At 10:00 PM on July 13, 2003, I joined some twenty-five people aboard the 100-foot Yankee Freedom and set out from Gloucester, Massachusetts. We were beginning the annual CORE Whales and Seabirds Canyons Trip, and were bound for the very edge of the continental shelf over 100 miles distant.

The Center For Oceanic Research and Education (CORE) is a nonprofit organization based in Gloucester and dedicated to the study and conservation of members of the order Cetacea, a biological order which includes whales, porpoises and dolphins.

The goal of the trip was to explore the waters above deep submarine canyons that are carved into the edge of the continental shelf. Many species of birds and cetaceans live only where the water is much deeper or much warmer than the water near the New England coast, and it was these species that we were seeking out in the depths.

Warm Water in a Cold Region

At first consideration, it might not seem that water in the deep portions of the North Atlantic would be particularly warm even in the summer, especially given how cold it can be in the winter. This would likely be true year-round, were it not for the particular influence of the Gulf Stream.

The Gulf Stream, the fastest ocean current in the world, continually carries tropical water from near the equator toward the north at up to 2 m/s (4 mph). The warm waters of the Gulf Stream often run within 50 miles of the North Carolina coast, but cut a course far from New England. How, then, does any water in the North Atlantic become warm?

Gulf Stream Eddies

As the Gulf Stream flows, its path does not remain constant. Instead, it changes position from day to day, meandering like the jet stream in the atmosphere or a like river on Earth. As it does so, it occasionally "pinches off" either to the north or to the south. When the Gulf Stream does this, it leaves behind eddies, or rings of captured water that continue rotating. These eddies are usually about 200 km (120 mi) across, and drift to the southwest very slowly, traveling less than a few kilometers, and possibly only centimeters, each day.

An animation simulating the formation of cold-core and warm-core eddies from the Gulf Stream. (Animation taken from The Cool Room: Rutgers University Coastal Ocean Observation Lab). Read more about Features of the Gulf Stream from an environmental science page at Rutgers University.

As shown in the diagram at right, the rings that break off south of the Gulf Stream contain trapped cold water and rotate counterclockwise. These cold-core rings can remain in the warm sea south of the Gulf Stream for up to a year or two.

The eddies that were a large reason for our ocean trip were the warm-core rings that are pinched off north of the Gulf Stream. These clockwise-rotating rings trap warm water from the Sargasso Sea and bring it northward toward the Gulf of Maine.