Primary production, light and vertical mixing in Potter Cove, a shallow bay in the maritime Antarctic

Abstract.

Phytoplankton photosynthesis was measured during spring–summer 1991–1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Z _t . The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*_max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)^–1 h^–1] and photosynthetic efficiency {α*; 0.073 and 0.0018 µg C (µg chlorophyll-a)^–1 h^–1 [(µmol m^–2 s^–1)^–1]} values were obtained for both sites during low mixing conditions (Z _t from 10 to 20 m), while no differences were found for high mixing situations (Z _t >20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*_max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.