Scientists are obsessed with this lake - Nicola Storelli and Daniele Zanzi

翻译人员: Tianyun Liu 校对人员: Sue Lu

Roughly 3 billion years ago,

大约 30 亿年前，

a single-celled photosynthetic bacterium began burping a new chemical

一种单细胞的光合作用细菌 开始释放一种新的化学物质，

that was poisonous to nearly every species on Earth.

这种物质对地球上 几乎所有的物种都是有毒的。

Over the following hundreds of millions of years,

在接下来的数亿年中，

more microorganisms began producing this toxic gas,

越来越多的微生物 开始产生这种有毒气体，

first saturating Earth's oceans and eventually its atmosphere.

首先充斥了地球的海洋， 最终进入了大气层。

Up here, this chemical changed the composition of pre-existing gases

该化学物质彻底改变了 大气层原有气体的成分，

so drastically that it caused a global ice age.

以至于引发了全球冰河时期。

And the name of this powerful, poisonous, world-changing gas? Oxygen.

这种强大、有毒、 能改变世界的气体叫什么？氧气。

In the millions of years since the Great Oxygen Catastrophe,

自“氧气大灾难”以来的 数百万年间，

most life, including all multicellular organisms,

大多数生命， 包括所有的多细胞生物，

have evolved to rely on this gas.

已经进化到依赖氧气为生。

However, there are some places where oxygen-averse microorganisms,

然而在有些地方，厌氧微生物，

like those from Earth's earliest days, have re-emerged.

就像地球最初时期的生物， 又重新出现了。

Many of these places are in the ocean depths,

许多这种地方都是在海洋深处，

beyond the reach of researchers.

超出了研究人员的触及范围。

But there are other bodies of water completely devoid of oxygen,

但是，还有一些完全缺氧的水体，

yet close enough to the surface to explore.

却足够靠近表面，可以进行探索。

And one such lake is hidden high in the Swiss Alps’ Piora Valley.

其中一个这样的湖泊隐藏在高高的 瑞士阿尔卑斯山皮奥拉谷 (Piora Valley) 。

Formed over 10,000 years ago,

卡达尼奥湖 (Lake Cadagno) 形成于一万多年前，

Lake Cadagno is one of roughly 200 known meromictic lakes,

是已知的大约 200 个分层湖之一，

meaning it's actually two distinct bodies of water stacked on top of each other.

也就是说它实际上是 两个相互叠加的截然不同的水域。

The top layer functions like a standard body of freshwater.

顶部那层就像标准的淡水体，

It’s safe for swimming and known mostly for a plump and plentiful fish population

适合游泳，主要以 肥美丰富的鱼类种群而闻名，

that’s been the subject of local fishing legends for centuries.

这一直是几个世纪以来 当地的渔猎传说主题。

But just 13 meters beneath that bounty is a dense, sulfurous, oxygen-free pool

但在那片富饶之下仅 13 米处， 是一个浓密的、含硫的无氧池，

lethal to any multicellular life forms, fish included.

对任何多细胞生物， 包括鱼类，都是致命的。

In a typical lake, the entire body of water would gradually mix,

在一个典型的湖泊中， 整个水体会逐渐混合，

diffusing oxygen from the surface throughout.

将表面的氧气扩散到整个湖泊中。

But these two layers never mix, as is the case with any meromictic lake.

就像任何分层湖一样， 卡达尼奥湖这两层永远不会混合。

And the reason for this divide in Cadagno

卡达尼奥湖水层分界的原因

is the waters’ unique chemical compositions.

是由于水体独特的化学成分。

Both layers are fed by rainwater flowing down the mountains,

这两层水都是由从山上流下的雨水补给，

however, this water can take two paths.

然而，这些雨水可以走两条路径。

The first is to trickle down the granitic mountain directly into the top layer.

第一条是沿着花岗岩山体直接滴入上层水体。

The second is to seep into the Piora Valley’s vein of dolomite—

第二条是渗入皮奥拉谷的白云岩脉—

a porous rock full of salts such as sulfate.

一种充满硫酸盐等盐类的多孔岩石。

Rainwater that sinks into the dolomite will slowly inch towards the lake,

渗入白云岩的雨水会慢慢流向湖泊，

all the while shedding its oxygen and picking up salts.

在此过程中逐渐失去氧气并吸收盐分。

Finally, this heavier water will cascade from sublacustrine springs

最终，这种较重的水会从湖底泉涌出，

below the lake’s surface,

即湖面下的湖底泉，

forming the dense, salt-rich bottom layer.

然后形成密集、富含盐分的底层水体。

This lower layer is anoxic, meaning oxygen free,

这一底层水无氧，即没有氧气，

and will suffocate any oxygen-dependent life.

会使任何依赖氧气的生命窒息，

But it’s ideal for the kind of anaerobic bacteria that died off

但却是厌氧细菌的理想生存环境，

in the Great Oxygen Catastrophe.

它们曾在氧气大灾难中灭绝。

The flow from the sublacustrine springs creates microenvironments

来自湖底泉的流动创造了微环境，

which feed large aggregates of microorganisms

以此养育大量的微生物群，

that emerge from the lakebed in strange and otherworldly shapes.

它们以奇怪而超凡的形状从湖底冒出。

Various anaerobic microorganisms take in the water's sulfate

各种厌氧微生物吸收水中的硫酸盐

and emit toxic sulfide.

并释放出有毒的硫化物。

And at the border of these layers,

在这些水层的边界上，

there’s a thin blanket mainly composed of pink-bodied Chromatium okenii:

有一层薄薄的覆盖物， 主要由粉红色的 Chromatium okenii 组成：

a photosynthesizing bacterium that relies on this sulfur

是一种依赖硫进行光合作用的细菌，

the way most plants rely on oxygen.

就像大多数植物依赖氧气一样。

However, while neither water nor organisms move between the layers,

然而，虽然水和生物 都不会在各层之间移动，

these ecosystems aren’t completely out of touch.

这些生态系统并非完全脱离接触。

Chromatium okenii live at the top of the bottom layer

Chromatium okenii 生活在底层水域的顶部，

because they need to be as close to the sun as possible.

因为它们需要尽可能接近太阳。

But while they never cross into the deadly oxygenated waters,

但虽然它们从未跨入致命的含氧水域，

they’re close enough that organisms like zooplankton can dive down,

因为离得太近，以至于 像浮游动物这种生物可以潜下去，

eat them, and get back up.

吃掉它们，然后重回上层水域。

In fact, this relationship forms the bottom of the upper layer’s

事实上，这种关系构成了 上层水域底部的强大食物链，

robust food chain

supporting the lake’s legendary fish population.

支撑着湖中传奇般的鱼类种群。

This unique ecology is more than just a boon for Cadagno’s fishermen.

这种独特的生态系统 不仅是卡达尼奥渔民的福音，

Having access to an isolated anaerobic ecosystem

能接触到与世隔绝的厌氧生态系统，

allows scientists to model the world before the Great Oxygen Catastrophe.

科学家就能够模拟 氧气大灾难之前的世界。

For example, when Chromatium okenii form their blanket,

例如，当 Chromatium okenii 形成其覆盖层时，

they increase the density of that thin layer of water.

它们增加了那层薄水的密度。

As the water sinks, these microorganisms are forced to swim back up,

随着水下沉， 这些微生物被迫游回上面，

creating a minute mixing of water called bioconvection.

创造了称为生物对流的微小水体混合。

This billions of years old phenomenon might be a clue

这一已有数十亿年历史的现象可能是

to how early life evolved the ability to swim.

早期生命如何进化出游泳能力的线索。

And it’s just one of the many insights that await researchers

这只是众多见解之一， 等待着研究人员进一步

studying Cadagno’s mysterious depths.

考察卡达尼奥湖神秘深处。