Ice cores yield rich history of climate change

A researcher inspects a freshly-drilled ice core. -  Kendrick Taylor, Chief Scientist, WAIS Divide Ice Core Project Research Professor, Desert Research Institute, Nevada System of Higher Education
A researcher inspects a freshly-drilled ice core. – Kendrick Taylor, Chief Scientist, WAIS Divide Ice Core Project Research Professor, Desert Research Institute, Nevada System of Higher Education

On Friday, Jan. 28 in Antarctica, a research team investigating the last 100,000 years of Earth’s climate history reached an important milestone completing the main ice core to a depth of 3,331 meters (10,928 feet) at West Antarctic Ice Sheet Divide (WAIS). The project will be completed over the next two years with some additional coring and borehole logging to obtain additional information and samples of the ice for the study of the climate record contained in the core.

As part of the project, begun six years ago, the team, funded by the National Science Foundation (NSF), has been drilling deep into the ice at the WAIS Divide site and recovering and analyzing ice cores for clues about how changes in the concentration of greenhouse gases in the atmosphere have influenced the Earth’s climate over time.

Friday’s milestone was reached at a depth of 3,331 meters–about two miles deep–creating the deepest ice core ever drilled by the U.S. and the second deepest ice core ever drilled by any group, second only to the ice core drilled at Russia’s Vostok Station as part of a joint French/U.S./Russian collaboration in the 1990s.

“By improving our understanding of how natural changes in greenhouse gas influenced climate in the past, the science community will be able to do a better job of predicting future climate changes caused by the emissions of greenhouse gases by human activity,” said Kendrick Taylor, chief scientist for the WAIS Divide Ice Core Project.

The drilling site is about 966 kilometers (600 miles) from the South Pole, at an ice divide (which is analogous to a watershed divide) in West Antarctica, where the ice is flowing out to the sea in opposing directions.

“This location was selected because it is the best place on the planet to determine how greenhouse gases have changed during the last 100,000 years” said Taylor. Since it began, the WAIS Divide Ice Core Project has continuously collected ice from the surface down to a depth of 3,331 meters. The ice at this depth fell as snow about 100,000 years ago. The high annual snowfall at the site enables individual annual layers of snowfall to be identified and counted (much like counting tree rings) back to about 40,000 years. Below that, the layers become too compressed to allow annual layers to be resolved. Scientists hope for at least decadal resolution to this point, sufficient for the science goals to be achieved.

The ice cores are 13-centimeter (5-inch) diameter cylinders of ice collected from deep in the ice sheet. Over time, the ice has formed when snow was compacted at the surface by subsequent snowfall. The compacted snow contains dust, chemicals and atmospheric gases, which are trapped in the ice.

The dust and other impurities in the ice are indicators of past climate, and the gas contained in air bubbles is a sample of the ancient atmosphere. The deeper the ice, the further back in time measurements can be made.

In addition to measuring what the atmospheric concentrations of carbon dioxide, methane and other gases were in the past, the research team can also determine what the surface air temperature was in the past by studying changes in the isotopic composition of the water that makes up the ice. The past atmospheric concentrations of the gases krypton and xenon are used to determine what the average temperature of the ocean was in the past.

The 13-centimeter diameter 3,331-meter-long ice core is cut into 1 meter (3 feet)-long pieces of ice and sent by ship and refrigerated truck to the NSF National Ice Core Laboratory in Denver. The ice is cut into smaller samples and sent to 27 investigators around the U.S., who make the measurements.

“Previous ice cores have shown that the current level of greenhouse gases is greater now than at any time during the last 650,000 years, and that concentrations today are increasing at the fastest rate,” said Taylor. “This increase is caused by human activity and is forcing the climate into a configuration that no human has ever experienced.”

The WAIS Divide Ice Core Project is specifically investigating the small timing offsets between past changes in the atmospheric concentration of greenhouse gases and changes in temperature. By understanding these timing offsets, the research team can determine the role that changes in ocean circulation had in the release of carbon dioxide from the ocean and how an increase in carbon dioxide in the atmosphere warms the planet.

The drilling ceased 100 meters (328 feet) above the contact between the ice and the underlying rock, to avoid contaminating a possible water layer at the ice-rock contact. The basal water system may consist of water-saturated, ground-up rock, and has not been exposed to the earth’s surface for millions of years. It may harbor a unique and pristine biological environment that the U.S. Antarctic Program does not wish to contaminate.

The core taken by the WAIS Ice Core Drilling Project is crucial for fine-tuning the researchers’ understanding of how the oceans, atmosphere and climate interact during climate changes. A Danish-led team recovered an ice core from Greenland this past summer with similar time resolution to the WAIS Divide record. The two cores provide an opportunity to compare the response of the northern and southern hemispheres to climate changes. The Greenland ice core cannot be used to study changes in the atmospheric concentration of carbon dioxide because there is too much dust in the Greenland ice, which decomposes and releases non-atmospheric carbon dioxide into the ice.

NSF’s Office of Polar Programs funds this research, primarily through its Antarctic Glaciology Program.

“We still have two more field seasons of work to complete the project, and reaching this goal should allow us to complete the project on schedule,” said Julie Palais, program director. “In addition, we are hoping to get as long a record as possible from this site, and getting all of the ice we planned on this year will allow the science community to do the work that they are funded to do. Drilling the ice core is just the first step in the process, albeit a very important one.”

A clearer picture of how rivers and deltas develop

This is a schematic model of a river-coast system. -  Geleynse et al
This is a schematic model of a river-coast system. – Geleynse et al

By adding information about the subsoil to an existing sedimentation and erosion model, researchers at Delft University of Technology (TU Delft, The Netherlands) have obtained a clearer picture of how rivers and deltas develop over time. A better understanding of the interaction between the subsoil and flow processes in a river-delta system can play a key role in civil engineering (delta management), but also in geology (especially in the work of reservoir geologists). Nathanaël Geleynse et al. recently published in the journals Geophysical Research Letters and Earth and Planetary Science Letters.

Model

Many factors are involved in how a river behaves and the creation of a river delta. Firstly, of course, there is the river itself. What kind of material does it transport to the delta? Does this material consist of small particles (clay) or larger particles (sand)? But other important factors include the extent of the tidal differences at the coast and the height of the waves whipped up by the wind. In this study, researchers at TU Delft are working together with Deltares and making use of the institute’s computer models (Delft3D software). These models already take a large number of variables into account. Geleynse et al. have now supplemented them with information on the subsoil. It transpires that this variable also exerts a significant influence on how the river behaves and the closely related process of delta formation.

Room for the River

The extra dimension that Geleynse et al. have added to the model is important to delta management, among other things. If – as the Delta Commission recommends – we should be creating “Room for the River”, it is important to know what a river will do with that space. Nathanaël Geleynse explains: “Existing data do not enable us to give ready-made answers to specific management questions … nature is not so easily tamed … but they do offer plausible explanations for the patterns and shapes we see on the surface. The flow system carries the signature of the subsoil, something we were relatively unaware of until now. Our model provides ample scope for further development and for studying various scenarios in the current structure.”

Geological information


River management is all about short-term and possible future scenarios. But the model developed by Geleynse et al. also offers greater insight into how a river/delta has developed over thousands of years. What might the subsoil have looked like and – a key factor for the oil industry – where might you expect to find oil reserves and what might their geometrical characteristics be? In combination with data from a limited number of core samples and other local measurements, the model can give a more detailed picture of the area in question than was possible until now.

The link between the creation of the delta and the structure of the delta subsoil is also of interest to engineers who wish to build there. Hundreds of millions of people across the globe live in deltas and these urban deltas are only expected to grow in the decades to come.

The water temperature in the subtropical Atlantic falls due to wind action

This is the argo profiler. -  Argo-Spain
This is the argo profiler. – Argo-Spain

The temperature of water situated in the subtropical Atlantic experienced a drop of 0.15ºC between 1998 and 2006. This has been revealed by a study led by the IEO (Spanish Oceanography Institute) which suggests that circulation caused by wind could be responsible for this “unusual” behavior.

Whilst the water temperature in this area, situated along the 24.5º north parallel, from the African coast to the Caribbean, rose by 0.27ºC between 1957 and 1998, researchers have recorded a drop of 0.15ºC in the same area between 1998 and 2006.

“In the ocean there are very pronounced cycles of change, and therefore, changes like those which took place in the coordinates analysed can reoccur in any location and at any time”, Pedro Joaquín Vélez Belchí, main author and researcher for the IEO’s Canarian Oceanography Centre, stresses to SINC.

According to the study, which was published recently in the Journal of Physical Oceanography, this phenomenon should not be linked to climate change. “The ocean’s natural variability mechanisms are more significant than we thought”, declares Vélez Belchí. The team is considering various hypotheses to explain the change in temperatures.

For the scientists, this cooling could be due to “circulation forced by the wind”. “Changes in the global structure of winds in the north Atlantic cause oscillations on the ocean’s surface layer which can be felt up to 2000 metres deep”, the expert points out.

However, the scientists discard the hypothesis of thawing despite the fact that some water masses, originating in the Antarctic and the Mediterranean, have an influence in the area analysed. The temperature drop “should have been observed clearly in the areas close to the North Pole”, maintains Vélez Belchí. And this was not the case.

The scientists measured the temperature and salinity of three oceanic layers: waters from the thermocline (300-800 metres), surface ocean (600-1800 metres) and intermediate waters (800-1.800 metros). The salinity recorded “similar” behaviour, as it is always linked to the temperature.

A new image of the ocean

The research team combined two methodologies: measurements using stations carried out from oceanographic research vessels, and the Argo network. With this network, consisting of 3000 indicators in all the oceans, “a new image of the surface ocean” is obtained. Spain is taking part in the Argo-Spain programme.

Through the new system, the scientists developed synthetic sections for each year (carried out from the laboratory with data from the Argo network’s buoys), and analysed the annual variability for 2005, 2006, 2007 and 2008. “Between 2006 and 2008 there were no significant changes”, the scientist declares.

As part of the Expedición Malaspina 2010, the team will go on a new expedition to the same area in the coming weeks. “The work is pioneering in verifying how the Argo network can be of use for large-scale studies into oceanic variability”, concludes Vélez Belchí.

Warming North Atlantic water tied to heating Arctic, according to new study

Photo of the German research vessel Maria S. Merian moving  through sea ice in Fram Strait northwest of Svalbard. The research team discovered the water there was the warmest in at least 2,000 years, which has implications for a warming and melting Arctic. -  Credit: Nicolas van Nieuwenhove (IFM-GEOMAR, Kiel)
Photo of the German research vessel Maria S. Merian moving through sea ice in Fram Strait northwest of Svalbard. The research team discovered the water there was the warmest in at least 2,000 years, which has implications for a warming and melting Arctic. – Credit: Nicolas van Nieuwenhove (IFM-GEOMAR, Kiel)

The temperatures of North Atlantic Ocean water flowing north into the Arctic Ocean adjacent to Greenland — the warmest water in at least 2,000 years — are likely related to the amplification of global warming in the Arctic, says a new international study involving the University of Colorado Boulder.

Led by Robert Spielhagen of the Academy of Sciences, Humanities and Literature in Mainz, Germany, the study showed that water from the Fram Strait that runs between Greenland and Svalbard — an archipelago constituting the northernmost part of Norway — has warmed roughly 3.5 degrees Fahrenheit in the past century. The Fram Strait water temperatures today are about 2.5 degrees F warmer than during the Medieval Warm Period, which heated the North Atlantic from roughly 900 to 1300 and affected the climate in Northern Europe and northern North America.

The team believes that the rapid warming of the Arctic and recent decrease in Arctic sea ice extent are tied to the enhanced heat transfer from the North Atlantic Ocean, said Spielhagen. According to CU-Boulder’s National Snow and Ice Data Center, the total loss of Arctic sea ice extent from 1979 to 2009 was an area larger than the state of Alaska, and some scientists there believe the Arctic will become ice-free during the summers within the next several decades.

“Such a warming of the Atlantic water in the Fram Strait is significantly different from all climate variations in the last 2,000 years,” said Spielhagen, also of the Leibniz Institute of Marine Sciences in Keil, Germany.

According to study co-author Thomas Marchitto, a fellow at CU-Boulder’s Institute of Arctic and Alpine Research, the new observations are crucial for putting the current warming trend of the North Atlantic in the proper context.

“We know that the Arctic is the most sensitive region on the Earth when it comes to warming, but there has been some question about how unusual the current Arctic warming is compared to the natural variability of the last thousand years,” said Marchitto, also an associate professor in CU-Boulder’s geological sciences department. “We found that modern Fram Strait water temperatures are well outside the natural bounds.”

A paper on the study will be published in the Jan. 28 issue of Science. The study was supported by the German Research Foundation; the Academy of Sciences, Humanities and Literature in Mainz, Germany; and the Norwegian Research Council.

Other study co-authors included Kirstin Werner and Evguenia Kandiano of the Leibniz Institute of Marine Sciences, Steffen Sorensen, Katarzyna Zamelczyk, Katrine Husum and Morten Hald from the University of Tromso in Norway and Gereon Budeus of the Alfred Wegener Institute of Polar and Marine Research in Bremerhaven, Germany.

Since continuous meteorological and oceanographic data for the Fram Strait reach back only 150 years, the team drilled ocean sediment cores dating back 2,000 years to determine past water temperatures. The researchers used microscopic, shelled protozoan organisms called foraminifera — which prefer specific water temperatures at depths of roughly 150 to 650 feet — as tiny thermometers.

In addition, the team used a second, independent method that involved analyzing the chemical composition of the foraminifera shells to reconstruct past water temperatures in the Fram Strait, said Marchitto.

The Fram Strait branch of the North Atlantic Current is the major carrier of oceanic heat to the Arctic Ocean. In the eastern part of the strait, relatively warm and salty water enters the Arctic. Fed by the Gulf Stream Current, the North Atlantic Current provides ice-free conditions adjacent to Svalbard even in winter, said Marchitto.

“Cold seawater is critical for the formation of sea ice, which helps to cool the planet by reflecting sunlight back to space,” said Marchitto. “Sea ice also allows Arctic air temperatures to be very cold by forming an insulating blanket over the ocean. Warmer waters could lead to major sea ice loss and drastic changes for the Arctic.”

The rate of Arctic sea ice decline appears to be accelerating due to positive feedbacks between the ice, the Arctic Ocean and the atmosphere, Marchitto said. As Arctic temperatures rise, summer ice cover declines, more solar heat is absorbed by the ocean and additional ice melts. Warmer water may delay freezing in the fall, leading to thinner ice cover in winter and spring, making the sea ice more vulnerable to melting during the next summer.

Air temperatures in Greenland have risen roughly 7 degrees F in the past several decades, thought to be due primarily to an increase in Earth’s greenhouse gases, according to CU-Boulder scientists.

“We must assume that the accelerated decrease of the Arctic sea ice cover and the warming of the ocean and atmosphere of the Arctic measured in recent decades are in part related to an increased heat transfer from the Atlantic,” said Spielhagen.

Geobiologists uncover links between ancient climate change and mass extinction

This is rock strata on Anticosti Island, Quebec, Canada, one of the sites from which the researchers collected fossils. -  Woody Fischer
This is rock strata on Anticosti Island, Quebec, Canada, one of the sites from which the researchers collected fossils. – Woody Fischer

About 450 million years ago, Earth suffered the second-largest mass extinction in its history-the Late Ordovician mass extinction, during which more than 75 percent of marine species died. Exactly what caused this tremendous loss in biodiversity remains a mystery, but now a team led by researchers at the California Institute of Technology (Caltech) has discovered new details supporting the idea that the mass extinction was linked to a cooling climate.

“While it’s been known for a long time that the mass extinction is intimately tied to climate change, the precise mechanism is unclear,” says Seth Finnegan, a postdoctoral researcher at Caltech and the first author of the paper published online in Science on January 27. The mass extinction coincided with a glacial period, during which global temperatures cooled and the planet saw a marked increase in glaciers. At this time, North America was on the equator, while most of the other continents formed a supercontinent known as Gondwana that stretched from the equator to the South Pole.

By using a new method to measure ancient temperatures, the researchers have uncovered clues about the timing and magnitude of the glaciation and how it affected ocean temperatures near the equator. “Our observations imply a climate system distinct from anything we know about over the last 100 million years,” says Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor.

The fact that the extinction struck during a glacial period, when huge ice sheets covered much of what’s now Africa and South America, makes it especially difficult to evaluate the role of climate. “One of the biggest sources of uncertainty in studying the paleoclimate record is that it’s very hard to differentiate between changes in temperature and changes in the size of continental ice sheets,” Finnegan says. Both factors could have played a role in causing the mass extinction: with more water frozen in ice sheets, the world’s sea levels would have been lower, reducing the availability of shallow water as a marine habitat. But differentiating between the two effects is a challenge because until now, the best method for measuring ancient temperatures has also been affected by the size of ice sheets.

The conventional method for determining ancient temperature requires measuring the ratios of oxygen isotopes in minerals precipitated from seawater. The ratios depend on both temperature and the concentration of isotopes in the ocean, so the ratios reveal the temperature only if the isotopic concentration of seawater is known. But ice sheets preferentially lock up one isotope, which reduces its concentration in the ocean. Since no one knows how big the ice sheets were, and these ancient oceans are no longer available for scientists to analyze, it’s hard to determine this isotopic concentration. As a result of this “ice-volume effect,” there hasn’t been a reliable way to know exactly how warm or cold it was during these glacial periods.

But by using a new type of paleothermometer developed in the laboratory of John Eiler, Sharp Professor of Geology and professor of geochemistry at Caltech, the researchers have determined the average temperatures during the Late Ordovician-marking the first time scientists have been able to overcome the ice-volume effect for a glacial episode that happened hundreds of millions of years ago. To make their measurements, the researchers analyzed the chemistry of fossilized marine animal shells collected from Quebec, Canada, and from the midwestern United States.

The Eiler lab’s method, which does not rely on the isotopic concentration of the oceans, measures temperature by looking at the “clumpiness” of heavy isotopes found in fossils. Higher temperatures cause the isotopes to bond in a more random fashion, while low temperatures lead to more clumping.

“By providing independent information on ocean temperature, this new method allows us to know the isotopic composition of 450-million-year-old seawater,” Finnegan says. “Using that information, we can estimate the size of continental ice sheets through this glaciation.” And with a clearer idea of how much ice there was, the researchers can learn more about what Ordovician climate was like-and how it might have stressed marine ecosystems and led to the extinction.

“We have found that elevated rates of climate change coincided with the mass extinction,” says Aradhna Tripati, a coauthor from UCLA and visiting researcher in geochemistry at Caltech.

The team discovered that even though tropical ocean temperatures were higher than they are now, moderately sized glaciers still existed near the poles before and after the mass extinction. But during the extinction intervals, glaciation peaked. Tropical surface waters cooled by five degrees, and the ice sheets on Gondwana grew to be as large as 150 million cubic kilometers-bigger than the glaciers that covered Antarctica and most of the Northern Hemisphere during the modern era’s last ice age 20,000 years ago.

“Our study strengthens the case for a direct link between climate change and extinction,” Finnegan says. “Although polar glaciers existed for several million years, they only caused cooling of the tropical oceans during the short interval that coincides with the main pulse of mass extinction.”

‘Hidden plumbing’ helps slow Greenland ice flow

Hotter summers may not be as catastrophic for the Greenland ice sheet as previously feared and may actually slow down the flow of glaciers, according to new research.

A letter published in Nature on 27 January explains how increased melting in warmer years causes the internal drainage system of the ice sheet to ‘adapt’ and accommodate more melt-water, without speeding up the flow of ice toward the oceans. The findings have important implications for future assessments of global sea level rise.

The Greenland ice sheet covers roughly 80% of the surface of the island and contains enough water to raise sea levels by 7 metres if it were to melt completely. Rising temperatures in the Arctic in recent years have caused the ice sheet to shrink, prompting fears that it may be close to a ‘tipping point’ of no return.

Some of the ice loss has been attributed to the speed-up of glaciers due to increased surface melting. Each summer, warmer temperatures cause ice at the surface of the sheet to melt. This water then runs down a series of channels to the base of the glacier where it acts as a lubricant, allowing the ice sheet to flow rapidly across the bedrock toward the sea.

Summertime acceleration of ice flow has proved difficult for scientists to model, leading to uncertainties in projections of future sea level rise.

“It had been thought that more surface melting would cause the ice sheet to speed up and retreat faster, but our study suggests that the opposite could in fact be true,” said Professor Andrew Shepherd from the University of Leeds School of Earth and Environment, who led the study.

“If that’s the case, increases in surface melting expected over the 21st century may have no affect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”

The researchers used satellite observations of six landlocked glaciers in south-west Greenland, acquired by the European Space Agency, to study how ice flow develops in years of markedly different melting.

Although the initial speed-up of ice was similar in all years, slowdown occurred sooner in the warmest ones. The authors suggest that in these years the abundance of melt-water triggers an early switch in the plumbing at the base of the ice, causing a pressure drop that leads to reduced ice speeds.

This behavior is similar to that of mountain glaciers, where the summertime speed-up of ice reduces once melt-water can drain efficiently.