C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/model/src/timestep_tracer.F,v 1.17 2011/12/13 15:12:53 mlosch Exp $
C $Name:  $

#include "PACKAGES_CONFIG.h"
#include "CPP_OPTIONS.h"

CBOP
C     !ROUTINE: TIMESTEP_TRACER
C     !INTERFACE:
      SUBROUTINE TIMESTEP_TRACER(
     I                     bi, bj, k, deltaTloc,
     I                     tracer,
     U                     gTracer,
     I                     myIter, myThid )
C     !DESCRIPTION: \bv
C     *==========================================================*
C     | S/R TIMESTEP_TRACER
C     | o Step model tracer field forward in time
C     *==========================================================*
C     \ev

C     !USES:
      IMPLICIT NONE
C     == Global variables ===
#include "SIZE.h"
#include "EEPARAMS.h"
#include "PARAMS.h"
#include "GRID.h"

C     !INPUT/OUTPUT PARAMETERS:
C     == Routine Arguments ==
      INTEGER bi, bj, k
      _RL     deltaTloc
      _RL  tracer (1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
      _RL  gTracer(1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
      INTEGER myIter, myThid

C     !LOCAL VARIABLES:
C     == Local variables ==
      INTEGER i,j
CEOP

C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|

C-    Step tracer forward in time and store provisional value in gTracer array
      DO j=1-Oly,sNy+Oly
       DO i=1-Olx,sNx+Olx
         gTracer(i,j,k,bi,bj)=tracer(i,j,k,bi,bj)
     &            +deltaTloc*gTracer(i,j,k,bi,bj)
#ifdef ALLOW_OBCS
CML   For the Stevens open boundary conditions, we need to step forward
CML   the tracer even on the boundary in order to include surface
CML   forcing and (vertical) diffusion contributions. For other cases
CML   this mask was meant to avoid unrealistic values on the open boundaries.
CML   Lets hope that we can live without this safety net.
C    &                      *maskInC(i,j,bi,bj)
#endif
       ENDDO
      ENDDO

      RETURN
      END