!CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
      !CC p4zbio : PISCES MODEL  - Standard parameterization
      !CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

      DO jk = 1, jpkm1
    
         !     Evolution of DOC
         !     ----------------     
         trn(:,:,jk,jpdoc) = trn(:,:,jk,jpdoc) + orem(:,:,jk) + excret2 * prorca2(:,:,jk)                       &
            &                                  + excret * prorca(:,:,jk) - olimi(:,:,jk) - denitr(:,:,jk)       &
            &                                  + grarem(:,:,jk) * (1.-sigma1) + grarem2(:,:,jk) * (1.-sigma2)   &
            &                                  - xaggdoc(:,:,jk) - xaggdoc2(:,:,jk)
     
         !     Evolution of Detritus
         !     ---------------------
         trn(:,:,jk,jppoc) = trn(:,:,jk,jppoc) - grazpoc(:,:,jk) + grapoc(:,:,jk) - grazm  (:,:,jk)                 &
            &                                  + respz  (:,:,jk) - xagg  (:,:,jk) + xaggdoc(:,:,jk)                 &
            &                                  + ( 1.-0.5 * zfracal(:,:,jk) ) * ( tortp(:,:,jk) + respp(:,:,jk) )   &
            &                                  +      0.5 * tortp2 (:,:,jk)                                         &
            &                                  + orem2(:,:,jk) + tortz(:,:,jk) - orem(:,:,jk)

         !     Evolution of rapid Detritus
         !     ---------------------------
         trn(:,:,jk,jpgoc) = trn(:,:,jk,jpgoc) + grapoc2(:,:,jk) + respp2(:,:,jk) + xagg (:,:,jk)            &
            &                                  + tortz2 (:,:,jk) + respz2(:,:,jk) - orem2(:,:,jk)            &
            &                                  + 0.5*zfracal(:,:,jk)*(respp(:,:,jk)+tortp(:,:,jk))           &
            &                                  + 0.5*tortp2(:,:,jk)+xaggdoc2(:,:,jk)-grazffe(:,:,jk)

         !     Evolution of small biogenic Iron
         !     --------------------------------
         trn(:,:,jk,jpsfe) = trn(:,:,jk,jpsfe) + unass * ( grazpf(:,:,jk) + grazsf(:,:,jk) )           &
            &                                  - grazpof(:,:,jk) - ( 1.- unass ) * grazmf(:,:,jk)      &
            &                                  + ( 1.- 0.5 * zfracal(:,:,jk) ) * ( tortnf(:,:,jk)      &
            &                                  + respnf(:,:,jk) ) + 0.5 * tortdf(:,:,jk) + ferat3 *    &
            &                                    ( tortz(:,:,jk) + respz(:,:,jk) ) - ofer(:,:,jk)      &
            &                                  + ofer2(:,:,jk) - xaggfe(:,:,jk)                        &
            &                                  + xscave(:,:,jk) * zdenom1(:,:,jk)

         !     Evolution of big biogenic Iron
         !     ------------------------------
         trn(:,:,jk,jpbfe) = trn(:,:,jk,jpbfe) + unass2 * ( graznf (:,:,jk) + grazf(:,:,jk) + grazfff(:,:,jk)   &
            &                                             + grazpof(:,:,jk) + ferat3 * grazz(:,:,jk) )          &
            &                                  + ferat3 * ( tortz2 (:,:,jk) + respz2(:,:,jk) )                  &
            &                                  - ofer2(:,:,jk)                                                  &
            &                                  + 0.5 * zfracal(:,:,jk) * ( respnf(:,:,jk) + tortnf(:,:,jk) )    &
            &                                  + 0.5 * tortdf (:,:,jk) + respdf(:,:,jk) + xaggfe(:,:,jk)        &
            &                                  + xbactfer(:,:,jk) - grazfff(:,:,jk) + xscave(:,:,jk) * zdenom2(:,:,jk)
         !
      END DO