Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island

Gas hydrates modulate methane and carbon dioxide benthic fluxes into the ocean and usually occur embedded in the sediment. Here we use acoustic surveys alongside optical and geochemical observations from remotely operated vehicles to show that CO2 hydrate mounds are forming directly on the seafloor atop a large liquid CO2 vent field offshore Mayotte Island. The venting, which initiated following volcanic activity in 2018, deleteriously impacts surrounding coral communities due to local acidification. Carbon dioxide hydrates on the seafloor are sustained by the venting of liquid CO2 associated with volcanic activity near Mayotte Island, according to observations from remotely operated vehicles and geochemical analyses.