[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-06] Effect of Sea Surface Warming on Primary Production and Phytoplankton Size Classes (PSCs) in the Coastal Oyashio and Oyashio Regions, Northwest Pacific

*Willy Angraini¹, Koji Suzuki², Hiromi Kasai³, Tomonori Isada⁴ (1.Graduate School of Environmental Science, Hokkaido University, Japan, 2.Faculty of Environmental Earth Science, Hokkaido University, Japan, 3.Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Japan, 4.Field Science Center for Northern Biosphere, Hokkaido University, Japan)

Keywords:primary production, phytoplankton, satellite, phytoplankton size class

Oceanic primary production by phytoplankton photosynthesis has a fundamental role as essential support on marine food webs and biogeochemical processes. Ocean color satellite remote sensing has recently estimated the global net primary production decline of approximately 0.8 Pg C y^-1 between 1998 to 2015, probably associated with increasing thermal water column stratification and decreasing nutrient supply to the surface mixed layer. A recent study reported the Oyashio Regions, northwest Pacific, which is well known as low temperature and rich in macronutrients, have shown the abruptly increasing temperature from 2010-2016 likely promoted the altered species abundance and distribution (e.g. phytoplankton, mesozooplankton, subtropical and tropical fish migrants). The environmental forces may change the biomass and community structure of marine phytoplankton as the basis of marine ecosystem in the northwest Pacific, which has the highest fishery production among the world’s oceans. Nonetheless, little is known about the impact of rising sea surface temperature (SST) on primary productivity (PP) associated with the phytoplankton size classes (PSC) and chlorophyll-a concentration. In this study, we conducted monthly field campaigns in the Coastal Oyashio water of Akkeshi Bay in 2022 to investigate the relationship between PP and PSC or the absorption coefficient of phytoplankton (a_ph(lambda)). Micro-sized phytoplankton with high chlorophyll-a concentration was predominant during spring (March-April), gradually declined with time and rapidly increased in summer (August). We also found a strong positive correlation between a_ph(443) and PP in surface waters. Therefore, a_ph(443) could be a promising parameter for estimating surface PP using satellite ocean color data such as from MODIS-Aqua. We will demonstrate the effect of enhanced SST on the spatiotemporal variation of surface PP and PSC in the Coastal Oyashio and oceanic Oyashio regions through the 20-year time series data of MODIS-Aqua.