Mechanisms Driving Recent Sea-Level Acceleration in the Gulf of Guinea

The Gulf of Guinea is experiencing accelerated sea-level rise (SLR), with localized rates exceeding 10 mm yr⁻¹, more than twice the global average. Integrated analysis of GRACE/FO ocean mass data, reanalysis products, and machine learning reveals a fundamental regime shift in the regional sea-level budget after 2015. Ocean mass increase, primarily driven by intensified terrestrial hydrological discharge, accounts for over 60% of observed SLR near major riverine outlets, indicating a transition from steric to barystatic-manometric dominance. This transition aligns with increased monsoonal precipitation, wind-driven changes in equatorial wave dynamics, and coupled Atlantic-Pacific climate variability. Piecewise regression identifies a significant 2015 breakpoint, with mean coastal SLR rates rising from 2.93 ± 0.1 to 5.4 ± 0.25 mm yr⁻¹. GRACE data show extreme mass accumulation (>10 mm yr⁻¹) along the eastern Gulf coast, strongly linked to elevated river discharge and estuarine retention. Physical analysis indicates that intensified wind stress curl has altered Rossby wave dispersion, enhancing zonal water mass convergence. Random Forest modeling attributes 16% of extreme SLR variance to terrestrial runoff, close to wind stress’s 19%, highlighting underestimated land-ocean coupling. Current global climate models underrepresent these manometric contributions by 20–45%, causing critical biases in projections for high-runoff regions. The societal impact is severe, with over 400 km² of urban land in Lagos and Abidjan at risk of inundation by 2050. These findings expose a hybrid steric-manometric regime in the Gulf of Guinea, challenging existing paradigms and indicating similar dynamics may affect tropical margins globally. This calls for urgent model recalibration and tailored regional adaptation strategies.