Netherlands Polar Data Center

On a cruise with the RV Polarstern (March-May 1999), natural phytoplankton communities were incubated to find out if the microalgae were able to acclimate to the variable light conditions that are characteristic of the well mixed water column in this region. The cruise covered an area that extended from the Polar Front in the north (ca. 49\260 S 20\260E) to the shelf ice in the south (ca 70\260S 6\260W). Phytoplankton abundance varied tenfold (0.04 - 0.4 mg chl.a L-1), with the higher biomass encountered at the Polar Front. At different sites, natural plankton communities were sampled and incubated in 20-L polycarbonate vessels, with and without addition of 2 nM of Fe, in a 'clean' cool container at ambient temperatures. The algae were exposed to 90 mmol photons m-2 s-1 for at least 24 h, to allow iron-uptake. Subsamples were then transferred to 1-L polycarbonate bottles. A light shift was imposed by incubation for an additional 10 h at 90 and 20 mmol photons m-2 s-1, respectively. Acclimation of the photosynthetic apparatus was studied using fluorescence techniques (dual modulation fluorometer, PSi), in relation to chlorophyll a and carbon content, and cell size (determined by flow cytometry). In addition samples were collected for pigment analyses on a transect from 44S to 71S, at the sea surface at 10,20,40,60,80,100 and 200m.