MODULE trcstp
   !!======================================================================
   !!                       ***  MODULE trcstp  ***
   !! Time-stepping    : time loop of opa for passive tracer
   !!======================================================================
#if defined key_top
   !!----------------------------------------------------------------------
   !!   trc_stp      : passive tracer system time-stepping
   !!----------------------------------------------------------------------
   !! * Modules used
   USE oce_trc          ! ocean dynamics and active tracers variables
   USE trc
   USE trctrp           ! passive tracers transport
   USE trcsms           ! passive tracers sources and sinks
   USE prtctl_trc       ! Print control for debbuging
   USE trcdia
   USE trcwri
   USE trcrst
   USE trdmod_trc_oce
   USE trdmld_trc
   USE iom
   USE in_out_manager

   IMPLICIT NONE
   PRIVATE

   !! * Routine accessibility
   PUBLIC trc_stp           ! called by step
   !!----------------------------------------------------------------------
   !!   TOP 1.0 , LOCEAN-IPSL (2005) 
   !! $Id: trcstp.F90 1285 2009-02-03 13:38:51Z cetlod $ 
   !! This software is governed by the CeCILL licence see modipsl/doc/NEMO_CeCILL.txt 
   !!----------------------------------------------------------------------

CONTAINS

   SUBROUTINE trc_stp( kt )
      !!-------------------------------------------------------------------
      !!                     ***  ROUTINE trc_stp  ***
      !!                      
      !! ** Purpose : Time loop of opa for passive tracer
      !! 
      !! ** Method  : 
      !!              Compute the passive tracers trends 
      !!              Update the passive tracers
      !!
      !! History :
      !!   9.0  !  04-03  (C. Ethe)  Original
      !!-------------------------------------------------------------------
      !! * Arguments
      INTEGER, INTENT( in ) ::  kt  ! ocean time-step index
      CHARACTER (len=25)    ::  charout

      ! this ROUTINE is called only every nn_dttrc time step
      IF( MOD( kt , nn_dttrc ) /= 0 ) RETURN

      IF(ln_ctl) THEN
         WRITE(charout,FMT="('kt =', I4,'  d/m/y =',I2,I2,I4)") kt, nday, nmonth, nyear
         CALL prt_ctl_trc_info(charout)
      ENDIF

      tra(:,:,:,:) = 0.

      IF( kt == nittrc000 .AND. lk_trdmld_trc  )  &
         &                   CALL trd_mld_trc_init        ! trends: Mixed-layer
                             CALL trc_rst_opn( kt )       ! Open tracer restart file 
                             CALL trc_sms( kt )           ! tracers: sink and source
                             CALL trc_trp( kt )           ! transport of passive tracers
      IF( kt == nittrc000 )  CALL iom_close( numrtr )     ! close input  passive tracers restart file
      IF( lrst_trc )         CALL trc_rst_wri( kt )       ! write tracer restart file
      IF( lk_iomput ) THEN
                             CALL trc_wri( kt )           ! output of passive tracers
      ELSE
                             CALL trc_dia( kt )   ! diagnostics
      ENDIF
      IF( lk_trdmld_trc  )   CALL trd_mld_trc( kt )     ! trends: Mixed-layer

   END SUBROUTINE trc_stp

#else
   !!----------------------------------------------------------------------
   !!   Default key                                     NO passive tracers
   !!----------------------------------------------------------------------
CONTAINS
   SUBROUTINE trc_stp( kt )        ! Empty routine
      INTEGER, INTENT(in) :: kt
      WRITE(*,*) 'trc_stp: You should not have seen this print! error?', kt
   END SUBROUTINE trc_stp
#endif

   !!======================================================================
END MODULE trcstp