subroutine overtn(dtime,dyear)
      use mod_xc         ! HYCOM communication interface
      use mod_cb_arrays  ! HYCOM saved arrays
      implicit none
!
      real*8  dtime,dyear
!
! --- diagnose meridional heat flux in basin model
!
      real*8     dsmall
      parameter (dsmall=0.001d0)
!
      integer i,j,k,l,noo
!
      logical lfirst
      save    lfirst
      data    lfirst / .true. /
!
#if defined(RELO)
      real*8, save, allocatable, dimension(:,:) :: &
             zonavt,zonavf
      real*8, save, allocatable, dimension(:) :: &
             anum,heatf,heatfl,hfxzon
#else
      real*8, save, dimension(jtdm,kdm) :: &
             zonavt,zonavf
      real*8, save, dimension(jtdm) :: &
             anum,heatf,heatfl,hfxzon
#endif
!
#if defined(RELO)
      if     (.not.allocated(zonavt)) then
        allocate( &
                      zonavt(jtdm,kdm), &
                      zonavf(jtdm,kdm) )
        call mem_stat_add( 2*jtdm*kdm )
                      zonavt = r_init
                      zonavf = r_init
        allocate( &
                        anum(jtdm), &
                       heatf(jtdm), &
                      heatfl(jtdm), &
                      hfxzon(jtdm) )
        call mem_stat_add( 4*jtdm )
                        anum = r_init
                       heatf = r_init
                      heatfl = r_init
                      hfxzon = r_init
      endif
#endif
!
! --- integrate meridional heat fluxes vertically and in zonal direction
      do j=1,jtdm
        hfxzon(j)=0.
        heatfl(j)=0.
      enddo
!
      do k=1,kk
        do j=1,jj
          do i=1,ii
            if     (iv(i,j).ne.0) then
              util1(i,j) = (temp(i,j,k,1)+temp(i,j-1,k,1))
              util2(i,j) = vflx(i,j,k)
              util3(i,j) = (temp(i,j,k,1)+temp(i,j-1,k,1))*vflx(i,j,k)
            endif
          enddo
        enddo
        call xcsumj(zonavt(1,k), util1,iv)
        call xcsumj(zonavf(1,k), util2,iv)
        call xcsumj(heatf,       util3,iv)
        if     (lfirst) then
          util4 = 1.0
          call xcsumj(anum, util4,iv)
        endif
        if     (mnproc.eq.1) then
          do j=1,jtdm
            if     (anum(j).ne.0.0) then
              heatfl(j)=heatfl(j)+heatf(j)
              hfxzon(j)=hfxzon(j)+zonavt(j,k)*zonavf(j,k)/anum(j)
            endif
          enddo
        endif
      enddo
      if     (mnproc.eq.1) then
        do j= 1,jtdm
          hfxzon(j)=.5*hfxzon(j)*spcifh/g * 1.e-15
          heatfl(j)=.5*heatfl(j)*spcifh/g * 1.e-15
        enddo
!diag      print 999, nstep,vflx(31,11,11)
!diag 999  format(' overtn - nstep,vflx=',i10,d20.12)
!       
! ---   save everything in a special file
        noo=26
!
        if     (lfirst) then
          open (unit=noo,file=flnmovr,status='new',form='formatted')
        endif
!
        write (noo,'(a,f10.2,i6,f7.2)') &
            ' time,year,day =',dtime,int((dtime+dsmall)/dyear), &
                                      mod(dtime+dsmall, dyear)
        write (noo,'(a/(11f7.3))') &
           ' northward heat flux (petawatts):', (heatfl(j),j=1,jtdm-1)
        write (noo,'(a/(11f7.3))') &
           ' meridional overturning component:',(hfxzon(j),j=1,jtdm-1)
        call flush(noo)
!
        write (lp, '(a/(11f7.3))') &
           ' northward heat flux (petawatts):', (heatfl(j),j=1,jtdm-1)
        call flush(lp)
      endif
      call xcsync(flush_lp)
!
      lfirst = .false.
!
      return
      end subroutine overtn