RAPID 26N autumn 2008: cruise background

Map of the North Atlantic region with a red line from UK to Canada

Figure 1: The UK lies at the same latitude as northeastern Canada, but escapes the harsh Canadian-style winters thanks to the Atlantic Ocean.

If you follow a straight line west from the UK across the Atlantic you'll notice that you end up in northeastern Canada - notorious for cold, bleak winters. Why, then, do we not get similar weather in the UK?

Well, firstly because there is a large body of water - the Atlantic - directly to our west. This warms the air above it, particularly in winter. The most common wind direction is from the west, so the Atlantic air warms the UK and other countries in western Europe. The warming effect is enhanced because the North Atlantic is warmer than it ought to be - thanks to a system of ocean currents known as the Atlantic Overturning Circulation.

Schematic showing warm surface water flowing northwestward, cooling and sinking in the Nordic and Labrador Seas, and returning as cold, deep currents

Figure 2: The Atlantic Ocean Overturning Circulation brings warm surface waters into the north Atlantic, whilst colder water below the surface returns south.

This system includes the well known Gulf Stream, which flows north along the eastern coast of the United States before peeling off into the north Atlantic (figure 2). Below the surface, colder water travels back towards the south. The whole system of warm surface currents and cold deep currents is sometime called the Atlantic Heat Conveyor.

Scientists are worried that because of global warming the Atlantic Conveyor may slow down. Even worse (but unlikely), it may stop. To find out what's going on, we have placed a line of instruments across the Atlantic Ocean to measure the strength of the overturning circulation. You can see the location of these instruments marked on the ocean floor in the illustration.

Figure showing how the flow of the MOC varies

Figure 3: Variability of the Atlantic overturning circulation at 26°N.

The array (line) of instruments at 26 degrees North were first put out in April 2004, as part of a research programme called RAPID. Measurements made by the array have already shown that the overturning varies a lot in one year, much more than we thought originally. This natural variability will make it more difficult to detect long term change; so a decision has been made to carry on making the measurements until 2014.

Last update:
31 October 2008

Contact:
o4s@noc.soton.ac.uk