原文網址：https://news.ufl.edu/2022/07/tropical-glaciers/
根據今日發表在《自然》的研究，驅動氣候變遷的因素對熱帶山區冰河造成的衝擊，就和南極與北半球極區的冰河受到的相當類似。
科學家在秘魯安地斯山脈高處的胡寧湖日以繼夜地工作了七周之久，往下鑽探了100公尺。他們透過採集到的沉積物建立起的冰河變化紀錄可以回溯至將近100萬年前。圖片來源：聯合學院
佛羅里達大學地質科學系的助理教授Robert
Hatfield是這組國際科學團隊的成員之一，他們的論文首度顯示了溫室氣體和其他驅動地球溫度變化的因素所導致的影響，會以同樣的進程對南半球的冰河以及北半球的冰原造成衝擊。研究人員從高踞在祕魯安地斯山脈的胡寧湖採集沉積物，利用其得到了延伸至70000年前的冰河變化紀錄，進而推導出這項發現。
Hatfield解釋關於過去的冰河如何變化，科學家的瞭解大部分是來自北半球冰河成長與消退的紀錄。
Hatfield表示：「當我們想要了解全球氣候的運作方式，我們需要的不能只有受北半球影響而偏向該區域的紀錄。」
Hatfield與同僚從陸地採集的湖泊紀錄長度可以與南極採到的冰芯紀錄匹敵，這也是迄今南半球採到涵蓋時間最長的湖泊紀錄。
「我們的發現獨特之處在於，這是首度成功得到連續且經過獨立定年的熱帶高山冰河紀錄，」他說。「其中的關鍵資訊是熱帶地區和北半球都隨著同樣的節拍與律動而變化。」
儘管兩個半球接收到的太陽輻射量有所差異，但研究顯示兩地的冰河都會在同樣的時間出現變化。這意味著大氣中的溫室氣體濃度升高，以及隨之產生的北方冰原體積變化，會同時對整個地球產生影響。
當安地斯山脈的高處有廣闊的冰河，它們會侵蝕周圍的山體，使得帶有沉積物的融雪進入胡寧湖。在氣候較為溫暖使得冰河消失的時候，湖泊中沉積的就會變成碳酸鹽。
為了蒐集數據，地質學家在2015年對胡寧湖發起了一項大型鑽探任務，經費來自美國國家科學基金會以及國際陸地科學鑽探計畫。在日以繼夜地工作七周之後，團隊從湖盆取回了100公尺長的沉積物。在接下來的幾年，研究人員利用這些沉積物建立起可信的年代模型。
勞倫斯利佛摩國家實驗室的科學家Christine
Y. Chen是研究共同作者，他分析了沉積物的鈾釷含量，藉此判定這根沉積物岩芯代表的時間。
「將近100年前科學家就已經知道溫室氣體升高會影響地球每個角落的氣候，但是極區冰層體積迅速變化會如何波及世界其他地方，我們就沒有那麼確定了，」Chen表示。「熱帶的高海拔山區基本上是離極區最遙遠的地方。我們證實這兩個地方將近一百萬年來，冰河的擴張與消退都和對方同步發生，也進一步強調出地球的每個角落都有著密不可分的關聯。」
2020年，團隊發表了有關這些沉積物年代的發現，並開始著手探討其中的氣候紀錄。結合礦物的磁性以及沉積物的地球化學性質，地質學家重建出最近70萬年當中，冰河發生變化的時間點與規模。
Hatfield表示在2009年的一場研討會中他們有了此研究的最初構想。最後發表的這篇論文包括了27名作者，主要作者為紐約斯克內克塔迪市聯合學院的Donald
T. Rodbell。
As temperatures rise, tropical
glaciers feel same impact as poles
Glaciers in tropical mountain ranges are
experiencing similar impact from the drivers of climate change as those in the
polar regions of Antarctica and the Northern Hemisphere, according to a study
published today in Nature.
The paper by a team of international scientists,
including Robert Hatfield, an assistant professor in the University of Florida
Department of Geological Sciences, is the first to show that the effects of
greenhouse gases and other drivers of the Earth’s temperature are impacting
glaciers in the Southern Hemisphere at the same pacing as ice sheets in the
north. To derive their findings, researchers used sedimentary deposits from
Lake Junín, high in the Peruvian Andes, to create a record of glacial changes
stretching back 700,000 years.
Hatfield explained that much of what scientists knew
about past glacial changes came from records of ice growth and decay that
occurred in the Northern Hemisphere.
“As we try to understand how climate works across the
globe, we need more than just records that are influenced by and biased toward
the Northern Hemisphere,” Hatfield said.
The land-based lake record collected by Hatfield and
his colleagues matches the duration of ice core records from Antarctica and
spans the longest time frame ever collected from the Southern Hemisphere.
“What makes our findings unique is that we were able
to get a continuous and independently dated record of tropical Alpine
glaciation for the first time,” he said. “The key takeaway was that the tropics
follow the same beat and same rhythm to what’s going on in the Northern
Hemisphere.”
Despite variations in solar radiation between the two
hemispheres, the study showed glacier changes in both regions occurred at the
same time. This suggests that the rise in atmospheric greenhouse gas
concentrations associated with changes in the volume of the ice sheets of the
north is influencing the entire planet simultaneously.
When glaciers were extensive in the high Andes, they
eroded the mountains around them, sending sediment contained in meltwater to
Lake Junín. In warmer times when the glaciers were absent, carbonate was
deposited in the lake instead.
To collect their data, geologists launched a massive
drilling mission at the lake in 2015, funded by the National Science Foundation
and International Continental Scientific Drilling Program. Working around the
clock for seven weeks, the group retrieved 100 meters of sediment from the
lake’s basin. With the sediment recovered, researchers spent the next few years
developing a solid age model.
Christine Y. Chen, a Lawrence Livermore National
Laboratory scientist and co-author of the paper, analyzed the uranium and
thorium content of the sediments to determine how much time was represented by
the sediment core.
“Scientists have known for nearly a century that
rising greenhouse gases will affect the climate in every corner of the world,
but we’ve been less certain about how rapidly changes in ice volume at the
poles will propagate to the rest of the world.” Chen said. “The high-altitude
mountains in the tropics are essentially as far away from the poles one can
get. We’ve now shown that ice in both regions have been growing and decaying
synchronously with one another for nearly a million years, which further
highlights the interconnectedness of our planet.”
In 2020, the group published its findings about the
age of the sediments and went to work at looking at its climate record. Using a
combination of mineral magnetism and sediment geochemistry, geologists
reconstructed the timing and magnitude of the glacial changes over the
700,000-year timeframe.
According to Hatfield, the initial plan for the
research was formed during a workshop in 2009 and included 27 authors on the
final published paper, including its lead author, Donald T. Rodbell, of Union
College in Schenectady, New York.
原始論文：D. T. Rodbell,
R. G. Hatfield, M. B. Abbott, C. Y. Chen, A. Woods, J. S. Stoner, D. McGee, P.
M. Tapia, M. Bush, B. L. Valero-Garcés, S. B. Lehmann, S. Z. Mark, N. C.
Weidhaas, A. L. Hillman, D. J. Larsen, G. Delgado, S. A. Katz, K. E. Solada, A.
E. Morey, M. Finkenbinder, B. Valencia, A. Rozas-Davila, N. Wattrus, S. M.
Colman, M. G. Bustamante, J. Kück, S. Pierdominici. 700,000 years of
tropical Andean glaciation. Nature, 2022; DOI: 10.1038/s41586-022-04873-0
引用自：University of Florida. "Impact of changing
climate on Andean glaciers in sync with polar ice."
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