Sensitivity analysis of the physicochemical oceanographic drivers on the gas hydrate thickness variability associated with the last glacial Maximum - the European continental margins as a study case

Abstract 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.