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2.4. Sample processing and size categories
2.4.1. Identification
Fluorescence and optical microscopy were alternatively used
depending upon the size of the cells, so that a wide range of size classes
could be observed. Samples for fluorescence and optical microscopy were
fixed with glutaraldehyde with a final concentration of 1 percent. From the
preserved sample, an appropriate portion was subsampled and doubledyed
with DAPI and FITC, and the cells were filtered on a 0.2-3 micron
nucleopore filter. These filters were then stored frozen until the laboratory
analysis after the cruise. In the laboratory, the organisms were identified
and counted along with size measurements on a fluorescent microscope
(Olympus IMT-2). For the optical microscopy, 1 litre of water samples,
preserved in neutral formalin (final concentration of 5%), was used, and the
organisms were identified and counted, and their size measured.
Identification was performed to species level, where possible. However,
data analysis was performed at the level of taxonomic class.
Figure 4 Vertical profiles of chlorophyll a (micrograms/l) in 1992 5 .
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