As described in the previous two sections, the Beckman oxygen sensor was used as the main oxygen sensor on HOT cruises 1 through 32. Up to cruise 24, only the Beckman sensor was used, on cruises 25 through 32 the YSI sensor SN 13-0233 was paired with the Beckman and the results obtained from both sensors were compared. During this period, the YSI sensor results demonstrated that the YSI sensor was superior to the Beckman especially in the upper 100 m of the water column (Figure 4.3). Therefore, we used the YSI as the primary sensor during HOT-31 and 32. As described in the previous section, extra weight was generally given to oxygen values below 1000 m for calibration purposes. This procedure was used on all cruises during 1991 with the exception of cruises 23, 25 and 26. On cruises where the Beckman was the primary sensor (22 through 30), the data from the upper 100 dbar was neglected for calibration purposes and flagged as suspect (see Figure 4.4); this was not done when the YSI was the primary sensor.

     Figure 4.4 shows the CTD oxygen data quality for every 2-dbar bin in each cast at Station ALOHA for cruises 23 through 32. The upper 100-200 dbar CTD data taken with the Beckman sensor during cruises 23 through 30 were flagged suspect.

     The quality of the O2 sensor calibration was assessed from Table 4.3.

Figure 4.3: Calibrated Beckman and YSI oxygen profiles in the upper ocean for HOT-25. Upper panel: Calibrated YSI and Beckman profiles for the upper 200 dbar. Bottle data are represented by open circles. Lower panel: Calibrated YSI and Beckman profiles for upper 600 dbar on this same cruise showing good agreement at pressures greater than 125 dbar.

 

Figure 4.4. CTD oxygen data quality per cast (vertical bars) and per 2-dbar bin at Station ALOHA during HOT cruises 23 through 32. The tick marks along the x-axis separate different casts. Casts from the same cruise are separated by vertical black lines.

Table 4.3: CTD-Bottle O2 (µmol kg-1) Comparison for Each Cruise

 

 

Station 1, Kahe Point

Station 2, ALOHA

 

0 < P < 1100

0 < P < 4700

500 < P < 4700

Cruise

Mean

St. Dev.

Mean

St. Dev.

Mean

St. Dev.

HOT-23

-0.02

2.56

0.28

2.99

0.32

2.95

HOT-24

---a

---a

-0.95

3.20

0.36

3.83

HOT-25

0.02

1.47

-0.11

2.44

-0.21

2.10

HOT 26

-0.09

2.29

0.08

3.21

0.06

2.76

HOT-27

0.00

2.33

-0.88

4.12

-0.94

2.70

HOT-28

-0.17

1.81

-0.25

2.02

-0.28

1.62

HOT-29

-0.06

2.51

0.18

1.93

0.47

1.34

HOT-30

-0.03

1.96

0.12

2.02

0.26

0.99

HOT-31

0.00

1.12

0.40

1.96

0.69

1.25

HOT-32

0.00

0.99

0.00b

2.40b

0.01b

1.54b

HOT-32

 

 

0.83c

3.22c

2.27c

2.64c

aNo station due to bad weather

bStation 2, cast 1

cAll other casts

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