Be careful what you wish for

aNorth Sunday late last month, jumped 15 kilometers from a torturous four-wheel drive to a lofty gorge on the side of the 3,425-meter Mount Hood volcano in Oregon. My goal was to see if my soon-to-be-69-year-old body could still climb 2,600 meters on the moraine of Mount Elliot Glacier, which a friend and I visited 34 years ago.

However, as I climbed, I was quickly struck by more than the thin air and the relentless climb. Where did the glacier go?

The mountain is covered with ice
Mount Hood in October 1988. Credit: Richard A Lovett

The answer, of course, was that it had regressed, dramatically, over a little less than half of my life. Where its nose once was just above the head of the trail, there was now nothing but a rock. The lowest remaining part of it was hundreds of meters higher and perhaps a kilometer away.

Of course, the retreat of mountain glaciers is well known. But paper in natureJust a few days into my career, I revealed their demise in a new light. Scientists have found that, at least once in Earth’s history, the rapid melting of glaciers not only eroded many volcanoes, but caused them to erupt.

Study author Professor Alan Meeks, an oceanographer and paleoclimatologist at Oregon State University in the US, says this happened by “loosening” them by reducing the weight of the ice pressing on them. “This relieves pressure, which can then lead to volcanoes,” he says.

Scientists have found that, at least once in Earth’s history, the rapid melting of glaciers not only eroded many volcanoes, but caused them to erupt.

This does not mean that the demise of the Elliot Glacier is likely to cause Mount Hood to explode in a giant explosion. “We’re not saying volcanoes are going to start erupting and they’re going to be wiped out,” Mix says, though I imagine some accounts would misquote that. ”

The mountainside is covered with snow
Glacier in 1988. Credit: Richard A Lovett

That’s because there’s a difference between what he calls “big ice” and “little ice,” and on that scale, the Elliot Glacier is a little ice.

In fact, the large ice he is talking about does not currently exist in many parts of the world. Yes, Greenland does, but Greenland has no volcanoes.

The ice his study examined was in the Cordilleran Ice Sheet, which covered most of western North America, from Alaska to Washington, at the height of the last ice age.

On this scale, Elliot Glacier is a small iceberg.

“Most of the Cordilleran Ice Sheet disappeared around 10,000 years ago,” says study lead author Dr. Jianghui Du, now a postdoctoral researcher at ETH Zurich, Switzerland. Remnants of the ice sheet were left in southern Alaska, mainly in the form of mountain glaciers [which] melt quickly. Some studies have suggested that the retreat of glaciers may be related to the increase in seismicity in this region, [but] The remaining ice is much smaller than there was in the Ice Age.”

Other volcanic regions with significant residual ice are Iceland, the Antarctic Peninsula, and possibly Patagonia. But even if volcanoes rose in these places as glaciers receded, the result wouldn’t be a disaster movie scenario because the opening of volcanoes is a slow process that happens over hundreds or thousands of years.

What really matters, Meeks and Doe say, is what the new discovery teaches about oceans, global warming, and the potential unintended consequences of potential efforts to protect the planet.

Mountain with trees in the foreground
Mount Hood in 2022. Credit: Richard A Lovett

That story began more than two decades ago in the North Pacific, when Meeks wrangled funding for a cruise to collect sediment samples from the region. The goal was to find out how the North Pacific Ocean plays in the global climate system, but in the process Meeks and other scientists discovered that they had experienced long periods of “giant” low-oxygen “dead zones” that lasted for thousands of years.

Understanding why this is happening is important, Du says, because global warming is already threatening oxygen levels in the ocean. As the water temperature rises, its ability to hold dissolved oxygen decreases. This means that oxygen-depleted dead zones are expected to expand, with potentially catastrophic consequences for marine ecosystems and the fisheries that depend on them.

“This threat is particularly pronounced in parts of the ocean where the natural oxygen background is already very low, especially in the northern and eastern Pacific,” Du says. “Slight decreases in oxygen in these areas may have disproportionately large effects.”

Even if volcanoes rise in these places as glaciers retreat, the result wouldn’t be a disaster movie scenario.

This is where volcanoes and glaciers enter the picture, because one of the things the MIX cores reveal is an extended, low-oxygen event at the end of the last ice age, roughly 17,000 to 10,000 years ago.

For years, scientists struggled to make sense of this, but now, Du and Mix’s team has discovered that sediments from oxygen-starved regions have been sprayed with unusually high levels of volcanic ash, indicative of not one large volcanic eruption, but a steady drumbeat. who is younger. Eruptions – They happen exactly at the time when the giant ice sheets were melting.

Glaciers and glaciers
Glacier in 1988. Credit: Richard A Lovett

The most likely sources, Du says, are volcanoes in the Aleutian Islands and the Wrangel Mountains in Alaska, all of which, at the height of the last ice age, were deeply (2,000 meters thick) covered in ice.

The importance of this in ocean dead zones is that volcanic ash is rich in iron, and is a very good fertilizer for the explosive blooms of marine phytoplankton. When these organisms gobble up all the available iron, they die, sink and decompose – in the process now absorbing too much available oxygen.

Unlike surface waters, the waters in which this occurs at depths of 200m to 1,000m below the surface are not in contact with the atmosphere. This means they cannot easily replenish oxygen, say Dr. Weiqi Yao and Associate Professor Ulrich Wurtmann, of the Southern University of Science and Technology, China, and the University of Toronto, Canada.

All of this, of course, happened thousands of years ago. But there are proposals to offset climate change with iron fertilization, in which iron powder is sprinkled into iron-poor ocean waters in a deliberate attempt to induce blooms of phytoplankton whose growth would capture massive amounts of carbon dioxide from the air, which would cause their death. Most of it falls to the depths and is buried in sediments.

Since 2002, this has been tested in an experiment called SOFeX – the Southern Ocean Iron (Fe) Experiment – and proposals have been put forward to do it on a larger scale not just there, but in the North Pacific. The idea is that for every atom of iron deposited in this water, a whopping 100,000 molecules of carbon dioxide could be removed from the air.

When organisms gobble up all the available iron, they die, sink, and decompose — absorbing much of the available oxygen.

But is it a good idea?

New research says probably not. “Earth did the experiment for us,” says Meeks. One lesson is that large-scale iron fertilization actually traps carbon dioxide in the deep sea. But there are serious consequences, as it creates dead zones. This would be very disastrous, so we have to be careful about it.”

Other scientists agree that “Du and colleagues’ work suggests that short periods of iron enrichment can lead to long-term anoxia in marine ecosystems,” Yao and Wurtmann write in their own paper in Nature. “The resulting marine dead zones could affect fisheries for thousands of years.”

“There has long been interest in the possibility of using iron fertilization to lower carbon dioxide,” adds Professor Richard Alley, a Nobel Prize-winning researcher in climate change at Penn State. “I am not an expert in this field, but it can be a major solution to human carbon dioxide.”

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