Shutdown of thermohaline circulation

A shutdown or slowdown of the thermohaline circulation is a postulated effect of global warming. There is some speculation  that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would particularly affect areas such as the British Isles and the Nordic countries, which are warmed by the North Atlantic drift. The chances of this occurring are unclear but 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. In coupled Atmosphere-Ocean General Circulation Models the THC tends to weaken somewhat rather than stop, and the warming effects outweigh the cooling, even over Europe. 

This would also Wipe out a lot of the deep living sea animals because the thermohaline circulation is also what brings oxygen down to the depths of the ocean, also they entirety of the sea will be a huge stagnant pool.