Catastrophic Flooding From Ancient Lake May Have Triggered Cold Period

Newswise ^ | 12-18-2004 | Jeff Donnelly

[blam]

Catastrophic Flooding from Ancient Lake May Have Triggered Cold Period

CLIMATE CHANGE, WOODS HOLE OCEANOGRAPHIC INSTITUTION, JEFF DONNELLY, ABRUPT CLIMATE CHANGE

Newswise — Imagine a lake three times the size of the present-day Lake Ontario breaking through a dam and flooding down the Hudson River Valley past New York City and into the North Atlantic. The results would be catastrophic if it happened today, but it did happen some 13,400 years ago during the retreat of glaciers over North America and may have triggered a brief cooling known as the Intra-Allerod Cold Period.

Assistant Scientist Jeffrey Donnelly of the Woods Hole Oceanographic Institution presented the findings at the American Geophysical Union's fall meeting in San Francisco today. Donnelly and colleagues analyzed data from sediment cores, walrus fossils and pollen to precisely date the discharge from Glacial Lake Iroquois down the Hudson River Valley at 13,350 years ago. The flood waters broke through a spot of land where the Verazanno Narrows Bridge now stands to reach the North Atlantic.

The discharge of glacial freshwater into the North Atlantic has long been thought to drive fluctuations in past climate because the huge volume of freshwater would alter thermohaline circulation in the ocean. Directly linking discharge events with individual climatic changes has been difficult because of the challenges in pinpointing the location, timing and amount of the discharge.

The Intra-Allerod Cold Period lasted only about 150 years and occurred just before the Younger Dryas, a sudden cold climate period lasting some 1,200 years and ending about 11,000 years ago. Many scientists believe the Younger Dryas was caused by the shutdown of the Gulf Stream in response to a sudden influx of fresh water from deglaciation in North America. Global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the North Atlantic Ocean.

The team compared their evidence for the massive flood down the Hudson Valley with data from sediment cores taken from the Cariaco Basin off Venezuela in the Caribbean, which show a slowing of thermohaline circulation and heat transport into the North Atlantic at that same time.

Donnelly and his colleagues were able to determine the timing of this event by analyzing data from sediment cores from the Hudson River Valley and the continental shelf. Sediment samples collected near the Tappan Zee Bridge indicate that ocean water flooded the lower Hudson Valley just after the flood event occurred. Pollen data from the first marine sediments deposited near the Holland Tunnel correlate with those from radiocarbon-dated sediments from nearby Sutherland Pond in New York and provide further constraint on the timing of the flood. Walrus remains recovered from gigantic sediment lobes deposited offshore during the flood were carbon dated to further pinpoint a precise time period.

Large rocks the size of Volkswagens, also associated with these sediment lobes, have been photographed on the outer continental shelf off the mouth of the Hudson River, where sediments normally are the size of grains of sand or smaller. Donnelly says the large rocks most likely came from the melting glacier and were carried down to the Atlantic in the floodwaters.

Glacial Lake Iroquois, in the same location and about three times the size as modern day Lake Ontario, was formed as the Laurentide Ice Sheet receded from its maximum extent along southern Long Island, New York, and northern New Jersey to southern Canada from about 21,000 to 13,000 years ago. Several other glacial lakes, Glacial Lake Albany and Glacial Lake Vermont, existed for several thousand years and deposited thick layers of silt and clay in the Hudson River Valley and Champlain Lowlands.

Donnelly says a dam north of the Adirondack Mountains in upstate New York holding back the ancient lake collapsed, allowing lake water to drain into the Hudson River Valley and the North Atlantic, dropping the level of Glacial Lake Iroquois some 120 meters (about 400 feet). Following the collapse of Glacial Lake Iroquois, another lake, Glacial Lake Candona, formed in the Ontario, Saint Lawrence and Champlain Lowlands, controlled in level by a sill or rock dam near Fort Ann, Vermont.

Lake Candona existed only about 100 to 200 years before it drained to the Atlantic when the ice sheet blocking the St. Lawrence Valley collapsed. Following the drainage of Lake Candona, seawater invaded the St. Lawrence and Champlain Lowlands and formed the Laurentian Seaway and the Champlain Sea. Glacial Lake Candona dropped about 40 meters (125 feet) as it drained into the North Atlantic via the Saint Lawrence River Valley. This opening of the St. Lawrence Valley as a conduit for glacial meltwater about 13,000 years ago likely played a role in causing the onset of the Younger Dryas cold interval.

The team will publish the results of the complete study in the February 2005 issue of the journal Geology. Donnelly's research was funded by the Postdoctoral Scholar Program, The John E. and Anne W. Sawyer Endowed Fund, The J. Lamar Worzel Assistant Scientist Fund, and the Ocean and Climate Change Institute at the Woods Hole Oceanographic Institution.

Woods Hole Oceanographic Institution (WHOI) is a private, independent marine research and engineering and higher education organization located in Falmouth, MA. Its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. Established in 1930 on a recommendation from the National Academy of Sciences, the Institution operates the US National Deep Submergence Facility that includes the deep-diving submersible Alvin, a fleet of global ranging ships and smaller coastal vessels, and a variety of other tethered and autonomous underwater vehicles. WHOI is organized into five departments, interdisciplinary institutes and a marine policy center, and conducts a joint graduate education program with the Massachusetts Institute of Technology.

[concentric circles]

Woods Hole Oceanographic Institution

Paleogeography 13,400 years ago. Glacial Lake Iroquois is held back by an ice dam in northern New York. When that dam collapsed it drained (red arrows) into the lakes within the Champlain and Hudson Valleys, breaching the Narrows Dam (near New York City). It cascaded across the then exposed continental shelf to the North Atlantic Ocean. This release of meltwater reduced the flow of the Gulf Stream and caused an abrupt climate cooling in the Northern Hemisphere that lasted several hundred years. (Illustration by Jack Cook ©WHOI)

Paleogeography 13,300 years ago. Glacial Lake Candona forms in northern New York and southern Canada as the ice sheet retreats north.

Paleogeography 13,100 years ago. Glacial Lake Candona has expanded into the St Lawrence Lowlands as the ice sheet continues to retreat.

Paleogeography 13,000 years ago. Glacial Lake Candona drains into the North Atlantic through the St. Lawrence Valley as the ice sheet retreats from the region. The drainage of Glacial Lake Candona and the opening of the drainage out the St. Lawrence initiated another shut down of the Gulf Stream, causing the Younger Dryas cold interval.

[BigBobber]

Thanks for the link.

As a former resident of the Hudson River Valley, I found this to be fascinating.

[Unam Sanctam]

Fascinating. Thanks for the article and the map.

[blam]

The Legacy of Lake Aggasiz

Imagine it's 11,000 years ago, and imagine that you are high above midwestern North America. All you see below you is a lake — a giant lake, born of a massive, continental glacier.

Bigger than Lake Superior, larger than any freshwater body on the earth today, ancient Lake Aggasiz extended from northern Saskatchewan in the west to northeastern Ontario in the east, and from southern Minnesota in the south to northern Manitoba in the north.

Rising and Falling: Glacial Lake Aggasiz (named for Louis Aggasiz, 19th century Swiss naturalist and glaciation theorist) began to form about 12,000 years ago, as the Laurentide Ice Sheet retreated northward. Over the next 5,000 years, it changed its boundaries several times, as glacial ice advanced and retreated. At the peak of its coverage, the lake drained to the south through the Minnesota River Valley, west through northern Saskatchewan to Alaska, and east to the Great Lakes. About 8,500 years ago, the southern part of the lake drained for the last time, and about 1,000 years later, it was gone from northern Canada.

Today, the Red River Valley exists in what was the southwestern portion of Lake Aggasiz, extending just over 500 kilometres from Lake Traverse in the south to Lake Winnipeg in the north.

[blam]

The Tibetans have flood myths of the 'mountain topping' variety.

I have seen this explained by placing the original Tibetans as a coastal people during the Ice Age and these myths are about the giant tsunamis they witnessed before they migrated/fled inland. The end of the Ice Age was a very unsettled time.

[Cold Heart]

BTTT

[F.J. Mitchell]

Science fiction is a very entertaining medium-but to avoid confusion among us laymen, it should be labeled as what it is.

[SunkenCiv]

missed you on the GGG ping.

[SunkenCiv]

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[SunkenCiv]

Pure scientific research triumphs again. A BTTT for a non-fiction topic on FR.

[SunkenCiv]

from 2005.

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A dash of cold water for global warming forecast
The Scotsman | April 21, 2003 | GEORGE KEREVAN
Posted on 04/20/2003 8:10:33 PM EDT by MadIvan
http://www.freerepublic.com/focus/f-news/896991/posts

[r9etb]

Donnelly and colleagues analyzed data from sediment cores, walrus fossils and pollen

I always say: you can never go wrong using walrus fossils.

[SunkenCiv]

Just an update/adding to the catalog -- no ping.

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[SunkenCiv]