Ocean currents

No two-dimensional, static map can show the three-dimensional ceaseless flow and mixing of the ocean, like the circulatory system of an animal. In places the oceans are nearly 10 kilometres deep; the water is cold and pressures close to 1 ton per square centimetre. Deep and cold ocean currents travel thousands of kilometres from polar regions before upwelling to the surface, bringing nutrients such as phosphorus and nitrogen, which are scarce there. Surface currents spread heat from warmer tropical waters to colder regions.

What’s in a sample of ocean?

A tissue sample from the surface waters of the ocean reveals many signs of Gaia. It would not seem particularly rich in life to the eye, but a microscope would show blooms of photosynthetic algae grazed by tiny zooplankton, which in turn provide food for larger marine organisms. In their intricate shells, the microflora segregate calcium and silicon, which later rain to the sea bed to form sediments — which in turn may be linked to the movements of the Earth’s plates. Salinity is within the tolerance levels of life, and dissolved carbon dioxide is present, pumped down from the air. Also present are trace gases released by the algae, such as dimethyl sulphide, which we now suspect to have a role in cloud formation and climate. (see variation 34)