What's soot got to do with it?


Aerial photograph of the Khumbu Glacier and the Everest Himalayan range May,15,2003 on the Nepal-Tibet border.


Paula Bronstein

LAKENLA, Tibet — The view from the prayer-flag covered mountain pass of Lakenla in Tibet is expansive.

The endless vista is rendered tapestry-like by a collection of sapphire lakes and jagged peaks. This is Namtso — Tibetan for "Heavenly Lake." On its high plateaus, rockslides echo like thunder in the valleys, and geography makes that shift from classroom dullness to vibrant story of man’s interaction with the Earth.

Here at 20,000 feet, there are significantly more yaks than humans; these hardy creatures are central to the culture, providing everything from fuel through transport to food in an environment that is not dominated by man. We think of the area as pristine. But is that true?

As I hunch over a warming bowl of yak butter tea, an 82-year old pilgrim talks about his journey … and about the many he has made before. Pointing nearby, the pilgrim describes where the glacier’s edge stood when he was a young man. From where we now sit, it would take at least a half-day of uphill hiking to reach the ice.

The retreat of glaciers in a couple of generations is staggering and I wonder: What will we see in the next two generations?

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The following day, our team climbs to the glacier, passing mounds of Mani stones inscribed with Buddhist scriptures and covered in prayer flags. Splendor is all around. Finally reaching the glacier, we take the samples we’ve trekked here for: 25 pounds of ice per person.

We like to think of places like Tibet and Alaska as being pristine, unsullied by human activity. But the samples we collect tell a different story. Even in a remote corner of the globe like Namtso, the glaciers are impregnated with black soot — carbon fallout from the incomplete burning of fossil fuels and biomass, the byproduct of coal, indoor-heating, traditional cooking stoves, crop burning, kilns and old diesel engines.

Why is black carbon a problem? The soot falls on glacial snow and ice cover, causing it to absorb more sunlight, which in turn accelerates melting of the glaciers. As much as one-third of recent glacier thinning has been attributed to increased amounts of black carbon deposited directly from industrial processes. It’s also a major health issue — 1.5 million people die from respiratory diseases associated with black carbon every year.

New clues as to how the Earth’s remote ecosystems have been altered by the byproducts of industry are being unlocked from the ice of these glaciers by a group of scientists from the Woods Hole Research Center, the University of Alaska Southeast, Yale University, the U.S. Geological Survey, Old Dominion University, the University of California-Davis, Virginia Polytechnic Institute and State University and Skidaway Institute of Oceanography. The results of our research were published in the March 2012 issue of Nature Geoscience.

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Globally, glacier ice loss is accelerating, driven in part by the deposition of “black carbon.” Our visit to Tibet was preceded by research at the Mendenhall Glacier near Juneau, Alaska. Mendenhall and other glaciers that end their journey in the Gulf of Alaska receive a high rate of rain and snow, making them ideal sites for the study of the black carbon process.

The key to the process is dissolved organic matter (DOM) that contains carbon found in the glacial ice. Glaciers deliver a great amount of carbon to downstream ecosystems.

Many scientists believe the source of this carbon is the ancient forests and peat lands overrun by the glaciers. Thanks to new evidence from radiocarbon dating and ultra-high resolution mass spectrometry, however, we believe the carbon comes mainly from burning fossil fuels and contemporary biomass. Once snow and rain deposit the organic matter containing black carbon on the glacier surface, the resultant DOM moves with the glacier and is eventually delivered downstream in melt waters, where it provides food for microorganisms at the base of the aquatic food web.

In frigid glacier environments, any new substance stands out, making glaciers ideal ecosystems for the detection and study of emissions. Organic material found in temperate or tropical zones is more difficult to study because it is quickly consumed in the general milieu of life. The Mendenhall glacier research site allows a unique perspective for studies such as this one. 

Glaciers and ice sheets together represent the second largest reservoir of water on the planet, and glacier ecosystems cover 10 percent of the Earth, yet the carbon dynamics underpinning those ecosystems remain poorly understood. Improving our understanding of glacier biogeochemistry is of great urgency, as glacier environments are among the most sensitive to climate change and the effects of industrial pollution.

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Our findings also reveal how the ocean may have changed over past centuries. The microbes that form the very bottom of the food web are particularly sensitive to changes in the quantity and quality of the carbon entering the marine system. Since the study found that the organic matter in glacier outflows stems largely from human activities, it means that the supply of glacier carbon to the coastal waters of the Gulf of Alaska is a modern, post-industrial phenomenon.

A warming climate will increase the outflow of the glaciers and the accompanying input of dissolved organic material into the coastal ocean. This will be most keenly felt in glacially dominated coastal regions, such as those off of the Gulf of Alaska, Greenland and Patagonia at the southern tip of South America. These are the areas that are experiencing the highest levels of glacier ice loss.

The story of soot and glaciers isn’t all bad news.

Since black carbon only stays in the atmosphere for a few days to a few weeks, any reduction in emissions, for example through utilization of cleaner technologies, will lead to a rapid decrease of black carbon in the atmosphere with associated benefits for human health and climate.

Dr. Robert Spencer is an assistant scientist at Woods Hole Research Center in Massachusetts, and a bio-geochemist whose current research is focused on a broad range of environments from the tropics to the Arctic.