Volcano in Iceland - flash flood from Eyjafjallajökull glacierGreenland massive runoff causing desalination of North Atlantic
Shutdown of thermohaline circulation
Every so often the earth chooses to remind us that we really aren't in control of this planet.
A shutdown or slowdown of the thermohaline circulation, trigger localised cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would particularly affect areas such as Ireland, Britain and Nordic countries that are warmed by the North Atlantic drift. The chances of this occurring are unclear; there is some evidence for the stability of the Gulf Stream but a possible weakening of the North Atlantic drift; and there is evidence of warming in northern Europe and nearby seas, rather than the reverse. The future is undecided, as studies of the Florida Current suggest that the Gulf Stream weakens with cooling and strengthens with warming, being weakest
Sub polar gyre, has weakened in the past in connection with certain phases of a large-scale atmospheric pressure system known as the North Atlantic Oscillation
It is a signal of large climate variability in the high latitudes," Hakkinen said. "If this trend continues, it could indicate reorganization of the ocean climate system, perhaps with changes in the whole climate system, but we need another good five to 10 years to say something like that is happening." Rhines said, "The subpolar zone of the Earth is a key site for studying the climate. It's like Grand Central Station there, as many of the major ocean water masses pass through from the Arctic and from warmer latitudes. They are modified in this basin. Computer models have shown the slowing and speeding up of the subpolar gyre can influence the entire ocean circulation system
satellite sea-surface height data to velocities of the subpolar gyre. The subpolar gyre can take 20 years to complete its route. Warm water runs northward through the Gulf Stream, past Ireland, before it turns westward near Iceland and the tip of Greenland.
The current loses heat to the atmosphere as it moves north. Westerly winds pick up that lost heat, creating warmer, milder European winters. After frigid Labrador Sea winters, the water in the current becomes cold, salty and dense, plunges beneath the surface, and heads slowly southward back to the equator. The cycle is sensitive to the paths of winter storms and to the buoyant fresh water from glacial melting and precipitation, all of which are experiencing great change.
While previous studies have proposed winds resulting from the NAO have influenced the subpolar gyre's currents, this study found heat exchanges from the ocean to the atmosphere may be playing a bigger role in the weakening current. Using Topex/Poseidon sea-surface height data, the researchers inferred Labrador Sea water in the core of the gyre warmed during the 1990s. This warming reduces the contrast with water from warmer southern latitudes, which is part of the driving force for ocean circulation.