Function AOU(S, T, O2)

'AOU computes the apparant oxygen utilization from the difference
'    between measured O2 concentration and the expected O2 conc
'    for seawater saturated with air at the sea surface.

' Source:  The solubility of nitrogen, oxygen and argon in water and
'         seawater - Weiss (1970) Deep Sea Research V17(4): 721-735.
 
' Molar volume of oxygen at STP obtained from NIST website on the
'         thermophysical properties of fluid systems:
'
'          http://webbook.nist.gov/chemistry/fluid/
'
'
' CALCULATE AOU BY DIFFERENCE:
 
'         AOU (umol/kg) = sat O2 (umol/kg) - obs o2 (umol/kg).
'
'
' Input:       S = Salinity (pss-78)
'              T = Potential Temp (deg C)
'              O2 = Meas'd Oxygen Conc (umol/kg)
'
' Output:      Apparant Oxygen Utilization (umol/kg).
'
'                        AOU = aou(S,T,O2).

' DEFINE CONSTANTS, ETC FOR SATURATION CALCULATION

'    The constants -177.7888, etc., are used for units of ml O2/kg.

  T1 = (T + 273.15) / 100

  OSAT = -177.7888 + 255.5907 / T1 + 146.4813 * log(T1) - 22.2040 * T1
  OSAT = OSAT + S * (-0.037362 + T1 * (0.016504 - 0.0020564 * T1))
  OSAT = exp(OSAT)


' CONVERT FROM ML/KG TO UM/KG

  OSAT = OSAT * 1000 / 22.392


' CALCULATE AOU

  AOU = OSAT - O2

End Function