!CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
      !CC p4zbio : PISCES MODEL  - Kriest parameterization
      !CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

      DO jk = 1, jpkm1
         DO jj = 1, jpj
            DO ji = 1, jpi
    
               !     Evolution of DOC
               !     ----------------     
               trn(ji,jj,jk,jpdoc) = trn(ji,jj,jk,jpdoc) + orem(ji,jj,jk)                                  &
                  &                                      + excret2 * prorca2(ji,jj,jk)                     &
                  &                                      + excret  * prorca (ji,jj,jk) - olimi(ji,jj,jk)   &
                  &                                      - denitr(ji,jj,jk)                                &
                  &                                      + grarem (ji,jj,jk) * (1.-sigma1)                 &
                  &                                      + grarem2(ji,jj,jk) * (1.-sigma2) - xaggdoc(ji,jj,jk)
     
               !     Evolution of Detritus
               !     ---------------------
               znumpoc = trn(ji,jj,jk,jpnum) / ( trn(ji,jj,jk,jppoc) + rtrn )
               znumdoc = znumpoc

               trn(ji,jj,jk,jppoc) = trn(ji,jj,jk,jppoc) - grazpoc(ji,jj,jk)                       &
                  &                                      + grapoc (ji,jj,jk) + grapoc2(ji,jj,jk)   &
                  &                                      - grazm  (ji,jj,jk) + tortz2 (ji,jj,jk)   &
                  &                                      + respz  (ji,jj,jk) + respz2 (ji,jj,jk)   &
                  &                                      + respp  (ji,jj,jk) + respp2 (ji,jj,jk)   &
                  &                                      + tortp2 (ji,jj,jk) + tortz  (ji,jj,jk)   &
                  &                                      + tortp  (ji,jj,jk) - orem   (ji,jj,jk)   &
                  &                                      + xaggdoc(ji,jj,jk) - grazffe(ji,jj,jk)

               !     Evolution of number of aggregates
               !     ---------------------------------
               trn(ji,jj,jk,jpnum) = trn(ji,jj,jk,jpnum) - xagg(ji,jj,jk)                                           &
                  &                                      - ( orem(ji,jj,jk) + grazpoc(ji,jj,jk) ) * znumpoc         &
                  &                                      + ( tortp(ji,jj,jk) ) * xkr_nnano                          &
                  &                                      + ( tortp2(ji,jj,jk) + respp(ji,jj,jk) + tortz(ji,jj,jk)   &
                  &                                        + grapoc(ji,jj,jk) - grazm(ji,jj,jk)                     &
                  &                                        + respz(ji,jj,jk) ) * xkr_ndiat                          &
                  &                                      + ( grapoc2(ji,jj,jk) + tortz2(ji,jj,jk)                   &
                  &                                        + respz2 (ji,jj,jk) ) * xkr_nmeso                        &
                  &                                      + respp2(ji,jj,jk) * xkr_naggr                             &
                  &                                      + xaggdoc(ji,jj,jk) * znumdoc                              &
                  &                                      - grazffe(ji,jj,jk) * znumpoc * wsbio4(ji,jj,jk)           &
                  &                                      / ( wsbio3(ji,jj,jk) + rtrn )

               trn(ji,jj,jk,jpnum) = MAX( trn(ji,jj,jk,jpnum), trn(ji,jj,jk,jppoc) / xkr_massp / xnumm(jk) )

               trn(ji,jj,jk,jpnum) = MIN( trn(ji,jj,jk,jpnum), trn(ji,jj,jk,jppoc) / xkr_massp / 1.1       )

               !     Evolution of biogenic Iron
               !     --------------------------
               trn(ji,jj,jk,jpsfe) = trn(ji,jj,jk,jpsfe) + unass * ( grazpf(ji,jj,jk) + grazsf(ji,jj,jk) )   &
                  &                - ( 1.- unass2 ) * grazpof(ji,jj,jk) - ( 1.- unass ) * grazmf(ji,jj,jk)   &
                  &                - ( 1.- unass2 ) * grazfff(ji,jj,jk) +       unass2  * ( graznf(ji,jj,jk)   &
                  &                + grazf(ji,jj,jk) + ferat3 * grazz(ji,jj,jk) ) + ferat3                   &
                  &                * (tortz2(ji,jj,jk)+respz2(ji,jj,jk)+tortz(ji,jj,jk)                      &
                  &                + respz(ji,jj,jk) ) - ofer(ji,jj,jk) + ( respnf(ji,jj,jk)                 &
                  &                + tortnf(ji,jj,jk) ) + tortdf(ji,jj,jk) + respdf(ji,jj,jk)                &
                  &                + xbactfer(ji,jj,jk) + xscave(ji,jj,jk) * zdenom1(ji,jj,jk)
            END DO
         END DO
      END DO