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Science and technology
科學技術
The Arctic
北極海域
Tequila sunset
龍舌蘭日落
Global warming may make the northernmost ocean less productive, not more so
全球變暖對北極海域生產力的負面影響
ON SEPTEMBER 16th 2012, at the height of the summer melt, the Arctic Ocean's ice sheet had shrunk to an area of 3.41m square kilometres, half what it was in 1979.
2012年9月16日，隨著夏日的深入，北冰洋的冰原面積縮減到341萬平方公里，該數字僅為1979年同期面積的二分之一。
And its volume had shrunk faster still, to a quarter of what it was in 1979, for the sheet is getting thinner as well as smaller.
同時，就冰原體積而言，目前北極冰原的體積僅為1979年的四分之一，其融化速度之快可想而知。如今的北極地區，不僅冰原的面積在減少，其體積也在縮小。
One culprit is global warming, which is fiercer at the poles than elsewhere.
而這一現象的罪魁禍首便是全球變暖。同時，相比于其他海域而言，全球變暖對兩極地區的沖擊尤為明顯。
The world's average temperature in 2012 was nearly 0.5C above the average for 1951-80.
與1951-1980年相比，2012年全球均溫上漲了0.5，
In the Arctic, it was up almost 2C.
其中僅北極地區便上漲了2。
This sudden warming is like the peeling back of a lid to reveal a new ocean underneath.
就如同是掀開了某個鍋蓋后發現了一片沸騰的海洋一般，全球溫度驟然上升。
That prospect is spreading alarm and excitement.
全球變暖加劇的前景不僅使人深感擔憂，也使人倍覺振奮。
Though most of the excitement has been about oil and gas, and the opening of sea routes between the Atlantic and the Pacific, some people hope for a fishing bonanza, too, as warmth and light bring ecological renewal to what is now an icy desert.
盡管大多數的掌聲來自油氣開發商與大西洋-太平洋新航道擁護者，然而由于全球變暖給這片冰雪荒原帶來了溫暖與陽光，為其生態環境注入了新的元素，不少人也夢想著在這里靠捕魚發一筆橫財，
But they may be disappointed.
只是后者很可能會抱憾而歸。
At the moment, the waters around the Arctic account for a fifth of the world's catch.
目前，北極地區占有全球總水量的五分之一。
There are few fish, however, under the ice itself.
然而在這厚厚的冰層下，卻鮮有魚類問津。
A fishing bonanza would require big ecological change.
在北極生態系統完全改變之前，捕魚或許不是當地的最佳致富之道。
Arctic Frontiers, a conference organised at the University of Tromso in January, looked at how warming will change the ecology, to estimate whether it will bring one about.
1月，挪威特羅姆瑟大學召開“北極邊境”會議，專門研究全球變暖對已有生態環境的影響，以及預估該現象是否會促進生成一個新的生態環境。
The consensus was that it won't—not because the Arctic will change too little, but because it will change too much.
會上，與會代表達成共識：北極海域將不會形成新的生態環境，這并不是因為北極的改變不足掛齒，恰恰相反，而是因為這里將會發生翻天覆地的變化。
Change and decay
變化與衰退
At first sight, this is counterintuitive.
乍讀此言，不免覺得有些互相矛盾。
As the ice melts, more light can reach the water, and that means more photosynthesis by marine algae.
然而隨著冰層進一步融化，大量陽光直射海面，海水中藻類植物的光合作用將會大大增強。
In the past, algae began to grow under the ice sheet in May and continued to do so until late September.
過去，冰原下的海藻于每年五月開始生長，至九月末結束，
Now, such growth starts in mid-March and continues until October.
但現在海藻的生長期已延長為每年三月中旬至十月。
These ice algae, attached to the sheet itself, account for half the mass of living things in Arctic waters.
在所有北極海洋生物中，約半數生物為此類附著在冰原下方的冰藻，
Much of the rest is unattached algae, known as phytoplankton, and tiny animals, known as zooplankton.
另外還有部分浮游植物及浮游動物，
Both sorts of plankton support, directly or indirectly, the fish and mammals that live in the Arctic Ocean.
而這兩類浮游生物便是北極地區魚類及哺乳動物直接或間接的養料來源。
And the plankton, too, are flourishing thanks to global warming.
此外，全球變暖也使得此類浮游生物的數量激增：
The Arctic phytoplankton bloom, which used to run from June to September, now runs from April to September.
北極浮游植物生長期已經由過去的六至九月延長到了四至九月。
The upshot is more plankton, farther north.
于是，隨著浮游生物進一步向北部蔓延，
That attracts more fish.
更多魚類被吸引至此。
In 2000 Atlantic cod were caught throughout the Barents Sea.
2000年，巴倫支海南北遍布大西洋鱈魚；
By 2012 their distribution was skewed towards the northern part of that sea.
2012年，大西洋鱈魚活動范圍北移至巴倫支海北部。
Stocks of capelin used to be concentrated south of Svalbard, at latitude 75N.
同時，曾主要分布于北緯75斯瓦爾巴群島海域的capelin，
In 2012 this had moved to 78N.
于2012年被發現已遷移至北緯78附近，
Some found their way as far up as 80N.
部分甚至已遷徙到北緯80附近海域。
Which all sounds most promising. But many researchers think it will not continue.
盡管種種跡象表明在此地捕魚致富的前景頗為樂觀，然而許多學者卻持不同意見。
First, the central Arctic is too deep for some important species, such as the polar cod.
首先，北冰洋中部海水過深，不利于極地鱈魚等重要物種的生存。
Young polar cod are pelagic, meaning they live at or near the surface.
極地鱈魚與大西洋鱈魚同屬，但前者活動范圍較后者更為偏北。
Those one or more years old are benthic, meaning they live near the bottom.
此外，極地鱈魚的幼魚為海面魚，這些幼魚僅在海面附近活動；一歲及以上的極地魚為深海魚，這些深海魚僅生活在類似于博福爾海域的海底。
In the Beaufort that bottom is 200 metres down.
鑒于博福爾海的深度為200米，
In the central Arctic it descends to about 4,000 metres, which is too deep for polar cod to survive.
而北冰洋中部深度約為4000米，因此極地鱈魚根本無法在北極地區生存。
A second reason why there may be no bonanza is acidification of the ocean.
其次，北冰洋的酸化現象也是此地不宜魚類生存的重要原因。
When water absorbs carbon dioxide, it produces carbonic acid. More CO?
水吸收二氧化碳后會釋放出碳酸，
means oceans everywhere are becoming more acidic, but the phenomenon is particularly marked at high latitudes because cold water absorbs CO? more readily than warm water does.
因此，隨著二氧化碳排放量增加，海水酸度也會隨之升高。另外，因為冷水比熱水更易吸收二氧化碳，所以這種現象在高緯度地區尤為明顯。
The retreat of the ice also exposes ever more sea to do the absorbing.
于是，冰原面積的銳減也意味著更多的低溫洋面將會暴露在空氣之中，吸收大量的二氧化碳。
Cruises by the United States Geological Survey and the University of South Florida over the past three years have found rising carbonic-acid levels north of Alaska.
在過去的三年里，美國地質調查局與南佛羅里達大學多次巡航此地進行調研，調研結果表明：阿拉斯加北部海域的碳酸值顯著上升，并且該海域有機物的外殼中霰石含量不足。
They have also discovered that the shells of many organisms in the area are short of aragonite, a form of calcium carbonate that gives them strength, but whose formation acid discourages.
霰石為碳酸鈣的一種形式，它不僅為有機物外殼提供支撐，而且其形成過程能夠降低酸性物質含量。
Weaker shells means fewer shelled organisms and less food for fish.
外殼硬度的降低則說明該海域帶殼有機物及魚類食物的數量均大大減少。
The most important reason, though, for thinking that global warming will not produce an Arctic feeding frenzy is that it may increase ocean stratification.
然而，全球變暖無法為北極地區帶來大量魚類養料的真正原因在于海水分層現象的加劇。
This is the tendency of seawater to separate into layers, because fresh water is lighter than salt and cold water heavier than warm.
由于淡水質量小于海水，而冷水質量大于熱水，水溫的上升會導致海水進一步分層。
The more stratified water is, the less nutrients in it move around.
同時，海水分層現越嚴重，則越不利于海水內部營養物質的流動。
Most free-swimming sea creatures are pelagic.
大多數海洋游泳生物均為海面生物。
Algae need light, so must live near the surface—as must the zooplankton and other animals that need the phytoplankton.
海藻需要陽光，因此海藻必須生活在海面附近，從而依靠海藻等浮游植物生存的浮游動物也必須在海面區域活動。
When they die, all these organisms sink to the bottom, where they become food for benthic creatures.
這類生物死亡后，其有機體沉入海底，變為海底生物的養料。
Once they have been consumed their component molecules, including nutrients such as nitrates, phosphates and iron, are stuck in Davy Jones's locker.
當有機體的硝酸鹽、磷酸鹽、鐵以及其他營養成分均被其他生物吸收后，他們便永遠地沉在了海底。
For the surface to be productive, the locker must be opened and the nutrients lifted back up, so that they can feed the growth of phytoplankton.
因此，如果海底為一個封閉的水層，則海底營養物質將無法上升到水面，從而也無法為浮游植物等其他水面生物提供其生長所需的養料。
Walking the plankton
浮游生物的流失
One of the most important ways this happens is by upwellings of water from the bottom—great churning columns caused by the collision of cold and temperate waters.
上升流是海底營養物質上浮至水面的重要方式。
Two of the most important are in the Arctic: south of Greenland on the Atlantic side and south of the Bering Strait on the Pacific side.
北極地區具有全球最著名的幾大上升流之二：大西洋側南格陵蘭上升流及太平洋側白令海峽上升流。
Nitrates are abundant at the surface in both places, which is why they are among the world's richest fishing grounds.
這兩個海域富有硝酸鹽，這便是這些地區以捕魚業著名的原因。
There are few upwellings in the tropics, which are thus nutrient-poor.
由于熱帶海域則幾乎沒有上升流，因此這些海域通常缺乏養分。
Stratification threatens this recycling system by suppressing the vertical movement of water.
然而，海水分層會妨礙海水的垂直交換運動，從而威脅海洋自身的循環系統。
And global warming encourages stratification because it turns the ice into a layer of fresh water that sits on the surface.
全球變暖現象使得海面冰層融化，而融化后的淡水則只能漂浮在海面。
Imagine the ocean as a Tequila sunrise sitting on a warm bar.
這就好像是一杯放在暖氣上的龍舌蘭日落雞尾酒，
The ice cubes at the top are melting away and the orange juice is sinking to the bottom.
上層的冰塊在融化，而橙汁全部沉淀在杯底。
At the conference, a paper by Jean-éric Tremblay and Marcel Babin of Laval University, in Quebec, described the effect by reporting the density difference of water at the surface and at a depth of 100 metres in different oceans.
“北極邊境”會上，Jean-éric Tremblay與拉瓦爾大學的Marcel Babin帶來了他們的研究性論文成果。
This density difference is an index of ocean stratification.
該論文描述了不同海洋中洋面海水與100米深處海水的密度差別及其影響，而正是這一密度差別決定著海水的分層情況。
Parts of the Arctic seem to be getting badly stratified.
如圖所示，北極地區部分海域已經出現了明顯的分層現象。
In winter, there is almost no density difference in the North Atlantic and the Barents Sea—as you would expect given the upwelling there.
冬季，北大西洋與巴倫支海之間幾乎沒有任何密度差別—即便前者本應受到上升流的影響。
But in summer, the northern part of the Barents Sea is even more stratified than the tropical Atlantic and Pacific.
夏季，巴倫支海北部的分層現象比大西洋及太平洋熱帶海域更為明顯。
And the Beaufort Sea's stratification is high in both summer and winter.
另外，波弗特海常年存在嚴重的分層現象。
Dr Tremblay concludes that the replenishment of nutrients is already limited by stratification, especially at high latitudes, and that global warming will make things worse.
Tremblay博士認為，海水分層現象已經對海洋營養物質的循環補給非常不利，全球變暖則會雪上加霜，使該現象加劇惡化。
For Arctic productivity, the consequences are likely to be dire.
就北極地區的生產力而言，其前景更是不容樂觀。
Paul Wassmann of the University of Tromso looked at the production of organic matter by algae in different parts of the European Arctic, and used a climate model to predict the future.
來自特羅姆瑟大學的Paul Wassmann在看過歐洲北極海域不同地區海藻生成的有機物質數量之后，用氣候模型預測了該地區的未來走勢：
The area is divided into five economic zones.
北極地區將會分化為五個經濟區。
By 2050, according to the model, primary production is likely to have fallen in three of them, to be flat in one and to rise only in the Russian zone.
根據該模型的預測，至2050年，在這五個經濟區中，三個經濟區將會完全衰落，一個經濟區將出現生產停滯，而最后一個經濟區—俄羅斯區會成為唯一一個生產力保持增勢的海域。
Primary production is measured as the weight of carbon fixed by photosynthesis per square metre of the Earth's surface.
初級生產的多少根據地球表面每平方米光合作用所生成的碳的質量來決定。
At the moment, in the most productive area of the Arctic, the Norwegian Sea, that figure is 142 grams a square metre a year.
目前，北極地區生產力最高的海域挪威海的初級生產量約為每年142克/平方米，
The model predicts this will fall to 128 grams.
然而該模型表示這一數值將會下降至128克/平方米。
And by 2100, according to the model, things will be worse.
該模型還預測，至2100年，以上現象將會進一步惡化，
By then, four of the five zones will have experienced a loss in primary production. Only Russia will benefit.
而且屆時除俄羅斯經濟區外，另外四個經濟區的初級生產值將會大大降低。
A warming Arctic will not, in other words, be full of fish. It will simply be an ice-free version of the desert it already is.
換言之，升溫后的北極地區不會搖身變為天然漁場。北極地區仍舊只是一片荒漠，無非是少了冰原而已。
