How do ocean currents work? - Jennifer Verduin

譯者: Regina Chu 審譯者: Helen Chang

In 1992,

1992 年

a cargo ship carrying bath toys got caught in a storm.

一艘載著洗澡玩具的貨船遇上風暴

Shipping containers washed overboard,

貨櫃被沖落水

and the waves swept 28,000 rubber ducks and other toys into the North Pacific.

海浪席捲了二萬八千隻橡皮鴨 及其它玩具沖進北太平洋

But they didn’t stick together.

但是這些玩具沒有擠在一起

Quite the opposite–

恰恰相反

the ducks have since washed up all over the world,

玩具鴨自此之後被沖到世界各地

and researchers have used their paths

研究人員觀察記錄它們的路逕

to chart a better understanding of ocean currents.

以更佳了解海流

Ocean currents are driven by a range of sources:

海流因受不同來源而驅動

the wind, tides, changes in water density,

風力、潮汐、水密度變化

and the rotation of the Earth.

及地球自轉

The topography of the ocean floor and the shoreline modifies those motions,

海底及海岸的地形會改變這些運動

causing currents to speed up,

導致海流加速

slow down, or change direction.

減慢或改變方向

Ocean currents fall into two main categories:

海流通常分為兩種主要類別

surface currents and deep ocean currents.

表層海流及深層海流

Surface currents control the motion

表層海流控制

of the top 10 percent of the ocean’s water,

海洋上方 10% 的水的運動

while deep-ocean currents mobilize the other 90 percent.

深層海流則使其它 90% 的水流動

Though they have different causes,

雖然兩者的啟動原因不同

surface and deep ocean currents influence each other

表層及深層海流彼此影響

in an intricate dance that keeps the entire ocean moving.

跳著錯綜複雜的舞步 使整座海洋流動

Near the shore,

靠近岸邊的地方

surface currents are driven by both the wind and tides,

表層海流受風力及潮汐而驅動

which draw water back and forth as the water level falls and rises.

這兩者都會讓水位下降及上升 而使岸邊的水漲起落下

Meanwhile, in the open ocean, wind is the major force behind surface currents.

同時在外海

風力則是表層海流的主要驅動力

As wind blows over the ocean,

隨著風吹過海洋

it drags the top layers of water along with it.

風力也會拖著表層水一起移動

That moving water pulls on the layers underneath,

移動的水又拖動底下的水

and those pull on the ones beneath them.

底下的水又拖動更下層的水

In fact, water as deep as 400 meters

事實上，深及四百公尺的水

is still affected by the wind at the ocean’s surface.

依然受到海洋表面的風力作用

If you zoom out to look at the patterns of surface currents all over the earth,

如果你拉遠距離看全球表層海流型態

you’ll see that they form big loops called gyres,

會看到它們形成 名為「環流」的大圈圈

which travel clockwise in the northern hemisphere

在北半球以順時鐘方向轉

and counter-clockwise in the southern hemisphere.

在南半球則以逆時鐘方向轉

That’s because of the way the Earth’s rotation

那是因為地球的自轉方向

affects the wind patterns that give rise to these currents.

影響到風流動的模式 進而影響到這些海流

If the earth didn’t rotate,

如果地球不會自轉

air and water would simply move back and forth

空氣及水只會

between low pressure at the equator

在赤道的低氣壓

and high pressure at the poles.

及兩極的高氣壓間來回移動

But as the earth spins,

但是地球會轉

air moving from the equator to the North Pole is deflected eastward,

從赤道吹向北極的氣流 會跟著向東偏轉

and air moving back down is deflected westward.

從北極吹回赤道的空氣則向西偏轉

The mirror image happens in the southern hemisphere,

在南半球的移動則是鏡像相反

so that the major streams of wind

因此大洋的主要環流系統

form loop-like patterns around the ocean basins.

在海盆形成環狀模式

This is called the Coriolis Effect.

這稱為「柯氏效應」

The winds push the ocean beneath them into the same rotating gyres.

風會推動下方的海洋 形成相同方向旋轉的環流

And because water holds onto heat more effectively than air,

因為水比空氣更能保持熱

these currents help redistribute warmth around the globe.

這些海流有助於重新分配全球的溫暖

Unlike surface currents,

不像表層海流

deep ocean currents are driven primarily by changes in the density of seawater.

深層海流主要受海水密度改變而驅動

As water moves towards the North Pole,

水往北極移動時

it gets colder.

會愈來愈冷

It also has a higher concentration of salt,

鹽的濃度也愈來愈高

because the ice crystals that form trap water while leaving salt behind.

因為結塊的冰晶會把水抓住，留下鹽

This cold, salty water is more dense,

這種又冷又鹹的水密度更高

so it sinks,

所以會往下沉

and warmer surface water takes its place,

比較溫暖的表層水取而代之

setting up a vertical current called thermohaline circulation.

造成一種垂直海流稱為「溫鹽環流」

Thermohaline circulation of deep water and wind-driven surface currents

深層的溫鹽環流

和由風力驅動的表層海流

combine to form a winding loop called the Global Conveyor Belt.

聯合形成一條彎曲的環帶 稱為全球「輸送帶」

As water moves from the depths of the ocean to the surface,

當水從海洋深處移動至表層

it carries nutrients that nourish the microorganisms

會帶著營養素以滋養微生物

which form the base of many ocean food chains.

構成多種海洋食物鏈的最底層

The global conveyor belt is the longest current in the world,

全球輸送帶是全世界最長的海流

snaking all around the globe.

蜿蜒環繞著全球

But it only moves a few centimeters per second.

但是它每秒鐘只移動幾公分

It could take a drop of water a thousand years to make the full trip.

一滴水要花一千年才能繞完一圈

However, rising sea temperatures are causing the conveyor belt

然而上升的海洋溫度

似乎讓此輸送帶放慢速度

to seemingly slow down.

Models show this causing havoc with weather systems

模式顯示這會對大西洋兩岸的

on both sides of the Atlantic,

天氣系統造成浩劫

and no one knows what would happen if it continues to slow

沒有人知道會發生什麼事 如果它持續放緩

or if it stopped altogether.

或者完全停止

The only way we’ll be able to forecast correctly and prepare accordingly

能正確預測並做好準備的唯一方法

will be to continue to study currents and the powerful forces that shape them.

就是持續研究海流

及塑造它們的強大力量