. We evaluated the trend of ocean acidification in the surface layer of extensive regions of the subtropical North Pacific using synthesized data for partial pressure of CO 2 for the past 40 years because no precise pH data were available. The results show significant trends of acidification (a pH decrease of 0.01 to 0.02 per decade) over the subtropical North Pacific. The rate of pH decrease, after excluding the contribution from changes in sea surface temperature, was highest in the eastern subtropical region. In this region in particular, the intrusion of subarctic waters with high concentrations of dissolved inorganic carbon could have contributed to the relatively high rate of acidification. Comparisons of the estimated rate of pH decrease for the past 26 years with those for the decade following 1969 and for 50 years into the future suggest an acceleration of acidification in recent years, as well as in the future, depending on the scenario of future anthropogenic CO 2 emission. © 2011 by the Japan Meteorological Agency / Meteorological Research Institute. Source


Nakamura T.,Mie University | Maekawa Y.,Mie University | Nakazato K.,Mie University | Koike T.,Mie University | Nagata Y.,Marine Information Research Center
Mer | Year: 2012

Sea level difference between Kushimoto and Uragami tide-gauge stations has been used as an indicator of flow pattern in the sea south of Japan: the difference is small when the Kuroshio has meandering path and is large when it has straight path. The difference exhibits seasonal variation, and it becomes large in the summer season in the years when the Kuroshio takes straight path throughout year as in 2003 and in 2009. We analyzed the sea level data of Kushimoto and Uragami tide-gauge stations for 17years from 1994 through 2010. It is shown that the Kuroshio takes straight path when the separation distance of the northern edge of the Kuroshio is smaller than 15km from the tip of Cape Shionomisaki. The sea level difference data were selected only for the time that the separation distance is smaller than 15km, and the average sea level for 17years are calculated. Significant seasonal variation can be seen in the averaged sea level difference curve. However, the seasonal variation is not so clear in comparison with cases in 2003 and 2009. The sea level changes at Kushimoto and Uragami tide-gauge stations were investigated for the years of 2003 and 2009. Both of the sea levels tend to rise in summer time, but the magnitude of the rise at Kushimoto is considerably larger than that at Uragami. Maekawa et al. (2011) showed that the water off the Kushimoto tide-gauge station is originated to the surface water of the current zone of the Kuroshio, when the Kuroshio takes straight pass.. Thus, the main cause of seasonal variation of the sea level difference would be sought for seasonal warming of the surface water of the Kuroshio area. The water would be brought from upstream (southern) area of the Kuroshio, and would be heated much more than surface water in Kumano-nada in summer season. Source


Nagata Y.,Marine Information Research Center | Oguma S.,Hokkaido National Fisheries Research Institute | Nagase K.,Nemuro City Fisheries Research Institute | Aikawa K.,Nemuro City Fisheries Research Institute | Hakata I.,Nemuro City Fisheries Research Institute
Mer | Year: 2010

The Nemuro City Fisheries Research Institute installed bottom temperature sensors off Sanri-hama Beach, Nemuro in in order to know seasonal variations of environmental circumstance of Hanasaki crabs. 8 stations were set along a straight line extended towards offshore. The depths of stations are 5m through 60m. The observations were made from December 28, 2005 through May 13, 2009. In the previous paper (Nagase et al., 2010) showed that temperature and salinity profiles have usually vertically homogeneous both in summer and in winter seasons. The temperature decreases from shore to offshore in summer season, and it increases in winter season. These trends appear to extend into temperature structure in the East Hokkaido Coastal Current (the Coastal Oyashio in winter season and the East Hokkaido Warm Current in winter season). By using the results of STD observation which were obtained 17 times during the observation. In contrast to temperature gradients, salinity gradients in the nearshore region are opposite to those inside the East Hokkaido Coastal Current: salinity increases toward offshore in summer season, and it decreases in winter season. This would be explained by supply of fresh land water was brought from offshore into the region in summer season. In winter season, the fresher Oyashio Water, originated from the sea area off the Kruil Islands, would be brought into the nearshore region from offshore.We examined the seasonal variation of water type of the 50m depth at the most offshore observation station St. 8, and compared with that of the East Hokkaido Coastal Current Water. The water is almost identical to that in the East Hokkaido Coastal Current Water at 50m depth, but some tendency that the phase of the seasonal variation in nearshore region advances to that of the he East Hokkaido Coastal Current Water. Source


Takatani Y.,Japan Meteorological Agency | Takatani Y.,Meteorological Research Institute | Enyo K.,Japan Meteorological Agency | Iida Y.,Japan Meteorological Agency | And 12 more authors.
Journal of Geophysical Research: Oceans | Year: 2014

Improved spatial and temporal representation of total alkalinity (TA) is expected to be an important component in monitoring changes in the oceanic carbon cycle and acidification over the coming decades. For this reason, previous authors have sought to develop and apply empirical methods to characterize TA in the surface ocean. However, there are regions such as the North Pacific that have proven difficult to successfully represent through empirical relationships based on temperature and salinity with linear regression. Here we propose a new empirical approach for reconstructing TA for the Pacific basin using sea surface salinity and sea surface dynamic height (SSDH). We propose five zones of the Pacific basin where the empirical relationships are applied separately. The root-mean-square error of the fittings of these equations to the measured TA is 7.8 μmol kg-1. The SSDH-based empirical equation helps especially to represent the TA in the North Pacific subtropical-subarctic frontal zone where salinity-normalized TA as well as other oceanographic variables exhibits a large meridional gradient and sizeable formation of Central Mode Water and Subtropical Mode Water occurs. Key Points Equations for TA were derived from relationships between NTA and SSDH New empirical equations can better represent the distribution of surface TA © 2014. American Geophysical Union. All Rights Reserved. Source

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