Fix the tracer advection outside of interior OBCs.

 - Otherwise, the tracer values just outside the OBC get updated
 based on fluxes at the OBC and quickly go out of bounds of the
 equation of state.

src/tracer/MOM_tracer_advect.F90

@@ -648,6 +648,19 @@ subroutine advect_x(Tr, hprev, uhr, uh_neglect, OBC, domore_u, ntr, Idt, &
       endif
     enddo
 
+    ! Update do_i so that nothing changes outside of the OBC (problem for interior OBCs only)
+    if (associated(OBC)) then ; if (OBC%OBC_pe) then
+      if (OBC%specified_u_BCs_exist_globally .or. OBC%open_u_BCs_exist_globally) then
+        do i=is,ie-1 ; if (OBC%segnum_u(I,j) /= OBC_NONE) then
+          if (OBC%segment(OBC%segnum_u(I,j))%direction == OBC_DIRECTION_E) then
+            do_i(i+1,j) = .false.
+          elseif (OBC%segment(OBC%segnum_u(I,j))%direction == OBC_DIRECTION_W) then
+            do_i(i,j) = .false.
+          endif
+        endif ; enddo
+      endif
+    endif ; endif
+
     ! update tracer concentration from i-flux and save some diagnostics
     do m=1,ntr
 
@@ -1039,6 +1052,19 @@ subroutine advect_y(Tr, hprev, vhr, vh_neglect, OBC, domore_v, ntr, Idt, &
       else ; do_i(i,j) = .false. ; endif
     enddo
 
+    ! Update do_i so that nothing changes outside of the OBC (problem for interior OBCs only)
+    if (associated(OBC)) then ; if (OBC%OBC_pe) then
+      if (OBC%specified_v_BCs_exist_globally .or. OBC%open_v_BCs_exist_globally) then
+        do i=is,ie-1 ; if (OBC%segnum_v(i,J) /= OBC_NONE) then
+          if (OBC%segment(OBC%segnum_v(i,J))%direction == OBC_DIRECTION_N) then
+            do_i(i,j+1) = .false.
+          elseif (OBC%segment(OBC%segnum_v(i,J))%direction == OBC_DIRECTION_S) then
+            do_i(i,j) = .false.
+          endif
+        endif ; enddo
+      endif
+    endif ; endif
+
     ! update tracer and save some diagnostics
     do m=1,ntr
       do i=is,ie ; if (do_i(i,j)) then