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

譯者: Lilian Chiu 審譯者: Zoe Walmsley

Roughly 3 billion years ago,

大約三十億年前，

a single-celled photosynthetic bacterium began burping a new chemical

有一種單細胞光合作用細菌

開始排放出一種新的化學物質，

that was poisonous to nearly every species on Earth.

該物質對地球上差不多 全部的物種來說都有毒。

Over the following hundreds of millions of years,

在接下來的數億年間，

more microorganisms began producing this toxic gas,

有更多微生物開始製造這種有毒氣體，

first saturating Earth's oceans and eventually its atmosphere.

首先充斥地球的海洋， 最終連大氣也被充滿了。

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

這種化學物質改變了 原本大氣層中的氣體組成，

so drastically that it caused a global ice age.

改變之大，讓整個地球進入冰河時期。

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

這個強大、有毒、 改變世界的氣體的名字是？

氧氣。

In the millions of years since the Great Oxygen Catastrophe,

在氧氣大浩劫發生後的數百萬年間，

most life, including all multicellular organisms,

大部分的生命，包括所有多細胞生物，

have evolved to rely on this gas.

都演化出依賴這個氣體的特性。

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

然而，在某些地方， 氧氣耐受度低的微生物，

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

如地球最早期的那些微生物，

重新出現了。

Many of these places are in the ocean depths,

這些地方多半位於海洋深處，

beyond the reach of researchers.

研究人員無法觸及。

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

但是還有一些完全沒有氧氣的水域，

yet close enough to the surface to explore.

離水面夠近，研究人員能探索的。

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

其中一個湖就藏身在瑞士 阿爾卑斯山的皮奧拉山谷中。

Formed over 10,000 years ago,

一萬多年前形成的卡達格諾湖

Lake Cadagno is one of roughly 200 known meromictic lakes,

是目前已知約兩百個 不完全對流湖的其中一個，

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

它其實是由兩個不同的水域相疊而成。

The top layer functions like a standard body of freshwater.

上層水域與標準的淡水水域相似，

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

在那裡游泳很安全，

最為人所知的特色 是有肥美且豐富的魚群，

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

數世紀以來，那一直 是當地捕魚傳說的主題。

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

距離那豐饒區域下方十三公尺處，

則是密度高、含硫且無氧的水域，

lethal to any multicellular life forms, fish included.

不存在任何多細胞生物， 包括魚類在内。

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

在典型的循環湖中， 整個水域的水會逐漸混合，

diffusing oxygen from the surface throughout.

把氧氣從表面擴散到整個水中。

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

但是這裡的兩層水域永遠都是分開的，

就跟所有的不完全對流湖一樣。

And the reason for this divide in Cadagno

卡達格諾的湖水分成兩層的原因是

is the waters’ unique chemical compositions.

因為水中的獨特化學成分。

Both layers are fed by rainwater flowing down the mountains,

兩個水域的水都來自山上流下的雨水，

however, this water can take two paths.

然而，這個水有兩條路徑可走。

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

一條是直接沿著花崗岩山脈 流進上層水域。

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

另一條則是滲入皮奧拉 山谷的白雲岩礦脈──

a porous rock full of salts such as sulfate.

一種富含硫酸鹽的多孔岩石中。

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

滲入白雲岩的雨水最終流進湖泊，

all the while shedding its oxygen and picking up salts.

沿路吸收鹽類卻流失氧氣。

Finally, this heavier water will cascade from sublacustrine springs

最後，這種比重較高的水

會以泉水的型態從湖底冒出，

below the lake’s surface,

forming the dense, salt-rich bottom layer.

形成密度高且富含鹽份的底層水域。

This lower layer is anoxic, meaning oxygen free,

此下層水體是缺氧的，完全沒有氧氣，

and will suffocate any oxygen-dependent life.

依賴氧氣的生物在此會窒息而死，

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

但它卻是厭氧細菌的最佳環境──

in the Great Oxygen Catastrophe.

那些無法逃過氧氣大浩劫的。

The flow from the sublacustrine springs creates microenvironments

湖底的湧泉創造出許多微環境，

which feed large aggregates of microorganisms

養活了湖床上那些 奇特又另類的生物群。

that emerge from the lakebed in strange and otherworldly shapes.

Various anaerobic microorganisms take in the water's sulfate

許多厭氧微生物吸收水中的硫酸鹽，

and emit toxic sulfide.

釋放出有毒的硫化物。

And at the border of these layers,

而在兩層水域的交界處，

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

有一層薄層，

主要由粉紅色的奧氏著色菌組成：

a photosynthesizing bacterium that relies on this sulfur

那是一種行光合作用的細菌， 仰賴硫化物維生，

the way most plants rely on oxygen.

如同大部分的植物仰賴氧氣一樣。

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

然而，即使水和生物都不會跨層移動，

these ecosystems aren’t completely out of touch.

這些生態系統也並非完全與世隔絕。

Chromatium okenii live at the top of the bottom layer

奧氏著色菌生活在底層水域的頂端，

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

因為它們需要盡可能靠近太陽。

But while they never cross into the deadly oxygenated waters,

但，雖然它們不會跨入 足以致命的含氧水中，

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

它們已經夠接近，近到浮游生物等

足可下潛、吃掉它們， 再返回上層水域。

eat them, and get back up.

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

事實上，這種關係正是

形成上層水域的食物鏈基礎，

robust food chain

supporting the lake’s legendary fish population.

讓該湖泊著名的魚群得以維生。

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

這個獨特的生態系統不僅僅 造福卡達格諾的漁民，

Having access to an isolated anaerobic ecosystem

這個與世隔絕的厭氧生態系統

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

也讓科學家能一窺 氧氣大浩劫前的世界的模樣。

For example, when Chromatium okenii form their blanket,

例如，當奧氏著色菌形成那層薄層時，

they increase the density of that thin layer of water.

它們同時也增加了那層水的密度。

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

而當水下沉時，

這些微生物被迫往上游，

creating a minute mixing of water called bioconvection.

因而促成一個所謂生物對流的 微小的混合水域。

This billions of years old phenomenon might be a clue

這個存在數十億年的現象

或許能解釋上古生物 如何演進出游泳能力。

to how early life evolved the ability to swim.

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

而這只是卡達格諾湖深處 等待研究人員探索的奧秘之一。

studying Cadagno’s mysterious depths.