Diurnal Variations of Surface Chlorophyll-a Concentration from in-situ and Satellite Measurements and its Relation to Physical Forcing

Diurnal variations of surface chlorophyll-a (chl-a) concentration have been limitedly observed. Remote sensing approaches based on geostationary orbit to monitor the ocean color enable us to observe the short-term temporal scales of chl-a concentration as one of components of low-trophic level marine ecosystem. Although the world’s first geostationary ocean color observation satellite, Geostationary Ocean Color Imager (GOCI), has monitored surface chl-a concentration on hourly base since 2010, the diurnal variability of surface chl-a have not been validated with in-situ measurements and its dynamic processes controlling the diurnal variations have been poorly known so far. In this study, the time series of chlorophyll fluorescence data, obtained from a mooring buoy named the East Sea Real-time Ocean Buoy (ESROB) for 3 years from 2012 to 2014, were analyzed and compared with GOCI data. The physical parameters such as water temperature, sea surface wind, and photosynthetically active radiation (PAR) governing photosynthesis were also quantitatively examined. As a result, the diurnal variations of in-situ chlorophyll fluorescence measurements showed good agreement with short-term variations of satellite GOCI data. In addition, the peculiar seasonality of the diurnal variations has been confirmed from both surface chlorophyll fluorescence and GOCI chl-a data as well. The diurnal changes of surface chl-a concentrations validated at the mooring site were extended throughout basin-scale regions by discussing the implications of the diurnal variations and relation to physical forcings.