Estimation of spatial distribution of coastal ocean primary production in Hiroshima Bay, Japan, with a geostationary ocean color satellite

Abstract

Ocean primary production measured by conventional methods using carbon isotope are mostly calculated from point sampling, which is not appropriate for estimating the temporal and spatial variations involved in marine ecosystems. Ocean color remote sensing can estimate spatial variation of ocean primary production at the global scale. However, the spatial resolution of the ocean color remote sensing is not adequate for estimating coastal ocean primary production. This study sought to establish a novel methodology for estimating coastal ocean primary production in Hiroshima Bay, Japan using high-resolution ocean color data (~500 m) and higher temporal resolution (hourly during the day) obtained by a geostationary ocean color satellite, GOCI-COMS. Estimated values of primary production derived from the ocean color satellite based on the Kameda & Ishizaka model did not correlate with observed primary production. We estimated primary production in Hiroshima Bay with a modified Kameda & Ishizaka model. The coefficient of determination between observed and estimated primary production by the ocean color satellite was 0.750. The slope of the linear regression was 1.00, and root mean square error was 165 mg-C m2 d−1. Our proposed method was thus sufficient for discussions of the changes in spatial distribution of primary production in Hiroshima Bay. Finally, spatial distribution of primary production in Hiroshima Bay was estimated using our proposed method. In January, the primary production of the Hiroshima Bay ranged <50-1000 mg-C m−2 d−1, and increased to 1000–1600< mg-C m−2 d−1 during seasonal blooms in spring and autumn. The primary production was relatively high at the innermost and western parts of the bay which affected by terrigeneous loads compared to other parts of the bay. In July 2016, highest primary production was observed at the innermost of the bay, ranging from 1200 to 1600< mg-C m−2 d−1. The high primary production was considered to be due to the supply of nutrients from terrigeneous load. Hence, our proposed method based on the high-resolution (approx. 500 m) ocean-color product has been enabled us to estimate primary production in coastal seas including complicated topographic areas such as enclosed seas or channels of less than 1 km wide.