In situ primary production in young Antarctic sea ice

An in situ incubation technique used successfully to measure the photosynthetic carbon assimilation of internal algal assemblages within thick multiyear Arctic ice was developed and improved to measure the photosynthetic carbon assimilation within young sea ice only 50 cm thick (Eastern Weddell Sea, Antarctica). The light transmission was improved by the construction of a cylindrical frame instead of using a transparent acrylic-glass barrel. The new device enabled some of the first precise measurements of in situ photosynthetic carbon assimilation in newly formed Antarctic sea ice, which is an important component in the sea ice ecosystem of the Antarctic Ocean. The rates of carbon assimilation of the interior algal assemblage (top to 5 cm from bottom) was 0.25 mg C m-2 d-1 whereas the bottom algal community (lowest 5 cm) attained only 0.02 mg C m-2 d-1. Chl a specific production rates (PChl) for bottom algae (0.020 - 0.056 µg C µg chl a-1 h-1) revealed strong light limitation, whereas the interior algae (PChl = 0.7 - 1.2 µg C µg chl a-1 h-1) were probably more limited by low temperatures (< -5°C) and high brine salinities.