A world of extreme pressure
The Kermadec Trench, a near-linear chasm in the southwest Pacific Ocean, stretches for over 1,000 kilometers northeast of New Zealand. It is the fifth-deepest oceanic trench on Earth, plunging to a maximum depth of 10,047 meters (32,963 feet) at a point known as the Scholl Deep. This region is part of the hadal zone, the ocean's deepest classification, which encompasses all depths greater than 6,000 meters. The name comes from Hades, the Greek underworld, and conditions are suitably extreme. At the bottom of the Kermadec Trench, hydrostatic pressure exceeds 1,000 atmospheres, the equivalent of placing 1,600 elephants on the roof of a small car. Temperatures hover near freezing, and the environment is one of absolute darkness.
This immense feature is formed by tectonics. It forms the boundary where the Pacific Plate subducts, or dives beneath, the Australian Plate. This convergence happens at one of the fastest rates on the planet, with the plates moving towards each other at up to 80 millimeters per year. This geological activity carved the trench but also feeds the Kermadec Arc, a chain of more than 50 submarine volcanoes that runs parallel to it.
Giants and gelatinous survivors
Life in the hadal zone requires radical adaptations. The organisms of the Kermadec Trench show how evolution answers the challenges of extreme pressure and cold. One of the most striking inhabitants is the supergiant amphipod, Alicella gigantea. While most amphipods are about 2.5 centimeters long, these milky-white crustaceans can reach lengths of up to 34 centimeters (13 inches). They are dominant scavengers, congregating around any organic matter that falls from the upper ocean.
The trench also contains one of the world's deepest-living fish, the hadal snailfish Notoliparis kermadecensis. This species is endemic to the trench, living at depths between 6,472 and 7,561 meters. First collected by the Danish Galathea expedition in 1952, these fish have gelatinous bodies and minimal skeletons to withstand the pressure. They cluster in groups to feed on the abundant amphipods. Expeditions using baited, free-falling camera systems have filmed large aggregations of these fish, changing the long-held belief that hadal fish were rare and solitary. Other specialized fauna include anemones, sea cucumbers, and polychaete worms that populate the seafloor.
Exploration of the trench is a major technological challenge. The first sampling dates to the 1950s, but modern understanding has been shaped by robotic and human-occupied vehicles. In 2014, the unmanned research submarine Nereus imploded at a depth of 9,990 meters during an exploratory mission in the trench. More recently, in 2022, the human-occupied vehicle Fendouzhe completed a series of dives to the trench floor, collecting biological samples and data that reveal new species and insights into this extreme environment.