Summertime episodic chlorophyll a blooms near the east coast of the Korean Peninsula

Abstract

We present intensive observational data of surface chlorophyll a bloom episodes occurring over several days in the summers of 2011, 2012 and 2013, accompanying the equatorward advection of low sea surface salinity (SSS) water near the east coast of the Korean Peninsula. Time-series analysis of meteorological and oceanographic (physical and biochemical) parameter data, such as chlorophyll fluorescence (CF) from surface mooring, ocean color (chlorophyll a and total suspended sediment), sea surface height (satellite-derived) and serial hydrographic data (from in situ measurements), was used to investigate the relationship between surface bloom events and changes in seawater characteristics and currents. In the summers of the 3 years, a total of 10 bloom events (E01-E10) were identified during which the surface CF was significantly (>2 μg L-1) enhanced over a relatively long (>1 day) period. The bloom events in the summers of 2011 and 2012 were accompanied by low or decreasing SSS for several days to a week after heavy rainfall at upstream stations and equatorward currents. Unlike the typical 8 of the 10 events (80 %), E07 was potentially derived from the onshore advection of high CF offshore water of southern origin into the coastal zone near the mooring, whereas E10 possibly prevailed by offshore advection of high CF plume water trapped by the coastal area. Contrasting with many coastal systems, these findings indicate that eventscale productivity near the east coast of the Korean Peninsula in summer is not controlled by local blooms triggered by either nutrients or light availability, but by the equatorward and cross-shore advection of high CF plume water.