How currents are measured
To measure the speed of currents, oceanographers have planted - or moored - instruments in the water that can calculate the rate of water movement at various times during the day. Other instruments known as drifters float on the surface and determine the paths and direction of the water. Aside from their speed, ocean currents are measured by the rate of their flow in millions of cubic metres per second. To put this into perspective, consider the outflow of water from the Mediterranean Sea into the North Atlantic Ocean. Flow from the Mediterranean Sea into the Atlantic Ocean occurs at a rate of 1 to 3 million cubic metres per second. By comparison, the Amazon River flows into the Atlantic at a rate of 0.2 million cubic metres per second. All of the rivers flowing into the Atlantic contribute water at a rate of 0.6 million cubic metres per second.