Correct location Zeb but wrong reason, The Gulf stream is warm water, so it evaporates a lot in its journey and by the time it gets to the arctic and cools down it is more saline (more dense) than the cold waters around it so it sinks to the bottom of the ocean and begins it return journey, this keeps the circulation going. OK but now ice is melting and there also more rain etc.. this adds fresh water to the flow which makes it less saline (less dense) and this reduces the sinking and flow rates.