Phytoplankton production after the collapse of the Larsen A Ice Shelf, Antarctica

Part of the Larsen A Ice Shelf (64°15′S to 74°15′S) collapsed during January 1995. A first oceanographic and biological data set from the newly free waters was obtained during December 1996. Typical shelf waters with temperatures near and below the freezing point were found. A nutrient-rich water mass (max: PO 4 3− 1.80 μmol L −1 and NO 3 − 27.64 μmol L −1 ) was found between 70 and 200 m depth. Chlorophyll- a (Chl- a ) values (max 14.24 μg L −1 ) were high; surface oxygen saturation ranged between 86 and 148%. Diatoms of the genera Nitzschia and Navicula and the prymnesiophyte Phaeocystis sp. were the most abundant taxa found. Mean daily primary production (Pc) estimated from nutrient consumption was 14.80 ± 0.17 mgC m −3 day −1 . Pc was significantly correlated with total diatom abundance and Chl- a . Calculated Δ p CO 2 (difference of the CO 2 partial pressure between surface seawater and the atmosphere) was –30.5 μatm, which could have contributed to a net CO 2 flux from the atmosphere to the sea and suggests the area has been a CO 2 sink during the studied period. High phytoplankton biomass and production values were found in this freshly open area, suggesting its importance for biological CO 2 pumping.