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 deter mined by HPLC on 40-m samples collected from the mixed layer during th e ANTXII/4 cruise in March-May 1995 aboard RV ''Polarstern''. A transe ct was covered (90 degrees W, from 51 degrees S to 70 degrees S), cros sing the Subantarctic Front in the north, the Polar Front, and the Sou thern Polar Front in the south. Coinciding with high concentrations of silicate, diatoms dominated in the Antarctic waters south of the Pola r Front. North of the Polar Front, silicate concentrations dropped to values less than 10 mu M. In this area flagellates (Prymnesiophyceae a nd green algae) were the dominant phytoplankton group. Nutrient deplet ion of the surface waters near the Southern Polar Front indicated form erly enhanced productivity. These findings confirmed previous observat ions by the British Sterna expedition. which described locally elevate d chlorophyll rr biomass near the southern boundary of the Southern Po lar Front. We propose a role for supply of bioavailable iron via the f ront and emphasise the importance of frontal systems for phytoplankton productivity in the Southern Ocean.