Arctic ice at low point compared to recent geologic history

Leonid Polyak
Leonid Polyak

Less ice covers the Arctic today than at any time in recent geologic history.

That’s the conclusion of an international group of researchers, who have compiled the first comprehensive history of Arctic ice.

For decades, scientists have strived to collect sediment cores from the difficult-to-access Arctic Ocean floor, to discover what the Arctic was like in the past. Their most recent goal: to bring a long-term perspective to the ice loss we see today.

Now, in an upcoming issue of Quarternary Science Reviews, a team led by Ohio State University has re-examined the data from past and ongoing studies — nearly 300 in all — and combined them to form a big-picture view of the pole’s climate history stretching back millions of years.

“The ice loss that we see today — the ice loss that started in the early 20th Century and sped up during the last 30 years — appears to be unmatched over at least the last few thousand years,” said Leonid Polyak, a research scientist at Byrd Polar Research Center at Ohio State University. Polyak is lead author of the paper and a preceding report that he and his coauthors prepared for the U.S. Climate Change Science Program.

Satellites can provide detailed measures of how much ice is covering the pole right now, but sediment cores are like fossils of the ocean’s history, he explained.

“Sediment cores are essentially a record of sediments that settled at the sea floor, layer by layer, and they record the conditions of the ocean system during the time they settled. When we look carefully at various chemical and biological components of the sediment, and how the sediment is distributed — then, with certain skills and luck, we can reconstruct the conditions at the time the sediment was deposited.”

For example, scientists can search for a biochemical marker that is tied to certain species of algae that live only in ice. If that marker is present in the sediment, then that location was likely covered in ice at the time. Scientists call such markers “proxies” for the thing they actually want to measure — in this case, the geographic extent of the ice in the past.

While knowing the loss of surface area of the ice is important, Polyak says that this work can’t yet reveal an even more important fact: how the total volume of ice — thickness as well as surface area — has changed over time.

“Underneath the surface, the ice can be thick or thin. The newest satellite techniques and field observations allow us to see that the volume of ice is shrinking much faster than its area today. The picture is very troubling. We are losing ice very fast,” he said.

“Maybe sometime down the road we’ll develop proxies for the ice thickness. Right now, just looking at ice extent is very difficult.”

To review and combine the data from hundreds of studies, he and his cohorts had to combine information on many different proxies as well as modern observations. They searched for patterns in the proxy data that fit together like pieces of a puzzle.

Their conclusion: the current extent of Arctic ice is at its lowest point for at least the last few thousand years.

As scientists pull more sediment cores from the Arctic, Polyak and his collaborators want to understand more details of the past ice extent and to push this knowledge further back in time.

During the summer of 2011, they hope to draw cores from beneath the Chukchi Sea, just north of the Bering Strait between Alaska and Siberia. The currents emanating from the northern Pacific Ocean bring heat that may play an important role in melting the ice across the Arctic, so Polyak expects that the history of this location will prove very important. He hopes to drill cores that date back thousands of years at the Chukchi Sea margin, providing a detailed history of interaction between oceanic currents and ice.

“Later on in this cruise, when we venture into the more central Arctic Ocean, we will aim at harvesting cores that go back even farther,” he said. “If we could go as far back as a million years, that would be perfect.”

Flow in Earth’s mantle moves mountains

    * Dynamic topography (gray surface) and mantle flow (vectors) as predicted by a geodynamic model for the Mediterranean      * E–MAIL     * PRINT     * SHAR
* Dynamic topography (gray surface) and mantle flow (vectors) as predicted by a geodynamic model for the Mediterranean * E–MAIL * PRINT * SHAR

If tectonic plate collisions cause volcanic eruptions, as every fifth grader knows, why do some volcanoes erupt far from a plate boundary?

A study in Nature suggests that volcanoes and mountains in the Mediterranean can grow from the pressure of the semi-liquid mantle pushing on Earth’s crust from below.

“The rise and subsidence of different points of the earth is not restricted to the exact locations of the plate boundary. You can get tectonic activity away from a plate boundary,” said study co-author Thorsten Becker of the University of Southern California.

The study connects mantle flow to uplift and volcanism in “mobile belts”: crustal fragments floating between continental plates.

The model should be able to predict uplift and likely volcanic hotspots in other mobile belts, such as the North American Cordillera (including the Rocky Mountains and Sierra Nevada) and the Himalayas.

“We have a tool to be able to answer these questions,” Becker said.

Scientists previously had suggested a connection between mantle upwelling and volcanism, Becker said. The Nature study is the first to propose the connection in mobile belts.

Becker and collaborator Claudio Faccenna of the University of Rome believe that small-scale convection in the mantle is partly responsible for shaping mobile belts.

Mantle that sinks at the plate boundary flows back up farther away, pushing on the crust and causing uplift and crustal motions detectable by global positioning system, the authors found.

The slow but inexorable motions can move mountains – both gradually and through earthquakes or eruptions.

The study identified two mountain ranges raised almost entirely by mantle flow, according to the authors: the southern Meseta Central plateau in Spain and the Massif Central in France.

Becker and Faccenna inferred mantle flow from interpreting seismic mantle tomography, which provides a picture of the deep earth just like a CAT scan, using seismic waves instead of X-rays.

Assuming that the speed of the waves depends mainly on the temperature of crust and mantle (waves travel slower through warmer matter), the authors used temperature differences to model the direction of mantle convection.

Regions of upward flow, as predicted by the model, mostly coincided with uplift or volcanic activity away from plate boundaries.

“Mantle circulation ? appears more important than previously thought, and generates vigorous upwellings even far from the subduction zone,” the authors wrote.

Temperature and salt levels of the Western Mediterranean are on the increase

Temperatures and salt levels of the Western Mediterranean are on the increase. -  Manuel Vargas-Yáñez
Temperatures and salt levels of the Western Mediterranean are on the increase. – Manuel Vargas-Yáñez

Spanish scientists have analyzed the temperature and salt levels of the Western Mediterranean Sea between 1943 and 2000 to study the evolution of each variable. Their research shows that, since at least the 1940s, the deep water has become progressively hotter and saltier, and that, since the 1990s, this process has speeded up.

Each year the temperature of the deep layer of the Western Mediterranean increases by 0.002ºC, and its salt levels increase by 0.001 units of salinity. These changes, although minimal from year to year, have been continuously and constantly occurring at a faster pace since the 1990s.

The results are consistent, “but to confirm this accelerating trend, we need to monitor it over the years to come”, Manuel Vargas-Yáñez, main author of the study and researcher at the Oceanic Centre of Malaga of the Spanish Institute of Oceanography (IEO), assures SINC.

In their study, published in the Journal of Geophysical Research, the researchers analysed the temperature and salt levels of the three layers of the Mediterranean Sea: the upper layer (from the surface to 150-200 metres deep with water that enters from the Atlantic), the middle layer (from 200 to 600 metres deep with water from the eastern Mediterranean that enters the western basin via the Strait of Sicily), and the deep layer (from 600 metres to the sea bed with water from the western Mediterranean).

“These layers, especially the deep one, take up a huge volume, and raising its temperature each year by one thousandth of a degree requires an enormous amount of heat”, the researcher points out.

The team has also observed an increase in the salt level and the temperature of the middle layer of the sea. This has not been clearly observed in the upper layer, “but it can be deduced from the heating of the deep water and from studies done by other teams and our current research projects”, Vargas-Yáñez states.

We need to monitor the sea

The research team compiled the data about temperature and salt levels by means of the MEDATLAS (Mediterranean Hydrographic Atlas) database, and using the IEO monitoring programmes. All the data were collected from the Alboran Sea, the Catalan-Balearic Sea, the Gulf of Lion, the Ligurian Sea, the Tyrrhenian Sea and the Algerian Basin, between 1943 and 2000.

“We need to support the networks that already exist and build new ones to monitor the sea. Only then will we be able to detect, in a reliable and effective way, the changes taking place in the sea”, Vargas-Yáñez concludes.

Experts gather as volcanic dust settles

Following the eruption of Iceland’s Eyjafjallajoekull volcano that spewed huge amounts of ash and grounded numerous flights, more than 50 experts from around the world gathered at a workshop organized by ESA and EUMETSAT to discuss what has been learned and identify future opportunities for volcanic ash monitoring.

The experts included meteorologists, ground-based, air-borne and Earth-observation specialists and modelers. While scientists and researchers shared information about the unique eruption, monitoring capabilities, modeling and validation techniques, the Volcanic Ash Advisory Centres (VAAC) explained their role and expectations of the scientific community.

Fred Prata, Senior Scientist for Atmosphere and Climate Change at the Norwegian Institute for Air Research, said: “Satellite data are extremely important for volcanic eruptions because they can occur anywhere, anytime, so you need a measurement system that can see the entire globe all the time.

“One missing part of the story is the vertical profile, which lidars in space can provide. ESA will launch a couple of scientific lidar missions in the future, ADM-Aeolus and EarthCARE.”

The crucial role of infrared instruments was emphasized in several talks, highlighting and EUMETSAT’s upcoming Meteosat Third Generation satellites, being developed by ESA.

“Infrared instruments are absolutely vital because they do not require sunlight so we can see volcanic emissions day or night. They also use a band between 8 and 12 microns, which is key because the particles that cause aviation problems are micron-sized,” Prata said.

The presentations on ground-based observations and modeling showed very good consistency, also with satellite observations, and it was well recognized all data and information needs to be combined for the best result.

“There has been an unprecedented amount of ground data collected by the European community on this ash cloud, providing a great opportunity to learn more about data-collection processes,” said David Schneider, Research Geophysicist at the US Geological Survey, Alaska Volcano Observatory.

Philippe Husson, Aviation Weather Forecast Deputy and the Toulouse VAAC Manager for Meteo France, explained that observation requirements of volcanic ash evolved during the eruption to include numbers and expressed the impact this will have on VAACS.

“In the past, we used qualitative results to depict hazards, but now that we have been provided with ash threshold values we will probably be required to provide concentration maps with absolute numbers. As we must go from qualitative to quantitative information about ash concentrations and the distribution and size of particles, we need satellites to provide numbers,” he said.

Husson said the threshold figures are not definitive and are being reassessed by aviation authorities. Several factors will be considered, including trial results of real ash in real engines, engine types and rates of ingestion, as flying 10 minutes in high concentration could be equivalent to six hours in weak concentration.

“As the decision was taken quickly there was not a lot of input from scientists, but now there is time to consult them to find out what confidence we can have in the numbers,” he added.

A set of recommendations were outlined at the workshop. These will be documented in a joint ESA-EUMETSAT publication and made available online.

“I’m looking forward to the recommendations because the things being discussed here are essential for doing our job,” said Jean-Paul Malingreau, Head of Unit Work Programme and Strategy of the Joint Research Centre of the European Commission.

“We also need to assess whether the available and future satellite instruments are sufficient, so recommendations on this can be made available to policymakers to decide what to finance.”

Oasis near Death Valley fed by ancient aquifer under Nevada Test Site

BYU geology professor Steve Nelson at Ash Meadows
BYU geology professor Steve Nelson at Ash Meadows

Every minute, 10,000 gallons of water mysteriously gush out of the desert floor at a place called Ash Meadows, an oasis that is home to 24 plant and animal species found nowhere else in the world.

A new Brigham Young University study indicates that the water arriving at Ash Meadows is completing a 15,000-year journey, flowing slowly underground from what is now the Nevada Test Site.

The U.S. government tested nuclear bombs there for four decades, and a crack in the Earth’s crust known as the “Gravity Fault” connects its aquifer with Ash Meadows.

It will presumably be another 15,000 years before radioactive water surfaces at Ash Meadows, Nelson said. A more pressing issue for wildlife managers at Ash Meadows is the current decline in populations of Devil’s Hole Pupfish and three other endangered fish species.

“Since the crust in Western states is being pulled apart east to west, it creates north-south fault lines such as this one that guides groundwater from one geographically closed basin to another,” said Stephen Nelson, a BYU geology professor and co-author of the study.

The study appears in the May 28 issue of the Journal of Hydrology.

Of the possible sources, only water from the Nevada Test Site matched the profile of dissolved minerals and had comparable hydrogen and oxygen isotopes. Water from the Spring Mountains near Las Vegas – previously assumed to be the source of Ash Meadows water – carried a different isotopic signature.

The BYU researchers combed through more than 4,000 published water samples from the region, many of those from U.S. Geological Survey wells. From this large data set emerged 246 distinct groundwater sources that they tested against the chemical make-up of water from Ash Meadows.

“The results are parsimonious,” Nelson said. “A majority of the water at Ash Meadows flows from the north through fractures in the Gravity Fault.”


New study reveals link between ‘climate footprints’ and mass mammal

An international team of scientists have discovered that climate change played a major role in causing mass extinction of mammals in the late quaternary era, 50,000 years ago. Their study, published in Evolution, takes a new approach to this hotly debated topic by using global data modeling to build continental ‘climate footprints.’

“Between 50,000 and 3,000 years before present (BP) 65% of mammal species weighing over 44kg went extinct, together with a lower proportion of small mammals,” said lead author Dr David Nogues-Bravo from the Center for Macroecology, Evolution and Climate in University of Copenhagen. “Why these species became extinct in such large numbers has been hotly debated for over a century.”

During the last 50,000 years the global climate became colder and drier, reaching full glacial conditions 21,000 years before present time. Since then the climate has become warmer, and this changing climate created new opportunities for colonization of new regions by humans. While both of these global change actors played significant roles in species extinction this study reveals that changing climate was a significant force driving this mass extinction.

“Until now global evidence to support the climate change argument has been lacking, a large part of existing evidence was based on local or regional estimates between numbers of extinctions, dates of human arrivals and dates of climate change,” said Dr Nogues-Bravo.
“Our approach is completely different. By dealing with the issue at a global scale we add a new dimension to the debate by showing that the impact of climate change was not equal across all regions, and we quantify this to reveal each continent’s “footprint of climate change.”

The study shows that climate change had a global influence over extinctions throughout the late quaternary, but the level of extinction seems to be related to each continent’s footprint of climate change. When comparing continents it can then be seen that in Africa, where the climate changed to a relatively lesser extent there were fewer extinctions. However, in North America, more species suffered extinction, as reflected by a greater degree of climate change.

A key piece of evidence in the humans versus climate debate is the size of the extinct mammals. It has always been assumed that humans mainly impacted on populations of large mammals, while if climate change played the key role there should be evidence of large impacts on small mammals as well as the larger animals.

The team’s results show that continents which suffered larger climate change impacts suffered larger extinctions of small mammals and viceversa, further strengthening the idea that climate change was a key factor in controlling past extinctions on a global scale.

This research has important implications for the current study of climate change, not only in revealing the role of the climate in causing extinction in mammals, but also by demonstrating how the effect will be different across regions and continents.

“Our results show that continents with the highest ‘climate footprints’ witnessed more extinctions then continents with lower ‘climate footprints’. These results are consistent across species with different body masses, reinforcing the view that past climate changes contributed to global extinctions.”

“While climate change is not the only factor behind extinction, past, present or future, we cannot neglect in any way that climate change, directly or indirectly, is a crucial actor to understand past and future species extinctions.”, said Miguel Araújo, a co-author of the paper from the National Museum of Natural Sciences in Spain.

Scientists detect huge carbon ‘burp’ that helped end last ice age

Scientists have found the possible source of a huge carbon dioxide ‘burp’ that happened some 18,000 years ago and which helped to end the last ice age.

The results provide the first concrete evidence that carbon dioxide (CO2) was more efficiently locked away in the deep ocean during the last ice age, turning the deep sea into a more ‘stagnant’ carbon repository – something scientists have long suspected but lacked data to support.

Working on a marine sediment core recovered from the Southern Ocean floor between Antarctica and South Africa, the international team led by Dr Luke Skinner of the University of Cambridge radiocarbon dated shells left behind by tiny marine creatures called foraminifera (forams for short).

By measuring how much carbon-14 (14C) was in the bottom-dwelling forams’ shells, and comparing this with the amount of 14C in the atmosphere at the time, they were able to work out how long the CO2 had been locked in the ocean.

By linking their marine core to the Antarctic ice-cores using the temperature signal recorded in both archives, the team were also able compare their results directly with the ice-core record of past atmospheric CO2 variability.

According to Dr Skinner: “Our results show that during the last ice age, around 20,000 years ago, carbon dioxide dissolved in the deep water circulating around Antarctica was locked away for much longer than today. If enough of the deep ocean behaved in the same way, this could help to explain how ocean mixing processes lock up more carbon dioxide during glacial periods.”

Throughout the past two million years (the Quaternary), the Earth has alternated between ice ages and warmer interglacials. These changes are mainly driven by alterations in the Earth’s orbit around the sun (the Milankovic theory).

But changes in Earth’s orbit could only have acted as the ‘pace-maker of the ice ages’ with help from large, positive feedbacks that turned this solar ‘nudge’ into a significant global energy imbalance.

Changes in atmospheric CO2 were one of the most important of these positive feedbacks, but what drove these changes in CO2 has remained uncertain.

Because the ocean is a large, dynamic reservoir of carbon, it has long been suspected that changes in ocean circulation must have played a major role in motivating these large changes in CO2. In addition, the Southern Ocean around Antarctica is expected to have been an important centre of action, because this is where deep water can be lifted up to the sea surface and ‘exhale’ its CO2 to the atmosphere.

Scientists think more CO2 was locked up in the deep ocean during ice ages, and that pulses or ‘burps’ of CO2 from the deep Southern Ocean helped trigger a global thaw every 100,000 years or so. The size of these pulses was roughly equivalent to the change in CO2 experienced since the start of the industrial revolution.

If this theory is correct, we would expect to see large transfers of carbon from the ocean to the atmosphere at the end of each ice age. This should be most obvious in the relative concentrations of radiocarbon (14C) in the ocean and atmosphere; 14C decays over time and so the longer carbon is locked up in the deep sea, the less 14C it contains.

As well as providing evidence for rapid release of carbon dioxide during deglaciation, the research illustrates how the ocean circulation can change significantly over a relatively short space of time.

“Our findings underline the fact that the ocean is a large and dynamic carbon pool. This has implications for proposals to pump carbon dioxide into the deep sea as a way of tackling climate change, for example. Such carbon dioxide would eventually come back up to the surface, and the question of how long it would take would depend on the state of the ocean circulation, as illustrated by the last deglaciation,” says Dr Skinner.

The results are published today in Science.

Deep subduction of the Indian continental crust beneath Asia

The map shows the location of the study area in the Himalayas. Inset: A schematic shows the Indian plate subducting beneath the Asian plate. -  NOC
The map shows the location of the study area in the Himalayas. Inset: A schematic shows the Indian plate subducting beneath the Asian plate. – NOC

Geological investigations in the Himalayas have revealed evidence that when India and Asia collided some 90 million years ago, the continental crust of the Indian tectonic plate was forced down under the Asian plate, sinking down into the Earth’s mantle to a depth of at least 200 km kilometers1.

“The subduction of continental crust to this depth has never been reported in the Himalayas and is also extremely rare in the rest of world,” said Dr Anju Pandey of the National Oceanography Centre in Southampton, who led the research.

Pandey and her colleagues used sophisticated analytical techniques to demonstrate the occurrence of relict majorite, a variety of mineral garnet, in rocks collected from the Himalayas.

Majorite is stable only under ultra-high pressure conditions, meaning that they must have been formed very deep down in the Earth’s crust, before the subducted material was exhumed millions of years later.

“Our findings are significant because researchers have disagreed about the depth of subduction of the Indian plate beneath Asia,” said Pandey.

In fact, the previous depth estimates conflicted with estimates based on computer models. The new results suggest that the leading edge of the Indian plate sank to a depth around double that of previous estimates.

“Our results are backed up by computer modelling and will radically improve our understanding of the subduction of the Indian continental crust beneath the Himalayas,” said Pandey.

The new discovery is also set to modify several fundamental parameters of Himalayan tectonics, such as the rate of Himalayan uplift, angle, and subduction of the Indian plate.

The new research findings were published this month in the journal Geology.