Dissolved oxygen concentrations at 1020 dbar are plotted in Figure 5. The mean was 40.9 µmol/kg.

Figure 5. Dissolved oxygen concentrations at the 1020 dbar horizon at Station ALOHA from HOT-1 through HOT-148. The horizontal dashed line is the overall mean. The vertical dashed lines indicate cruises 10 and 30.

     The oxygen concentrations at 1020 dbar (Fig. 5) span a significant range of values (34-51 µmol/kg). Four data points from HOT-33 stand out from the surrounding data with values ranging between 46-51 µmol /kg. It is difficult to determine if the general trend of decreasing oxygen concentrations in the first twenty cruises represents real data or if it is the result of some change in methodology, however there was only one documented change in methodology during the time frame, which was the switch from the Strickland and Parsons (1972) method to the Carpenter (1965) method before HOT-11 (Sect 2.2.1). In addition, the data from cruises 1-50 show generally higher concentrations than the later cruises.


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