Human migration out of Africa may have followed monsoons in the Middle East

By: Thomas Schmitt Attorney on November 26, 2019 / comment : 0 Archaeology, Early Humans, Earth Science, Israel, Jordan, Middle East, Palaeoclimate, Palestine, Syria

Last year, scientists announced that a human jawbone and prehistoric tools found in 2002 in Misliya Cave, on the western edge of Israel, were between 177,000 and 194,000 years old.

Ian Orland at Soreq Cave, Israel, where some calcite cave formations are 185,000 years old [Credit: Ian Orland]

The finding suggested that modern humans, who originated in Africa, began migrating out of the continent at least 40,000 years earlier than scientists previously thought.

But the story of how and when modern humans originated and spread throughout the world is still in draft form. That's because science hasn't settled how many times modern humans left Africa, or just how many routes they may have taken.

A new study published this week in the Proceedings of the National Academy of Sciences by American and Israeli geoscientists and climatologists provides evidence that summer monsoons from Asia and Africa may have reached into the Middle East for periods of time going back at least 125,000 years, providing suitable corridors for human migration.

The likely timing of these northward monsoon expansions corresponds with cyclical changes in Earth's orbit that would have brought the Northern Hemisphere closer to the sun and led to increased summer precipitation. With increased summer precipitation there may have been increased vegetation, supporting animal and human migration into the region.

"It could be important context for experts studying how, why, and when early modern humans were migrating out of Africa," says lead author Ian Orland, a University of Wisconsin-Madison geoscientist now at the Wisconsin Geological and Natural History Survey, in the Division of Extension. "The Eastern Mediterranean was a critical bottleneck for that route out of Africa and if our suggestion is right, at 125,000 years ago and potentially at other periods, there may have been more consistent rainfall on a year-round basis that might enhance the ability of humans to migrate."

For as long as humans have kept records, winters have been wet and summers have been hot and dry in the Levant, a region that includes Israel, Syria, Lebanon, Jordan and Palestine. Before modern times, those hot, dry summers would have presented a significant barrier to people trying to move across the landscape.

Scientists, though, have found it difficult to determine what kinds of precipitation patterns might have existed in the prehistoric Levant. Some studies examining a variety of evidence, including pollen records, ancient lake beds, and Dead Sea sediments, along with some climate modeling studies, indicate summers in the region may have, on occasion, been wet.

To try to better understand this seasonality, Orland and colleagues looked at cave formations called speleothems in Israel's Soreq Cave. Speleothems, such as stalactites and stalagmites, form when water drips into a cave and deposits a hard mineral called calcite. The water contains chemical fingerprints called isotopes that keep a record, like an archive, of the timing and environmental conditions under which speleothems have grown.

Among these isotopes are different forms of oxygen molecules -- a light form called O16 and a heavy form called O18. Today, the water contributing to speleothem growth throughout much of the year has both heavy and light oxygen, with the light oxygen predominantly delivered by rainstorms during the winter wet season.

Orland and his colleagues hypothesized they might be able to discern from speleothems whether two rainy seasons had contributed to their growth at times in the past because they might show a similar signature of light oxygen in both winter and summer growth.

But to make this comparison, the scientists had to make isotope measurements across single growth bands, which are narrower than a human hair. Using a sensitive instrument in the UW-Madison Department of Geoscience called an ion microprobe, the team measured the relative amounts of light and heavy oxygen at seasonal increments across the growth bands of two 125,000-year-old speleothems from Soreq Cave.

This was the first time that seasonal changes were directly measured in a speleothem this old.

At the same time that Orland was in pursuit of geologic answers, his UW-Madison colleague in the Nelson Institute for Environmental Studies Center for Climatic Research, Feng He, was independently using climate models to examine how vegetation on the planet has changed with seasonal fluctuations over the last 800,000 years. Colleagues since graduate school, He and Orland teamed up to combine their respective approaches after learning their studies were complementary.

A previous study in 2014 from UW-Madison climatologist and Professor Emeritus John Kutzbach showed that the Middle East may have been warmer and wetter than usual during two periods of time corresponding roughly to 125,000 years ago and 105,000 years ago. Meanwhile, at a point in between, 115,000 years ago, conditions there were more similar to today.

The wetter time periods corresponded to peak summer insolation in the Northern Hemisphere, when Earth passes closer to the sun due to subtle changes in its orbit. The drier time period corresponded to one of its farthest orbits from the sun. Monsoon seasons tend to be stronger during peak insolation.

This provided He an opportunity to study high and low insolation rainfall during summer seasons in the Middle East and to study its isotopic signatures.

The climate model "fueled the summer monsoon hypothesis" because it suggested that "under these conditions, the monsoons could have reached the Middle East and would have a low O18 signature," He, a study co-author, says. "It's a very intriguing period in terms of climate and human evolution."

His model showed that northward expansion of the African and Asian summer monsoons was possible during this time period, would have brought significant rainfall to the Levant in the summer months, would have nearly doubled annual precipitation in the region, and would have left an oxygen isotope signature similar to winter rains.

At the same time, Orland's speleothem isotype analysis also suggested summers were rainier during peak insolation at 125,000 and 105,000 years ago.

For similar reasons, the Middle East may have also been warm and humid around 176,000 years ago, the researchers say -- about when the jawbone made its way to Misliya Cave. And before the jawbone, the previous oldest modern human fossils found outside of Africa were at Israel's Skh?l Cave, dating back between 80,000 and 120,000 years ago.

Overall, the study suggests that during a period of time when humans and their ancestors were exploring beyond the African continent, conditions may have been favorable for them to traverse the Levant.

"Human migration out of Africa occurred in pulses, which is definitely consistent with our idea that every time the Earth is closer to the sun, the summer monsoon is stronger and that's the climatic window that opened and provided opportunities for human migration out of Africa," says He.

Author: Kelly April Tyrrell | Source: University of Wisconsin-Madison [November 26, 2019]

Two million-year-old ice cores provide first direct observations of an ancient climate

By: Thomas Schmitt Attorney on November 21, 2019 / comment : 0 Antarctic, Climate Change, Earth Science, Palaeoclimate, Palaeontology

Princeton University-led researchers have extracted 2 million-year-old ice cores from Antarctica that provide the first direct observations of Earth's climate at a time when the furred early ancestors of modern humans still roamed.

Princeton University-led researchers have extracted 2 million-year-old ice cores from Antarctica -- the oldest yet recovered -- that provide the first direct observations of prehistoric atmospheric conditions and temperatures. They used data from the ice cores to answer long-held questions about how our current colder, longer glacial cycle emerged [Credit: Sean Mackay, Boston University]

Gas bubbles trapped in the cores -- which are the oldest yet recovered -- contain pristine samples of carbon dioxide, methane and other gases that serve as "snapshots" of prehistoric atmospheric conditions and temperatures, the researchers recently reported in the journal Nature. The cores were collected in the remote Allan Hills of Antarctica.

First author Yuzhen Yan, who received his Ph.D. in geosciences from Princeton in 2019, explained that because ice flows and compresses over time, continual ice cores only extend back to 800,000 years ago. The cores he and his co-authors retrieved are like scenes collected from a very long movie that do not show the whole film, but convey the overall plot.

"You don't get a sense of how things changed continually, but you get an idea of big changes over time," said Yan, whose graduate research on ice cores supported by a 2016 Walbridge Fund Graduate Award for Environmental Research from the Princeton Environmental Institute (PEI) was a basis for the current work.

The ice cores reported in Nature are the latest to come out of the research group of senior author John Higgins, a Princeton associate professor of geosciences, PEI associated faculty and Yan's doctoral co-adviser. A previous team led by Higgins recovered a 1 million-year-old ice core from the Allan Hills, which was the oldest ice core ever recorded by scientists when it was reported in the journal Proceedings of the National Academy of Sciences in 2015. The cores were dated by measuring isotopes of the gas argon trapped in bubbles in the ice, a technique developed by co-author Michael Bender, Princeton professor of geosciences, emeritus, and PEI associated faculty.

Gas bubbles trapped in the cores contain pristine samples of carbon dioxide, methane and other gases that serve  as 'snapshots' of the ancient climate. Because ice flows and compresses over time, the cores the researchers retrieved are like scenes collected from a very long movie that do not show the whole film, but convey the overall plot [Credit: Sean Mackay, Boston University]

"The ability to measure atmospheric composition directly is one of the biggest advantages of ice cores," Yan said. "That's why people spend years and years in the most isolated places getting them."

In the latest publication, the researchers use data from the ice cores to answer long-held questions about how our current glacial cycle emerged. Up until roughly 1.2 million years ago, Earth's ice ages consisted of thinner, smaller glaciers that came and went every 40,000 years on average.

Then, after what is known as the Mid-Pleistocene Transition, there emerged our current world characterized by colder and longer glacial cycles of 100,000 years. The two periods are known as the 40k and 100k world, respectively.

Some existing theories have stated that the 100k world -- which includes the last ice age that ended 11,700 years ago -- came about because of a long-term decline in atmospheric carbon dioxide, Yan said. But the researchers found that this was not the case -- average carbon dioxide was relatively steady through the 40k and 100k worlds. While the lowest temperatures and carbon dioxide levels of the 40k world were greater than the low points of the 100k world, the highest levels of both ages were similar.

"It could be the case that after the Mid-Pleistocene Transition, something occurred that lowered global glacial temperatures and atmospheric carbon dioxide values," Yan said. "This is the first time we have direct access to these greenhouse gas measurements. The ice core also opens up an array of new measurement possibilities that can give us insights into the 40k world when glacial cycles were very different from what we have today."

The researchers collected the 2 million-year-old ice cores in the remote Allan Hills, where high winds help create  the environmental conditions that draw ancient ice toward the surface. They found that although a long-term decline in atmospheric carbon dioxide did not directly lead to today's colder glacial cycle, temperature and global ice volume nonetheless tracked carbon dioxide closely [Credit: Sean Mackay, Boston University]

Although a long-term decline in average atmospheric carbon dioxide may not have directly led to the 100k world, the researchers nonetheless observed a correlation between carbon dioxide and global temperature, Bender said.

"To say that carbon dioxide is not a factor would be completely wrong," Bender said. "During the 40,000- and 100,0000-year glacial-interglacial cycles, temperature and global ice volume tracks carbon dioxide rather closely. Carbon dioxide changes are required to get from the cooler glacial temperatures to the warmer interglacial temperatures."

The amount of carbon dioxide now in the atmosphere tops 400 parts-per-million (ppm), which is nearly 100 ppm higher than the highest levels of the 40k world, Yan said.

"We're seeing carbon dioxide levels not seen in 2 million years," Yan said. "While our data suggest that long-term carbon dioxide decline was not the decisive factor in the Mid-Pleistocene Transition, it does not mean that carbon dioxide does not have the capability to bring about global-scale changes.

"We're in a different situation now -- carbon dioxide is the major player in our current world," he said. "If we want to look into the geologic past for an analogy of what's going on in our world today, we need to go beyond 2 million years to find it."

Author: Morgan Kelly | Source: Princeton University [November 21, 2019]

Geoscientists reconstruct the climate of the past by analysing dripstones

By: Thomas Schmitt Attorney on November 12, 2019 / comment : 0 Climate Change, Earth Science, Geology, India, Palaeoclimate, Palaeontology, South Asia

In the last interglacial period on Earth about 125,000 years ago, the Indian monsoon was longer, more extreme and less reliable than it is today. This is the conclusion drawn by geoscientists from Ruhr-Universitat Bochum (RUB) and the University of Oxford, together with other colleagues from the UK, New Zealand, China and the USA. The team analysed a dripstone from a cave in north-eastern India, combining various methods that provide information about supra-regional and local weather phenomena and the climate dynamics of the past.

Five centimetres of this dripstone sample contain 40,000 years of climate history [Credit: RUB, Marquard]

The team headed by Matthias Magiera, Dr. Franziska Lechleitner, Professor Ola Kwiecien and Dr. Sebastian Breitenbach describe the results in the journal Geophysical Research Letters.

Last and next interglacial period

"The last interglacial period is often considered an analogy to the expected climate changes," says Ola Kwiecien from the RUB Institute of Geology, Mineralogy and Geophysics. "Even though the factors that led to the warming were different then than they are today, of course." Findings about weather and climate phenomena from the last interglacial period provide researchers with clues as to how the climate might change as the earth warms up.

Just like a tree has annual rings, a dripstone has a lamination that develops over time when the dripstone grows under different environmental conditions [Credit: RUB, Marquard]

The team analysed a dripstone from the Mawmluh Cave in north-eastern India. For one, the researchers determined so-called delta-18-O values, which are a measure of the strength of the Indian monsoon. In the process, they compared the ratio of heavy and light oxygen in the dripstone; this depends on the one hand on the source area of the monsoon, but also on the seasonal distribution of rainfall, temperature and intensity of precipitation. These factors play an important role for the strength of the monsoon weather phenomenon.

Relevant for farmers in the region

"The delta-18-O value tells us something about the strength of the monsoon, but not how much precipitation falls and how the rain spreads over time," explains Sebastian Breitenbach from the RUB Institute of Geology, Mineralogy and Geophysics. "But that is in fact the crucial information," adds Ola Kwiecien. "For a farmer, it makes a big difference whether precipitation falls constantly and reliably over a certain period of time, or whether surprising and extreme rainfall alternates with longer dry periods."

The Mawmluh Cave in north-eastern India is located in the most humid place on Earth [Credit: Franziska Lechleitner]

In order to gather clues on the seasonal distribution of rainfall, the researchers defined additional measured values. While the delta-18-O value is a supra-regional parameter that tells them something about the distant sources of monsoon rainfall, other parameters record local phenomena, including the ratio of different elements such as strontium or magnesium to calcium or the ratio of different calcium isotopes in the dripstone. This isotope ratio, known as the delta-44-Ca value, has so far rarely been applied to cave samples.

Precipitation in the vicinity of the cave

During dry winter and longer dry periods, a phenomenon occurs in the karst rock above the cave that affects the elemental conditions in the dripstone. If rain falls over the Mawmluh Cave, it seeps through the soil, dissolves calcium from the rock and transports it into the cave. The calcium is stored in a dripstone formed by the water; the dripstone, which grows during a moist phase, thus has a high calcium content compared to other elements.

The composition of the dripstones in the cave reveals something about the climate of the past Credit: Franziska Lechleitner]

However, during the dry period between November and May, some of the calcium can get lost on the way, if there are any air-filled cavities in the rock. These cause calcium to precipitate before it reaches the cave, while elements such as strontium and magnesium remain in the water, are transported to the dripstones and integrated into them. The ratio of magnesium or strontium to calcium in the dripstone thus indicates whether there was much or little rain in the immediate vicinity of the cave. The delta-44-Ca value also provides clues on the precipitation near the cave and, moreover, allows researchers to gain more information on the intensity of the dry phase.

The combination of these different parameters enabled the researchers to reconstruct changes in precipitation during the monsoon and non-monsoon periods and, consequently, to gain insight into the distribution of precipitation before, during and after the last interglacial period.

Monsoon was less reliable

"On the whole, our data show that the Indian monsoon was less reliable in the last interglacial period than it is today, which suggests that global warming today might be having the same effect," concludes Ola Kwiecien. "This tallies with the tendency for weather extremes to become more frequent." According to the researchers, human impact on the climate in the Indian summer monsoon has not yet fully manifested itself. If the assumptions underlying the current study are correct, however, this could change in the next 20 to 30 years.

Source: Ruhr-University Bochum [November 12, 2019]

Ancient rain gauge: New evidence links groundwater, climate changes in deep time

By: Thomas Schmitt Attorney on November 12, 2019 / comment : 0 Climate Change, Earth Science, Geology, North America, Palaeoclimate, Palaeontology

Changes in groundwater millions of years ago created alternating layers of vivid yellow and brown in the mineral sphalerite, and those variations align with movements in Earth's orbit that impacted climate in the deep past, Penn State scientists found.

Yellow and brown banding in the mineral sphalerite are caused by changes in rainfall and groundwater. Penn State scientists found patterns in the banding match movement in Earth's orbit that impacted climate in the deep past [Credit: Mingsong Li]

The findings provide new evidence for how changes in climate influenced the planet's rainfall and groundwater, a process that scientists have not well documented, the researchers said.

"This study shows sphalerite banding can be used as a fingerprint of groundwater in the geological past," said Mingsong Li, assistant research professor of geosciences at Penn State. "Groundwater is crucial for understanding global sea level change, chemical weathering and landscape evolution, and this study presents a new idea to help discern the role of groundwater in the Earth system."

Increased precipitation influenced the colored banding in sphalerite samples from the Upper Mississippi Valley Ore Mineral District in the U.S. Midwest, the scientists said. More rainfall lead to oxygen-rich groundwater flowing to depths where the mineral formed, and the increased oxidation resulted in lighter yellow bands. Drier times yielded darker brown colors.

Using new dating technology, the scientists found these deposition patterns corresponded with changes in Earth's orbit over tens of thousands to hundreds of thousands of years, known as Milankovitch astronomical cycles.

These cycles refer to changes in the shape of Earth's orbit and variations in the tilt of its rotation that may have led to warmer, wetter conditions for periods from 299 million to 252 million years ago, when the sphalerite formed, the scientists said.

"What we are doing is marrying geochemical research on ores with what we know about astronomical cycles from very different research," said Hubert Barnes, distinguished professor emeritus at Penn State. "No one has ever made an attempt at this before."

The research builds on previous work that shows hydrothermal fluids that created ore deposits in modern day Iowa, Illinois and Wisconsin started as groundwater in the Appalachian Mountains. The water was heated by geothermal processes and picked up metals and solutes along it journey.

But during times of high precipitation, new sources of groundwater flowed to roughly 3,000 feet below the surface carrying higher oxygen levels and mixing with the hydrothermal fluids to create different colored bands in the sphalerite.

The researchers digitized a grayscale profile of the sphalerite from Wisconsin and analyzed the bands using new computer software that can detect periodic signals in the samples. They found distinct frequency peaks in the banding that correlate with the Milankovitch cycles.

The results - published in the journal Geochemical Perspective Letters - could help explain changes in sea level during times in Earth's history when the planet was too warm for ice, the scientists said.

Changes in groundwater can have real impacts on sea level. If all groundwater drained into oceans today, sea level would rise more than 180 feet, according to the scientists.

Yet projections of long-term global mean sea level on times scales of hundreds to thousands of years often do not include the contributions of land water storage, the scientists said. The Intergovernmental Panel on Climate Change, for instance, considers water storage on land contribution to sea level rise to be small.

"This research opens a new way to evaluate climate control on groundwater activities linked to global water cycles," Li said. "This is the first direct evidence to show groundwater activities in the deep past."

Author: Matthew Carroll | Source: Pennsylvania State University [November 12, 2019]

A novel method for analyzing marine sediments contributes to paleoclimate reconstitution

By: Thomas Schmitt Attorney on November 06, 2019 / comment : 0 Climate Change, Earth Science, Geology, Palaeoclimate, Palaeontology

The analysis of marine sediments has become a powerful research method in paleoclimatology. The composition of the sediments carried by rivers from the mainland to the ocean can be used as a basis for calculating variables such as temperature, precipitation and marine salinity. In the context of ongoing global climate change, the study of the past is fundamental to validating the accuracy of the climate models used to make predictions.

Storm over Campo de Sao Joao, Piaui State, where sediment samples for paleoclimate research were collected [Credit: Vinicius Mendes]

A novel method of sediment analysis was proposed by Vinicius Ribau Mendes, a professor at the Federal University of Sao Paulo (UNIFESP), in Brazil, in an article published in Paleoceanography and Paleoclimatology, a journal of the American Geophysical Union (AGU). As a tribute to its originality, the study was also featured in the section “Research Spotlights” of EOS: Earth & Space Science News, another AGU publication.

The study was conducted during Mendes’s PhD research with the support of a scholarship from FAPESP and was supervised by Paulo Cesar Fonseca Giannini. The study also received funding via a Young Investigator Grant awarded to Cristiano Mazur Chiessi, a co-author of the article, and a research grant under FAPESP’s Multiuser Equipment Program awarded to Giannini.

Mendes and collaborators analyzed marine sediment cores collected off Brazil’s northeastern coast. A marine sediment core is a tubular sample of mud extracted from the sea bed to capture stratigraphic layers while preserving the depositional sequence; younger sediments are at the top, and older sediments are at the bottom.

The cores analyzed by the researchers contained clay minerals, quartz and feldspar transported from the continent by the Parnaiba, the most important river in the region. Feldspars, a group of aluminosilicate minerals containing calcium, sodium and potassium, make up more than half of the Earth's crust.

Any substantial change undergone by the river, such as variations in the rainfall regime, is potentially reflected by these sediments. “We propose a new method of reconstructing the changes that have occurred in continental precipitation during the past 30,000 years based on the luminescence of quartz and feldspar grains. This luminescence varies according to the geological constitution of the areas in which the crystals originated and the length of time they were exposed to surface processes before reaching the ocean bottom. A crystal from the headwaters of the river has a specific signature that differs from the signature of a crystal from the middle or lower reaches of the river. In the case of the Parnaiba, an increase in rainfall has a significant impact on its source, so a larger proportion of grains from this area in a marine sediment core reflects a rise in precipitation,” Mendes told Agencia FAPESP.

Luminescence is light emitted by materials that have been exposed to ionizing radiation and are subjected to a stimulus such as heat or light. Other studies have discovered that for quartz, the intensity of light emission or sensitivity depends on the geological medium in which the grain was formed and the duration of its exposure to sunlight during successive transportation events down the river until it reached the ocean. “We proved this empirically by collecting quartz and feldspar samples along the Parnaiba. We found significant differences between samples from the headwaters and from the lower reaches of the river,” Mendes said.

The physicochemical basis for these differences is not fully understood. Quartz is a simple material that is more abundant in sediments than feldspar. Quartz mainly consists of silica (silicon dioxide, SiO2) but may contain defects formed by the incorporation of chemical elements other than silicon and oxygen or due to the absence of these elements in the crystal lattice (“vacancies”). Luminescence results from these alterations in the lattice; the alterations depend on the chemical composition of the medium in which the rock was formed. Once formed and transformed into the sediment, the mineral is influenced by other factors, such as fragmentation, which changes the way it interacts with ionizing radiation in the environment, exposure to sunlight, and a high incidence of cosmic rays.

Exactly how these factors influence the capacity of defects to create luminescence is unknown, but a study conducted in the Amazon River basin by Andre Oliveira Sawakuchi, a professor at the University of Sao Paulo’s Institute of Geosciences (IGc-USP), and collaborators showed that the longer quartz remains exposed to terrestrial surface processes, the greater its luminescence.

“These physicochemical hypotheses about the differences are still being studied,” Mendes said. “We don’t have a definitive explanation. What we can say for sure, because we have the empirical data, is that crystals from various sites along the course of the river are different. So when we found grains of these crystals in marine sediment cores, we were able to measure their luminescence to determine where they were formed and map the process that took them from the continent to the ocean.”

Luminescence was measured in samples taken every 2 cm along the core. All samples were exposed to the same type and quantity of ionizing radiation and then stimulated by heat or light.

“Our novel method complements two others that are well established in the scientific literature. One produces precise and accurate information about rainfall and is based on measuring the proportion of hydrogen isotopes present in highly resistant molecules of terrestrial plants transported to the ocean. These isotopes, which the plants incorporate into their molecules, come from rainwater,” Mendes explained.

The stable isotopes of hydrogen are protium, with one proton and one electron, and deuterium (heavy hydrogen), with one proton, one neutron and one electron. Protium, the most abundant isotope, combines with oxygen to form ordinary water (H2O), and deuterium combines with oxygen to form heavy water (D2O).

Rainclouds in Brazil’s Northeast region travel from the ocean to the continent, so the more it rains, the less deuterium falls on the land because heavy water is denser and tends to fall first. The proportions of deuterium and protium in plants deposited at different depths of marine sediments therefore provide very precise information on variations in the amount of precipitation over time.

“Despite its precision, however, this method is very laborious and costly. It also depends on the preservation of the organic matter in the sediment, which isn’t always the case,” Mendes said.

The second method is based on analyses of the chemical composition of sediments using X-ray fluorescence. The technique entails exciting the sample with X-rays and analyzing the characteristics of the electromagnetic signal emitted in response. Each chemical element emits information in a specific frequency band, and the elements present in the sample can be identified based on this information. The goal is to determine the proportions of titanium and iron, which are continental elements, and that of calcium, which is from the shells of marine animals. Increases in the percentages of titanium and iron indicate that more material was transported from the land into the ocean due to more intense rainfall in a given period compared to the conditions in previous periods.

This second method is simple, fast and inexpensive. Although determining the percentages of hydrogen isotopes takes several months of analysis in a laboratory, samples can be scanned for titanium, iron and calcium in a day. The problem is a lack of precision compared with the first method. Variations in the percentages of titanium and iron indicate an increase or decrease in precipitation in a given period, but the variations are not proportional to the amount of rainfall because they are also affected by rising and falling sea levels. If the sea level falls, the mouth of the river moves closer to the area from which the sediment is collected. If the sea rises, the distance to the river mouth increases. In this case, any increase or decrease in the proportions of titanium and iron in the sediment core may not be caused by rain variations. Thus, the lack of precision of this method offsets its advantages in terms of speed and cost.

“Our new method lies somewhere between the two,” Mendes said. “It is less precise than the first and more precise than the second. It is also intermediate in terms of difficulty and cost. Additionally, quartz is a highly resistant material, so there is no risk it will degrade in the sediment, as can happen with organic molecules in the first method. Because the new method is based on the intrinsic properties of these crystals, there is also no risk they will be affected by external factors such as rising sea levels, as there is with the second method. We do not propose substitution of one method for another. They’re complementary and should be used as appropriate in each case.”

The researchers are also assessing the possibility of constructing a luminescence scanner for marine sediment cores.

“The equipment used to measure luminescence sensitivity is sophisticated, but the laboratory procedure involved is relatively simple and fast, and the targeted minerals are more common in sediments coming from the continent. The method developed by Vinicius Mendes therefore promises to become routine from now on in the study of paleoprecipitation based on marine sediments in the areas of influence of major rivers,” Giannini said.

Source: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo [November 06, 2019]

Preserved pollen tells the history of North American floodplains

By: Thomas Schmitt Attorney on October 30, 2019 / comment : 0 Earth Science, Fossils, North America, Palaeoclimate, Palaeontology

Many of us think about pollen only when allergy season is upon us. However, for soil scientists like Matthew Ricker, pollen can be an invaluable tool. By tracking fossil pollen in soil, scientists can look back in time to better understand past land use and climate dynamics.

This floodplain in the southeastern US can preserve pollen for land use reconstruction [Credit: M.C. Ricker]

For example, when European settlers cleared forests in the eastern United States and planted crops, the pollen profile in soil changed. Ragweed and grass pollen became more common. Tree pollen became rarer.

But, the study of fossil pollen has been restricted to relatively few sites, usually those near lakes or bogs. In a new study, Ricker and colleagues report that fossil pollen can be a viable tool in floodplain soils.

"We show that floodplains can contain abundant preserved pollen," says Ricker, a scientist at North Carolina State University. "Therefore, floodplains can be useful sites to explore past climate and land uses."

The study also showed that certain soil properties, such as the concentration of organic matter, are positively correlated to pollen abundance. That's important because pollen extraction and counting is relatively expensive if sent to a commercial lab. "It can often cost hundreds to thousands of dollars," says Ricker. "If done in-house, it can be a very time-consuming process."

The new findings will allow scientists to use easy-to-measure soil properties to predict whether preserved pollen is likely to be found in specific soil layers. Soil properties that correlate with pollen abundance include organic matter concentration and carbon-to-nitrogen ratio.

For the study, the researchers collected a total of 117 soil samples. Study sites were spread across 18 locations in Connecticut, Rhode Island and Massachusetts.

The researchers measured several soil properties, including organic matter, particle size and iron content. "We measured these soil properties as proxies for processes known to impact the preservation of pollen in natural systems," says Ricker.

Fossil pollen can break down over time in soils with high levels of oxygen. "One of the challenges of working in floodplains is that these soils are usually well oxygenated," says Ricker. "That can result in greater pollen degradation."

Very wet landscapes, such as lakes and bogs, are good sites to find preserved pollen. "These sites lack oxygen, which limits microbial breakdown of pollen," explains Ricker.

However, many areas of the world lack natural lakes or bogs. "So, alternative landscapes - such as floodplains - need to be used for climate and land use reconstruction," he says.

Surprisingly, even within floodplains, up to 40% of soil layers contained no pollen. Other nearby horizons had abundant preserved pollen. "This highlights the importance of being able to use easily measured soil properties to estimate the likelihood of pollen presence in specific soil layers," says Ricker.

In addition to land use changes, fossil pollen can also help reconstruct past climate shifts. For example, certain soils in the eastern United States show shifts in pollen over the past 11,000 years.

After the last ice age, as glaciers retreated, pollen analysis showed changes in tree species, corresponding with the change in climate. Tundra sedges, characteristic of artic regions, were replaced by spruce trees - which we now find in the boreal forests of the subarctic regions. Then, as the climate continued to warm, mixed pine and deciduous forests (like we see today) became more common.

"Pollen can tell us how plants responded to past climate changes," says Ricker. That can allow scientists to better predict future shifts in plant species and agriculture as global temperatures continue to rise. "We hope researchers start to use floodplains more frequently to reconstruct land use and paleoclimate," he says.

Ricker is already looking beyond floodplains. "We are aiming to expand studying fossil pollen to other areas that have not been extensively studied," he explains.

The study is published in Soil Science Society of America Journal.

Source: American Society of Agronomy [October 30, 2019]

Two million-year-old ice provides snapshot of Earth's greenhouse gas history

By: Thomas Schmitt Attorney on October 30, 2019 / comment : 0 Antarctic, Climate Change, Earth Science, Palaeoclimate, Palaeontology

Two million-year old ice from Antarctica recently uncovered by a team of researchers provides a clearer picture into the connections between greenhouse gases and climate in ancient times and will help scientists understand future climate change.

Oregon State University Professor Ed Brook holding 2 million-year-old ice [Credit: Oregon State University]

In a paper published in Nature, a group of scientists used air trapped in the bubbles in ice as old as 2 million years to measure levels of the greenhouse gases carbon dioxide and methane. The group was led by John Higgins and Yuzhen Yan of Princeton University and Andrei Kurbatov of the University of Maine, and included Ed Brook at Oregon State University and Jeff Severinghaus at the University of California, San Diego.

This is the first time scientists were able to study an ice core that old. Previously, the oldest complete ice core provided data back to 800,000 years. Past studies using that core and others have shown that atmospheric carbon dioxide levels are directly linked to Antarctic and global temperature during the past 800,000 years. Prior to that, the connection between climate and carbon dioxide levels has not been as well understood. The paper published in Nature begins to change that.

During the past one million years the cycle of ice ages followed by warm periods occurred every 100,000 years. But between 2.8 million years ago and 1.2 million years ago, those cycles were shorter, about 40,000 years, and ice ages were less extreme.

The team that included Brook wanted to find out how carbon dioxide levels varied during that older time period, which until now was known only indirectly from the chemistry of sediments in the ocean and on land.

They found that the highest levels of carbon dioxide matched the levels in warm periods of more recent times. The lowest levels, however, did not reach the very low concentrations found in the ice ages of the last 800,000 years.


"One of the important results of this study is to show that carbon dioxide is linked to temperature in this earlier time period," Brook said.

This conclusion is based on studies of the chemistry of the ice, which provide an indication of temperature change in Antarctica at the same time as the carbon dioxide variations.

"That's an important baseline for understanding climate science and calibrating models that predict future change," Brook said.

The ice core with the 2 million-year-old ice comes from an area known as Allan Hills, which is about 130 miles from the U.S. Antarctic research station known as McMurdo Station. Ancient meteorites had been found on the surface in this area, leading scientists to believe there could be ancient ice in the ice sheet.

The core with the 2 million-year-old ice was drilled to a depth of 200 meters during the 2015-16 field season. It takes one to two weeks to drill and recover a core like that, and several cores were collected in the region.

The research team is on its way back to Allan Hills in the coming days for two months of additional work. They will be collecting larger quantities of the 2 million year old ice and searching for even older samples.

"We don't know the age limit in this area," Brook said "It could be much older in some places. That's why we're going back. Pushing beyond two million years would be pretty amazing".

Author: Sean Nealon | Source: Oregon State University [October 30, 2019]

Mutated ferns shed light on ancient mass extinction

By: Thomas Schmitt Attorney on October 28, 2019 / comment : 0 Earth Science, Fossils, Palaeoclimate, Palaeontology

Most researchers believe that the mass extinction 201 million years ago was caused by release of CO2 by volcanism with global warming as a consequence. Now, new data from fern spores suggest there might have been more to it than that.

Reconstruction of a Triassic Forest landscape [Credit: Jorge Gonzalez]

At the end of the Triassic around 201 million years ago, three out of four species on Earth disappeared. Up until now, scientists believed the cause of the catastrophe to be the onset of large-scale volcanism resulting in abrupt climate change. Now, new research suggest there might be several factors in play.

An international research team led by the Geological Survey of Denmark and Greenland (GEUS) show that increased concentrations of the toxic element mercury in the environment contributed to the mass extinction. They recently published their finds in Science Advances.

"By looking at fern spores in sediments from the mass extinction, it was evident that these ferns were negatively affected by the mercury levels. Since mercury is accumulated in the food chain, it seems likely that other species have suffered as well," says lead scientist Sofie Lindstrom.

"These results suggest that the end-Triassic mass extinction was not just caused by greenhouse gases from volcanoes causing global climate change, but that they also emitted toxins such as mercury wreaking havoc," she says.

The mercury-volcano link

One of the co-authors of the study, Professor Hamed Sanei from Aarhus University, has previously demonstrated increased mercury levels from volcanism in a Large Igneous Province (LIP) during the most severe mass extinction known, the end-Permian crisis, where perhaps as much as 95% of life on Earth disappeared. Volcanic activity in LIPs is thought to be responsible for four of the five largest mass extinctions during the last 500 million years.

"Prior to industrialism, volcanic activity was the major release mechanism of large amounts of mercury from the Earth's crust. That makes it possible to use mercury in sediments to trace major volcanic activity in the Earth's past and in extent tie the extinctions of fossil organisms to LIP volcanism," Hamed Sanei explains.

Other previous studies have shown elevated mercury concentrations in Triassic-Jurassic boundary sediments over a very large area stretching from Argentina to Greenland and from Nevada to Austria and that made the team curious about the impact on the end-Triassic event.

"We decided to examine whether mercury could have played a role," Hamed Sanei says.

Fern spores as indicators

When looking at fern spores from core samples dating from 201 million years ago at the end of the Triassic the team indeed saw a link between increased mercury levels and mutations in the spores.

Microscopy shows a normal fern spore and four mutated spores [Credit: Sofie Lindstrom, GEUS]

"During the mass extinction the mutated spores become increasingly common, and in turn the mutations get more and more severe. In some of my counts I found almost only mutated spores and no normal ones, which is very unusual," Sofie Lindstrom explains.

This rise in mutations happened during a period of increased volcanic activity in a LIP called the Central Atlantic Magmatic Province (CAMP) leading to rising mercury levels. Since mercury is a mutagenic toxin, its' increased distribution from the volcanic activity could help to explain the sudden deterioration of the ecosystem. Therefore, the fern spores could serve as indicators of increased mercury poisoning.

"This could hint to that the whole food chain might have been negatively affected," says Sofie Lindstrom.

Previous studies have found increased amounts of malformed pollen during the end-Permian mass extinction 252 million years ago, which like the end-Triassic crisis is blamed on volcanism. These studies have suggested that the mutations during the end-Permian crisis were caused by increased UVB radiation, due to thinning of the ozone layer from the volcanism.

"This could also be a possible explanation for the mutations that we see during the end-Triassic crisis," explains co-author Bas van de Schootbrugge from Utrecht University. "However, in our study we found only low amounts of mutated pollen, and during the end-Permian crisis spores do not appear to exhibit the same types of malformations registered during the end-Triassic mass extinction. This may indicate different causes for the plant mutations at the two events."

Not a simple explanation

However, it is important not to lock on to just one cause when looking at a global crisis such as the end-Triassic event, says Sofie Lindstrom:


"Generally, we prefer simple explanations to mass extinctions such as meteorite impacts or climate change, but I don't think it's that simple. As our study suggests there could very well be a cocktail effect of CO2 and global warming, toxins like mercury, and other factors as well."

Most of the prehistoric mass extinctions have indeed come in the wake of LIP volcanism, causing climate change and emitting toxic substances, Sofie Lindstrom says.

"Still, it is very difficult to say how big the importance of one factor is, because mass extinctions like this are very likely very complex events. Our study shows that mercury affected the ferns and likely also other plants, and it may also have had an impact on the entire food chain."

Present pollution looks like past volcanism

The researchers point out that their study of the end-Triassic mass extinction in many ways draws parallels to the current global situation.

"Our global society emits a lot of the same substances and greenhouse gases as these huge volcanic provinces did during these mass extinctions. Therefore, studies in what happened back then might help us to prevent it from happening again," says Sofie Lindstrom.

Source: Aarhus University [October 28, 2019]

300-year thinning may have predisposed Antarctic ice shelves to collapse

By: Thomas Schmitt Attorney on October 24, 2019 / comment : 0 Antarctic, Climate Change, Earth Science, Natural Heritage, Palaeoclimate

Ice shelves in the eastern Antarctic Peninsula may have been predisposed to collapse by hundreds years of thinning according to a study in Scientific Reports.

Credit: Bernhard Staehli/Shutterstock

To investigate past drivers of ice mass loss and its effect on the present, William Dickens and colleagues constructed a 6,250 year record of glacial meltwater discharge by analysing oxygen variants (isotopes) in single-celled algae preserved within a marine sediment core from the northeastern tip of the Antarctic Peninsula. Lower isotope values correspond to higher glacial discharge of fresh water.

The authors found that an increasing trend in glacial discharge occurred after the year 1400 reaching unprecedented levels after 1706. Another marked acceleration in glacial melting was observed after 1912. The findings suggest that ice shelves in this region have been thinning at an accelerating rate for approximately 300 years, which may predispose them to collapse as anthropogenic warming intensifies.

The authors suggest accelerated thinning was in part linked to shifts in the Southern Annular Mode that drove stronger westerly winds, atmospheric warming and ice shelf melting on the eastern Antarctic Peninsula, while also pulling warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. Similar, more frequent shifts in the Southern Annular Mode observed more recently may reflect the dominant influence of greenhouse gas levels and ozone depletion and lead to accelerated ice mass loss in the future.

Source: Nature Publishing Group [October 24, 2019]

Mystery solved: Ocean acidity in the last mass extinction

By: Thomas Schmitt Attorney on October 21, 2019 / comment : 0 Earth Science, Fossils, Geology, Palaeoclimate, Palaeontology

A new study led by Yale University confirms a long-held theory about the last great mass extinction event in history and how it affected Earth's oceans. The findings may also answer questions about how marine life eventually recovered.

A new study led by Yale University confirms a long-held theory about the last great mass extinction event in history and how it affected Earth's oceans. The findings may also answer questions about how marine life eventually recovered [Credit: Michael Henehan & Pincelli Hull]

The researchers say it is the first direct evidence that the Cretaceous-Paleogene extinction event 66 million years ago coincided with a sharp drop in the pH levels of the oceans -- which indicates a rise in ocean acidity.

The Cretaceous-Paleogene die-off, also known as the K-Pg mass extinction event, occurred when a meteor slammed into Earth at the end of the Cretaceous period. The impact and its aftereffects killed roughly 75% of the animal and plant species on the planet, including whole groups like the non-avian dinosaurs and ammonites.

"For years, people suggested there would have been a decrease in ocean pH because the meteor impact hit sulphur-rich rocks and caused the raining-out of sulphuric acid, but until now no one had any direct evidence to show this happened," said lead author Michael Henehan, a former Yale scientist who is now at GFZ German Research Centre for Geosciences in Potsdam, Germany.

Turns out all they had to do was look at the foraminifera: tiny plankton that grow a calcite shell and have an amazingly complete fossil record going back hundreds of millions of years. Analysis of the chemical composition of foraminifera fossils from before, during, and after the K-Pg event produced a wealth of data about changes in the marine environment over time. Specifically, measurements of boron isotopes in these shells allowed the Yale scientists to detect changes in the ocean's acidity.

Previous K-Pg research had shown that some marine calcifiers -- animal species that develop shells and skeletons from calcium carbonate -- were disproportionately wiped out in the mass extinction. The new study suggests that higher ocean acidity (lower pH) may have prevented these calcifiers from creating their shells. This was important, researchers note, because these calcifiers made up an important part of the first rung on the ocean food chain, supporting the rest of the ecosystem.

"The ocean acidification we observe could easily have been the trigger for mass extinction in the marine realm," said senior author Pincelli Hull, assistant professor of geology and geophysics at Yale.

The picture shows the Cretaceous-Palaeogene boundary at Geulhemmerberg in the Netherlands, where the boundary clay samples were taken. The event bed is clearly visible as a grey clay-rich layer, between the otherwise  yellowish carbonate sediments. It was thought to have been laid down during calm periods between strong storm events [Credit: Michael Henehan]

Meanwhile, the team's boron isotope analysis and modeling techniques may have reconciled some competing theories and puzzling facts relating to ocean life after the K-Pg event.

Why, for example, are carbon isotope signatures (analyzed from deep sea core samples) immediately after the K-Pg asteroid impact identical in fossil material from the sea floor and the surface waters, when normal carbon cycling in oceans should lead to different signatures?

One theory, the "Strangelove Ocean" theory, argued that for a time after K-Pg, the ocean was essentially dead and the normal carbon cycle just stopped. The problem with the "Strangelove Ocean," according to some researchers, is that many organisms on the sea floor that rely on food sinking from the ocean's surface continued unharmed across the K-Pg event -- an unlikely occurrence in a dead ocean. Another popular theory, called the "Living Ocean," suggested that K-Pg killed off larger plankton species, disrupting the carbon cycle by making it harder for organic matter to sink to the deep sea, but allowed for some marine life to survive.

The new study splits the difference. It says the oceans had a major, initial loss of species productivity -- by as much as 50% --followed by a transitional period in which marine life began to recover.

"In a way, we reconciled both of these 'Strangelove' and 'Living Ocean' scenarios," Henehan said. "Both of them were partially right; they just happened in sequence."

The new study also may have settled a question regarding ocean pH levels leading up to K-Pg. Some researchers have theorized that volcanic eruptions starting hundreds of thousands of years before K-Pg had progressively made Earth more prone to a mass extinction event. This should be reflected in a steady decline in ocean pH levels up until the extinction.

"What we can show is that there is no real signal of gradual pH decline in the ocean in the lead-up to K-Pg," Henehan said. "Our results do not support any major role for volcanic activity in priming the world for extinction."

One offshoot from the study may be its ability to help understand early Earth atmosphere and climate. The boron isotopes from foraminifera in this study are an excellent proxy for estimating carbon dioxide levels in the geological past, the authors said.

The study appears in the online edition of the journal Proceedings of the National Academy of Sciences.

Author: Jim Shelton | Source: Yale University [October 21, 2019]

New research suggests global ice age changed the face of the planet

By: Thomas Schmitt Attorney on October 15, 2019 / comment : 0 Earth Science, Geology, Palaeoclimate, Palaeontology

Curtin University researchers have discovered that a global ice age more than 600 million years ago dramatically altered the face of the planet, leaving a barren, flooded landscape and clear oceans.

Credit: NASA

The research, published in Terra Nova, examined how distinctive carbonate sedimentary rocks formed over the course of millions of years after the Snowball Earth.

The sedimentary rocks, much like the limestone in tropical oceans today, formed in oceans starved of sand and mud eroded from the land.

Lead author Ph.D. candidate Adam Nordsvan, from the School of Earth and Planetary Sciences at Curtin University, said the new research called into question previous suggestions that the formation of the characteristic rocks took place over a much shorter period of time.

"It was previously thought that these distinctive carbonate rocks were deposited over less than 10 thousand years, as the sea level rose when the ice that covered the entire globe melted, but we have shown that they were likely deposited over hundreds of thousands to millions of years following the sea-level rise," Mr Nordsvan said.

"There is already some evidence that suggested these rocks took a long time to form, but no one had been able to explain why this might have occurred. What is intriguing about the period following Snowball Earth is that the planet surface was essentially completely renovated. It appears that the extended glacial period removed all the beaches, deserts, rivers and floodplains, and reset important Earth systems that took millions of years to recover."

Co-author Dr. Milo Barham, also from Curtin's School of Earth and Planetary Sciences, said the findings may have important implications for the evolution of complex life.

"The melting of ice sheets after Snowball Earth caused a dramatic rise in sea level, ultimately flooding the continents, driving a remarkable retreat of shorelines and the development of clearer ocean water," Dr. Barham said.

"Researchers have long been aware that the timing of Snowball Earth and the development of more complex life seem to have coincided, but no one has really thought about how the oceans being starved of sediment might have helped ancient organisms thrive in the oceans."

Author: Lucien Wilkinson | Source: Curtin University [October 15, 2019]

Geologists reveal anoxia caused loss in biodiversity in ancient seas

By: Thomas Schmitt Attorney on October 15, 2019 / comment : 0 Biodiversity, Earth Science, Fossils, Geology, Oceans, Palaeoclimate, Palaeontology

Since 2016 the researchers of the Department of Geology at Tallinn University of Technology have been engaged in a research project analysing the causes of Silurian biodiversity crisis. The findings of the study are summarized in the article "Linking the progressive expansion of reducing conditions to a stepwise mass extinction event in the late Silurian oceans" published recently in the journal Geology.

Eurypterus, a common Upper Silurian eurypterid [Credit: WikiCommons]

The international research team included scientists from the University of Florida, Tallinn University of Technology, the University of South Carolina and Lund University. A member of the research group, Professor of Bedrock Geology at Tallinn University of Technology Olle Hints says, "Our research focused on the changes in the Earth's environmental conditions and biodiversity during the Silurian period, ca 425 million years ago".

Five big mass extinctions are known from the last half a billion years of Earth's history. For example, 250 million years ago, at the end of the Permian period, 95% of the plant and animal species of that time disappeared in a short time. Today, too, we are facing major biodiversity loss and knowledge of past extinction events enables us to assess its potential course and consequences. In severe biotic crisis in the Silurian, known as the Lau Event, extinction of nearly 25% of the marine species took place. The scientists set out to determine the chronology and possible mechanisms of the event.

Information on the biota and environment of the distant past is best preserved in marine sedimentary rocks. Study of fossils enables us to document the evolution and biodiversity dynamics. Fossils also play a crucial role in constructing the geologic time scale and dating rocks. Only if precise time scale is available can it be investigated how and why environmental conditions changed and how this influenced the biosphere. For example, the atoms making up the minerals of limestone provide the evidence of the chemical composition of the ancient ocean and the atmosphere and their evolution. By combining paleontological and geochemical data, conclusions can be drawn about the relationships between biota and the environment.

In this work, the researchers focused on the study of carbon, sulphur and thallium isotopes. "What makes our research unique is that for the first time, thallium isotopes were analysed from the Paleozoic rocks indicating changes in redox conditions of the global ocean. The rock samples analysed were collected from Latvia and the island of Gotland, which once were part of the Baltic paleosea. In this region, rocks have altered very little over the last 500 million years, and thus the original information is still present. The Baltic region is a rewarding natural laboratory for geologists - there are very few places in the world where the rocky archives of the Paleozoic era are so well preserved," professor Hints says.

PhD student Chelsie N. Bowman and Professor Seth A. Young from the Florida State University collecting samples from the 425 million years old Earth history archives that are deposited at Tallinn University of Technology [Credit: Olle Hints]

This fact ensures that the results of the analyses are reliable. Alongside the unique rock samples, the cutting-edge analytical equipment that makes it possible to measure stable isotope ratios from small amounts of rock powders played a crucial role. Most of the geochemical analyses were carried out by Chelsie N. Bowman and Professor Seth A. Young in the National High Magnetic Field Laboratory at Florida State University, one of the most modern analytical facilities for this kind of research in the world.

The results of the analyses showed for the first time that the extinction of late Silurian species began with a progressive decrease in the oxygen content in the ocean and culminated when anoxic and likely sulphidic water masses reached the shallow seas. This change was relatively slow - it took probably 175-270 k.y. from the the initial phase until the crisis reached its peak. Among the first organisms to suffer from the environmental change were there vertebrates, represented by fish and conodonts, whose diversity decreased by nearly 70%. The environmental change had also a major impact on plankton, although it occurred somewhat later.

Professor Hints said, "What are the benefits of studying such a distant past? On the one hand, we can confirm that changes in marine redox conditions and oxygen levels have catastrophic consequences for the life in oceans and that the vertebrates are the first to be affected by the changes." This is a highly topical issue since measurements as well as models indicate progressive expansion of oceanic anoxia in the present-day oceans. Geological data prove that if a system is shifted out of equilibrium, it will take hopelessly long time from human perspective in order to return to the pre-event conditions.

"On the other hand, we can learn from this particular example, as well as from the Earth history in general, that every crisis creates the basis for evolutionary innovations, allowing better adaptable organisms to survive and new ones to emerge," Professor Hints says.

Source: Estonian Research Council [October 15, 2019]

Ice core source discovery adds to study of volcanic activity, climate system interactions

By: Thomas Schmitt Attorney on October 10, 2019 / comment : 0 Antarctic, Climate Change, Earth Science, Geology, Palaeoclimate, Palaeontology

A new discovery by University of Maine researchers that challenges the established volcanic source of particles found in an ice core from the South Pole adds to the global record of volcanism and is relevant to several   research disciplines.

The Ice Drilling Design and Operations (IDDO) group at the University of Wisconsin-Madison designed and built the South Pole Ice Core (SPICE) drilling system, called the Intermediate Depth Drill. Based on a Danish drill called the Hans-Taunsen drill, the Intermediate Depth Drill was purpose-built for coring 1,500 meters of ice. The ice cores collected at this depth (from the South Pole) contain atmospheric gases from the past 40,000 years,  the time of transition from the last ice age to the present warm climate [Credit: T.J. Fudge]

Understanding how the Earth's volcanic activity interacts with the climate system, as well as volcanic hazard mitigation studies and reconstructions of how past volcanic events have affected human history often rely on detailed records of past volcanic eruptions. Unfortunately, in many parts of the world, historical records are sporadic, short and not well documented, according to Andrei Kurbatov, associate professor at the University of Maine School of Earth and Climate Sciences and Climate Change Institute.

In the last decade, Kurbatov and Martin Yates, electron beam laboratory manager and instructor of Earth sciences at UMaine, in collaboration with Nelia Dunbar and Nels Iverson from the New Mexico Institute of Mining and Technology, developed a method of extracting volcanic ash particles from ice core samples to measure their geochemical composition.

The new methodology provides additional means to refine the history of global volcanism captured in polar ice core records, according to Kurbatov.

Laura Hartman, a graduate student at the CCI, used the methodology while examining microscopic volcanic ash particles in ice core samples from Antarctica's South Pole. Hartman was advised by Kurbatov and Earth and Climate Sciences assistant professor Alicia Cruz-Uribe.

She found several particles from a volcanic interval that in the last three decades was attributed to a volcanic eruption from the Kuwae volcanic center in Vanuatu.

Hartman determined the geochemical signatures of the particles, that provide a unique volcanic source fingerprint, and compared the signatures with the known composition of Kuwae volcanic products.

She discovered the composition was similar to volcanic products from the South American volcano Reclus, not Kuwae.

"The discovery challenges the established volcanic source for one of the largest ice core sulfate signals from the last millennium," Kurbatov says. "The new source location will impact how climate models calculate atmospheric loading and ultimately will guide how climate models determine the impact of this volcanic event on the climate system."

The relatively young, unknown explosive volcanic eruption from Reclus volcano, located close to several national parks in South America, provides new important constraints for regional volcanic hazards assessments and air-traffic safety, Kurbatov says. The new data also question the existing paradigm on long-range transport of ultrafine volcanic particles in the atmosphere.

With funding from the National Science Foundation, Kurbatov and his team plan to continue to explore volcanic deposits in the South Pole ice core using the new methodology to further refine the global record of volcanism.

The study was published in Scientific Reports.

Source: University of Maine [October 10, 2019]