As described in the previous section, the YSI Inc. oxygen probe SN 13-0233 was used as the main oxygen probe on HOT cruises beginning with HOT-31. This sensor was used throughout HOT-40.

     In previous years (Sect. 4.1, 4.2), extra weight was generally given to oxygen values below 1000 m for the purpose of calibrating the O2 sensor. It was not necessary to apply this procedure for data collected in CY 1992. Very low oxygen values were observed, however, in the upper 15 to 25 m of several casts, specifically, HOT-35 Station 2, casts 4 and 7; HOT-37, Station 2, casts 1 - 14; HOT-38, Station 2, cast 1, 2, 6, 7, 11-14 and 16; HOT-39, Station 1, cast 1, Station 2, casts 1 and 3 - 18. These oxygen values were flagged as suspect (see Fig. 4.5). Furthermore, the deep cast of HOT-38 had spikes in the oxygen signal and the deep casts of HOT 33-35 showed abrupt offsets below 2200 db. These data were also flagged as suspect. The cause of these errors may have been related to deterioration of the sensor membrane. The membrane was replaced on 5 September 1992, just before HOT-40. Surface oxygen values appeared normal for this cruise but spikes were still observed in deep water. The sensor SN 13-0233 was sent back to Sea-Bird and was replaced by a new YSI sensor SN 13-0251 before HOT-41. The new sensor performed well on this cruise.

     Figure 4.5 shows the CTD oxygen data quality for every 2-dbar bin in each cast at Station ALOHA for cruises 33 through 41.

     CTD O2 calibration was performed as explained before. The quality of the O2 sensor calibration was assessed from Table 4.4.

Figure 4.5. CTD oxygen data quality per cast (vertical bars) and per 2-dbar bin at Station ALOHA during HOT cruises 33 through 41. The tick marks along the x-axis separate different casts. Casts from the same cruise are separated by vertical black lines.

Table 4.4: CTD-Bottle O2 (µmol kg-1) Comparison for Each Cruise

 

 

Station 1, Kahe Point

Station 2, ALOHA

 

0 < P < 1500

0 < P < 4700

500 < P < 4700

Cruise

Mean

St. Dev.

Mean

St. Dev.

Mean

St. Dev.

HOT-33

0.03

2.06

0.18

1.34

0.30

1.50

HOT-34

0.00

1.37

0.02

2.72

0.32

2.78

HOT-35

0.01

1.50

-0.12

2.46

0.20

2.45

HOT 36

0.01

1.65

0.06

3.31

0.29

3.23

HOT-37

0.11

2.98

0.28

2.88

0.44

3.15

HOT-38

0.00

1.75

0.45

2.45

0.97

2.25

HOT-39

0.15

2.56

0.04

2.06

0.00

1.76

HOT-40

0.01

1.19

0.17

1.70

0.27

1.54

HOT-41

0.00

2.25

0.02

1.63

0.00

1.47

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