Parameter: oxygen

Dissolved oxygen; Acquired with Sea-Bird Scientific SBE 63 Optical Dissolved Oxygen Sensor. Dissolved oxygen concentration [umol/kg] was calculated and corrected for salinity and pressure effects according to the 2016 Argo recommendations for processing of dissolved oxygen data (Thierry et al. 2016). As per these recommendations, an initial pressure correction was made to the raw measured oxygen phase delay Phi [usec] according to Bittig et al. 2015:

Phi adj = Phi raw + Pcoef1 * P / 1000

where Pcoef1 = 0.115 usec and P [dbar] is the collocated SBE 41CP CTD pressure measurement. The adjusted oxygen phase delay [usec] was then converted to voltage by applying the factory conversion:

V = Phiadj / 39.457071

Uncorrected dissolved oxygen concentration [mL/L] was calculated by applying the factory calibration:

Oxygen_uncorr [mL/L] = {(A0 + A1*T + A2*V2) / (B0 + B1*V) - 1.0} / (C0 + C1*T + C2*T2)

where T is SBE 63 temperature [deg C] and V is adjusted SBE 63 phase delay [V]. The oxygen calibration coefficients (A0, A1, A2, B0, B1, C0, C1, C2) are provided in Table 1. Dissolved oxygen concentration [mL/L] was then corrected for salinity and pressure effects according to the 2016 Argo recommendations.

Oxygen_corr [mL/L] = Oxygenun corr [mL/L] * Scorr * Pcorr

where

Scorr = A(T,S,Spreset) * exp(S*(SolB0 + SolB1*Ts + SolB2*Ts2 + SolB3*Ts3) + SolC0*S2)

A(T,S,Spreset) = (1013.25 - pH2O(T,Spreset)) / (1013.25 - pH2O(T,S))

pH2O = 1013.25 * exp(D0 + D1*(100 / (T + 273.15)) + D2*ln((T + 273.15) / 100) + D3*S)

Spreset = 0

TS = ln [(298.15 - T) / (273.15 + T)]

T and S are the collocated temperature and salinity measurements from the SBE 41CP CTD, respectively. Salinity correction coefficients are from Benson and Krause 1984 (SolB0 = -6.24523e-3, SolB1 = -7.37614e-3, SolB2 = -1.03410e-3, SolB3 = -8.17083e-3, SolC0 = -4.88682e-7) and pH2O coefficients are from Weiss and Price 1980 (D0 = 24.4543, D1 = -67.4509, D2 = -4.8489, D3 = -5.44e-4). The pressure correction factor Pcorr is calculated as outlined in Bittig et al. 2015 as

Pcorr = 1 + (Pcoef2 * T + Pcoef3) * P / 1000

with Pcoef2 = 0.00022 and Pcoef3 = 0.0419. Dissolved oxygen concentration [mL/L] was converted to dissolved oxygen concentration [umol/kg]:

Oxygen [umol/kg] = Oxygen [mL/L] * (44.6596 umol/mL) / (rTheta/1000)

where rth is the potential density of seawater [kg/m3] at zero pressure and the potential temperature calculated from collocated SBE 41CP CTD salinity, temperature, and pressure measurements using the pden function in the SEAWATER Matlab library (Morgan and Pender 1993). The value of 44.6596 umol/mL is derived from the molar volume of oxygen gas at standard temperature and pressure, 22.3916 L/mole (e.g., Garc?a and Gordon 1992).

See https://www.bco-dmo.org/dataset/728371 for calibration coefficients.