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: PO43− 1.80 μmol L−1 and NO3− 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 ΔpCO2 (difference of the CO2 partial pressure between surface seawater and the atmosphere) was –30.5 μatm, which could have contributed to a net CO2 flux from the atmosphere to the sea and suggests the area has been a CO2 sink during the studied period. High phytoplankton biomass and production values were found in this freshly open area, suggesting its importance for biological CO2 pumping.