The deep ocean is one of the harshest places to live on our planet – cold, dark and with pressures up to 250 times greater than on land. When scientists discovered the first hydrothermal vent in 1977, they were amazed to see heaps of clamshells clinging to it and large colonies of shrimp.
Volcanic, or hydrothermal, vents (also called smokers) are similar to hot springs on land, but sit around 2,100 metres (7,000 feet) beneath the ocean surface. Superheated water spews out of cracks in the seabed forming plumes of mineral particles that look like smoke.
Fragile chimneys of minerals up to ten metres (33 feet) high form around the plumes and can grow upwards at 30 centimeters (12 inches) a day.
Temperatures vary between two degrees Celsius (35.6 degrees Fahrenheit) in the deep ocean to above boiling point around the vents. The water is heated by molten rock close to the seabed. Cracks and hot rocks are found at rifts where vast tectonic plates that make up Earth’s crust are slowly V moving apart. New ocean crust is created fl in the gaps between plates.
The vents cool after a few years or decades as new ocean crust moves outwards from the mid-ocean ridges by 6-18 centimeters (2.4-7 inches) per year. New vents are quickly colonized by bacteria, which live in deep-sea rocks and water in small numbers.
Since vents were discovered, they’ve been found in the Pacific and Indian Oceans, in the mid-Atlantic and the Arctic. Species vary between vents. In the Atlantic Ocean, for example, there are no worms, clams nor mussels, but many white shrimp.
Living without sunlight
The first life able to exist without energy from sunlight was discovered around a black smoker vent. Before then, scientists believed life in the dark deep ocean survived by eating food scraps that had fallen from shallower waters.
More than 300 species of shrimp, clams, predatory anemones and others live around vents – many unique – with around 35 new species discovered each year. All rely for food on mats of white bacteria, which use poisonous hydrogen sulphide from vent water as fuel to convert carbon dioxide and water into edible carbohydrates. Some species, such as vent worms, have bacteria living in their bodies. These bacteria take the place of plants on the Earth’s surface. When the vent cools, tiny organisms can also eat the iron and sulphur inside the chimneys.
Water gushing from volcanic vents can be four times hotter than 100 degrees Celsius (212 degrees Fahrenheit) – the approximate boiling point of water in your kettle. Yet it doesn’t turn into steam…
The reason for this is the immense pressure in the deep ocean. Imagine you’re standing on the seabed with a huge column of water above. The ocean weighs down on you with a pressure some 250 times greater than on land; it’s similar to having an elephant stand on your big toe!
These high pressures squeeze water in volcanic vents, stopping it expanding when heated. When liquid water boils into steam, molecules that were close together absorb enough heat energy to fly off in different directions. But these huge pressures prevent water molecules flying around as steam – they can’t get far enough before hitting another moving molecule.
Superheated water can enter rock cracks like steam, but is as effective as water at dissolving minerals.