Solid-Phase Carbon Sequestration in Ultra-Deep Ocean Trenches: A Feasibility Analysis of Graphite Deposition in the Mariana Trench Including Cascade Feedback Dynamics and Energy Infrastructure Sizing

This paper presents a CDR pathway combining CO₂ capture with electrochemical conversion to solid elemental carbon (graphite) and permanent deposition in the Mariana Trench (>6,000 m). The analysis quantifies trench capacity at 73,000–147,000 Gt CO₂, integrates cascade feedback dynamics (permafrost, Amazon dieback, sink weakening), sizes Sahara-scale PV infrastructure for various CDR rates, and assesses MSCC-EC technology readiness (TRL 2–3). Even under worst-case cascade scenarios, storage volume is never the binding constraint. The binding constraints are energy supply and conversion technology maturity. The concept is framed as a quantified physical thought experiment. Keywords: carbon dioxide removal, solid carbon, graphite, molten salt electrolysis, Mariana Trench, cascade dynamics, tipping points, permafrost, Sahara PV, Permian–Triassic