25 Mar 2014

MH370: what lies beneath the southern Indian Ocean?

As the search for missing Malaysia flight MH370 narrows, questions are being asked about what lies under the vast southern Indian Ocean.

The average depth of the Indian Ocean is 12,762ft. It is the third largest of the world’s oceanic divisions, covering approximately 20 per cent of the water on the earth’s surface.

Its deepest point is Diamantina Deep in the Diamantina Trench. Diamantina Trench is the south-eastern basin of the India Ocean. Its maximum depth is more than 26,401 ft deep.

Diamantia Deep is located 621 miles west-south west of the city of Perth in Australia.

‘Islands and volcanos’

The southern Indian Ocean, between Indonesia and Australia, is broken up only by the Australian territories of Christmas Island and the Cocos (Keeling) Islands.

These remote islands, with a population of fewer than 1,000 people, have a small airport.

Further south, the only habitation is a handful of research stations and a group of volcanic outcrops between Africa, Australia and Antarctica.

One of these is Big Ben, an active volcano that makes up most of Heard Island in the southern Indian Ocean. Much of it is covered by ice, including 14 major glaciers.

‘Underwater mountains’

The south west Indian Ocean ridge (an underwater mountain system that consists of various mountain ranges and a valley) is a major geological feature which extends from the central Indian Ocean to join the mid-Atlantic ridge in the southern ocean.

It is rich in seamounts (mountains rising from the ocean seafloor that do not reach to the water’s surface) and supports a productive deep-water fishery. Yet in terms of biodiversity and ecosystem functioning, it is one of the least sampled regions of the global ocean.

The south east India Ridge, which separates the Indo-Australian tectonic plate and the Antarctic plate, extends from the far southern area of the central Indian Ocean to the far western edge of the Pacific Ocean off the southern coast of Australia. The ridge is a divergent tectonic boundary as the two plates are moving away from each other.

The greater part of the water area of the Indian Ocean lies within the tropical and temperate zones.

The shallow waters of the tropical zone are characterised by numerous corals and other organisms capable of building, together with calcareous red algae, reefs and coral islands.

These coralline structures shelter a thriving marine fauna consisting of sponges, worms, crabs, molluscs, sea urchins, brittle stars, starfish, and small but exceedingly brightly coloured reef fish.

Fishing is confined to subsistence levels, because its fish are of great and growing importance to the bordering countries for domestic consumption and export.

‘Lungs of the ocean’

Joellen Russell, an associate professor in biogeochemical dynamics at the University of Arizona, writes: “This is where you see the lungs of the ocean working, where you get oxygen in, and you bring up carbon-rich and nutrient rich waters to the surface. It’s what makes it so productive.”

He added: “The southern ocean takes up something like 70 per cent – plus or minus 30 per cent – of all the anthropogenic heat that goes under the ocean.

This is where you see the lungs of the ocean working, where you get oxygen in, and you bring up carbon-rich and nutrient rich waters to the surface – Joellen Russell

“This is one of the few areas of the global ocean that is immediately and definitely playing a role in the temperature on land, because it’s taking up all this anthropogenic heat and carbon. The whole ocean is doing that, but here it’s doing it more than it ought to.”

The westerly winds here have increased by about 20 per cent over the last 20 years, according to Mr Russell’s 2006 investigation into the trends.

‘An ocean in motion’

Erik van Sebille, lecturer in oceanography at University of New South Wales, Australia, blogs that the southern Indian Ocean is extremely volatile, with currents changing speed and direction from day to day.

One of its unique features is that it is the only place in the world where water can keep on moving eastward without ever hitting land.

Because of this, and the strong winds, the water is swept along at very high speeds, sometimes almost two metres a second – much faster than any other place in the world.