In 1992, a cargo ship carrying bath toys got caught in a storm. Shipping containers washed overboard, and the waves swept 28,000 rubber ducks and other toys into the North Pacific. But they didn’t stick together. Quite the opposite– the ducks have since washed up all over the world, and researchers have used their paths to chart a better understanding of ocean currents.
1992 年 一艘載著洗澡玩具的貨船遇上風暴 貨櫃被沖落水 海浪席捲了二萬八千隻橡皮鴨 及其它玩具沖進北太平洋 但是這些玩具沒有擠在一起 恰恰相反 玩具鴨自此之後被沖到世界各地 研究人員觀察記錄它們的路逕 以更佳了解海流
Ocean currents are driven by a range of sources: the wind, tides, changes in water density, and the rotation of the Earth. The topography of the ocean floor and the shoreline modifies those motions, causing currents to speed up, slow down, or change direction.
海流因受不同來源而驅動 風力、潮汐、水密度變化 及地球自轉 海底及海岸的地形會改變這些運動 導致海流加速 減慢或改變方向
Ocean currents fall into two main categories: surface currents and deep ocean currents. Surface currents control the motion of the top 10 percent of the ocean’s water, while deep-ocean currents mobilize the other 90 percent. Though they have different causes, surface and deep ocean currents influence each other in an intricate dance that keeps the entire ocean moving.
海流通常分為兩種主要類別 表層海流及深層海流 表層海流控制 海洋上方 10% 的水的運動 深層海流則使其它 90% 的水流動 雖然兩者的啟動原因不同 表層及深層海流彼此影響 跳著錯綜複雜的舞步 使整座海洋流動
Near the shore, surface currents are driven by both the wind and tides, which draw water back and forth as the water level falls and rises. Meanwhile, in the open ocean, wind is the major force behind surface currents. As wind blows over the ocean, it drags the top layers of water along with it. That moving water pulls on the layers underneath, and those pull on the ones beneath them. In fact, water as deep as 400 meters is still affected by the wind at the ocean’s surface.
靠近岸邊的地方 表層海流受風力及潮汐而驅動 這兩者都會讓水位下降及上升 而使岸邊的水漲起落下 同時在外海 風力則是表層海流的主要驅動力 隨著風吹過海洋 風力也會拖著表層水一起移動 移動的水又拖動底下的水 底下的水又拖動更下層的水 事實上,深及四百公尺的水
If you zoom out to look at the patterns of surface currents all over the earth, you’ll see that they form big loops called gyres, which travel clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere. That’s because of the way the Earth’s rotation affects the wind patterns that give rise to these currents.
依然受到海洋表面的風力作用 如果你拉遠距離看全球表層海流型態 會看到它們形成 名為「環流」的大圈圈 在北半球以順時鐘方向轉 在南半球則以逆時鐘方向轉 那是因為地球的自轉方向
If the earth didn’t rotate, air and water would simply move back and forth between low pressure at the equator and high pressure at the poles. But as the earth spins, air moving from the equator to the North Pole is deflected eastward, and air moving back down is deflected westward. The mirror image happens in the southern hemisphere, so that the major streams of wind form loop-like patterns around the ocean basins. This is called the Coriolis Effect. The winds push the ocean beneath them into the same rotating gyres. And because water holds onto heat more effectively than air, these currents help redistribute warmth around the globe.
影響到風流動的模式 進而影響到這些海流 如果地球不會自轉 空氣及水只會 在赤道的低氣壓 及兩極的高氣壓間來回移動 但是地球會轉 從赤道吹向北極的氣流 會跟著向東偏轉 從北極吹回赤道的空氣則向西偏轉 在南半球的移動則是鏡像相反 因此大洋的主要環流系統 在海盆形成環狀模式 這稱為「柯氏效應」 風會推動下方的海洋 形成相同方向旋轉的環流 因為水比空氣更能保持熱
Unlike surface currents, deep ocean currents are driven primarily by changes in the density of seawater. As water moves towards the North Pole, it gets colder. It also has a higher concentration of salt, because the ice crystals that form trap water while leaving salt behind. This cold, salty water is more dense, so it sinks, and warmer surface water takes its place, setting up a vertical current called thermohaline circulation.
這些海流有助於重新分配全球的溫暖 不像表層海流 深層海流主要受海水密度改變而驅動 水往北極移動時 會愈來愈冷 鹽的濃度也愈來愈高 因為結塊的冰晶會把水抓住,留下鹽 這種又冷又鹹的水密度更高 所以會往下沉 比較溫暖的表層水取而代之 造成一種垂直海流稱為「溫鹽環流」
Thermohaline circulation of deep water and wind-driven surface currents combine to form a winding loop called the Global Conveyor Belt. As water moves from the depths of the ocean to the surface, it carries nutrients that nourish the microorganisms which form the base of many ocean food chains.
深層的溫鹽環流 和由風力驅動的表層海流 聯合形成一條彎曲的環帶 稱為全球「輸送帶」 當水從海洋深處移動至表層 會帶著營養素以滋養微生物
The global conveyor belt is the longest current in the world, snaking all around the globe. But it only moves a few centimeters per second. It could take a drop of water a thousand years to make the full trip. However, rising sea temperatures are causing the conveyor belt to seemingly slow down. Models show this causing havoc with weather systems on both sides of the Atlantic, and no one knows what would happen if it continues to slow or if it stopped altogether. The only way we’ll be able to forecast correctly and prepare accordingly will be to continue to study currents and the powerful forces that shape them.
構成多種海洋食物鏈的最底層 全球輸送帶是全世界最長的海流 蜿蜒環繞著全球 但是它每秒鐘只移動幾公分 一滴水要花一千年才能繞完一圈 然而上升的海洋溫度 似乎讓此輸送帶放慢速度 模式顯示這會對大西洋兩岸的 天氣系統造成浩劫 沒有人知道會發生什麼事 如果它持續放緩 或者完全停止 能正確預測並做好準備的唯一方法 就是持續研究海流