Gschwend%20thesis.pdf

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production by the plankton or may represent oxidation products of algal
lipids. Potential precursors and a viable mechanism for chemical oxidation
of algal fatty acids to C6-CiO aldehydes are described in detail in
chapter 2 (figure 2-l2).
A group of longer-chain aldehydes became particularly abundant
during the phytoplankton bloom of February, 1978. These included Cl2 to
Cl5 saturated and unsaturated aldehydes (figure 3-20). The bloom was more
than 85% Thalassiosira nordenskioeldii as mentioned previously; thus it
seemed likely that this diatom was the ultimate source of this material.
Figure 3-21 demonstrates the correlation of these compounds with cell
numbers of this diatom.
Accordingly, pure cultures of this diatom were grown in the laboratory.
4
Cultures (1600 ml of ~ 3 x IO cells/ml in log phase growth) were extracted
with CH2Cl2 after collection on a glass fiber filter, and the extract
chromatographed. No evidence for the presence of any aldehydes could be
found. Another culture was stripped directly as normal volatile analysis
of water samples is
performed, but no aldehydes were found by this approach.
Finally, approximately 100 ml of CD seawater were added to a culture and
incubated for two additional weeks (stationary phase). Stripping this
cuI ture did not provide any aldehydes ei ther ~ Thus, it seems that the
diatom does not produce the aldehydes directly.
Possibly, zooplankton plays a role in aldehyde production. Another
possibility is that photochemical oxidation (which cannot occur with the
lights used to incubate algae) of algal
metabolites produced the aldehydes.
Also, a less abundant phytoplankton species may have released these
compounds during the bloom.
Dimethyl Polysulfides. Another group of compounds (figure 3-22) observed