Gschwend%20thesis.pdf

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These analyses provided a lower limit of detection of about
1 ng/kg. Reproducibility based on previous work (Schwarzenbach et
al., 1978) was about + LO%. Greater stripping efficiency was obtained
using the Grob method, such that nonpolar and slightly polar compounds
were recovered with an efficiency exceeding 80%. Relatively polar
volatile compounds such as the aldehydes were recovered at about 30%.
Only samples which were both filtered and poisoned are discussed.
Comparison to untreated samples showed that these procedures did not
contaminate the samples (Appendix I). Surface samples which were
filtered sometimes showed lower concentrations (about 50%) for aldehydes
and n-pentadecane than unfiltered replicates (Appendix I, Table 1-3).
RESULTS
The winter Sargasso Sea station had a well-mixed surface layer
to 400 meters as evidenced by the temperature, salinity, and oxygen
data (figure 2-2). Pentadecane was the only volatile organic compound
found at greater than trace (~ 2 ng/kg) concentrations (Table 2-1).
Three samples from 10 m and one from 100 m contained between LO and
25 ng pentadecane!kg. The 1200-m sample had less than lng/kg.
The hydrographic data from the western Equatorial Atlantic cruise
reveal the presence of a seasonal thermocline at about 100 m for
6 stations studied (figure 2-3, Appendix
II). No anomalously low surface salinity samples were found; thus
the influence of the Amazon was not important for any of these
surface samples. Nutrients were depleted in the surface mixed layer
and increased in the deeper waters to a maximum at several hundred
meters. Chlorophyll a showed low values (0. i - O. 6 ~g/kg above 50 m
the