DCM - Introduction
The inverse gradients of light and nutrients (nitrogen) with depth
have result in an unique phytoplankton distribution and primary production in oligotrophic
stratified (tropical) oceans. These gradients can only partly explain why a Deep
Chlorophyll Maximum (DCM) is found here world-wide at depths of 80 or 150 m. The microbial
composition of this layer is remarkably constant in spite of the high activity of the
photosynthetic, microbial and heterotrophic components which indicate a highly dynamic
system. The phytoplankton composition is dominated by picoplankton (< 2 µm in
diameter) and consists of a mixture of prokaryotic (Synechococcus and Prochlorococcus) and
various (unknown) eukaryotic species of which various subpopulations dominate at different
depths. By modelling the production processes and trophic interaction the contribution of
the DCM to the sedimentation of particulate carbon will be studied. The expedition on
board Hr.Ms. Tydeman focuses on the factors which prevent (major) fluctuations in the structure
and organisation of microbial populations present near the Deep Chlorophyll Maximum.
|
