Big Currents

The ancient Greeks of Homeric times imagined the earth as a flat surface surrounded by the river Okeanos, the source of all waters – also described, in a few passages, as the source of all the gods, and even of all things (Turning Signs, Chapter 10.) “Okeanos” was not only a precursor of the meaning cycle but also of current models of the circulation of water in the planet Earth’s oceans.

While warm-water currents such as the Gulf Stream flow near the surface of the oceans toward the poles, cold-water currents are flowing in roughly the opposite direction close to the sea floor. Near the poles, water brought by the warm currents cools and sinks, and the water brought close to the equator by the cold currents rises and begins the poleward flow again. This circulation helps to moderate the planetary climate and maintain oxygen levels in the deep oceans. Its breakdown during a period of global warming about 250 million years ago contributed to the greatest extinction event in the planet’s history. This three-dimensional manifestation of the Big Current is purely physical, but its effects on ocean chemistry are intimately related to all life on Earth. We can think of it as part of Gaia’s circulatory system.