Ice age plants suited mammoth appetites

Artists’ renditions of northern ice-age landscapes could do with a bit more colour, says Yukon paleontologist Grant Zazula. Instead of fields of uniformly bleak grasslands, future paintings of late-Pleistocene Yukon, Alaska and eastern Siberia should include brilliant dabs of blue, yellow and orange...

Artists’ renditions of northern ice-age landscapes could do with a bit more colour, says Yukon paleontologist Grant Zazula.

Instead of fields of uniformly bleak grasslands, future paintings of late-Pleistocene Yukon, Alaska and eastern Siberia should include brilliant dabs of blue, yellow and orange scattered among the mammoths, horses, camels and other ancient mammals, he says.

Recent research, presented in “Fifty thousand years of Arctic vegetation and megafaunal diet” in the journal Nature last month, suggests that our favoured image of ice-age Beringia may well have been too grim.

That paper was co-authored and co-ordinated by Danish biologist Eske Willerslev and supported by a veritable international army of experts.

It helps explain why our concept of late Pleistocene plant life didn’t jive with the great numbers of large mammal bones found in northern permafrost, says Zazula, one of the authors.

“This paper really pushes a different concept,” he says.

Our misconceptions about Beringian plant life were seemingly supported by the science of palynology since the mid 20th century when that discipline, the study of ancient pollen and other particulates, really got up and running.

Core samples taken from permafrost-rich sites like the goldfields of the Klondike revealed a preponderance of pollen from grasses (graminoids).

There was less evidence of more nourishing plants, more easily digested vegetation, that could have supported of population of hungry megafauna.

“Grasses are pretty tough to digest,” says Zazula. “There is not a lot of  nutrients, there’s not a lot of protein in most grasses. Animals like bison, cows and horses, to compensate for a lack of nutrients in the grass, eat a lot.”

Because of all that ancient grass pollen some scientists claimed that the ice-age steppes couldn’t have supported many large mammals.

They said that the myriad bones and tusks found in Beringia were the remains of relatively few animals that would have survived during warmer episodes of the late Pleistocene, or roughly since 50,000 years ago.

The evidence was “really problematic,” says Zazula. “Grass is an immense pollen producer and it later became known that grass pollen was an over-representation of what was on the landscape.”

Zazula’s own 1990s PhD research had revealed evidence of many other plants, non-grasses, in ancient Arctic ground squirrel nests that had been preserved in Klondike permafrost.

Willerslev had spent years among the reindeer herders of the Russian North and was familiar with permafrost and its ability to preserve organic matter for millennia.

“Willerslev started thinking, ‘We’ve got DNA preserved in museum specimens of modern animals. That’s interesting, how far back can we push this?’”

“Willerslev had the idea that instead of needing bones to look at ancient DNA, we’d see what DNA is preserved from soils in the ancient past,” says Zazula. “Animals live and they die and they pee and they defecate and slough off hair and skin all the time and that stuff gets incorporated in the soil. That’s what soil is, basically – broken-down organic material.”

“The Viking,” as the Yukon scientist calls his Danish colleague, came to believe that the ancient soils preserved in the permafrost would contain ancient DNA of “a whole swack of things that were once living in the area – the whole kit and kaboodle,” says Zazula. “You can have animals, plants, potentially people, bacteria, insects…”

Fortunately for the Viking, and science in general, the new technique of DNA analysis had recently progressed away from some initial flaws and weaknesses by the first few years of the 21st century.

Earlier attempts to identify DNA strands had been thwarted by contaminants.

In one famous case, samples from an Egyptian mummy revealed a contemporary geneticist!

But researchers were well aware the problem by the time Willerslev, Zazula and University of Alberta Quaternary specialist Duane Froese excavated cores in Beringia.

“When the first cores were taken, it had to be made certain that there was no way for DNA in upper levels to migrate down,” stressed Zazula. “It had to be clear that once stuff was frozen it was permanently frozen.

Willerslev did a bunch of experimental work that showed that these stratigraphic levels of permafrost were really stable, that there wasn’t a mixing of material up and down within the profile.”

Cores from within a time period that could be covered by radio-carbon dating, back about 50,000 years, were taken in the North.

They were filled with organic treasures, including DNA from forbs.

Forbs are non-graminoid plants and include wildflowers such as poppies, buttercups, Jacob’s ladder, and a diversity of draba and other mustards.

Easily digested and plentiful, forbs could have satisfied the hunger of giant mammoths and have kept other such large animals alive during the colder periods of the ice age.

“It’s likely that those diets were quite nutrient rich because of all these different flowering forbs,” says Zazula.

One constant in science is that an answer to a question raises more questions. Why were these wonderful forbs so plentiful, tens of thousands of years ago, back in the Pleistocene?

Thank wind-blown dust.

Loess was carried onto the landscape from outwash streams at the edge of glaciers.

Dust even arrived from exposed portions of the ocean floor after sea levels dropped and the Beringia Land Bridge was exposed.

Such particulates make the soil more porous so water can percolate down rather than pool in bogs.

“Boggy landscape isn’t good for much,” says Zazula, perhaps speaking for a mammoth.

Evidence of this percolating process is readily seen today in the windblown flats east of Kluane Lake because of dust coming off the Kaskawulsh Glacier, says the paleontologist.

Meanwhile, the dust-darkened soil absorbs heat from the sun.

Moisture and heat help make for more nutrient-rich earth, more nutrient-rich plants and better-fed beasts.

That conclusion is only one of many we can expect from further DNA analysis of Beringian permafrost samples, says Zazula.

We will likely come to better understand the forces behind mass extinctions that occurred, along with the changing northern climate, at the end of the ice age.
 

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at  http://www.yukoncollege.yk.ca/research/publications/newsletters_articles

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