2012: Advent Atmosphere: Ocean Currents

by on December 11, 2012

The ocean currents are a single vast system, spanning the globe. Water rises in the north Pacific and flows, a few hundred metres below the surface, past the northern coast of Australia to join the water rising in the Indian Ocean. The combined current flows past the tip of Africa and all the way north to Greenland, where it sinks, and flows back south, along the coast of South America and all the way east along the sea bed of the Antarctic Ocean, until it turns north again to rise in the Pacific and Indian oceans.

The Greenland sink is the only place in the world where surface water sinks to the deeps, and it drives the whole system. So why there? What happens off the coast of Greenland to make water sink that happens nowhere else on the planet?

The Gulf Stream happens. The Gulf Stream is a surface current that starts south of the tip of Florida, and flows north to the UK and Greenland. As it travels across the ocean, the sunlight evaporates some of the water, making what remains ever saltier. Because it’s warmer than the underlying water, it doesn’t sink and mix with it. It just gets ever saltier, until finally it reaches the icy Arctic Ocean, cools, and the extra salt makes it dense enough to sink, all the way to the ocean floor.

The Gulf Stream, in other words, powers the entire circulatory system of the oceans. And you thought keeping England warmer than Siberia (we’re just as far north) was all it did.

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