Off the coast of Okinawa, a slim stretch of land among Japan’s southern Ryuku islands, thousands of metres below the surface, there are the remains of extinct hydrothermal vent systems scattered about the ocean floor.
The minerals at these long-dead former vent sites are now gaining attention due to increasing international interest in deep-sea mining. Just one of these deposits is thought to contain enough zinc to supply Japan’s demand for a year. For a country that imports the vast majority of its mineral resources, seafloor sulphide deposits are seen as a tantalising potential domestic alternative. But there is a high price: disrupting these sites through mining could put unique and fragile ecosystems at risk.
These mineral-rich deposits – known as seafloor massive sulphides – mark the point where scaldingly hot water used to surge up from chimney-like fissures in the seafloor crust near the boundaries between tectonic plates. They form when cold seawater seeps down through fractures in the crust, heating up and leaching minerals from the rocks as it passes. The heated water then rises back to the seafloor, exiting explosively to produce smoker chimneys.