diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index a52e73701ab..9147f750330 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -33,7 +33,6 @@
     _normalize_path,
 )
 from xarray.backends.locks import _get_scheduler
-from xarray.backends.zarr import _zarr_v3
 from xarray.core import indexing
 from xarray.core.combine import (
     _infer_concat_order_from_positions,
@@ -2131,66 +2130,25 @@ def to_zarr(
 
     See `Dataset.to_zarr` for full API docs.
     """
+    from xarray.backends.zarr import _choose_default_mode, _get_mappers
+
+    # validate Dataset keys, DataArray names
+    _validate_dataset_names(dataset)
 
     # Load empty arrays to avoid bug saving zero length dimensions (Issue #5741)
+    # TODO: delete when min dask>=2023.12.1
+    # https://github.com/dask/dask/pull/10506
     for v in dataset.variables.values():
         if v.size == 0:
             v.load()
 
-    # expand str and path-like arguments
-    store = _normalize_path(store)
-    chunk_store = _normalize_path(chunk_store)
-
-    kwargs = {}
-    if storage_options is None:
-        mapper = store
-        chunk_mapper = chunk_store
-    else:
-        if not isinstance(store, str):
-            raise ValueError(
-                f"store must be a string to use storage_options. Got {type(store)}"
-            )
-
-        if _zarr_v3():
-            kwargs["storage_options"] = storage_options
-            mapper = store
-            chunk_mapper = chunk_store
-        else:
-            from fsspec import get_mapper
-
-            mapper = get_mapper(store, **storage_options)
-            if chunk_store is not None:
-                chunk_mapper = get_mapper(chunk_store, **storage_options)
-            else:
-                chunk_mapper = chunk_store
-
     if encoding is None:
         encoding = {}
 
-    if mode is None:
-        if append_dim is not None:
-            mode = "a"
-        elif region is not None:
-            mode = "r+"
-        else:
-            mode = "w-"
-
-    if mode not in ["a", "a-"] and append_dim is not None:
-        raise ValueError("cannot set append_dim unless mode='a' or mode=None")
-
-    if mode not in ["a", "a-", "r+"] and region is not None:
-        raise ValueError(
-            "cannot set region unless mode='a', mode='a-', mode='r+' or mode=None"
-        )
-
-    if mode not in ["w", "w-", "a", "a-", "r+"]:
-        raise ValueError(
-            "The only supported options for mode are 'w', "
-            f"'w-', 'a', 'a-', and 'r+', but mode={mode!r}"
-        )
-
-    # validate Dataset keys, DataArray names
-    _validate_dataset_names(dataset)
+    kwargs, mapper, chunk_mapper = _get_mappers(
+        storage_options=storage_options, store=store, chunk_store=chunk_store
+    )
+    mode = _choose_default_mode(mode=mode, append_dim=append_dim, region=region)
 
     if mode == "r+":
         already_consolidated = consolidated
@@ -2198,6 +2156,7 @@ def to_zarr(
     else:
         already_consolidated = False
         consolidate_on_close = consolidated or consolidated is None
+
     zstore = backends.ZarrStore.open_group(
         store=mapper,
         mode=mode,
@@ -2209,30 +2168,14 @@ def to_zarr(
         append_dim=append_dim,
         write_region=region,
         safe_chunks=safe_chunks,
-        stacklevel=4,  # for Dataset.to_zarr()
         zarr_version=zarr_version,
         zarr_format=zarr_format,
         write_empty=write_empty_chunks,
         **kwargs,
     )
 
-    if region is not None:
-        zstore._validate_and_autodetect_region(dataset)
-        # can't modify indexes with region writes
-        dataset = dataset.drop_vars(dataset.indexes)
-        if append_dim is not None and append_dim in region:
-            raise ValueError(
-                f"cannot list the same dimension in both ``append_dim`` and "
-                f"``region`` with to_zarr(), got {append_dim} in both"
-            )
-
-    if encoding and mode in ["a", "a-", "r+"]:
-        existing_var_names = set(zstore.zarr_group.array_keys())
-        for var_name in existing_var_names:
-            if var_name in encoding:
-                raise ValueError(
-                    f"variable {var_name!r} already exists, but encoding was provided"
-                )
+    dataset = zstore._validate_and_autodetect_region(dataset)
+    zstore._validate_encoding(encoding)
 
     writer = ArrayWriter()
     # TODO: figure out how to properly handle unlimited_dims
diff --git a/xarray/backends/zarr.py b/xarray/backends/zarr.py
index 50755ebf1f7..2c60d93548f 100644
--- a/xarray/backends/zarr.py
+++ b/xarray/backends/zarr.py
@@ -4,8 +4,7 @@
 import json
 import os
 import struct
-import warnings
-from collections.abc import Iterable
+from collections.abc import Hashable, Iterable, Mapping
 from typing import TYPE_CHECKING, Any, Literal
 
 import numpy as np
@@ -46,6 +45,66 @@
     from xarray.core.datatree import DataTree
 
 
+def _get_mappers(*, storage_options, store, chunk_store):
+    # expand str and path-like arguments
+    store = _normalize_path(store)
+    chunk_store = _normalize_path(chunk_store)
+
+    kwargs = {}
+    if storage_options is None:
+        mapper = store
+        chunk_mapper = chunk_store
+    else:
+        if not isinstance(store, str):
+            raise ValueError(
+                f"store must be a string to use storage_options. Got {type(store)}"
+            )
+
+        if _zarr_v3():
+            kwargs["storage_options"] = storage_options
+            mapper = store
+            chunk_mapper = chunk_store
+        else:
+            from fsspec import get_mapper
+
+            mapper = get_mapper(store, **storage_options)
+            if chunk_store is not None:
+                chunk_mapper = get_mapper(chunk_store, **storage_options)
+            else:
+                chunk_mapper = chunk_store
+    return kwargs, mapper, chunk_mapper
+
+
+def _choose_default_mode(
+    *,
+    mode: ZarrWriteModes | None,
+    append_dim: Hashable | None,
+    region: Mapping[str, slice | Literal["auto"]] | Literal["auto"] | None,
+) -> ZarrWriteModes:
+    if mode is None:
+        if append_dim is not None:
+            mode = "a"
+        elif region is not None:
+            mode = "r+"
+        else:
+            mode = "w-"
+
+    if mode not in ["a", "a-"] and append_dim is not None:
+        raise ValueError("cannot set append_dim unless mode='a' or mode=None")
+
+    if mode not in ["a", "a-", "r+"] and region is not None:
+        raise ValueError(
+            "cannot set region unless mode='a', mode='a-', mode='r+' or mode=None"
+        )
+
+    if mode not in ["w", "w-", "a", "a-", "r+"]:
+        raise ValueError(
+            "The only supported options for mode are 'w', "
+            f"'w-', 'a', 'a-', and 'r+', but mode={mode!r}"
+        )
+    return mode
+
+
 def _zarr_v3() -> bool:
     # TODO: switch to "3" once Zarr V3 is released
     return module_available("zarr", minversion="2.99")
@@ -555,7 +614,6 @@ def open_store(
         append_dim=None,
         write_region=None,
         safe_chunks=True,
-        stacklevel=2,
         zarr_version=None,
         zarr_format=None,
         use_zarr_fill_value_as_mask=None,
@@ -575,7 +633,6 @@ def open_store(
             consolidate_on_close=consolidate_on_close,
             chunk_store=chunk_store,
             storage_options=storage_options,
-            stacklevel=stacklevel,
             zarr_version=zarr_version,
             use_zarr_fill_value_as_mask=use_zarr_fill_value_as_mask,
             zarr_format=zarr_format,
@@ -610,7 +667,6 @@ def open_group(
         append_dim=None,
         write_region=None,
         safe_chunks=True,
-        stacklevel=2,
         zarr_version=None,
         zarr_format=None,
         use_zarr_fill_value_as_mask=None,
@@ -630,7 +686,6 @@ def open_group(
             consolidate_on_close=consolidate_on_close,
             chunk_store=chunk_store,
             storage_options=storage_options,
-            stacklevel=stacklevel,
             zarr_version=zarr_version,
             use_zarr_fill_value_as_mask=use_zarr_fill_value_as_mask,
             zarr_format=zarr_format,
@@ -1092,7 +1147,10 @@ def _auto_detect_regions(self, ds, region):
             region[dim] = slice(idxs[0], idxs[-1] + 1)
         return region
 
-    def _validate_and_autodetect_region(self, ds) -> None:
+    def _validate_and_autodetect_region(self, ds: Dataset) -> Dataset:
+        if self._write_region is None:
+            return ds
+
         region = self._write_region
 
         if region == "auto":
@@ -1140,8 +1198,26 @@ def _validate_and_autodetect_region(self, ds) -> None:
                 f".drop_vars({non_matching_vars!r})"
             )
 
+        if self._append_dim is not None and self._append_dim in region:
+            raise ValueError(
+                f"cannot list the same dimension in both ``append_dim`` and "
+                f"``region`` with to_zarr(), got {self._append_dim} in both"
+            )
+
         self._write_region = region
 
+        # can't modify indexes with region writes
+        return ds.drop_vars(ds.indexes)
+
+    def _validate_encoding(self, encoding) -> None:
+        if encoding and self._mode in ["a", "a-", "r+"]:
+            existing_var_names = set(self.zarr_group.array_keys())
+            for var_name in existing_var_names:
+                if var_name in encoding:
+                    raise ValueError(
+                        f"variable {var_name!r} already exists, but encoding was provided"
+                    )
+
 
 def open_zarr(
     store,
@@ -1316,7 +1392,6 @@ def open_zarr(
         "overwrite_encoded_chunks": overwrite_encoded_chunks,
         "chunk_store": chunk_store,
         "storage_options": storage_options,
-        "stacklevel": 4,
         "zarr_version": zarr_version,
         "zarr_format": zarr_format,
     }
@@ -1385,7 +1460,6 @@ def open_dataset(  # type: ignore[override]  # allow LSP violation, not supporti
         consolidated=None,
         chunk_store=None,
         storage_options=None,
-        stacklevel=3,
         zarr_version=None,
         zarr_format=None,
         store=None,
@@ -1403,7 +1477,6 @@ def open_dataset(  # type: ignore[override]  # allow LSP violation, not supporti
                 consolidate_on_close=False,
                 chunk_store=chunk_store,
                 storage_options=storage_options,
-                stacklevel=stacklevel + 1,
                 zarr_version=zarr_version,
                 use_zarr_fill_value_as_mask=None,
                 zarr_format=zarr_format,
@@ -1440,7 +1513,6 @@ def open_datatree(
         consolidated=None,
         chunk_store=None,
         storage_options=None,
-        stacklevel=3,
         zarr_version=None,
         zarr_format=None,
         **kwargs,
@@ -1461,7 +1533,6 @@ def open_datatree(
             consolidated=consolidated,
             chunk_store=chunk_store,
             storage_options=storage_options,
-            stacklevel=stacklevel,
             zarr_version=zarr_version,
             zarr_format=zarr_format,
             **kwargs,
@@ -1485,7 +1556,6 @@ def open_groups_as_dict(
         consolidated=None,
         chunk_store=None,
         storage_options=None,
-        stacklevel=3,
         zarr_version=None,
         zarr_format=None,
         **kwargs,
@@ -1509,7 +1579,6 @@ def open_groups_as_dict(
             consolidate_on_close=False,
             chunk_store=chunk_store,
             storage_options=storage_options,
-            stacklevel=stacklevel + 1,
             zarr_version=zarr_version,
             zarr_format=zarr_format,
         )
@@ -1554,7 +1623,6 @@ def _get_open_params(
     consolidate_on_close,
     chunk_store,
     storage_options,
-    stacklevel,
     zarr_version,
     use_zarr_fill_value_as_mask,
     zarr_format,
@@ -1599,7 +1667,7 @@ def _get_open_params(
             # ValueError in zarr-python 3.x, KeyError in 2.x.
             try:
                 zarr_group = zarr.open_group(store, **open_kwargs)
-                warnings.warn(
+                emit_user_level_warning(
                     "Failed to open Zarr store with consolidated metadata, "
                     "but successfully read with non-consolidated metadata. "
                     "This is typically much slower for opening a dataset. "
@@ -1612,7 +1680,6 @@ def _get_open_params(
                     "error in this case instead of falling back to try "
                     "reading non-consolidated metadata.",
                     RuntimeWarning,
-                    stacklevel=stacklevel,
                 )
             except missing_exc as err:
                 raise FileNotFoundError(