USGS scientists Doug Halm, Paul Schuster, and Kathy Kelsey collecting melt water samples from Gulkana Glacier. Results of recent analyses identified old carbonin the Yukon River, but also indicated that the chemical source was not derived from ancient plant material stored in the glacier, but from fossil fuel sources derived from atmospheric deposition. This add new complications to the interpretation of carbon sources and sinks in high latitudes and of the apparent sources of old organic carbon exported by arctic rivers.

A new study concludes that fossil fuel emissions are likely contributors to a substantial amount of organic carbon found on glaciers in Alaska.

Fossil fuel emissions, which contain organic carbon, can speed up the rate of glacier melt when deposited on glacier surfaces. In addition, the organic molecules associated with these deposits can be transported in rivers and streams, affecting downstream aquatic ecosystems. Knowledge of the source and age of organic carbon in glaciers allows for a better understanding of these and other impacts.

Prior research suggested that the main sources of organic carbon in Alaska’s glaciers were from forests and peatlands overrun by glaciers as far back as ten thousand years ago. While old soil and plant material are still possible sources of glacial organic carbon, new research indicates that human-created, or anthropogenic, sources are also important.

“We knew the organic carbon present in Alaska’s glaciers was old, but identifying the sources of this material has been difficult due to the lack of chemical data,” said USGS scientist George Aiken.

While extensive burning of fossil fuels is, geologically speaking, a relatively modern practice, the fuels themselves and the resulting carbon emissions are ancient. This is because the fuels are formed from plants and microorganisms that lived millions of years ago.

“Now we know that a substantial amount of ancient organic matter associated with these and other glaciers is of anthropogenic origin,” continued Aiken.

Why Study Carbon Levels?

When organic matter and other materials from the atmosphere are deposited on the surface of a glacier, less sunlight can be reflected and, therefore, more radiation and heat are absorbed. Having these materials on snow and ice surfaces causes them to melt faster.

Another concern is impacts to ecosystems and species habitats. As an example, organic matter exported to coastal areas is a potential nutrient or food source for aquatic bacteria, phytoplankton, and small grazing zooplankton. Climate warming or other factors may change the amount and quality of organic carbon available to these organisms. These aquatic organisms are also the base of the food web for all aquatic communities.

“When trying to understand climate change and decipher the carbon cycle puzzle, we need to make sure that we are using all of the right pieces,” said USGS scientist Rob Striegl. “As part of that puzzle, we are studying the source and amount of carbon flowing into the Arctic Ocean. An understanding of the complete picture allows for the most informed decisions to protect our environment.”

Melt water stream discharging from Gulkana Glacier, Alaska. USGS research of the Yukon River has had a long term goal of determining the source and fate of organic carbon transported by the river to the Bering Sea and ultimately the Arctic Ocean.

“The Arctic is of special interest because what happens there, such as extensive glacier melt, has impacts on the rest of the world,” continued Striegl. “Glacier environments, especially those in the high latitudes of the Arctic, are also among the most sensitive to climate warming.”

New Twist to Understanding Carbon in Glaciers

“Our new paper describes, for the first time, the detailed chemical composition of dissolved organic matter associated with glaciers and glacial meltwater in coastal Alaska and in Wyoming,” said Aiken.

“This study adds a twist to previous understandings, showing there is another source of organic carbon out there that needs to be considered,” said Striegl.

This study, published in the journal Nature Geosciences, was a collaborative effort of many institutions led primarily by the University of Alaska Southeast, Skidaway Institute of Oceanography, Woods Hole Research Center, and the USGS.

The Role of USGS Science

Earlier studies by the USGS, in collaboration with university researchers, found the presence of ancient organic carbon in the Yukon River and traced it back to meltwater from glaciers. For further analyses, USGS scientists continued those collaborations to sample meltwater from Mendenhall Glacier and Herbert Glacier in southeastern Alaska. The samples were then analyzed at USGS and university laboratories to develop the conclusions outlined in this new study.

“This truly is a collaborative effort, taking the expertise of many scientists to put the story together on the source of the carbon,” said Striegl. “The original work of the USGS in the Yukon basin helped form the questions and lab results contributed to answering the questions; but it took specialized instrumentation and scientific expertise from several other organizations to determine the final answer.”

Additional samples used for age dating and for other chemical characterization of the organic carbon of glaciers from other locations came from Gulkana Glacier in Alaska and from Fremont Glacier in Wyoming.

USGS scientists Doug Halm, Paul Schuster, Peter Murdoch, and Kathy Kelsey collecting melt water samples from Gulkana Glacier.

The Big Picture of Aquatic Carbon

The USGS has a long term goal of determining the source and fate of organic and inorganic carbon transported to coastal areas and oceans across the entire Nation. USGS research on the Yukon and other Arctic rivers is particularly focused on climate warming effects on mobilizing ancient carbon from permafrost to coastal regions and the Arctic Ocean. The USGS participates in the Arctic Great Rivers Observatory project, which is an international effort to study the six largest rivers, including the Yukon, which flow into the Arctic Ocean.

Learn more about USGS Yukon River Basin studies.

Contact: Jessica Robertson

USGS scientist Peter Van Metre examines a parking lot where coal-tar sealcoat has been applied.A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

What is sealcoat?

Coal-tar-based sealant is the black liquid sprayed or painted on many parking lots, driveways, and playgrounds.

Several PAHs are probable human carcinogens, and many are toxic to fish and other aquatic life. Coal tar, which can cause cancer in humans, is made up of more than 50 percent PAHs. An estimated 85 million gallons of coal-tar-based sealant are used on parking lots and driveways each year, primarily in the central and eastern United States.

What are the rates of PAH emissions to the air from coal-tar-based sealcoat?

Coal-tar-based sealants are emitting PAHs into the air at rates that could be greater than annual emissions from vehicles in the United States based on a study in which USGS scientists tracked PAH levels in air and in dried sealcoat following sealcoat application to a parking lot. Two hours after sealcoat application, PAH emissions were 30,000 times higher than those from unsealed pavement. In a second study, USGS scientists measured PAHs in air above parking lots with and without sealcoat, in suburban Austin, Texas. Parking lots with three- to eight-year-old sealant still released 60 times more PAHs to the air than parking lots without sealant.

A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Children living near sealed parking lots are exposed to PAHs

Children living near coal-tar-sealed pavement are exposed to twice as many PAHs from ingestion of contaminated house dust than from food, according to a separate new study by Baylor University and the USGS. Baylor University scientist Spencer Williams used USGS measurements of PAHs in house dust to estimate the potential ingestion of PAHs by young children living near coal-tar-sealed parking lots. Ingestion of PAHs from food has long been thought to be the primary route by which children are exposed to PAHs. PAH ingestion by children living near coal-tar-sealed parking lots  is estimated to be 14 times higher than by children in apartments adjacent to unsealed parking lots.

Sealcoat is a major source of PAHs to the environment

Past and current  research on environmental contamination and coal-tar-based pavement sealants and implications for human health and stormwater management are summarized in a new Feature Article in the journal Environmental Science and Technology. The article is jointly authored by researchers with the USGS, Minnesota Pollution Control Agency, University of New Hampshire, City of Austin, Texas, and Baylor University.

Bans on coal-tar sealcoat

Some governments have taken action on the use of coal-tar-based sealcoat.  Fifteen municipalities and two counties in four states (Minnesota, New York, Texas and Wisconsin), the District of Columbia and the state of Washington all have enacted some type of ban, affecting almost 10.4 million people. Several national and regional hardware and home-improvement retailers have voluntarily ceased selling coal-tar-based driveway-sealer products.

Coal-tar sealcoat compared to asphalt-based sealcoat

USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Two kinds of sealcoat products are widely used: coal-tar-based and asphalt-based.  The coal-tar products have PAH levels about 1,000 times higher than the asphalt products. Coal-tar-based sealcoat is more commonly used in the Midwest, southern, and eastern United States. Asphalt-based sealcoat is more commonly used in the western United States.  Consumers can determine whether a product contains coal tar by reading the product label or the associated Materials Safety Data Sheet (MSDS), available from the applicator, retailer or on the Internet.

For more information, please visit the USGS website on PAHs and sealcoat, or contact Jennifer LaVista.

Human health, ecological health, and environmental health are closely connected.

Human health, ecological health, and environmental health are closely connected. Environmental changes that affect the spread of disease are a growing public health concern worldwide. Join us to learn how USGS science contributes to our understanding of how such environmental factors affect health threats.

learn more http://www.usgs.gov/public_lecture_series/default.asp