September 19-28, 2007
On this research expedition we travel north, to part of the north Atlantic Ocean called the Labrador Sea, which lies between Canada and Greenland.
Our ship will be loaded with all the science gear we’ll need, and, of course, food for everyone. Hoping for fine seas, we’ll travel 1700 nautical miles, (1956 land miles), to reach our work site. It will take us almost seven days to get there!
How do we know where we’re going when there are no roads or signs to show us the way? We use latitude and longitude, imaginary lines that can be used to define any spot on earth, even in the ocean. We are traveling to a place with the latitude 60.6 degrees North and the longitude 52.4 degrees West.
Our goal is to learn about how currents of ocean water flow around near that spot. We especially want to learn about parts of currents that break free and move through the sea on their own. Oceanographers call these eddies or rings. We have an even more specific name for the eddies in our work area. That name is Irminger Rings, since they broke free from the Irminger current.
Ocean Currents and Eddies
Water in the ocean is always on the move, with big currents flowing like rivers in different directions and at different layers in the sea. These ocean currents help carry heat around the Earth. In the Atlantic Ocean, near the equator, the water on the surface gets warm from the sun. The warm water flows toward the north as a big current, called the Gulf Stream, and it carries heat north with it.
Meanwhile, in the Labrador Sea in winter, the cold air from Canada cools the water at the ocean’s surface down to near freezing, like placing a pan of warm water in the refrigerator. The cold surface water is now denser and heavier than underlying water, so it sinks down—through warmer layers of water—to the sea floor. Then the cold dense water flows back southward along the bottom of the ocean – underneath the current of warm water going north – back toward the equator. The water makes a big loop: getting warm at the equator, flowing north at the surface, getting cold in winter, sinking, flowing south back to the equator, rising up and getting warm again.
In this way, the cooling of the ocean in the Labrador Sea in winter helps keep all the seawater moving around the Atlantic Ocean. Such winter sinking of cold water only happens in a few places in the world, and we think they are important for the whole Earth’s distribution of warmth.
We want to find out more about the currents of warmer and cooler water in the Labrador Sea. In one specific area, a current of slightly warmer water flows around the outer edge of the sea without mixing into the cold water in the center of the sea – a little like a warm breeze flowing past a cool, quiet, shady courtyard but not coming in. Once in a while, though, a bit of the current breaks away from the main flow and carries a blob of spinning, warmer water into the center of the sea – a little like a stray swirl of wind coming into the courtyard. These are called “Irminger Rings.”
What happens to warm eddies in the cold center of the Labrador Sea? Where do they go? Do they fall apart? Do they stay warm for a long time? That’s what we are going to find out, using the measuring and recording instruments we’ll put into the Labrador Sea on this expedition.
It isn’t easy to measure one a swirl of warmer water within a sea of colder water – we have to use sophisticated programmed instruments to gather data for us. Some instruments will be attached to a mooring, and they will stay in one place for two years, recording the temperature of water that moves by – that way, we should be able to detect the Irminger Rings going by. Our other instruments will be in 12 little floats that will be released from the mooring to drift along with the warm eddies and see what they do.
The answers could be important: Oceanographers think that these eddies might carry just enough warmth to the interior of the Labrador Sea to keep it a little warmer than the winter-chilled dense sinking water. And it’s a good thing, too! Because if the whole sea got too cold and dense, there wouldn’t be any more sinking water, and the circulation loop in the Atlantic Ocean might not happen, and the warmth from the equator might not be carried north with the Gulf Stream.