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Tracking Glacial Waters

This is a photo taken by the Landsat 8 satellite showing the Mackenzie River Delta in northern Canada. The Mackenzie is the longest river in Canada and produces the second largest river delta on the Arctic Ocean. The watershed of this river includes territory far to the southeast, in areas of central Canada that were once covered by the great Laurentide Ice Sheet. This river, therefore, is one potential route for water out of the center of the continent, and new evidence suggests it could be an important one. About 13,000 years ago, the great ice sheets of the last ice age were melting as the amount of sun reaching northern Canada increased and as CO2 contents in the atmosphere increased. As the Laurentide ice sheet melted, most of its water was draining down to the modern day Gulf of Mexico – meltwater that can be tracked using isotopes of hydrogen and oxygen.

Both hydrogen and oxygen have heavy and light isotopes. For hydrogen, that isotope is deuterium – hydrogen with a neutron. For oxygen, there are stable isotopes that have mass 17 and 18, with 9 and 10 neutrons respectively; both of those are heavier than oxygen 16, which has 8 neutrons.

It turns out that heavier isotopes of hydrogen and oxygen have a pretty useful property; they stay in the water. Rainwater is missing some of its heavy oxygen and deuterium, and snow in the far north is missing even more. Ice sheets, therefore, are extremely light – they are extremely pure in the light isotopes of both hydrogen and oxygen.

As the ice sheets melted, that light water traveled down the Mississippi River system and dumped into the Gulf of Mexico. There, organisms lived in that water and made shells, recording the isotope composition of the water and showing that the light, glacial water was coming to the Gulf, at least until 13,000 years ago.

13,000 years ago something major changes in the Earth’s climate. In an event known as the Younger Dryas to scientists who named it based on the appearance of a cold-weather flower called the Dryas in Europe at the time, the world that was for a while melting suddenly chilled again for a few hundred years. Ice sheets and glaciers advanced, particularly in the Northern Hemisphere.

A disturbance in ocean circulation is the best explanation for the Younger Dryas. If the water going to the Gulf of Mexico suddenly shifted north, that cold water could affect ocean circulation globally, as cold but still salty water sinking in the North Atlantic is a major driver of global ocean circulation. Adding a major pulse of fresh water to the North Atlantic could disrupt this circulation, but if it happened it should leave an isotope signature.

As with the Gulf of Mexico, sending a bunch of glacial meltwater to the ocean should make the ocean lighter, leaving an imprint in shells right at the time of the Younger Dryas. Scientists hadn’t yet found a candidate for where that water went, until a paper that was just published looking at shells from the Mackenzie River Delta.

13,000 years ago, just as the Younger Dryas was happening, shells from this river delta become dramatically lighter for a period of over 100 years. At the same time, shells from the Gulf of Mexico become heavier – as though they lost their supply of glacial meltwater.

The Mackenzie River Delta, therefore, might have been the place that glacial meltwater entered the ocean. The cold, fresh water could have entered the Arctic Ocean, filtered its way down into the North Atlantic, and disrupted North Atlantic Deep Water formation, triggering the Younger Dryas cooling pulse.

-JBB

Image credit: https://flic.kr/p/QFWJa5

Original paper: https://www.nature.com/articles/s41561-018-0169-6

#Science #geology #research #glacial #mackenzie delta #mackenzie river #canada #younger dryas #ice age #the earth story #gulf of mexico #water

Archaeologists race to save ancient Arctic sites from rising ocean

Arctic archaeologists are fighting to learn what they can from one of the most extensive ancient sites in the North before climate change eats away centuries of history.

"It's really happening in a big way," said Max Friesen, a University of Toronto archaeologist who's heading this week to a remote island near the Northwest Territories and Yukon. "We have no idea what we're missing."

Friesen is in the middle of a multi-year program to try and preserve what's left of the cultural heritage of the Mackenzie Delta, an area rich in archaeological remains from before European contact.

But the region is also seeing some of the fastest global warming on Earth. That means melting permafrost and increased erosion along the coastlines where the sites are located.

Kuukpak is one of those sites. Read more.

#archaeology #arctic #climate change #archeology #mackenzie delta #kuukpak

69.309347°N, 135.612199°W Mackenzie Delta, Inuvik Region, Northwest Territories, Canada photo by plgrenon

#Mackenzie Delta #Inuvik #Northwest Territories #Canada

Archeologists unearth first complete Inuvialuit driftwood house

An archeologist from the University of Toronto is celebrating the discovery this summer of the first complete example of a cruciform pit home across from Tuktoyaktuk, N.W.T. in the Mackenzie Delta.

The structures were built by Inuvialuit from about 500 years ago up until around 1900.

“For me, it was almost the capping of my career,” says Max Friesen, who’s been working in the area off and on since 1986.

Friesen says large, cruciform houses are one of the things most spoken about in early histories, recollections of elders and the writings of early explorers in the delta.

“But even though others have excavated parts of these houses, there’s never been one that’s fully dug, so you can actually see how it all fits together.” Read more.

#archaeology #Inuvialuit #cruciform house #Mackenzie Delta