To reprocess CTD data with bottle oxygen in um/Kg, a DECODR utility for inserting additional columns into existing point-checked, annotated sta.csvs & casts.csv was created. The new DECODR module under the CSV tab - [Add um/kg cols to csvs] updates older cruises whose csvs are missing columns for DIC, Ttl_Alk, and um/kg columns (5: OxBumKg=bottle O2, Ox1umKg=CTD Ox1, Ox2umKg=CTD Ox2, OumDC=DataCode based on bottle OxB (ml/L) datacode, OumPI=Point-check code for future use.
Rerunning the O2 module with sta.csv update checked will populate the new columns. Since only observed data is used to correct CTD sensor data, the module uses & updates the non-standard level sta.csvs. Updating the station t.csvs standard levels with um/Kg may be added to [Derive Bottle Data] module later.
Other fixes - lots of reformatting done to sta & casts csvs so visual parsing of columns with a text editor is easier. Changed some column widths to match headers in both sta & casts csvs.
Reporting CTD oxygen(s) in umole/Kg from the Seabird sensor(s) is standard practice. Reporting bottle oxygens in um/Kg in the CalCOFI Data Reports will formally begin in 2013 (1301).
Using draw temperatures saved by CESL (CalCOFI Electronic Sample Log) into the sta.csvs, we can calculate sigma-theta for each O2 sample at draw time. Using this value, pressure=0, & CTD salinity, the ml/L values are converted to umoles/Kg using Seabird's conversion algorithm (Seabird Application Note 64):
[µmole/Kg] = [ml/L] * 44660 / (sigma_theta(P,T,S) + 1000); P = 0
CESL1304 will generate the latest casts & sta.csv formats which allow oxygen values in um/Kg to be archived.
BtlVsCTD1304 will compile the CTD sensor values plus the bottle values, include O2 in um/Kg. This allows bottle oxygen in um/Kg to be regressed against sensor values. The combined CTD+bottle data csv includes: CTD primary & secondary oxygen sensor values in ml/L & um/Kg. Plus bottle corrected CTD oxygen values - cruise-average corrected oxygen in ml/L & um/Kg; station-corrected oxygen in ml/L & um/Kg. Cruise-average corrected = CTD sensor data vs all cruise bottle oxygen regression coefficients are applied (n = ~1300 samples) . Station-corrected = primary & secondary CTD oxygen sensor data are corrected using the corresponding station bottle oxygen samples only (n = ~20 samples). Station-corrected CTD oxygen values are considered the best since station-to-station variability in sensor performance is addressed. Stations that do not have adequate calibration samples are cruise-corrected only and those CTD oxygen values are the best available.
For the µmole/Kg conversion, there is disagreement in the scientific community about the conversion constant 44660:
The value 44660 is exact for oxygen gas.
The value 44615 is the average value for atmospheric gas (N2,O2,Ar,H2O,CO2,...). It is not exact for any individual gas, but has been used historically by oceanographers.
The argument distills to exact versus historic, with oceanographers split; Sea-Bird uses 44660 in all calculations."
CTD asc files contain CTD primary & secondary (when installed) oxygen measurements in umoles/kg. These data were not included in the CTD-bottle data merged csvs. With the mandate to include oxygen in umoles/kg as part of our dataset, these columns are now included in the ctd.csvs. Eight additional columns have been added: Ox1uM, Ox1uM_CruiseCorr, Ox1uM_StaCorr, Ox2uM, Ox2uM_CruiseCorr, Ox2uM_StaCorr, OxuMAve_StaCorr, plus the OxBuM column for the bottle value.
Reporting of bottle oxygens in umoles/kg should begin on CalCOFI 1301SH (Jan 2013). With the addition of bottle oxygens in umoles/kg, bottle-corrected CTD oxygens in umoles/kg will populate the ctd.csvs. These data will be archive with final data.
CalCOFI started running oxygens with the ODF auto-titrator in Oct 2003 so it may be possible to generate umoles/kg values from archived runs as time permits (which it rarely does). Further investigation of this possibility is necessary ie whether older cruise bottle oxygens can be reprocessed to umoles/kg easily.
