Merge pull request mom-ocean#1605 from GEOS-ESM/mathomp4-patch-1

GNU bug fix for MOM_variables.F90

src/core/MOM_variables.F90

@@ -261,7 +261,7 @@ module MOM_variables
 
   ! The following elements are pointers so they can be used as targets for pointers in the restart registry.
   real, pointer, dimension(:,:) :: MLD => NULL() !< Instantaneous active mixing layer depth [Z ~> m].
-  real, pointer, dimension(:,:) :: sfc_buoy_flx !< Surface buoyancy flux (derived) [Z2 T-3 ~> m2 s-3].
+  real, pointer, dimension(:,:) :: sfc_buoy_flx => NULL() !< Surface buoyancy flux (derived) [Z2 T-3 ~> m2 s-3].
   real, pointer, dimension(:,:,:) :: Kd_shear => NULL()
                 !< The shear-driven turbulent diapycnal diffusivity at the interfaces between layers
                 !! in tracer columns [Z2 T-1 ~> m2 s-1].