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Scientists working in the southern Atlantic Ocean have found a 407 °C hydrothermal vent, the hottest yet known on an ocean floor. Although only 5 °C hotter than the previous deep-sea high of 402 °C, recorded in the Pacific Ocean, the new hotspot bumps seawater into the strange state of being a supercritical fluid.

Expedition leader Andrea Koschinsky of International University in Bremen, Germany, and her team found the hydrothermal vent, also known as a black smoker, just south of the Equator on the Mid-Atlantic Ridge at a depth of 2,990 metres — or 299 bar pressure. At pressures and temperatures above 298 bar and 407 °C, seawater becomes something between a thin liquid and a dense vapour: a supercritical fluid.