地球化學偵探利用實驗室模擬來回推過去

原文網址：www.sciencedaily.com/releases/2016/04/160428151836.htm

Geochemical detectives use lab mimicry to look back in time

地球化學偵探利用實驗室模擬來回推過去

New work from a research team led by Carnegie's Anat Shahar contains some unexpected findings about iron chemistry under high-pressure conditions, such as those likely found in the Earth's core, where iron predominates and creates our planet's life-shielding magnetic field. Their results, published in Science, could shed light on Earth's early days when the core was formed through a process called differentiation--when the denser materials, like iron, sunk inward toward the center, creating the layered composition the planet has today.

由卡內基實驗室的Anat Shahar領導的研究團隊最新發表的工作成果中，包含了某些意料之外的發現：有關於鐵的化學性質在高壓環境之下的行為。地核可能即屬這種環境，此處的成分以鐵為主，並由此產生了保護地球生命的磁場。他們刊登在期刊《科學》(Science)的成果，或許可以闡明當地球年幼時，地核經由「分異作用」(differentiation)而形成時的細節。當這種作用發生時，像鐵這類密度較高的物質會往下沉至地球中心，使得今日的地球成分呈現層狀分布。

Earth formed from accreted matter surrounding the young Sun. Over time, the iron in this early planetary material moved inward, separating from the surrounding silicate. This process created the planet's iron core and silicate upper mantle. But much about this how this differentiation process occurred is still poorly understood, due to the technological impossibility of taking samples from the Earth's core to see which compounds exist there.

地球是由環繞在幼年太陽周遭的物質聚積而成。隨著時間流逝，這些初生行星物質中的鐵會逐漸往內部移動，而跟周圍的矽酸鹽分離開來。這種作用使得地球擁有鐵質核心以及位於上方的矽酸鹽質地函。但有關於這種分異作用的更多細節究竟是如何進行，卻還是所知甚少。這是因為技術上的限制使我們不可能從地核取得樣品，觀察存在於此的到底是什麼物質。

Seismic data show that in addition to iron, there are "lighter" elements present in the core, but which elements and in what concentrations they exist has been a matter of great debate. This is because as the iron moved inward toward the core, it interacted with various lighter elements to form different alloyed compounds, which were then carried along with the iron into the planet's depths.

地震波資料顯示除了鐵之外，地核內部還有其他較「輕」的元素，但是這些元素的真實身分以及濃度多寡仍然眾說紛紜。這是因為當鐵往下沉至地核的旅途中，它會跟周遭各式各樣的較輕元素交互作用，而產生許多種不同的合金，接著它們會夥同鐵一起進入地球深處。

Which elements iron bonded with during this time would have been determined by the surrounding conditions, including pressure and temperature. As a result, working backward and determining which iron alloy compounds were created during differentiation could tell scientists about the conditions on early Earth and about the planet's geochemical evolution.

在這段時期鐵會跟什麼樣的元素結合跟它們所處的環境條件有關，像是溫度和壓力。因此，反過來研究並找出在分異作用進行時形成的合金種類，可以告訴科學家早期地球的環境條件，以及地球的化學性質如何演變。

The team--including Carnegie's Jinfu Shu and Yuming Xiao--decided to investigate this subject by researching how pressures mimicking the Earth's core would affect the composition of iron isotopes in various alloys of iron and light elements. Isotopes are versions of an element where the number of neutrons differs from the number of protons. (Each element contains a unique number of protons.)

包括Jinfu Shu和Yuming Xiao這兩位卡內基科學家的研究團隊決定研究這道難題。他們用的方法是模擬鐵和輕元素的不同合金中，鐵的同位素成分會如何受地核內部壓力高低影響。同位素是隸屬同一種元素但中子數不同的版本，這點與質子數並不相同(每一種元素都有各自獨一無二的質子數)。

Because of this accounting difference, isotopes' masses are not the same, which can sometimes cause small variations in how different isotopes of the same element are partitioned in, or are "picked up" by, either silicate or iron metal. Some isotopes are preferred by certain reactions, which results in an imbalance in the proportion of each isotope incorporated into the end products of these reactions--a process that can leave behind trace isotopic signatures in rocks. This phenomenon is called isotope fractionation and is crucial to the team's research.

由於在中子數目上的差異，同位素的質量也各不相同，這種微小的差異有時會導致矽酸鹽或金屬鐵在分配(partition)，也就是「揀選」同一元素的同位素時會有些許的不同。特定反應會偏好某些種類的同位素，這會導致每一種同位素的比例在各個反應終產物中的分配並不均衡。這種過程可以在岩石當中留下可供追循的同位素訊號。對此團隊的研究來說，這種稱作同位素分餾(isotope fractionation)的現象相當重要。

Before now, pressure was not considered a critical variable affecting isotope fractionation. But Shahar and her team's research demonstrated that for iron, extreme pressure conditions do affect isotope fractionation.

在此之前，科學家並不認為壓力是影響同位素分餾的重要因素。但Shahar 和她的團隊在研究中顯示，對鐵而言，極端的壓力環境確實會影響同位素分餾。

More importantly, the team discovered that due to this high-pressure fractionation, reactions between iron and two of the light elements often considered likely to be present in the core--hydrogen and carbon--would have left behind an isotopic signature in the mantle silicate as they reacted with iron and sunk to the core. But this isotopic signature has not been found in samples of mantle rock, so scientists can exclude them from the list of potential light elements in the core.

更重要的是，研究團隊發現由於高壓分餾作用的進行，兩種常被視為可能出現在地核中的輕元素—氫和碳，在跟鐵產生反應並往下沉至地核的過程中，會在地函矽酸鹽內留下某種同位素訊號。然而目前為止還尚未在地函岩石的樣品當中找到這種同位素訊號，因此科學家可以將氫和碳從可能出現在地函的輕元素名單上剔除。

Oxygen, on the other hand, would not have left an isotopic signature behind in the mantle, so it is still on the table. Likewise, other potential core light elements still need to be investigated, including silicon and sulfur.

另一方面，氧並不會在地函留下同位素訊號，因此它仍然列於名單上。類似地，其他可能出現在地函，像是矽和硫之類的輕元素還有待調查。

"What does this mean? It means we are gaining a better understanding of our planet's chemical and physical history," Shahar explained. "Although Earth is our home, there is still so much about its interior that we don't understand. But evidence that extreme pressures affect how isotopes partition, in ways that we can see traces of in rock samples, is a huge step forward in learning about our planet's geochemical evolution."

「這意味著什麼？這代表說我們對我們星球的化學和物理發展史有了更深一層的認識。」Shahar如此解釋。「雖然地球是我們的家園，但我們對它的內部仍有諸多不瞭解之處。然而，現在我們有了證據顯示極度的高壓會影響同位素分餾作用，而我們可以從岩石樣本中看到這種作用留下來的痕跡。對了解我們星球的地球化學是如何演變來說，這是相當重大的進展。」

引用自：Carnegie Institution for Science. "Geochemical detectives use lab mimicry to look back in time." ScienceDaily. ScienceDaily, 28 April 2016. 

地球最老礦物源自何方？

原文網址：www.sciencedaily.com/releases/2016/04/160428173233.htm

Origin of Earth's oldest crystals

地球最老礦物源自何方？

New research suggests that the very oldest pieces of rock on Earth -- zircon crystals -- are likely to have formed in the craters left by violent asteroid impacts that peppered our nascent planet, rather than via plate tectonics as was previously believed. Rocks that formed over the course of Earth's history allow geologists to infer things such as when water first appeared on the planet, how our climate has varied, and even where life came from. However, we can only go back in time so far, as the only material we have from the very early Earth comes in the form of tiny, naturally zircon crystals.

最新的研究提出地球上最老的岩石碎片—即鋯石的晶體，可能是小行星群猛烈轟炸初生地球後，在留下來的隕石坑內部形成，而非先前認為的是由板塊運動產生。在地球歷史漫漫軌跡中形成的諸多岩石可以讓地質學家從中推論出種種事物，像是地球上何時出現第一滴水，我們的氣候如何變化，甚至是生命的源頭。然而，至今我們僅能追溯自唯一從地球相當早期遺留下來的物質，也就是這些自然產生的微小鋯石結晶形成之時。

Naturally then, the origin of these crystals, which are approximately the width of a human hair and more than four billion years old (the Earth being just over four and a half billion years old), has become a matter of major debate. Fifteen years ago these crystals first made headlines when they revealed the presence of water on the surface of the Earth (thought to be a key ingredient for the origin of life) when they were forming.

自然而然地，這些僅約人髮寬，年代超過40億年的礦物起源為何，之後便成為一項眾說紛紜的議題。15年前，這些礦物因為顯示出在它們形成的時候地球表面已經有水(被認為是生物起源所需的關鍵要素之一)而首度聲名大噪。

Ten years ago, a team of researchers in the US1 argued that the ancient zircon crystals probably formed when tectonic plates moving around on the Earth's surface collided with each other in a similar fashion to the disruption taking place in the Andes Mountains today, where the ocean floor under the Pacific Ocean is plunging under South America.

10年前，一群來自US1的研究人員聲稱這些古老的鋯石結晶可能形成於板塊在地球表面移動而彼此碰撞時，就像今日太平洋底部的海床俯衝至南美洲之下，而在安地斯山脈內部發生的劇烈變動一般。

However, current evidence suggests that plate tectonics -- as we know it today -- was not occurring on the early Earth. So, the question remained: Where did the crystals come from?

然而，現有的證據顯示出我們今日熟悉的板塊構造運動在地球早期還尚未發生。因此問題仍然懸而未解：這些結晶究竟來自何方？

Recently, geologists suggested these grains may have formed in huge impact craters produced as chunks of rock from space, up to several kilometres in diameter, slammed into a young Earth. To test this idea, researchers from Trinity College Dublin decided to study a much younger impact crater to see if zircon crystals similar to the very old ones could possibly have formed in these violent settings.

最近，地質學家提出的一則新說法認為由半徑最高可達7公里，從太空來的岩石群重擊年幼地球時，所產生的巨大撞擊坑中形成了這些礦物顆粒。為了證實他們的想法，都柏林聖三一大學的研究人員決定研究年輕許多的撞擊坑，以觀察在這種嚴酷的環境當中，是否會產生跟那些相當古老的鋯石十分相似的鋯石結晶。

In the summer of 2014, with the support of the Irish Reseach Council (IRC) and Science Foundation Ireland (SFI), the team collected thousands of zircons from the Sudbury impact crater, Ontario, Canada -- the best preserved large impact crater on Earth and the planet's second oldest confirmed crater at almost two billion years old.

2014年夏季，在愛爾蘭研究學會和愛爾蘭科學基金會的協助之下，研究團隊從加拿大安大略省的索德柏立(Sudbury)撞擊坑中採集了數以千計的鋯石。這個撞擊坑是地球上被研究得最為透徹的大型撞擊坑，同時也是已確認年代的撞擊坑中第二古老者，年代將近20億年。

After analysing these crystals at the Swedish Museum of Natural History in Stockholm, they discovered that the crystal compositions were indistinguishable from the ancient set.

在斯德哥爾摩的瑞典自然史博物館中詳盡分析這些晶體後，他們發現這些晶體的成分幾乎無法跟那些古老的鋯石區分開來。

PhD Researcher in Trinity's School of Natural Sciences, Gavin Kenny, is first author of the article which explains these findings, and which has just been published in leading international journal, Geology.

此篇論文的第一作者，聖三一大學自然科學院的博士後研究員 Gavin Kenny解釋了他們剛刊登於國際頂尖期刊《地質》(Geology)上的新發現。

He said: "What we found was quite surprising. Many people thought the very ancient zircon crystals couldn't have formed in impact craters, but we now know they could have. There's a lot we still don't fully understand about these little guys but it looks like we may now be able to form a more coherent story of Earth's early years -- one which fits with the idea that our planet suffered far more frequent bombardment from asteroids early on than it has in relatively recent times."

他說：「我們發現的事物相當令人驚訝。許多人認為年代十分久遠的鋯石不可能在撞擊坑中形成，但現在我們知道其實它們可以。對於這些小傢伙我們還有許多尚未完全了解的地方，但現在看起來我們可以將地球早年的故事拼湊得更加完整。我們的發現跟現行的想法相當符合，認為早期地球飽受小行星的頻繁轟炸，與較為近期相比頻率高出許多。」

Gavin Kenny recently travelled to the annual Lunar and Planetary Science Conference (LPSC) in Houston, Texas, to present these findings to the space science community.

Gavin Kenny近日前往於休士頓舉行的年度月球和行星科學會議，向天文學社群發表他們的發現。

He added: "There was a lot of enthusiasm for our findings. Just two years ago a group2 had studied the likely timing of impacts on the early Earth and they suggested that these impacts might explain the ages of the ancient zircons. They were understandably very happy to see that the chemistry of the zircons from the Canadian impact crater matched the oldest crystals known to man."

他補充說：「有很多人對我們的新發現抱持著熱切關注。就在兩年前有另外一個團隊研究了同樣形成於早期地球，年代相近的撞擊坑，並提出這些撞擊事件或許可以用來解釋遠古鋯石的年代。可以想見他們會很樂意看到從加拿大的撞擊坑中取得的鋯石，其化學成分跟這些人類所知最古老的晶體竟然如此吻合。」

引用自：Trinity College Dublin. "Origin of Earth's oldest crystals." ScienceDaily. ScienceDaily, 28 April 2016. 

在引發地震的過程中雨水或許扮演了重要腳色

原文網址：www.sciencedaily.com/releases/2016/04/160427094859.htm

Rainwater may play an important role in process that triggers earthquakes

在引發地震的過程中雨水或許扮演了重要腳色

It's the rain's Fault

都是雨水惹的禍(斷層，兩者英文皆為fault)

Rainwater may play an important role in the process that triggers earthquakes, according to new research.

根據新的研究顯示，在引發地震的過程中雨水或許扮演了重要腳色。

Researchers from the University of Southampton, GNS Science (New Zealand), the University of Otago, and (Germany), identified the sources and fluxes of the geothermal fluids and mineral veins from the Southern Alps of New Zealand where the Pacific and Australian Plates collide along the Alpine Fault.

來自南安普敦大學、紐西蘭地質與核子科學研究所、奧塔哥大學以及德國波茨坦地質科學研究中心的研究人員，發現了紐西蘭南阿爾卑斯山脈的地熱流體和礦脈的來源與流量。紐西蘭的阿爾卑斯斷層為太平洋板塊跟印澳板塊聚合碰撞之處。

From careful chemical analyses, they discovered that fluids originating from the mantle, the layer below Earth's crust, and fluids derived from rainwater, are channelled up the Alpine Fault.

經過審慎的化學分析之後，他們發現源自地殼下方的地函流體以及從降雨而來的液體，會在阿爾卑斯斷層中彼此連通。

By calculating how much fluid is flowing through the fault zone at depth, the researchers showed for the first time that enough rainwater is present to promote earthquake rupture on this major plate boundary fault.

經由計算會有多少的液體流經斷層帶深部後，研究人員首次呈現出在這條大型板塊邊界斷層帶中，具有相當含量的雨水能夠促使斷層破裂並產生地震。

Lead researcher Dr Catriona Menzies, from Ocean and Earth Science at the University of Southampton, said: "Large, continental-scale faults can cause catastrophic earthquakes, but the trigger mechanisms for major seismic events are not well known. Geologists have long suspected that deep groundwaters may be important for the initiation of earthquakes as these fluids can weaken the fault zones by increasing pressures or through chemical reactions.

此篇研究的第一作者，南安普敦大學的海洋和地球科學博士Catriona Menzies說：「大型斷層帶可能會引起毀滅性的地震，但我們對於大型地震的觸發機制仍未具有全面性的了解。地質學家長久以來便猜測深層地下水對地震的引發而言相當重要。這是因為液體會增強水壓或是產生化學反應而弱化斷層帶。」

"Fluids are important in controlling the evolution of faults between earthquake ruptures. Chemical reactions may alter the strength and permeability of rocks, and if enough fluid is present at sufficiently high pressures they may aid earthquake rupture by 'pumping up' the fault zone."

「斷層在一次次破裂而引發地震的演化過程中，液體具有相當重要的控制地位。化學反應或許會改變岩石的強度以及滲透性，另外，若有相當多的液體在斷層帶中而產生夠高的水壓，這些液體或許能將其『抬起』而助長地震破裂發生。」

The Alpine Fault is a major strike-slip fault, like the San Andreas, that fails in very large (Magnitude 8+) earthquakes around every 300 years. It last ruptured in 1717 AD and consequently it is under intense scientific scrutiny because it is a rare example of a major fault that is late in the strain-build up before rupture.

阿爾卑斯斷層跟聖安地列斯斷層一樣是條大型平移斷層。它大約每300年就會發生一次相當大型(規模8以上)的地震，而上一次破裂發生在西元1717年。因為如此，它成為可能正在破裂邊緣，應力正不斷累積的罕有大型斷層例子，使得現在有許多科學監測活動正在進行。

Dr Menzies said: "We show that the Alpine Fault acts as a barrier to lateral fluid flow from the high mountains of the Southern Alps towards the Tasman Sea in the west. However, the presence of mantle-derived fluids indicates that the fault also acts as a channel for fluids, from more than 35 km depth, to ascend to the surface.

Menzies博士說：「我們的結果顯示出地下水在從南阿爾卑斯的高山地區往西方的塔斯曼海側向流動時，阿爾卑斯斷層具有阻斷的作用。然而，斷層中具有源自地函的流體的這件事指出，它同時也可以作為液體流通的管道。來自深度超過地下35km處的液體，能夠經此而上升至地表。」

"As well as mantle derived fluids, our calculations indicate that 0.02-0.05 per cent of surface rainfall reaches around six kilometres depth but this is enough to overwhelm contributions from the mantle and fluids generated during mountain-building by metamorphic reactions in hot rocks. This rainwater is then focused onto the fault, forced by the hydraulic head of the high mountains above and the sub-vertical fluid flow barrier of the Alpine Fault."

「除了來自地函的液體之外，我們的計算指出地表的降雨有百分之0.02至0.05可以到達地下6公里深。即使如此，這些量已遠遠超過地函來的液體，以及在造山運動時熾熱岩石經由變質作用而產生的液體。在上方高山造成的水頭，以及近乎垂直的阿爾卑斯斷層作為液體流動的屏障作用下，這些雨水會集中於斷層上。」

Funding for this research, published in Earth and Planetary Science Letters, was provided by the Natural Environmental Research Council (NERC), Deutsche Forschungsgemeinschaft, and GNS Science (New Zealand).

此篇刊登於期刊《地球和行星科學通訊》的研究，資金來自於自然環境研究委員會、德國研究學會和 紐西蘭地質與核子科學研究所。

引用自：University of Southampton. "Rainwater may play an important role in process that triggers earthquakes." ScienceDaily. ScienceDaily, 27 April 2016. 

兩起火山噴發事件引發了古典時代晚期的社會危機

原文網址：www.sciencedaily.com/releases/2016/04/160419083247.htm

Two volcanoes trigger crises of the late antiquity

兩起火山噴發事件引發了古典時代晚期的社會危機

International team of climate researchers reconstruct global cooling in the reign of emperor Justinian

由國際氣候學家組成的團隊重建了於查士丁尼一世統治時期發生的全球冷化事件

Contemporary chroniclers wrote about a "mystery cloud" which dimmed the light of the sun above the Mediterranean in the years 536 and 537 CE. Tree rings testify poor growing conditions over the whole Northern Hemisphere -- the years from 536 CE onward seem to have been overshadowed by an unusual natural phenomenon. Social crises including the first European plague pandemic beginning in 541, are associated with this phenomenon. Only recently have researchers found conclusive proof of a volcanic origin of the 536 solar dimming, based on traces of volcanic sulfur from two major eruptions newly dated to 536 CE and 540 CE in ice cores from Greenland and Antarctica.

同時期的編年史學者於文獻中寫道，西元536年到537年地中海上空因「神秘雲霧」的籠罩而變得天昏地暗。樹輪紀錄證實了當時整個北半球的植物皆處於相當惡劣的生長情況，顯然自西元536年起北半球便因一種不尋常的自然現象而蒙上了一層陰影。包括始於西元541年歐陸史上首次發生的瘟疫大流行在內，種種的社會危機似乎都跟此現象有所關聯。科學家直到最近才發現決定性的證據證明西元536年陽光變得昏暗是由火山造成。這些證據來自於格陵蘭和南極的冰芯，其中含有最新定出年代為西元536年和540年，由兩次大型火山噴發出的火山硫磺造成的痕跡。

An international team of climate scientists led by Dr. Matthew Toohey at the GEOMAR Helmholtz Centre for Ocean Research Kiel and Prof. Dr. Kirstin Krüger of the University of Oslo (UiO), with financial support from the Centre for Earth Evolution and Dynamics (CEED) at the UiO, has investigated the time period using the new ice core data, historical evidence and climate models. As they write in the international journal Climatic Change, the impact of the volcanic double event of 536/540 on Northern Hemisphere climate was stronger than any other documented or reconstructed event of the past 1200 years. "One of the eruptions would have led to a significant cooling of Earth's surface. Two of them, so close in time, caused what is probably the coldest decade of the past 2000 years," says Dr. Matthew Toohey from GEOMAR, lead author of the study today at a press conference at the annual EGU Meeting in Vienna where he presented the results.

由德國基爾的萊布尼茨海洋科學研究所的 Matthew Toohey博士，以及奧斯陸大學的Kirstin Krüger博士領導的國際氣侯學家團隊，在奧斯陸大學地球演化及動力學中心的資助之下，利用新的冰芯資料、歷史證據以及氣候模型來調查這段時期究竟發生了什麼事件。就他們發表於國際期刊《氣候變遷》(Climatic Change)的論文，在536年和540年發生的兩次火山爆發對北半球氣候造成的影響之大，在過去1200年以來有文獻紀錄或重建出來的所有事件中，沒有任何一個可以與之相提並論。「這兩次火山噴發中的任何一者其強度便足以劇烈冷卻地表。而這兩次發生的間距如此之短，恐怕造成了過去2000年以來最冷的10年。」此研究的第一作者，萊布尼茨海洋科學研究所的 Matthew Toohey說。今日他於舉辦在維也納的歐洲地質年會上的記者會中發表他們的成果。

To simulate the impact of the 536 and 540 eruptions, the scientists used the available data from ice cores and the descriptions of the solar dimming from contemporary scholars. With this data they estimated the magnitude of the eruptions and their approximate locations on Earth, and then simulated the spread and impacts of the aerosol clouds resulting from the volcanic injection of sulfur into the stratosphere. This revealed that following the eruptions, the solar radiation at Earth's surface was strongly reduced over the Northern Hemisphere for several years, and caused decreases in the hemispheric average temperature of up to 2 degrees Celsius.

為了模擬536年和540年火山爆發造成的影響，科學家利用了自冰芯中取得的數據，以及當時學者描述的陽光變弱現象。他們憑藉這些資料來推測這兩起噴發事件的規模以及發生在地球上的大致位置，接著他們模擬由火山爆發而進入平流層中的硫磺在形成氣膠雲霧後會如何擴散，以及造成何種影響。結果顯示火山噴發之後，北半球照射至地表的太陽輻射會大幅降低數年之久，因此使北半球均溫下降了多達攝氏2度。

The relationship between the "mystery cloud" of 536 and the transition from Antiquity to the Middle Ages is an issue of great popular interest. Volcanic eruptions in the more recent past have impacted human societies. For example, in 1815 the Indonesian volcano Tambora hurled so much ash and sulfur into the atmosphere that the year 1816 became known as "the year without summer" in Europe and North America, where unusually low temperatures led to crop failures and famines. For eruptions of the more distance past, connections between eruptions and societal impacts become less clear.

536年的「神秘雲霧」以及歷史同時從古典時期進入中世紀，兩者之間的關聯是許多人相當感興趣的議題。距今較不遠的火山爆發事件確實曾對人類社會造成了重大影響。舉例來說，1815年印尼的坦博拉火山往大氣中拋出的火山灰及硫磺其量之多，使得1816年成為歐洲以及北美洲眾人所知的「夏天消失的一年」，當時不尋常的低溫造成這些地方作物歉收以及飢荒爆發。但對於更遙遠之前的火山噴發事件來說，火山爆發與社會動盪之間的關聯就不是那麼清楚。

Toohey and his colleagues used their climate model simulations to directly estimate the impact of the eruptions on agriculture in Europe, and identified Northern Europe and in particular Scandinavia as the most likely locations to have suffered under the cold conditions after the eruptions. This result supports the theory of a connection between the eruptions and archaeological evidence of a large-scale societal crisis in Scandinavia in the 6th century. "Each one of the eruptions of 536/540 would have strongly impacted societies, and it happened twice within four years," says co-author Prof. Dr. Kirstin Krüger from the University of Oslo.

Toohey 和他的同僚利用他們建立的氣候來直接預估這兩次火山爆發影響歐洲農業的程度，他們發現在歐陸北端以及部份的斯堪地那維亞是噴發過後最因環境變冷而深受其害的地區。這些結果也支持了一項理論，其認為考古證據顯示出6世紀斯堪地那維亞發生的大規模社會危機，跟火山爆發之間有一定的關聯。「536年和540年的火山噴發事件中的任何一次都能對社會造成重大影響，更別說它們倆發生的間距僅僅相隔4年。」奧斯陸大學的共同作者Kirstin Krüger博士說。

Which volcanoes exactly were responsible for these aerosols clouds is still enigmatic. "Several candidates are being discussed, including volcanoes in Central America, Indonesia and North America. Future studies will be necessary to show the exact source of the aerosol clouds of 536/540," says Dr. Toohey.

究竟是哪座火山造成了這些氣膠雲霧仍然沒有解答。「我們討論到的一些候選者包括了位於中美洲、印尼和北美的火山。未來的研究勢必能準確找出536年和540年氣膠雲霧的來源。」Toohey.博士說。

引用自：Helmholtz Centre for Ocean Research Kiel (GEOMAR). "Two volcanoes trigger crises of the late antiquity: International team of climate researchers reconstruct global cooling in the reign of emperor Justinian." ScienceDaily. ScienceDaily, 19 April 2016. 

地球在數百萬年中逐漸發生的氣候變遷跟火山有重大關聯

原文網址：www.sciencedaily.com/releases/2016/04/160421150056.htm

Volcanoes tied to shifts in Earth's climate over millions of years

地球在數百萬年中逐漸發生的氣候變遷跟火山有重大關聯

A new study in the April 22 edition of Science reveals that volcanic activity associated with the plate-tectonic movement of continents may be responsible for climatic shifts from hot to cold over tens and hundreds of millions of years throughout much of Earth's history.

在地球歷史上的許多時期，都曾發生氣候於數千萬年至數億年間由酷熱逐漸轉變成嚴寒的現象。4月22日發表在《科學》(Science)期刊上的新研究顯示，這或許跟大陸板塊移動時伴隨產生的火山活動大有關係。

The study, led by researchers at The University of Texas at Austin Jackson School of Geosciences, addresses why the Earth has fluctuated from periods when the planet was covered in ice to times when even the polar regions were ice-free.

此篇由德克薩斯大學奧斯汀分校傑克遜地球科學院的研究人員領導的研究，提出了可能的成因來解釋這個問題：地球為何會在整顆星球被冰封的時期，與連極區都未見一絲冰霜的時期之間來回變化。

The study explores very long-term shifts in Earth's baseline climate, not short-term or human-induced climate change.

這篇研究探討了地球的基準氣候(baseline climate)在相當長的一段時間中如何變化，而非短期或者人為導致的氣候變遷。

Lead researcher Ryan McKenzie said the team found that periods when volcanoes along continental arcs were more active coincided with warmer, or greenhouse, conditions over the past 720 million years. Conversely, periods when continental arc volcanos were less active coincided with colder, or icehouse, conditions.

率領此研究的 Ryan McKenzie說研究團隊發現自過去的7億2000萬年以來，當陸弧(continental arc)中的火山活動較為活躍時，也是氣候較溫暖的時期，此時的地球處於溫室(greenhouse)環境。反之，當陸弧火山活動趨緩時，此時的氣候就較為寒冷，地球便處於冰室(icehouse)環境。

Continental volcanic arc systems such as the Andes Mountains are created at active continental margins where two tectonic plates meet and the oceanic plate descends under the continental plate, forming a subduction zone. When this happens, magma mixes with carbon trapped in the Earth's crust and releases carbon dioxide (CO2) gas into the atmosphere when volcanoes in the system erupt.

當兩個板塊之間彼此擠壓，海洋板塊下沉至大陸板塊之下而形成隱沒帶時，在上方的活動型大陸邊緣便會有陸弧系統生成，現今的安地斯山脈即為一例。此構造環境形成後，當陸弧系統中的火山爆發時，就會噴發出混有地殼內部的碳的岩漿，並釋放二氧化碳氣體至大氣中。

"Continental arc systems are plumbed through the Earth's crust and they tend to interact with carbon reservoir rock preserved beneath the surface," said McKenzie, who began the work as a postdoctoral researcher at the Jackson School and finished the study at Yale University.

「陸弧系統會貫穿地殼，因此它們有相當大的機會能跟保存在地表下方岩石中的碳儲存庫之間發生交互作用。」 McKenzie說。他在傑克遜地球科學院擔任博士後研究員時開始進行這項研究，之後在耶魯大學任職時完成。

Scientist have long known that the amount of carbon dioxide in the atmosphere influences the Earth's climate, McKenzie said. The unanswered question is what caused the fluctuations in CO2 observed in the geologic record. Other theories have suggested that geological forces such as mountain building have, at different times in the planet's history, introduced large amounts of new material to the Earth's surface, and weathering of that material has drawn CO2 out of the atmosphere. The new study points to the amount of CO2 being released into the atmosphere, rather than the amount removed from it, as the primary driver of Earth's climate.

McKenzie說長久以來科學家就已經知道大氣中的二氧化碳含量會影響地球氣候。然而從地質紀錄中觀察到的二氧化碳含量變化究竟是由什麼原因所造成，仍尚未有人可以回答。某些理論認為在地球歷史的不同時期，像是造山運動之類的地質營力會將大量的新鮮岩石帶到地球表面，這些物質遭受風化作用時便會從大氣中吸收二氧化碳。但是，此篇新研究指出驅動地球氣候變化的動力是釋放至大氣中二氧化碳的多寡，而非被吸收的量有多少。

Using nearly 200 published studies and their own fieldwork and data, researchers created a global database to reconstruct the volcanic history of continental margins over the past 720 million years.

利用將近200篇已發表的研究，以及研究團隊自身的野外工作和資料，他們創建了一個資料庫可以用來重建過去7億2000萬年以來全球大陸邊緣的火山活動史。

"We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years," said co-author Brian Horton, a professor in the Jackson School's Department of Geological Sciences. "The distinguishing part of our study is that we looked at a very long geologic record -- 720 million years -- through multiple greenhouse-icehouse events."

「由於火山弧會在數億年的時光中被慢慢侵蝕殆盡，因此我們研究了過往位於它們附近的沉積盆地。」任職於傑克遜地球科學院的共同作者 Brian Horton說。「我們這篇研究裡最突出的一部份是我們觀察了地球在歷經多次溫室—冰室事件後而留下來的一段相當長期的地質紀錄，時間長達7億2000萬年。」

Specifically, researchers looked at the uranium-lead crystallization ages of the mineral zircon, which is largely created during continental volcanic arc activity. Zircon is less common in other types of volcanic settings, such as hot spots like Hawaii or island arc volcanoes such as the Marianas, so the mineral can be used to track continental arc volcanism. For the study, they looked at data for roughly 120,000 zircon grains from thousands of samples across the globe.

精確而言，研究人員探討的是鋯石礦物顆粒的鈾鉛結晶年代，這些礦物多半是在陸弧火山活動時產生出來的。鋯石很少在其他類型的火山構造環境中看到，像是夏威夷所處的熱點(hotspot)以及馬里亞納群島位於的火山島弧(island arc)，因 此這種礦物便能夠用來追蹤陸弧的火山活動。為了進行這項研究，研究人員從全世界蒐集到的數千個樣品裡，將近12萬顆的鋯石顆粒中探討他們需要的資訊。

"We're looking at changes in zircon production on various continents throughout Earth's history and seeing how the changes correspond with the various icehouse and greenhouse transitions," McKenzie said. "Ultimately, we find that during intervals of high zircon production we have greenhouse conditions, and as zircon production diminishes, we see a shift into our icehouse conditions."

「我們想要知道地球歷史上各個陸塊產生鋯石的速率是如何改變，並且觀察這些變化如何對應至溫室地球及冰室地球之間的多次轉換。」McKenzie說。「最後我們發現在鋯石產量較高的時期，地球便處於溫室環境；而隨著鋯石產量逐漸下滑，我們看到地球也逐漸轉變成冰室環境。」

The cooler icehouse periods tended to correlate with the assembly of the Earth's supercontinents, which was a time of diminished continental volcanism, Horton said. The warmer greenhouse periods correlated with continental breakup, a time of enhanced continental volcanism.

Horton說較為寒冷的冰室時期傾向對應至當地球陸地組合成超大陸的時期，此時陸地的火山活動較為平靜。而較為溫暖的溫室時期則對應至大陸分裂時，此時陸地的火山活動較為活躍。

Jackson School researchers Shannon Loomis and Daniel Stockli, Yale University's Noah Planavsky, and Rice University's Cin-Ty Lee also worked on the study. The research was funded by the National Science Foundation.

傑克遜地球科學院的研究人員 Shannon Loomis和Daniel Stockli、耶魯大學的 Noah Planavsky以及萊斯大學的 Cin-Ty Lee 也共同參與了此研究。研究由美國國家科學基金會贊助。

引用自：University of Texas at Austin. "Volcanoes tied to shifts in Earth's climate over millions of years." ScienceDaily. ScienceDaily, 21 April 2016.