Surface chlorophyll a variability near the Dokdo Islets, East Sea (Japan Sea) observed from a moored buoy: Possible consequences of eddy-driven vertical mixing

Abstract

As part of the Dokdo East Sea Time Series Studies (DETS) of the East Sea (Sea of Japan), a DETSbuoy system equipped with a set of meteorological sensors (wind, temperature, humidity,pressure, and wave height) 2 m above sea level, a conductivity-temperature-depth (CTD) sensorwith a fluorescence detector 1 m below the sea surface, and CTD sensors at 20-, 40-, 60-, 80-,100-, and 120-m depths was deployed on the 130-m-deep continental shelf of the Dokdo Islets inthe center of the East Sea. Sensor observations have been taken every 10 min since February2009 and transmitted to an onshore laboratory in Uljin on the east coast of the Korean Peninsula.Chlorophyll a concentrations in surface water at the DETS buoy exhibited frequentlow-concentration maxima in addition to low-frequency bimodal annual chlorophyll aconcentration variations due to a spring phytoplankton bloom and a smaller fall bloom. Thesesmaller frequent blooms appear to have been triggered by injection of nutrient-rich deepsubsurface water to sunlit surface water. This eddy-pumping mechanism was hypothesizedbased on cross-correlation analyses among daily mean water temperature and salinity at variousdepths (2–120 m below sea surface) and wind speed, wave height, and in vivo chlorophyll a atthe sea surface using a one-year data set from 30 March to 7 February retrieved from the DETSbuoy. This mechanism is also responsible for uctivity-temperature-depth (CTD) sensorwith a fluorescence detector 1 m below the sea surface, and CTD sensors at 20-, 40-, 60-, 80-,100-, and 120-m depths was deployed on the 130-m-deep continental shelf of the Dokdo Islets inthe center of the East Sea. Sensor observations have been taken every 10 min since February2009 and transmitted to an onshore laboratory in Uljin on the east coast of the Korean Peninsula.Chlorophyll a concentrations in surface water at the DETS buoy exhibited frequentlow-concentration maxima in addition to low-frequenc