diff --git a/pyleoclim/core/series.py b/pyleoclim/core/series.py
index a7da9b64..3f10144a 100644
--- a/pyleoclim/core/series.py
+++ b/pyleoclim/core/series.py
@@ -1129,7 +1129,7 @@ def plot(self, figsize=[10, 4],
             fig, ax = ts_18.plot(figsize=(10, 4),linewidth=0.5)
             ax.invert_yaxis() # d18O is traditionally inverted
 
-            fig, ax = pyleo.add_GTS(fig, ax, ranks=['Period', 'Epoch'], location='above')
+            fig, ax = pyleo.add_GTS(fig, ax, time_unit=ts_18.time_unit, ranks=['Period', 'Epoch'], location='above')
 
         '''
         # generate default axis labels
diff --git a/pyleoclim/utils/datasets.py b/pyleoclim/utils/datasets.py
index 94d275a9..a52b847d 100644
--- a/pyleoclim/utils/datasets.py
+++ b/pyleoclim/utils/datasets.py
@@ -233,7 +233,7 @@ def _localname(term):
 
 
 def load_ics_chart_to_df(ttl_path_or_url="https://raw.githubusercontent.com/i-c-stratigraphy/chart/refs/heads/main/chart.ttl",
-                         time_units='Ma', lang='en') -> pd.DataFrame:
+                         time_unit='Ma', lang='en') -> pd.DataFrame:
 
     def _first_lang(iterable, lang=None):
         for lit in iterable:
@@ -366,7 +366,7 @@ def boundary_ma(node_pred):
     df["Rank"] = pd.Categorical(df["Rank"], categories=type_order + sorted(set(df["Rank"]) - set(type_order)), ordered=True)
     df = df.sort_values(["Rank", "UpperBoundary"], na_position="last").reset_index(drop=True)
 
-    time_name, time_unit = disambiguate_time_metadata(time_units)
+    time_name, time_unit = disambiguate_time_metadata(time_unit)
     print(f"Time name: {time_name}")
     print(f"Time unit: {time_unit}")
     if time_unit not in ['Ma']:#['Ma', 'Mya', 'My']:
diff --git a/pyleoclim/utils/plotting.py b/pyleoclim/utils/plotting.py
index bd830cf0..8fb7bfdf 100644
--- a/pyleoclim/utils/plotting.py
+++ b/pyleoclim/utils/plotting.py
@@ -1518,9 +1518,9 @@ def text_loc(fig, ax, rect, label_text, width, yloc):
     text.remove()
     return loc
 
-def add_GTS(fig, ax, time_units, GTS_df=None, ranks=None, location='above', label_pref='full',
-            allow_abbreviations=True, ax_name='gts', v_offset=0, height=.05, text_color=None, fontsize=None, edgecolor='k',
-            edgewidth=0, alpha=1,zorder=10,reverse_rank_order=True, lang='en',
+def add_GTS(fig, ax, time_unit, GTS_df=None, ranks=None, location='above', label_pref='full',
+            allow_abbreviations=True, lang='en', ax_name='gts', v_offset=0, height=.05, text_color=None, fontsize=None, edgecolor='k',
+            edgewidth=0, alpha=1,zorder=10,reverse_rank_order=True,
             gts_url = "https://raw.githubusercontent.com/i-c-stratigraphy/chart/refs/heads/main/chart.ttl"):
 
     '''
@@ -1531,7 +1531,7 @@ def add_GTS(fig, ax, time_units, GTS_df=None, ranks=None, location='above', labe
         The figure object where the GTS will be added.
     ax : dict
         The axis where the GTS will be plotted.
-    time_units : str
+    time_unit : str
         Time units of the GTS data. Supported: 'Ma' (default), 'ka', 'Ga'.
     GTS_df : pd.DataFrame, optional
         DataFrame containing the GTS data with columns for 'Rank', 'Name', 'Abbrev', 'Color', 'UpperBoundary', 'LowerBoundary'.
@@ -1544,6 +1544,8 @@ def add_GTS(fig, ax, time_units, GTS_df=None, ranks=None, location='above', labe
         Preference for labels: 'full' (default) for full names, 'abbrev' for abbreviations, 'none' for no labels (only colors).
     allow_abbreviations : bool, optional
         If True, allows abbreviations for labels that don't fit. Default is True.
+    lang : str, optional
+        Language for GTS labels. Default is 'en'.
     ax_name : str, optional
         Name of the axis to create for the GTS. Default is 'gts'.
     v_offset : float, optional
@@ -1587,7 +1589,7 @@ def add_GTS(fig, ax, time_units, GTS_df=None, ranks=None, location='above', labe
         fig, ax = ms.stackplot(figsize=(10, 5),linewidth=0.5, fill_between_alpha=0)
         ax[0].invert_yaxis() # d18O is traditionally inverted
 
-        fig, ax = pyleo.utils.plotting.add_GTS(fig, ax, time_units='Ma', location='above', label_pref='full',
+        fig, ax = pyleo.utils.plotting.add_GTS(fig, ax, 'Ma', location='above', label_pref='full',
                     allow_abbreviations=True, ax_name='gts', v_offset=0, height=.05)
 
     '''
@@ -1608,7 +1610,7 @@ def add_GTS(fig, ax, time_units, GTS_df=None, ranks=None, location='above', labe
         assert all(duration >= 0), "GTS_df 'LowerBoundary' must be greater than (further back in time) or equal to 'UpperBoundary (more modern)'"
 
     if GTS_df is None:
-        GTS_df = datasets.load_ics_chart_to_df(gts_url, time_units=time_units, lang=lang)
+        GTS_df = datasets.load_ics_chart_to_df(gts_url, time_unit=time_unit, lang=lang)
 
     if ranks is None:
         ranks = ['Period', 'Epoch', 'Stage']