近200萬年前地球的二氧化碳循環(huán)

古老的冰揭示了近200萬年前地球的二氧化碳循環(huán)

After more than two years of analysis, the oldest complete ice core has served up a reliable snapshot of our planet's atmosphere from nearly 2 million years ago. And the results are not what many expected.

經過兩年多的分析，最古老的完整的冰核提供了近200萬年前地球大氣的可靠快照。結果也不是很多人所期望的。

We know that roughly 1 million years ago, the cycle of Earth's ice ages suddenly shifted, with deeper and longer freezes occurring only every 100,000 years, instead of once every 40,000 years.

我們知道，大約100萬年前，地球冰期的周期突然發(fā)生了變化，每10萬年才會發(fā)生一次更深、更長的冰期，而不是每4萬年一次。

Nothing in our planet's orbit could explain the 'abrupt' change, known as the Mid-Pleistocene transition (MPT), and with few other explanations, some hypothesised there must have been a long-term decline in atmospheric CO2 concentrations, cooling the planet to a new threshold.

在我們星球的軌道上，沒有任何東西可以解釋這種被稱為中更新世轉變(MPT)的“突然”變化，而且由于幾乎沒有其他的解釋，一些人猜測一定是大氣中的二氧化碳濃度長期下降，使地球降溫到一個新的閾值。

Ancient air bubbles trapped in the Antarctic ice sheet have now revealed a somewhat different picture. Dating back roughly 1.5 million years, these tiny doses of our ancient atmosphere contain "amazingly low" CO2 levels, according to paleoclimatologist Yige Zhang from Texas A&M University, who was not involved in the study and who told Science Magazine he found the results "quite interesting".

被困在南極冰蓋的古代氣泡現(xiàn)在呈現(xiàn)出了一幅有些不同的畫面。來自德克薩斯農工大學的古氣候學家張翼格(Yige Zhang)表示，這些微小的古大氣中二氧化碳含量“低得驚人”，這可以追溯到大約150萬年前。張翼格沒有參與這項研究，他對《科學》雜志(Science)說，他發(fā)現(xiàn)這個結果“非常有趣”。

These are the first direct observations of atmospheric greenhouse gases before the ice ages on Earth began to grow longer, and they suggest something other than a long-term decline in CO2 was at play to shift our planet's entire ice age cycle.

這些是在地球冰河時代開始變長之前，對大氣溫室氣體的首次直接觀測，它們表明，在改變地球整個冰河時代周期的過程中，除了二氧化碳的長期下降外，還有其他因素在起作用。

The oldest sample of ice we could test for CO2 levels previous to this new core was a 'mere' 800,000 years old; other estimates based on the chemistry of Earth's sediments are only useful as a proxy for greenhouse gas levels - they're not useless, but more verification is necessary.

在新地核形成之前，我們能夠檢測到的最古老的冰樣本的二氧化碳含量只有80萬年;其他基于地球沉積物化學成分的估算只能作為衡量溫室氣體水平的指標——它們并非毫無用處，但需要更多的驗證。

The new ice analysis, which used more precise measurements than before, has revealed that "although CO2 levels during glacials stayed well above the lows that occurred during the deep glacials of the past 800,000 years, the maximum CO2 concentrations during interglacials did not decline," Earth scientist Eric Wolff from the University of Cambridge writes in a review of the research.

新的冰分析,使用比以前更精確的測量,揭示,“雖然在冰川的二氧化碳水平仍遠遠高于低位的深冰川發(fā)生在過去的800000年里,最大的二氧化碳濃度在間冰期沒有下降,”劍橋大學的地球科學家埃里克·沃爾夫在審查的研究中寫道。

One of the important results of this study is to show that carbon dioxide is linked to temperature in this earlier time period, says atmospheric scientist Ed Brook from Oregon State University.

“這項研究的一個重要結果是表明二氧化碳與早期的溫度有關，”俄勒岡州立大學的大氣科學家Ed Brook說。

That's an important baseline for understanding climate science and calibrating models that predict future change.

“這是理解氣候科學和校準預測未來變化的模型的重要基礎。”

In other words, the relationship between CO2 levels and Antarctic temperature hasn't changed much over this time span. And the lower CO2 levels during ice ages are probably just a consequence of the shorter glacial periods that occurred before the MPT.

換句話說，在這段時間內，二氧化碳水平和南極溫度之間的關系并沒有改變多少。在冰河時代，二氧化碳含量較低可能只是MPT之前較短的冰河時期的結果。

In fact, the authors found the lowest levels of CO2 didn't show up for the first 40,000 years after the MPT occurred.

事實上，作者發(fā)現(xiàn)，在MPT發(fā)生后的最初4萬年里，二氧化碳的最低水平并沒有出現(xiàn)。

Our findings appear to be inconsistent with hypotheses that attribute the transition into the 100k world to a long-term decline in both interglacial and glacial atmospheric CO2, they write.

他們寫道:“我們的發(fā)現(xiàn)似乎與那些將向10萬千瓦世界的轉變歸因于間冰期和冰川期大氣二氧化碳長期減少的假設不一致。”

In his review of the research, Wolff commended the researchers on their precise estimates and "tantalising" snapshots. But he argues a more "complete, undisturbed time series" is needed to put CO2 levels in context.

在他的研究綜述中，沃爾夫稱贊了研究人員的精確估計和“誘人的”快照。但他認為，需要一個更“完整、不受干擾的時間序列”來解釋二氧化碳水平。

Luckily for us, the ancient ice core, which was found in Antarctica's Allan Hills, may soon have company. Researchers say the ice sheet here dates back 2.7 million years and maybe even longer.

對我們來說幸運的是，在南極洲的艾倫山發(fā)現(xiàn)的古老的冰核可能很快就有同伴了。研究人員表示，這里的冰原可以追溯到270萬年前，甚至更早。

Given how much the ice has shifted in this region, any new cores we dig up will probably come in discontinuous sections, but their information may help us piece together at least some of the secrets of our planet's mysterious past.

考慮到這一地區(qū)的冰已經發(fā)生了巨大的變化，我們挖掘出的任何新核心可能都是不連續(xù)的部分，但它們的信息可能會幫助我們拼湊起至少一部分地球神秘過去的秘密。

We don't know the age limit in this area, Brook says. "It could be much older in some places. That's why we're going back. Pushing beyond two million years would be pretty amazing."

“我們不知道這個地區(qū)的年齡限制，”布魯克說。“有些地方可能更古老。這就是為什么我們要回去。如果能超過200萬年，那就太神奇了。”

The study was published in Nature.

這項研究發(fā)表在《自然》雜志上。