Upper boundary variation of the gas hydrate stability zone in the Sea of Okhotsk: Error assessment and climate change scenarios based on 131286 oceanographic stations (1929-2020)

Abstract

Gas hydrate (GH) dissociation and its interaction with global warming represent a critical yet poorly constrained climate feedback. This study aims to quantify the instrumental and methodological errors in estimating the upper boundary of the gas hydrate stability zone (GHSZ) in the Sea of Okhotsk and to assess how this boundary shifts under various global warming scenarios, thereby evaluating the thermal stability of known GH accumulations in the region. A total of 131286 oceanographic stations (1929-2020) from multiple data centers were compiled and quality-controlled; the upper GHSZ boundary was computed using the Dickens GR and Quinby-Hunt MS phase equilibrium equation for a pure methane-seawater system (100% CH₄, S = 33.5‰) on a 0.35°×0.55° trapezoidal grid, with comprehensive observational errors quantified as three standard deviations within each grid cell, and five warming scenarios (1°C-5°C) applied to full-depth temperature profiles at 22 representative deep-water nodes. The total observational error in upper GHSZ boundary depth is approximately ±25 m, distributed randomly with no dependence on data density or location; each 1°C of warming causes a downward shift of about 40 m, and the boundary of the zone lacking thermobaric conditions for GH formation extends to a maximum isobath of about 170 m under the most extreme scenario considered. Critically, known GH accumulations in the Sea of Okhotsk are not threatened by thermal dissociation even under a conservative 1°C/100 a warming sustained for 300 years or a rapid 3°C warming over 100 years, consistent with global simulations and regional vessel-based observations. These findings provide essential GHSZ boundary constraints for numerical modeling of hydrate-climate interactions, support quantitative assessment of GH sensitivity to environmental changes, and inform hydrate exploration and methane seep monitoring across marginal seas of the western Pacific.

Keywords

Methane hydrates / Combustible ice / Upper boundary of stability zone / Oceanographic conditions / Climate change / Greenhouse effect / Atmospheric CO₂ rise / Methodological errors / Sea of Okhotsk

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