Gschwend%20thesis.pdf

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Potential precursors for chemical oxidation to aldehydes are the
unsaturated fatty acids. TWo of the most common fatty acids found in phyto-
plankton are cis-9-hexadecenoic acid and cis-9-octadecenoic acid (Ackman et
al., 1968; Chuecas and Riley, 1969). Oxidation by reactants such as ozone
which add to the double bond would yield only heptanal and nonanal from
these compounds. It is difficult to produce octanal and decanal from such
reactions, given that the appropriate fatty acids are uncommon. A second
mechanism which produces all the C6-C10 aldehydes is shown in figure 2-13.
This mechanism does not have to be the dominant pathway of decomposition of
the fatty acids, as these adds are found in l.g/kg quantities (Jeffrey, 1966;
Kattner and Brockman, 1978) while the aldehydes are found at only ng/kg
levels. Side products in this reaction are omega-carboxy-aldehydes which
are not volatile. The 2 fatty acids mentioned above are also found at
l.gs/kg in surface slicks (Kattner and Brockman, 1978), which may be the site
,
of (photo?) oxidation.
SUMRY
Individual volatile organic compounds appear at less than 40 ng/kg in
open-ocean samples from diverse areas such as the Sargasso Sea, the western
Equatorial Atlantic, and the Peru upwelling region. Total volatiles for
the analytical window investigated range between 10 and ioa ng/kg. These
low levels may indicate: (I) insignificant sources were present, (2) rapid
turnover of these organic compounds occurred, or (3) degassing to the atmos-
ph ere was important.
Pentadecane is present in most surface seawater samples at about LO-40
ng/kg, which is very near the calculated thermodynamic solubility (Schwarzenbach
et al., 1978). This hydrocarbon may be produced from an abundant phytoplankton