经济学人下载:北极 龙舌兰日落

Science and technology
科学技术

The Arctic
北极

Tequila sunset
龙舌兰日落

Global warming may make the northernmost ocean less productive, not more so
全球变暖可能降低最北部海域的活力，而不是使之更有生命力。

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日当天已经达到了夏季海洋冰面融化的温度，北冰洋的冰盖缩小到了341万平方公里，这个数字只有1979年冰盖面积的一半。

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.
而且，冰盖的面积仍旧以越来越快的速度在减少，将来的面积仅仅只有1979年总面积的四分之一。

One culprit is global warming, which is fiercer at the poles than elsewhere.
造成这种情况的原因之一就是全球变暖，全球变暖的后果在两极地区更为明显。因为冰盖正在越来越薄，也越来越小。

The world's average temperature in 2012 was nearly 0.5°C above the average for 1951-80.
2012年全球的平均温度比1951-1980年的平均温度高了约0.5°C。

In the Arctic, it was up almost 2°C.
而在北极，平均温度则高了近2°C。

This sudden warming is like the peeling back of a lid to reveal a new ocean underneath.
突然的变暖像一个被剥离的盖子一样，给人们呈现了一个新的海底世界。

That prospect is spreading alarm and excitement.
这种情形正在向周围发出警报，也让全世界兴奋不已。

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.
虽然，最让人兴奋的是发现了石油和天然气，还有大西洋和太平洋之间海上航线的开通，但是还是有一些人希望，在人们通过温暖和光明对现在这个冰冷沙漠进行生态重建时，也能带来渔业的发展机会。

But they may be disappointed.
但是他们可能要失望了。

At the moment, the waters around the Arctic account for a fifth of the world's catch.
目前，北极附近海域的捕获量占世界总和的五分之一。

There are few fish, however, under the ice itself.
然而，在北极冰面下很少有鱼。

A fishing bonanza would require big ecological change.
渔业的发展机遇将需要极大的生态改革。

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.
今年一月，由特罗姆瑟大学主办的北极前沿会议上，讨论了全球变暖将会对北极生态产生的变化，以预测是否有利于渔业的发展。

The consensus was that it won't—not because the Arctic will change too little, but because it will change too much.
达成的共识是—不，不是因为北极几乎没什么变化，而是因为北极的变化太大。

Change and decay
改革和衰退

At first sight, this is counterintuitive.
乍看之下，这简直违背常理。

As the ice melts, more light can reach the water, and that means more photosynthesis by marine algae.
当冰块融化时，水中将会有更多的光线，那就意味着海藻可能进行更多的光合作用。

In the past, algae began to grow under the ice sheet in May and continued to do so until late September.
过去，当五月来临时，冰下的海藻开始生长，整个生长期会持续到九月末。

Now, such growth starts in mid-March and continues until October.
现在，海藻在三月中旬就开始生长，生长期会持续到十月。

These ice algae, attached to the sheet itself, account for half the mass of living things in Arctic waters.
这些依附于冰盖生长的冰藻数量占了北极海域生物中的一半。

Much of the rest is unattached algae, known as phytoplankton, and tiny animals, known as zooplankton.
而其它大多数是独立生长的海藻，被称为浮游植物，还有被称为浮游动物的小动物。

Both sorts of plankton support, directly or indirectly, the fish and mammals that live in the Arctic Ocean.
同时，这两种浮游生物都直接或间接地供养了生活在北冰洋的鱼类和哺乳类动物。

And the plankton, too, are flourishing thanks to global warming.
而且，由于全球变暖也让这些浮游生物大量繁殖。

The Arctic phytoplankton bloom, which used to run from June to September, now runs from April to September.
以前，北极浮游生物的大量繁殖期是六月到九月，而现在繁殖期则早在四月就开始了，直到九月才结束。

The upshot is more plankton, farther north.
结果是越往北，浮游生物越多。

That attracts more fish.
于是就吸引了更多的鱼类。

In 2000 Atlantic cod were caught throughout the Barents Sea.
2000年，在巴比伦海域捕获了大西洋鲟鱼。

By 2012 their distribution was skewed towards the northern part of that sea.
到2012年，这些浮游生物的影响更倾向于北极海域的北部地区。

Stocks of capelin used to be concentrated south of Svalbard, at latitude 75°N.
以前，大量的毛鳞鱼—是鲟鱼的食物—集中于北纬75度的斯瓦尔巴群岛南部。

In 2012 this had moved to 78°N. Some found their way as far up as 80°N.
而2012年，发现它们已经迁移到了北纬78度。还有些人甚至发现它们已经远移至北纬80度。

Which all sounds most promising.
这些似乎让大多数人看到了希望。

But many researchers think it will not continue.
但是，许多研究者认为，这种情况不会再持续下去。

First, the central Arctic is too deep for some important species, such as the polar cod.
首先，对某些重要物种来说，比如，极地鲟鱼北极中心的海域太深。

Young polar cod are pelagic, meaning they live at or near the surface.
年幼的极地鲟鱼是海洋生物，也就是说他们生活在或者接近海平面。

Those one or more years old are benthic, meaning they live near the bottom. In the Beaufort that bottom is 200 metres down.
那些一岁或者以上的鲟鱼是深海生物，他们生活的区域接近海底。

In the central Arctic it descends to about 4,000 metres, which is too deep for polar cod to survive.
在博福尔，最深处就是200米以下。而北极中心的海底是约4,000米以下，那里对鲟鱼来说太深了无法生存。

A second reason why there may be no bonanza is acidification of the ocean.
渔业没有发展前途的第二个原因是海洋的酸化。

When water absorbs carbon dioxide, it produces carbonic acid.
当水吸收二氧化碳时会产生碳酸。

More CO2 means oceans everywhere are becoming more acidic, but the phenomenon is particularly marked at high latitudes because cold water absorbs CO2 more readily than warm water does.
更多的二氧化碳意味着海洋的各个地方都会变得更加酸化，但是这种现象在高纬度地区特别明显，因为寒冷的水会更易于吸收二氧化碳。

The retreat of the ice also exposes ever more sea to do the absorbing.
加上冰块的融化也暴露了更多的海水，加速了对二氧化碳的吸收。

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.
美国地质调查局和美国南佛罗里达大学在过去三年里的巡查发现，阿拉斯加北部海水的酸化程度在上升。

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.
他们也发现，这里许多生物的外壳缺少文石—一种让这些生物产生力量的碳酸钙形式—但是，它们体内的酸性形式阻碍了这种物质的合成。

Weaker shells means fewer shelled organisms and less food for fish.
不够强硬的外壳就表示带壳生物和供鱼类食用的生物越来越少。

The most important reason, though, for thinking that global warming will not produce an Arctic feeding frenzy is that it may increase ocean stratification.
但是，认为全球变暖不会使北极成为巨大“经济资源”最重要的原因是，它可能会加剧海洋的分层化。

This is the tendency of seawater to separate into layers, because fresh water is lighter than salt and cold water heavier than warm. The more stratified water is, the less nutrients in it move around.
这是一种海水分层的趋势，因为新鲜水比又咸又冷的水轻，而又比温暖的水重。海水分层程度越高，那么它的营养成分流动得就越少。

Most free-swimming sea creatures are pelagic.
大多数自由移动的海洋生物都是海面生物。

Algae need light, so must live near the surface—as must the zooplankton and other animals that need the phytoplankton.
海藻需要光线，所以必须生活在接近海面的区域—还有需要浮游植物的浮游动物和其它动物也同样如此。

When they die, all these organisms sink to the bottom, where they become food for benthic creatures.
当它们死亡时，所有这些生物都会下沉到海底，在那里它们会成为底栖生物的食物。

Once they have been consumed their component molecules, including nutrients such as nitrates, phosphates and iron, are stuck in Davy Jones's locker.
一旦它们消耗掉这些成份分子，包括硝酸盐，磷酸盐和铁等营养成份，就会成为戴维-琼斯小柜子的装饰了。

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.
因为要保持海面的多样性，小柜子必须要打开，滋养物会重新恢复生机，因此它们能够给浮游植物提供养份。

Walking the plankton
移动的浮游生物

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.
产生这种情况最重要的一种方式是通过海底水的上升流—通过寒冷和温和水域的碰撞产生巨大的水柱。

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.
还有两种最重要方式的实现就在北极：大西洋岸格陵兰岛南部和太平洋一侧白令海峡南部。

Nitrates are abundant at the surface in both places, which is why they are among the world's richest fishing grounds.
这两个地区的海面都有丰富的硝酸盐，这也是为什么这两处是世界上最大渔场的原因。

There are few upwellings in the tropics, which are thus nutrient-poor.
热带地区很少有上升流，因此缺乏硝酸盐。

Stratification threatens this recycling system by suppressing the vertical movement of water.
而海水分层会抵制水的垂直流动，从而威胁着这种再循环系统。

And global warming encourages stratification because it turns the ice into a layer of fresh water that sits on the surface.
而全球变暖却推动了海水分层，因为变暖会让冰融化成为覆盖着海面的新鲜水层。

Imagine the ocean as a Tequila sunrise sitting on a warm bar.
可以把海洋想象为坐落在一个温馨酒巴上的龙舌兰日出。

The ice cubes at the top are melting away and the orange juice is sinking to the bottom.
顶部的冰柱正在融化，桔汁慢慢滑到底部。

At the conference, a paper by Jean-eric 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.
在这次会议上，魁北克拉瓦尔大学的让-埃里克-特伦布莱和马塞尔-巴宾提交的报告中，通过报告不同海洋海平面和100米深处不同的水密度，描述了这种效应。

This density difference is an index of ocean stratification.
这种水密度差就是海洋分层的标志。

Parts of the Arctic seem to be getting badly stratified.
北极部分地区的分层现象正越来越严重。

In winter, there is almost no density difference in the North Atlantic and the Barents Sea—as you would expect given the upwelling there.
北大西洋和巴伦支海在冬天几乎不会出现水密度差—鉴于那里的上涌现象，人们会有所期待。

But in summer, the northern part of the Barents Sea is even more stratified than the tropical Atlantic and Pacific.
但是在夏天，巴伦支海的北部比大西洋和太平洋热带区域的分层程度还严重。

And the Beaufort Sea's stratification is high in both summer and winter.
波弗特海在夏冬两季的分层都很活跃。

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.
特伦布博士的结论是，养份的补充已经被分层抵制，特别是在高纬度地区，加上全球变暖会让这种现象更加严重。

For Arctic productivity, the consequences are likely to be dire.
考虑到北极地区的生产力，这种后果可能更加可怕。

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.
特罗姆瑟大学的保罗-威萨曼仔细研究了欧洲北极不同地区藻类产生有机物的过程，使用一种气候模型以预测未来的形式。

The area is divided into five economic zones.
这个区域会被区分为五个经济区。

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.
根据这个模式，到2050年，其中三个经济区的初级生产量会下降，第四个会持平，只有俄罗斯经济区的初级生产量会上升。

Primary production is measured as the weight of carbon fixed by photosynthesis per square metre of the Earth's surface.
初级生产量是衡量地球表面每平米光合作用固定的碳重量的指标。

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，在北极最有生产力的区域-挪威海，这个数字为每平米年均142克。

The model predicts this will fall to 128 grams.
而根据模式预测，这个数字会跌至128克。

And by 2100, according to the model, things will be worse.
到2100年，情况会变得更糟。

By then, four of the five zones will have experienced a loss in primary production. Only Russia will benefit.
到那时，五个经济区的四个会发生初级生产量大幅减少的现象。届时，只有俄罗斯还会从中受益。

A warming Arctic will not, in other words, be full of fish.
换句话说，变暖的北极不会满眼是鱼。

It will simply be an ice-free version of the desert it already is.
它将还是现在看到的北方沙漠，不同的是浮在海面上的冰消失了。