The Azimuth Project
Thermohaline circulation (Rev #6)



The thermohaline circulation or THC is that part of the large-scale ocean circulation that is driven by water density gradients. The adjective thermohaline comes from ‘thermo-’ referring to temperature and ‘-haline’ referring to salt content, factors which together determine the density of sea water.

In the North Atlantic, for example, the wind-driven current called the Gulf Stream heads northwards, cooling and eventually sinking at high latitudes, where it forms North Atlantic Deep Water?. This cold dense water then flows back south, deep below the ocean’s surface. While the bulk of it upwells in the southern Atlantic, some continues on to the Pacific, and so on, as shown here:

For this reason, the THC is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. It mixes water between oceans, and transports energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe.

As a result, the state of THC has a large impact on the climate of the Earth. During the Younger Dryas episode, the Northern Atlantic portion of the THC appears to have ‘shut down’ due to large amounts of fresh water from melting glaciers — or more precisely, Lake Agassiz. The possibility of a similar shut-down, caused by global warming, has been widely studied. See for example:

The term ‘thermohaline circulation’ is sometimes used to refer to the Atlantic meridional overturning circulation or AMOC. The term AMOC is actually more well-defined as it is difficult to separate the part of the circulation which is actually driven by temperature and salinity alone as opposed to other factors such as the wind. Conversely, temperature and salinity gradients can also lead to a circulation which does not add to the MOC itself.


For starters, try:

Also read Stefan Rahmstorf’s review articles:

category: climate, oceans