Pigment distribution in the Pacific region of the Southern Ocean (autumn 1995)

Phytoplankton distribution patterns are still largely unknown for the Pacific region of the Southern Ocean. Pigment distributions were determined by HPLC on 40-m samples collected from the mixed layer during the ANTXII/4 cruise in March-May 1995 aboard RV "Polarstern". A transect was covered (90 degrees W, from 51 degrees S to 70 degrees S), crossing the Subantarctic Front in the north, the Polar Front, and the Southern Polar Front in the south. Coinciding with high concentrations of silicate, diatoms dominated in the Antarctic waters south of the Polar Front. North of the Polar Front, silicate concentrations dropped to values less than 10 mu M. In this area flagellates (Prymnesiophyceae and green algae) were the dominant phytoplankton group. Nutrient depletion of the surface waters near the Southern Polar Front indicated formerly enhanced productivity. These findings confirmed previous observations by the British Sterna expedition. which described locally elevated chlorophyll rr biomass near the southern boundary of the Southern Polar Front. We propose a role for supply of bioavailable iron via the front and emphasise the importance of frontal systems for phytoplankton productivity in the Southern Ocean.