anchor.diff:  
     !     INPUT variables:
     !     ================
  +  !     Patm    = atmospheric pressure [atm]
     !     depth   = depth [m]     (with optP='m', i.e., for a z-coordinate model vertical grid is depth, not pressure)
     !             = pressure [db] (with optP='db')
     !     lat     = latitude [degrees] (needed to convert depth to pressure, i.e., when optP='m')
  
positive.code:         invtk=1.0d0/tk
          dlogtk=LOG(tk)
  
  !       Pressure effect (prb is in bars)
          prb = DBLE(p(i)) / 10.0d0
  
  
negative.code: !!    total alkalinity (ALK), dissolved inorganic carbon (DIC),
  !!    silica and phosphate concentrations (all 1-D arrays)
  SUBROUTINE vars(ph, pco2, fco2, co2, hco3, co3, OmegaA, OmegaC, BetaD, rhoSW, p, tempis,  &
                  temp, sal, alk, dic, sil, phos, Patm, depth, lat, N,                          &
                  optCON, optT, optP, optB, optK1K2, optKf                                  )
  
    !   Purpose:
  