Study hints that ancient Earth made its own water — geologically

A new study is helping to answer a longstanding question that has recently moved to the forefront of earth science: Did our planet make its own water through geologic processes, or did water come to us via icy comets from the far reaches of the solar system?

The answer is likely “both,” according to researchers at The Ohio State University– and the same amount of water that currently fills the Pacific Ocean could be buried deep inside the planet right now.

At the American Geophysical Union (AGU) meeting on Wednesday, Dec. 17, they report the discovery of a previously unknown geochemical pathway by which the Earth can sequester water in its interior for billions of years and still release small amounts to the surface via plate tectonics, feeding our oceans from within.

In trying to understand the formation of the early Earth, some researchers have suggested that the planet was dry and inhospitable to life until icy comets pelted the earth and deposited water on the surface.

Wendy Panero, associate professor of earth sciences at Ohio State, and doctoral student Jeff Pigott are pursuing a different hypothesis: that Earth was formed with entire oceans of water in its interior, and has been continuously supplying water to the surface via plate tectonics ever since.

Researchers have long accepted that the mantle contains some water, but how much water is a mystery. And, if some geological mechanism has been supplying water to the surface all this time, wouldn’t the mantle have run out of water by now?

Because there’s no way to directly study deep mantle rocks, Panero and Pigott are probing the question with high-pressure physics experiments and computer calculations.

“When we look into the origins of water on Earth, what we’re really asking is, why are we so different than all the other planets?” Panero said. “In this solar system, Earth is unique because we have liquid water on the surface. We’re also the only planet with active plate tectonics. Maybe this water in the mantle is key to plate tectonics, and that’s part of what makes Earth habitable.”

Central to the study is the idea that rocks that appear dry to the human eye can actually contain water–in the form of hydrogen atoms trapped inside natural voids and crystal defects. Oxygen is plentiful in minerals, so when a mineral contains some hydrogen, certain chemical reactions can free the hydrogen to bond with the oxygen and make water.

Stray atoms of hydrogen could make up only a tiny fraction of mantle rock, the researchers explained. Given that the mantle is more than 80 percent of the planet’s total volume, however, those stray atoms add up to a lot of potential water.

In a lab at Ohio State, the researchers compress different minerals that are common to the mantle and subject them to high pressures and temperatures using a diamond anvil cell–a device that squeezes a tiny sample of material between two diamonds and heats it with a laser–to simulate conditions in the deep Earth. They examine how the minerals’ crystal structures change as they are compressed, and use that information to gauge the minerals’ relative capacities for storing hydrogen. Then, they extend their experimental results using computer calculations to uncover the geochemical processes that would enable these minerals to rise through the mantle to the surface–a necessary condition for water to escape into the oceans.

In a paper now submitted to a peer-reviewed academic journal, they reported their recent tests of the mineral bridgmanite, a high-pressure form of olivine. While bridgmanite is the most abundant mineral in the lower mantle, they found that it contains too little hydrogen to play an important role in Earth’s water supply.

Another research group recently found that ringwoodite, another form of olivine, does contain enough hydrogen to make it a good candidate for deep-earth water storage. So Panero and Pigott focused their study on the depth where ringwoodite is found–a place 325-500 miles below the surface that researchers call the “transition zone”–as the most likely region that can hold a planet’s worth of water. From there, the same convection of mantle rock that produces plate tectonics could carry the water to the surface.

One problem: If all the water in ringwoodite is continually drained to the surface via plate tectonics, how could the planet hold any in reserve?

For the research presented at AGU, Panero and Pigott performed new computer calculations of the geochemistry in the lowest portion of the mantle, some 500 miles deep and more. There, another mineral, garnet, emerged as a likely water-carrier–a go-between that could deliver some of the water from ringwoodite down into the otherwise dry lower mantle.

If this scenario is accurate, the Earth may today hold half as much water in its depths as is currently flowing in oceans on the surface, Panero said–an amount that would approximately equal the volume of the Pacific Ocean. This water is continuously cycled through the transition zone as a result of plate tectonics.

“One way to look at this research is that we’re putting constraints on the amount of water that could be down there,” Pigott added.

Panero called the complex relationship between plate tectonics and surface water “one of the great mysteries in the geosciences.” But this new study supports researchers’ growing suspicion that mantle convection somehow regulates the amount of water in the oceans. It also vastly expands the timeline for Earth’s water cycle.

“If all of the Earth’s water is on the surface, that gives us one interpretation of the water cycle, where we can think of water cycling from oceans into the atmosphere and into the groundwater over millions of years,” she said. “But if mantle circulation is also part of the water cycle, the total cycle time for our planet’s water has to be billions of years.”

Study hints that ancient Earth made its own water — geologically

A new study is helping to answer a longstanding question that has recently moved to the forefront of earth science: Did our planet make its own water through geologic processes, or did water come to us via icy comets from the far reaches of the solar system?

The answer is likely “both,” according to researchers at The Ohio State University– and the same amount of water that currently fills the Pacific Ocean could be buried deep inside the planet right now.

At the American Geophysical Union (AGU) meeting on Wednesday, Dec. 17, they report the discovery of a previously unknown geochemical pathway by which the Earth can sequester water in its interior for billions of years and still release small amounts to the surface via plate tectonics, feeding our oceans from within.

In trying to understand the formation of the early Earth, some researchers have suggested that the planet was dry and inhospitable to life until icy comets pelted the earth and deposited water on the surface.

Wendy Panero, associate professor of earth sciences at Ohio State, and doctoral student Jeff Pigott are pursuing a different hypothesis: that Earth was formed with entire oceans of water in its interior, and has been continuously supplying water to the surface via plate tectonics ever since.

Researchers have long accepted that the mantle contains some water, but how much water is a mystery. And, if some geological mechanism has been supplying water to the surface all this time, wouldn’t the mantle have run out of water by now?

Because there’s no way to directly study deep mantle rocks, Panero and Pigott are probing the question with high-pressure physics experiments and computer calculations.

“When we look into the origins of water on Earth, what we’re really asking is, why are we so different than all the other planets?” Panero said. “In this solar system, Earth is unique because we have liquid water on the surface. We’re also the only planet with active plate tectonics. Maybe this water in the mantle is key to plate tectonics, and that’s part of what makes Earth habitable.”

Central to the study is the idea that rocks that appear dry to the human eye can actually contain water–in the form of hydrogen atoms trapped inside natural voids and crystal defects. Oxygen is plentiful in minerals, so when a mineral contains some hydrogen, certain chemical reactions can free the hydrogen to bond with the oxygen and make water.

Stray atoms of hydrogen could make up only a tiny fraction of mantle rock, the researchers explained. Given that the mantle is more than 80 percent of the planet’s total volume, however, those stray atoms add up to a lot of potential water.

In a lab at Ohio State, the researchers compress different minerals that are common to the mantle and subject them to high pressures and temperatures using a diamond anvil cell–a device that squeezes a tiny sample of material between two diamonds and heats it with a laser–to simulate conditions in the deep Earth. They examine how the minerals’ crystal structures change as they are compressed, and use that information to gauge the minerals’ relative capacities for storing hydrogen. Then, they extend their experimental results using computer calculations to uncover the geochemical processes that would enable these minerals to rise through the mantle to the surface–a necessary condition for water to escape into the oceans.

In a paper now submitted to a peer-reviewed academic journal, they reported their recent tests of the mineral bridgmanite, a high-pressure form of olivine. While bridgmanite is the most abundant mineral in the lower mantle, they found that it contains too little hydrogen to play an important role in Earth’s water supply.

Another research group recently found that ringwoodite, another form of olivine, does contain enough hydrogen to make it a good candidate for deep-earth water storage. So Panero and Pigott focused their study on the depth where ringwoodite is found–a place 325-500 miles below the surface that researchers call the “transition zone”–as the most likely region that can hold a planet’s worth of water. From there, the same convection of mantle rock that produces plate tectonics could carry the water to the surface.

One problem: If all the water in ringwoodite is continually drained to the surface via plate tectonics, how could the planet hold any in reserve?

For the research presented at AGU, Panero and Pigott performed new computer calculations of the geochemistry in the lowest portion of the mantle, some 500 miles deep and more. There, another mineral, garnet, emerged as a likely water-carrier–a go-between that could deliver some of the water from ringwoodite down into the otherwise dry lower mantle.

If this scenario is accurate, the Earth may today hold half as much water in its depths as is currently flowing in oceans on the surface, Panero said–an amount that would approximately equal the volume of the Pacific Ocean. This water is continuously cycled through the transition zone as a result of plate tectonics.

“One way to look at this research is that we’re putting constraints on the amount of water that could be down there,” Pigott added.

Panero called the complex relationship between plate tectonics and surface water “one of the great mysteries in the geosciences.” But this new study supports researchers’ growing suspicion that mantle convection somehow regulates the amount of water in the oceans. It also vastly expands the timeline for Earth’s water cycle.

“If all of the Earth’s water is on the surface, that gives us one interpretation of the water cycle, where we can think of water cycling from oceans into the atmosphere and into the groundwater over millions of years,” she said. “But if mantle circulation is also part of the water cycle, the total cycle time for our planet’s water has to be billions of years.”

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.

No laughing matter: Nitrous oxide rose at end of last ice age

Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. -  Adrian Schilt
Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. – Adrian Schilt

Nitrous oxide (N2O) is an important greenhouse gas that doesn’t receive as much notoriety as carbon dioxide or methane, but a new study confirms that atmospheric levels of N2O rose significantly as the Earth came out of the last ice age and addresses the cause.

An international team of scientists analyzed air extracted from bubbles enclosed in ancient polar ice from Taylor Glacier in Antarctica, allowing for the reconstruction of the past atmospheric composition. The analysis documented a 30 percent increase in atmospheric nitrous oxide concentrations from 16,000 years ago to 10,000 years ago. This rise in N2O was caused by changes in environmental conditions in the ocean and on land, scientists say, and contributed to the warming at the end of the ice age and the melting of large ice sheets that then existed.

The findings add an important new element to studies of how Earth may respond to a warming climate in the future. Results of the study, which was funded by the U.S. National Science Foundation and the Swiss National Science Foundation, are being published this week in the journal Nature.

“We found that marine and terrestrial sources contributed about equally to the overall increase of nitrous oxide concentrations and generally evolved in parallel at the end of the last ice age,” said lead author Adrian Schilt, who did much of the work as a post-doctoral researcher at Oregon State University. Schilt then continued to work on the study at the Oeschger Centre for Climate Change Research at the University of Bern in Switzerland.

“The end of the last ice age represents a partial analog to modern warming and allows us to study the response of natural nitrous oxide emissions to changing environmental conditions,” Schilt added. “This will allow us to better understand what might happen in the future.”

Nitrous oxide is perhaps best known as laughing gas, but it is also produced by microbes on land and in the ocean in processes that occur naturally, but can be enhanced by human activity. Marine nitrous oxide production is linked closely to low oxygen conditions in the upper ocean and global warming is predicted to intensify the low-oxygen zones in many of the world’s ocean basins. N2O also destroys ozone in the stratosphere.

“Warming makes terrestrial microbes produce more nitrous oxide,” noted co-author Edward Brook, an Oregon State paleoclimatologist whose research team included Schilt. “Greenhouse gases go up and down over time, and we’d like to know more about why that happens and how it affects climate.”

Nitrous oxide is among the most difficult greenhouse gases to study in attempting to reconstruct the Earth’s climate history through ice core analysis. The specific technique that the Oregon State research team used requires large samples of pristine ice that date back to the desired time of study – in this case, between about 16,000 and 10,000 years ago.

The unusual way in which Taylor Glacier is configured allowed the scientists to extract ice samples from the surface of the glacier instead of drilling deep in the polar ice cap because older ice is transported upward near the glacier margins, said Brook, a professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences.

The scientists were able to discern the contributions of marine and terrestrial nitrous oxide through analysis of isotopic ratios, which fingerprint the different sources of N2O in the atmosphere.

“The scientific community knew roughly what the N2O concentration trends were prior to this study,” Brook said, “but these findings confirm that and provide more exact details about changes in sources. As nitrous oxide in the atmosphere continues to increase – along with carbon dioxide and methane – we now will be able to more accurately assess where those contributions are coming from and the rate of the increase.”

Atmospheric N2O was roughly 200 parts per billion at the peak of the ice age about 20,000 years ago then rose to 260 ppb by 10,000 years ago. As of 2014, atmospheric N2Owas measured at about 327 ppb, an increase attributed primarily to agricultural influences.

Although the N2O increase at the end of the last ice age was almost equally attributable to marine and terrestrial sources, the scientists say, there were some differences.

“Our data showed that terrestrial emissions changed faster than marine emissions, which was highlighted by a fast increase of emissions on land that preceded the increase in marine emissions,” Schilt pointed out. “It appears to be a direct response to a rapid temperature change between 15,000 and 14,000 years ago.”

That finding underscores the complexity of analyzing how Earth responds to changing conditions that have to account for marine and terrestrial influences; natural variability; the influence of different greenhouse gases; and a host of other factors, Brook said.

“Natural sources of N2O are predicted to increase in the future and this study will help up test predictions on how the Earth will respond,” Brook said.

No laughing matter: Nitrous oxide rose at end of last ice age

Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. -  Adrian Schilt
Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. – Adrian Schilt

Nitrous oxide (N2O) is an important greenhouse gas that doesn’t receive as much notoriety as carbon dioxide or methane, but a new study confirms that atmospheric levels of N2O rose significantly as the Earth came out of the last ice age and addresses the cause.

An international team of scientists analyzed air extracted from bubbles enclosed in ancient polar ice from Taylor Glacier in Antarctica, allowing for the reconstruction of the past atmospheric composition. The analysis documented a 30 percent increase in atmospheric nitrous oxide concentrations from 16,000 years ago to 10,000 years ago. This rise in N2O was caused by changes in environmental conditions in the ocean and on land, scientists say, and contributed to the warming at the end of the ice age and the melting of large ice sheets that then existed.

The findings add an important new element to studies of how Earth may respond to a warming climate in the future. Results of the study, which was funded by the U.S. National Science Foundation and the Swiss National Science Foundation, are being published this week in the journal Nature.

“We found that marine and terrestrial sources contributed about equally to the overall increase of nitrous oxide concentrations and generally evolved in parallel at the end of the last ice age,” said lead author Adrian Schilt, who did much of the work as a post-doctoral researcher at Oregon State University. Schilt then continued to work on the study at the Oeschger Centre for Climate Change Research at the University of Bern in Switzerland.

“The end of the last ice age represents a partial analog to modern warming and allows us to study the response of natural nitrous oxide emissions to changing environmental conditions,” Schilt added. “This will allow us to better understand what might happen in the future.”

Nitrous oxide is perhaps best known as laughing gas, but it is also produced by microbes on land and in the ocean in processes that occur naturally, but can be enhanced by human activity. Marine nitrous oxide production is linked closely to low oxygen conditions in the upper ocean and global warming is predicted to intensify the low-oxygen zones in many of the world’s ocean basins. N2O also destroys ozone in the stratosphere.

“Warming makes terrestrial microbes produce more nitrous oxide,” noted co-author Edward Brook, an Oregon State paleoclimatologist whose research team included Schilt. “Greenhouse gases go up and down over time, and we’d like to know more about why that happens and how it affects climate.”

Nitrous oxide is among the most difficult greenhouse gases to study in attempting to reconstruct the Earth’s climate history through ice core analysis. The specific technique that the Oregon State research team used requires large samples of pristine ice that date back to the desired time of study – in this case, between about 16,000 and 10,000 years ago.

The unusual way in which Taylor Glacier is configured allowed the scientists to extract ice samples from the surface of the glacier instead of drilling deep in the polar ice cap because older ice is transported upward near the glacier margins, said Brook, a professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences.

The scientists were able to discern the contributions of marine and terrestrial nitrous oxide through analysis of isotopic ratios, which fingerprint the different sources of N2O in the atmosphere.

“The scientific community knew roughly what the N2O concentration trends were prior to this study,” Brook said, “but these findings confirm that and provide more exact details about changes in sources. As nitrous oxide in the atmosphere continues to increase – along with carbon dioxide and methane – we now will be able to more accurately assess where those contributions are coming from and the rate of the increase.”

Atmospheric N2O was roughly 200 parts per billion at the peak of the ice age about 20,000 years ago then rose to 260 ppb by 10,000 years ago. As of 2014, atmospheric N2Owas measured at about 327 ppb, an increase attributed primarily to agricultural influences.

Although the N2O increase at the end of the last ice age was almost equally attributable to marine and terrestrial sources, the scientists say, there were some differences.

“Our data showed that terrestrial emissions changed faster than marine emissions, which was highlighted by a fast increase of emissions on land that preceded the increase in marine emissions,” Schilt pointed out. “It appears to be a direct response to a rapid temperature change between 15,000 and 14,000 years ago.”

That finding underscores the complexity of analyzing how Earth responds to changing conditions that have to account for marine and terrestrial influences; natural variability; the influence of different greenhouse gases; and a host of other factors, Brook said.

“Natural sources of N2O are predicted to increase in the future and this study will help up test predictions on how the Earth will respond,” Brook said.

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.

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.