Until now, researchers had not fully understood how the ocean's currents, such as the Gulf Stream and the North Atlantic, could suddenly change course though the phenomenon was widely recognized. Variations in ocean circulation speeds account for significant instances of climate change, changing the hydrological cycle and altering atmospheric circulation patterns as well. A combination of numerical models, palaeoclimate data and modern observations indicated that ocean saltiness was key to understanding it.
While a surge in heavy, salty water can invigorate deep water circulation, a dilution of the waters prompts a more lethargic flow. This occurs because rising concentrations of salt, which increase the density of water, cause the body of water to sink and draw in water from adjacent areas, initiating a loop known as thermohaline overturning."Salt plays a far more important role that we first thought," says Rainer Zahn, a palaeoclimatologist at the Autonomous University of Barcelona in Spain.Zahn and his colleagues found that a build up of salty water off the coast of South Africa could jump start ocean circulation in the North Atlantic (this despite the two regions being thousands of kilometers apart) while a reduction in the South African waters' saltiness could cause the opposite effect.
Since ocean water can't travel on the time-scales predicated by the models the scientists conceived to record these measurements (less than 10 - 20 years), they think that energy is transferred instead along a deep pressure wave. "The surge of salt generates a pressure gradient in the ocean that sends energy to the north without water actually being transported," said Zahn.
Zahn believes that a large-scale salt monitoring system should be established to regularly measure the waters around South Africa and New Zealand, two key areas that could alert scientists to future climate change incidents.