Optical studies in the Southern Ocean

During the Austral summer of 1997–1998, measurements of absorption, attenuation, downwelling and upwelling irradiance were made in the Southern Ocean along a S–N transect at 6°E. Measurements were made to quantify the penetration of ultraviolet B radiation (UVBR) in the water column and daily doses of UVBR at different water depths, to study the attenuation of photosynthetically active radiation (PAR), and to judge if in the investigated areas of the Southern Ocean phytoplankton are light limited. The results show that the UVBR affects a substantial portion of the upper mixed layer. The diffuse attenuation coefficients (KPAR) for PAR were found to vary between 0.03 and 0.09 m−1. Using the values for KPAR and the definition of the Sverdrup critical depth, the studied Southern Ocean plankton systems were found not to be light limited.