diff --git a/xarray/backends/zarr.py b/xarray/backends/zarr.py
index f0d0d081a5d..b134921419f 100644
--- a/xarray/backends/zarr.py
+++ b/xarray/backends/zarr.py
@@ -29,6 +29,7 @@
 from xarray.core.treenode import NodePath
 from xarray.core.types import ZarrWriteModes
 from xarray.core.utils import (
+    Default,
     FrozenDict,
     HiddenKeyDict,
     _default,
@@ -1405,7 +1406,7 @@ def _validate_encoding(self, encoding) -> None:
 def open_zarr(
     store,
     group=None,
-    chunks=_default,
+    chunks: int | dict | Literal["auto"] | Default | None = _default,
     decode_cf=True,
     mask_and_scale=True,
     decode_times=True,
diff --git a/xarray/core/dataarray.py b/xarray/core/dataarray.py
index 8af786e1e56..5c576ff9680 100644
--- a/xarray/core/dataarray.py
+++ b/xarray/core/dataarray.py
@@ -6014,7 +6014,7 @@ def pad(
             (stat_length,) or int is a shortcut for before = after = statistic
             length for all axes.
             Default is ``None``, to use the entire axis.
-        constant_values : scalar, tuple or mapping of Hashable to tuple, default: 0
+        constant_values : scalar, tuple or mapping of Hashable to tuple, default: None
             Used in 'constant'.  The values to set the padded values for each
             axis.
             ``{dim_1: (before_1, after_1), ... dim_N: (before_N, after_N)}`` unique
@@ -6023,7 +6023,7 @@ def pad(
             dimension.
             ``(constant,)`` or ``constant`` is a shortcut for ``before = after = constant`` for
             all dimensions.
-            Default is 0.
+            Default is ``None``, pads with ``np.nan``.
         end_values : scalar, tuple or mapping of Hashable to tuple, default: 0
             Used in 'linear_ramp'.  The values used for the ending value of the
             linear_ramp and that will form the edge of the padded array.