Seawater leaches some other elements from the rocks during its circulation beneath deep-sea vents - particularly manganese, iron, copper and zinc. It also picks up hydrogen sulphide, which provides an energy source for the microbes that form the base of the food chain at vents. So the fluid that pours out of deep-sea vents has a different chemistry to that of seawater - it lacks some of the dissolved elements usually found in seawater, but is enriched in others.

But the chemistry of deep-sea vents varies with their geological setting. Vents found around fresh undersea volcanoes show some differences in their fluids to vents found on older crust, for example. And in 2000 a new type of deep-sea vent was discovered on the Mid-Atlantic Ridge. The chemistry of that vent, which was nicknamed 'Lost City', was unlike any seen before - and geochemists are still figuring out the reactions that drive it.

In November last year, a US-led survey of the waters of the Cayman Trough detected hints of three different types of deep-sea vents on the ocean floor below. One set of vents may be a 'classic' vent field, in a recently-active volcanic area. Another may be the type found on older crust. And there are tantalising signs of a 'Lost City' type of vent - if so, it will be the second one seen so far anywhere in the world.

The temperature of deep-sea vents can be affected by their depth, because they are under greater pressures at greater depths. The vents in the Cayman Trough could theoretically be the hottest known so far, possibly even producing 'supercritical' fluids - a form of water found at extreme temperatures and pressure, which is little understood outside computer simulations.

The extreme depth of the Cayman Trough may also alter the chemistry of its deepest vents, which could mean new species of marine life around them. We won't know for sure until we find the vents, take samples of their fluids, and see what is living down there.

Page 1: Pool cleaners of the world's oceans
Page 2: Deepest and hottest?
Page 3: Getting the big picture

Want to dive deeper?

Visit Venture Ocean to find out more about deep-sea vents

Explore the different types of deep-sea vents found so far on the ocean floor

Read more about the 'Lost City' vent field


Find out more about the Cayman Trough, undersea volcanoes, deep-sea vents,
and the inhabitants of the abyss.
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