Reprocessing 2012 CTD data to include oxygen in um/Kg
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.
From Seabird Application Note No. 64: SBE 43 Dissolved Oxygen Sensor
"[µmole/Kg] = [ml/L] * 44660 / (sigma_theta(P,T,S) + 1000)
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."
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.
From Seabird Application Note No. 64: SBE 43 Dissolved Oxygen Sensor
"[µmole/Kg] = [ml/L] * 44660 / (sigma_theta(P,T,S) + 1000)
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."