Monsoonal differences in primary production in the eastern Banda Sea (Indonesia)

Abstract

14C incorporation into phytoplankton of the eastern Banda Sea was registered during incubations of samples, both in situ and in an incubator equipped with blue filters. Light conditions throughout the euphotic zone were apparently simulated quite well in the deck incubator: the agreement between the two series of measurements was very good. Primary production was 1.85 g C·m −2..d t-1 in August 1984, after upwelling forced by the southeast monsoon; values ranged from 0.5 g C·m −2..d t-1 in the open Banda Sea up to 7 g C·m −2..d t-1 south of Irian Jaya. In February 1985, when the upper part of the water column was stratified due to persistent monsoonal winds from the northwest, primary production was less: 0.91 g C·m −2..d t-1. In August 1984 production was also measured with the oxygen method. The photosynthetic quotient was 1.05 near the surface and up to 1.86 near the bottom of the euphotic zone. Extrapolation of all measurements to an estimate of annual primary production resulted in a value as high as 5·10 2 g C·m −2..d t-1. The assimilation ratio in surface samples was locally up to 8 mg C·(mg chl. a) −1.h −1 (in the photoperiod) during both cruises, with a mean of 5.85 in August 1984 and 5.95 in February 1985. The surprisingly high values during the oligotrophic conditions of February underline the importance of rapid recycling of nutrients in the euphotic zone.