Ancient Glacial Lake had Massive Impact on Climate, Slowed Warming of Earth
The Canadian province of Manitoba has an intimate connection with historical climate change thanks to having the largest lake in the world …. tens of thousands of years ago.
Ancient glacial Lake Agassiz, which existed from 13,000 to about 8,400 years ago, was responsible for stalling the warming of the earth on a few occasions as the last ice age was drawing to a close.
“It was the largest lake in the world during much of that time,” said Dr. James Teller, who works in the Department of Geological Sciences at the University of Manitoba.
When it completely drained, Lake Agassiz left behind its modern-day descendants of Lake Winnipeg and Lake Manitoba, the 11th and 33rd largest freshwater lakes in the world, respectively.
Throughout its existence, Teller noted, Lake Agassiz covered about 1.5 million square kilometres, which is over twice the area of current-day Manitoba.
However, Lake Agassiz didn’t cover that area all at the same time.
As the Laurentide Ice Sheet retreated northward and the lake drained various amounts of water at various times throughout its history, it changed in shape and its shoreline fluctuated.
Lake Agassiz covered most of Manitoba, Teller said, and stretched westward into north-central Saskatchewan, southward to around modern-day Fargo, North Dakota, and eastward to around current-day Thunder Bay, Ontario, where it swallowed glacial Lake Ojibway.
As the ice retreated and melted, it would pour more water into Lake Agassiz, causing it to occasionally burst its banks.
“Every lake gets to a point where it flows over, and Lake Agassiz was the same,” Teller pointed out. “Lake Agassiz drained at different times in different ways in different directions.”
Teller is one of the foremost experts on glacial Lake Agassiz, having spent much of his career studying it and having written numerous research papers on it, including ones discussing how the ancient lake altered the world’s climate when it would sporadically release large amounts of fresh water into the ocean.
“Abrupt reductions in lake level, ranging from eight to 110 metres, occurred on at least 18 occasions when new outlets were opened, reducing the extent of the lake, and sending large outbursts to the oceans,” says the intro to a research paper by Teller and David W. Leverington, with the Center for Earth and Planetary Studies at the National Air and Space Museum of the Smithsonian Institution in Washington, D.C.
Another research paper entitled “Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation” by Teller, Leverington and Jason D. Mann outlines the different routes the water would take on its way out from Lake Agassiz.
“These waters were variably routed to the Gulf of Mexico, Arctic Ocean, North Atlantic Ocean and Hudson Bay,” the research paper says.
When that fresh water hit the salty marine water, it floated on the surface, Teller explained, and affected the gulf stream.
The gulf stream is a powerful, warm and swift Atlantic ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.
It is this current of warm air and water that the cold, fresh water of Lake Agassiz would cause to slow down and, in some cases, stop completely. This would also slow down or stop the warming of the earth.
These stoppages would be temporary, Teller said, with the gulf stream reactivating and starting to flow again anywhere from a few centuries to about 1,000 years after the various freshwater inundations.
How much the intermittent torrents of freshwater affected the gulf stream depended on how much water was released at a time and what route it took to the ocean, Teller said.
The outbursts from Lake Agassiz ranged from 10,000–163,000 cubic kilometres at a time.
The largest outburst, according to the aforementioned “Freshwater outbursts to the oceans from glacial Lake Agassiz …” research paper, happened 8,400 years ago when 163,000 cubic kilometres of water drained out of a northern route from Lake Agassiz and caused what is referred to in the research paper as the “8.2 ka cold event.”
“These are truly gigantic numbers,” Teller observed. “It is really an extraordinary event.”
Scientists made their conclusions about the effect of fresh water on the oceans and the warming of the climate by looking at the land on both sides of the Atlantic Ocean, Teller revealed.
Core samples of earth taken from various depths tell the tale of what the climate was like at a certain time in history.
The cores are cylinders of mud and dirt about 10 centimetres in diameter and can be taken at depths of up to 20 metres if needed, Teller explained.
By looking at the material in the core, scientists can track the warming and cooling of the earth, he said.
The telltale signs of cooling in the earth correspond to the outbursts from Lake Agassiz, the geologist noted.
Once the lake drained completely, he said, the earth was free to warm up uninterrupted, he explained, until deglaciation was complete and the last ice age was done.
These outbursts of fresh water from Lake Agassiz, which could take years to happen, would have also affected the people living at that time, in addition to the earth itself.
The level of the ocean would have gone up something like 0.5 metres over a six-month period because of the input of fresh water from the lake.
Many areas around the Persian Gulf, for example, Teller said, are quite flat and if the ocean level went up by 0.5 metres, that would have pushed the shoreline back by about 12 kilometres, affecting the people living along the shore.
“You’re having to keep pace with the ocean,” he observed.
Teller then broke away from the science and pondered whether some of the great flood stories throughout history may have been due to Lake Agassiz’s outbursts.
The Epic of Gilgamesh, an ancient Persian work of literature (one of the earliest works of literature known), involves a flood, as does the biblical story of Noah, Teller pointed out.
“Somebody sat down and chiseled that into tablets,” he said.
Whether or not Lake Agassiz spawned such epics is open to speculation, but science has proven that the lake that drained down to Lakes Winnipeg and Manitoba, and which used to cover much of Manitoba, has a direct link to historic climate change and the slowing and stalling of the earth’s warming during the last deglaciation period.