PLANKTONIC PRIMARY PRODUCTION AND MICROBIAL RESPIRATION MEASURED BY C-14 ASSIMILATION AND DISSOLVED-OXYGEN CHANGES IN COASTAL WATERS OF THEANTARCTIC PENINSULA DURING AUSTRAL SUMMER - IMPLICATIONS FOR CARBON FLUX STUDIES

Oxygen consumption and production and carbon fixation by micro-organis ms were measured simultaneously in coastal surface waters near the Ant arctic Peninsula. Although there was a good qualitative agreement betw een the oxygen and carbon measurements, total daily water-column integ rated carbon incorporation measured by radiocarbon uptake in the parti culate fraction underestimated net community production measured by th e oxygen method by 29 to 54 % (using a photosynthetic quotient of 1.5) . Unaccounted-for exudation of dissolved organic carbon during the C-1 4 uptake experiments may explain this discrepancy. Respiratory carbon losses by micro-organisms (largely phytoplankton) ranged between 10 an d 50% of gross production, the highest values corresponding to the mor e productive stations. These estimates are, however, slightly conserva tive, since they refer to the upper 30 m of the water column, correspo nding approximately to the euphotic zone in this region. Our results s how that microbial respiration is an important part of the carbon flux of coastal. Antarctic plankton. Unless it is considered in carbon flu x models, the contribution of higher trophic levels to the carbon flux es in marine food webs may be seriously overestimated.