Physical and Biological Processes Underlying the Sudden Appearance of a Red-Tide Surface Patch in the Nearshore

摘要

The factors contributing to the timing and intensity of phytoplankton blooms ('red tides') in very shallow water are poorly understood. Here, the sudden and brief (3h) appearance at the surface of an alongshore- parallel band of red tide is described. The bloom, near Huntington Beach CA, was dominated by the locally common red-tide forming dinoflagellate Lingulodinium polyedrum (F. Stein). Surface chlorophyll-a (Chl a) and temperature (T) were mapped with a novel GPS-tracked jetski. The surface red- tide band, with maximum Chl approximately 7 microgram L-1, was visible for more than 3h, was located 500 m from shore (approximately 8m water depth), was approximately 200m wide and extended approximately 1km alongshore. The subsurface bloom, with maximum Chl a > 30 microgram L-1, developed farther offshore, near the 17-deg C isotherm over 4-7 days prior to the surface appearance. A few hours before the surface band appeared, an intense Chl a> patch was observed in 13m total depth in the mid-water column trough of a shoreward-propagating supertidal internal wave. The Chl a> patch intensification was consistent with dinoflagellate vertical swimming interacting with the wave-driven circulation.