Dynamics of carbon dioxide uptake and nutrients in subtropical oceanic waters

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Spatial variations of trace concentrations of nutrients and partial pressure of carbon dioxide (pCO_2) were compared for surface waters of the subtropical ocean. For this purpose, a pCO_2 monitoring system with high resolution of temporal variation was designed, and its performance was tested from 2005 through 2006. The developed system was carried onboard RAT Umitaka-maru of the Tokyo University of Marine Science and Technology, and surface monitoring in the subtropical waters was conducted during the period from 29 Nov to 14 Dec. in 2006, on a cruise leg from Tokyo to Sydney. Along with pCO_2 monitoring, the continuous observation of pH by colorimetric determination and the high-sensitive continuous flow analysis of nutrients were also performed. The pCO_2 showed variations of smaller spatial scales (〜tens of km), and these variations were categorized into three patterns. The first pattern accompanies decrease of temperature, increase of salinity, and increase of nutrient concentrations, which can be ascribed to enhanced vertical mixing and/or upwelling. The second pattern accompanies an extensive decrease of salinity and may reflect dilution of seawater by precipitation. The third and most frequently observed pattern was co-variation of pCO_2 and trace phosphate, which was presumably caused by biological activity