Like an oxbow lake on land, sometimes a loop of the meandering Gulf Stream becomes cut off from the main current. This forms an eddy of water that may move at speeds of 2-3 knots and may occasionally persist for 3-5 years. Eddies can be up to 200 miles in diameter. Eddies or "rings" are features that are easily seen from space by infrared sensors.
The Gulf Stream separates two distinct water masses. The nearshore "slope water" to the northwest of the Gulf Stream (nearer the coast) is colder and more fertile than the water to the southeast of the Gulf Stream (the warm Sargasso Sea). The temperature of the nearshore water is less than 10°C (50°F), while Sargasso Sea temperatures range from 15°C to 25°C (59°F-77°F). Depending on which side of the Gulf Stream the water at the center of the eddy is "kidnapped" from, it may be a cold-core ring or a warm-core ring.
A cold-core ring or eddy is a ring of Gulf Stream water flowing counterclockwise around a cold, less saline mass of water. It is formed when a branch of the Gulf Stream meanders and encircles a piece of colder water from the west. A cold ring often can be tracked for 2 years before it dissipates into the surrounding Sargasso Sea, east of the Gulf Stream. A warm-core ring or eddy forms when the edge of the Gulf Stream jogs into the warmer water of the Sargasso Sea and forms a warm-core, clockwise flow of water. This drifts towards the coast and usually dissipates within a year as it collides with the shallow continental shelf.
Warm rings trap and transport a variety of different kinds of animals within the eddy, but cold rings carry greater biomass (that is, more life), but less diversity of species. A cold ring traps the nutrient-rich water from the north of the Gulf Stream and transports both nutrients and plankton into the relatively-barren Sargasso Sea. The Gulf Stream and the Sargasso Sea support less phytoplankton-the minute plant life at the bottom of the ocean food chain than the waters directly off the coast.
Determine whether an eddy is a cold-core ring or a warm-core ring.
- Explain about cold core rings and warm water rings and how they form. Discuss how they move nutrients and phytoplankton, and occasionally, large animals like fish, sea turtles, and Portuguese Man-O-War jellyfish into different parts of the Atlantic.
- Look at an infrared satellite photo to find the circular loops of Gulf Stream eddies.
- Use the temperature scale to determine the relative temperature difference between the center of the ring and of the surrounding water.
After you know the temperature difference between the core and surrounding water, you should be able to determine whether it is turning clockwise or counterclockwise.
- Where do you predict the rings will drift over the next several months?