By Michelle
Klampe
在末次冰期期間，覆蓋北美大片地區的冰層會週期性的斷裂而產生大量冰山，並讓融冰快速流入格陵蘭附近的北大西洋，引發急遽的氣候變遷而波及全球。
漂冰碎屑事件期間全球各地的反應。格陵蘭：毫無反應；北大西洋：溫度降低與冰山流入；亞洲：季風減弱；南美：季風增強；南極：暖化。圖片來源：Oliver Day, Oregon State University
這些突如其來的事件稱為「漂冰碎屑事件」(Heinrich Events)，發生在距今16,000到60,000年前。它們可以改變全世界的海洋環流，促成北大西洋氣溫下降並且對許多地方的季風降雨造成衝擊。
一般認為就在附近的格陵蘭對於北大西洋發生的事件相當敏感，但漂冰碎屑事件究竟對格陵蘭造成了什麼影響，我們卻所知不多。由奧勒岡州立大學的研究人員最近發表在期刊《自然》(Nature)的新研究給出了確切解答。
「答案是格陵蘭完全不為所動，溫度就跟之前一模一樣，」研究主要作者Kaden
Martin表示。他是奧勒岡州立大學地球、海洋與大氣科學學院四年級的博士候選人。「格陵蘭就像是坐在前面幾排卻沒有在看表演的觀眾。」
相反地，研究人員發現漂冰碎屑事件造成遠在地球另一端的南極洲溫度迅速上升。
研究人員本來期望靠近冰層的格陵蘭溫度應該會有某種程度的下降。奧勒岡州立大學地球、海洋與大氣科學學院的助理教授Christo
Buizert是本研究的共同作者，他說發現漂冰碎屑事件不會對格陵蘭的溫度產生可見的影響令他們感到相當驚訝，也衝擊了科學家對於過去氣候動力學的認知。
Buizert表示：「事實上，我們的發現引起的問題比解決的還多。」Buizert是氣候變遷的專家，他運用格陵蘭和南極的冰芯來重建並瞭解地球的氣候歷史。「結果讓我們對於北大西洋的重大事件有了截然不同的看法。遠在天邊的南極比附近的格陵蘭出現的反應還要大，真的是讓人困惑。」
科學家會將冰芯鑽出並保存起來，透過分析隨著時間被包進冰裡的塵埃與微小氣泡，就能探討過去的氣候歷史。格陵蘭與南極的冰芯提供了重要紀錄，讓我們瞭解地球大氣在過去數百萬年之間有什麼樣的變化。
Martin表示從這些地區取出的冰芯構成了科學家瞭解過往氣候事件時的基礎，而格陵蘭與南極冰芯訴說的故事情節大都相當類似。
科學家之前並不是很清楚漂冰碎屑事件對於格陵蘭和南極的衝擊，促使Martin和Buizert試著去找出那些地方究竟發生了什麼事情。
這篇最新研究運用的冰芯是1992年採自格陵蘭的最高點，當地的冰層大約有兩英里(3.2公里)厚。它在鑽取出來之後就一直存放在丹佛的國家科學基金會冰芯設施。
最近幾十年科學儀器與測量技術的進步，使得Martin、Buizert和他們的同事有機會利用新的方法來重新檢視這根冰芯。
分析結果顯示漂冰碎屑事件期間格陵蘭的溫度沒有變化，卻清楚指出漂冰碎屑事件和南極出現的反應有所關聯。
「我們現在知道北極有大型冰山流進海裡的時候，南極就會立刻出現反應，」Buizert表示。「地球某處發生的事情會對其餘地方造成影響，這種不同半球之間的關連可能是由全球氣流模式的變化所造成。」
Buizert表示就這些大型事件期間的全球氣候動力學來說，此發現挑戰了我們目前的理解，同時也為研究人員帶來了新的問題。他們的下一步是要將這些新的資訊輸入氣候模型並進行模擬，觀察模型是否可以重現過去的事件。
「勢必有個故事可以符合所有的證據，把所有的問題點給串聯起來，」他說。「我們的發現增添了兩個新的節點——它們並不是故事的全貌，或許也不是主要的情節。說不定太平洋扮演了重要的腳色，只是我們還沒有挖掘出來。」
研究人員表示最終目標是要更加瞭解氣候系統如何連動，以及各個元件之間的所有交互作用。
「雖然漂冰碎屑事件近期還不會發生，但是在全球互相連結的氣候系統中，勢必會再次發生急劇的變化，」Martin表示。「瞭解全球氣候系統的動力學可以幫助我們更準確地預估未來的衝擊，並告訴我們該如何應對及調適。」
其他共同作者包括奧勒岡州立大學的Ed
Brook、Jon
Edwards、Michael
Kalk、Ben
Riddell-Young，斯克里普斯海洋研究所的Ross
Beaudette和Jeffrey
Severinghaus，賓夕法尼亞州立大學的Todd
Sowers。
研究經費來自美國國家科學基金會、全球氣候變遷基金會以及蓋瑞‧康莫科學文教基金會。
Massive iceberg discharges during the
last ice age had no impact on nearby Greenland, raising new questions about
climate dynamics
During the last ice age, massive icebergs
periodically broke off from an ice sheet covering a large swath of North
America and discharged rapidly melting ice into the North Atlantic Ocean around
Greenland, triggering abrupt climate change impacts across the globe.
These sudden episodes, called Heinrich Events,
occurred between 16,000 and 60,000 years ago. They altered the circulation of
the world’s oceans, spurring cooling in the North Atlantic and impacting
monsoon rainfall around the world.
But little was known about the events’ effect on
nearby Greenland, which is thought to be very sensitive to events in the North
Atlantic. A new study from Oregon State University researchers, just published
in the journal Nature, provides a
definitive answer.
“It turns out, nothing happened in Greenland. The
temperature just stayed the same,” said the study’s lead author, Kaden Martin,
a fourth-year doctoral candidate in OSU’s College of Earth, Ocean, and
Atmospheric Sciences. “They had front-row seats to this action but didn’t see
the show.”
Instead, the researchers found that these Heinrich
events caused rapid warming in Antarctica, at the other end of the globe.
The researchers anticipated Greenland, in close
proximity to the ice sheet, would have experienced some kind of cooling. To
find that these Heinrich Events had no discernible impact on temperatures in
Greenland is surprising and could have repercussions for scientists’
understanding of past climate dynamics, said study co-author Christo Buizert,
an assistant professor in the College of Earth, Ocean, and Atmospheric
Sciences.
“If anything, our findings raise more questions than
answers,” said Buizert, a climate change specialist who uses ice cores from
Greenland and Antarctica to reconstruct and understand the Earth’s climate history.
“This really changes how we look at these massive events in the North Atlantic.
It’s puzzling that far-flung Antarctica responds more strongly than nearby
Greenland.”
Scientists drill and preserve ice cores to study past
climate history through analysis of the dust and tiny air bubbles that have
been trapped in the ice over time. Ice cores from Greenland and Antarctica
provide important records of Earth’s atmospheric changes over hundreds of
thousands of years.
Records from ice cores from those regions have served
as pillars for scientists’ understanding of past climate events, with ice
collected from both locations often telling similar stories, Martin said.
The impact of Heinrich Events on Greenland and
Antarctica was not well understood, spurring Martin and Buizert to try to find
out more about what was happening in those parts of the world.
The core used for the latest study was collected in
1992 from the highest point of Greenland, where the ice sheet is around 2 miles
thick. Since then, the core has been in storage in the National Science
Foundation Ice Core Facility in Denver.
Advancement in scientific tools and measurements over
the last few decades gave Martin, Buizert and their colleagues the opportunity
to re-examine the core using new methods.
The analysis shows that no changes in temperatures
occurred in Greenland during Heinrich Events. But it also provides a very clear
connection between Heinrich Events and the Antarctic response.
“When these big iceberg discharges happen in the
Arctic, we now know that Antarctica responds right away,” Buizert said. “What
happens in one part of the world has an effect on the rest of the world. This
inter-hemispheric connection is likely caused by change in global wind
patterns.”
The finding challenges the current understanding of
global climate dynamics during these massive events and raises new questions
for researchers, Buizert said. The researchers’ next step is to take the new
information and run it through climate models to see if the models can
replicate what occurred.
“There has to be a story that fits all of the
evidence, something that connects all the dots,” he said. “Our discovery adds
two new dots; it’s not the full story, and it may not be the main story. It is
possible that the Pacific Ocean plays an important role that we haven’t figured
out yet.”
The ultimate goal is to better understand how the
climate system is connected and how the components all interact, the
researchers said.
“While Heinrich Events are not going to happen in the
future, abrupt changes in the globally interconnected climate system will
happen again,” Martin said. “Understanding the global dynamics of the climate
system can help us better project future impacts and inform how we respond and
adapt.”
Additional co-authors are Ed Brook, Jon Edwards,
Michael Kalk and Ben Riddell-Young of OSU; Ross Beaudette and Jeffrey
Severinghaus of the Scripps Institution of Oceanography; and Todd Sowers of
Pennsylvania State University.
The research was supported by the National Science
Foundation, the Global Climate Change Foundation and the Gary Comer Science and
Education Foundation.
原始論文：Kaden C.
Martin, Christo Buizert, Jon S. Edwards, Michael L. Kalk, Ben Riddell-Young,
Edward J. Brook, Ross Beaudette, Jeffrey P. Severinghaus, Todd A. Sowers. Bipolar
impact and phasing of Heinrich-type climate variability. Nature,
2023; DOI: 10.1038/s41586-023-05875-2
引用自：Oregon State University. "Massive iceberg
discharges during the last ice age had no impact on nearby Greenland, raising
new questions about climate dynamics."
原文網址：https://today.oregonstate.edu/news/massive-iceberg-discharges-during-last-ice-age-had-no-impact-nearby-greenland-raising-new
沒有留言:
張貼留言