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.
(Reuters) – The Times Atlas of the World exaggerated the rate of Greenland’s ice loss in its thirteenth edition last week, scientists said on Monday.
The atlas, published by HarperCollins, showed that Greenland lost 15 percent of its ice cover over the past 12 years, based on information from the National Snow and Ice Data Center in Colorado in the United States.
The Greenland ice sheet is the second biggest in the world and significant shrinking could lead to a global rise in sea levels.
“While global warming has played a role in this reduction, it is also as a result of the much more accurate data and in-depth research that is now available,” HarperCollins said on its website on Monday.
However, a number of scientists disputed the claim.
“We believe that the figure of a 15 percent decrease in permanent ice cover since the publication of the previous atlas 12 years (ago) is both incorrect and misleading,” said Poul Christoffersen, glaciologist at the Scott Polar Research Institute (SPRI) at the University of Cambridge.
“We concluded that a sizable portion of the area mapped as ice-free in the Atlas is clearly still ice-covered.”
Other scientists agreed.
“These new maps are ridiculously off base, way exaggerated relative to the reality of rapid change in Greenland,” said Jeffrey S. Kargel, senior research scientist at the University of Arizona.
The Times Atlas suggested the Greenland ice sheet has lost 300,000 square kilometers in the past 12 years, at a rate of 1.5 percent per year.
However, measurements suggest this rate is at least 10 times faster than in reality, added J. Graham Cogley, Professor of Geography at Trent University, Ontario, Canada.
“It could easily be 20 times too fast and might well be 50 times too fast,” he added.
Last year, a U.N. committee of climate scientists came under fire for bungling a forecast of when Himalayan glaciers would thaw.
The panel’s 2007 report, the main guide for governments in fighting climate change, included an incorrect projection that all Himalayan glaciers could vanish by 2035, hundreds of years earlier than scientists’ projections.
(Reuters) – Arctic sea ice this summer melted to a record low extent or will come a close second, two different research institutes said on Tuesday, confirming a trend which could yield an ice-free summer within a decade.
The five biggest melts in a 32-year satellite record have all happened in the past five years, likely a result of both manmade climate change and natural weather patterns.
One impact of an ice-free summer may be disrupted world weather, with hints already as some scientists blame recent chill winters in Europe and North America on warmer, open Arctic seas diverting polar winds south.
Researchers at the University of Bremen in Germany say that this year has already toppled 2007 after sea ice retreated to a record low on September 8.
The U.S.-based National Snow and Ice Data Center (NSIDC) says this year is number two with the melt season all but over before winter returns to the high Arctic.
“I’m increasingly confident it will remain number two,” said Mark Serreze, head of the NSIDC. But the result may be close enough to declare a tie, he added.
Most important than the record was the trend, said University of Bremen’s Georg Heygsterall, referring to how the years since 2007 had all since bigger summer melts than those before.
A tie would echo the World Meteorological Organization’s view on recent rising global temperatures, after it declared 2010 a tie with 1998 and 2005 for the hottest year since such records began about a century and a half ago.
Bremen and NSIDC use satellites to measure microwave radiation from the ice pack, but with slightly different methods: NSIDC can achieve a sharper image, but Bremen to a higher resolution of 6 kilometers compared with 25 km.
Researchers agree that summer sea ice is disappearing faster than expected.
“An ‘ice-free’ summer Arctic is rapidly on its way. Most data indicate that the models are underestimating the rate of ice-loss,” said Kim Holmen, research director at the Norwegian Polar Institute.
“That means that we see more rapid change than the model scenarios have suggested. It also means that there are processes out there that influence ice that we have yet to understand.”
The summer ice retreat has already reached levels which were forecast three decades from now in models used in the U.N. climate panel’s flagship report four years ago.
The Intergovernmental Panel on Climate Change (IPCC) used models which forecasted an ice-free summer at the end of this century.
But that could happen as early as 2013, according to one of the most aggressive estimates. Other experts predict an ice-free Arctic Ocean in summer anywhere from 2020-2050.
“I still see a high likelihood of a near ice-free Arctic Ocean during summer around 2016, plus or minus three years,” said Wieslaw Maslowski at the California-based Naval Postgraduate School.
More difficult to measure than area is ice thickness, which is also diminishing, most scientists agree.
Researchers at the University of Washington in Seattle calculated ice volume, combining area and thickness, reached a record low last year and would do so again this year.
(Reporting by Gerard Wynn)
<span class="articleLocation”>(Reuters) – Sea ice on the Arctic Ocean shrank to its second-smallest extent since modern records began, in keeping with a long-term trend, the U.S. National Snow and Ice Data Center reported on Thursday.
The annual sea ice minimum was reached on September 9, the center said on its website here in a preliminary finding.
“Changing winds could still push ice flows together reducing ice extend further,” the researchers said. A full analysis will be available in October, when monthly data are available for all of September, which is usually the month when the annual minimum is reached.
Arctic Sea ice is an important sign of a changing climate, and what happens in the Arctic has a major influence on global weather patterns.
At its apparent minimum, sea ice around the North Pole covered 1.67 million square miles (4.33 million square km). That measurement is 61,800 square miles (160,000 square km) above the all-time record low reached in 2007, the center said.
However, it is far below the average minimum for the period 1979 through 2000, according to NSIDC. The satellite record began in 1979.
These figures differ from those reported by the University of Bremen in German, which issued a statement that the Arctic ice reached a record low minimum on September 8.
PATCHES OF WATER AMID THE ICE
Both the University of Bremen and NSIDC use microwave sensors to observe Arctic ice, but these sensors are on different satellites. The Bremen report uses images with higher spatial resolution, according to Walter Meier of NSIDC.
“They can see in more detail, they can see these little patches of water, whereas we see these areas as just ice covered,” Meier said by telephone. He said there can be higher potential for error with these high-resolution images, though there is no evidence of error in this case.
NSIDC’s records go back to 1979; the records used by Bremen go back to 2003. Both indicate the last five years were the least icy in the Arctic sea ice satellite record.
It’s not surprising that this year has not eclipsed the record year of 2007, Meier said.
That year was “a perfect storm” of ice-melting conditions in the Arctic, he said: warmer and sunnier than usual, with extremely warm ocean water and winds all acting in concert.
The fact that 2011 has seen the second-lowest ice extent without these extreme conditions shows a change in the character of the ice cover, Meier said.
Back in 2007, the ice was a consolidated mass which melted from the edges. This year, he said, the ice is more dispersed and the area is dominated by seasonal ice cover — less hardy than multi-year ice — which is more prone to melt.
“Now it doesn’t take as extreme of weather conditions to get to the 2007 ballpark,” Meier said.
(Reporting by Deborah Zabarenko in Washington, Editing by Cynthia Osterman)
New pictures have revealed the extent to which a huge glacier in northern Greenland has broken up in just two years, claims a glaciologist.
Dr Alun Hubbard of Aberystwyth University said he was “gob-smacked” by the scale of the Petermann Glacier’s break-up since he last visited in 2009.
The glacier is 186 miles (300km) long and 3,280ft (1000m) high – over three times the height of the Eiffel Tower.
Last year, it shed a piece of ice measuring 77 square miles (200 sq km).
Dr Hubbard has been researching the Greenland ice sheet for some years.
His team of researchers and scientists from Aberystwyth and Swansea universities have made several trips to the country.
Located in north west Greenland, the Petermann Glacier accounts for 6% of the area of the Greenland ice sheet, said Dr Hubbard.
It’s like looking into the Grand Canyon full of ice and coming back two years later to find it’s full of water”
Dr Alun Hubbard Aberystwyth University
It terminates as a floating tongue of ice, measuring around 43 miles (70km) long by 12 miles (20km) wide, the largest of its kind in the northern hemisphere.
“Although I knew what to expect in terms of ice loss from satellite imagery, I was still completely unprepared for the gob-smacking scale of the break-up, which rendered me speechless,” said Dr Hubbard.
“It was incredible to see. This glacier is huge, 20km across and 1000m high.
“It’s like looking into the Grand Canyon full of ice and coming back two years later to find it’s full of water.”
He said data recovered from global positioning system (GPS) sensors at the site was being analysed at Aberystwyth.
Cracks and rifts
With support from the US National Science Foundation and the Natural Environment Research Council in the UK, Dr Hubbard travelled by helicopter to the glacier to gather data from time lapse cameras and GPS sensors set up in July and August 2009, with the help of Greenpeace.
The GPS sensors were set in anticipation of a large break-up of ice that eventually occurred by on 3 August, 2010.
Dr Hubbard said this led to the formation of an ice island measuring more than 77 square miles (200 sq km).
He believes the cracks and rifts in what remains of the ice shelf means it is also likely to break up at some point in the near future.
Dr Hubbard visited the Petermann glacier at the end of July, and returns to Aberystwyth on Sunday.
His work is part of a wider project involving researchers from Bristol, Cambridge, Edinburgh, Denmark, Sweden, the Netherlands, Germany and the United States.