instance, the Gulf Stream leaves the vicinity of Florida with surface temperatures
in excess of 27°C in the summer and the temperature decreases with the trip north-
ward. By the time the remnants reach Ireland, a dip of the human hand would con-
firm that it is cold to the touch at 13°C. Yet, the current is still considered “warm”
because it is warm relative to the rest of the water at that latitude. There are many
notable ocean currents in the world. In general, ocean currents are set up wherever
wind is strong and prolonged from one direction, seasonally or yearly. The largest
flow of water on the planet is the Antarctic Circumpolar Current. It girdles the
globe in the region of the Southern Hemisphere’s westerly winds and does not
experience significant interference from land masses. So, too, there are many turns
and splits of currents because of the particular shapes of the various ocean basins.
The currents have undoubtedly changed with the drift of continents caused by
plate tectonics. Central America did not exist as an isthmus until about three
million years ago. Thirty million years ago the region was a string of volcanic islands
between widely spaced North and South America and there was a west to east ocean
current where today there can be none; this change in current configuration doubtless
had some important climatic impacts.
As currents are examined it can be seen that there are several fluid characteris-
tics in common with rivers. Ocean current meanders are progressively moving fea-
tures that take months to form, progress, and dissipate. They are readily seen on
satellite images. Additionally, great eddies swirl at the edge of the currents mix-
ing current water with the ocean waters surrounding them. With great contrasts
of water characteristics at the edge of ocean currents, these moving features are
often the site of large biologic productivity.
The Gulf Stream is a warm current supplying water to eastern North America. It
was discovered in the early 1500s and thereafter used as a boost to sailing ships
returning to Europe. The water has tropical origins in the Atlantic and the Gulf of
Mexico and is tightly focused as it passes through the straits between Florida and
Cuba. It has an average speed of about 3 to 4 kph. It has been estimated that the Gulf
Stream near Newfoundland transports 150,000,000 cubic meters per second, making
it much larger than the combined flow of all the river discharges into the Atlantic
Ocean. As it travels across the North Atlantic it becomes known as the North Atlantic
Drift and comes against the European continent to split north and south. The northern
extension, the Norwegian Current, keeps the Barents Sea ice free year round, which
played a pivotal role in keeping the Soviet Union port of Murmansk supplied with
arms during World War II. Although there is scientific controversy regarding the
nature of the climatic influences, there is no doubt that these waters of tropical origin
play an important role in the mildness of climate in Western Europe.
The Peru Current, also known as the Humboldt Current after the geographer
Humboldt, is a huge flow of cold water off of the western coast of South America244 Ocean Currents