Satellite-detected sea surface chlorophyll-a blooms in the Japan/East Sea: magnitude and timing

The Japan/East Sea (JES) is known as a mid-latitude “Miniature Ocean” that features multiscale oceanic dynamics processes. We investigate the variability of the sea surface chlorophyll-a concentration (SSC) and bloom timing in the JES based on satellite remote sensing products spanning 1998–2019. The JES SSC exhibits strong seasonal variability and blooms twice annually, which are mainly governed by the physical environmental conditions. However, the influences of local oceanic dynamic processes (e.g., upwelling, oceanic fronts, mesoscale eddies, and near-inertial oscillations) on the bloom magnitude and timing of the entire JES are not critical, compared with the PAT and stratification. In addition, significant interannual variabilities of spring bloom magnitude occur along the JES's northwestern coast, and that of fall bloom magnitude occur in the deep Japan Basin. For spring bloom, the interannual variability of the bloom timing (initiation timing, termination timing and duration), which significantly affect the interannual bloom magnitude anomalies, are correlated with climate modes such as AO and ENSO. For fall bloom, on the interannual time scale, the bloom duration is mainly affected by the initiation timing. Both of them have a significant influence on the bloom magnitude. The initiation/termination timing of spring blooms has shifted earlier by 0.37/0.45 days annually along the JES's northwestern coast; the counterpart of fall blooms has shifted 0.49/1.28 days earlier annually in the deep Japan Basin.