Rocky Mountains Drive Ocean Currents in Atlantic

A system of big warm and cool water ocean currents, which dwarf the flow of even the largest rivers, work to mix heat and nutrients around the globe. This circulation is ultimately driven by two things: differences in heat and salt content in the water, and prevailing winds, which can generate currents as they move across the ocean surface.

One crucial process for the whole system, the Atlantic Meridional Overturning Circulation (AMOC), happens in the far North Atlantic near Greenland. A flow of warm and very salty water from the south cools as it moves towards the pole. Once it becomes sufficiently cool and salty, and thus sufficiently dense, it sinks and becomes a cool deep water current heading south. Why does this same process not happen in the Pacific Ocean? The presence of the Rocky Mountains in North America and the Andes Mountains in South America block the westerly winds blowing moisture from the Pacific towards the Atlantic, reducing the amount of rainfall and freshwater the Atlantic gets.

On the other hand, the Atlantic’s trade winds, which move over the mountain gaps of the thin Central American Isthmus, do bring moisture to the Pacific. This unequal exchange means the Pacific Ocean is dominated by a freshwater surface layer sitting on top of dense salty water, as opposed to in the Atlantic, where there is mobile salty surface water. Without the presence of these mountains, our oceans and climate would function quite differently.