What's an Ocean Gyre?

A few years ago, the Gulf Stream swiftly carried me home from the Bahamas while simultaneously tormenting me with waterspouts. It got me thinking: cruisers often consider currents when determining where to sail, when to leave, and the how best to get there, but what about the bigger picture? 

Here are four things to ponder when sailing (or planning to sail) in the gyres of the North Atlantic and Pacific Ocean. 

Gyres are currents that flow in a circular pattern around the periphery of the major oceans. They are driven by wind and pressure gradients, and directed by the Coriolis effect, which explains how the Earth’s rotation deflects objects. For example, in the North Atlantic, westerly winds push water east across the North Atlantic. Blocked by Europe, the water accumulates until it has more pressure than the surrounding water, so a pressure gradient forms and the water wants to flow down. The Coriolis effect comes into play and makes the water flow south, forming the Canary Current. This pattern continues around the periphery of the ocean, forming a circle of currents called a gyre. 

There are five gyres in the world: North Pacific Gyre, North Atlantic Gyre, South Pacific Gyre, South Atlantic Gyre and Indian Ocean Gyre. All northern hemisphere gyres flow clockwise and all southern hemisphere gyres flow counterclockwise, thanks to the rotation of the Earth. 

Western Boundary Currents are found on the western side of ocean basins and are the deepest and fastest currents. The western boundary current in the North Atlantic is the Gulf Stream. It carries warm water from the equator to northern latitudes to be cooled. Eastern Boundary Currents, such as the California Current, are slow and shallow and carry cool polar water south toward the equator.

Currents moderate the world’s climate by circulating heat from the equator. For example, The Canary Current brings cool northern water south to absorb tropical heat and the Gulf Stream carries warm water back to the poles where it is cooled. This helps the Earth maintain a moderate temperature. Ocean gyres also explain why cities near the same latitude, such as Oakland, California, and Washington DC, have such different climates. Oakland stays cooler in the summer because of the cool air above the California Current while the air above the Gulf Stream warms Washington DC and turns its summers into scorchers.