North Atlantic signalled Ice Age thaw 1,000 years before it happened, reveals new research

The Atlantic Ocean at mid-depths may have given out early warning signals – 1,000 years in advance – that the last Ice Age was going to end, scientists report today in the journal Paleoceanography.

Scientists had previously known that at the end of the last Ice Age, around 14,700 years ago, major changes occurred to the Atlantic Ocean in a period known as the Bolling-Allerod interval. During this period, as glaciers melted and the Earth warmed, the currents of the Atlantic Ocean at its deepest levels changed direction.

The researchers have analysed the chemistry of 24 ancient coral fossils from the North Atlantic Ocean to learn more about the circulation of its waters during the last Ice Age. They found that the corals recorded a high variability in the currents of the Atlantic Ocean at mid-depths, around 2km below the surface, up to 1,000 years prior to the Bolling-Allerod interval. The team suggests that these changes may have been an early warning signal that the world was poised to switch from its glacial state to the warmer world we know today, and that the changes happened first at mid-depths.

The study was carried out by researchers from Imperial College London in conjunction with academics from the Scottish Marine Institute, the University of Bristol and Caltech Division of Geology and Planetary Sciences.

Dr David Wilson, from the Department of Earth Science and Engineering at Imperial College London, said: “The world’s oceans have always been an important barometer when it comes to changes in our planet. Excitingly, the coral fossils we’ve studied are showing us that the North Atlantic Ocean at mid-depths was undergoing changes up to 1,000 years earlier than we had expected. The tantalising prospect is that this high variability may have been a signal that the last Ice Age was about to end.”

The fossil corals analysed by the team come from a species called Desmophyllum dianthus, which are often around 5cm in diameter and look like budding flowers. They typically only live for 100 years, giving the team a rare insight into what was happening to the ocean’s currents during this relatively brief time. Thousands of years ago they grew on the New England Seamounts, which are a chain of undersea mountains approximately 1000km off the east coast of the US, located at mid-depths 2km beneath the surface. This underwater area is important for understanding the North Atlantic’s currents.

While some of the corals analysed by the team come from historical collections, most have been collected by researchers from previous expeditions in 2003 and 2005 to the New England Seamounts. The researchers used deep sea robotic submergence vehicles called Hercules and Alvin to collect the ancient coral fossils.

These ancient coral fossils accumulated rare earth elements from seawater, including neodymium, which leached from rocks on land into the Atlantic Ocean and circulated in its currents, eventually ending up in the coral skeletons. Neodymium isotopes in different regions of the world have specific signatures, created by radioactive decay over billions of years. The scientists studied the chemistry of the coral fossils to determine where the neodymium isotopes had come from, giving them a glimpse into the circulation of the Atlantic Ocean at the end of the Ice Age.

Since the world’s oceans are connected by currents, the next step will see the team integrating the evidence they gathered from the North Atlantic Ocean into a picture of global changes in the mid-depths of oceans around the world. In particular, the team is interested in exploring how the Southern Ocean around Antarctica changed around the same time by analysing neodymium isotopes in a collection of Southern Ocean corals.

North Atlantic signalled Ice Age thaw 1,000 years before it happened, reveals new research

The Atlantic Ocean at mid-depths may have given out early warning signals – 1,000 years in advance – that the last Ice Age was going to end, scientists report today in the journal Paleoceanography.

Scientists had previously known that at the end of the last Ice Age, around 14,700 years ago, major changes occurred to the Atlantic Ocean in a period known as the Bolling-Allerod interval. During this period, as glaciers melted and the Earth warmed, the currents of the Atlantic Ocean at its deepest levels changed direction.

The researchers have analysed the chemistry of 24 ancient coral fossils from the North Atlantic Ocean to learn more about the circulation of its waters during the last Ice Age. They found that the corals recorded a high variability in the currents of the Atlantic Ocean at mid-depths, around 2km below the surface, up to 1,000 years prior to the Bolling-Allerod interval. The team suggests that these changes may have been an early warning signal that the world was poised to switch from its glacial state to the warmer world we know today, and that the changes happened first at mid-depths.

The study was carried out by researchers from Imperial College London in conjunction with academics from the Scottish Marine Institute, the University of Bristol and Caltech Division of Geology and Planetary Sciences.

Dr David Wilson, from the Department of Earth Science and Engineering at Imperial College London, said: “The world’s oceans have always been an important barometer when it comes to changes in our planet. Excitingly, the coral fossils we’ve studied are showing us that the North Atlantic Ocean at mid-depths was undergoing changes up to 1,000 years earlier than we had expected. The tantalising prospect is that this high variability may have been a signal that the last Ice Age was about to end.”

The fossil corals analysed by the team come from a species called Desmophyllum dianthus, which are often around 5cm in diameter and look like budding flowers. They typically only live for 100 years, giving the team a rare insight into what was happening to the ocean’s currents during this relatively brief time. Thousands of years ago they grew on the New England Seamounts, which are a chain of undersea mountains approximately 1000km off the east coast of the US, located at mid-depths 2km beneath the surface. This underwater area is important for understanding the North Atlantic’s currents.

While some of the corals analysed by the team come from historical collections, most have been collected by researchers from previous expeditions in 2003 and 2005 to the New England Seamounts. The researchers used deep sea robotic submergence vehicles called Hercules and Alvin to collect the ancient coral fossils.

These ancient coral fossils accumulated rare earth elements from seawater, including neodymium, which leached from rocks on land into the Atlantic Ocean and circulated in its currents, eventually ending up in the coral skeletons. Neodymium isotopes in different regions of the world have specific signatures, created by radioactive decay over billions of years. The scientists studied the chemistry of the coral fossils to determine where the neodymium isotopes had come from, giving them a glimpse into the circulation of the Atlantic Ocean at the end of the Ice Age.

Since the world’s oceans are connected by currents, the next step will see the team integrating the evidence they gathered from the North Atlantic Ocean into a picture of global changes in the mid-depths of oceans around the world. In particular, the team is interested in exploring how the Southern Ocean around Antarctica changed around the same time by analysing neodymium isotopes in a collection of Southern Ocean corals.

Antarctica: Heat comes from the deep

The Antarctic ice sheet is a giant water reservoir. The ice cap on the southern continent is on average 2,100 meters thick and contains about 70 percent of the world’s fresh water. If this ice mass were to melt completely, it could raise the global sea level by 60 meters. Therefore scientists carefully observe changes in the Antarctic. In the renowned international journal Science, researchers from Germany, the UK, the US and Japan are now publishing data according to which water temperatures, in particular on the shallow shelf seas of West Antarctica, are rising. “There are many large glaciers in the area. The elevated temperatures have accelerated the melting and sliding of these glaciers in recent decades and there are no indications that this trend is changing,” says the lead author of the study, Dr. Sunke Schmidtko from GEOMAR Helmholtz Centre for Ocean Research Kiel.

For their study, he and his colleagues of the University of East Anglia, the California Institute of Technology and the University of Hokkaido (Japan) evaluated all oceanographic data from the waters around Antarctica from 1960 to 2014 that were available in public databases. These data show that five decades ago, the water masses in the West Antarctic shelf seas were already warmer than in other parts of Antarctica, for example, in the Weddell Sea. However, the temperature difference is not constant. Since 1960, the temperatures in the West Antarctic Amundsen Sea and the Bellingshausen Sea have been rising. “Based on the data we were able to see that this shelf process is induced from the open ocean,” says Dr. Schmidtko.

Around Antarctica in greater depth along the continental slope water masses with temperatures from 0.5 to 1.5°C (33-35°F) are predominant. These temperatures are very warm for Antarctic conditions. “These waters have warmed in West Antarctica over the past 50 years. And they are significant shallower than 50 years ago,” says Schmidtko. Especially in the Amundsen Sea and Bellingshausen Sea they now increasingly spill onto the shelf and warm the shelf.

“These are the regions in which accelerated glacial melting has been observed for some time. We show that oceanographic changes over the past 50 years have probably caused this melting. If the water continues to warm, the increased penetration of warmer water masses onto the shelf will likely further accelerate this process, with an impact on the rate of global sea level rise ” explains Professor Karen Heywood from the University of East Anglia.

The scientists also draw attention to the rising up of warm water masses in the southwestern Weddell Sea. Here very cold temperatures (less than minus 1.5°C or 29°F) prevail on the shelf and a large-scale melting of shelf ice has not been observed yet. If the shoaling of warm water masses continues, it is expected that there will be major environmental changes with dramatic consequences for the Filchner or Ronne Ice Shelf, too. For the first time glaciers outside the West Antarctic could experience enhanced melting from below.

To what extent the diverse biology of the Southern Ocean is influenced by the observed changes is not fully understood. The shelf areas include spawning areas for the Antarctic krill, a shrimp species widespread in the Southern Ocean, which plays a key role in the Antarctic food chain. Research results have shown that spawning cycles could change in warmer conditions. A final assessment of the impact has not yet been made.

The exact reasons for the increase of the heating and the rising of warm water masses has not yet been completely resolved. “We suspect that they are related to large-scale variations in wind systems over the southern hemisphere. But which processes specifically play a role must be evaluated in more detail.” says Dr. Schmidtko.

Antarctica: Heat comes from the deep

The Antarctic ice sheet is a giant water reservoir. The ice cap on the southern continent is on average 2,100 meters thick and contains about 70 percent of the world’s fresh water. If this ice mass were to melt completely, it could raise the global sea level by 60 meters. Therefore scientists carefully observe changes in the Antarctic. In the renowned international journal Science, researchers from Germany, the UK, the US and Japan are now publishing data according to which water temperatures, in particular on the shallow shelf seas of West Antarctica, are rising. “There are many large glaciers in the area. The elevated temperatures have accelerated the melting and sliding of these glaciers in recent decades and there are no indications that this trend is changing,” says the lead author of the study, Dr. Sunke Schmidtko from GEOMAR Helmholtz Centre for Ocean Research Kiel.

For their study, he and his colleagues of the University of East Anglia, the California Institute of Technology and the University of Hokkaido (Japan) evaluated all oceanographic data from the waters around Antarctica from 1960 to 2014 that were available in public databases. These data show that five decades ago, the water masses in the West Antarctic shelf seas were already warmer than in other parts of Antarctica, for example, in the Weddell Sea. However, the temperature difference is not constant. Since 1960, the temperatures in the West Antarctic Amundsen Sea and the Bellingshausen Sea have been rising. “Based on the data we were able to see that this shelf process is induced from the open ocean,” says Dr. Schmidtko.

Around Antarctica in greater depth along the continental slope water masses with temperatures from 0.5 to 1.5°C (33-35°F) are predominant. These temperatures are very warm for Antarctic conditions. “These waters have warmed in West Antarctica over the past 50 years. And they are significant shallower than 50 years ago,” says Schmidtko. Especially in the Amundsen Sea and Bellingshausen Sea they now increasingly spill onto the shelf and warm the shelf.

“These are the regions in which accelerated glacial melting has been observed for some time. We show that oceanographic changes over the past 50 years have probably caused this melting. If the water continues to warm, the increased penetration of warmer water masses onto the shelf will likely further accelerate this process, with an impact on the rate of global sea level rise ” explains Professor Karen Heywood from the University of East Anglia.

The scientists also draw attention to the rising up of warm water masses in the southwestern Weddell Sea. Here very cold temperatures (less than minus 1.5°C or 29°F) prevail on the shelf and a large-scale melting of shelf ice has not been observed yet. If the shoaling of warm water masses continues, it is expected that there will be major environmental changes with dramatic consequences for the Filchner or Ronne Ice Shelf, too. For the first time glaciers outside the West Antarctic could experience enhanced melting from below.

To what extent the diverse biology of the Southern Ocean is influenced by the observed changes is not fully understood. The shelf areas include spawning areas for the Antarctic krill, a shrimp species widespread in the Southern Ocean, which plays a key role in the Antarctic food chain. Research results have shown that spawning cycles could change in warmer conditions. A final assessment of the impact has not yet been made.

The exact reasons for the increase of the heating and the rising of warm water masses has not yet been completely resolved. “We suspect that they are related to large-scale variations in wind systems over the southern hemisphere. But which processes specifically play a role must be evaluated in more detail.” says Dr. Schmidtko.

West Antarctic melt rate has tripled: UC Irvine-NASA

A comprehensive, 21-year analysis of the fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade.

The glaciers in the Amundsen Sea Embayment in West Antarctica are hemorrhaging ice faster than any other part of Antarctica and are the most significant Antarctic contributors to sea level rise. This study is the first to evaluate and reconcile observations from four different measurement techniques to produce an authoritative estimate of the amount and the rate of loss over the last two decades.

“The mass loss of these glaciers is increasing at an amazing rate,” said scientist Isabella Velicogna, jointly of the UC Irvine and NASA’s Jet Propulsion Laboratory. Velicogna is a coauthor of a paper on the results, which has been accepted for Dec. 5 publication in the journal Geophysical Research Letters.

Lead author Tyler Sutterley, a UCI doctoral candidate, and his team did the analysis to verify that the melting in this part of Antarctica is shifting into high gear. “Previous studies had suggested that this region is starting to change very dramatically since the 1990s, and we wanted to see how all the different techniques compared,” Sutterley said. “The remarkable agreement among the techniques gave us confidence that we are getting this right.”

The researchers reconciled measurements of the mass balance of glaciers flowing into the Amundsen Sea Embayment. Mass balance is a measure of how much ice the glaciers gain and lose over time from accumulating or melting snow, discharges of ice as icebergs, and other causes. Measurements from all four techniques were available from 2003 to 2009. Combined, the four data sets span the years 1992 to 2013.

The glaciers in the embayment lost mass throughout the entire period. The researchers calculated two separate quantities: the total amount of loss, and the changes in the rate of loss.

The total amount of loss averaged 83 gigatons per year (91.5 billion U.S. tons). By comparison, Mt. Everest weighs about 161 gigatons, meaning the Antarctic glaciers lost a Mt.-Everest’s-worth amount of water weight every two years over the last 21 years.

The rate of loss accelerated an average of 6.1 gigatons (6.7 billion U.S. tons) per year since 1992.

From 2003 to 2009, when all four observational techniques overlapped, the melt rate increased an average of 16.3 gigatons per year — almost three times the rate of increase for the full 21-year period. The total amount of loss was close to the average at 84 gigatons.

The four sets of observations include NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, laser altimetry from NASA’s Operation IceBridge airborne campaign and earlier ICESat satellite, radar altimetry from the European Space Agency’s Envisat satellite, and mass budget analyses using radars and the University of Utrecht’s Regional Atmospheric Climate Model.

The scientists noted that glacier and ice sheet behavior worldwide is by far the greatest uncertainty in predicting future sea level. “We have an excellent observing network now. It’s critical that we maintain this network to continue monitoring the changes,” Velicogna said, “because the changes are proceeding very fast.”

###

About the University of California, Irvine:

Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 30,000 students and offers 192 degree programs. Located in one of the world’s safest and most economically vibrant communities, it’s Orange County’s second-largest employer, contributing $4.8 billion annually to the local economy.

Media access: Radio programs/stations may, for a fee, use an on-campus ISDN line to interview UC Irvine faculty and experts, subject to availability and university approval. For more UC Irvine news, visit news.uci.edu. Additional resources for journalists may be found at communications.uci.edu/for-journalists.

West Antarctic melt rate has tripled: UC Irvine-NASA

A comprehensive, 21-year analysis of the fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade.

The glaciers in the Amundsen Sea Embayment in West Antarctica are hemorrhaging ice faster than any other part of Antarctica and are the most significant Antarctic contributors to sea level rise. This study is the first to evaluate and reconcile observations from four different measurement techniques to produce an authoritative estimate of the amount and the rate of loss over the last two decades.

“The mass loss of these glaciers is increasing at an amazing rate,” said scientist Isabella Velicogna, jointly of the UC Irvine and NASA’s Jet Propulsion Laboratory. Velicogna is a coauthor of a paper on the results, which has been accepted for Dec. 5 publication in the journal Geophysical Research Letters.

Lead author Tyler Sutterley, a UCI doctoral candidate, and his team did the analysis to verify that the melting in this part of Antarctica is shifting into high gear. “Previous studies had suggested that this region is starting to change very dramatically since the 1990s, and we wanted to see how all the different techniques compared,” Sutterley said. “The remarkable agreement among the techniques gave us confidence that we are getting this right.”

The researchers reconciled measurements of the mass balance of glaciers flowing into the Amundsen Sea Embayment. Mass balance is a measure of how much ice the glaciers gain and lose over time from accumulating or melting snow, discharges of ice as icebergs, and other causes. Measurements from all four techniques were available from 2003 to 2009. Combined, the four data sets span the years 1992 to 2013.

The glaciers in the embayment lost mass throughout the entire period. The researchers calculated two separate quantities: the total amount of loss, and the changes in the rate of loss.

The total amount of loss averaged 83 gigatons per year (91.5 billion U.S. tons). By comparison, Mt. Everest weighs about 161 gigatons, meaning the Antarctic glaciers lost a Mt.-Everest’s-worth amount of water weight every two years over the last 21 years.

The rate of loss accelerated an average of 6.1 gigatons (6.7 billion U.S. tons) per year since 1992.

From 2003 to 2009, when all four observational techniques overlapped, the melt rate increased an average of 16.3 gigatons per year — almost three times the rate of increase for the full 21-year period. The total amount of loss was close to the average at 84 gigatons.

The four sets of observations include NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, laser altimetry from NASA’s Operation IceBridge airborne campaign and earlier ICESat satellite, radar altimetry from the European Space Agency’s Envisat satellite, and mass budget analyses using radars and the University of Utrecht’s Regional Atmospheric Climate Model.

The scientists noted that glacier and ice sheet behavior worldwide is by far the greatest uncertainty in predicting future sea level. “We have an excellent observing network now. It’s critical that we maintain this network to continue monitoring the changes,” Velicogna said, “because the changes are proceeding very fast.”

###

About the University of California, Irvine:

Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 30,000 students and offers 192 degree programs. Located in one of the world’s safest and most economically vibrant communities, it’s Orange County’s second-largest employer, contributing $4.8 billion annually to the local economy.

Media access: Radio programs/stations may, for a fee, use an on-campus ISDN line to interview UC Irvine faculty and experts, subject to availability and university approval. For more UC Irvine news, visit news.uci.edu. Additional resources for journalists may be found at communications.uci.edu/for-journalists.

First harvest of research based on the final GOCE gravity model

This image, based on the final GOCE gravity model, charts current velocities in the Gulf Stream in meters per second. -  TUM IAPG
This image, based on the final GOCE gravity model, charts current velocities in the Gulf Stream in meters per second. – TUM IAPG

Just four months after the final data package from the GOCE satellite mission was delivered, researchers are laying out a rich harvest of scientific results, with the promise of more to come. A mission of the European Space Agency (ESA), the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) provided the most accurate measurements yet of Earth’s gravitational field. The GOCE Gravity Consortium, coordinated by the Technische Universität München (TUM), produced all of the mission’s data products including the fifth and final GOCE gravity model. On this basis, studies in geophysics, geology, ocean circulation, climate change, and civil engineering are sharpening the picture of our dynamic planet – as can be seen in the program of the 5th International GOCE User Workshop, taking place Nov. 25-28 in Paris.

The GOCE satellite made 27,000 orbits between its launch in March 2009 and re-entry in November 2013, measuring tiny variations in the gravitational field that correspond to uneven distributions of mass in Earth’s oceans, continents, and deep interior. Some 800 million observations went into the computation of the final model, which is composed of more than 75,000 parameters representing the global gravitational field with a spatial resolution of around 70 kilometers. The precision of the model improved over time, as each release incorporated more data. Centimeter accuracy has now been achieved for variations of the geoid – a gravity-derived figure of Earth’s surface that serves as a global reference for sea level and heights – in a model based solely on GOCE data.

The fifth and last data release benefited from two special phases of observation. After its first three years of operation, the satellite’s orbit was lowered from 255 to 225 kilometers, increasing the sensitivity of gravity measurements to reveal even more detailed structures of the gravity field. And through most of the satellite’s final plunge through the atmosphere, some instruments continued to report measurements that have sparked intense interest far beyond the “gravity community” – for example, among researchers concerned with aerospace engineering, atmospheric sciences, and space debris.

Moving on: new science, future missions


Through the lens of Earth’s gravitational field, scientists can image our planet in a way that is complementary to approaches that rely on light, magnetism, or seismic waves. They can determine the speed of ocean currents from space, monitor rising sea level and melting ice sheets, uncover hidden features of continental geology, even peer into the convection machine that drives plate tectonics. Topics like these dominate the more than 100 talks scheduled for the 5th GOCE User Workshop, with technical talks on measurements and models playing a smaller role. “I see this as a sign of success, that the emphasis has shifted decisively to the user community,” says Prof. Roland Pail, director of the Institute for Astronomical and Physical Geodesy at TUM.

This shift can be seen as well among the topics covered by TUM researchers, such as estimates of the elastic thickness of the continents from GOCE gravity models, mass trends in Antarctica from global gravity fields, and a scientific roadmap toward worldwide unification of height systems. For his part Pail – who was responsible for delivery of the data products – chose to speak about consolidating science requirements for a next-generation gravity field mission.


TUM has organized a public symposium on “Seeing Earth in the ‘light’ of gravity” for the 2015 Annual Meeting of the American Association for the Advancement of Science in San Jose, California. This session, featuring speakers from Australia, Canada, Denmark, France, Germany and Italy, takes place on Feb. 14, 2015. (See http://meetings.aaas.org/.)

This research was supported in part by the European Space Agency.

Publication:


“EGM_TIM_RL05: An Independent Geoid with Centimeter Accuracy Purely Based on the GOCE Mission,” Jan Martin Brockmann, Norbert Zehentner, Eduard Höck, Roland Pail, Ina Loth, Torsten Mayer-Gürr, and Wolf-Dieter Shuh. Geophysical Research Letters 2014, doi:10.1002/2014GL061904.

First harvest of research based on the final GOCE gravity model

This image, based on the final GOCE gravity model, charts current velocities in the Gulf Stream in meters per second. -  TUM IAPG
This image, based on the final GOCE gravity model, charts current velocities in the Gulf Stream in meters per second. – TUM IAPG

Just four months after the final data package from the GOCE satellite mission was delivered, researchers are laying out a rich harvest of scientific results, with the promise of more to come. A mission of the European Space Agency (ESA), the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) provided the most accurate measurements yet of Earth’s gravitational field. The GOCE Gravity Consortium, coordinated by the Technische Universität München (TUM), produced all of the mission’s data products including the fifth and final GOCE gravity model. On this basis, studies in geophysics, geology, ocean circulation, climate change, and civil engineering are sharpening the picture of our dynamic planet – as can be seen in the program of the 5th International GOCE User Workshop, taking place Nov. 25-28 in Paris.

The GOCE satellite made 27,000 orbits between its launch in March 2009 and re-entry in November 2013, measuring tiny variations in the gravitational field that correspond to uneven distributions of mass in Earth’s oceans, continents, and deep interior. Some 800 million observations went into the computation of the final model, which is composed of more than 75,000 parameters representing the global gravitational field with a spatial resolution of around 70 kilometers. The precision of the model improved over time, as each release incorporated more data. Centimeter accuracy has now been achieved for variations of the geoid – a gravity-derived figure of Earth’s surface that serves as a global reference for sea level and heights – in a model based solely on GOCE data.

The fifth and last data release benefited from two special phases of observation. After its first three years of operation, the satellite’s orbit was lowered from 255 to 225 kilometers, increasing the sensitivity of gravity measurements to reveal even more detailed structures of the gravity field. And through most of the satellite’s final plunge through the atmosphere, some instruments continued to report measurements that have sparked intense interest far beyond the “gravity community” – for example, among researchers concerned with aerospace engineering, atmospheric sciences, and space debris.

Moving on: new science, future missions


Through the lens of Earth’s gravitational field, scientists can image our planet in a way that is complementary to approaches that rely on light, magnetism, or seismic waves. They can determine the speed of ocean currents from space, monitor rising sea level and melting ice sheets, uncover hidden features of continental geology, even peer into the convection machine that drives plate tectonics. Topics like these dominate the more than 100 talks scheduled for the 5th GOCE User Workshop, with technical talks on measurements and models playing a smaller role. “I see this as a sign of success, that the emphasis has shifted decisively to the user community,” says Prof. Roland Pail, director of the Institute for Astronomical and Physical Geodesy at TUM.

This shift can be seen as well among the topics covered by TUM researchers, such as estimates of the elastic thickness of the continents from GOCE gravity models, mass trends in Antarctica from global gravity fields, and a scientific roadmap toward worldwide unification of height systems. For his part Pail – who was responsible for delivery of the data products – chose to speak about consolidating science requirements for a next-generation gravity field mission.


TUM has organized a public symposium on “Seeing Earth in the ‘light’ of gravity” for the 2015 Annual Meeting of the American Association for the Advancement of Science in San Jose, California. This session, featuring speakers from Australia, Canada, Denmark, France, Germany and Italy, takes place on Feb. 14, 2015. (See http://meetings.aaas.org/.)

This research was supported in part by the European Space Agency.

Publication:


“EGM_TIM_RL05: An Independent Geoid with Centimeter Accuracy Purely Based on the GOCE Mission,” Jan Martin Brockmann, Norbert Zehentner, Eduard Höck, Roland Pail, Ina Loth, Torsten Mayer-Gürr, and Wolf-Dieter Shuh. Geophysical Research Letters 2014, doi:10.1002/2014GL061904.

Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu

Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu