Gschwend%20thesis.pdf

CHAPTER 6. SUMRY AND CONCLUDING REMARKS
The major objectives of this thesis were to identify and quantify
vola tile organic compounds in seawater, and to deduce their sources,
transformations ,and transport mechanisms. Two approaches have been
taken to accomplish these goals. First, samples from 3 open-ocean regions,
the Sargasso Sea, the western Equatorial Atlantic, and the upwelling region
off Peru, were analyzed for volatiles, and correlations with ancillary
data were sought. In the second approach, temporal variations of the
concentrations of volatile organic compounds in coastal seawater were
investigated and interpreted by comparison with those of known coastal
processes.
Open-Ocean Seawater
Total volatile concentrations found in oligotrophic surface Sargasso
Sea samples were only 10-30 ng/kg, while
total concentrations in samples
from the biologically productive upwelling region off Peru were about
100 ng/kg.
Pentadecane was found in surface seawater samples from all 3 regions,
typically at lO-40 ng/kg. This compound was not derived from fossil fuel
inputs as other homologues (e.g. nCi4.and nCi6) were present at only
trace levels. Based on a calculation, it appeared that a phytoplankton
source was impronable, as the literature suggest that these organisms do
not contain sufficient amounts of pentadecane. A transformtion of the
abundant fatty acid, hexadecanoic acid, to pentadecane by zooplankton, in
a manner analogous to the production of pristane from phytanic acid, may
have been the source of open-ocean pentadecane.
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