PLATE 4a The great ocean conveyor belt. This is a schematic generally summarizing some important features of the world’s ocean circulation. Warm, low-salinity water, flows north along the surface of the Atlantic, becoming saltier (red arrows). Cooling of this to saltier water in the North Atlantic produces high enough densities for the water to sink and flow southward in the deep ocean and into other ocean basins (blue arrows) (after Broecker, 1995).