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e-Science

To be or not to be circulating

Giant circulation engines in the atmosphere and ocean help drive and regulate Earth's climate. Some of the great circulation engines in nature can be either 'on' or 'off'. The global ocean conveyor (thermohaline circulation) is the most famous example. But some recent studies have questioned whether it really has just two stable states?

GENIE scientists have used computers from around the UK to map out the possible states of the ocean circulation using different Earth system models.

In all models there are certain combinations of ocean and atmospheric conditions for which the circulation can be moving (on) or could have faltered (off).

To the team's surprise, in the more sophisticated models where the oceans and atmosphere fully interact, they found that once certain conditions (such as changes in temperature or salinity) had caused the ocean conveyor to switch off, the atmosphere makes it much harder for it to switch back on again. That is, the circulation can remain switched off even when environmental conditions have returned to a state which had previously allowed it to move.