Microbial dynamics in coastal waters of East Antarctica: plankton production and respiration

The rates of plankton community production and respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen and the incorporation of (NaHCO3)-C-14 at a coastal site in East Antarctica between 16 December 1993 and 12 February 1994. The breakout of seasonal fast ice was associated with a succession of dominant phytoplankton from Cryptomonas to Phaeocystis to a diatom assemblage. Gross production reached 33 mmol C m(-3) d(-1) and C-14 incorporation peaked at 24 mmol C m(-3) d(-1) on 23 January 1994, at the time of the chlorophyll a maximum (22 mg chi a m(-3)). Dark community respiration reached its maximum (13 mmol C m(-3) d(-1)) 4 d later. Photosynthetic rates calculated from C-14 incorporation were significantly lower (17 to 59%) than rates of gross production. The derivation of plankton processes from changes in both dissolved oxygen and dissolved inorganic carbon allowed the direct measurement of photosynthetic and respiratory quotients. A linear regression of all data gave a photosynthetic quotient of 1.33 +/- 0.23 and a respiratory quotient of 0.88 +/- 0.14. Concurrent determinations of bacterial, heterotrophic dinoflagellate, nanoflagellate and ciliate respiration could account for 15 to 58% of measured dark-community respiration. This study has improved the sparse data set of plankton respiration measurements, confirmed that heterotrophic respiration is a significant process in the carbon flux of coastal Antarctic waters and achieved a first apportionment of community respiration to the major microbial groups in this region.