原文網址：https://news.ucsc.edu/2021/01/groundwater-discharge.html
在了解岩石的風化作用以及這會對氣候造成的效應時，一項評估全球地下水對海洋化學影響的結果具有相當重要的啟發
By Tim Stephens
在世界各地的海岸線都有看不見的地下水流悄悄滲入海洋。以往科學家大都忽視它們對於海洋化學的貢獻，而注重於體積大上許多，從河川溪流進入海洋的水以及其中的溶解物質。但是一項新研究發現地下水帶來的影響其實比過往認為的還要高出許多。
在歐胡島沙灘上從沙子流出的地下水滲流。一項評估全球地下水滲流的成果發現其對於海洋化學的影響比過往認為的還要更高。圖片來自：Jenny Bernier
這項新發現1月8日發表在《自然通訊》(Nature
Communications)。對於全球生地化循環的模型以及運用同位素紀錄來解讀地球氣候歷史的研究來說，此發現可以帶來重要的啟發。
「地下水滲流的特性非常難以描述，因此一直都在模擬全球生地化循環時造成不確定性，」主持這項研究的第一作者，加州大學聖塔克魯茲分校的研究生Kimberley
Mayfield表示。「世界各地的研究人員齊聚一堂，花費了大量心力才成功完成這項研究。」
研究人員的探討對象為五種重要的元素：鋰、鎂、鈣、鍶、鋇。他們在全世界20個不同的地方測量海岸地下水中這些元素的濃度和同位素比例，並且加上其他地方已經發表過的數據。
「這些元素非常重要，因為它們是岩石風化的產物，而從長時間尺度來說，從大氣中吸收二氧化碳的作用有很大一部份是來自於矽酸岩的風化作用。」
加州大學聖塔克魯茲分校的研究教授Adina
Paytan是共同作者。她說雖然地下水是海水相當重要的來源之一，但因為人們無法看見它們而且難以進行測量，因此很容易就會忽略它們。
「這些元素當中，有很多是首次對它們在全球地下水滲流裡的量進行評估，」Paytan表示。「不論是從現在或過去的角度來說，這項資訊在了解岩石的風化作用和氣候的關聯時都很有用。」
研究根據全球地下水流量的最新估計結果，評估這些元素透過地下水進入海洋的量，大約是從河川進入海洋的量的5%到16%。結果也顯示出地下水滲流的同位素成分跟河水的會有很大的差異。
「地下水滲流的成分跟海岸的地質有很大的關係，而河水的成分則有更多來自內陸的影響，」Mayfield表示。「體認到地下水在全世界都有很大的影響十分重要。在我們建立了這份龐大的資料庫之後，科學家可以持續蒐集樣品來加以擴充，並運用它來發展更好的地下水滲流模型。」
New analysis highlights importance of
groundwater discharge into oceans
A global assessment of the impact of
groundwater on ocean chemistry is important for understanding the weathering of
rocks and its effects on climate
An invisible flow of groundwater seeps
into the ocean along coastlines all over the world. Scientists have tended to disregard
its contributions to ocean chemistry, focusing on the far greater volumes of
water and dissolved material entering the sea from rivers and streams, but a
new study finds groundwater discharge plays a more significant role than had
been thought.
The new findings, published January 8 in Nature Communications, have implications
for global models of biogeochemical cycles and for the interpretation of
isotope records of Earth’s climate history.
“It’s really hard to characterize groundwater
discharge, so it has been a source of uncertainty in the modeling of global
cycles,” said first author Kimberley Mayfield, who led the study as a graduate
student at UC Santa Cruz. “It took a large effort by researchers around the
world who came together to make this happen.”
The researchers focused on five key elements—lithium,
magnesium, calcium, strontium, and barium—measuring concentrations and isotope
ratios in coastal groundwater at 20 sites around the world, and using
previously published data from additional sites.
“Those elements are important because they come from
the weathering of rocks, and weathering of silicate rocks accounts for a huge
uptake of carbon dioxide from the atmosphere over long time scales,” Mayfield
explained.
Coauthor Adina Paytan, a research professor in UCSC’s
Institute of Marine Sciences, said groundwater is an important source of inputs
to the oceans, but has been easy to ignore because it is unseen and hard to
measure.
“This is the first global assessment of groundwater
discharge for most of these elements,” Paytan said. “This information is useful
for our understanding of how weathering of rock is related to climate, not only
in the present but also in the past.”
The study estimated that the amount of these elements
entering the sea from groundwater is at least 5%, and up to 16%, of the
contributions from rivers based on the latest global groundwater flux
estimates. The results also showed that the isotopic composition of groundwater
discharge can be different from that of rivers.
“The composition of groundwater discharge is very
dependent on coastal geology, whereas river water is more influenced by the
interiors of continents,” Mayfield said. “It’s important to recognize that
groundwater makes a difference globally, and now that we have this large data
set, people can keep improving it with more sampling and develop better models
of global groundwater discharge.”
原始論文：Kimberley K.
Mayfield, Anton Eisenhauer, Danielle P. Santiago Ramos, John A. Higgins,
Tristan J. Horner, Maureen Auro, Tomas Magna, Nils Moosdorf, Matthew A.
Charette, Meagan Eagle Gonneea, Carolyn E. Brady, Nemanja Komar, Bernhard
Peucker-Ehrenbrink, Adina Paytan. Groundwater discharge impacts marine
isotope budgets of Li, Mg, Ca, Sr, and Ba. Nature Communications,
2021; 12 (1) DOI: 10.1038/s41467-020-20248-3
引用自：University of California - Santa Cruz.
"New analysis highlights importance of groundwater discharge into oceans.”
沒有留言:
張貼留言