Antarctic ice core sheds new light on how the last ice age ended

Brian Bencivengo, assistant curator of the National Ice Core Laboratory, in Lakewood, Colo., holds a one-meter-long section of the West Antarctic Ice Sheet (WAIS) Divide Ice Core. -  Geoffrey Hargreaves, National Science Foundation
Brian Bencivengo, assistant curator of the National Ice Core Laboratory, in Lakewood, Colo., holds a one-meter-long section of the West Antarctic Ice Sheet (WAIS) Divide Ice Core. – Geoffrey Hargreaves, National Science Foundation

Analysis of an ice core taken by the National Science Foundation- (NSF) funded West Antarctic Ice Sheet (WAIS) Divide drilling project reveals that warming in Antarctica began about 22,000 years ago, a few thousand years earlier than suggested by previous records.

This timing shows that West Antarctica did not “wait for a cue” from the Northern Hemisphere to start warming, as scientists had previously supposed.

For more than a century scientists have known that Earth’s ice ages are caused by the wobbling of the planet’s orbit, which changes its orientation to the sun and affects the amount of sunlight reaching higher latitudes.

The Northern Hemisphere’s last ice age ended about 20,000 years ago, and most evidence had indicated that the ice age in the Southern Hemisphere ended about 2,000 years later, suggesting that the South was responding to warming in the North.

But research published online Aug. 14 in the journal Nature shows that Antarctic warming began at least two, and perhaps four, millennia earlier than previously thought.

Most previous evidence for Antarctic climate change had come from ice cores drilled in East Antarctica, the highest and coldest part of the continent. However, a U.S.-led research team studying the West Antarctic core found that warming there was well underway 20,000 years ago.

WAIS Divide is a large-scale and multi-year glaciology project supported by the U.S. Antarctic Program (USAP), which NSF manages. Through USAP, NSF coordinates all U.S. science on the southernmost continent and aboard vessels in the Southern Ocean and provides the necessary logistics to make the science possible.

The WAIS Divide site is in an area where there is little horizontal flow of the ice, so the data are known to be from a location that remained consistent over long periods.

The WAIS Divide ice core is more than two miles deep and covers a period stretching back 68,000 years, though so far data have been analyzed only from layers going back 30,000 years. Near the surface, one meter of snow is equal to a year of accumulation, but at greater depths the annual layers are compressed to centimeters of ice.

“Sometimes we think of Antarctica as this passive continent waiting for other things to act on it. But here it is showing changes before it ‘knows’ what the North is doing,” said T.J. Fudge, a University of Washington doctoral student in Earth and Space Sciences and lead corresponding author of the Nature paper. Fudge’s 41 co-authors are other members of the WAIS project.

Fudge identified the annual layers by running two electrodes along the ice core to measure higher electrical conductivity associated with each summer season. Evidence of greater warming turned up in layers associated with 18,000 to 22,000 years ago, the beginning of the last deglaciation.

“This deglaciation is the last big climate change that we’re able to go back and investigate,” he said. “It teaches us about how our climate system works.”

West Antarctica is separated from East Antarctica by a major mountain range. East Antarctica has a substantially higher elevation and tends to be much colder, though there is recent evidence that it too is warming.

Rapid warming in West Antarctica in recent decades has been documented in previous research by Eric Steig, a professor of Earth and Space Sciences at the University of Washington who serves on Fudge’s doctoral committee and whose laboratory produced the oxygen isotope data used in the Nature paper. The new data confirm that West Antarctica’s climate is more strongly influenced by regional conditions in the Southern Ocean than East Antarctica is.

“It’s not surprising that West Antarctica is showing something different from East Antarctica on long time scales, but we didn’t have direct evidence for that before,” Fudge said.

He noted that the warming in West Antarctica 20,000 years ago is not explained by a change in the sun’s intensity. Instead, how the sun’s energy was distributed over the region was a much bigger factor. It not only warmed the ice sheet but also warmed the Southern Ocean that surrounds Antarctica, particularly during summer months when more sea ice melting could take place.

Changes in Earth’s orbit today are not an important factor in the rapid warming that has been observed recently, he added. “Earth’s orbit changes on the scale of thousands of years, but carbon dioxide today is changing on the scale of decades so climate change is happening much faster today,” Fudge said.

Julie Palais, the Antarctic Glaciology Program director in NSF’s Division of Polar Programs, said new findings will help scientists to “better understand not only what happened at the end of the last ice age but it should also help inform our understanding of what might be happening as the climate warms and conditions begin to change in and around the Antarctic continent.”

She added, “West Antarctica is currently experiencing some of the largest changes on the continent, such as the large calving events in the Amundsen Sea Embayment linked to warm ocean currents undercutting the outlet glaciers. The recent changes are consistent with the WAIS Divide results that show West Antarctica is sensitive to changes in ocean conditions in the past.”

Mountaintop mining pollution has distinct chemical signatures

Three elements commonly found at elevated levels in an Appalachian river polluted by runoff from mountaintop coal mining have distinctive chemistries that can be traced back to their source, according to a Duke University-led study.

The distinctive chemistries of sulfur, carbon and strontium provide scientists with new, more accurate ways to track pollution from mountaintop mining sites and to distinguish it from contamination from other sources.

“Essentially, we found that these elements have unique isotopic fingerprints, meaning we can use them as diagnostic tools to quantify mountaintop mining’s relative contribution to contamination in a watershed,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment.

The newly identified tracers will be especially useful in watersheds with more than one source of potential contamination, he said. “Because they allow us to distinguish if contaminants are coming from natural sources, fracking and shale gas development, coal mining, coal ash disposal, or other causes.”

Vengosh and his team’s findings were published today in the online edition of the peer-reviewed journal Environmental Science & Technology.

The researchers measured the chemical and isotopic compositions of water samples collected monthly from 23 locations along West Virginia’s Upper Mud River and its tributaries between May and December 2012.

They found that the isotopic signatures of sulfur (in sulfate), carbon (in dissolved inorganic carbon) and strontium from water samples collected from tributaries adjacent to mountaintop mining sites are distinguishable from those collected from unaffected upstream waters. They also found that the strontium isotope ratio is a sensitive tracer for selenium contamination, one of the major pollutants of mountaintop mining.

In mountaintop mining, companies use explosives and heavy machinery to clear away surface rocks and extract shallow deposits of high-quality coal. The companies typically dispose of the waste rock in adjacent valleys, where they bury existing headwater streams.

Previous studies by the Duke team and others have shown that runoff from these “valley fills” contains elevated levels of salts and selenium, a known fish toxin. The contamination can persist and accumulate in downstream waters for decades after active mining stops and the fills are reclaimed.

By conducting tests that simulated the natural leaching of contaminants from local rocks, Vengosh and his team were able to characterize the chemistry of the different geological formations that end up as waste rock in these fills. They found significant differences in strontium isotope ratios and selenium concentrations in streams flowing from reclaimed valley fills versus those flowing from active fills.

“This helps us further pinpoint the source of contamination by linking it directly to the type of rocks in the valley fills,” Vengosh said.

The Upper Mud River flows through sparsely populated areas of southern West Virginia as a headwater stream. For about 10 kilometers, the river passes through the Hobet 21 surface mining complex, which has been active since the 1970s and is among the largest in the Appalachian coalfields.

Earth orbit changes key to Antarctic warming that ended last ice age

A West Antarctica Ice Sheet Divide project researcher stands in a snow pit next to an ice core with data from 68,000 years ago. The prominent line across the middle of the ice separates one year's ice and snow accumulation from the next year's. -  Kendrick Taylor/Desert Research Institute
A West Antarctica Ice Sheet Divide project researcher stands in a snow pit next to an ice core with data from 68,000 years ago. The prominent line across the middle of the ice separates one year’s ice and snow accumulation from the next year’s. – Kendrick Taylor/Desert Research Institute

For more than a century scientists have known that Earth’s ice ages are caused by the wobbling of the planet’s orbit, which changes its orientation to the sun and affects the amount of sunlight reaching higher latitudes, particularly the polar regions.

The Northern Hemisphere’s last ice age ended about 20,000 years ago, and most evidence has indicated that the ice age in the Southern Hemisphere ended about 2,000 years later, suggesting that the south was responding to warming in the north.

But new research published online Aug. 14 in Nature shows that Antarctic warming began at least two, and perhaps four, millennia earlier than previously thought.

Most previous evidence for Antarctic climate change has come from ice cores drilled in East Antarctica, the highest and coldest part of the continent. However, a U.S.-led research team studying a new ice core from West Antarctica found that warming there was well under way 20,000 years ago.

“Sometimes we think of Antarctica as this passive continent waiting for other things to act on it. But here it is showing changes before it ‘knows’ what the north is doing,” said T.J. Fudge, a University of Washington doctoral student in Earth and space sciences and lead corresponding author of the Nature paper.

Co-authors are 41 other members of the West Antarctic Ice Sheet Divide project, which is primarily funded by the National Science Foundation.

The findings come from a detailed examination of an ice core taken from the West Antarctic Ice Sheet Divide, an area where there is little horizontal flow of the ice so the data are known to be from a location that remained consistent over long periods.

The ice core is more than 2 miles deep and covers 68,000 years, though so far data have been analyzed only from layers going back 30,000 years. Near the surface, 1 meter of ice covers one year, but at greater depths the annual layers are compressed to centimeters.

Fudge identified the annual layers by running two electrodes along the ice core to measure higher electrical conductivity associated with each summer season. Evidence of greater warming turned up in layers associated with 18,000 to 22,000 years ago, the beginning of the last deglaciation.

“This deglaciation is the last big climate change that that we’re able to go back and investigate,” he said. “It teaches us about how our climate system works.”

West Antarctica is separated from East Antarctica by a major mountain range. East Antarctica has a substantially higher elevation and tends to be much colder, though there is recent evidence that it too is warming.

Rapid warming in West Antarctica in recent decades has been documented in previous research by Eric Steig, a UW professor of Earth and space sciences who serves on Fudge’s doctoral committee and whose laboratory produced the oxygen isotope data used in the Nature paper. The new data confirm that West Antarctica’s climate is more strongly influenced by regional conditions in the Southern Ocean than East Antarctica is.

“It’s not surprising that West Antarctica is showing something different from East Antarctica on long time scales, but we didn’t have evidence for that before,” Fudge said.

He noted that the warming in West Antarctica 20,000 years ago is not explained by a change in the sun’s intensity. Instead, how the sun’s energy was distributed over the region was a much bigger factor. It not only warmed the ice sheet but also warmed the Southern Ocean that surrounds Antarctica, particularly during summer months when more sea ice melting could take place.

Changes in Earth’s orbit today are not an important factor in the rapid warming that has been observed recently, he added.

“Earth’s orbit changes on the scale of thousands of years, but carbon dioxide today is changing on the scale of decades so climate change is happening much faster today,” Fudge said.

Melting water’s lubricating effect on glaciers has only ‘minor’ role in future sea-level rise

Scientists had feared that melt-water which trickles down through the ice could dramatically speed up the movement of glaciers as it acts as a lubricant between the ice and the ground it moves over.

But in a paper published today in PNAS, a team led by scientists from the University of Bristol found it is likely to have a minor role in sea-level rise compared with other effects like iceberg production and surface melt.

The results of computer modelling, based on fieldwork observations in Greenland, revealed that by the year 2200 lubrication would only add a maximum of 8mm to sea-level rise – less than 5 per cent of the total projected contribution from the Greenland ice sheet.

In fact in some of their simulations the lubricating effect had a negative impact on sea-level rise – in other words it alone could lead to a lowering of sea-level (ignoring the other major factors).

Lead author, Dr Sarah Shannon, from the University of Bristol, said: “This is an important step forward in our understanding of the factors that control sea-level rise from the Greenland Ice Sheet. Our results show that melt-water enhanced lubrication will have a minor contribution to future sea-level rise. Future mass loss will be governed by changes in surface melt-water runoff or iceberg calving.”

Previous studies of the effects of melt-water on the speed of ice movement had assumed the water created cavities at the bottom of ice masses. These cavities lifted the ice slightly and acted as a lubricant, speeding up flow.

This theory had led scientists to think that increased melt-water would lead directly to more lubrication and a consequent speeding up of the ice flow.

But the Bristol-led study took into account recent observations that indicate larger amounts of melt-water may form channels beneath the ice that drain the water away, reducing the water’s lubricating effect. The scientists found that no matter whether more melt-water increases or decreases the speed of ice flow, the effect on sea level is small.

Dr Shannon said: “We found that the melt-water would lead to a redistribution of the ice, but not necessarily to an increase in flow.”

The findings are part of research undertaken through the European funded ice2sea programme. Earlier research from the programme has shown that changes in surface melting of the ice sheet will be the major factor in sea-level rise contributions from Greenland.

Professor David Vaughan, ice2sea co-ordinator based at the British Antarctic Survey in Cambridge, said: “This is important work but it’s no reason for complacency. While this work shows that the process of lubrication of ice flow by surface melting is rather insignificant, our projections are still that Greenland will be a major source of future sea-level rise. As we have reported earlier this year, run-off of surface melt water directly into the ocean and increased iceberg calving are likely to dominate.”

Scientists look into Earth’s ‘deep time’ to predict future effects of climate change

This is a time spiral: Looking back through time to understand future climate change. -  NASA
This is a time spiral: Looking back through time to understand future climate change. – NASA

Climate change alters the way in which species interact with one another–a reality that applies not just to today or to the future, but also to the past, according to a paper published by a team of researchers in this week’s issue of the journal Science.

“We found that, at all time scales, climate change can alter biotic interactions in very complex ways,” said paleoecologist Jessica Blois of the University of California, Merced, the paper’s lead author.

“If we don’t incorporate this information when we’re anticipating future changes, we’re missing a big piece of the puzzle.”

Blois asked for input from researchers who study “deep time,” or the very distant past, as well as those who study the present, to help make predictions about what the future holds for life on Earth as climate shifts.

Co-authors of the paper are Phoebe Zarnetske of Yale University, Matthew Fitzpatrick of the University of Maryland, and Seth Finnegan of the University of California, Berkeley.

“Climate change and other human influences are altering Earth’s living systems in big ways, such as changes in growing seasons and the spread of invasive species,” said Alan Tessier, program director in the National Science Foundation’s (NSF) Division of Environmental Biology, which co-funded the research with NSF’s Division of Earth Sciences.

“This paper highlights the value of using information about past episodes of rapid change from Earth’s history to help predict future changes to our planet’s ecosystems.”

Scientists are seeing responses in many species, Blois said, including plants that have never been found in certain climates–such as palms in Sweden–and animals like pikas moving to higher elevations as their habitats grow too warm.

“The worry is that the rate of current and future climate change is more than species can handle,” Blois said.

The researchers are studying how species interactions may change between predators and prey, and between plants and pollinators, and how to translate data from the past and present into future models.

“One of the most compelling current questions science can ask is how ecosystems will respond to climate change,” said Lisa Boush, program director in NSF’s Division of Earth Sciences.

“These researchers address this using the fossil record and its rich history,” said Boush. “They show that climate change has altered biological interactions in the past, driving extinction, evolution and the distribution of species.

“Their study allows us to better understand how modern-day climate change might influence the future of biological systems and the rate at which that change will occur.”

While more research is needed, Blois said, changes can be observed today as well as in the past, although it’s harder to gather information from incomplete fossil records.

Looking back, there were big changes at the end of major climate change periods, such as the end of the last Ice Age when large herbivores went extinct.

Without those mega-eaters to keep certain plants at bay, new communities of flora developed, most of which in turn are now gone.

“People used to think climate was the major driver of all these changes,” Blois said, “but it’s not just climate. It’s also extinction of the megafauna, changes in the frequency of natural fires, and expansion of human populations. They’re all linked.”

People are comfortable with the way things have been, said Blois. “We’ve known where to plant crops, for example, and where to find water.”

Now we need to know how to respond, she said, to changes that are already happening–and to those coming in the near future.

Simulating flow from volcanoes and oil spills

Some time around 37,000 BCE a massive volcano erupted in the Campanian region of Italy, blanketing much of Europe with ash, stunting plant growth and possibly dooming the Neanderthals. While our prehistoric relatives had no way to know the ash cloud was coming, a recent study provides a new tool that may have predicted what path volcanic debris would take.

“This paper provides a model for the pattern of the ash cloud if the wind is blowing past an eruption of a given size,” said Peter Baines, a scientist at the University of Melbourne in Australia who did the study. He published his work in the journal Physics of Fluids.

Volcanic eruptions are an example of what Baines calls an “intrusion.” Other examples include exhaust rising from a chimney, sewage flowing into the ocean, and the oil spilling underwater in the 2010 Deepwater Horizon disaster. In all these events, a fluid rises into a density-stratified environment like the atmosphere or the ocean. As the fluid rises, it is pushed by winds or currents, and this crossflow can cause the intruding fluid to disperse far from its origin.

Scientists have previously modeled intrusions into a completely calm environment, but before Baines nobody had ever attempted to introduce the effect of crosswinds, a necessary step toward making such models more realistic and useful.

Predicting Ash and Oil Flows

Baines thinks his work could be used to estimate how much ash is pouring out of a volcano, or how fast oil is gushing from a hole in the sea floor.

Baines is now working with volcanologists in Britain to apply his model to historic eruptions like the Campanian event and the catastrophic Toba supereruption that occurred around 73,000 years ago in Indonesia. The scientists are hoping to use ash deposits from these volcanoes to develop a sharper picture of the amount and speed of the ejected material.

“Most of what we know about prehistoric eruptions is from sedimentary records,” said Baines. “You then have to try to infer what the nature of the eruption was, when this is the only information you’ve got.”

Baines said his model can also help forecast the deposition patterns of future eruptions. And that should give us a big leg up on the poor Neanderthals.

How the Model Works

To understand how intrusions work in the presence of crossflows, Baines developed what he calls a semi-analytical model. He began with fluid dynamics equations, and then used numerical calculations to arrive at approximate solutions for specifics combinations of source flow and spread rates, and crosswind speed. He found that, under normal wind speeds, the intruding fluid reached a maximum thickness at a certain distance upstream from the source, and thinned in the downstream direction. The distance to the upstream stagnation point depended much more on the rate of source flow than the crossflow speed.

California seafloor mapping reveals hidden treasures

This is a kelp greenling fish swimming above a seafloor of mixed gravel, cobble and rock outcrop with scattered shell. Fish is approx. 20 cm (8 inches) long. Image acquired 1 km (0.62 miles) offshore Half Moon Bay, Calif., at a depth of 14 meters (46 ft). Also in the image are encrusting sponges, red algae (seaweed), and orange cup corals. -  US Geological Survey
This is a kelp greenling fish swimming above a seafloor of mixed gravel, cobble and rock outcrop with scattered shell. Fish is approx. 20 cm (8 inches) long. Image acquired 1 km (0.62 miles) offshore Half Moon Bay, Calif., at a depth of 14 meters (46 ft). Also in the image are encrusting sponges, red algae (seaweed), and orange cup corals. – US Geological Survey

Science and technology have peeled back a veil of water just offshore of California, revealing the hidden seafloor in unprecedented detail. New imagery, specialized undersea maps, and a wealth of data from along the California coast are now available. Three new products in an ongoing series were released today by the U.S. Geological Survey – a map set for the area offshore of Carpinteria, a catalog of data layers for geographic information systems, and a collection of videos and photos of the seafloor in state waters along the entire California coast.

“A program of this vast scope can’t be accomplished by any one organization. By working with other government agencies, universities, and private industry the USGS could fully leverage all its resources,” said USGS Pacific Region Director Mark Sogge. “Each organization brings to the table a unique and complementary set of resources, skills, and know-how.”

The USGS is a key partner in the California Seafloor Mapping Program, a large, unique, and historically ambitious collaboration between state and federal agencies, academia, and the private sector to create a comprehensive base-map series for all of California’s ocean waters. Scientists are collecting sonar data, video and photographic imagery, seismic surveys, and bottom-sediment data to create a series of maps of seafloor bathymetry, habitats, geology, and more, in order to inform coastal managers and planners, government entities, and researchers. With the new maps, decision makers and elected officials can better design and monitor marine reserves, evaluate ocean energy potential, understand ecosystem dynamics, recognize earthquake and tsunami hazards, regulate offshore development, and improve maritime safety.

“The Ocean Protection Council recognized early on that seafloor habitats and geology were a fundamental data gap in ocean management,” said California’s Secretary for Natural Resources and Ocean Protection Council Chair John Laird. “After an impressive effort by many partners to collect and interpret the data, the maps being produced now are providing pioneering science that’s changing the way we manage our oceans.”

“Our collaboration with the state and more than 15 other partners is critical to the success of this program. We’ve come together to make the maps, and then to use them. We all like to say that you can’t manage it, monitor it, or model it if you don’t know what the ‘it’ is, and our seafloor mapping gives that important ‘it’ to the entire coastal management and research community,” said the USGS’ lead researcher on this project, Sam Johnson.

USGS California Seafloor Mapping Program Map Series

The heart of the USGS California Seafloor Mapping Program effort is a series of map sets. To date, three sets have been published, including the most recent one released today covering the area “Offshore of Carpinteria,” USGS Scientific Investigations Map 3261. Each of the map sets includes 10 or more sheets, illustrating different features of the seafloor, including geology, bathymetry, habitats, and geology within the three-nautical-mile limit of California’s state waters. The maps are created through the collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. Fourteen other map sets are being formatted for publication; the California State Waters Map Series is planned to comprise 83 such seafloor map sets spanning the entire coast of California.

USGS California Seafloor Mapping Program Data Catalog


Underlying the series of published seafloor map sets are large geospatial digital files, including bathymetry, acoustic backscatter, offshore geology and geomorphology, faults, folds, potential marine habitats, seafloor character, sediment thickness, visual observations of bottom habitat from video, and more. These data sets are now available through a new California State Waters Map Series Data Catalog for users to create their own maps or engage in further investigations of the seafloor. The catalog, USGS Data Series 781, provides all GIS data layers associated with the map sets published by the California Seafloor Mapping Program. Data will be continually added to the data series catalog as new seafloor map sets are published. All data files can be viewed and downloaded at no charge. As the California Seafloor Mapping Program continues to produce new maps, they -and all the background data- will be made available online.

USGS California Seafloor Mapping Program Video & Photo Portal


The unique set of seafloor images (video and still photography) collected by the USGS from the U.S.-Mexico border to the Oregon state line is now available via a new California Seafloor Mapping Program Video and Photograph Portal. More than 500 hours of video and 87,000 photographs were collected and are now posted in the online portal for viewing. Scientists are using these data to ground-truth their interpretations of sonar data, to provide a framework for understanding seafloor ecosystems, and to create maps of seafloor materials and habitats. The video and photo portal is based on an interactive map, allowing users to zoom into a particular area, and see the imagery available. The video and still photographs of the same locations are displayed simultaneously, just as they were acquired along the track-line.

Greenland ice is melting — also from below

The Greenland ice sheet is melting from below, caused by a high heat flow from the mantle into the lithosphere. This influence is very variable spatially and has its origin in an exceptionally thin lithosphere. Consequently, there is an increased heat flow from the mantle and a complex interplay between this geothermal heating and the Greenland ice sheet. The international research initiative IceGeoHeat led by the GFZ German Research Centre for Geosciences establishes in the current online issue of Nature Geoscience (Vol 6, August 11, 2013) that this effect cannot be neglected when modeling the ice sheet as part of a climate study.

The continental ice sheets play a central role in climate. Interactions and feedback processes between ice and temperature rise are complex and still a current research topic. The Greenland ice sheet loses about 227 gigatonnes of ice per year and contributes about 0.7 millimeters to the currently observed mean sea level change of about 3 mm per year. Existing model calculations, however, were based on a consideration of the ice cap and considered the effect of the lithosphere, i.e. the earth’s crust and upper mantle, too simplistic and primarily mechanical: the ice presses the crust down due to its weight. GFZ scientists Alexey Petrunin and Irina Rogozhina have now coupled an ice/climate model with a thermo-mechanical model for the Greenland lithosphere. “We have run the model over a simulated period of three million years, and taken into account measurements from ice cores and independent magnetic and seismic data”, says Petrunin. “Our model calculations are in good agreement with the measurements. Both the thickness of the ice sheet as well as the temperature at its base are depicted very accurately. “

The model can even explain the difference in temperature measured at two adjacent drill holes: the thickness of the Greenland lithosphere and thus the geothermal heat flow varies greatly in narrow confines.

What does this mean for climate modeling? “The temperature at the base of the ice, and therefore the current dynamics of the Greenland ice sheet is the result of the interaction between the heat flow from the earth’s interior and the temperature changes associated with glacial cycles,” explains corresponding author Irina Rogozhina (GFZ) who initiated IceGeoHeat. “We found areas where the ice melts at the base next to other areas where the base is extremely cold.”

The current climate is influenced by processes that go far back into the history of Earth: the Greenland lithosphere is 2.8 to 1.7 billion years old and is only about 70 to 80 kilometers thick under Central Greenland. It remains to be explored why it is so exceptionally thin. It turns out, however, that the coupling of models of ice dynamics with thermo-mechanical models of the solid earth allows a more accurate view of the processes that are melting the Greenland ice.

The ‘genetics of sand’ may shed new light on evolutionary process over millions of years

This image shows a close-up of planktonic foraminifera. -  The University of Southampton
This image shows a close-up of planktonic foraminifera. – The University of Southampton

An evolutionary ecologist at the University of Southampton, is using ‘grains of sand’ to understand more about the process of evolution. Dr Thomas Ezard is using the fossils of microscopic aquatic creatures called planktonic foraminifera, often less than a millimetre in size, which can be found in all of the world’s oceans. The remains of their shells now resemble grains of sand to the naked eye and date back hundreds of millions of years.

A new paper by Dr Ezard, published today (9 August 2013) in the journal Methods in Ecology & Evolution, opens the debate on the best way to understand how new species come into existence (speciation). The debate concerns whether fossil records such as those of the planktonic foraminifera, contain useful evidence of speciation over and above the molecular study of evolution. Molecular evolution traditionally uses evidence from species that are alive today to determine what their ancestors may have looked like, whereas this new research promotes the importance of using fossil records in conjunction with the molecular models.

Dr Ezard, from Biological Sciences and the Institute for Life Sciences at Southampton, says: “Because planktonic foraminifera have been around for many millions of years and rocks containing groups of their species can be dated precisely, we can use their fossils to see evidence of how species evolve over time. We can also see how differences between individual members of species develop and, in theory, how a new species comes into existence.

“The controversial hypothesis we test is that the processes leading to a new species coming into existence provoke a short, sharp burst of rapid genetic change. This is controversial because it is very difficult to detect these new species coming into existence accurately without the fossil data; it is more commonly determined from assumptions made from the study of species alive today using molecular evidence.”

In the paper, Dr Ezard and colleagues, Dr Gavin Thomas from the University of Sheffield and Professor Andy Purvis from Imperial College London, highlight the importance of using fossil and molecular evidence to study evolution. Their intention is that the use of both types of data will become widespread in the future study of evolution. To support his research, Dr Ezard has received an Advanced Fellowship from the Natural Environment Research Council (NERC) to study how variation among individuals generates variation among species. He will conduct this interdisciplinary research in the Centre for Biological Sciences at the University, in close collaboration with researchers from Ocean and Earth Science at the National Oceanography Centre, Southampton.

Ice ages only thanks to feedback

Ice ages and warm periods have alternated fairly regularly in the Earth’s history: the Earth’s climate cools roughly every 100,000 years, with vast areas of North America, Europe and Asia being buried under thick ice sheets. Eventually, the pendulum swings back: it gets warmer and the ice masses melt. While geologists and climate physicists found solid evidence of this 100,000-year cycle in glacial moraines, marine sediments and arctic ice, until now they were unable to find a plausible explanation for it.

Using computer simulations, a Japanese, Swiss and American team including Heinz Blatter, an emeritus professor of physical climatology at ETH Zurich, has now managed to demonstrate that the ice-age/warm-period interchange depends heavily on the alternating influence of continental ice sheets and climate.

“If an entire continent is covered in a layer of ice that is 2,000 to 3,000 metres thick, the topography is completely different,” says Blatter, explaining this feedback effect. “This and the different albedo of glacial ice compared to ice-free earth lead to considerable changes in the surface temperature and the air circulation in the atmosphere.” Moreover, large-scale glaciation also alters the sea level and therefore the ocean currents, which also affects the climate.

Weak effect with a strong impact


As the scientists from Tokyo University, ETH Zurich and Columbia University demonstrated in their paper published in the journal Nature, these feedback effects between the Earth and the climate occur on top of other known mechanisms. It has long been clear that the climate is greatly influenced by insolation on long-term time scales. Because the Earth’s rotation and its orbit around the sun periodically change slightly, the insolation also varies. If you examine this variation in detail, different overlapping cycles of around 20,000, 40,000 and 100,000 years are recognisable (see box).

Given the fact that the 100,000-year insolation cycle is comparatively weak, scientists could not easily explain the prominent 100,000-year-cycle of the ice ages with this information alone. With the aid of the feedback effects, however, this is now possible.

Simulating the ice and climate

The researchers obtained their results from a comprehensive computer model, where they combined an ice-sheet simulation with an existing climate model, which enabled them to calculate the glaciation of the northern hemisphere for the last 400,000 years. The model not only takes the astronomical parameter values, ground topography and the physical flow properties of glacial ice into account but also especially the climate and feedback effects. “It’s the first time that the glaciation of the entire northern hemisphere has been simulated with a climate model that includes all the major aspects,” says Blatter.

Using the model, the researchers were also able to explain why ice ages always begin slowly and end relatively quickly. The ice-age ice masses accumulate over tens of thousands of years and recede within the space of a few thousand years. Now we know why: it is not only the surface temperature and precipitation that determine whether an ice sheet grows or shrinks. Due to the aforementioned feedback effects, its fate also depends on its size. “The larger the ice sheet, the colder the climate has to be to preserve it,” says Blatter. In the case of smaller continental ice sheets that are still forming, periods with a warmer climate are less likely to melt them. It is a different story with a large ice sheet that stretches into lower geographic latitudes: a comparatively brief warm spell of a few thousand years can be enough to cause an ice sheet to melt and herald the end of an ice age.

Box: The Milankovitch cycles


The explanation for the cyclical alternation of ice and warm periods stems from Serbian mathematician Milutin Milankovitch (1879-1958), who calculated the changes in the Earth’s orbit and the resulting insolation on Earth, thus becoming the first to describe that the cyclical changes in insolation are the result of an overlapping of a whole series of cycles: the tilt of the Earth’s axis fluctuates by around two degrees in a 41,000-year cycle. Moreover, the Earth’s axis gyrates in a cycle of 26,000 years, much like a spinning top. Finally, the Earth’s elliptical orbit around the sun changes in a cycle of around 100,000 years in two respects: on the one hand, it changes from a weaker elliptical (circular) form into a stronger one. On the other hand, the axis of this ellipsis turns in the plane of the Earth’s orbit. The spinning of the Earth’s axis and the elliptical rotation of the axes cause the day on which the Earth is closest to the sun (perihelion) to migrate through the calendar year in a cycle of around 20,000 years: currently, it is at the beginning of January; in around 10,000 years, however, it will be at the beginning of July.

Based on his calculations, in 1941 Milankovitch postulated that insolation in the summer characterises the ice and warm periods at sixty-five degrees north, a theory that was rejected by the science community during his lifetime. From the 1970s, however, it gradually became clearer that it essentially coincides with the climate archives in marine sediments and ice cores. Nowadays, Milankovitch’s theory is widely accepted. “Milankovitch’s idea that insolation determines the ice ages was right in principle,” says Blatter. “However, science soon recognised that additional feedback effects in the climate system were necessary to explain ice ages. We are now able to name and identify these effects accurately.”