Tag Archives: paleoclimatology

Prehistoric greenhouse data from ocean floor could predict Earth's future

Prehistoric greenhouse data from ocean floor could predict Earth’s future, study finds.

ScienceDaily (Oct. 27, 2011) — New research from the University of Missouri indicates that Atlantic Ocean temperatures during the greenhouse climate of the Late Cretaceous Epoch were influenced by circulation in the deep ocean. These changes in circulation patterns 70 million years ago could help scientists understand the consequences of modern increases in greenhouse gases.

“We are examining ocean conditions from several past greenhouse climate intervals so that we can understand better the interactions among the atmosphere, the oceans, the biosphere, and climate,” said Kenneth MacLeod, professor of geological sciences in the College of Arts and Science. “The Late Cretaceous Epoch is a textbook example of a greenhouse climate on earth, and we have evidence that a northern water mass expanded southwards while the climate was cooling. At the same time, a warm, salty water mass that had been present throughout the greenhouse interval disappeared from the tropical Atlantic.”

The study found that at the end of the Late Cretaceous greenhouse interval, water sinking around Greenland was replaced by surface water flowing north from the South Atlantic. This change caused the North Atlantic to warm while the rest of the globe cooled. The change started about five million years before the asteroid impact that ended the Cretaceous Period.

To track circulation patterns, the researchers focused on “neodymium,” an element that is taken up by fish teeth and bones when a fish dies and falls to the ocean floor. MacLeod said the ratio of two isotopes of neodymium acts as a natural tracking system for water masses. In the area where a water mass forms, the water takes on a neodymium ratio like that in rocks on nearby land. As the water moves through the ocean, though, that ratio changes little. Because the fish take up the neodymium from water at the seafloor, the ratio in the fish fossils reflects the values in the area where the water sank into the deep ocean. Looking at changes through time and at many sites allowed the scientists to track water mass movements.

While high atmospheric levels of carbon dioxide caused Late Cretaceous warmth, MacLeod notes that ocean circulation influenced how that warmth was distributed around the globe. Further, ocean circulation patterns changed significantly as the climate warmed and cooled.

“Understanding the degree to which climate influences circulation and vice versa is important today because carbon dioxide levels are rapidly approaching levels most recently seen during ancient greenhouse times,” said MacLeod. “In just a few decades, humans are causing changes in the composition of the atmosphere that are as large as the changes that took millions of years to occur during geological climate cycles.”

The paper, “Changes in North Atlantic circulation at the end of the Cretaceous greenhouse interval,” was published in the October online edition of the journal Nature Geoscience. Coauthors include C. Isaza Londoño of the University of Missouri; E.E. Martin and C. Basak of the University of Florida, and A. Jiménez Berrocoso of the Unviersity of Manchester, United Kingdom. The study was sponsored by the National Science Foundation.

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The above story is reprinted from materials provided by University of Missouri-Columbia.

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Journal Reference:

  1. K. G. MacLeod, C. Isaza Londoño, E. E. Martin, Á. Jiménez Berrocoso, C. Basak. Changes in North Atlantic circulation at the end of the Cretaceous greenhouse interval. Nature Geoscience, 2011; DOI: 10.1038/ngeo1284

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MLA

University of Missouri-Columbia (2011, October 27). Prehistoric greenhouse data from ocean floor could predict Earth’s future, study finds. ScienceDaily. Retrieved November 1, 2011, from http://www.sciencedaily.com­/releases/2011/10/111027150213.htm

Note: If no author is given, the source is cited instead.

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Long-lost Lake Agassiz offers clues to climate change

Long-lost Lake Agassiz offers clues to climate change.

ScienceDaily (Oct. 5, 2011) — What caused water levels to drop in an immense yet long-vanished lake? Research by a University of Cincinnati geologist suggests that conditions 12,000 years ago encouraged evaporation.

Not long ago, geologically speaking, a now-vanished lake covered a huge expanse of today’s Canadian prairie. As big as Hudson Bay, the lake was fed by melting glaciers as they receded at the end of the last ice age. At its largest, Glacial Lake Agassiz, as it is known, covered most of the Canadian province of Manitoba, plus a good part of western Ontario. A southern arm straddled the Minnesota-North Dakota border.

Not far from the ancient shore of Lake Agassiz, University of Cincinnati Professor of Geology Thomas Lowell will present a paper about the lake to the Geological Society of America annual meeting in Minneapolis. Lowell’s paper is one of 14 to be presented Oct. 10 in a session titled: “Glacial Lake Agassiz — Its History and Influence on North America and on Global Systems: In Honor of James T. Teller.”

Although Lake Agassiz is gone, questions about its origin and disappearance remain. Answers to those questions may provide clues to our future climate. One question involves Lake Agassiz’ role in a thousand-year cold snap known as the Younger Dryas.

As the last ice age ended, thousands of years of warming temperatures were interrupted by an abrupt shift to cold. Tundra conditions expanded southward, to cover the land exposed as the forests retreated. This colder climate is marked in the fossil record by a flowering plant known as Dryas, which gives the period its name.

“My work focuses on abrupt or rapid climate change,” Lowell said. “The Younger Dryas offers an opportunity to study such change. The climate then went from warming to cooling very rapidly, in less than 30 years or so.”

Scientists noted that the Younger Dryas cold spell seemed to coincide with lower water levels in Lake Agassiz. Had the lake drained? And, if so, had the fresh water of the lake caused this climate change by disrupting ocean currents? This is the view of many scientists, Lowell said.

Lowell investigated a long-standing mystery involving Lake Agassiz — a significant drop in water level known as the Moorhead Low. It has long been believed that the Moorehead Low when water drained from Lake Agassiz through a new drainage pathway. Could this drainage have flowed through the St. Lawrence Seaway into the North Atlantic Ocean?

“The most common hypothesis for catastrophic lowering is a change in drainage pathways,” Lowell said.

The problem is, better dating of lake levels and associated organic materials do not support a rapid outflow at the right time.

“An alternative explanation is needed,” he said.

Lowell’s research shows that, although water levels did drop, the surface area of the lake increased more than seven-fold at the same time. His research suggests that the lower water levels were caused by increased evaporation, not outflow. While the melting glacier produced a lot of water, Lowell notes that the Moorhead Low was roughly contemporaneous with the Younger Dryas cold interval, when the atmosphere was drier and there was increased solar radiation.

“The dry air would reduce rainfall and enhance evaporation,” Lowell said. “The cold would reduce meltwater production, and shortwave radiation would enhance evaporation when the lake was not frozen and sublimation when the lake was ice-covered.”

Further research will attempt a clearer picture of this ancient episode, but researchers will have to incorporate various factors including humidity, yearly duration of lake ice, annual temperature, and a better understanding of how and where meltwater flowed from the receding glaciers.

Lowell’s efforts to understand changes in ancient climates have taken him from Alaska to Peru, throughout northern Canada and Greenland.

In Greenland, Lowell and a team of graduate students pulled cores of sediment from lakes that are still ice-covered for most of the year. Buried in those sediments are clues to long-ago climate.

“We look at the mineralogy of the sediments,” Lowell said, “and also the chironomids. They’re a type of midge and they’re very temperature sensitive. The exact species and the abundance of midges in our cores can help pinpoint temperature when these sediments were deposited.”

Lowell’s research was initially funded by the Comer Foundation. In recent years, the National Science Foundation has provided funding for this work.

When the Geological Society of America meets this year the University of Cincinnati will be well represented, with more than two dozen papers and presentations. Topics range from ice-age climate to the health effects of corrosion in drinking water pipes.

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Mystery Fossils Link Fungi to Ancient Mass Extinction

Mystery Fossils Link Fungi to Ancient Mass Extinction | Wired Science | Wired.com.

By Scott K. Johnson, Ars Technica

Of the five mass extinctions in the Earth’s past, one stands above the rest in magnitude: the Permian-Trassic extinction, known as the Great Dying. It saw the disappearance of almost 60 percent of all families, and over 80 percent of all genera — in the ocean, that added up to about 96 percent of all species. The cause of this event, 250 million years in the past, is still a matter of debate.

The most likely culprit is the prolific volcanism of the Siberian Traps— the erupted basalt still covers about 2 million square kilometers — but other events may have also played a role. Evidence for a massive destabilization of methane hydrates on the seafloor (a phenomenon described as “The Big Burp”), ocean anoxia and even contemporary asteroid impacts have all been found.

A couple of recent papers in the journal Geology have brought some new information to the discussion, and may help make the picture just a little bit clearer.

 

One source of significant mystery has been the nature of the organic microfossils that are common in rocks dated to the time of the extinction worldwide. The tiny fossils resemble filamentous colonies of cells, but have evaded positive identification.

Some researchers think they are the remains of fungi, while others argue that they are algae instead. There’s evidence on both sides, but the two scenarios represent very different conditions. The fungus indicates a widespread dying of woody vegetation, while algae suggest extensive swamps forming along river systems.

A paper published this month shows that the microfossils are almost identical morphologically to a group of pathogenic soil fungi that can infect trees. If its authors have identified these correctly, it fits in well with an overall picture showing loss of forests and topsoil. The demise of tree species is clear in pollen studies, and there is a lot of evidence for greatly accelerated soil erosion, including increased sediment deposition in deltas with lots of soil-derived organic debris.

Modern studies show that drought stress and UV damage, both of which could be caused by the massive releases of volcanic gases from the Siberian Traps, can make trees susceptible to fungal infection.

Connecting a fungus to a global mass extinction may seem tenuous, but the authors point out that processes down in the world of the very small are often overlooked in any extinction discussions. They summarize by saying, “There may have been a variety of other globally operating environmental stress factors, but whatever sequence of events triggered ecosystem destabilization on land, the aggressiveness of soil-borne pathogenic fungi must have been an integral factor involved in Late Permian forest decline worldwide.”

Separately, another recent paper has pinned down the timing of the extinction. It’s not considered to have been as sudden as the End Cretaceous extinction that killed off the dinosaurs, but the precise timeline has been tough to get a handle on, and estimates have varied.

The research group looked at some marine Permian-Triassic rocks in China that recorded cyclical global climate patterns. Climate controlled the amount of terrestrial sediment that was deposited in this area, which shows up as changes in grain size through the rock layers. Using a device that measures magnetic susceptibility, they were able to precisely quantify changes in grain size across the rock layers. Together with some uranium-lead isotopic ages, they were able to pick out the orbital cycles that control climate, including the prominent 400,000-year eccentricity cycle, and use them to precisely date the extinction interval.

A couple of interesting things show up in the data. For one, minima in several of the orbital cycles coincide shortly before the start of the extinction period. (Think of three sine waves with different wavelengths — at certain points in time, all three troughs will line up by chance.) That could have made for some unusual climatic conditions. Additionally, the effect of the 100,000-year orbital cycle on climate seems diminished for as long as 2 million years afterward.

It’s dangerous to extrapolate to the big picture from records like this, but there’s enough there to warrant further investigation of the orbital forcings.

In the end, they found that the extinction took 600,000 to 700,000 years to play out. This is consistent with the idea that several events acted in concert to destabilize ecosystems and cause the loss of so many species, meaning a significant length of time would be needed. It was simply a nasty time to be a living thing on planet Earth. Some advice for any time travelers out there — steer well clear of the Great Dying.

Image: Photomicrographic comparison of fossil and modern filamentous fungal structures. A: Sclerotium of modern Rhizoctonia aff. solani, aggregated monilioid hyphae (Paul Cannon/Centre for Agriculture and Biosciences International, CABI). B: Modern R. solani, branched monilioid hyphae (Lane Tredway/American Phytopathological Society). C, D: Late Permian Reduviasporonites stoschianus, branched monilioid hyphae. E: R. stoschianus, aggregated hyphae with dominant narrow cells. F: R. stoschianus, aggregated monilioid hyphae. G: R. stoschianus, segment of small intact disk-like sclerotium. Scale bar for all images is 100 ?m.

See Also:

Citation: Geology, 2011. DOI: 10.1130/G32126.1 and Geology, 2011. DOI: 10.1130/G32178.1

Sea level rise more from Antarctica than from Greenland during last interglacial

Sea level rise less from Greenland, more from Antarctica, than expected during last interglacial.

Where did all that extra water come from? Mainly from melting ice sheets on Greenland and Antarctica, and many scientists, including University of Wisconsin-Madison geoscience assistant professor Anders Carlson, have expected that Greenland was the main culprit.

But Carlson’s new results, published July 29 in Science, are challenging that assertion, revealing surprising patterns of melting during the last interglacial period that suggest that Greenland’s ice may be more stable — and Antarctica’s less stable — than many thought.

“The Greenland Ice Sheet is melting faster and faster,” says Carlson, who is also a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies. But despite clear observations of that fact, estimates of just how much the ice will melt and contribute to sea level rise by the end of this century are highly varied, ranging from a few centimeters to meters. “There’s a clear need to understand how it has behaved in the past, and how it has responded to warmer-than-present summers in the past.”

The ice-estimation business is rife with unknown variables and has few known physical constraints, Carlson explains, making ice sheet behavior — where they melt, how much, how quickly — the largest source of uncertainty in predicting sea level rises due to climate change.

His research team sought a way to constrain where ice remained on Greenland during the last interglacial period, around 125,000 years ago, to better define past ice sheet behavior and improve future projections.

The researchers analyzed silt from an ocean-floor core taken from a region off the southern tip of Greenland that receives sediments carried by meltwater streams off the ice sheet. They used different patterns of radiogenic isotopes to identify sources of the sediment, tracing the silt back to one of three “terranes” or regions, each with a distinct geochemical signature. The patterns of sedimentation show which terranes were still glaciated at that time.

“If the land deglaciates, you lose that sediment,” Carlson explains. But to their surprise, they found that all the terranes were still supplying sediment throughout the last interglacial period and thus still had some ice cover.

“The ice definitely retreated to smaller than present extent and definitely raised sea level to higher than present” and continued to melt throughout the warm period, he adds, but the sediment analysis indicates that “the ice sheet seems to be more stable than some of the greater retreat values that people have presented.”

The team used their results to evaluate several existing models of Greenland ice sheet melting during the last interglacial period. The models consistent with the new findings indicate that melting Greenland ice was responsible for a sea level rise of 1.6 to 2.2 meters — at most, roughly half of the minimum four-meter total increase.

Even after accounting for other Arctic ice and the thermal expansion of warmer water, most of the difference must have come from a melting Antarctic ice sheet, Carlson says.

“The implication of our results is that West Antarctica likely was much smaller than it is today,” and responsible for much more of the sea level rise than many scientists have thought, he says. “If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary.”

Ultimately, Carlson says he hopes this line of research will improve the representation of ice sheet responses to a warming planet in future Intergovernmental Panel on Climate Change (IPCC) reports. Temperatures during the last interglacial period were similar to those expected by the end of this century, and present-day temps have already reached a point that Greenland’s glaciers are melting.

The Science paper was co-authored by UW-Madison colleagues Elizabeth Colville, Brian Beard, Alberto Reyes, and David Ullman and Oregon State University researchers Robert Hatfield and Joseph Stoner, and supported by UW-Madison and the National Science Foundation.

Valle Grande, New Mexico, reveals evidence of ancient megadrought

Valle Grande, New Mexico : Image of the Day.

Valle Grande, New Mexico

acquired May 25, 2011 download large image (5 MB, JPEG)
acquired May 25, 2011 download GeoTIFF file (41 MB, TIFF)

The American Southwest is prone to drought, and the summer of 2011 proved no exception, when a severe drought extended from Arizona to Florida. But a sediment core from New Mexico suggests that today’s droughts—even the 1930s Dust Bowl—are fleeting events compared to conditions of the ancient past. Hundreds of thousands of years ago, some droughts could persist for centuries. Researchers find one ancient period of warm, dry conditions especially intriguing because it was, in many ways, similar to conditions on Earth during the last 10,000 years.

Clues about this ancient period are preserved in a dry lakebed in New Mexico named Valle Grande. On May 25, 2011, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-color image of the lakebed. It is an unevenly shaped expanse of beige grassland situated inside the larger Valles Caldera.

Researchers extracted a 260-foot (80-meter) sediment core from this lakebed in 2004, and published their analysis in 2011. Ancient lake muds in the core document the region’s climate between 360,000 and 550,000 years ago. During that time, glaciers advanced over North America in recurring ice ages, and conditions warmed in interglacial periods. The core includes sediments from two warm interglacials.

One interglacial covered in the sediment core that particularly interested the research team is known as Marine Isotope Stage 11 (MIS 11), which occurred around 400,000 years ago. Our planet’s orbit around the Sun has varied over geologic time, but the 50,000-year period comprising MIS 11 experienced an orbital configuration similar to that of the last 10,000 years and, consequently, the amount of solar radiation reaching the Earth was similar.

During MIS 11, the researchers found, the climate of the American Southwest underwent a series of changes. As ice-age conditions gave way to warming, plant life thrived in a seasonally wet climate. But the warming continued, withering grasses and shrubs, and drying out lakes. Mud cracks in the sediment core illustrate the aridity. The drought documented by the sediment core lasted thousands of years—a megadrought.

The sediment core suggests that the megadrought occurring in MIS 11 not only began abruptly, but also ended abruptly, replaced by cooler, wetter conditions. As geologists explain, we live in an interglacial today; Earth’s most recent ice age ended only about 10,000 years ago. The similarity of the Earth’s orbital configuration between MIS 11 and now suggests that, as happened hundreds of thousands of years ago, the Southwest might eventually experience cool, wet conditions again. Such a transition could be derailed, however, by warming caused by increased concentrations of greenhouse gases.

  1. References

  2. Fawcett, P.J., Werne, J.P., Anderson, R.S., Heikoop, J.M., Brown, E.T., Berke, M.A., Smith, S.J., Goff, F., Donohoo-Hurley, L., Cisneros-Dozal, L.M., Schouten, S., Sinninghe Damste, J.S., Huang, Y., Toney, J., Fessenden, J., WoldeGabriel, G., Atudorei, V., Geissman, J.W., Allen, C.D. (2011). Extended megadroughts in the southwestern United States during Pleistocene interglacials. Nature, 470, 518–521.
  3. Rickman, J.E. (2011, February 28). Dry lake reveals evidence of southwestern “megadroughts.” Los Alamos National Laboratory. Accessed July 18, 2011.
  4. U.S. Drought Monitor. (2011, July 14). Conditions for July 12, 2011. (PDF file) University of Nebraska, Lincoln. Accessed July 16, 2011.
  5. University of California Museum of Paleontology. The Pleistocene. Accessed July 18, 2011.
  6. Williams, J. (2011). Climate change: Old droughts in New Mexico. Nature, 470, 473–474.

NASA image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 Team. Caption by Michon Scott.

Instrument: 
EO-1 – ALI

Dramatic climate swings likely as world warms: Ancient El Niño clue to future floods

Dramatic climate swings likely as world warms: Ancient El Niño clue to future floods.

ScienceDaily (July 14, 2011) — Dramatic climate swings behind both last year’s Pakistan flooding and this year’s Queensland floods in Australia are likely to continue as the world gets warmer, scientists predict.

Researchers at the Universities of Oxford and Leeds have discovered that the El Niño Southern Oscillation (ENSO), the sloshing of the warmest waters on the planet from the West Pacific towards the East Pacific every 2-7 years, continued during Earth’s last great warm period, the Pliocene.

Their results suggest that swings between the two climatic extremes, known as El Niño and La Niña, may even have occurred more frequently in the warmer past and may increase in frequency in the future. Extreme ENSO events cause droughts, forest fires and floods across much of the world as well as affecting fishery production.

Reporting in the journal Paleoceanography, the team of geochemists and climate modellers use the Pliocene as a past analogue and predictor of the workings of Earth’s future climate.

The Pliocene (which lasted from 5 to 3 million years ago) had carbon dioxide levels similar to the present day, with global mean temperatures about 2-3ºC higher, so it is a useful test-ground for climate research.

Lead Scientist Nick Scroxton from Oxford University’s Department of Earth Sciences said: ‘We know from previous studies that the mean state of the Pacific during the warm Pliocene was similar to the climate patterns observed during a typical El Niño event that we see today.

‘However, until recently it was believed that a warmer Pacific would reduce the climate swings that cause the dramatic weather extremes throughout the region leading to a permanent state of El Niño. What we didn’t expect was that climatic variability would remain strong under these warmer conditions.’

The team combined experiments performed on the Met Office Hadley Centre climate model, HadCM3, with the analysis of the chemical composition of lots of individual shells of small organisms, known as foraminifera.

These were collected from a deep sea sediment core in the East Equatorial Pacific, and provided a record of temperature in the upper layer of the ocean through time. They discovered that the range of temperatures experienced by these organisms during the Pliocene, was higher than what would be expected from just the seasonal cycle.

The extra variation in temperature can be explained by the additional extreme temperature swings provided by the El Niño/La Niña system.

The authors say the agreement in findings from both ocean data and modelling leaves little doubt that ENSO will persist in a warmer world. Earlier this year a team from Japan studying corals from the same period showed climatic variability in the western Pacific on a similar scale to today, questioning the idea of a permanent El Niño during the Pliocene.

This new study goes further, showing that the oscillation is Pacific-wide, and is likely to be caused by the El Niño/La Niña. This suggests that our warmer future will continue to be dogged, maybe even more regularly, by extreme climatic events.

The Last Great Global Warming

The Last Great Global Warming: Scientific American.

Surprising new evidence suggests the pace of Earth’s most abrupt prehistoric warm-up paled in comparison with what we face today. The episode has lessons for our future

Image: Illustration by Ron Miller

In Brief

  • Global temperature rose five degrees Celsius 56 million years ago in response to a massive injection of greenhouse gases into the atmosphere.
  • That intense gas release was only 10 percent of the rate at which heat-trapping greenhouse gases are building up in the atmosphere today.
  • The speed of today’s rise is more troubling than the absolute magnitude, because adjusting to rapid climate change is very difficult.

Polar bears draw most visitors to Spitsbergen, the largest island in Norway’s Svalbard archipelago. For me, rocks were the allure. My colleagues and I, all geologists and climate scientists, flew to this remote Arctic island in the summer of 2007 to find definitive evidence of what was then considered the most abrupt global warming episode of all time. Getting to the rocky outcrops that might entomb these clues meant a rugged, two-hour hike from our old bunkhouse in the former coal-mining village of Longyearbyen, so we set out early after a night’s rest. As we trudged over slippery pockets of snow and stunted plants, I imagined a time when palm trees, ferns and alligators probably inhabited this area.

Back then, around 56 million years ago, I would have been drenched with sweat rather than fighting off a chill. Research had indicated that in the course of a few thousand years—a mere instant in geologic time—global temperatures rose five degrees Celsius, marking a planetary fever known to scientists as the Paleocene-Eocene Thermal Maximum, or PETM. Climate zones shifted toward the poles, on land and at sea, forcing plants and animals to migrate, adapt or die. Some of the deepest realms of the ocean became acidified and oxygen-starved, killing off many of the organisms living there. It took nearly 200,000 years for the earth’s natural buffers to bring the fever down.

 

REST HIDDEN BEHIND PAYWALL

Sea levels rising at fastest rate in 2,000 years and other sea level news

Sea levels rising at fastest rate in 2,000 years – Telegraph.

Sea levels rising at fastest rate in 2,000 years

Sea levels are rising faster than at any point in the past 2,000 years because of the impact of global warming, scientists have found.

Sea levels rising at fastest rate in 2,000 years

Since then the average rise in sea levels in North Carolina, where the study was based, it has been higher than 2mm per year Photo: ALAMY

How Ocean Currents Once Warmed the Arctic

How Ocean Currents Once Warmed the Arctic: Scientific American.

ANCIENT ARCTIC: Why was the Arctic three million years ago–when average temperatures and CO2 levels were similar to those today–so much warmer? The answer may be currents. Image: Andy Mahoney, NSIDC

New research could explain why the Arctic was much warmer during a period millions of years ago that scientists say most closely resembles Earth’s climate today.

The climate during the mid-Pliocene Epoch, roughly 3 million years ago, is a good overall match for conditions today with regard to average temperature and the level of carbon dioxide in the atmosphere. But there are some differences that scientists have had trouble explaining.

Analyses of fossils, pollen and chemicals contained in core samples of seafloor sediments suggest the North Atlantic Ocean and the Arctic were much warmer during the mid-Pliocene than they are today. But climate models haven’t been able to accurately reproduce that past Arctic warming.

Now, researchers in the United States and United Kingdom say the difference between the Arctic of the Pliocene and that of the present may boil down to shifts in the topography of the ocean floor — in particular, of a group of underwater ridges and channels that extend from Greenland to Scotland.

Known as the Greenland-Scotland Ridge, the undersea mountain range divides the basin of the North Atlantic Ocean from those of the Nordic Seas. Researchers believe it was about 300 meters (roughly 984 feet) deeper during the mid-Pliocene.

“Geophysicists have studied this ridge in the past. It’s a hot spot, with mantle coming up from underneath” the ocean floor, said lead author Marci Robinson, a micropaleontologist with the U.S. Geological Survey. “The Earth’s crust will swell when it’s hot and condense when it’s cold, and that changes the height of the ridge.”

When Robinson and her colleagues tweaked their climate model to account for the ridge’s depth during the mid-Pliocene, “almost like magic, the data and the model results matched up really well,” she said.

A help to ‘hindcasting’
Today, the ridge traps North Atlantic Ocean water as it sinks to lower depths, redirecting it back toward the equator. But the new study suggests that during the mid-Pliocene, when the ridge was lower, it allowed deep ocean currents to flow freely. That ultimately increased the flow of warm surface water, leading to the unusual warming in the North Atlantic and Arctic.

Robinson said the study results could help improve the accuracy of climate models, leading to better predictions of the future climate.

That’s because scientists who work with the models test them by seeing how well they can replicate the climate of the past, a process called “hindcasting.” If a model can accurately reproduce past conditions, the thinking goes, researchers can be more confident about the model’s ability to project the future climate.

But Robinson said there is still work to be done to test the new theory about the influence of the Greenland-Scotland Ridge on the Pliocene-era Arctic and North Atlantic Ocean.

She and her colleagues used a simplified model of the ocean ridge for their initial research, for example.

“The [paleoclimate] data say the ridges only dropped by about 300 meters,” Robinson said. “In this study, we just removed them. It’s the equivalent of dropping by about 800 meters, more than what’s realistic. But this was a pilot study.”

The research team plans to conduct new analyses that incorporate a more realistic picture of the drops and ridges, she said.

The study was published online last month in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. Its authors include researchers from the U.S. Geological Survey, the British Geological Survey and several universities in the United Kingdom.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500