Interplay of Subduction Tectonics, Sedimentation, and Carbon Cycling Interplay of subduction tectonics, sedimentation, and carbon cycling

Several carbonate‐rich layers, up to 11 m in thickness, were recovered in sediments collected at Site U1379 in the outer shelf of the Costa Rica margin, offshore the Osa Peninsula. These layers coincide with minima in the magnetic mineral assemblages. To investigate the processes and mechanisms that led to the formation of these carbonates, we used geochemical and sedimentological analyses of pore water and solid phase samples collected at two sites (U1378 and U1379) during the Integrated Ocean Drilling Program (IODP) Expedition 334. Our results, in the context of available dating and tectonic reconstructions, indicate that the discrete carbonate layers formed near the seafloor driven by anaerobic oxidation of methane, which was released from deeper sediments. The methane discharge events can be related to the subsidence and uplift history of the margin following the subduction of the Cocos Ridge beneath the Caribbean plate. Methane discharge at Site U1379 began ~1.1 Ma, when the ongoing margin uplift brought this site to a depth shallower than that where gas hydrates are stable, breaking a permeability barrier that had kept methane trapped within the sediment. Since then, methane continued to be released in discrete events modulated by characteristics of the gas reservoir