03-14 12:38:20 浏览次数: 689
Ebbysemeyer—King of Currents
On December 9, 1994, the Huundai Seattle, a large freighter, lost 49 containers of cargo during a storm in the middle of the Pacific Ocean. Among the cargo that fell overboard were some 34, 000 hockey gloves. Unable to retrieve the lost cargo, the ship headed for its destination in the United States.
What happened to the hockey gloves? Eight months later, the crew of a fishing boat found seven of them 1, 300 kilometers off the Oregon coast. Six months after that, the rest of the gloves began washing up on beaches in Washington state.
“Just as my colleague Jay Ingraham and I predicted,” said Ebbyesemeyer, a scientist in Seattle. An authority on ocean currents, Ebbysemeyer has been called the “King of Currents.” For more than 30 years, he has been tracking an assortment of floating objects—everything from huge icebergs to tiny bathtub toys. With his knowledge of ocean currents and sophisticated computer program developed by Ingraham, he can now predict with amazing accuracy which way floating objects will drift and where and when they will reach shore.
Why is it important to know such things? Because, Ebbysemeyer points out, knowledge of ocean currents can help determine how far an oil spill might spread or where the sewage from a treatment plant will go. By mapping currents, scientists can also figure out where plankton might drift or what paths salmon will take through the ocean to reach the streams of their birth.
Ebbysemeyer says currents are like giant rivers in the ocean. They are found both at the ocean's surface and several thousands feet down on the seafloor.
Surface currents are driven mainly by the wind and by earth's rotation, through a force called the Coriolis effect. As the wind pushes the water forward, the Coriolis effect nudges it slightly sideways. The two influences combine to make surface waters move in great loops.
Deep ocean currents are created as seawater approaches the North and South Poles. As the water cools, its molecules draw closer together, making each gallon denser. Heavier than warm water, the cold water sinks to the ocean floor, miles beneath the surface flows. The deep currents then drift toward the equator, where they are gradually heated by the sun. The water molecules spread out again, and the lighter, less dense fluid rises to the surface.
That is not the whole story, Ebbysemeyer says. Before you can accurately predict where or when a floating object will reach a particular shore, you must also consider certain details. One detail is windage. To calculate windage, Ebbysemeyer floats various items—cans, bottles, shoes—in a tank, then blasts each one with the breeze from a powerful fan.
“Some things sit on the water and just scoot right along,” said Ebbysemeyer. “Others are fairly well submerged and are not exposed to the wind much at all. A rubber bathtub toy might move at a rate of around 48 kilometers per day, compared with an athletic shoe, which will cover only 32 kilometers in the same period.”
Ebbysemeyer estimates that a thousand containers of cargo fall into the sea from ships every year. His data suggest that some of those items can remain adrift for years before washing shore. He cites the case of an unknown Nike sneaker that washed ashore in Washington after floating for three years in the Pacific Ocean. “It was still quite wearable,” said Ebbysemeyer.
1. What happened to those hockey gloves that fell overboard?
A. They were retrieved by the crew.
B. Some of them reached shore at last.
C. They sank to the seafloor.
D. They were completely lost in the vast ocean.
2. Why does Ebbysemeyer study ocean currents?
A. For pragmatic purposes.
B. For fun.
C. Just out of curiosity.
D. To study the lives of plankton.
3. All the factors that affect ocean currents are discussed in the passage EXCEPT
A. the sun's heat
B. rotation of the earth.
C. gravitational force.
4. What creates deep ocean currents?
A. High temperatures near the equator.
B. Magnetic force near the South Pole.
C. Magnetic force near the North Pole.
D. Low temperatures near the two Poles.
5. What does the example of a Nike sneaker given in the last paragraph indicate?
A. Nike products are most durable.
B. Sometimes, objects may drift in the ocean for years.
C. Seawater erodes drifting objects including Nike products.
D. The Nike sneaker is still wearable after years of drifting.