MODULE ad_rho_eos_mod
!
!git $Id$
!svn $Id: ad_rho_eos.F 1188 2023-08-03 19:26:47Z arango $
!================================================== Hernan G. Arango ===
!  Copyright (c) 2002-2023 The ROMS/TOMS Group       Andrew M. Moore   !
!    Licensed under a MIT/X style license                              !
!    See License_ROMS.md                                               !
!=======================================================================
!                                                                      !
!  This routine computes  "in situ" density and other associated       !
!  quantitites as a function of potential temperature,  salinity,      !
!  and pressure from a polynomial expression (Jackett and McDougall,   !
!  1992). The polynomial expression was found from fitting to 248      !
!  values  in the  oceanographic  ranges of  salinity,  potential      !
!  temperature,  and pressure.  It  assumes no pressure variation      !
!  along geopotential surfaces, that is, depth (meters; negative)      !
!  and pressure (dbar; assumed negative here) are interchangeable.     !
!                                                                      !
!  Check Values: (T=3 C, S=35.5 PSU, Z=-5000 m)                        !
!                                                                      !
!     alpha = 2.1014611551470d-04 (1/Celsius)                          !
!     beta  = 7.2575037309946d-04 (1/PSU)                              !
!     gamma = 3.9684764511766d-06 (1/Pa)                               !
!     den   = 1050.3639165364     (kg/m3)                              !
!     den1  = 1028.2845117925     (kg/m3)                              !
!     sound = 1548.8815240223     (m/s)                                !
!     bulk  = 23786.056026320     (Pa)                                 !
!                                                                      !
!  Reference:                                                          !
!                                                                      !
!  Jackett, D. R. and T. J. McDougall, 1995, Minimal Adjustment of     !
!    Hydrostatic Profiles to Achieve Static Stability, J. of Atmos.    !
!    and Oceanic Techn., vol. 12, pp. 381-389.                         !
!                                                                      !
!=======================================================================
!
      implicit none
!
      PRIVATE
      PUBLIC  :: ad_rho_eos
!
      CONTAINS
!
!***********************************************************************
      SUBROUTINE ad_rho_eos (ng, tile, model)
!***********************************************************************
!
      USE mod_param
      USE mod_parallel
      USE mod_coupling
      USE mod_grid
      USE mod_mixing
      USE mod_ocean
      USE mod_stepping
!
!  Imported variable declarations.
!
      integer, intent(in) :: ng, tile, model
!
!  Local variable declarations.
!
      character (len=*), parameter :: MyFile =                          &
     &  "ROMS/Adjoint/ad_rho_eos.F"
!
      integer :: IminS, ImaxS, JminS, JmaxS
      integer :: LBi, UBi, LBj, UBj, LBij, UBij
!
!  Set horizontal starting and ending indices for automatic private
!  storage arrays.
!
      IminS=BOUNDS(ng)%Istr(tile)-3
      ImaxS=BOUNDS(ng)%Iend(tile)+3
      JminS=BOUNDS(ng)%Jstr(tile)-3
      JmaxS=BOUNDS(ng)%Jend(tile)+3
!
!  Determine array lower and upper bounds in the I- and J-directions.
!
      LBi=BOUNDS(ng)%LBi(tile)
      UBi=BOUNDS(ng)%UBi(tile)
      LBj=BOUNDS(ng)%LBj(tile)
      UBj=BOUNDS(ng)%UBj(tile)
!
!  Set array lower and upper bounds for MIN(I,J) directions and
!  MAX(I,J) directions.
!
      LBij=BOUNDS(ng)%LBij
      UBij=BOUNDS(ng)%UBij
!
      CALL wclock_on (ng, model, 14, 72, MyFile)
      CALL ad_rho_eos_tile (ng, tile, model,                            &
     &                      LBi, UBi, LBj, UBj,                         &
     &                      IminS, ImaxS, JminS, JmaxS,                 &
     &                      nrhs(ng),                                   &
     &                      GRID(ng) % rmask,                           &
     &                      GRID(ng) % z_r,                             &
     &                      GRID(ng) % ad_z_r,                          &
     &                      OCEAN(ng) % t,                              &
     &                      OCEAN(ng) % ad_t,                           &
     &                      OCEAN(ng) % rho,                            &
     &                      OCEAN(ng) % ad_rho)
      CALL wclock_off (ng, model, 14, 114, MyFile)
!
      RETURN
      END SUBROUTINE ad_rho_eos
!
!***********************************************************************
      SUBROUTINE ad_rho_eos_tile (ng, tile, model,                      &
     &                            LBi, UBi, LBj, UBj,                   &
     &                            IminS, ImaxS, JminS, JmaxS,           &
     &                            nrhs,                                 &
     &                            rmask,                                &
     &                            z_r, ad_z_r,                          &
     &                            t, ad_t,                              &
     &                            rho, ad_rho)
!***********************************************************************
!
      USE mod_param
      USE mod_eoscoef
      USE mod_scalars
!
      USE ad_exchange_2d_mod
      USE ad_exchange_3d_mod
      USE mp_exchange_mod, ONLY : ad_mp_exchange2d, ad_mp_exchange3d
!
!  Imported variable declarations.
!
      integer, intent(in) :: ng, tile, model
      integer, intent(in) :: LBi, UBi, LBj, UBj
      integer, intent(in) :: IminS, ImaxS, JminS, JmaxS
      integer, intent(in) :: nrhs
!
      real(r8), intent(in) :: rmask(LBi:,LBj:)
      real(r8), intent(in) :: z_r(LBi:,LBj:,:)
      real(r8), intent(in) :: t(LBi:,LBj:,:,:,:)
      real(r8), intent(in) :: rho(LBi:,LBj:,:)
      real(r8), intent(inout) :: ad_z_r(LBi:,LBj:,:)
      real(r8), intent(inout) :: ad_t(LBi:,LBj:,:,:,:)
      real(r8), intent(inout) :: ad_rho(LBi:,LBj:,:)
!
!  Local variable declarations.
!
      integer :: i, ised, itrc, j, k
      real(r8) :: SedDen, Tp, Tpr10, Ts, Tt, sqrtTs
      real(r8) :: ad_SedDen, ad_Tp, ad_Tpr10, ad_Ts, ad_Tt, ad_sqrtTs
      real(r8) :: cff, cff1, cff2, cff3
      real(r8) :: ad_cff, ad_cff1, ad_cff2, ad_cff3
      real(r8) :: adfac, adfac1, adfac2, adfac3
      real(r8), dimension(0:9) :: C
      real(r8), dimension(0:9) :: ad_C
      real(r8), dimension(0:9) :: dCdT(0:9)
      real(r8), dimension(0:9) :: ad_dCdT(0:9)
      real(r8), dimension(0:9) :: d2Cd2T(0:9)
      real(r8), dimension(IminS:ImaxS,N(ng)) :: DbulkDS
      real(r8), dimension(IminS:ImaxS,N(ng)) :: DbulkDT
      real(r8), dimension(IminS:ImaxS,N(ng)) :: Dden1DS
      real(r8), dimension(IminS:ImaxS,N(ng)) :: Dden1DT
      real(r8), dimension(IminS:ImaxS,N(ng)) :: Scof
      real(r8), dimension(IminS:ImaxS,N(ng)) :: Tcof
      real(r8), dimension(IminS:ImaxS,N(ng)) :: wrk
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_DbulkDS
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_DbulkDT
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_Dden1DS
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_Dden1DT
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_Scof
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_Tcof
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_wrk
      real(r8), dimension(IminS:ImaxS,N(ng)) :: bulk
      real(r8), dimension(IminS:ImaxS,N(ng)) :: bulk0
      real(r8), dimension(IminS:ImaxS,N(ng)) :: bulk1
      real(r8), dimension(IminS:ImaxS,N(ng)) :: bulk2
      real(r8), dimension(IminS:ImaxS,N(ng)) :: den
      real(r8), dimension(IminS:ImaxS,N(ng)) :: den1
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_bulk
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_bulk0
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_bulk1
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_bulk2
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_den
      real(r8), dimension(IminS:ImaxS,N(ng)) :: ad_den1
!
!-----------------------------------------------------------------------
!  Set lower and upper tile bounds and staggered variables bounds for
!  this horizontal domain partition.  Notice that if tile=-1, it will
!  set the values for the global grid.
!-----------------------------------------------------------------------
!
      integer :: Istr, IstrB, IstrP, IstrR, IstrT, IstrM, IstrU
      integer :: Iend, IendB, IendP, IendR, IendT
      integer :: Jstr, JstrB, JstrP, JstrR, JstrT, JstrM, JstrV
      integer :: Jend, JendB, JendP, JendR, JendT
      integer :: Istrm3, Istrm2, Istrm1, IstrUm2, IstrUm1
      integer :: Iendp1, Iendp2, Iendp2i, Iendp3
      integer :: Jstrm3, Jstrm2, Jstrm1, JstrVm2, JstrVm1
      integer :: Jendp1, Jendp2, Jendp2i, Jendp3
!
      Istr   =BOUNDS(ng) % Istr   (tile)
      IstrB  =BOUNDS(ng) % IstrB  (tile)
      IstrM  =BOUNDS(ng) % IstrM  (tile)
      IstrP  =BOUNDS(ng) % IstrP  (tile)
      IstrR  =BOUNDS(ng) % IstrR  (tile)
      IstrT  =BOUNDS(ng) % IstrT  (tile)
      IstrU  =BOUNDS(ng) % IstrU  (tile)
      Iend   =BOUNDS(ng) % Iend   (tile)
      IendB  =BOUNDS(ng) % IendB  (tile)
      IendP  =BOUNDS(ng) % IendP  (tile)
      IendR  =BOUNDS(ng) % IendR  (tile)
      IendT  =BOUNDS(ng) % IendT  (tile)
      Jstr   =BOUNDS(ng) % Jstr   (tile)
      JstrB  =BOUNDS(ng) % JstrB  (tile)
      JstrM  =BOUNDS(ng) % JstrM  (tile)
      JstrP  =BOUNDS(ng) % JstrP  (tile)
      JstrR  =BOUNDS(ng) % JstrR  (tile)
      JstrT  =BOUNDS(ng) % JstrT  (tile)
      JstrV  =BOUNDS(ng) % JstrV  (tile)
      Jend   =BOUNDS(ng) % Jend   (tile)
      JendB  =BOUNDS(ng) % JendB  (tile)
      JendP  =BOUNDS(ng) % JendP  (tile)
      JendR  =BOUNDS(ng) % JendR  (tile)
      JendT  =BOUNDS(ng) % JendT  (tile)
!
      Istrm3 =BOUNDS(ng) % Istrm3 (tile)            ! Istr-3
      Istrm2 =BOUNDS(ng) % Istrm2 (tile)            ! Istr-2
      Istrm1 =BOUNDS(ng) % Istrm1 (tile)            ! Istr-1
      IstrUm2=BOUNDS(ng) % IstrUm2(tile)            ! IstrU-2
      IstrUm1=BOUNDS(ng) % IstrUm1(tile)            ! IstrU-1
      Iendp1 =BOUNDS(ng) % Iendp1 (tile)            ! Iend+1
      Iendp2 =BOUNDS(ng) % Iendp2 (tile)            ! Iend+2
      Iendp2i=BOUNDS(ng) % Iendp2i(tile)            ! Iend+2 interior
      Iendp3 =BOUNDS(ng) % Iendp3 (tile)            ! Iend+3
      Jstrm3 =BOUNDS(ng) % Jstrm3 (tile)            ! Jstr-3
      Jstrm2 =BOUNDS(ng) % Jstrm2 (tile)            ! Jstr-2
      Jstrm1 =BOUNDS(ng) % Jstrm1 (tile)            ! Jstr-1
      JstrVm2=BOUNDS(ng) % JstrVm2(tile)            ! JstrV-2
      JstrVm1=BOUNDS(ng) % JstrVm1(tile)            ! JstrV-1
      Jendp1 =BOUNDS(ng) % Jendp1 (tile)            ! Jend+1
      Jendp2 =BOUNDS(ng) % Jendp2 (tile)            ! Jend+2
      Jendp2i=BOUNDS(ng) % Jendp2i(tile)            ! Jend+2 interior
      Jendp3 =BOUNDS(ng) % Jendp3 (tile)            ! Jend+3
!
!-------------------------------------------------------------------------
!  Initialize adjoint private variables.
!-------------------------------------------------------------------------
!
      ad_Tt=0.0_r8
      ad_Ts=0.0_r8
      ad_Tp=0.0_r8
      ad_Tpr10=0.0_r8
      ad_sqrtTs=0.0_r8
      ad_cff=0.0_r8
      ad_cff1=0.0_r8
      ad_cff2=0.0_r8
      ad_cff3=0.0_r8
      ad_C=0.0_r8
      ad_dCdT=0.0_r8
      DO k=1,N(ng)
        DO i=IminS,ImaxS
          ad_DbulkDS(i,k)=0.0_r8
          ad_DbulkDT(i,k)=0.0_r8
          ad_Dden1DS(i,k)=0.0_r8
          ad_Dden1DT(i,k)=0.0_r8
          ad_Scof(i,k)=0.0_r8
          ad_Tcof(i,k)=0.0_r8
          ad_wrk(i,k)=0.0_r8
          ad_bulk(i,k)=0.0_r8
          ad_bulk0(i,k)=0.0_r8
          ad_bulk1(i,k)=0.0_r8
          ad_bulk2(i,k)=0.0_r8
          ad_den(i,k)=0.0_r8
          ad_den1(i,k)=0.0_r8
        END DO
      END DO
!
!=======================================================================
!  Adjoint  nonlinear equation of state.  Notice that this equation
!  of state is only valid for potential temperature range of -2C to 40C
!  and a salinity range of 0 PSU to 42 PSU.
!=======================================================================
!
!-----------------------------------------------------------------------
!  Exchange boundary data.
!-----------------------------------------------------------------------
!
!^    CALL mp_exchange3d (ng, tile, model, 1,                           &
!^   &                    LBi, UBi, LBj, UBj, 1, N(ng),                 &
!^   &                    NghostPoints,                                 &
!^   &                    EWperiodic(ng), NSperiodic(ng),               &
!^   &                    tl_rho)
!^
      CALL ad_mp_exchange3d (ng, tile, model, 1,                        &
     &                       LBi, UBi, LBj, UBj, 1, N(ng),              &
     &                       NghostPoints,                              &
     &                       EWperiodic(ng), NSperiodic(ng),            &
     &                       ad_rho)
!
      IF (EWperiodic(ng).or.NSperiodic(ng)) THEN
!^      CALL exchange_r3d_tile (ng, tile,                               &
!^   &                          LBi, UBi, LBj, UBj, 1, N(ng),           &
!^   &                          tl_rho)
!^
        CALL ad_exchange_r3d_tile (ng, tile,                            &
     &                             LBi, UBi, LBj, UBj, 1, N(ng),        &
     &                             ad_rho)
      END IF
!
!-----------------------------------------------------------------------
!  Compute BASIC STATE related variables.
!-----------------------------------------------------------------------
!
      DO j=JstrT,JendT
        DO k=1,N(ng)
          DO i=IstrT,IendT
            Tt=MAX(-2.0_r8,t(i,j,k,nrhs,itemp))
            Ts=MAX(0.0_r8,t(i,j,k,nrhs,isalt))
            sqrtTs=SQRT(Ts)
            Tp=z_r(i,j,k)
            Tpr10=0.1_r8*Tp
!
!  Compute local nonlinear equation of state coefficients and their
!  derivatives when appropriate.
!
            C(0)=Q00+Tt*(Q01+Tt*(Q02+Tt*(Q03+Tt*(Q04+Tt*Q05))))
            C(1)=U00+Tt*(U01+Tt*(U02+Tt*(U03+Tt*U04)))
            C(2)=V00+Tt*(V01+Tt*V02)
            C(3)=A00+Tt*(A01+Tt*(A02+Tt*(A03+Tt*A04)))
            C(4)=B00+Tt*(B01+Tt*(B02+Tt*B03))
            C(5)=D00+Tt*(D01+Tt*D02)
            C(6)=E00+Tt*(E01+Tt*(E02+Tt*E03))
            C(7)=F00+Tt*(F01+Tt*F02)
            C(8)=G01+Tt*(G02+Tt*G03)
            C(9)=H00+Tt*(H01+Tt*H02)
!
            dCdT(0)=Q01+Tt*(2.0_r8*Q02+Tt*(3.0_r8*Q03+Tt*(4.0_r8*Q04+   &
     &                      Tt*5.0_r8*Q05)))
            dCdT(1)=U01+Tt*(2.0_r8*U02+Tt*(3.0_r8*U03+Tt*4.0_r8*U04))
            dCdT(2)=V01+Tt*2.0_r8*V02
            dCdT(3)=A01+Tt*(2.0_r8*A02+Tt*(3.0_r8*A03+Tt*4.0_r8*A04))
            dCdT(4)=B01+Tt*(2.0_r8*B02+Tt*3.0_r8*B03)
            dCdT(5)=D01+Tt*2.0_r8*D02
            dCdT(6)=E01+Tt*(2.0_r8*E02+Tt*3.0_r8*E03)
            dCdT(7)=F01+Tt*2.0_r8*F02
            dCdT(8)=G02+Tt*2.0_r8*G03
            dCdT(9)=H01+Tt*2.0_r8*H02
!
            d2Cd2T(0)=2.0_r8*Q02+Tt*(6.0_r8*Q03+Tt*(12.0_r8*Q04+        &
     &                               Tt*20.0_r8*Q05))
            d2Cd2T(1)=2.0_r8*U02+Tt*(6.0_r8*U03+Tt*12.0_r8*U04)
            d2Cd2T(2)=2.0_r8*V02
            d2Cd2T(3)=2.0_r8*A02+Tt*(6.0_r8*A03+Tt*12.0_r8*A04)
            d2Cd2T(4)=2.0_r8*B02+Tt*6.0_r8*B03
            d2Cd2T(5)=2.0_r8*D02
            d2Cd2T(6)=2.0_r8*E02+Tt*6.0_r8*E03
            d2Cd2T(7)=2.0_r8*F02
            d2Cd2T(8)=2.0_r8*G03
            d2Cd2T(9)=2.0_r8*H02
!
!  Compute BASIC STATE density (kg/m3) at standard one atmosphere
!  pressure.
!
            den1(i,k)=C(0)+Ts*(C(1)+sqrtTs*C(2)+Ts*W00)
!
!  Compute BASIC STATE d(den1)/d(S) and d(den1)/d(T) derivatives used
!  in the computation of thermal expansion and saline contraction
!  coefficients.
!
            Dden1DS(i,k)=C(1)+1.5_r8*C(2)*sqrtTs+2.0_r8*W00*Ts
            Dden1DT(i,k)=dCdT(0)+Ts*(dCdT(1)+sqrtTs*dCdT(2))
!
!  Compute BASIC STATE secant bulk modulus.
!
            bulk0(i,k)=C(3)+Ts*(C(4)+sqrtTs*C(5))
            bulk1(i,k)=C(6)+Ts*(C(7)+sqrtTs*G00)
            bulk2(i,k)=C(8)+Ts*C(9)
            bulk (i,k)=bulk0(i,k)-Tp*(bulk1(i,k)-Tp*bulk2(i,k))
!
!  Compute local "in situ" density anomaly (kg/m3 - 1000).  The (i,k)
!  DO-loop is closed here because of the adjoint to facilitate vertical
!  integrals of the BASIC STATE.
!
            cff=1.0_r8/(bulk(i,k)+Tpr10)
            den(i,k)=den1(i,k)*bulk(i,k)*cff
            den(i,k)=den(i,k)-1000.0_r8
            den(i,k)=den(i,k)*rmask(i,j)
          END DO
        END DO
!
!-----------------------------------------------------------------------
!  Load adjoint "in situ" density anomaly (kg/m3 - 1000) and adjoint
!  potential density anomaly (kg/m3 - 1000) referenced to the surface
!  into global arrays.
!-----------------------------------------------------------------------
!
        DO k=1,N(ng)
          DO i=IstrT,IendT
!^          tl_rho(i,j,k)=tl_den(i,k)
!^
            ad_den(i,k)=ad_den(i,k)+ad_rho(i,j,k)
            ad_rho(i,j,k)=0.0_r8
          END DO
        END DO
!
!-----------------------------------------------------------------------
!  Adjoint nonlinear equation of state.
!-----------------------------------------------------------------------
!
        DO k=1,N(ng)
          DO i=IstrT,IendT
!
!  Check temperature and salinity minimum valid values. Assign depth
!  to the pressure.
!
            Tt=MAX(-2.0_r8,t(i,j,k,nrhs,itemp))
            Ts=MAX(0.0_r8,t(i,j,k,nrhs,isalt))
            sqrtTs=SQRT(Ts)
            Tp=z_r(i,j,k)
            Tpr10=0.1_r8*Tp
!
!  Compute local nonlinear equation of state coefficients and their
!  derivatives when appropriate.  These coefficients can be stored
!  in slab (i,k) arrays to avoid recompute them twice. However, the
!  equivalent of 50 slabs arrays are required.
!
            C(0)=Q00+Tt*(Q01+Tt*(Q02+Tt*(Q03+Tt*(Q04+Tt*Q05))))
            C(1)=U00+Tt*(U01+Tt*(U02+Tt*(U03+Tt*U04)))
            C(2)=V00+Tt*(V01+Tt*V02)
            C(3)=A00+Tt*(A01+Tt*(A02+Tt*(A03+Tt*A04)))
            C(4)=B00+Tt*(B01+Tt*(B02+Tt*B03))
            C(5)=D00+Tt*(D01+Tt*D02)
            C(6)=E00+Tt*(E01+Tt*(E02+Tt*E03))
            C(7)=F00+Tt*(F01+Tt*F02)
            C(8)=G01+Tt*(G02+Tt*G03)
            C(9)=H00+Tt*(H01+Tt*H02)
!
            dCdT(0)=Q01+Tt*(2.0_r8*Q02+Tt*(3.0_r8*Q03+Tt*(4.0_r8*Q04+   &
     &                      Tt*5.0_r8*Q05)))
            dCdT(1)=U01+Tt*(2.0_r8*U02+Tt*(3.0_r8*U03+Tt*4.0_r8*U04))
            dCdT(2)=V01+Tt*2.0_r8*V02
            dCdT(3)=A01+Tt*(2.0_r8*A02+Tt*(3.0_r8*A03+Tt*4.0_r8*A04))
            dCdT(4)=B01+Tt*(2.0_r8*B02+Tt*3.0_r8*B03)
            dCdT(5)=D01+Tt*2.0_r8*D02
            dCdT(6)=E01+Tt*(2.0_r8*E02+Tt*3.0_r8*E03)
            dCdT(7)=F01+Tt*2.0_r8*F02
            dCdT(8)=G02+Tt*2.0_r8*G03
            dCdT(9)=H01+Tt*2.0_r8*H02
!
            d2Cd2T(0)=2.0_r8*Q02+Tt*(6.0_r8*Q03+Tt*(12.0_r8*Q04+        &
     &                               Tt*20.0_r8*Q05))
            d2Cd2T(1)=2.0_r8*U02+Tt*(6.0_r8*U03+Tt*12.0_r8*U04)
            d2Cd2T(2)=2.0_r8*V02
            d2Cd2T(3)=2.0_r8*A02+Tt*(6.0_r8*A03+Tt*12.0_r8*A04)
            d2Cd2T(4)=2.0_r8*B02+Tt*6.0_r8*B03
            d2Cd2T(5)=2.0_r8*D02
            d2Cd2T(6)=2.0_r8*E02+Tt*6.0_r8*E03
            d2Cd2T(7)=2.0_r8*F02
            d2Cd2T(8)=2.0_r8*G03
            d2Cd2T(9)=2.0_r8*H02
!
!-----------------------------------------------------------------------
!  Compute local adjoint "in situ" density anomaly (kg/m3 - 1000).
!-----------------------------------------------------------------------
!
            cff=1.0_r8/(bulk(i,k)+Tpr10)
!^          tl_den(i,k)=tl_den(i,k)*rmask(i,j)
!^
            ad_den(i,k)=ad_den(i,k)*rmask(i,j)
!^          tl_den(i,k)=tl_den1(i,k)*bulk(i,k)*cff+                     &
!^   &                  den1(i,k)*(tl_bulk(i,k)*cff+                    &
!^   &                             bulk(i,k)*tl_cff)
!^
            adfac1=den1(i,k)*ad_den(i,k)
            ad_den1(i,k)=ad_den1(i,k)+bulk(i,k)*cff*ad_den(i,k)
            ad_bulk(i,k)=ad_bulk(i,k)+cff*adfac1
            ad_cff=ad_cff+bulk(i,k)*adfac1
            ad_den(i,k)=0.0_r8
!^          tl_cff=-cff*cff*(tl_bulk(i,k)+tl_Tpr10)
!^
            adfac=-cff*cff*ad_cff
            ad_bulk(i,k)=ad_bulk(i,k)+adfac
            ad_Tpr10=ad_Tpr10+adfac
            ad_cff=0.0_r8
!
!  Compute adjoint secant bulk modulus.
!
!^          tl_bulk (i,k)=tl_bulk0(i,k)-                                &
!^   &                     tl_Tp*(bulk1(i,k)-Tp*bulk2(i,k))-            &
!^   &                     Tp*(tl_bulk1(i,k)-                           &
!^   &                         tl_Tp*bulk2(i,k)-                        &
!^   &                         Tp*tl_bulk2(i,k))
!^
            adfac=Tp*ad_bulk(i,k)
            ad_bulk0(i,k)=ad_bulk0(i,k)+ad_bulk(i,k)
            ad_bulk1(i,k)=ad_bulk1(i,k)-adfac
            ad_bulk2(i,k)=ad_bulk2(i,k)+adfac*Tp
            ad_Tp=ad_Tp-                                                &
     &            ad_bulk(i,k)*(bulk1(i,k)-Tp*bulk2(i,k))+              &
     &            adfac*bulk2(i,k)
            ad_bulk(i,k)=0.0_r8
!^          tl_bulk2(i,k)=tl_C(8)+tl_Ts*C(9)+Ts*tl_C(9)
!^
            ad_C(8)=ad_C(8)+ad_bulk2(i,k)
            ad_C(9)=ad_C(9)+Ts*ad_bulk2(i,k)
            ad_Ts=ad_Ts+ad_bulk2(i,k)*C(9)
            ad_bulk2(i,k)=0.0_r8
!^          tl_bulk1(i,k)=tl_C(6)+                                      &
!^   &                    tl_Ts*(C(7)+sqrtTs*G00)+                      &
!^   &                    Ts*(tl_C(7)+tl_sqrtTs*G00)
!^
            adfac=Ts*ad_bulk1(i,k)
            ad_C(6)=ad_C(6)+ad_bulk1(i,k)
            ad_C(7)=ad_C(7)+adfac
            ad_Ts=ad_Ts+ad_bulk1(i,k)*(C(7)+sqrtTs*G00)
            ad_sqrtTs=ad_sqrtTs+adfac*G00
            ad_bulk1(i,k)=0.0_r8
!^          tl_bulk0(i,k)=tl_C(3)+                                      &
!^   &                    tl_Ts*(C(4)+sqrtTs*C(5))+                     &
!^   &                    Ts*(tl_C(4)+tl_sqrtTs*C(5)+                   &
!^   &                        sqrtTs*tl_C(5))
!^
            adfac=Ts*ad_bulk0(i,k)
            ad_C(3)=ad_C(3)+ad_bulk0(i,k)
            ad_C(4)=ad_C(4)+adfac
            ad_C(5)=ad_C(5)+sqrtTs*adfac
            ad_Ts=ad_Ts+ad_bulk0(i,k)*(C(4)+sqrtTs*C(5))
            ad_sqrtTs=ad_sqrtTs+C(5)*adfac
            ad_bulk0(i,k)=0.0_r8
!^          tl_C(9)=tl_Tt*dCdT(9)
!^          tl_C(8)=tl_Tt*dCdT(8)
!^          tl_C(7)=tl_Tt*dCdT(7)
!^          tl_C(6)=tl_Tt*dCdT(6)
!^          tl_C(5)=tl_Tt*dCdT(5)
!^          tl_C(4)=tl_Tt*dCdT(4)
!^          tl_C(3)=tl_Tt*dCdT(3)
!^
            ad_Tt=ad_Tt+ad_C(9)*dCdT(9)+                                &
     &                  ad_C(8)*dCdT(8)+                                &
     &                  ad_C(7)*dCdT(7)+                                &
     &                  ad_C(6)*dCdT(6)+                                &
     &                  ad_C(5)*dCdT(5)+                                &
     &                  ad_C(4)*dCdT(4)+                                &
     &                  ad_C(3)*dCdT(3)
            ad_C(9)=0.0_r8
            ad_C(8)=0.0_r8
            ad_C(7)=0.0_r8
            ad_C(6)=0.0_r8
            ad_C(5)=0.0_r8
            ad_C(4)=0.0_r8
            ad_C(3)=0.0_r8
!
!  Compute d(den1)/d(S) and d(den1)/d(T) derivatives used in the
!  computation of thermal expansion and saline contraction
!  coefficients.
!
!^          tl_Dden1DT(i,k)=tl_dCdT(0)+                                 &
!^   &                      tl_Ts*(dCdT(1)+sqrtTs*dCdT(2))+             &
!^   &                      Ts*(tl_dCdT(1)+tl_sqrtTs*dCdT(2)+           &
!^   &                                     sqrtTs*tl_dCdT(2))
!^
            adfac1=Ts*ad_Dden1DT(i,k)
            ad_dCdT(0)=ad_dCdT(0)+ad_Dden1DT(i,k)
            ad_dCdT(1)=ad_dCdT(1)+adfac1
            ad_dCdT(2)=ad_dCdT(2)+sqrtTs*adfac1
            ad_Ts=ad_Ts+                                                &
     &            (dCdT(1)+sqrtTs*dCdT(2))*ad_Dden1DT(i,k)
            ad_sqrtTs=ad_sqrtTs+dCdT(2)*adfac1
            ad_Dden1DT(i,k)=0.0_r8
!^          tl_Dden1DS(i,k)=tl_C(1)+                                    &
!^   &                      1.5_r8*(tl_C(2)*sqrtTs+                     &
!^   &                              C(2)*tl_sqrtTs)+                    &
!^   &                      2.0_r8*W00*tl_Ts
!^
            adfac1=1.5_r8*ad_Dden1DS(i,k)
            ad_C(1)=ad_C(1)+ad_Dden1DS(i,k)
            ad_C(2)=ad_C(2)+sqrtTs*adfac1
            ad_Ts=ad_Ts+2.0_r8*W00*ad_Dden1DS(i,k)
            ad_sqrtTs=ad_sqrtTs+C(2)*adfac1
            ad_Dden1DS(i,k)=0.0_r8
!^          tl_dCdT(2)=tl_Tt*d2Cd2T(2)
!^          tl_dCdT(1)=tl_Tt*d2Cd2T(1)
!^          tl_dCdT(0)=tl_Tt*d2Cd2T(0)
!^
            ad_Tt=ad_Tt+d2Cd2T(2)*ad_dCdT(2)+                           &
     &                  d2Cd2T(1)*ad_dCdT(1)+                           &
     &                  d2Cd2T(0)*ad_dCdT(0)
            ad_dCdT(2)=0.0_r8
            ad_dCdT(1)=0.0_r8
            ad_dCdT(0)=0.0_r8
!
!  Compute basic state and tangent linear density (kg/m3) at standard
!  one atmosphere pressure.
!
!^          tl_den1(i,k)=tl_C(0)+                                       &
!^   &                   tl_Ts*(C(1)+sqrtTs*C(2)+Ts*W00)+               &
!^   &                   Ts*(tl_C(1)+tl_sqrtTs*C(2)+                    &
!^   &                       sqrtTs*tl_C(2)+tl_Ts*W00)
!^
            adfac=Ts*ad_den1(i,k)
            ad_C(0)=ad_C(0)+ad_den1(i,k)
            ad_C(1)=ad_C(1)+adfac
            ad_C(2)=ad_C(2)+adfac*sqrtTs
            ad_Ts=ad_Ts+                                                &
     &            ad_den1(i,k)*(C(1)+sqrtTs*C(2)+Ts*W00)+               &
     &            adfac*W00
            ad_sqrtTs=ad_sqrtTs+adfac*C(2)
            ad_den1(i,k)=0.0_r8
!^          tl_C(2)=tl_Tt*dCdT(2)
!^          tl_C(1)=tl_Tt*dCdT(1)
!^          tl_C(0)=tl_Tt*dCdT(0)
!^
            ad_Tt=ad_Tt+ad_C(2)*dCdT(2)+                                &
     &                  ad_C(1)*dCdT(1)+                                &
     &                  ad_C(0)*dCdT(0)
            ad_C(2)=0.0_r8
            ad_C(1)=0.0_r8
            ad_C(0)=0.0_r8
!
!  Check temperature and salinity minimum valid values. Assign depth
!  to the pressure.
!
!^          tl_Tpr10=0.1_r8*tl_Tp
!^
            ad_Tp=ad_Tp+0.1_r8*ad_Tpr10
            ad_Tpr10=0.0_r8
!^          tl_Tp=tl_z_r(i,j,k)
!^
            ad_z_r(i,j,k)=ad_z_r(i,j,k)+ad_Tp
            ad_Tp=0.0_r8
            IF (Ts.ne.0.0_r8) THEN
!^            tl_sqrtTs=0.5_r8*tl_Ts/SQRT(Ts)
!^
              ad_Ts=ad_Ts+0.5_r8*ad_sqrtTs/SQRT(Ts)
              ad_sqrtTs=0.0_r8
            ELSE
!^            tl_sqrtTs=0.0_r8
!^
              ad_sqrtTs=0.0_r8
            END IF
!^          tl_Ts=(0.5_r8-SIGN(0.5_r8,-t(i,j,k,nrhs,isalt)))*
!^   &            tl_t(i,j,k,nrhs,isalt)
!^
            ad_t(i,j,k,nrhs,isalt)=ad_t(i,j,k,nrhs,isalt)+              &
     &                             (0.5_r8-SIGN(0.5_r8,                 &
     &                                          -t(i,j,k,nrhs,isalt)))* &
     &                             ad_Ts
            ad_Ts=0.0_r8
!^          tl_Tt=(0.5_r8-SIGN(0.5_r8,-2.0_r8-t(i,j,k,nrhs,itemp)))*
!^   &            tl_t(i,j,k,nrhs,itemp)
!^
            ad_t(i,j,k,nrhs,itemp)=ad_t(i,j,k,nrhs,itemp)+              &
     &                             (0.5_r8-SIGN(0.5_r8,-2.0_r8-         &
     &                                          t(i,j,k,nrhs,itemp)))*  &
     &                             ad_Tt
            ad_Tt=0.0_r8
          END DO
        END DO
      END DO
!
      RETURN
      END SUBROUTINE ad_rho_eos_tile
      END MODULE ad_rho_eos_mod