Ricardo León

Supplementary methods, multibeam and seismic datasets (Tables S1–S2), and Supplementary Figures S1–S10 documenting tectonic, seismic, bathymetric, gravity, GPS, and seismicity data used in this study.

Supplementary methods, multibeam and seismic datasets (Tables S1–S2), and Supplementary Figures S1–S10 documenting tectonic, seismic, bathymetric, gravity, GPS, and seismicity data used in this study.

High-latitude continental margins host some of the largest submarine landslide worldwide. Much speculation has focused on their relationship to glaciomarine sedimentation, gas hydrates and seismic shaking and, ultimately, the climatic variations that link to the former three factors. In this study we aim to better understand the causal mechanisms of such events in high-latitude margins. We focus on the Antarctic continental margins, particularly the Pacific Margin of the Antarctic Peninsula, which have been less studied than its Arctic counterparts. We use a combined dataset of archive and recently acquired swath bathymetry and seismic data. Two distinct submarine landslide groups are identified according to the water depth they show up. The shallowest cluster has mode depth centered around 1500 mwd, while the deepest cluster mode depth is centered around 4500 mwd. Most of their source areas are in 15-20 º slopes and, opposed to the Arctic counterparts, exhibit relatively small magnitudes, ranging from 0.1 to 10 km2 in areal extent and between 0.1 to 1 km3 in volume. The identified submarine landslides are mainly located in tectonically active environments. In addition to glaciomarine sedimentation, both tectonics and gas hydrates, may act as triggering mechanisms for submarine landslides in the Antarctic Peninsula margin. Few landslides occur in gas hydrate bearing sediments, as evidenced by the occurrence of a BSR, and there is no evidence of submarine landslides rooted at the base of the gas hydrate stability zone. Approximately one half of the landslides occur along the area dominated by the glaciomarine sedimentary wedge, but the location of the deepest landslide cluster lays outside this wedge. Overall, high-exponents of a power-law fit to the frequency-magnitude relationship and fault-landslide neighborhood relationships suggest a potential seismic control on submarine landslide occurrence.

Antarctica InSync is a global effort to synchronise research across Antarctica and the Southern Ocean, connecting ice, ocean, land, climate, and life to protect this vital region. This roadmap paper introduces the scientific and technological motivation and action plan to build an international programme for a coordinated field season in Antarctica and its surrounding seas. It lays out the international collaboration that is required to realise an ambitious action plan and the opportunities for the science community to address important scientific themes that identify current knowledge gaps. In the spirit of the Antarctic Treaty Consultative Meeting (ATCM), the planned scientific action mandates free data exchange, facilitates international collaboration, and derives expert scientific advice together with the Scientific Committee on Antarctic Research (SCAR). Aligned with challenges of the United Nation Ocean and Cryosphere Decades, we plan a shared global effort to better understand the role of Antarctica and its surrounding ocean for our global futures, building on decades of achievements in polar and ocean science. As a milestone leading up to the next International Polar Year in 2032/33 (IPY5), the ambition is to achieve a new level of cooperation, with opportunities for the next generation of polar scientists around the world by enhancing practices in sharing of ideas, infrastructure and information.

Theme 1 addresses the Southern Ocean’s (south of 30°S) critical role in regulating Earth’s climate through circulation patterns that mediate global exchanges of heat, carbon, freshwater, and nutrients. The region has absorbed over 70% of anthropogenic heat and has contributed to about 40% of the global ocean uptake of human-emitted carbon dioxide (CO₂) while also controlling ice shelf stability and sea level rise. However, fundamental gaps in year-round observations, particularly during austral autumn, winter, and spring, severely limit our understanding of these processes and their responses to rapid climate change. This white paper establishes key knowledge gaps and high-priority recommendations that are tractable within the InSync timeframe through coordinated program execution with strong engagement from national operators and funding agencies. Critical needs include seasonal observations of the marginal ice zone where carbon, heat and nutrient-rich waters upwell, year-round continental shelf measurements where dense water formation and ice-ocean interactions occur, standardized air-sea flux measurements, and strategic monitoring of regional choke points. Success requires international resource sharing, coordinated deployments, and sustained commitment to both process studies and long-term monitoring.

This study provides a sensitivity analysis of the main physicochemical (PC) oceanographic variables (pressure-depth, bottom water temperature and salinity) that control the theoretical stability of marine gas hydrates and quantifies their relative importance. It focuses on how glacial-interglacial periods, such as the Last Glacial Maximum (LGM), influence the variability of the gas hydrate stability zone (GHSZ) thickness along the water depth range of the study area. The European continental margins have been used as an example to establish ranges of variability for bottom salinity and temperature. Our results show that LGM-driven variations in PC oceanographic variables had contrasting impacts across water depths, amplified under colder bottom-water conditions. Bottom-water temperature is the main driver, reducing GHSZ thickness by 300–450 m from the LGM to the present. In shallow waters (< 500 mwd), salinity shifts (21.5–38.5 psu from basin restriction, 0–35.5 psu from marine intrusions into glacier-occupied areas, or 35.5–0 psu from runoff/glacier melt) and sea-level drops of up to 120 m (SLD-120 m) independently generate absolute GHSZ thickness variations of 100–300 m on the continental shelf and upper slope. The logarithmic pressure–temperature relationship within the hydrate stability field causes the impact of PC variables to diminish with depth, stabilizing at near-constant values in the abyssal plains, with larger effects from salinity increases (76–36 m) than from SLD-120 m (6–10 m). In deep areas, minor salinity variations (e.g., 35.5–38.5 psu or vice versa) and a SLD-120 m have a negligible impact on GHSZ thickness. These results highlight the dominant role of bottom water temperature in controlling GHSZ thickness over glacial–interglacial cycles, while also demonstrating that the impact of salinity and sea-level changes is strongly depth-dependent.

The land and seascape of the Canary Islands witnesses a long history of volcanic growth and volcano-tectonic deformation. This interplay has generated a spectacular morphology that stretches over almost 8 km (vertically) from the foot of the western volcanic islands at 4.000 m water depth to the top of the Pico del Teide at 3.718 m above sea level. On 19th September 2021, Cumbre Vieja volcano on the island of La Palma, experienced its longest eruption in historic times, lasting for three months. The eruption was accompanied by widespread deformation, expressed among others by tens of thousands of earthquakes, meter-scale vertical elevation changes, fractures and eruptive fissures that opened along the onshore flank, and the build-up and collapse of volcanic cones. It is now a major task for researchers to identify and untangle the different deformation patterns in order to learn about volcano-tectonic and related sedimentary processes before, during, and after the eruption. Because the largest volume of the volcano locates underwater, a comprehensive analysis of volcano-tectonic deformation requires marine data. Here we present a synthesis of legacy hydroacoustic data from the last century together with new data collected in recent years and especially after the 2021 eruption. The new data include multibeam bathymetry from VULCANA_1015, VULCANA_0318 and VULCANA_III_LP_0921/1021-0222 cruises which were supported by the Spanish Institute of Oceanography (IEO-CSIC) funds through the VULCANA project. These data cover the submerged flank down to a water depths of 1940 m with a 10x10 m grid spacing. We further collected multibeam and sediment echosounder data from the lower part of the island slope and adjacent abyssal seafloor between the islands of La Palma and El Hierro during RV MARIA S. MERIAN Cruise 113 in January 2023. Together the different data cover the western side of La Palma, which has collapsed repeatedly in a likely catastrophic manner over geologic times, with the Cumbre Nueva debris avalanche at 125–536 ka representing the youngest event. We use the data to map sedimentary and tectonic structures including fault outcrops, submarine canyons and channels, mass-transport deposits, landslide scars and blocks as well as folded and faulted strata between the coast and about 4500 m water depth. The results add to a land-to-sea analysis of volcano-tectonic deformation at Cumbre Vieja volcano including the spatial extent and outline of the mobile western flank, which seems to be moving into the Atlantic Ocean.

The continental margin off the Antarctic Peninsula hosts significant gas hydrates accumulations off the South Shetland Islands. The area has experienced remarkable isostatic rebound due to ice sheet retreat since the Last Glacial Maximum (LGM). Considering heat flow data reported in the area, hydrates could undergone active dissociation. Such dissociation may modify the mechanical properties of hydrate bearing sediments, eventually leading to slope failures and related fluid seepage may also translate in methane emissions to the ocean. Here we use legacy seismic data to map the occurrence of gas hydrates and free gas and their relation to tectonic structures with the aim of determining the nature of fluid emissions (diffuse or focused).The subduction of the former Phoenix plate beneath the Shetland plate is the main tectonic control of the area. Normal faults are particularly apparent in the upper part of the slope. These faults disrupt the seafloor or the upper subsurface (within 0.25 to 1 s TWTT below seafloor).Seismic indicators related to the presence of marine gas hydrates, referred to as bottom simulator reflectors (BSRs), have been observed in the continental slope between Snow and Greenwich Islands and among the Shackleton Fracture Zone and Nelson Island. They are located at water depths between 450 and 4800 m and 0.12 to 0.9 s TWTT below seafloor, becoming shallower towards the shelf edge. The BSRs are commonly affected by normal faults.In seismic data, free gas is inferred by acoustic blanking and chimneys. However, the same acoustic response could result from intense tectonic activity, particularly at the foot of the slope, where the Shetland block overthrusts the Phoenix plate. Acoustic blanking and seismic chimneys are often found on the slope in water depths between 590 to 5175m and 0 to 2 s TWTT below seafloor. In general the acoustic blanking is identified in the upper part of the sedimentary record, particularly in the accretionary prism. In most seismic profiles, BSRs occur together with faults, chimneys and acoustic blanking.According to our results, faulting plays a significant role in the migration of fluids trapped in the sedimentary record. In addition, the presence of chimneys and acoustic blanking in replacement of BSRs suggests unstable gas hydrates under the present-day Pressure/Temperature conditions.

In the Antarctic Peninsula, a marine gas hydrate system has been identified based on geophysical data (Lodolo et al., 1993; Tinivella et al., 2002). These data suggest gas hydrates average volume concentration of 6.0 ± 1.2% for in the accretionary wedge of the South Shetlands Islands (Tinivella, 2002). Based on legacy seismic profiles (belonging to 17 oceanographic cruises) retrieved from the Antarctic Seismic Data Library System (SDLS), a continuous Bottom Simulating Reflector (BSR) has been mapped in the accretionary wedge, between Elephant and King George islands. This BSR is located at a sub-bottom depth between ca. 250 ms TWTT in the upper slope and ca. 1s TWTT at the base of the accretionary wedge. The theoretical Base of Gas Hydrate Stability Zone (BGHSZ) calculated with a static model (León et al., 2009) for the present oceanographic conditions (pressure/bathymetry, seafloor temperature, geothermal gradient and salinity) is located 100 to 400 m shallower than this BSR level, considering available geothermal data for the area. The BSR-BGHSZ mismatch points that gas hydrates in the area seem to be in a transient state with respect to their theoretical location calculated from both pure methane and thermogenic compositions. Dynamic models developed with TOUGH+HYDRATE in the frame of ICEFLAME project (PID2020-114856RB-I00, Spanish Ministry of Science and Innovation), reveal two possible scenarios for the above mismatch between BSR and BSGHZ: isostatic rebound and/or tectonic uplift. References León, R., Somoza, L., Giménez-Moreno, C.J., Dabrio, C.J., Ercilla, G., Praeg, D., Díaz-del-Río, V., Gómez-Delgado, M., 2009. A predictive numerical model for potential mapping of the gas hydrate stability zone in the Gulf of Cadiz. Mar. Pet. Geol. 26, 1564–1579. https://doi.org/10/czq8vq Lodolo, E., Camerlenghi, A., Brancolini, G., 1993. A bottom simulating reflector on the South Shetland margin, Antarctic Peninsula. Antarct. Sci. 5. https://doi.org/10/bfcb22 Tinivella, U., 2002. The seismic response to overpressure versus gas hydrate and free gas concentration. J. Seism. Explor. 11, 283–305. Tinivella, U., Accaino, F., Camerlenghi, A., 2002. Gas hydrate and free gas distribution from inversion of seismic data on the South Shetland margin (Antarctica). Mar. Geophys. Res. 23, 109–123. https://doi.org/10/fcgq3q