The research area is located at Hercules Névé, Victoria Land, Antarctica, at 73°03′ S, 165°25′ E (Fig. 1). Situated at an altitude of 2864 m and approximately 80 km inland from the sea, the climatic conditions of this mountainous area are affected by its position near the northern edge of the Transantarctic Mountains, which strongly influence atmospheric circulation by acting as a barrier to the flow of air masses (Tewari et al., 2021). Because the interaction between the mountains and the prevailing winds generates various microclimates at Hercules Névé, it has become an area of interest for understanding the complex interactions between the local geography and climate (Maggi and Petit, 1998).

Victoria Land has long been used as a research site to study the impact of atmospheric and oceanic variability on snow accumulation and ice core records (Maggi and Petit, 1998; Nardin et al., 2020; Nyamgerel et al., 2024; Yan et al., 2021; Yang et al., 2018). This region is characterized by austral summer-dominant precipitation patterns influenced by easterly winds that bring moist air from the ocean onto the continent (Scarchilli et al., 2011). Katabatic winds descending from the East Antarctic Plateau are typically cold and extremely dry. Their dryness enhances sublimation from the snow surface, which can lead to isotopic modification of near-surface layers (Nyamgerel et al., 2024; Vihma et al., 2011). However, their impact on local temperature and the surface energy balance is not always unidirectional and may vary depending on synoptic conditions (Davrinche et al., 2024). Broader climatic drivers such as the Southern Annular Mode and sea ice variability also impact regional weather patterns and precipitation (Yang et al., 2018). Hercules Névé is thus a useful site for the analysis of how regional climate variability influences snow deposition and ice core records, which can be used to reconstruct past climate conditions. Furthermore, previous studies have reported a high snowfall rate in the surrounding area (Maggi and Petit, 1998; Nyamgerel et al., 2020; Stenni et al., 1999, 2000), making this region particularly suitable for ice core seasonal analysis.

Figure 2 presents the water isotope data from Hercules Névé for the period 1979–2015. The δ18O values ranged from -42.29 ‰ to -29.67 ‰, with a standard deviation of 1.69 ‰, while those for δ2H ranged from -334.5 ‰ to -226.1 ‰, with a standard deviation of 11.75 ‰. These values are comparable to other near-coastal Antarctic sites in Victoria Land, such as Styx–M, Whitehall Glacier, and Talos Dome, which represent a range of altitudes and moisture conditions (Table S1 in the Supplement). Using the annual mean δ18O and δ2H in Hercules Névé core, we derived a local meteoric water line (LMWL) with a slope of 8 and an intercept of 8.2 (R2=0.99). While there slope and intercept are higher than those of the Antarctica meteoric water line (AMWL, slope = 7.75 and intercept = -4.93 Masson-Delmotte et al., 2008), yet similar to the global meteoric water line (GMWL, slope = 8 and intercept = 10; Craig, 1961). The similarity suggests that, owing to its coastal proximity, the Hercules Névé region, experiences moisture conditions more characteristic of oceanic environments, resulting in a steeper δ18O–δ2H relationship (Fernandoy et al., 2010; Goursaud et al., 2018; Nyamgerel et al., 2024).

Seasonally, the δ18O-δ2H relationship in the Hercules Névé core range from 8 to 8.3 and 7.8 to 18 (Fig. S4). During the austral summer, the slope (8.0) and the intercept (7.8) closely match the annual LMWL, indicating that the summer precipitation is more likely to reflect the temperature–isotope relationship with minimal post-depositional alteration. ERA5 reanalysis data from 1979–2015 show that precipitation minus evaporation during DJF accounts for approximately 23 %–40 % (mean 35 %, standard deviation 4 %) of the annual total. While DJF does not dominate the annual accumulation in terms of volume, it occurs under conditions of relatively frequent snowfall, warmer atmospheric temperatures, and higher moisture flux from open ocean areas due to reduced sea ice extent. Such conditions may enhance the direct imprint of summer climatic signals into the isotopic composition of snow, making the DJF season particularly valuable for interpreting isotope–climate relationships in coastal Antarctica.

To confirm that this seasonal signal is preserved without significant isotopic smoothing, we empirically estimated the diffusion length from the δ18O time series using a spectral fitting approach (Münch et al., 2016). The resulting diffusion length of approximately 6 cm, comparable to the 5 cm sampling interval, indicates that seasonal variability is well resolved at this resolution and that the isotopic cycles retain their original amplitude.

Using ERA5 climate reanalysis data for 1979–2015, we examined how temperature, precipitation, and wind components (v- and u-winds) relate to δ18O variability during thre austral summer (DJF) at Hercules Névé site (Fig. 3). When using annual mean temperature, δ18O shows a weak correlation (r=0.13 likely due to the superposition of several process that obscure a direct isotopic–thermal relationship: varying moisture sources (Masson-Delmotte et al., 2008; Noone and Simmonds, 2004), strong synoptic variability associated with the Ross Sea region (Schlosser et al., 2016), seasonal difference in precipitation frequency (Casado et al., 2018), and post-depositional modifications of the surface snow (Casado et al., 2021; Mahalinganathan et al., 2022). Such effect dilute the annual isotope–temperature signal, underscoring the limitations of paleoclimate reconstructions based solely on annual mean annual signatures (Laepple et al., 2025).

By contrast, the austral summer correlation between δ18O and temperature is more pronounced (r=0.32, p<0.05; slope of 0.59 ‰ °C⁻¹). Although slightly lower than the Styx site (0.66 ‰ °C⁻¹; Nyamgerel et al., 2024), this summer slope is comparable to other East Antarctic locations such as Whitehall Glacier (0.62 ‰ °C⁻¹; Sinclair et al., 2012), Taylor Dome (0.50 ‰ °C⁻¹; Steig et al., 2000) and Talos Dome (0.60 ‰ °C⁻¹; Stenni et al., 2002) (Fig. S5). This consistency demonstrates that isotope–temperature scaling at Hercules Névé is regionally coherent despite differences in topography and moisture-transport pathways. It also highlights the necessity of seasonal discrimination, while annual values are confounded, summer months preserve the most direct temperature signature (Sinclair et al., 2013).

Several factors may account for this stronger summer correlation: (1) reduced impact of post-depositional process under high accumulation rates, despite enhanced metamorphism under warmer conditions (Town et al., 2008; Waddington et al., 2002), (2) simplified moisture transport pathways during summer circulation (Helsen et al., 2005), and (3) a higher frequency of precipitation events, leading to more direct incorporation of local climatic signals into the ice (Steen-Larsen et al., 2011). Together, these mechanisms indicate that δ18O in summer snowfall is more directly coupled to surface air temperature. These mechanisms imply that δ18O in summer snowfall is a more directly associated by surface air temperature. Precipitation shows positive correlation with δ18O during summer (r=0.6; Fig. 3B), exceeding its annual mean correlation (r=0.3, not shown). This pattern suggests that precipitation in coastal Antarctica is often isotopically enriched during periods of heavy snowfall, reflecting moisture sourced from the nearby ocean (Servettaz et al., 2020 and Jackson et al., 2023).

For wind components, the austral summer v-wind (southerly) and u-wind (westerly) are generally negative values, indicating prevailing southerly and westerly winds flows. A positive correlation was observed between δ18O and v-wind, suggesting that stronger southerly winds are associated with isotopically enriched snowfall (Fig. 3C). Although this relationship may appear counterintuitive, it likely reflects inland advection of mixed continental–oceanic air masses with higher isotopic (Clem et al., 2017; Noone and Simmonds, 2004). Conversely, δ18O is negatively correlated with the u-wind (Fig. 3D), indicating that intensified westerlies transport colder, isotopically depleted air from marine sectors west of the Ross Embayment (Markle et al., 2012). There findings emphasize that temperature, precipitation, and wind directions collectively modulated isotopic variability in the Hercules Névé region.

During DJF, the Hercules Névé ice core record shows a clear co-variation between dexc and local ocean-ice conditions. When SIC is higher, dexc is generally higher, and when SST is higher, dexc is generally lower (Fig. 4A, B). Taken together with the δ18O–climate associations described above, this DJF dexc pattern suggests that summertime isotopic variability at Hercules Névé, located near the Ross Sea, is most closely related to local ocean–ice conditions and polynya-influenced moisture sources. This highlights that not only temperature and precipitation but also moisture source variability has a discernible influence on the isotopic signal, reinforcing the value of summer snowfall as a recorder of regional climate (Noone and Simmonds, 2002; Risi et al., 2010; Uemura et al., 2008).

In summary, the combination of temperature, precipitation, and wind patterns during austral summer exerts a marked influence on δ18O. These results provide a process-based framework for interpreting how coastal Antarctic ice cores can record regional climatic conditions, highlighting the importance of focusing on the season (DJF) that reflects a clearer signal of local temperature and marine moisture influence.

The Hercules Névé record reveals a positive correlation between summer sea-ice concentration (SIC) in the Ross Sea and dexc (Fig. 4A). This association can be understood through the interplay of katabatic winds, sea-ice extent, and polynya processes (Dale et al., 2020; Turner et al., 2016). Under high SIC conditions, katabatic forcing enhances coastal divergence, supporting the persistence of coastal polynyas. These polynyas enhance local evaporation, initially generating vapor with low dexc values due to kinetic fractionation (Merlivat and Jouzel, 1979). Subsequent mixing with continental air masses relatively enriched in dexc (Noone and Simmonds, 2004) modifies the resultant isotopic composition of snowfall. Meanwhile, extensive sea ice coverage modifies the relative contribution of distant, isotopically depleted oceanic sources (Uemura et al., 2008), enhancing the relative influence of locally derived moisture. Comparable mechanisms have been observed in both Antarctic and Arctic regions, where variability in sea-ice extent exerts a strong control on stable isotope compositions (Kurita, 2011; Steen-Larsen et al., 2013).

In contrast, low SIC exposes a broader open-ocean surface, intensifying evaporation under conditions that promote kinetic fractionation and resulting in lower dexc values (Bertler et al., 2018; Kurosaki et al., 2020). This seasonal contrast highlights the role of sea-ice extent and polynya activity in modulating the isotopic characteristics of coastal Antarctic precipitation by altering both moisture source and atmospheric transport pathways. Overall, these findings indicate that isotopic variations in coastal Antarctic precipitation are governed by a combination of sea-ice dynamics, katabatic wind influence, and continental moisture interactions, rather than by temperature alone. This complexity underscores the need to account for source-related processes when interpreting coastal isotope records for paleoclimate applications.

The relationship between dexc and SST further complicates interpretation. Theory anticipates a positive SST–dexc linkage based on fractionation dynamics (Gat et al., 2003; Merlivat and Jouzel, 1979). However, our results reveal a negative correlation between dexc and SST (Fig. 4B), which differs from the expected positive relationship (Merlivat and Jouzel, 1979). We hypothesize that complex ocean–atmosphere interactions in polynya regions, where sea-ice dynamics, variable SST, and atmospheric circulation converge, modify the typical SST–d-exc linkage. Further numerical modeling that includes both SST and humidity variability would be necessary to elucidate these processes more precisely (Pfahl and Sodemann, 2014; Uemura et al., 2008). These findings carry two key implications: (1) coastal Antarctic ice core dexc provides a sensitive proxy for sea-ice extent and local air–sea coupling rather than open-ocean temperature, and (2) isotope-based reconstructions using dexc must account for the dominance of polynya processes in regions such as the Ross Sea.

The ASL has a profound impact on both δ18O variability and local wind dynamics in the Ross Sea and Victoria Land (Coggins and McDonald, 2015; Turner et al., 2013). In this study, a significant negative correlation was found between ASL-related mean sea-level pressure and δ18O values in the Hercules Névé region (Fig. 5A). When the ASL intensifies (i.e., its central pressure drops), cold and dry air from the Antarctic continent tends to intrude into the Hercules Névé region, which is associated with more deplete δ18O in precipitation (Emanuelsson et al., 2023). This observation agrees with prior findings linking a stronger ASL activity to enhanced cold-air advection and lowered isotopic content of snowfall (Hosking et al., 2013; Raphael et al., 2019). Wind patterns also influence the isotopic composition. As discussed in Sect. 3.2, δ18O exhibits a positive correlation with the v-wind (southerly) but a negative correlation with the u-wind (westerly), indicating advection of relatively warm, moist versus cold, dry air masses (Fig. 5C–D; Clem et al., 2017).

To further characterize ASL behavior, we conducted a PCA using DJF ASL strength (actual central pressure), latitude, and longitude (Hosking et al., 2013). The first three principal components (PCs) explained all variance in the dataset (PC1: 57.7 %, PC2: 31.2 %, PC3: 11.2 %) (Fig. 6A). PC1 reflects a general displacement toward a stronger, poleward, and eastward ASL but is only weakly associated with δ18O (r = 0.15). PC2 captures a zonal shift with moderate association (r = 0.27), while PC3, though explaining the least variance, exhibits the strongest negative correlation with δ18O (r = -0.34) (Fig. 6B). Loadings (Table 1) indicate that PC3 is characterized by a southward shift in ASL position combined with increased central pressure and slight eastward movement. This coupled ASL pattern appears to be notably associated with changes in the isotopic signature at Hercules Névé, possibly reflecting modified moisture transport pathways. Figure 7 presents the results of the HYSPLIT back-trajectory clustering for summers with strong and weak ASL conditions, illustrating contrasting transport regimes. During intensified ASL phases in DJF (lower central pressure over the Amundsen Sea), the trajectories indicate that moisture is primarily transported meridionally from the Antarctic interior and the Ross Ice Shelf, producing in longer, more continental air-mass pathways. These conditions correspond to colder, isotopically depleted precipitation with higher dexc values, consistent with enhanced inland and shelf-derived moisture contributions. Conversely, during periods of a weak ASL phase (higher central pressure), trajectories become more zonal, with increased transport of marine air masses from the open Ross Sea. This pattern is associated with warmer, isotopically enriched precipitation and lower dexc, reflecting the greater influence of oceanic moisture sources. These contrasting circulation regimes demonstrate that ASL variability plays a key role in modulating the origin and isotopic signature of precipitation at Hercules Névé, linking regional-scale atmospheric dynamics to local ice-core records.

In contrast, periods of diminished ASL show an increased proportion of zonal, ocean-originating trajectories, particularly from the Amundsen Sea sector and lower-latitude open waters. These pathways favor the transport of relatively warm, isotopically enriched air and lower dexc values, reflecting a greater contribution of oceanic vapor. This shift underscores the role of large-scale circulation variability in mediating both surface climate and the isotopic imprint preserved in the Hercules Névé ice core. Collectively, these findings indicate that ASL variability is statistically associated with both pressure-related advection and wind-driven changes in regional circulation. Although PC3 explains only 11 % of the total variance, its statistically significant negative correlation with δ18O, emphasizes that structural shifts in ASL circulation importantly influence isotope variability in coastal Antarctica.

A significant positive correlation was identified between the DJF seasonal mean strength of ZW3 and δ18O (r = 0.47, p < 0.01) in the Hercules Névé region based on interannual values from 1979 to 2015. The ZW3 index (Goyal et al., 2022) represents monthly variability in the hemispheric wave-3 structure, which we averaged over DJF to align with the period of isotopic signal accumulation in the snowpack. To examine the influence of broader atmospheric circulation patterns, we also examined the Southern Annular Mode (SAM) using principal components from an EOF analysis of 500 hPa geopotential height fields during DJF from ERA5. The first mode (EOF1), associated with SAM, showed no significant relationship with δ18O (r = 0.09, p = 0.58), whereas the second mode (EOF2), consistent with ASL–ZW3 variability, had a statistically significant negative correlation (r = -0.44, p < 0.01). These results suggest that regional wave activity (ZW3) and pressure anomalies (ASL) are more closely associated with δ18O variability in this region than hemispheric SAM variability.

ZW3 is linked to changes in meridional airflow patterns; its intensification enhances the advection of warm, isotopically enriched air masses toward the Ross Sea, resulting in higher δ18O values (Raphael, 2007). While the amplitude of ZW3 strength showed a moderately related to δ18O, the phase of this wave did not exhibit significant influence, indicating that wave amplitude rather than longitudinal displacement is more relevant for isotope variability at this site. The interaction between ZW3 and the ASL introduces additional complexity. Enhanced ZW3 activity coincides with increased ASL intensity (Cohen et al., 2013), which can coincide with southward transport of cold, dry continental air, partially offsetting the warming influence of ZW3. This dynamic interplay suggests that δ18O variability at Hercules Névé may represent a net balance between warm marine and cold continental air mass effects, both associated with the coupled ZW3–ASL system (Hosking et al., 2013; Turner et al., 2013). These findings highlight the importance of considering regional atmospheric wave activity and its coupling with local pressure systems when interpreting isotopic records. Further investigation into the phase relationships and the relative contributions of competing air masses would be essential to clarify the mechanisms controlling isotope variability in the Ross Sea sector.