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Dissolved oxygen concentrations at 4750 dbar are plotted in Figure 6. The mean was 153.9 µmol/kg.
Figure 6. Dissolved oxygen concentrations at the 4750 dbar horizon
at Station ALOHA. The horizontal dashed line is the overall mean. The
vertical dashed lines indicate cruises 10 and 30. Prior to HOT-27 (June
3-6, 1991), oxygen samples were only collected at 4750 dbar during HOT-16
(April 11-15, 1990).
The bottom water oxygen concentrations (Fig. 6) mostly clustered near 154 µmol /kg with two main exceptions. The first exception is the first data point of the graph (HOT-16), which seems suspiciously low for no apparent reason. The second exception is the area from HOT-142 through HOT-147, which exhibits a decreasing trend similar to the one observed in the 5 dbar data (see Sect 4.2.1).
The problems with the oxygen data observed during HOT-142 through HOT-147 are also apparent at other depths. Figure 7a is a plot of all the bottle oxygen data between HOT-141 through HOT-148.
Figure 7a. Vertical distribution of dissolved oxygen concentrations
from HOT-141 through HOT-148.
Figure 7a shows that the bottle results from HOT-145 and HOT-146 are offset from the normal scattering. The effect is even more noticeable when the graph focuses on just the deep water (Figure 7b), which shows low values in cruises HOT-142 through 147, compared to HOT-141 and 148.
Figure 7b. Vertical distribution of dissolved oxygen concentrations
for depths below 1020 dbar from HOT-141 through HOT-148.
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