The Antarctic Peninsula (AP) has witnessed dramatic ice shelf disintegration since the early 1990s, most notably the collapse of Larsen A and B ice shelves. This has resulted in accelerated glacier thinning and flow, contributing significantly to global sea level rise. The remaining Larsen C Ice Shelf, the largest in the region, is also experiencing thinning and calving events. These changes are strongly linked to anomalous warm summer temperatures causing significant surface melt, often facilitated by foehn winds – warm, dry winds that descend the AP's eastern slopes. While previous research associated this warming with intensified circumpolar westerly winds and the Southern Annular Mode (SAM), recent studies suggest a role for remote tropical forcing. This study investigates the influence of central tropical Pacific (CPAC) convection on the extreme summertime surface melt and record-high temperatures observed on Larsen C Ice Shelf, aiming to quantify the impact of this remote forcing and its contribution to ice shelf instability.

Prior research has established a link between the warming climate on the Antarctic Peninsula and the disintegration of its ice shelves, with surface melt playing a crucial role. Increased summertime circumpolar westerly winds and a positive trend in the SAM index have been qualitatively linked to these events, particularly concerning foehn wind activity over the northeast AP. Foehn events are characterized by significant warming as high-altitude air descends the eastern slopes of the AP, potentially exceeding +10°C and causing strong surface melt. However, quantitative evidence directly connecting circumpolar westerlies/SAM to long-term surface melt variability, especially extreme melt events, was lacking. Emerging evidence points to the possibility of remote tropical forcing as a significant contributor to surface melt on Larsen C, warranting further investigation into potential mechanisms and the relative contribution of tropical and high-latitude drivers.

This study uses multiple datasets to analyze the connection between CPAC convection and Larsen C surface melt. Atmospheric circulation data comes from the ERA5 reanalysis, providing monthly and 6-hourly fields for various atmospheric parameters. Tropical variability is examined using NOAA's ERSSTv5 SST data and NOAA's interpolated OLR dataset, alongside the SOI and SAM indices. Larsen C surface melt is derived from a high-resolution Polar-WRF model simulation (December 1991 to March 2015). The study employs correlation and regression analyses to assess the relationships between Larsen C surface melt and various climate indices. Case studies of two extreme foehn events (March 2015 and February 2020) are analyzed using 6-hourly ERA5 data. A sensitivity experiment with the NCAR Community Earth System Model (CESM) examines the direct atmospheric response to CPAC convection. Atmospheric rivers (ARs) are identified using an AR catalog and a custom algorithm based on ERA-Interim and ERA5 data, respectively, to explore their role in the observed phenomena. Statistical significance is assessed using Student's t-tests.

The study's key findings demonstrate a strong negative correlation (-0.63, p<0.01) between Larsen C surface melt and CPAC OLR anomalies (indicating enhanced convection). In contrast, Larsen C surface melt exhibits no significant relationship with the SAM index during summer. Instead, positive surface melt anomalies are linked to a zonally asymmetric atmospheric circulation pattern triggered by CPAC convection, featuring a cyclonic anomaly over the South Pacific and a high-pressure anomaly over Drake Passage. This pattern fosters moist southwesterly flow across the AP, resulting in foehn warming and increased surface melt over Larsen C. Analysis of extreme melt events reveals that anomalous deep CPAC convection occurred in 13 of the 15 most extreme events. The two recent record-high temperature events (March 2015 and February 2020) are shown to be driven by similar synoptic conditions, featuring anomalous CPAC convection, a wave train across the South Pacific, and strong southwesterly flow across the AP. A CESM sensitivity experiment confirms that CPAC surface heating generates an atmospheric circulation pattern mirroring the observed correlations and case study results, with increased precipitation and near-surface warming along the southwest AP. Further investigation reveals CPAC convection is primarily driven by mid-latitude baroclinic wave activity and cold frontal intrusions, suggesting a less significant role for ENSO or other tropical climate modes. Finally, a strong correlation (0.79, p<0.01) is found between Larsen C surface melt and the frequency of extreme AP landfalling ARs, with CPAC convection being a key driver of this AR variability.

This research significantly advances our understanding of the drivers of extreme high temperatures and surface melt on the Larsen C Ice Shelf. The findings highlight the crucial role of CPAC convection as a key remote forcing mechanism, surpassing the influence of the SAM in this context. The identified atmospheric circulation pattern, characterized by elongated cyclones and associated anticyclones, represents a previously underappreciated pathway for transporting substantial amounts of moisture and heat from low latitudes to the Antarctic Peninsula, leading to extreme melt events. The results also demonstrate a strong connection between CPAC convection, the frequency of extreme atmospheric rivers, and the total summer surface melt. This emphasizes the importance of considering remote tropical influences when projecting future Antarctic climate and ice shelf stability.

This study demonstrates that variability in CPAC convection is a key driver of extreme high temperatures and surface melt on the Larsen C Ice Shelf, exceeding the impact of the SAM. The findings underscore the importance of considering remote tropical forcing when assessing future Antarctic ice shelf stability and its contribution to sea level rise. Future research should focus on improving our understanding and modeling of CPAC convection variability and the associated atmospheric circulation patterns to provide more reliable projections of Antarctic high-temperature extremes and ice shelf dynamics.

The study's reliance on reanalysis data and model simulations introduces inherent uncertainties. The Polar-WRF model's accuracy in capturing surface melt processes requires careful consideration. The focus on Larsen C might limit the generalizability of findings to other ice shelves. The sensitivity experiment's simplified representation of CPAC convection could affect the precise quantification of its impact.