1,000 years of glacial ice reveal ‘prosperity and peril’ in Europe

1,000 years of glacial ice reveal ‘prosperity and peril’ in Europe

Above: Researchers’ ice core drilling camp on Colle Gnifetti in 2015. Two ice cores extracted from this area preserved a continuous one-thousand-year record of European climate and vegetation. Credit: Margit Schwikowski.

Evidence preserved in glaciers provides continuous climate and vegetation records during major historical events

Reposted from AGU – https://news.agu.org/press-release/1000-years-of-glacial-ice-reveal-prosperity-and-peril-in-europe/

RENO, Nev. – Europe’s past prosperity and failure, driven by climate changes, has been revealed using thousand-year-old pollen, spores and charcoal particles fossilized in glacial ice. This first analysis of microfossils preserved in European glaciers unveils earlier-than-expected evidence of air pollution and the roots of modern invasive species problems.

A new study analyzed pollen, spores, charcoal and other pollutants frozen in the Colle Gnifetti glacier on the Swiss and Italian border. The research found changes in the composition of these microfossils corresponded closely with known major events in climate, such as the Little Ice Age and well-established volcanic eruptions.

The work was published in Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

The industrialization of European society also appeared clearly in the microfossil record and, in some cases, showed up sooner than expected. Pollen from the introduction of non-native crops was found to go back at least 100 years ago and pollution from the burning of fossil fuels shows up in the 18th century, about 100 years earlier than expected.

Existing historical sources such as church records or diaries record conditions during major events like droughts or famines. However, studying data from the glaciers contributes to the understanding of climate and land use surrounding such events, providing non-stop context for them with evidence from a large land area. Precisely identifying the timing of these events can help scientists better understand current climate change.

“The historical sources that were available before, I don’t think [the sources] got the full picture of the environmental context,” said Sandra Brugger, a paleoecologist at the Desert Research Institute in Nevada and lead researcher on the study. “But also, with the ice core, we couldn’t get the full picture until we started collaborating with historians on this. It needs those two sides of the coin.”

Evidence on High

The new study analyzed microfossils frozen in two 82- and 75-meter-long ice cores pulled from the Colle Gnifetti glacier, which are the first two ice cores from the continent of Europe studied for microfossils. Similar studies have sampled ice cores in South America, Central Asia and Greenland, but those regions lack the breadth of written historical records that can be directly correlated with the continuous microfossil data in ice cores.

Over the centuries, wind, rain and snow carried microfossils from European lowlands, the United Kingdom and North Africa to the exposed glacier. Ice in this glacier site dates back tens of thousands of years, and the altitude of Colle Gnifetti — 4,450 meters above sea level — means the ice was likely never subjected to melting, which would mix the layers of samples and create uncertainty in the chronology of the record.

“They can actually pinpoint and identify the relationships between what’s happening on the continent with climatic records inherent in the ice,” said John Birks, a paleoecologist at the University of Bergen who was not associated with the study. “They can develop, in a stronger way, this link between human civilization and change and climate, particularly in the last thousand years or so where conventional pollen analysis is rather weak.”

Evidence of pollution due to fossil fuel combustion also appeared earlier in the chronological record than expected. The researchers found evidence of the early burning of coal in the United Kingdom around 1780, much earlier than the expected onset of industrialization around 1850, which could have implications for global climate change modeling.

The records also showed evidence of pollen from non-native European plants from 100 years ago, showing a long legacy of the existing ecological problems created by invasive species transported across continents through trade.

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The Desert Research Institute (DRI) is a recognized world leader in basic and applied environmental research. Committed to scientific excellence and integrity, DRI faculty, students who work alongside them, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge on topics ranging from humans’ impact on the environment to the environment’s impact on humans. DRI’s impactful science and inspiring solutions support Nevada’s diverse economy, provide science-based educational opportunities, and inform policymakers, business leaders, and community members. With campuses in Las Vegas and Reno, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

Featured Research: DRI scientists analyze origins of the Saharan dust plume

Featured Research: DRI scientists analyze origins of the Saharan dust plume

On June 18, 2020, NASA-NOAA’s Suomi NPP satellite captured this visible image of the large light brown plume of Saharan dust over the North Atlantic Ocean. The image showed that the dust from Africa’s west coast extended almost to the Lesser Antilles in the western North Atlantic Ocean. Credit: NASA Worldview.


 

In late June 2020, a phenomenon known as the Saharan dust plume made headlines in the U.S., as warm, dry winds from northern Africa carried an unusually thick layer of dust more than 5,000 miles across the Atlantic Ocean into parts of the southeastern US, Puerto Rico, and Caribbean.

The arrival of this African dust cloud may have seemed unusual to residents of Florida and other Gulf-coast states, who experienced several days of darkened skies, degraded air quality and spectacular sunsets, but it came as no surprise to DRI Professor Emeritus Michael Kaplan, Ph.D., and Saroj Dhital, M.S., who have been working to understand the origins of Saharan dust plumes for some time.

Dhital, a graduate researcher with DRI’s Division of Atmospheric Sciences in Reno, joined DRI in 2016 as a member of Kaplan’s research group. He is originally from Nepal, and holds a master’s degree in Atmospheric Physics from Tribhuvan University in Kathmandu. In his doctoral work, Dhital is studying the weather patterns and processes that are responsible for large-scale Saharan dust storms that move north from Africa toward Europe and the Tropical Atlantic.

DRI researcher Saroj Dhital

Saroj Dhital presents research on a 2017 dust case at the 2019 AGU Fall meeting.

Working in collaboration with Kaplan and researchers from Spain and Germany, Dhital has been actively involved in an effort to analyze case studies of extreme African dust plumes that impacted the Iberian Peninsula, in the southwest corner of Europe, during 2007, 2008, and 2016. In a new paper in the Journal Atmospheric Environment, Dhital and his colleagues examine the weather patterns and processes that occurred before each one of these major dust events.

“What we are trying to see in this research is what are the precursors before the formation of the dust system,” Dhital explained. “If we can see those types of features in the weather predictions, we could then possibly forecast that there will be a dust storm.”

The analyses of these case studies involve the observational datasets and high-resolution Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) simulations. Numerical simulations are performed inside the National Center for Atmospheric Research (NCAR) high-performance computer, “Cheyenne”.

“Because this area of the Earth is virtually uninhabited, there are almost no surface observations,” Dhital explained. “Remote sensing via satellites and numerical simulations employing a state-of-the-science computer model are our only way of diagnosing the physics of this phenomenon.”

The technology involves the NASA A-train satellite instruments and the supercomputer at NCAR, which can perform more than a trillion operations per second. Without both forms of powerful information processing technology, little would be understood about Sharan dust storms and their long-range transport of dust.

Above: WRF-Chem simulated dust transport video from a 2017 case study that shows the emission of dust over North Africa and subsequent transport towards the tropical Atlantic Ocean (Cape Verde Islands). Credit: Saroj Dhital.

Dhital and his team have recently submitted a second paper for publication on a case study of a 2017 Saharan dust outbreak over the Cape Verde Islands, which lie 650km off the coast of Senegal, West Africa, and is shown in the simulation above. This dust plume led to significant disruptions of local air traffic – disruptions that could have potentially been managed differently if we had the ability to forecast these dust storms or provide early warning to residents.

Additionally, the dust represents a major health hazard as it combines with other pollutants to create respiratory stress in people with lung and breathing problems. This could exacerbate the effect of the COVID-19 epidemic on vulnerable populations in Europe and elsewhere.

”Knowing more about the conditions that lead to dust storms is critically important for operational forecasting and in the development of an early warning system,” Dhital said. “Our research group is now analyzing finer scale meteorological details involved in 2007, 2008, and 2016 dust storm cases utilizing observational and high-resolution WRF-Chem simulations, and we look forward to sharing our findings.”


To learn more about the work of Kaplan, Dhital and their colleagues, read their new paper “Large scale upper-level precursors for dust storm formation over North Africa and poleward transport to the Iberian Peninsula. Part I: An observational analysis” in Atmospheric Environment: https://www.sciencedirect.com/science/article/abs/pii/S1352231020304209?via%3Dihub 

Eruption of Alaska’s Okmok volcano linked to mysterious period of extreme cold in ancient Rome

Eruption of Alaska’s Okmok volcano linked to mysterious period of extreme cold in ancient Rome

Reno, Nev. (June 22, 2020) – An international team of scientists and historians has found evidence connecting an unexplained period of extreme cold in ancient Rome with an unlikely source: a massive eruption of Alaska’s Okmok volcano, located on the opposite side of the Earth.

Around the time of Julius Caesar’s death in 44 BCE, written sources describe a period of unusually cold climate, crop failures, famine, disease, and unrest in the Mediterranean Region – impacts that ultimately contributed to the downfall of the Roman Republic and Ptolemaic Kingdom of Egypt. Historians have long suspected a volcano to be the cause, but have been unable to pinpoint where or when such an eruption had occurred, or how severe it was.

In a new study published this week in Proceedings of the National Academy of Sciences (PNAS), a research team led by Joe McConnell, Ph.D. of the Desert Research Institute in Reno, Nev. uses an analysis of tephra (volcanic ash) found in Arctic ice cores to link the period of unexplained extreme climate in the Mediterranean with the caldera-forming eruption of Alaska’s Okmok volcano in 43 BCE.

“To find evidence that a volcano on the other side of the earth erupted and effectively contributed to the demise of the Romans and the Egyptians and the rise of the Roman Empire is fascinating,” McConnell said. “It certainly shows how interconnected the world was even 2,000 years ago.”

Landsat Image of Alaska's Okmok Caldera in the Aleutian Islands

Alaska’s Umnak Island in the Aleutians showing the huge, 10-km wide caldera (upper right) largely created by the 43 BCE Okmok II eruption at the dawn of the Roman Empire. Landsat-8 Operational Land Imager image from May 3, 2014. Credit: U.S. Geological Survey.

The discovery was initially made last year in DRI’s Ice Core Laboratory, when McConnell and Swiss researcher Michael Sigl, Ph.D. from the Oeschger Centre for Climate Change Research at the University of Bern happened upon an unusually well-preserved layer of tephra in an ice core sample and decided to investigate.

New measurements were made on ice cores from Greenland and Russia, some of which were drilled in the 1990s and archived in the U.S., Denmark, and Germany. Using these and earlier measurements, they were able to clearly delineate two distinct eruptions – a powerful but short-lived, relatively localized event in early 45 BCE, and a much larger and more widespread event in early 43 BCE with volcanic fallout that lasted more than two years in all the ice core records.

The researchers then conducted a geochemical analysis of the tephra samples from the second eruption found in the ice, matching the tiny shards with those of the Okmok II eruption in Alaska – one of the largest eruptions of the past 2,500 years.

“The tephra match doesn’t get any better,” said tephra specialist Gill Plunkett, Ph.D. from Queen’s University Belfast. “We compared the chemical fingerprint of the tephra found in the ice with tephra from volcanoes thought to have erupted about that time and it was very clear that the source of the 43 BCE fallout in the ice was the Okmok II eruption.”

Ice core samples contain records of past climate such as layers of ash from volcanic eruptions

Detailed records of past explosive volcanic eruptions are archived in the Greenland ice sheet and accessed through deep-drilling operations. Credit: Dorthe Dahl-Jensen.

Working with colleagues from the U.K., Switzerland, Ireland, Germany, Denmark, Alaska, and Yale University in Connecticut, the team of historians and scientists gathered supporting evidence from around the globe, including tree-ring-based climate records from Scandinavia, Austria and California’s White Mountains, and climate records from a speleothem (cave formations) from Shihua Cave in northeast China. They then used Earth system modeling to develop a more complete understanding of the timing and magnitude of volcanism during this period and its effects on climate and history.

According to their findings, the two years following the Okmok II eruption were some of the coldest in the Northern Hemisphere in the past 2,500 years, and the decade that followed was the fourth coldest. Climate models suggest that seasonally averaged temperatures may have been as much as 7oC (13oF) below normal during the summer and autumn that followed the 43 BCE eruption of Okmok, with summer precipitation of 50 to 120 percent above normal throughout Southern Europe, and autumn precipitation reaching as high as 400 percent of normal.

“In the Mediterranean region, these wet and extremely cold conditions during the agriculturally important spring through autumn seasons probably reduced crop yields and compounded supply problems during the ongoing political upheavals of the period,” said classical archaeologist Andrew Wilson, D.Phil. of the University of Oxford. “These findings lend credibility to reports of cold, famine, food shortage and disease described by ancient sources.”

“Particularly striking was the severity of the Nile flood failure at the time of the Okmok eruption, and the famine and disease that was reported in Egyptian sources,” added Yale University historian Joe Manning, Ph.D.  “The climate effects were a severe shock to an already stressed society at a pivotal moment in history.”

Timeline showing the Okmok II eruption in relation to European summer temperatures, volcanic sulphur and ash levels, and significant historical events in the Mediterranean from 59 to 20 BCE

Timeline showing European summer temperatures and volcanic sulphur and ash levels in relation to the Okmok II Eruption and significant historic events of the Roman Republic and Ptolemaic Kingdom from 59 to 20 BCE.

Volcanic activity also helps to explain certain unusual atmospheric phenomena that were described by ancient Mediterranean sources around the time of Caesar’s assassination and interpreted as signs or omens – things like solar halos, the sun darkening in the sky, or three suns appearing in the sky (a phenomenon now known as a parahelia, or ‘sun dog’). However, many of these observations took place prior to the eruption of Okmok II in 43 BCE, and are likely related to a smaller eruption of Mt. Etna in 44 BCE.

Although the study authors acknowledge that many different factors contributed to the fall of the Roman Republic and Ptolemaic Kingdom, they believe that the climate effects of the Okmok II eruption played an undeniably large role – and that their discovery helps to fill a knowledge gap about this period of history that has long puzzled archaeologists and ancient historians.

“People have been speculating about this for many years, so it’s exciting to be able to provide some answers,” McConnell said.


Additional information

This project received support from the National Science Foundation, the Sir Nicholas Shackleton Visiting Fellowship, Clare Hall, Cambridge and the John Fell Oxford University Press Research Fund. Additional authors from DRI included Nathan Chellman, Ph.D.

To view the full text of the article “Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom”  in PNAS, please visit:  [add link]

For more information on lead author Joe McConnell, Ph.D., and his research, please visit: https://www.dri.edu/directory/joe-mcconnell/

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About the Desert Research Institute

The Desert Research Institute (DRI) is a recognized world leader in basic and applied interdisciplinary research. Committed to scientific excellence and integrity, DRI faculty, students, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge, supported Nevada’s diversifying economy, provided science-based educational opportunities, and informed policymakers, business leaders, and community members. With campuses in Reno and Las Vegas, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, visit www.dri.edu.

 

DRI ice core research makes Discover magazine’s list of top breakthroughs in 2018

DRI ice core research makes Discover magazine’s list of top breakthroughs in 2018

Reno, Nev. (Thurs. January 17th) – For the second time, research out of the Ultra-trace Ice Core Chemistry Laboratory at the Desert Research Institute (DRI) in Reno, Nevada, has been named one of the year’s biggest scientific discoveries by Discover magazine.

The research, originally published in the Proceedings of the National Academies of Science last May, used ice samples from the North Greenland Ice Core Project (NGRIP) to measure, date, and analyze European lead emissions that were captured in Greenland ice between 1100 BC and AD 800. Their results provide new insights for historians about how European civilizations and their economies fared over time.

“Our record of sub-annually resolved, accurately dated measurements in the ice core starts in 1100 BC during the late Iron Age and extends through antiquity and late antiquity to the early Middle Ages in Europe, a period that included the rise and fall of the Greek and Roman civilizations,” said the study’s lead author Joe McConnell, Ph.D., Research Professor of Hydrology at DRI and Director of the Ice Core Lab. “We found that lead pollution in Greenland very closely tracked known plagues, wars, social unrest and imperial expansions during European antiquity.”

The research team on the project included scientists, archaeologists, and economists from the Desert Research Institute (DRI), the University of Oxford, NILU – Norwegian Institute for Air Research and the University of Copenhagen.

This is the second time research out of the DRI Ice Core Lab has been recognized in the Discover magazine round up of the year’s top science stories. In the January 2008 issue, findings on rising black carbon levels in Greenland ice cores during the industrial revolution made the magazine’s 2007 top 100 list.

“Selection of these findings as among the world’s top science stories of 2018 is very exciting for the members of our research group and our international collaborators. It is especially rewarding for me in that a largely ice core based study was selected as among the top stories in archaeology rather than in earth or environmental sciences. This all demonstrates the vast potential of highly interdisciplinary research teams working together.”

Other DRI researchers who worked on this study are Monica Arienzo, Ph.D., assistant research professor, and graduate student researcher Nathan Chellman.

First non-polar historical iodine record shows impact of fossil fuel emissions

First non-polar historical iodine record shows impact of fossil fuel emissions

Reno, Nev. (Nov. 13, 2018): A new ice core record from the French Alps shows impacts of fossil fuel emissions in the form of a steep increase in iodine levels during the second half of the 20th century, according to a study released this week by an international team of scientists from the Université Grenoble Alpes-CNRS of France, the Desert Research Institute (DRI) in Reno, Nev., and the University of York in England.

“Model and laboratory studies had suggested that atmospheric iodine should have increased during recent decades as a result of increasing fossil fuel emissions but few long-term records of iodine existed with which to test these model findings, and none in Western Europe where modeled iodine increases were especially pronounced,” said French researcher and lead author Michel Legrand, Ph.D.

Iodine is an important nutrient for human health, key in the formation of thyroid hormones. It is present in ocean waters, and is released into the atmosphere when Iodide (I-) reacts with ozone (03) at the water’s surface. From the atmosphere, iodine is deposited onto Earth’s land surfaces, and absorbed by humans in the foods that we eat.

The new study, published in the Proceedings of the National Academy of Sciences, was initiated after scientists observed a three-fold increase in iodine between 1950 and the 1990s measured in an ice core from the Col du Dome region of France. The core was collected by French scientists and analyzed in 2017 in DRI’s Ultra Trace Ice Core Analysis Laboratory.

 

Researchers examine an ice core sample drilled from Mont Blanc.

Researchers examine an ice core sample drilled from Mont Blanc. Credit: B. Jourdain, L’Institut des Géosciences de l’Environnement.

Although previous modeling simulations had indicated a similar increase in global iodine emissions during the 20th century, this new record provides the first ice core iodine record from outside of the polar regions.

“Iodine has been measured previously in polar ice cores but changes there largely can be attributed to variations in sea ice,” said Joe McConnell, Ph.D., research professor of hydrology and head of DRI’s ice core laboratory. “These variations mask the larger scale trends linked to fossil fuel emissions and changes in ozone chemistry. Our new iodine record extends from 1890 to 2000 and is from the French Alps, a part of the world where there are no sea ice influences.”

As part of this study, more than 120 meters (nearly 400 feet) of ice core from the French Alps was analyzed for iodine and a broad range of chemical species by a group of DRI researchers that included McConnell, Monica Arienzo, Ph.D., Nathan Chellman, and Kelly Gleason, Ph.D., using DRI’s unique continuous analytical system.

The study team then analyzed the ice core record alongside modeling simulations to investigate past atmospheric iodine concentrations and changes in iodine deposition across Europe. According to their results, the observed tripling of iodine levels in the ice during the 1950s to 1990s were caused by increased iodine emissions from the ocean.

An ice core sample is processed in DRI’s Ultra-Trace Ice Core Laboratory in Reno, Nev.

An ice core sample is processed in DRI’s Ultra-Trace Ice Core Laboratory in Reno, Nev. Credit: Joe McConnell/DRI.

Ozone in the lower atmosphere acts as an air pollutant and greenhouse gas. Because iodine emissions from the ocean occur when iodine in the water reacts with ozone in the lower atmosphere, the study results indicate that increased ozone levels are increasing the availability of iodine in the atmosphere – and also that iodine is helping to destroy this “bad” ozone.

“Iodine’s role in human health has been recognized for some time – it is an essential part of our diets,” said Lucy Carpenter, Ph.D., Professor with University of York’s Department of Chemistry. “Its role in climate change and air pollution, however, has only been recognized recently and the impact of iodine in the atmosphere is not currently a feature of the climate or air quality models that predict future global environmental changes.”

According to the World Health Organization, iodine deficiency remains a significant health problem in parts of Europe, including France, Italy and certain regions of Spain – regions that now appear to have received a boost in iodine levels in recent years.

“The silver lining in the findings of this study is that the increase in human-caused pollution during the latter half of the 20th century may be leading to an increase in the availability of iodine as an essential nutrient,” Legrand said.

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To view the study, titled Alpine ice evidence of a three-fold increase in atmospheric iodine deposition since 1950 in Europe due to increasing oceanic emissions, published in the journal Proceedings of the National Academy of Sciences on 12 November 2018, please visit:  http://www.pnas.org/content/early/2018/11/07/1809867115

Samantha Martin from the University of York contributed to this release.

The Desert Research Institute (DRI) is a recognized world leader in basic and applied interdisciplinary research. Committed to scientific excellence and integrity, DRI faculty, students, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge, supported Nevada’s diversifying economy, provided science-based educational opportunities, and informed policy makers, business leaders, and community members. With campuses in Reno and Las Vegas, DRI serves as the non-profit research arm of the Nevada System of Higher Education. Learn more at dri.edu, and connect with us on social media on Facebook, Instagram and Twitter

Lead pollution in Greenland ice shows rise and fall of ancient European civilizations

Lead pollution in Greenland ice shows rise and fall of ancient European civilizations

Dr. Monica Arienzo inspects an ice core sample in the ice core lab at the Desert Research Institute in Reno, Nev. Photo credit: DRI.


Reno, NV (May 14, 2018): To learn about the rise and fall of ancient European civilizations, researchers sometimes find clues in unlikely places: deep inside of the Greenland ice sheet, for example.

Thousands of years ago, during the height of the ancient Greek and Roman empires, lead emissions from sources such as the mining and smelting of lead-silver ores in Europe drifted with the winds over the ocean to Greenland – a distance of more than 2800 miles (4600 km) – and settled onto the ice. Year after year, as fallen snow added layers to the ice sheet, lead emissions were captured along with dust and other airborne particles and became part of the ice-core record that scientists use today to learn about conditions of the past.

In a new study published in PNAS, a team of scientists, archaeologists and economists from the Desert Research Institute (DRI), the University of Oxford, NILU – Norwegian Institute for Air Research and the University of Copenhagen used ice samples from the North Greenland Ice Core Project (NGRIP) to measure, date and analyze European lead emissions that were captured in Greenland ice between 1100 BC and AD 800. Their results provide new insight for historians about how European civilizations and their economies fared over time.

“Our record of sub-annually resolved, accurately dated measurements in the ice core starts in 1100 BC during the late Iron Age and extends through antiquity and late antiquity to the early Middle Ages in Europe – a period that included the rise and fall of the Greek and Roman civilizations,” said the study’s lead author Joe McConnell, Ph.D., Research Professor of Hydrology at DRI. “We found that lead pollution in Greenland very closely tracked known plagues, wars, social unrest and imperial expansions during European antiquity.”

Map showing location of NGRIP ice core.

Map showing location of NGRIP ice core in relation to Roman lead/silver mines. Credit: DRI.

A previous study from the mid-1990s examined lead levels in Greenland ice using only 18 measurements between 1100 BC and AD 800; the new study provides a much more complete record that included more than 21,000 precise lead and other chemical measurements to develop an accurately dated, continuous record for the same 1900-year period.

To determine the magnitude of European emissions from the lead pollution levels measured in the Greenland ice, the team used state-of-the-art atmospheric transport model simulations.

“We believe this is the first time such detailed modeling has been used to interpret an ice-core record of human-made pollution and identify the most likely source region of the pollution,” said co-author Andreas Stohl, Ph.D., Senior Scientist at NILU.

Most of the lead emissions from this time period are believed to have been linked to the production of silver, which was a key component of currency.

“Because most of the emissions during these periods resulted from mining and smelting of lead-silver ores, lead emissions can be seen as a proxy or indicator of overall economic activity,” McConnell explained.

Using their detailed ice-core chronology, the research team looked for linkages between lead emissions and significant historical events. Their results show that lead pollution emissions began to rise as early as 900 BC, as Phoenicians expanded their trading routes into the western Mediterranean. Lead emissions accelerated during a period of increased mining activity by the Carthaginians and Romans primarily in the Iberian Peninsula and reached a maximum under the Roman Empire.

Graph of European lead emissions.

Chronology of European lead emissions that were captured in Greenland ice between 1100 BC and AD 800 in relation to major historic events. Credit: DRI.

The team’s extensive measurements provide a different picture of ancient economic activity than previous research had provided. Some historians, for example, had argued that the sparse Greenland lead record provided evidence of better economic performance during the Roman Republic than during the Roman Empire.

According to the findings of this study, the highest sustained levels of lead pollution emissions coincided with the height of the Roman Empire during the 1st and 2nd centuries AD, a period of economic prosperity known as the Pax Romana. The record also shows that lead emissions were very low during the last 80 years of the Roman Republic, a period known as the Crisis of the Roman Republic.

“The nearly four-fold higher lead emissions during the first two centuries of the Roman Empire compared to the last decades of the Roman Republic indicate substantial economic growth under Imperial rule,” said coauthor Andrew Wilson, Professor of the Archaeology of the Roman Empire at Oxford.

The team also found that lead emissions rose and fell along with wars and political instability, particularly during the Roman Republic, and took sharp dives when two major plagues struck the Roman Empire in the 2nd and 3rd centuries. The first, called the Antonine Plague, was probably smallpox. The second, called the Plague of Cyprian, struck during a period of political instability called the third-century crisis.

“The great Antonine Plague struck the Roman Empire in AD 165 and lasted at least 15 years. The high lead emissions of the Pax Romana ended exactly at that time and didn’t recover until the early Middle Ages more than 500 years later,” Wilson explained.

The research team for this study included ice-core specialists, atmospheric scientists, archaeologists, and economic historians – an unusual combination of expertise.

“Working with such a diverse team was a unique experience in my career as a scientist,” McConnell said. “I think that our results show that there can be great value in collaborating across disciplines.”

Analysis and interpretation of archived NGRIP2 ice-core samples were supported by the John Fell Oxford University Press Research Fund and All Souls College, Oxford, as well as the Desert Research Institute.

Photo of the project team.

The project team included an interdisciplinary team of researchers, including (left to right) Dr. Audrey Yau, ice core specialist and former DRI post-doc; Dr. Monica Arienzo, ice core specialist, DRI; Elisabeth Thompson, doctoral student, Oxford University; Professor Andrew Wilson, historian, Oxford University; and Professor Joe McConnell, ice core specialist, DRI.