Journal of Oceanography, Vol. 64 (No. 2), pp. 195-210, 2008
Koichi Ara* and Juro Hiromi
Department of Marine Science and Resources, College of Bioresource Sciences, Nihon University, Kameino, Fujisawa, Kanagawa 252-8510, Japan
(Received 28 May 2007; in revised form 15 October 2007; accepted 16 October 2007)
Abstract: Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower than ca. 15 cm, respectively. Temperature difference (DFT) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4+-N, NO3-+NO2--N, NH4++NO3-+NO2--N, PO43--P and SiO2-Si) increased and decreased with DFT, respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate (Si) revealed seasonal variations in the ranges of 0.57-16.08, 0.0070-0.91 and 0.22-46.38 μM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P = 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0-20 m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient limitations, which could restrict phytoplankton (diatom) growth as a limiting factor.