经济学人下载:北极海域 龙舌兰日落

Science and technology
科学技术

The Arctic
北极海域

Tequila sunset
龙舌兰日落

Global warming may make the northernmost ocean less productive, not more so
全球变暖对北极海域生产力的负面影响

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，随着夏日的深入，北冰洋的冰原面积缩减到341万平方公里，该数字仅为1979年同期面积的二分之一。

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.
同时，就冰原体积而言，目前北极冰原的体积仅为1979年的四分之一，其融化速度之快可想而知。如今的北极地区，不仅冰原的面积在减少，其体积也在缩小。

One culprit is global warming, which is fiercer at the poles than elsewhere.
而这一现象的罪魁祸首便是全球变暖。同时，相比于其他海域而言，全球变暖对两极地区的冲击尤为明显。

The world's average temperature in 2012 was nearly 0.5C above the average for 1951-80.
与1951-1980年相比，2012年全球均温上涨了0.5，

In the Arctic, it was up almost 2C.
其中仅北极地区便上涨了2。

This sudden warming is like the peeling back of a lid to reveal a new ocean underneath.
就如同是掀开了某个锅盖后发现了一片沸腾的海洋一般，全球温度骤然上升。

That prospect is spreading alarm and excitement.
全球变暖加剧的前景不仅使人深感担忧，也使人倍觉振奋。

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.
尽管大多数的掌声来自油气开发商与大西洋-太平洋新航道拥护者，然而由于全球变暖给这片冰雪荒原带来了温暖与阳光，为其生态环境注入了新的元素，不少人也梦想着在这里靠捕鱼发一笔横财，

But they may be disappointed.
只是后者很可能会抱憾而归。

At the moment, the waters around the Arctic account for a fifth of the world's catch.
目前，北极地区占有全球总水量的五分之一。

There are few fish, however, under the ice itself.
然而在这厚厚的冰层下，却鲜有鱼类问津。

A fishing bonanza would require big ecological change.
在北极生态系统完全改变之前，捕鱼或许不是当地的最佳致富之道。

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，挪威特罗姆瑟大学召开“北极边境”会议，专门研究全球变暖对已有生态环境的影响，以及预估该现象是否会促进生成一个新的生态环境。

The consensus was that it won't—not because the Arctic will change too little, but because it will change too much.
会上，与会代表达成共识：北极海域将不会形成新的生态环境，这并不是因为北极的改变不足挂齿，恰恰相反，而是因为这里将会发生翻天覆地的变化。

Change and decay
变化与衰退

At first sight, this is counterintuitive.
乍读此言，不免觉得有些互相矛盾。

As the ice melts, more light can reach the water, and that means more photosynthesis by marine algae.
然而随着冰层进一步融化，大量阳光直射海面，海水中藻类植物的光合作用将会大大增强。

In the past, algae began to grow under the ice sheet in May and continued to do so until late September.
过去，冰原下的海藻于每年五月开始生长，至九月末结束，

Now, such growth starts in mid-March and continues until October.
但现在海藻的生长期已延长为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.
在所有北极海洋生物中，约半数生物为此类附着在冰原下方的冰藻，

Much of the rest is unattached algae, known as phytoplankton, and tiny animals, known as zooplankton.
另外还有部分浮游植物及浮游动物，

Both sorts of plankton support, directly or indirectly, the fish and mammals that live in the Arctic Ocean.
而这两类浮游生物便是北极地区鱼类及哺乳动物直接或间接的养料来源。

And the plankton, too, are flourishing thanks to global warming.
此外，全球变暖也使得此类浮游生物的数量激增：

The Arctic phytoplankton bloom, which used to run from June to September, now runs from April to September.
北极浮游植物生长期已经由过去的六至九月延长到了四至九月。

The upshot is more plankton, farther north.
于是，随着浮游生物进一步向北部蔓延，

That attracts more fish.
更多鱼类被吸引至此。

In 2000 Atlantic cod were caught throughout the Barents Sea.
2000年，巴伦支海南北遍布大西洋鳕鱼；

By 2012 their distribution was skewed towards the northern part of that sea.
2012年，大西洋鳕鱼活动范围北移至巴伦支海北部。

Stocks of capelin used to be concentrated south of Svalbard, at latitude 75N.
同时，曾主要分布于北纬75斯瓦尔巴群岛海域的capelin，

In 2012 this had moved to 78N.
于2012年被发现已迁移至北纬78附近，

Some found their way as far up as 80N.
部分甚至已迁徙到北纬80附近海域。

Which all sounds most promising. But many researchers think it will not continue.
尽管种种迹象表明在此地捕鱼致富的前景颇为乐观，然而许多学者却持不同意见。

First, the central Arctic is too deep for some important species, such as the polar cod.
首先，北冰洋中部海水过深，不利于极地鳕鱼等重要物种的生存。

Young polar cod are pelagic, meaning they live at or near the surface.
极地鳕鱼与大西洋鳕鱼同属，但前者活动范围较后者更为偏北。

Those one or more years old are benthic, meaning they live near the bottom.
此外，极地鳕鱼的幼鱼为海面鱼，这些幼鱼仅在海面附近活动；一岁及以上的极地鱼为深海鱼，这些深海鱼仅生活在类似于博福尔海域的海底。

In the Beaufort that bottom is 200 metres down.
鉴于博福尔海的深度为200米，

In the central Arctic it descends to about 4,000 metres, which is too deep for polar cod to survive.
而北冰洋中部深度约为4000米，因此极地鳕鱼根本无法在北极地区生存。

A second reason why there may be no bonanza is acidification of the ocean.
其次，北冰洋的酸化现象也是此地不宜鱼类生存的重要原因。

When water absorbs carbon dioxide, it produces carbonic acid. More CO?
水吸收二氧化碳后会释放出碳酸，

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，随着二氧化碳排放量增加，海水酸度也会随之升高。另外，因为冷水比热水更易吸收二氧化碳，所以这种现象在高纬度地区尤为明显。

The retreat of the ice also exposes ever more sea to do the absorbing.
于是，冰原面积的锐减也意味着更多的低温洋面将会暴露在空气之中，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.
在过去的三年里，美国地质调查局与南佛罗里达大学多次巡航此地进行调研，调研结果表明：阿拉斯加北部海域的碳酸值显著上升，并且该海域有机物的外壳中霰石含量不足。

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.
霰石为碳酸钙的一种形式，它不仅为有机物外壳提供支撑，而且其形成过程能够降低酸性物质含量。

Weaker shells means fewer shelled organisms and less food for fish.
外壳硬度的降低则说明该海域带壳有机物及鱼类食物的数量均大大减少。

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，全球变暖无法为北极地区带来大量鱼类养料的真正原因在于海水分层现象的加剧。

This is the tendency of seawater to separate into layers, because fresh water is lighter than salt and cold water heavier than warm.
由于淡水质量小于海水，而冷水质量大于热水，水温的上升会导致海水进一步分层。

The more stratified water is, the less nutrients in it move around.
同时，海水分层现越严重，则越不利于海水内部营养物质的流动。

Most free-swimming sea creatures are pelagic.
大多数海洋游泳生物均为海面生物。

Algae need light, so must live near the surface—as must the zooplankton and other animals that need the phytoplankton.
海藻需要阳光，因此海藻必须生活在海面附近，从而依靠海藻等浮游植物生存的浮游动物也必须在海面区域活动。

When they die, all these organisms sink to the bottom, where they become food for benthic creatures.
这类生物死亡后，其有机体沉入海底，变为海底生物的养料。

Once they have been consumed their component molecules, including nutrients such as nitrates, phosphates and iron, are stuck in Davy Jones's locker.
当有机体的硝酸盐、磷酸盐、铁以及其他营养成分均被其他生物吸收后，他们便永远地沉在了海底。

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，如果海底为一个封闭的水层，则海底营养物质将无法上升到水面，从而也无法为浮游植物等其他水面生物提供其生长所需的养料。

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.
上升流是海底营养物质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.
北极地区具有全球最著名的几大上升流之二：大西洋侧南格陵兰上升流及太平洋侧白令海峡上升流。

Nitrates are abundant at the surface in both places, which is why they are among the world's richest fishing grounds.
这两个海域富有硝酸盐，这便是这些地区以捕鱼业著名的原因。

There are few upwellings in the tropics, which are thus nutrient-poor.
由于热带海域则几乎没有上升流，因此这些海域通常缺乏养分。

Stratification threatens this recycling system by suppressing the vertical movement of water.
然而，海水分层会妨碍海水的垂直交换运动，从而威胁海洋自身的循环系统。

And global warming encourages stratification because it turns the ice into a layer of fresh water that sits on the surface.
全球变暖现象使得海面冰层融化，而融化后的淡水则只能漂浮在海面。

Imagine the ocean as a Tequila sunrise sitting on a warm bar.
这就好像是一杯放在暖气上的龙舌兰日落鸡尾酒，

The ice cubes at the top are melting away and the orange juice is sinking to the bottom.
上层的冰块在融化，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.
“北极边境”会上，Jean-éric Tremblay与拉瓦尔大学的Marcel Babin带来了他们的研究性论文成果。

This density difference is an index of ocean stratification.
该论文描述了不同海洋中洋面海水与100米深处海水的密度差别及其影响，而正是这一密度差别决定着海水的分层情况。

Parts of the Arctic seem to be getting badly stratified.
如图所示，北极地区部分海域已经出现了明显的分层现象。

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，北大西洋与巴伦支海之间几乎没有任何密度差别—即便前者本应受到上升流的影响。

But in summer, the northern part of the Barents Sea is even more stratified than the tropical Atlantic and Pacific.
夏季，巴伦支海北部的分层现象比大西洋及太平洋热带海域更为明显。

And the Beaufort Sea's stratification is high in both summer and winter.
另外，波弗特海常年存在严重的分层现象。

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博士认为，海水分层现象已经对海洋营养物质的循环补给非常不利，全球变暖则会雪上加霜，使该现象加剧恶化。

For Arctic productivity, the consequences are likely to be dire.
就北极地区的生产力而言，其前景更是不容乐观。

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.
来自特罗姆瑟大学的Paul Wassmann在看过欧洲北极海域不同地区海藻生成的有机物质数量之后，用气候模型预测了该地区的未来走势：

The area is divided into five economic zones.
北极地区将会分化为五个经济区。

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.
根据该模型的预测，至2050年，在这五个经济区中，三个经济区将会完全衰落，一个经济区将出现生产停滞，而最后一个经济区—俄罗斯区会成为唯一一个生产力保持增势的海域。

Primary production is measured as the weight of carbon fixed by photosynthesis per square metre of the Earth's surface.
初级生产的多少根据地球表面每平方米光合作用所生成的碳的质量来决定。

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，北极地区生产力最高的海域挪威海的初级生产量约为每年142克/平方米，

The model predicts this will fall to 128 grams.
然而该模型表示这一数值将会下降至128克/平方米。

And by 2100, according to the model, things will be worse.
该模型还预测，至2100年，以上现象将会进一步恶化，

By then, four of the five zones will have experienced a loss in primary production. Only Russia will benefit.
而且届时除俄罗斯经济区外，另外四个经济区的初级生产值将会大大降低。

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.
换言之，升温后的北极地区不会摇身变为天然渔场。北极地区仍旧只是一片荒漠，无非是少了冰原而已。