Natural Ocean Thermostat May Protect Some Coral Reefs


by Staff Writers
Boulder CO (SPX) Feb 08, 2008
Natural processes may prevent oceans from warming beyond a certain point, helping protect some coral reefs from the impacts of climate change, new research finds. The study, by scientists at the National Center for Atmospheric Research (NCAR) and Australian Institute of Marine Science (AIMS), finds evidence that an ocean "thermostat" appears to be helping to regulate sea-surface temperatures in a biologically diverse region of the western Pacific.
The research will be published online Saturday in Geophysical Research Letters. It was funded by the National Science Foundation, NCAR's primary sponsor, with support from the U.S. Department of Energy; the Japanese Ministry of Education, Culture, Sports, Science, and Technology; and AIMS.

The research team, led by NCAR scientist Joan Kleypas, looked at the Western Pacific Warm Pool, a region northeast of Australia where naturally warm sea-surface temperatures have risen little in recent decades. As a result, the reefs in that region appear to have suffered relatively few episodes of coral bleaching, a phenomenon that has damaged reefs in other areas where temperature increases have been more pronounced.

The study lends support to a much-debated theory that a natural ocean thermostat prevents sea-surface temperatures from exceeding about 88 degrees Fahrenheit (31 degrees Celsius) in open oceans. If so, this thermostat would protect reefs that have evolved in naturally warm waters that will not warm much further, as opposed to reefs that live in slightly cooler waters that face more significant warming.

"Global warming is damaging many corals, but it appears to be bypassing certain reefs that support some of the greatest diversity of life on the planet," Kleypas says. "In essence, reefs that are already in hot water may be more protected from warming than reefs that are not. This is some rare hopeful news for these important ecosystems."

Coral bleaching: The warm pool exception Coral reefs face a multitude of threats, including overfishing, coastal development, pollution, and changes to ocean chemistry caused by rising levels of carbon dioxide in the atmosphere. But global warming presents a particularly grave threat because unusually warm ocean temperatures can lead to episodes of coral bleaching, in which corals turn white after expelling the colorful microscopic algae that provide them with nutrition. Unless cooler temperatures return in a few days or weeks, allowing algae to grow again, bleached corals often collapse and die.

Bleaching can occur naturally, but it has become increasingly widespread in recent decades. This is largely because sea-surface temperatures in tropical waters where corals live have increased about 0.5-0.7 degrees Fahrenheit (0.3-0.4 degrees Celsius) over the last two to three decades, with temperatures occasionally spiking higher.

However, between 1980 and 2005, only four episodes of bleaching have been reported for reefs in the Western Pacific Warm Pool. This is a lower rate than any other reef region, even though the western Pacific reefs appear to be especially sensitive to temperature changes. Sea-surface temperatures in the warm pool naturally average about 84 degrees Fahrenheit (29 degrees Celsius), which is close to the proposed thermostat limit. They have warmed up about half as much as in cooler areas of the oceans.

To study the correlation between temperatures and bleaching, the authors analyzed sea-surface temperatures from the period 1950-2006 in tropical waters that are home to corals, relying on measurements taken by ships, buoys, and satellites. They also used the NCAR-based Community Climate System Model to study computer simulations of past and future sea-surface temperatures. The team compared the actual and simulated temperatures to a database of coral bleaching reports, mostly taken from 1980 to 2005.

Will more warming raise the thermostat? Researchers have speculated about several processes that could regulate ocean temperatures. As surface waters warm, more water evaporates, which can increase cloud cover and winds that cool the surface. In some areas, warming alters ocean currents in ways that bring in cooler waters. In addition, the very process of evaporation removes heat.

"This year, 2008, is the International Year of the Reef, and we need to go beyond the dire predictions for coral reefs and find ways to conserve them," Kleypas says. "Warming waters are just one part of the picture, but they are an important part. As we evaluate how and where to protect reefs, we need to determine whether the ocean thermostat offers some protection against coral bleaching."

Kleypas and her co-authors say more research needs to be conducted on the thermostat. In particular, scientists are uncertain whether global warming may alter it, raising the upper limit for sea-surface temperatures. Computer model simulations tend to capture the slow rate of warming in the western Pacific over the last few decades, but they show the warm pool heating rapidly in the future.

"Computer models of Earth's climate show that sea-surface temperatures will rise substantially this century," says NCAR scientist Gokhan Danabasoglu, a co-author of the study. "Unfortunately, these future simulations show the Western Pacific Warm Pool warming at a similar rate as the surrounding areas instead of being constrained by a thermostat. We don't know if the models are simply not capturing the processes that cause the thermostat, or if global warming is happening so rapidly that it will overwhelm the thermostat."


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River Carbon Impacts On The Arctic Ocean


by Staff Writers
Woods Hole MA (SPX) Feb 14, 2008
Arctic rivers transport huge quantities of dissolved organic carbon (DOC) to the Arctic Ocean. The prevailing paradigm regarding DOC in arctic rivers is that it is largely refractory, making it of little significance for the biogeochemistry of the Arctic Ocean.
However, a recent study by R. M. Holmes of the Woods Hole Research Center and colleagues at collaborating institutions challenges that assumption by showing that DOC in Alaskan arctic rivers is remarkably labile during the spring flood period when the majority of annual DOC flux occurs. The research was published February 9 in Geophysical Research Letters.

According to Dr. Holmes, "Though only about 1% of global ocean volume, the Arctic Ocean receives almost 10% of global river discharge. As a consequence, organic carbon transported by arctic rivers has the potential to strongly impact the chemistry and biology of the Arctic Ocean".

The primary focus of the paper is the lability of dissolved organic carbon in Alaskan arctic rivers, or how available the DOC is for microbial decomposition. Because of logistical challenges, past studies have focused almost exclusively on the summer low-flow period, when numerous studies have shown arctic river DOC to be refractory.

However, by timing their sampling to include the high-flow period just after the spring ice break, the authors found that much of the DOC discharged by Alaskan rivers to the Arctic Ocean is labile. Consequently, riverine inputs of DOC to the Arctic Ocean may have a much larger influence on coastal ocean biogeochemistry than previously realized, and reconsideration of the role of terrigenous DOC on carbon, microbial, and food-web dynamics on the arctic shelf is warranted.

Holmes says, "Though tantalizing evidence has been emerging in recent years, this study was the first to directly show that dissolved organic carbon in rivers during the spring flood period is highly labile."

Rivers sampled for this project were the Kuparuk, Sagavanirktok, and Colville rivers on the North Slope of Alaska. The next step will be to conduct similar experiments on larger arctic rivers, including the massive rivers entering the Arctic Ocean from Siberia.

Holmes adds, "If the pattern we've shown for Alaskan arctic rivers holds for the much larger Siberian rivers, and preliminary evidence suggests that it will, then we'll have to rethink the role of terrestrially-derived DOC as a potential energy source driving the coastal ocean foodweb in the Arctic."


www.terradaily.com/reports/..._999.html

Scientists Solve 50-Year-Old Mystey Of Oceans' Seismic Buzz


by Staff Writers
Pasadena CA (SPX) Mar 10, 2008
The latest buzz in Earth science literally comes from out of the blue-the deep blue seas. For the first time, scientists have pinpointed a specific area in the North Atlantic where microseisms, small Earth tremors created when ocean waves traveling in opposite directions merge together, are emitted from the depths of the ocean.
Scientists have long known about microseisms, but no one could figure out where they came from - until now. They were first recorded as a strange, continuous buzz on the earliest seismometers, devices that measure Earth vibrations over periods from one to several seconds long. Scientists use seismometers to "hear" everything from earthquake tremors to these tiny microseismic vibrations of the ocean floor.

Every year, the cumulative energy of these small vibrations equals the combined annual energy release from earthquakes. Finding out where ocean microseisms originate could help scientists monitor stress in Earth's crust with a technique called "noise tomography." The technique uses seismic waves to image sections of the crust.

Records of microseismic activity give us a history of wave interaction in Earth's oceans since the early 20th century. They are also used to examine the history of storms over the ocean, according to Frank Webb, a geophysicist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Webb has studied this phenomenon extensively and is co-author of a new study on microseisms appearing in the March 8 issue of the Proceedings of the Royal Society, Series A. JPL's Sharon Kedar led the interdisciplinary science team, which included researchers from JPL; University of California, San Diego; the California Institute of Technology, Pasadena; and the Hydrologic Research Center in San Diego.

"It's been an interesting project, because people from very different fields were working together to address this problem," Webb said, adding that the team included both oceanographers and seismologists. "That's something that has rarely been done since we first started to look for areas where microseisms originate."

The theory of the origin of microseisms was first introduced in 1950 by Michael Longuet-Higgins from the University of Cambridge in England, who also worked on this recent project. Longuet-Higgins suggested that the vibrations originated in places where ocean waves were traveling at the same frequency opposite to each other at a certain ocean depth. According to his theory, the interacting waves combine to form stationary waves over large areas of the ocean.

These waves create tall, pulsing columns of pressure that repeatedly beat down on the ocean floor, causing it to vibrate at double the frequency of the wave. The vibrations generate seismic surface waves, which propagate thousands of miles and are detected by seismometers as noise.

Longuet-Higgin's theory was used to predict regions of the ocean where microseisms could originate. Webb said that actually finding an area of the ocean with the right conditions to generate microseisms was difficult.

"You could have two opposing waves generating these pressure fluctuations, but they have to be interacting at exactly the right depth for the ocean floor to resonate," Webb said. "Or you could have a section of ocean floor at a depth favorable to microseisms, but you then need storms to generate opposing waves that meet right over that area."

Using ocean wave models that determine the states of the ocean in different areas, the team located a region of the ocean that matches the criteria from Longuet-Higgin's theory in a region of the North Atlantic that extends from the Labrador Sea (between Greenland and the northeast coast of Canada) to the south of Iceland. The team found the region by comparing opposing wave interactions to seismic data recorded at the same area.

"With Longuet-Higgin's theory, we located areas of the ocean with high potential for microseisms, but then we needed to see if storms in those areas generated the right waves," Webb said. "The area we found in the North Atlantic Ocean had the right depth and the right storm system to generate microseisms."

While this region is not the only one to produce microseisms, it is the first region in which the source of microseisms has been located.

Webb said it was a privilege to be on a team with the originator of the theory of how microseisms form.

"It's been an honor to work with Michael Longuet-Higgins. He was really happy to revive this project, even a few decades later," Webb sai



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Giant ocean eddy shadows Sydney
The giant ocean eddy that cooled Sydney's shores a year ago has been superseded by another 300 km diameter giant

CSIRO Wealth from Oceans National Research Flagship scientist, Dr David Griffin, says the ‘birth’ of the eddy has been traced to last August.

“From satellite maps of sea-level we can see that it had been loitering this side of Lord Howe Island for some time and began approaching the NSW coast near Christmas,” Dr Griffin says.

“It remained stationary during January and simply grew larger but, because it remained offshore, less people would have noticed its impacts on water temperatures.”

The cold water at the new eddy’s centre has welled up about 500m from the ocean depths.

“In the southern hemisphere, a cold eddy has to rotate clockwise,” Dr Griffin says. “This one completes a full revolution every 10 days and the sea level at its centre is reduced by nearly 1m, which is how researchers can tell where the eddy is.”

Four people who definitely noticed the eddy were the crew who rowed across the Tasman Sea from New Zealand in late December. Skirting its southern boundary, they received a homeward boost of 3km/h or more.

“The eddy appears to be on the wane now and the question of interest for oceanographers is what have been the factors that influenced its development and led to its evolution into an ocean feature approaching the size of Tasmania,” Dr Griffin says.

Instruments that detect the height of the world’s oceans are carried by satellites such as Jason-1 (Jet Propulsion Laboratory-NASA and the French Space Agency CNES) and the European Space Agency’s Envisat. These are valuable aids to scientists developing ocean forecasting systems such as Australia’s BlueLINK.

Source: CSIRO


www.physorg.com/news125658173.html

The Antarctic deep sea gets colder

The Antarctic deep sea gets colder, which might stimulate the circulation of the oceanic water masses. This is the first result of the Polarstern expedition of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association that has just ended in Punta Arenas/Chile. At the same time satellite images from the Antarctic summer have shown the largest sea-ice extent on record. In the coming years autonomous measuring buoys will be used to find out whether the cold Antarctic summer induces a new trend or was only a "slip".

The Polarstern expedition ANT-XXIV/3 was dedicated to examining the oceanic circulation and the oceanic cycles of materials that depend on it. Core themes were the projects CASO (Climate of Antarctica and the Southern Ocean) and GEOTRACES, two of the main projects in the Antarctic in the International Polar Year 2007/08.

Under the direction of Dr. Eberhard Fahrbach, Oceanographer at the Alfred Wegener Institute, 58 scientists from ten countries were on board the research vessel Polarstern in the Southern Ocean from 6 February until 16 April, 2008. They studied ocean currents as well as the distribution of temperature, salt content and trace substances in Antarctic sea water.

"We want to investigate the role of the Southern Ocean for past, present and future climate," chief scientist Fahrbach said. The sinking water masses in the Southern Ocean are part of the overturning in this region and thus play a major role in global climate. "While the last Arctic summer was the warmest on record, we had a cold summer with a sea-ice maximum in the Antarctic. The expedition shall form the basis for understanding the opposing developments in the Arctic and in the Antarctic," Fahrbach said.

In the frame of the GEOTRACES project the scientists found the smallest iron concentrations ever measured in the ocean. As iron is an essential trace element for algal growth, and algae assimilate CO2 from the air, the concentration of iron is an important parameter against the background of the discussion to what extent the oceans may act as a carbon sink.

As the oceanic changes only become visible after several years and also differ spatially, the data achieved during the Polarstern expeditions are not sufficient to discern long-term developments. The data gap can only be closed with the aid of autonomous observing systems, moored at the seafloor or drifting freely, that provide oceanic data for several years. "As a contribution to the Southern Ocean Observation System we deployed, in international cooperation, 18 moored observing stations, and we recovered 20. With a total of 65 floating systems that can also collect data under the sea ice and are active for up to five years we constructed a unique and extensive measuring network," Fahrbach said.

In order to get the public, and especially the young generation, interested in science and research and to sensitise them for environmental processes, two teachers were on board Polarstern. Both took an active part in research work and communicated their experiences to pupils, colleagues and the media via internet and telephone. "We will bring home many impressions from this expedition, and we will be able to provide a lively picture of the polar regions and their impact on the whole earth to the pupils," Charlotte Lohse, teacher at the Heisenberg-Gymnasium in Hamburg, and Stefan Theisen from the Free Waldorf School in Kiel said.

Source: Helmholtz Association of German Research Centres



www.physorg.com/news127988684.html

Scientists reveal presence of ocean current 'stripes'

An international collaborative of scientists led by Peter Niiler, a physical oceanographer at Scripps Institution of Oceanography, UC San Diego, and Nikolai Maximenko, a researcher at the International Pacific Research Center, University of Hawaii, has detected the presence of crisscrossing patterns of currents running throughout the world’s oceans. The new data could help scientists significantly improve high-resolution models that help them understand trends in climate and marine ecosystems.

The basic dimensions of these steady patterns called striations have slowly been revealed over the course of several research papers by Niiler, Maximenko and colleagues. An analysis by Maximenko, Niiler and colleagues appearing today in the journal Geophysical Research Letters has produced the clearest representation of these striated patterns in the eastern Pacific Ocean to date and revealed that these complex patterns of currents extend from the surface to at least depths of 700 meters (2,300 feet). The discovery of similarly detailed patterns around the world is expected to emerge from future research.

Niiler credits the long-term and comprehensive ocean current measurements made over more than 20 years by the Global Drifter Program, now a network of more than 1,300 drifting buoys designed by him and administered by the National Oceanic and Atmospheric Administration (NOAA) for detecting these new current patterns on a global basis. Niiler added that the foresight of the University of California to provide long-term support to scientists was crucial to the discovery.

“I’m most grateful to the University of California for helping to support the invention and the 20-year maintenance of a comprehensive program of ocean circulation measurements,” he said. “Scripps Institution of Oceanography is unique because of its commitment to long-term observations of the climate. Instrumental measurements of the ocean are fundamental to the definition of the state of the climate today and improvement of its prediction into the future.”

In portions of the Southern Ocean, these striations—also known as ocean fronts—produce alternating eastward and westward accelerations of circulation and portions of them nearly circumnavigate Antarctica. These striations also delineate the ocean regions where uptake of carbon dioxide is greatest. In the Atlantic Ocean, these flows bear a strong association to the Azores Current along which water flowing south from the North Atlantic circulation is being subducted. The spatial high-resolution view of the linkage between the striations and the larger scale patterns of currents could improve predictions of ocean temperatures and hurricane paths.

In addition, the striations are connected to important ecosystems like the California and Peru-Chile current systems. Off California, the striations are linked to the steady east-west displacements, or meanders, of the California Current, a major flow that runs from the border of Washington and Oregon to the southern tip of Baja California. The striations run nearly perpendicular to the California Current and continue southwestward to the Hawaiian Islands.

Niiler said there are a number of scientists who have theorized the existence of striations in the ocean. He was the first to formulate such a theory as a postdoctoral researcher at Harvard University in 1965. Niiler’s theory today is that the steady-state striations in the eastern North Pacific are caused by the angular momentum of the swirling eddies within the California Current System.

The new maps of ocean circulation produced by a combination of drifter and satellite measurements will eventually be the yardstick for judging the accuracy of the circulation patterns portrayed by climate and ocean ecosystem models —a major deficiency in current simulations—and to generate substantially more reliable forecast products in climate and ecosystem management. Niiler noted, for example, that there are a large number of computer models that can simulate equatorial currents, but fail in the attempt to accurately simulate the meandering flow of the California Current and the striations that exude from it.

“I think this research presents the next challenge in ocean modeling,” said Niiler. “I’m looking forward to the day when we can correctly portray most ocean circulation systems with all climate and ecosystem models.”

Maximenko said the clear resolution of the subtle striations would not have been possible without the use of data from both the drifters and satellites.

“Our finding was so unbelievable that our first proposal submitted to the National Science Foundation failed miserably because most reviewers said ‘You cannot study what does not exist,’” Maximenko said. “The striations are like ghosts. To see them one needs to believe in them. No doubt, armed with our hint, scientists will start finding all kinds of striations all around the world.”

Maximenko, Niiler and their international colleagues are now writing a series of papers that reveal new details about the crisscross patterns and their ties to currents such as the Kuroshio, which flows in western Pacific Ocean waters near Japan.

Source: University of California - San Diego



www.physorg.com/news128337250.html

The Antarctic Deep Sea Gets Colder

by Staff Writers
Bremerhaven, Germany (SPX) Apr 29, 2008
The Antarctic deep sea gets colder, which might stimulate the circulation of the oceanic water masses. This is the first result of the Polarstern expedition of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association that has just ended in Punta Arenas/Chile. At the same time satellite images from the Antarctic summer have shown the largest sea-ice extent on record. In the coming years autonomous measuring buoys will be used to find out whether the cold Antarctic summer induces a new trend or was only a "slip".
The Polarstern expedition ANT-XXIV/3 was dedicated to examining the oceanic circulation and the oceanic cycles of materials that depend on it. Core themes were the projects CASO (Climate of Antarctica and the Southern Ocean) and GEOTRACES, two of the main projects in the Antarctic in the International Polar Year 2007/08.

Under the direction of Dr. Eberhard Fahrbach, Oceanographer at the Alfred Wegener Institute, 58 scientists from ten countries were on board the research vessel Polarstern in the Southern Ocean from 6 February until 16 April, 2008. They studied ocean currents as well as the distribution of temperature, salt content and trace substances in Antarctic sea water. "We want to investigate the role of the Southern Ocean for past, present and future climate," chief scientist Fahrbach said. The sinking water masses in the Southern Ocean are part of the overturning in this region and thus play a major role in global climate. "While the last Arctic summer was the warmest on record, we had a cold summer with a sea-ice maximum in the Antarctic. The expedition shall form the basis for understanding the opposing developments in the Arctic and in the Antarctic," Fahrbach said. In the frame of the GEOTRACES project the scientists found the smallest iron concentrations ever measured in the ocean. As iron is an essential trace element for algal growth, and algae assimilate CO2 from the air, the concentration of iron is an important parameter against the background of the discussion to what extent the oceans may act as a carbon sink.

As the oceanic changes only become visible after several years and also differ spatially, the data achieved during the Polarstern expeditions are not sufficient to discern long-term developments. The data gap can only be closed with the aid of autonomous observing systems, moored at the seafloor or drifting freely, that provide oceanic data for several years. "As a contribution to the Southern Ocean Observation System we deployed, in international cooperation, 18 moored observing stations, and we recovered 20. With a total of 65 floating systems that can also collect data under the sea ice and are active for up to five years we constructed a unique and extensive measuring network," Fahrbach said. In order to get the public, and especially the young generation, interested in science and research and to sensitise them for environmental processes, two teachers were on board Polarstern. Both took an active part in research work and communicated their experiences to pupils, colleagues and the media via internet and telephone. "We will bring home many impressions from this expedition, and we will be able to provide a lively picture of the polar regions and their impact on the whole earth to the pupils," Charlotte Lohse, teacher at the Heisenberg-Gymnasium in Hamburg, and Stefan Theisen from the Free Waldorf School in Kiel said.


www.awi.de/en/home/

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Formation Of Ice Sheets 34 Million Years Ago Changed Ocean Acidity

ScienceDaily (Apr. 29, 2008) — Before ice first began to form in Antarctica around 34 million years ago, the Earth was a very different place - but then greenhouse conditions swiftly gave way to an icehouse climate, causing the oceans to become less acidic.

Scientists at the University of Southampton's School of Ocean and Earth Science, based at the National Oceanography Centre, Southampton UK and Germany's GKSS Research Centre have been piecing together how Earth's changing climate affected ocean chemistry during this period of transition. Their work sheds light on the links between glaciation and the ocean carbon cycle.

Their research, published in Nature (24 April 2008), confirms the connection between two separate phenomena that occurred at the same time: a fall in sea-level caused by Antarctic glaciation and a change in ocean acidity - revealed by a change in the depth at which calcium carbonate shells start dissolving on the sea floor.

Dr Toby Tyrrell of the National Oceanography Centre, Southampton said:

"We were keen to discover why the oceans became suddenly less acidic - the reverse of what is happening today. Although the changes took place 34 million years ago, by understanding how the Earth System operated at this time of dramatic change we can gain insights as to how Earth will respond as we modify it by adding carbon dioxide from burning fuels."

The team used a global biogeochemical ocean model to test different explanations as to what was happening during the transition from the Eocene period - a time of warm greenhouse conditions with higher ocean acidity, to the Oligocene period - characterised by ice, cooler temperatures and lower ocean acidity.

Dr Tyrrell continued:

"This work has advanced our understanding of how the Earth System worked during this critical period. When most explanations were incorporated into our computer model, it produced results in conflict with the available data. Only one scenario was found to be compatible with the data."

Dr Tyrrell's colleague, Professor Paul Wilson also of the University of Southampton's School of Ocean and Earth Science said:

"Our work suggests that a fall in sea-level had the effect of leaving coral reefs stranded above the high-tide level where they were then eroded by wind and rain. Corals are composed of calcium carbonate - chalk - which reduces the acidity when it dissolves in seawater."

The third member of the team, Dr Agostino Merico, who is a former postdoctoral researcher at the National Oceanography Centre, Southampton and is now with the GKSS Research Centre in Geesthacht, said:

"With this powerful tool we can peer into the deep past to gain insights into arguably the most important climatic transition of the last 100 million years. With this work we have been able to put together different components and complex processes of the Earth System, and to relate them to each other. The whole point of a model is to abstract core ideas or hypothesis in a way that enables us to learn about them."

Adapted from materials provided by University of Southampton.



www.sciencedaily.com/release...0641.htm

Global Warming? Expect Cooling in Near Future


April 24, 2008 -- Global warming could take a break in the next decade thanks to a natural shift in ocean circulations, although Earth's temperature will rise as previously expected over the longer term, according to a study published on Thursday in the British journal Nature.

Climate scientists in Germany base the prediction on what they believe is an impending change in the Gulf Stream -- the conveyor belt that transports warm surface water from the tropical Atlantic to the northern Atlantic and returns cold water southwards at depth.

The Gulf Stream will temporarily weaken over the next decade, in line with what has happened regularly in the past, the researchers say.

This will lead to slightly cooler temperatures in the North Atlantic and in North America and Europe, and also help the temperatures in the tropical Pacific to remain stable, they suggest.

Last year, scientists in the UN's Intergovernmental Panel on Climate Change (IPCC) said that by 2100, global average surface temperatures could rise by between 1.1 C and 6.4 C (1.98 and 11.52 F) compared to 1980-99 levels.

In the next 20 years alone, the global climate would warm by around 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade, the IPCC said.

These calculations are based on atmospheric concentrations of carbon gases -- the famous "greenhouse effect" in which solar heat is stored in the air rather than released into space.

The heat is eventually transferred to the sea and land, ultimately disrupting Earth's complex climate system.

Climate experts have long warned, though, that warming is unlikely to be a gradual trend, but a movement in stops and starts.

The main reason for this is that the oceans -- the biggest store of heat -- go through natural cycles of circulation.

The long churning of the seas can have a far-reaching effect, sometimes delaying for years the moment when the stored warmth is released at the surface.

The authors of the new study stress that they do not dispute the IPCC's figures.

"Just to make things clear, we are not stating that anthropogenic [man-made] climate change won't be as bad as previously thought," said Mojib Latif, a professor at the Leibniz Institute of Marine Sciences in Kiel, northern Germany.

"What we are saying is that on top of the warming trend, there is a long-periodic oscillation that will probably lead to a lower temperature increase than we would expect from the current trend during the next years."

Fellow author Johann Jungclaus of the Max Planck Institute for Meteorology in Hamburg, likened the trend to "driving from the coast to a mountainous area and crossing some hills and valleys before you reach the top."

In some years, the natural long-term variation in ocean circulation would work in the other direction, temporarily pushing on the warming accelerator, Jungclaus warned.

In a commentary also published by Nature, Richard Wood, a scientist at Britain's Hadley Centre for climate change, said it was useful to get some idea about the jagged variability of global warming.

Such information could be precious for planners seeking to beef up protection against the impact of climate change, and who need to know when these expensive defences have to be completed.

But Wood queried the study's focus on the Gulf Stream, saying its turnover was affected not just by temperature but also by saltiness.

The salinity of water entering the North Atlantic is being affected by meltwater running off Greenland glaciers and Siberian permafrost, and some research suggests this is already slowing the conveyor belt.




dsc.discovery.com/news/2008...oling.html

Scientists discover new ocean current

Scientists at the Georgia Institute of Technology have discovered a new climate pattern called the North Pacific Gyre Oscillation. This new pattern explains, for the first time, changes in the water that are important in helping commercial fishermen understand fluctuations in the fish stock.

They’re also finding that as the temperature of the Earth is warming, large fluctuations in these factors could help climatologists predict how the oceans will respond in a warmer world. The research appears in April 30 edition of the journal Geophysical Research Letters.

“We’ve been able to explain, for the first time, the changes in salinity, nutrients and chlorophyll that we see in the Northeast Pacific,” said Emanuele Di Lorenzo, assistant professor in Georgia Tech’s School of Earth and Atmospheric Sciences.

Since 1945, fishermen in the California current of the Pacific Ocean have been tracking temperature, salinity and nutrients, among other things, in the ocean to help them predict changes in fish populations like sardines and anchovies that are important for the industry. Studying this data, along with satellite images, Di Lorenzo discovered a pattern of current that he named the North Pacific Gyre Oscillation.

Recent satellite data suggest that this current is undergoing intensification as the temperature of the Earth has risen over the past few decades.

"Although the North Pacific Gyre Oscillation is part of a natural cycle of the climate system, we find evidence suggesting that its amplitude may increase as global warming progresses," said Di Lorenzo.

If this is true, this newly found climate pattern mey help scientists predict how the ecosystem of the Pacific Ocean is likely to change if the world continues to warm, as predicted by the Intergovernmental Panel on Climate Change.

Source: Georgia Institute of Technology



www.physorg.com/news128782819.html

Ocean Acidification: Another Undesired Side Effect Of Fossil Fuel-burning

ScienceDaily (May 24, 2008) — Up to now, the oceans have buffered climate change considerably by absorbing almost one third of the worldwide emitted carbon dioxide. The oceans represent a significant carbon sink, but the uptake of excess CO2 stemming from man's burning of fossil fuels comes at a high cost: ocean acidification.

Research on ocean acidification is a newly emerging field and was one of the major topics at this year's European Geosciences Union (EGU) General Assembly held in Vienna in April.*

The chemistry is very straight-forward: ocean acidification is linearly related to the amount of CO2 we produce. CO2 dissolves in the ocean, reacts with seawater and decreases the pH. Since the industrial revolution, the oceans have become 30 percent more acidic (from 8.2 pH to 8.1 pH). "Under a "business as usual scenario, predictions for the end of the century are that we will lower the surface ocean pH by 0.4 pH units, which means that the surface oceans will become 150 percent more acidic -- and this is a 'hell of a lot' ", said Jelle Bijma, chair of the EuroCLIMATE programme Scientific Committee and a biogeochemist at the Alfred-Wegener-Institute Bremerhaven.

"Ocean acidification is more rapid than ever in the history of the earth and if you look at the pCO2 (partial pressure of carbon dioxide) levels we have reached now, you have to go back 35 million years in time to find the equivalents" continued Bijma. A maximum allowed change in pH, where the system is still controllable, needs to be found. This is a major challenge considering the multifaceted unknowns that still are to be clarified. This so-called "tipping point" is currently estimated to allow a drop of about 0.2 pH units, a value that could be reached in as near as 30 years. More research and further modeling needs to be undertaken to verify the predictions.

The expected biological impact of ocean acidification remains still uncertain. Most calcifying organisms such as corals, mussels, algae and plankton investigated so far, respond negatively to the more acidic ocean waters. Because of the increased acidity, less carbonate ions are available, which means the calcification rates of the organisms are decreasing and thus their shells and skeletons thinning. However, a recent study suggested that a specific form of single-celled algae called coccolithophores actually gets stimulated by elevated pCO2 levels in the oceans, creating even bigger uncertainties when it comes to the biological response.

"There are thousands of calcifying organisms on earth and we have investigated only six to ten of them, we need to have a much better understanding of the physiological mechanisms" demanded Jean-Pierre Gattuso, a speaker from Laboratoire d'Océanographie Villefranche invited by EuroCLIMATE. In addition, higher marine life forms are likely to be affected by the rapidly acidifying oceans and entire food webs might be changing.

So far, hardly any economic impact assessments of ocean acidification exist, but with the fragile marine ecosystems under threat, it can be assumed that fisheries and many coastal economies will be severely affected. Many of these societies depend on the sea as their main source of food and the loss of species is highly detrimental to them; coral reefs serve as highly valuable tourist destinations and as natural protections against natural hazards such as tsunamis. Together with climate change, ocean acidification poses a major challenge to the oceans as a human habitat.

"Ocean acidification is happening today and it's happening on top of global warming, so we are in double trouble" stated Bijma. Only a serious cut of CO2 emission can reduce ocean acidification. Therefore, knowledge on ocean acidification is being disseminated and awareness among policymakers and the general public raised. "We need to make sure that the message gets delivered to the right people at the right time" urged Carol Turley, lead author of the Nobel prize-winning IPCC report and scientist at the Plymouth Marine Laboratory. According to her, a concise integrated opinion of leading scientists is necessary, and it would be useful for policy makers to devote one integrated chapter on the impacts of climate change including ocean acidification on the marine environment in a future IPCC report.

European science has taken the initiative to act and gain more urgently needed insight on this phenomenon of global change; an EU project on ocean acidification will be launched next month. The European Geosciences Union (EGU), an influential interdisciplinary organization, is also being proactive: "EGU is in the process of putting together a position statement on ocean acidification" said Gerald Ganssen, President of the EGU. As a result attained at a strategic workshop held in January, the ESF is currently producing a 'Science Policy Briefing' which is to be targeted at the major stakeholders and actors in the field. In addition it was felt that the issue of ocean acidification needs to be addressed in a pan-European effort and that more intensive European collaboration is required, which could be achieved through one of the ESF Science Synergy tools such as EUROCORES.

The climate for the next century, and thereafter, is expected to be largely different from the present and the recent past. CO2 concentration is expected to reach levels unequalled over the past millions of years. Temperature is also rising rapidly. The last 150 years of meteorological observations and the reconstruction over the last millennium display a quite uniform climate. Only the reconstruction of paleoclimates extending much further back in time can help build a database with a broader climatic diversity. Such a database will, in addition, offer the possibility to test the reliability and robustness of the models used for future climate scenarios and thus to better understand how the climate system works. EuroCLIMATE focuses both on reconstructing past climates using different well-dated and calibrated proxy records and on modelling climate and climate variations for a better understanding of the underlying physical, chemical and biological processes involved.

*The European Science Foundation EUROCORES (European Collaborative Research) programme EuroCLIMATE, which addresses in particular global carbon cycle dynamics, organized and co-sponsored several sessions on ocean acidification.


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Adapted from materials provided by European Science Foundation.


www.sciencedaily.com/release...5251.htm

Tidal Cycle Could Amplify Global-warming Related Sea-level Rises

ScienceDaily (May 24, 2008) — The results of several scientific studies conducted since 1993 have confirmed a 3.2 cm sea level rise. Although this variation might appear negligible, it has in fact turned out to be twice as high as that recorded over the whole of the previous century. This increase in sea level is a consequence of global warming. When sea temperature rises, the sea expands and therefore occupies a greater volume. This phenomenon is now well known to scientists, but other processes that have received less research attention, such as the tidal cycle, seem to contribute at global scale just as much to changes in sea level.

A team coordinated by IRD scientists compared a series of satellite images collected at regular intervals over 20 years to measure the contribution of the bidecennial tidal cycle on global sea-level variations. In the first phase of the study, the scientists focused on the 350 km of French Guianan coastline found to be highly suitable for observation of the phenomenon. This is a virgin region completely unaffected by any human activity and bears the certainty that the slightest change observed in the geomorphology of that coast is natural in origin. The geographical zone is moreover covered by an ecosystem of mangroves whose coastal fringe reacts almost immediately to fluctuations in marine conditions.

The study used 60 images taken by Spot, Landsat, ASAR and JERS satellites to follow-up the changes and developments of the mangrove areas over the 20-year period from 1986 to 2006, in other words a complete bidecennial tidal cycle. In parallel and over the same period, altimetric satellites (Ssalto data produced by Aviso) gave a measure of the change in the sea level. By comparing and contrasting the data resulting from these two types of satellite device, the scientists arrived at a measure of the process’s contribution of the physical features of the coastline.

Their analysis indicated that a 3% increase in tidal amplitude on the French Guiana coast, and along the whole of the 1500 km stretch of coastline of the Guiana Plateau, induced more than 100 m of coastal erosion and shoreline retreat during the first ten years of the cycle. A subsequent 3% fall in the course of the second half of the cycle then allowed regeneration of the mangrove colonies, a sure sign of coastal advance. The results also suggested that 75% of the rise of the open sea level recorded for this coastal zone during the first ten years of the cycle was attributable to the tidal cycle.

On the Guiana Plateau coast, the tidal range –the difference between the high-tide and low-tide water levels– is quite low as it settles at around two metres on average. In this context, it is predicted that between 2006 and 2015 the rise in open sea level, directly linked to the bidecennial cycle, will not exceed a few centimetres. It should therefore be about the same order of magnitude as the sea level increase linked to thermal expansion of the ocean.

Extrapolation of the results obtained for the Guiana Plateau coast led to an estimate of the impact of the tidal cycle on the sea level rise at global scale (see Map). Coastal zones exist where the tidal range is much more spectacular in size than on the Guianan coasts. At Mont Saint-Michel in France, for example, it can be more than 12 m. And in Ungava Bay, on the East coast of Canada, where the world’s largest tidal amplitudes are recorded, it reaches as high as 20 m. In these regions, from the present day (2008) to 2015, the bidecennial tidal cycle could cause a rise in the open sea level of more than 50 cm, or 25 times greater than the rise linked to global-warming induced oceanic thermal expansion.

Over the period 2015-2025, the second phase of this cycle is predicted to contribute to a regular fall in the open sea level. At planetary scale, it could thus partly compensate for the effects of the global-warming related rise in the sea water. Thanks to a better awareness of the cyclic nature of the tides, probably one of the most predictable cyclic systems in the world, this research should, over the next 20 years, lead to a better understanding of coastal geomorphology and in particular the processes of coastal erosion.


--------------------------------------------------------------------------------

Journal reference:

N. Gratiot, E. J. Anthony, A. Gardel, C. Gaucherel, C. Proisy, J. T. Wells, Significant contribution of the 18.6 year tidal cycle to regional coastal changes. Nature Geoscience. volume 1, March 2008. Doi: 10.1038/ngeo127
Adapted from materials provided by Institut de Recherche pour le Développement, via AlphaGalileo.



www.sciencedaily.com/release...4943.htm

Invisible Waves Shape Continental Slope, Researcher Says


A class of powerful, invisible waves hidden beneath the surface of the ocean can shape the underwater edges of continents and contribute to ocean mixing and climate, researchers from The University of Texas at Austin have found.


The scientists simulated ocean conditions in a laboratory aquarium and found that "internal waves" generate intense currents when traveling at the same angle as that of the continental slope. The continental slope is the region where the relatively shallow continental shelf slants down to meet the deep ocean floor.

They suspect that these intense currents, called boundary flows, lift sediments as the waves push into the continental slope, maintaining the angle of the slope through erosion. The action of the internal waves could also mix layers of colder and warmer water.

"Surprisingly little is known about how internal waves are generated and how they could lead to the mixing of the deep ocean, but it's very important," said physicist Hepeng Zhang. "Understanding ocean mixing is crucial for us to know whether changes in ocean circulation are the result of climate change or just variability."

Zhang said that as long as there is tidal motion that generates internal waves traveling along the continental slope, intense boundary flow will be produced.

"Twenty-four hours a day, seven days a week over a long geological time scale, and this will maintain the angle of the continental slope," he said.

He published his research with colleagues Harry Swinney and Benjamin King in Physical Review Letters.

Zhang studied internal waves using a simple saltwater aquarium equipped with a sloping bottom simulating the continental slope. Water in the tank increased in density from top to bottom, just as water is denser on the ocean floor. Thousands of very small particles, 10 microns or smaller, were suspended in the water.

As Zhang generated waves in the tank, he took photographs and video footage of the particles and then analyzed the particles' direction of flow and velocity.

Particle motion revealed intense boundary flows when the angle of the bottom matched the angle at which internal waves can travel.

Oceanic continental slopes could theoretically reach angles of 15 to 20 degrees as sediments continually pour down from the continents, but Zhang said that the internal waves are limiting the angle to around three degrees, the average angle of continental slopes.

The internal waves could also play a role in larger ocean currents by bringing cold water up from the deep ocean to the surface at the equator.

Ocean currents form closed loops, with warm surface water, like the Gulf Stream, moving toward the poles and cold water circulating back toward the equator at depth. The warm surface water heated at the equator is largely driven to the poles by wind. At the poles, this water is cooled by the cold air and mixes with cold water from melting glaciers and ice. Although fresh water is less dense than sea water, the cooling effect wins out and the density increases until the water sinks.

Zhang found that the internal waves could help bring this cold water closer to the surface when the boundary flow pushes heavier, colder water over warmer lighter water on the continental slope. This results in the internal wave breaking and mixing on the slope, just as a surface wave breaks on the shore.

"How exactly this will contribute to ocean circulation, I really don't know," said Zhang. "But it is definitely a step we have to understand before we can understand global ocean circulation."

Source: University of Texas at Austin



www.physorg.com/news134052639.html

Epic Ebbs And Flows

by Staff Writers
Madison WI (SPX) Jul 01, 2008
If you are curious about Earth's periodic mass extinction events such as the sudden demise of the dinosaurs 65 million years ago, you might consider crashing asteroids and sky-darkening super volcanoes as culprits.
But a new study, published online June 15 in the journal Nature, suggests that it is the ocean, and in particular the epic ebbs and flows of sea level and sediment over the course of geologic time, that is the primary cause of the world's periodic mass extinctions during the past 500 million years.

The study highlights the important connections between life on Earth and our planet's changing environment.

"The expansions and contractions of those environments have pretty profound effects on life on Earth," says Shanan Peters, a University of Wisconsin-Madison assistant professor of geology and geophysics and the author of the new Nature report.

In short, according to Peters, changes in ocean environments related to sea level exert a driving influence on rates of extinction, which animals and plants survive or vanish, and generally determine the composition of life in the oceans.

Since the advent of life on Earth 3.5 billion years ago, scientists think there may have been as many as 23 mass extinction events, many involving simple forms of life such as single-celled microorganisms. During the past 540 million years, there have been five well-documented mass extinctions, primarily of marine plants and animals, with as many as 75 to 95 percent of species lost.

For the most part, scientists have been unable to pin down the causes of such dramatic events. In the case of the demise of the dinosaurs, scientists have a smoking gun, an impact crater that suggests dinosaurs were wiped out as the result of a large asteroid crashing into the planet. But the causes of other mass extinction events have been murky, at best.

"Paleontologists have been chipping away at the causes of mass extinctions for almost 60 years," explains Peters, whose work was supported by the National Science Foundation. "Impacts, for the most part, aren't associated with most extinctions. There have also been studies of volcanism, and some eruptions correspond to extinction, but many do not."

Arnold I. Miller, a paleobiologist and professor of geology at the University of Cincinnati, says the new study is striking because it establishes a clear relationship between the tempo of mass extinction events and changes in sea level and sediment: "Over the years,researchers have become fairly dismissive of the idea that marine mass extinctions like the great extinction of the Late Permian might be linked to sea-level declines, even though these declines are known to have occurred many times throughout the history of life. The clear relationship this study documents will motivate many to rethink their previous views."

Peters measured two principal types of marine shelf environments preserved in the rock record, one where sediments are derived from erosion of land and the other composed primarily of calcium carbonate, which is produced in-place by shelled organisms and by chemical processes.

"The physical differences between (these two types) of marine environments have important biological consequences," Peters explains, noting differences in sediment stability, temperature, and the availability of nutrients and sunlight.In the course of hundreds of millions of years, the world's oceans have expanded and contracted in response to the shifting of the Earth's tectonic plates and to changes in climate.

There were periods of the planet's history when vast areas of the continents were flooded by shallow seas, such as the shark- and mosasaur-infested seaway that neatly split North America during the age of the dinosaurs.

As those epicontinental seas drained, animals such as mosasaurs and giant sharks went extinct, and conditions on the marine shelves where life exhibited its greatest diversity in the form of things like clams and snails changed as well.

The new Wisconsin study, Peters says, does not preclude other influences on extinction such as physical events like volcanic eruptions or killer asteroids, or biological influences such as disease and competition among species. But what it does do, he argues, is provide a common link to mass extinction events over a significant stretch of Earth history.

"The major mass extinctions tend to be treated in isolation (by scientists)," Peters says. "This work links them and smaller events in terms of a forcing mechanism, and it also tells us something about who survives and who doesn't across these boundaries. These results argue for a substantial fraction of change in extinction rates being controlled by just one environmental parameter."



www.terradaily.com/reports/..._999.html

Oscillation Rules as the Pacific Cools
Space & Earth science / Earth Sciences


The latest image of sea-surface height measurements from the U.S./French Jason-1 oceanography satellite shows the Pacific Ocean remains locked in a strong, cool phase of the Pacific Decadal Oscillation, a large, long-lived pattern of climate variability in the Pacific associated with a general cooling of Pacific waters. The image also confirms that El Niño and La Niña remain absent from the tropical Pacific.

The image is based on the average of 10 days of data centered on Nov. 15, 2008, compared to the long-term average of observations from 1993 through 2008. In the image, places where the Pacific sea-surface height is higher (warmer) than normal are yellow and red, and places where the sea surface is lower (cooler) than normal are blue and purple. Green shows where conditions are near normal. Sea-surface height is an indicator of the heat content of the upper ocean.

The Pacific Decadal Oscillation is a long-term fluctuation of the Pacific Ocean that waxes and wanes between cool and warm phases approximately every five to 20 years. In the present cool phase, higher-than-normal sea-surface heights caused by warm water form a horseshoe pattern that connects the north, west and southern Pacific. This is in contrast to a cool wedge of lower-than-normal sea-surface heights spreading from the Americas into the eastern equatorial Pacific. During most of the 1980s and 1990s, the Pacific was locked in the oscillation's warm phase, during which these warm and cool regions are reversed. For an explanation of the Pacific Decadal Oscillation and its present state, see: jisao.washington.edu/pdo/ and www.esr.org/pdo_index.html .

Sea-surface temperature satellite data from the National Oceanic and Atmospheric Administration mirror Jason sea-surface height measurements, clearly showing a cool Pacific Decadal Oscillation pattern, as seen at: www.cdc.noaa.gov/map/image...t.anom.gif .

"This multi-year Pacific Decadal Oscillation 'cool' trend can cause La Niña-like impacts around the Pacific basin," said Bill Patzert, an oceanographer and climatologist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The present cool phase of the Pacific Decadal Oscillation will have significant implications for shifts in marine ecosystems, and for land temperature and rainfall patterns around the Pacific basin."

According to Nathan Mantua of the Climate Impacts Group at the University of Washington, Seattle, whose research contributed to the early understanding of the Pacific Decadal Oscillation, "Even with the strong La Niña event fading in the tropics last spring, the North Pacific's sea surface temperature anomaly pattern has remained strongly negative since last fall. This cool phase will likely persist this winter and, perhaps, beyond. Historically, this situation has been associated with favorable ocean conditions for the return of U.S. west coast Coho and Chinook salmon, but it translates to low odds for abundant winter/spring precipitation in the southwest (including Southern California)."

Jason's follow-on mission, the Ocean Surface Topography Mission/Jason-2, was successfully launched this past June and will extend to two decades the continuous data record of sea surface heights begun by Topex/Poseidon in 1992. The new mission has produced excellent data, which have recently been certified for operational use. Fully calibrated and validated data for science use will be released next spring.

Provided by NASA


www.physorg.com/news148148961.html

Acid oceans 'need urgent action'


The world's marine ecosystems risk being severely damaged by ocean acidification unless there are dramatic cuts in CO2 emissions, warn scientists.

More than 150 top marine researchers have voiced their concerns through the "Monaco Declaration", which warns that changes in acidity are accelerating.

The declaration, supported by Prince Albert II of Monaco, builds on findings from an earlier international summit.

It says pH levels are changing 100 times faster than natural variability.

Based on the research priorities identified at The Ocean in a High CO2 World symposium, held in October 2008, the declaration states:

"We scientists who met in Monaco to review what is known about ocean acidification declare that we are deeply concerned by recent, rapid changes in ocean chemistry and their potential, within decades, to severely affect marine organisms, food webs, biodiversity and fisheries."

'The other CO2 problem'

It calls on policymakers to stabilise CO2 emissions "at a safe level to avoid not only dangerous climate change but also dangerous ocean acidification".


The researchers warn that ocean acidification, which they refer to as "the other CO2 problem", could make most regions of the ocean inhospitable to coral reefs by 2050, if atmospheric CO2 levels continue to increase.

The also say that it could lead to substantial changes in commercial fish stocks, threatening food security for millions of people.

"The chemistry is so fundamental and changes so rapid and severe that impacts on organisms appear unavoidable," said Dr James Orr, chairman of the symposium.

"The questions are now how bad will it be and how soon will it happen."

Another signatory, Patricio Bernal, executive secretary of the UN Intergovernmental Oceanographic Commission, outlined how the marine research community intended to respond to the challenge.

"We need to bring together the best scientists to share their latest research results and to set priorities for research to improve our knowledge of the processes and of the impacts of acidification on marine ecosystems."

Prince Albert II used the declaration to voice his concerns, adding that he hoped the world's leaders would take the "necessary action" at a key UN climate summit later this year.

"I strongly support this declaration. I hope that it will be heard by all the political leaders meeting in Copenhagen in December 2009."




news.bbc.co.uk/1/hi/sci/tech/7860350.stm

Research indicates ocean current shutdown may be gradual

July 16th, 2009 The findings of a major new study are consistent with gradual changes of current systems in the North Atlantic Ocean, rather than a more sudden shutdown that could lead to rapid climate changes in Europe and elsewhere.

The research, based on the longest experiment of its type ever run on a "general circulation model" that simulated the Earth's climate for 21,000 years back to the height of the last Ice Age, shows that major changes in these important ocean current systems can occur, but they may take place more slowly and gradually than had been suggested.

The newest findings, to be published Friday in the journal Science, are consistent with other recent studies that are moving away from the theory of an abrupt "tipping point" that might cause dramatic atmospheric temperature and ocean circulation changes in as little as 50 years.

"Research is now indicating that this phenomenon may happen, but probably not as a sudden threshold we're crossing," said Peter Clark, a professor of geosciences at Oregon State University. "For those who have been concerned about extremely abrupt changes in these ocean current patterns, that's good news.

"In the past it appears the ocean did change abruptly, but only because of a sudden change in the forcing," he said. "But when the ocean is forced gradually, such as we anticipate for the future, its response is gradual. That would give ecosystems more time to adjust to new conditions."

The findings do not change broader concerns about global warming. Temperatures are still projected to increase about four to 11 degrees by the end of this century, and the study actually confirms that some of the world's most sophisticated climate models are accurate.

"The findings from this study, which also match other data we have on recorded climate change, are an important validation of the global climate models," Clark said. "They seem to be accurately reflecting both the type and speed of changes that have taken place in the past, and that increases our ability to trust their predictions of the future."

The intensity of computation on this experiment, involving a quadrillion calculations each second, was so great that it took more than a year to run, Clark said. It was the longest such study of its type that ever examined past climate in such detail and complexity. The research was supported by the National Science Foundation and other agencies.

It included the height of the last Ice Age about 21,000 years ago, the emergence of the Earth from that Ice Age around 14,000 years ago, and some other fairly sudden warming and cooling events during those periods that are of considerable interest to paleoclimatologists.

The period when the Earth emerged from its last Ice Age actually had amounts of natural warming similar to those that may be expected in the next century or two, with some of the same effects - melting of ice sheets, sea level rise, increases in atmospheric carbon dioxide. Studies of those periods, researchers say, will provide valuable insights into how the Earth may respond to its current warming.

A particular concern for some time has been the operation of an ocean current pattern called the Atlantic meridional overturning circulation, or AMOC. This current system is part of what keeps Europe much warmer than it would otherwise be, given its far northern latitudes, and there is evidence that it has "shut down" with some regularity in Earth's past - apparently in response to large influxes of fresh water, and sometimes quite rapidly.

"Our data still show that current is slowing, and may decline by 30 percent by the end of this century," Clark said. "That's very significant, and it could cause substantial climate change. But it's not as abrupt as some concerns that it could shut down within a few decades."

Climate changes, Clark said, are actually continuing to occur somewhat more rapidly than had been predicted in recent years. Arctic Sea ice is both thinning and shrinking, and atmospheric carbon dioxide levels are going up faster than had been projected by the Intergovernmental Panel on Climate Change.

Source: Oregon State University


www.physorg.com/news166973872.html