A 600-km-long Seafloor Disruption in the Arctic Ocean (~2.8 Ma): Geochemical Evidence for a Marine Impact Event

Marine geophysical surveys of the Alpha Ridge in the central Arctic Ocean reveal an exceptionally large zone of seafloor disruption extending approximately 600 × 200 km along the ridge crest and flanks. Sedimentary strata within this corridor are truncated, rotated, and chaotically deformed to depths of ~300–500 m below the seafloor, accompanied by widespread mass-wasting deposits. Because the Alpha Ridge is tectonically quiescent and lacks evidence for sustained intraplate deformation, the scale, coherence, and asymmetric geometry of this disturbance require an unusually energetic triggering mechanism. Here we synthesize multibeam bathymetry, seismic reflection profiles, sediment-core constraints, and present distal geochemical, mineralogical, and magnetic susceptibility records to evaluate the hypothesis that a large marine impact occurred on the Alpha Ridge. Stratigraphic constraints suggest that the disturbance occurred near the late Pliocene–early Pleistocene transition, with available age models placing the event close to ~2.8 Ma. Distal elemental and mineralogical anomalies recorded in a drill core on the Lomonosov Ridge, approximately 600 km away, mark the largest extraterrestrial-sensitive metal enrichment observed in the past ~12.3 Myr at that site. Although these anomalies are not uniquely diagnostic of an impact event, they are consistent with such an event. Two-dimensional hydrocode simulations suggest that a shallow-angle (~6°) impact by a ~7 km bolide into ~1.5–2 km of ocean water can reproduce the first-order characteristics of the disturbed zone, including its elongated downrange footprint, depth of sediment disruption, chaotic internal structure, and the absence of a preserved classical crater. Non-unique hydrocode-modeled processes include catastrophic projectile fragmentation, asymmetric cavity excavation, shock-induced sediment liquefaction and block rotation, intense bottom currents, and basin-scale water motions capable of generating extensive erosion and redeposition. We therefore interpret a large, shallow-angle marine impact as a physically coherent and testable explanation for the current evidence. Direct recovery of diagnostic shock or geochemical impact markers for definitive confirmation must await additional seismic profiling, drilling expeditions. If confirmed, the Alpha Ridge disturbance would represent the largest known impact-related structure on Earth by areal extent, and it would demonstrate that major marine impacts can leave subtle but detectable regionally extensive signatures in ocean basins.