Alarming stories from Antarctica are now more frequent than ever; the ice surface is melting, floating ice shelves are collapsing and glaciers are flowing faster into the ocean.
來自南極洲的驚人情況,目前比往昔更加頻繁。冰面正在融化,浮動冰棚正在倒塌,冰川入海的速度更快。
Antarctica will be the largest source of future sea-level rise. Yet scientists don’t know exactly how this melting will unfold as the climate warms. Our latest research looks at how the Antarctic ice sheet advanced and retreated over the past 10,000 years. It holds stark warnings, and possibly some hope, for the future.
南極洲會是未來海平面上升的最大來源。然而,科學家們並不確切知曉,隨著氣候變遷,這種融化將如何展開。我們的最新研究探究了,南極冰原過去1萬年間如何消、長。對未來而言,這擁有十足的警訊,不過可能還有些希望。
Future sea-level rise presents one of the most significant challenges of climate change, with economic, environmental and societal impacts expected for coastal communities around the globe.
未來的海平面上升是氣候變遷,最重大的挑戰之一。預期對全球沿海社區,具有經濟、環境及社會的影響。
While it seems like a distant issue, the changes in Antarctica may soon be felt on our doorsteps, in the form of rising sea levels.
儘管這好似一個遙遠的問題,不過南極洲的變化可能很快,以海平面上升的形式,在咱們的門階上,被感受到。
Antarctica is home to the world’s largest single mass of ice: the Antarctic ice sheet. This body of glacier ice is several kilometres thick, nestled on top of solid land. It covers entire mountain ranges beneath it.
南極洲是世界最大的單一冰團,南極冰原的所在地。這片冰川冰的體,貼靠於堅實的陸地上,厚達數公里。它覆蓋了其下面綿亙的整個山脈。
The ice sheet “flows” over the land from the Antarctic interior and towards the surrounding ocean. As a whole it remains a solid mass, but its shape slowly deforms as the ice crystals move around.
該冰原於此陸地上“流動”,從南極內陸朝向周圍的海洋。整體說來,它仍然是個固體的團,不過隨著冰晶的到處移動,其形狀慢慢地變形。
短片網址:https://youtu.be/LSG8Dm-ZPzc
While the ice sheet flows outward, snowfall from above replenishes it. This cycle is supposed to keep the system in balance, wherein balance is achieved when the ice sheet is gaining the same amount of ice as it’s losing to the ocean each year.
當該冰原向外流動時,來自上方的降雪填補它。此循環被認為,使該體系保持平衡。由於這一點,當冰原獲得與每年流失到海洋的相同冰數量時,達成平衡。
However, satellites keeping watch from above show the ice sheet is currently not in balance. Over the past 40 years, it has lost more ice than it has gained. The result has been global rising sea levels.
不過,從上方監視的衛星顯示,目前冰原不平衡。在過去40年間,它一直失去比獲得的冰多。結果,已經是全球海平面上升。
But these historical observations span only four decades, limiting our understanding of how the ice sheet responds to climate change over much longer periods. We wanted to look further back in time – before satellites – and even before the first polar explorers. For this, we needed natural archives.
不過,此些歷史觀察僅橫跨40年,限制了我們有關冰原,在更長很多的時間裡,如何對氣候變遷作出反應的瞭解。我們想進一步回顧過去(在衛星之前)甚至在首度極地探險者之前。為此,我們需要自然的記錄。
We brought together various natural archives to unearth how the Antarctic ice sheet changed over the past 10,000 years or so. These included:
我們匯集了各種自然的記錄,以揭露過去1萬年左右期間,南極冰原如何變化。此些包括:
ice cores collected from Antarctica’s remote interior, which can show us how snow accumulated in the past
從南極洲偏遠內陸收集的冰芯,這能為我們展現,雪於過去如何累積。
rocks collected from exposed mountain peaks, which reveal how the ice sheet has thickened or thinned with time
從曝露之山峰收集的岩石,這能揭露隨著時間推移,冰原曾如何變厚或變薄
sediment cores collected from the seafloor, which reveal how the ice sheet margin – where the edge of the land ice meets the ocean – advanced or retreated
從海床收集的沉積物芯,這能揭露冰原邊緣(陸地冰的邊緣與海洋相遇的地方)是如何前進或後退。
lake mud and old beaches, which reveal how the coastline changed in response to the ice sheet growing or shrinking.
湖泥及古老海灘,這能揭露在對冰原消、長作出反應時,海岸線如何變化。
圖1. 冰芯提供了,過去雪累積如何變化的記錄。 (圖援用自原文)
When we started our research, I wasn’t sure what to expect. After all, this period of time was long considered fairly dull, with only small changes to the ice margin.
當我們開始研究時,我不確定預期什麼。畢竟這段時間,長期被認為是相當不活躍的,冰邊緣僅有小變化。
Nevertheless, we studied the many different natural archive one by one. The work felt like a 1,000-piece jigsaw puzzle, full of irregular-shaped pieces and seemingly no straight edge. But once we put them together, the pieces lined up and the picture was clear.
儘管如此,我們逐一研究了諸多不同的自然記錄。這項研究感覺像一種,充滿不規則形狀、似乎沒有直邊之小片的千塊拼圖玩具。不過,一旦我們把它們併合,此些小片排列好,結果畫面是清晰的。
Most striking was a period of ice loss that took place in all regions of Antarctica about 10,000 to 5,000 years ago. It resulted in many metres of sea-level rise globally.
最引人注目的是,大約 1萬到5千年前,在南極洲所有地區發生的冰層流失的時期。它導致了,全球海平面上升數米。
In some regions of Antarctica, however, this ice loss was then followed by ice gain during the past 5,000 years – and a corresponding global sea-level fall – as the ice sheet margin advanced to where it is today.
不過,在南極洲的某些地區,此冰層流失之後,隨之在過去5千年期間,冰層增加(結果是相應的全球海平面下降)。這事實是,冰原邊緣推進到當今的位置。
圖2. 收集自海床的沉積物芯,告訴我們冰原何時消退。 (圖援用自原文)
Understanding how and why the Antarctic ice sheet changed in this fashion offers lessons for the future.
瞭解南極冰原如何及為何以此種方式變化,為未來提供諸多殷鑒。
The first lesson is more of a warning. The period of ice loss from 10,000 to 5,000 years ago was rapid, occurring at a similar rate to the most dramatically changing parts of the Antarctic ice sheet today.
首個殷鑒更是一種警訊。從1萬到5千年前,冰層流失是迅速的。其以類似當今南極冰原變化,最劇烈部分的速度發生。
We think it was likely the result of warm ocean water melting the underside of floating ice shelves – something that has also happened in recent decades. These ice shelves hold back the ice on land, so once they’re removed the ice on the land flows faster into the ocean.
我們認為,這可能是暖和的海水,融化了浮冰棚底下的結果。這是近幾十年來,也已經發生的事。此些冰棚阻擋了陸地上的冰層,因此一旦它們遭移除,陸地上的冰層會更快流入海洋。
In the future, it’s predicted ice loss will accelerate as the ice sheet retreats into basins below sea level. This may already be under way in some regions of Antarctica. And based on what happened in the past, the resulting ice loss could persist for centuries.
於未來,隨著冰原消退到海平面以下的盆地,據預測冰的流失會加速。在南極洲的某些地區,這可能已經進展中。那麼,根據過去所發生的,從而產生的冰層流失可能持續達幾個世紀。
The second lesson from our work may bring some hope. Some 5,000 years ago the ice sheet margin stopped retreating in most locations, and in some regions actually started to advance. One explanation for this relates to the previous period of ice loss.
來自我們研究的第二個殷鑒,可能帶來一些希望。大約5000年前,大部分地區的冰原邊緣停止消退,且在一些地區實際上已經開始長進。對此的一種解釋與先前冰層流失的期間有關。
Before the ice began melting away, the Antarctic ice sheet was much heavier, and its weight pushed down into the Earth’s crust (which sits atop a molten interior). As the ice sheet melted and became lighter, the land beneath it would have lifted up – effectively hauling the ice out of the ocean.
在冰層開始融化之前,南極冰原是更重得多,因此其重量向下擠進地殼(位於融化了之內部的頂部)。當冰原融化且變得較輕時,其下面的陸地可能曾上升。這有效地將冰層拖曳離開海洋。
Another possible explanation is climate change. At Antarctica’s coastal fringe, the ocean may have temporarily switched from warmer to cooler waters around the time the ice sheet began advancing again. At the same time, more snowfall took place at the top of the ice sheet.
另一種可能的解釋是氣候變遷。大約在冰原再次開始長進時,在南極洲的沿海外緣,海洋可能曾暫時性地,從暖和的水域轉變成較冷的水域。在此同時,冰原頂部發生更多的降雪量。
圖3. 在過去一萬年裡,冰層的消、長是由幾個因素驅動,其中諸多被預期,於未來發生。 (圖援用自原文)
Our research supports the idea that the Antarctic ice sheet is poised to lose more ice and raise sea levels – particularly if the ocean continues to warm. It also suggests uplift of the land and increased snowfall have the potential to slow or offset ice loss. However, this effect is not certain.
我們的研究支持,南極冰原即將失去更多冰層,而提高海平面的見解。特別是,倘若海洋繼續暖化。這也暗示,陸地的隆起及降雪量的增加,有可能減緩或抵消冰層的流失。不過,此效應並不明確。
The past can never be a perfect test for the future. And considering the planet is warming faster now than it was back then, we must err on the side of caution.
過去絕不可能是未來的一種完美檢驗。因此,思考目前地球正比當時暖化得更快,我們必須謹慎行事。
網址:https://theconversation.com/we-studied-how-the-antarctic-ice-sheet-advanced-and-retreated-over-10-000-years-it-holds-warnings-for-the-future-185505
翻譯:許東榮
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