Characteristics of the ratio of dissolved cadmium to phosphate in subtropical coastal waters of Ishigaki Island,Okinawa, Japan |
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Authors: | Kazuo Abe Kouki Fukuoka Toru Shimoda |
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Institution: | (1) Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Fisheries Research Agency, 148-446 Fukai-Ota, Ishigaki Okinawa, 907-0451, Japan;(2) Present address: Seikai National Fisheries Research Institute, Fisheries Research Agency, 1551-8, Taira-machi, Nagasaki Nagasaki, 851-2213, Japan |
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Abstract: | The ratio of dissolved cadmium (Cd) to phosphate (PO4) in the subtropical coastal area of Ishigaki Island, Okinawa, Japan, was investigated. Twenty vertical seawater samplings
were carried out once a month from May 2008 to January 2010. In order to examine how the Cd/PO4 ratio in seawater varies with the oceanographic conditions (i.e., the water temperature–salinity characteristics), the water
masses at the study sites were classified into two types: group 1 with a water temperature of >25°C and a salinity range of
34.0–34.4, and group 2 with a water temperature of <25°C and a salinity of >34.4. A different phytoplankton assemblage was
observed in each water mass defined. Different Cd/PO4 ratios were obtained for the two water mass types, due to the differences between the types in terms of the environmental
conditions such as the water temperature–salinity (T–S) characteristics and phytoplankton assemblages, as well as possible variations in the concentrations of dissolved iron, zinc,
manganese, and CO2 in seawater in each water mass. |
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