anchor.diff:    REAL(kind=r4) :: ssal, salk, sdic, ssil, sphos
   
     REAL(kind=r4) :: tempot, tempis68, tempot68
  -  REAL(kind=r8) :: dfCO2, dpCO2
  -  REAL(kind=r8) :: drho
  -  REAL(kind=r8) :: invtk,dlogtk
  +  REAL(kind=r8) :: dtempot, drho
   
     REAL(kind=r8) :: K0, K1, K2, Kb, Kw, Ks, Kf, Kspc
     REAL(kind=r8) :: Kspa, K1p, K2p, K3p, Ksi
  
positive.code:   USE mp80
    USE mrho
    USE msw_temp
    USE mphsolvers
  
    IMPLICIT NONE
  
  
negative.code:   !       -> 'pf' means use Perez & Fraga (1987) formulation for Kf (recommended by Dickson et al., 2007)
    !               **** BUT Valid for  9 < T < 33°C and 10 < S < 40.
    !       -> 'dg' means use Dickson & Riley (1979) formulation for Kf (recommended by Dickson & Goyet, 1994)
    !     -----------
    !     optGAS: choose in situ vs. potential fCO2 and pCO2
    !     ---------
    !       PRESSURE corrections for K0 and the fugacity coefficient (Cf) 
    !       -> 'Pzero'   = 'zero order' fCO2 and pCO2 (typical approach, which is flawed)
    !                      considers in situ T & only atm pressure (hydrostatic=0)
    !       -> 'Ppot'    = 'potential' fCO2 and pCO2 (water parcel brought adiabatically to the surface)
    !                      considers potential T & only atm pressure (hydrostatic press = 0)
    !       -> 'Pinsitu' = 'in situ' fCO2 and pCO2 (accounts for huge effects of pressure)
    !                      considers in situ T & total pressure (atm + hydrostatic)
    !     ---------
  
    !     OUTPUT variables:
    !     =================
    !     ph   = pH on total scale
    !     pco2 = CO2 partial pressure (uatm)
    !     fco2 = CO2 fugacity (uatm)
    !     co2  = aqueous CO2 concentration in [mol/kg] or [mol/m^3] depending on optCON
    !     hco3 = bicarbonate (HCO3-) concentration in [mol/kg] or [mol/m^3] depending on optCON
    !     co3  = carbonate (CO3--) concentration in [mol/kg] or [mol/m^3] depending on optCON
    !     OmegaA = Omega for aragonite, i.e., the aragonite saturation state
    !     OmegaC = Omega for calcite, i.e., the   calcite saturation state
    !     BetaD = Revelle factor   dpCO2/pCO2 / dDIC/DIC
  