Measuring the flow of currents
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 also measured by their rate in flow of 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, South Americaís Amazon River discharges 0.2 million cubic metres per second. The large, fast Gulf Stream Current moves at a rate of 150 million cubic metres per second; thatís equivalent to 30,000 Olympic sized pools full of water being emptied every second! The Pacific equivalent to the Gulf Stream is the Kuroshio Current, which originates in the Sea of Japan, and carries a volume of 50 million cubic metres per second - about 500 times the volume of water flowing out of the great Amazon river.