The Ocean Conveyor Belt

The thermohaline circulation that distributes heat through the world’s oceans both influences and is influenced by the climate, and is often referred to as the ‘conveyor belt’.

• 20 August 2008 | Updated 14 October 2011

• The conveyor belt in the Southern Ocean
• The conveyor belt is changing

Wealth from Oceans Flagship researchers are working to better understand the complex interactions the conveyor belt has with climate.

The global ocean conveyor belt originates in the Southern Ocean’s Antarctic Circumpolar Current.

It comprises a series of ocean currents that transfer the warm waters of the tropics towards the polar regions and contains an ‘overturning’ system that brings salty, cold water from the deep ocean to the surface. The conveyor belt absorbs carbon dioxide and supplies oxygen to the deep ocean.

These processes have an influence on climate around the globe. They can take hundreds of years and are distinct from other natural oceanic features such as El Niño/La Niña that influence the patterns and distribution of rainfall, and wind and storm systems.

The conveyor belt in the Southern Ocean

The deep layers of the Australia-Antarctic basin are supplied by water sinking in two locations near the coast of Antarctica, where cold temperatures and sea-ice formation make water at the sea surface so dense and salty that it can sink to depths of four or five kilometres and influence deep ocean circulation.

Observing change in these inhospitable waters is difficult but scientists have been building a profile of conditions using:

• research and commercial ship
• moored and drifting instruments
• robots profiling the upper ocean
• earth-observing satellites capturing ocean surface conditions.

The conveyor belt is changing

Measurements suggest that the movement of water between the warm surface layers of the ocean and the cool deep layers is changing.

New observations show that the dense water produced around the periphery of Antarctica is capable of rapid and widespread change.

Salinity data show significant changes to the conveyor belt. In global analyses, the waters at high latitudes (north of 50°N and south of 70°S) are fresher in the upper 500m. In contrast, the upper 500m of sub-tropical latitudes in both hemispheres are characterised by an increase in salinity.

During January and February 2005, Flagship scientists on the Antarctic Research Vessel Aurora Australis, with partners from the Antarctic and Climate Ecosystem CRC, repeated a series of measurements first made 10 years ago in the Southern Ocean south of Australia to observe any changes in the deep ocean currents that form part of the ocean conveyor belt.

At every measurement site in the deep basin adjacent to Antarctica, scientists found waters near the sea floor were cooler and less salty than they were a decade ago. The results suggest:

• the deep ocean is a much more dynamic environment than anticipated
• changes in the sinking regions can influence a large region of the ocean in just a few years.

Find out more about CSIRO’s research in Oceans.