Floodfill landIceFraction, not landIceMask

During the `cull_mesh` step of creating a global ocean mesh,
if ice-shelf cavities are present, we need to flood fill to make
sure all land ice is connected (no islands of isolated land ice).
This merge changes the flood fill to be on all locations where
`landIceFraction > 0`, not all locations where `landIceFraction > 0.5`.
It then masks all `landIce*` fields to only be nonzero within the
flood-filled region.  This prevents islands of nonzero
`landIceFraction`, `landIcePressure`, `landIceDraft`, etc.

compass/ocean/mesh/cull.py

@@ -543,22 +543,33 @@ def _add_land_ice_mask_and_mask_draft(ds_topo, ds_base_mesh,
 
     land_ice_frac = ds_topo.landIceFracObserved
 
-    # we want the mask to be 1 where there's at least half land-ice
-    land_ice_mask = xr.where(land_ice_frac > 0.5, 1, 0)
+    land_ice_present = xr.where(land_ice_frac > 0.0, 1, 0)
 
     gf = GeometricFeatures()
     fc_ocean_seed = gf.read(componentName='ocean', objectType='point',
                             tags=['seed_point'])
 
     fc_south_pole_seed = read_feature_collection('south_pole.geojson')
 
-    # flood fill the ice portion to remove isolated land ice
+    # flood fill anywhere land ice is present to remove isolated land ice
 
     ds_mask = compute_mpas_flood_fill_mask(dsMesh=ds_base_mesh,
-                                           daGrow=land_ice_mask,
+                                           daGrow=land_ice_present,
                                            fcSeed=fc_south_pole_seed,
                                            logger=logger)
-    land_ice_mask = ds_mask.cellSeedMask
+    land_ice_present = ds_mask.cellSeedMask
+
+    # update land-ice variables and ocean fraction accordingly
+    for var in ['landIceFracObserved', 'landIcePressureObserved',
+                'landIceDraftObserved', 'landIceGroundedFracObserved',
+                'landIceFloatingFracObserved', 'landIceThkObserved']:
+        ds_topo[var] = ds_topo[var].where(land_ice_present, 0.0)
+
+    ds_topo['oceanFracObserved'] = \
+        ds_topo['oceanFracObserved'].where(land_ice_present, 1.0)
+
+    land_ice_frac = ds_topo.landIceFracObserved
+    land_ice_mask = xr.where(land_ice_frac > 0.5, 1, 0)
 
     # now, remove land-locked or land-ice-locked cells