Single-Species Dominance in a Subsurface Phytoplankton Concentration at aMediterranean Sea Front

摘要

A narrow band of high Chl a (23.1 ug liter-1) was observed at a salinity front inthe western Mediterranean Sea in late November 1987. The biomass peak was found deep in the photic zone, at 54 m, in a region of low light. A single diatom species, Thalassiosira partheneia Schrader in gelationous colonies, represented 98% of the total phytoplankton biomass in the layer and achieved abundance. Although lack of temporal sampling precludes precise determination of the processes responsible, the high biomass accumulation and dominance by this species was likely due to its preference for low light coupled with turbulence-induced high nutrient levels. Interleaving patterns in the temperature, salinity, and nutrient profiles suggest increased horizontal advection at the front. High shear at the boundaries of the interleavings might confine the biomass to a thin band, as well as generate turbulence to mix nutrients in from surrounding layers. Alternatively, stabilization of the water column following a brief, pulsed upwelling event could have reduced dispersion of the biomass, thereby confining it to the thin layer we observed. Keywords: Ocean environments; Phytoplankton; Chemical oceanography; Ocean currents. (jes)