diff --git a/malariagen_data/anoph/base_params.py b/malariagen_data/anoph/base_params.py
index 87e7a704e..c338c00b4 100644
--- a/malariagen_data/anoph/base_params.py
+++ b/malariagen_data/anoph/base_params.py
@@ -10,6 +10,8 @@
     single_contig_param_type,
     single_region_param_type,
     chunks_param_type,
+    zarr_chunks_type,
+    dask_chunks_type,
 )
 
 contig: TypeAlias = Annotated[
@@ -256,6 +258,13 @@ def validate_sample_selection_params(
 # amounts of data.
 native_chunks: chunks = "native"
 
+
+def call_chunks_func(zarr_chunks: zarr_chunks_type) -> dask_chunks_type:
+    return tuple([10 * i for i in zarr_chunks])
+
+
+call_chunks: chunks = call_chunks_func
+
 gff_attributes: TypeAlias = Annotated[
     Optional[Union[Sequence[str], str]],
     """
diff --git a/malariagen_data/anoph/pca.py b/malariagen_data/anoph/pca.py
index 18cd0bdb3..7f2e0012d 100644
--- a/malariagen_data/anoph/pca.py
+++ b/malariagen_data/anoph/pca.py
@@ -76,7 +76,7 @@ def pca(
         fit_exclude_samples: Optional[base_params.samples] = None,
         random_seed: base_params.random_seed = 42,
         inline_array: base_params.inline_array = base_params.inline_array_default,
-        chunks: base_params.chunks = base_params.native_chunks,
+        chunks: base_params.chunks = base_params.call_chunks,
     ) -> Tuple[pca_params.df_pca, pca_params.evr]:
         # Change this name if you ever change the behaviour of this function, to
         # invalidate any previously cached data.