Model failure during north-fold iceberg transport

Context

An ORCA2_ICE_PISCES run of a branch_5.0 NEMO build has been found to fail with a segmentation fault.

Analysis

The stack trace suggests that this failure was caused by the use of a corrupted linked list during iceberg transport across the north fold in subroutine icb_lbc_mpp_nfld (module icblbc).

Fix

Further analysis exposes the loss of the pointer used to traverse the linked list following a node removal. This can be avoided with the modification

--- a/src/OCE/ICB/icblbc.F90
+++ b/src/OCE/ICB/icblbc.F90
@@ -621,12 +621,18 @@ CONTAINS
                               CALL flush( numicb )
                            ENDIF
                            CALL icb_pack_into_buffer( tmpberg, obuffer_f, ibergs_to_send)
+                           this => tmpberg%next
                            CALL icb_utl_delete(first_berg, tmpberg)
+                        ELSE
+                           this => this%next
                         ENDIF
                         !
+                     ELSE
+                        this => this%next
                      ENDIF
+                  ELSE
+                     this => this%next
                   ENDIF
-                  this => this%next
                END DO
             ENDIF
             if( nn_verbose_level >= 3) then