Late winter chlorophyll a distributions in the Weddell Sea

Abstract

As part of the Weddell Polynya Expedition to the Weddell Sea (in the vicinity of 2.degree. East/60.degree. South) during Oct. and Nov. 1981, measurements of chlorophyll a and phytoplankton photosynthesis were reported. Chlorophyll a measurements were made in 3 different environments: beneath the pack ice, in pack ice cores and in the water volume in the ice edge zone (IEZ, defined as 6/10''s-1/10 ice cover). Photosynthesis measurements were made on samples from beneath the pack ice and from a station at the IEZ. Chlorophyll a values in the mixed layer beneath the pack ice average 12 mg m-2. Within the IEZ (at 6/10''s coverage) water column chlorophyll a doubles. Compared to values beneath the pack ice, the IEZ is characterized by a localized 10-fold increase in surface chlorophyll a (1-2 mg m-3). Photosynthesis parameters likewise increase at the ice edge and a rate of primary production of 300-400 mg m-2 day-1 is estimated for this region. Significant amounts of chlorophyll a are found near the base of the pack ice column and evidence is presented which suggests an active biological community living within the pack ice. Overall, the data are consistent with the idea that phytoplankton distributions are regulated by the availability of light. Data indicate the importance of the IEZ to primary producton in the Southern Ocean.