Preliminary screening of the water sample salinities is done by comparing against all previous data deemed reliable that had been collected at the particular site (Stations Kahe, ALOHA, Kaena, etc.). The nominally calibrated CTD salinity trace is also used to identify questionable discrete samples. Potential rosette mistrip problems are resolved, where possible, before data are excluded from use in the calibration of the conductivity cell.

After an initial calibration of the conductivity cell using all casts within a cruise, the deviations between CTD salinity and bottle salinity are tested against limits within 4 pressure ranges (see below). Bottle salinities outside these limits are marked as "suspect" or "bad", and are not used in further iterations of the calibration.

The procedure for screening the bottles against calibrated CTD salinities includes a method to prevent the flagging of bottles with moderate CTD minus bottle salinity differences due to bottle closure and mark pressure mismatch, especially in high gradient regions. The method includes the calculation of the local vertical salinity gradient from a least squares fit to 5 levels of the 2-dbar averaged data on both sides of the mark. The absolute value of the CTD minus bottle salinity difference (ΔS), divided by the absolute value of the gradient yields a pressure Δp that is used as an additional parameter to determine the bottle quality.

The quality of each bottle is determined by comparing ΔS against the standard deviation (SD) of the ensemble of "good data", and comparing Δp against a pressure cutoff value (P) as follows:

The pressure cutoff value P was set to 7 dbar. This cutoff value represents the maximum vertical distance that a bottle can travel between the time of the mark and the closing of the bottle as a result of a ship roll or changing wire angle. A greater P value would imply vertical motion of more than 7 dbar, which is unlikely.  

The salinity standard deviation values of the ensemble of "good" data (SD) used for the bottle screening in the 4 pressure ranges were: 0.0035 (0-150 dbar), 0.0048 (150-500 dbar), 0.0020 (500-1050 dbar), and 0.0011 (1050-5000 dbar).

In order to show the salinity sample variability in deep and bottom waters at the ALOHA station, bottle salinities from HOT cruises at levels below 3000 dbar are plotted in potential temperature coordinates in figures 7 through 11. Only bottles flagged "good" are included in the plots.

The salinity variability below 3000 dbar at the ALOHA station can also be seen in figure 12. This figure shows contours of bottle-calibrated CTD data, plotted versus potential temperature throughout the HOT program. Also indicated on the plot are the IAPSO standards (Table 6), and lab substandard batches used (Table 7), as well as the initials of the operator that measured the salinities (Table 2).

Figure 7. Bottle salinities below 3000 dbar for HOT cruises during 1988-1989, 1990 and 1991.

Figure 8. Bottle salinities below 3000 dbar for HOT cruises during 1992, 1993 and 1994.

Figure 9. Bottle salinities below 3000 dbar for HOT cruises during 1995, 1996 and 1997.

Figure 10. Bottle salinities below 3000 dbar for HOT cruises during 1998, 1999 and 2000.

Figure 11. Bottle salinities below 3000 dbar for HOT cruises during 2001, 2002 and 2003.

Figure 12. CTD salinity contours at Station ALOHA below 3000 dbar throughout the HOT cruises. The vertical dashed lines indicate the first time that the IAPSO batch shown in the upper axis was used (Table 6). Lab substandard batches used during cruises (Table 7) are indicated by the tick mark along the upper axis. The salinity operator measuring the samples (Table 2) is indicated below the lower axis (TW: Ted Walsh, SK: Sean Kennan, S-R-J: Sophia Asghar, Reka Domokos, Jim Potemra; JY: Jinchun Yuan, CN: Craig Nosse, ML: Molly Lucas, MC: Matt Cochran, DW: Don Wright, JJ: Jeremiah Johnson, NL: Noel Larson, DF: Daniel Fitzgerald, MI: Maya Iriondo). The onset of "cold events" (Lukas et al., 2001), is indicated by white vertical dashed lines. The tick marks along the lower axis indicate HOT cruises. The blue line indicates the mean temperature at the level of the sill depth separating the Maui sill from the Kauai sill (4450-4500 m).

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