Long-lost Lake Agassiz offers clues to climate change

Oct 05, 2011

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 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 known as the Younger Dryas.

As the 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 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 by disrupting ? 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 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 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 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."

Explore further: Famine in the Horn of Africa (1984) was caused by El Niño and currents in the Indian Ocean

add to favorites email to friend print save as pdf

Related Stories

Geologists Study Historic Patterns of Climate Change

Apr 30, 2010

(PhysOrg.com) -- University of Cincinnati geologist Tom Lowell is part of a team studying the effects of melting ancient glaciers. The research has implications for global warming, as published this week in ...

8,200-year-old cooling is analyzed

Aug 20, 2007

Canadian scientists studying ice core records are questioning current theories about the rapid cooling of the Northern Hemisphere 8,200 years ago.

Big freeze plunged Europe into ice age in months

Nov 30, 2009

In the film, 'The Day After Tomorrow' the world enters the icy grip of a new glacial period within the space of just a few weeks. Now new research shows that this scenario may not be so far from the truth after all.

Ice sheet melt identified as trigger of Big Freeze

Mar 31, 2010

The main cause of a rapid global cooling period, known as the Big Freeze or Younger Dryas - which occurred nearly 13,000 years ago - has been identified thanks to the help of an academic at the University of Sheffield.

Recommended for you

NASA sees zombie Tropical Depression Genevieve reborn

9 hours ago

Infrared imagery from NASA's Aqua satellite helped confirm that the remnant low pressure area of former Tropical Storm Genevieve has become a Zombie storm, and has been reborn as a tropical depression on ...

Wave energy impact on harbour operations investigated

14 hours ago

Infragravity period oscillations—waves that occur between 25 and 300 seconds with a wavelength between 100m and 10km—can have an impact on berthing operations, depending on a harbour's geometry.

User comments : 0