Nature: The accepted picture of how a massive oceanic conveyor belt of water turns has been complicated by findings published today in Nature Geoscience1. The results could help to boost the precision of climate-change models. As tropical water from the Equator flows north in the Atlantic Ocean, it becomes cooler and denser. Evaporation along the way makes it saltier and further increases its density. In the frigid Arctic, the water sinks into the depths and then moves southward; returning to …