First, light intensity, which is quite lower in austral winter could lead to higher chlorophyll a concentrations independently of the phytoplankton biomass (as carbon, for instance). Such a light effect likely explains the higher chlorophyll a concentrations at 30 m, part of it being due also to inputs from the sediments and a different phytoplankton composition with a different carbon/chlorophyll a ratios. The second hypothesis lies in the wind regime, somewhat different in winter from other periods,