Study shows rivers a major transport of black carbon to the ocean

Black carbon, formed from the burning of biomass and fossil fuels, may account for as much as ten percent of the carbon transported by rivers into the ocean and play a significant role in controlling the balance of two of the most important carbon pools on earth – the soil and the ocean.

This is the finding of a group of scientists, including Aron Stubbins of the Skidaway Institute of Oceanography. This research will appear in the April 19, 2013 issue of the journal Science, published by the AAAS, the science society, the world’s largest general scientific organization. See http://www.sciencemag.org, and also http://www.aaas.org.

Black carbon is organic material that has been altered by heat or combustion, such as the remnants of forest fires or burning fossil fuels. The burning of biomass generates between 40 million and 250 million tons of black carbon every year. Part of that is preserved for thousands of years in soils and sediments where it makes up approximately ten percent of the total carbon there.

Another portion is picked up by drainage and carried by rivers to the ocean. According to Stubbins and his colleagues, as much as ten percent of the carbon dumped by rivers into the ocean may be this black carbon.

This movement of black carbon involves two of the Earth’s three main stores of reactive carbon — in the soil and in the dissolved phase in the ocean. Both are approximately the same size as the third store – the carbon in the atmosphere, in the form of carbon dioxide.

“The balance between those three carbon pools is very important,” said Stubbins. “It controls the levels of carbon dioxide in the atmosphere, which in turn influences local and global climate.”

Black carbon is fairly stable in the marine environment, especially in the deep ocean. However, near the surface black carbon is very photo-sensitive. So when it is exposed to sunlight, it will degrade rapidly.

“In the deep ocean, the degradation is so slow that it would take up to 40 thousand years for the black carbon to be removed,” said Stubbins, “However, stick it in sunlight and 95 percent will disappear in two weeks.”

When exposed to sunlight, the relatively complex black carbon molecules break down into smaller molecules, including carbon dioxide. The CO₂ is dissolved in the ocean water where it can be utilized in photosynthesis by microscopic plants called phytoplankton. It can also be released into the atmosphere as part of the constant exchange of gasses between the atmosphere and the water at the ocean surface.

This degradation of black carbon in the surface ocean is apparently happening at a fairly rapid rate. The data in this project suggests that the Earth’s rivers are dumping much more black carbon into the ocean than can be found there.

“So where is it going?” asked Stubbins. “The rivers are dumping ten to 100 times more carbon into the ocean than we are finding there. That means we are losing ten to 99 percent of it.”

Stubbins continued, if that black carbon had remained in the soil, it would have remained stable for thousands of years.

“If you are losing it in the oceans, it is likely being converted into carbon dioxide. This freeing of black carbon from the soils, followed by its conversion to CO₂ is analogous to the production of CO₂ that occurs when we dig up and burn fossil fuels.”

The Science article is titled “Global Charcoal Mobilization from Soils via Dissolution and Riverine Transport to the Oceans.” The lead author is Rudolf Jaffé from Florida International University. In addition to Stubbins, the co-authors include Yan Ding, also from Florida International University; Jutta Niggemann and Thorsten Dittmar from the Max Planck Research Group for Marine Geochemistry; Anssi V. Vähätalo from the University of Helsinki; Robert G.M. Spencer from the Woods Hole Research Center; and John Campbell from the U.S. Department of Agriculture Forest Service Northern Research Station.

The entire article can be viewed online at: www.sciencemag.org

Stubbins has a website detailing this and other work on black carbon at: http://www.skio.usg.edu/?p=research/chem/biogeochem/blkcarbon

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Slash-and-burn activities source of oceanic black carbon

For years, “slash-and-burn” techniques were used to clear Brazil’s massive Atlantic Forest.  Although the large-scale burning was halted in 1973, the black carbon left behind from those forest fires is still draining into the area’s rivers and eventually into the ocean. For the first time, a team of scientists, including Aron Stubbins from the Skidaway Institute of Oceanography, has studied this carbon outflow and produced estimates of the amount of black carbon being introduced to the ocean. Their study has been published in the August issue of Nature Geoscience. Stubbins was one of seven co-authors of the paper. Thorsten Dittmar from the Max Planck Research Group for Marine Geochemistry in Oldenburg, Germany, and Eduardo de Rezende from the Universidade Estadual do Norte Fluminense in Rio de Janeiro, Brazil were the lead authors.

Photo Courtesy: Laboratorio de Ciencias Ambientais, Universidade Estadual do Norte Fluminense, Rio de Janeiro, Brazil

Humans have used fire extensively as a tool to shape the Earth’s vegetation. Brazil’s Atlantic Forest once covered 1.3 million square kilometers and was one of the largest tropical forest ecosystems on Earth. Because of the extensive burning for land-clearing, the forest has been reduced to less than ten percent of its original size.

The research team estimated that prior to 1973, the burning of the Atlantic Forest generated as much of 500 million tons of black carbon. The burned plant material initially sits on the ground or is absorbed into the soil, but eventually it is carried away by rainfall drainage into creeks, rivers, and, eventually, the ocean.

One river in the area carries 2,700 tons of dissolved black carbon to the ocean annually.

“We scaled our findings up to cover the remainder of the watershed,” said Stubbins. We estimate the former-forest contributes 50,000-70,000 tons of dissolved black carbon to the marine environment.”

What is not known is the fate of the dissolved carbon once it reaches the ocean. Black carbon is thought to be very slow to decay in the oceans. So the black carbon entering the oceans maybe accumulating as a carbon store that locks carbon away from the atmosphere for hundreds if not thousands of years. Its influence on marine life is also unknown at present.

“What is certain is that slash-and-burn will continue to ravish forests creating more black carbon in the soils left behind,” said Stubbins. “This study shows that the effects of these fires extend on the carbon cycle extend through both time and space. Although the initial impact is immediate and local, the long lasting export of black carbon spreads the impact of these fires throughout the global ocean.”

The article can be viewed at: www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1541.html.

Fossil fuels fire glacier carbon cycle according to Skidaway Institute scientist

New clues as to how the Earth’s remote ecosystems have been influenced by the industrial revolution are locked, frozen in the ice of glaciers. That is the finding of a group of scientists, including Aron Stubbins of the Skidaway Institute of Oceanography.

The research is published in the March 2012 issue of Nature Geoscience.

The key to the process is carbon-containing dissolved organic matter (DOM) in the glacial ice. Glaciers provide a great deal of carbon to downstream ecosystems. Many scientists believe the source of this carbon is the ancient forests and peatlands overrun by the glaciers. However, Stubbins and his colleagues believe the carbon comes mainly from contemporary biomass and fossil fuel burning that gets deposited on the glacier surfaces. Once deposited on the glacier surface by snow and rain, the DOM moves with the glacier and is eventually delivered downstream where it provides food for microorganisms at the base of the marine food web.

Aron Stubbins

“In vibrant ecosystems like in the temperate or tropical zones, once this atmospheric organic material makes landfall it is quickly consumed by the plants, animals and microbial populations,” said Stubbins. “However in frigid glacier environments, these carbon signals are preserved and standout.”

“Remote regions are often perceived as being pristine and devoid of human influence”, Stubbins continued. “Glaciers show us that nowhere goes untouched by industry. Instead, burning fuels has an impact upon the natural functioning of ecosystems far removed from industrial activity.”

Glaciers and ice sheets together represent the second largest reservoir of water on earth, and glacier ecosystems cover ten percent of the Earth, yet the carbon dynamics underpinning those ecosystems remain poorly understood.

“Increased understanding of glacier biogeochemistry is a priority, as glacier environments are among the most sensitive to climate warming and the effects of industrial emissions” said Stubbins.

Globally, glacier ice loss is accelerating, driven in part by the deposition of carbon in the form of soot or “black carbon”, which darkens glacier surfaces and increases their absorption of light and heat. Biomass and fossil fuel burning by people around the globe are the major sources of that black carbon.

Stubbins and his fellow scientists have conducted much of their 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 precipitation. High levels of rain and snow acts to strip the atmosphere clean of organics, dumping it on the glacier. Consequently, these glaciers are among the most sensitive to global emissions of soot.

The researchers’ 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. “When we look at the marine food webs today, we may be seeing a picture that is significantly different from what existed before the late-18th century,” said Stubbins. “It is unknown how this manmade carbon has influenced the coastal food webs of Alaska and the fisheries they support.”

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. These are the areas that are experiencing the highest levels of glacier ice loss.

“Although it is not known to what extent organic material deposition has changed and will continue to alter glacially-dominated coastal ecosystems or the open ocean, it is clear that glaciers will continue to provide a valuable and unique window into the role that the deposition of organic material plays in our changing environment,” Stubbins said.

Stubbins collaborators on the project included Eran Hood and Andrew Vermilyea from the University of Alaska Southeast; Peter Raymond and David Butman from Yale University; George Aiken, Robert Striegl and Paul Schuster from the U.S. Geological Survey; Patrick Hatcher, Rachel Sleighter  and Hussain Abdulla from Old Dominion University; Peter Hernes from the University of California-Davis; Durelle Scott from Virginia Polytechnic Institute and State University; and Robert Spencer from Woods Hole Research Center.

The paper can be viewed on-line at http://dx.doi.org/10.1038/NGEO1403

Further details are available at http://www.skio.usg.edu/?p=research/chem/biogeochem/glaciers. This work is being continued with support from the National Science Foundation: http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1146161

The Skidaway Institute of Oceanography is an autonomous research unit of the University System of Georgia located on Skidaway Island in Savannah, Ga. The mission of the Institute is to provide the State of Georgia with a nationally and internationally recognized center of excellence in marine science through research and education.

Skidaway Institute receives research grant to study glacier carbon

Aron Stubbins

Skidaway Institute of Oceanography researchers Aron Stubbins and Marc Frischer have been awarded a research grant from the National Science Foundation for $224,037 to study the origins of organic carbon in glaciers. Stubbins and Frischer are part of an international team working on the two-year project.

Glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system. Although, the carbon contained in the glacial ice is a major contributor to the downstream ecosystems, the dynamics of glacial biogeochemistry are poorly understood. Much of the carbon has been thought to have come from ancient peat lands and forests overrun by the glaciers. However, recent research by Stubbins and his colleagues challenges that explanation. They hypothesize that the main source is atmospheric carbon from the combustion of fossil fuels and biomass.

Marc Frischer

The proposed work will determine the extent to which fossil fuels contribute to the dissolved organic material (DOM) in the glaciers. They will verify the age and stability of the glacial DOM and quantify the extent to which it is being exported to downstream ecosystems.

Stubbins and Frischer will be working with other scientists, including Robert Spencer, Woods Hole Research Center; Eran Hood, University of Alaska Southeast; Peter A. Raymond, Yale University; Greg Kok, Droplet Measurement Technologies; and Thorsten Dittmar, Max Planck Group for Marine Geochemistry, Oldenburg, Germany.

 

Barrow — January 17

17 January 2012

We woke up a little late this morning after yesterday’s late night. Victoria and I met to go over plans for the day and to discuss the details of the experiment that we plan to start today. The experiment is a component of SSU graduate student Zac Tait’s thesis project. Zac couldn’t come this time because he is about to be a father. His daughter, who they will name Iris, is due on 4 February. Zac left me and Victoria with extensive notes and prepared all the supplies but we’ll run it.

The goal of this experiment, as in previous ones, is to test the hypothesis that Arctic Ocean bacteria can utilize the carbon locked up in the humic material that makes up the permafrost, but doing so will require them to acquire more nitrogen. The most abundant source of nitrogen in the water is found in the mineral form of nitrate (NO₃). One of the major questions of our project is whether the release of the carbon stored in the permafrost will set-up increased competition for NO₃ between the photosynthesizing autotrophs (phytoplankton) and the CO₂ respiring heterotrophs (bacteria). The idea is that the more organic carbon that gets released into the ocean the more bacteria activity will occur.  However, that increase in activity will be at the expense of nitrate resources that the phytoplankton need in the spring (when the lights come back on) to grow.  If there is less nitrate available there will be less phytoplankton and therefore less fish, seals, whales etc that depend on a food web whose base is the phyotoplankton. So it’s somewhat of a counterintuitive idea; add more nutrients and get less out.

In previous experiments we found generally that this hypothesis is true, but that the carbon-rich humic material we collected directly from the tundra is used very slowly which makes the question hard to address given the practical constraints of our time here. Because our time is short and the temperatures are cold which slows everything down, we decided on a new twist for these experiments. This time, we are using humic material that has already been broken down some by exposure to sunlight. This process is called photo degradation. Photo degrading complex carbon molecules occurs naturally (It’s reasonable to expect that humics derived from melting permafrost will be exposed to sunlight on their trip to the ocean.) and it increases its availability to bacteria as a nutrient source. So, prior to the trip Zac exposed humics in a solar simulator for 0, 5 and 15 days resulting in increasingly degraded humic materials.  Amazingly, after 15 days of simulated exposure to sunlight the brown humic material was almost completely colorless. The carbon is still there but since it has been broken into smaller and less condensed molecules it doesn’t absorb as much light, thus it appears lighter in color.

Photo degraded humics used in our bioassay experiment

Our experimental design is relatively simple. We use 4 liter (1 gal) milk jugs (actually they are a special nontoxic plastic but they look like milk jugs) to incubate bacteria with the humics and allow them to grow.  Over the course of the week we’ll be here we take samples to watch the bacteria grow track the dynamics of the carbon and nitrogen. Our hypothesis will be supported if we see the bacteria grow and the carbon disappear in coordination with the disappearance of the NO₃.

After 9 hours of filtering and rinsing we finally got the experiment set-up and running. We’ll sample it daily (or every other day) for the time we’re up here.

Zac’s experiment running

 

But the real excitement happened on the ice today. Because we are so concerned about the stability of the ice the UMIAQ crew went out to check our ice camp which we had left standing. When they got out there they realized that the ice was moving a lot and that large cracks were beginning to appear. The crew was scared enough that they just came back leaving the tent behind. But Brower thought they could get it and made a heroic trip back out with Tony and Glenn. They ripped the tents out of the ice leaving the stakes behind, quickly lashed it on two sleds, and hightailed it back jumping cracks with open water. We heard some of it on the radio. The whole situation has us pretty nervous and thinking very carefully about safety.

[Picture –

Brower and Glenn standing by the rescued tents.

Either way tomorrow we won’t go out.  We’ll re-group and re-evaluate.

Sunday 1 May 2011 – Last Lab Day

Today was our last full lab day and the beginning of the end for this trip.

After breakfast in the cafeteria, Zac and I began to purify bacterial messenger RNA (mRNA) from the water we had filtered yesterday. mRNA is the molecule that acts as the intermediate between DNA and proteins. All the information necessary to code for complex macromolecules like proteins are stored in DNA, but in order to use those instructions a cell must transcribe its DNA information into RNA that can then be translated by another complex molecule called a ribosome into proteins.

Truly life is amazing and it boggles the mind how complex and elegant it is. From the very smallest scale of atoms and molecules to the grandest scales of the universe, everything is connected. Anyway, I digress.

Our goal today was to purify RNA from the bacteria that we had captured on our filters so that we can determine which genes are turned on and how active those genes are. We are particularly interested in those genes that bacteria use to assimilate inorganic nitrogen because we suspect that the addition of new carbon in the form of the humics released from the melting permafrost will require bacteria to use more inorganic nitrogen. If this is true we should see an increase in the genetic expression of the genes involved in inorganic nitrogen assimilation.  Anyway, that’s why we need the RNA.

The initial step of our purification procedure requires two sets of hands and that was my job this morning.  Once we had safely gotten our filters containing all those bacteria into the first extraction reagent which stabilizes the RNA I was free to start packing-up our labs while Zac completed the RNA extractions.

Zac purifying RNA

I started with the cold room where we had filtered all the water.  Although it took us many hours to set-up the lab and to make sure that we had everything in exactly the right place, it only took me about half an hour to dismantle it.

Cold room during use and after being cleaned-up.

It’s kind of sad to tear down a lab that was so functional, but we know we’ll be back in the summer to do it again. Just for grins we left one little piece of orange tape on the floor to see if anyone else uses the space before we get back.

Once Zac finished the purifications we really got busy rinsing and cleaning all our gear and getting everything ready to be packed away.  At around 3pm we stopped to sample Zac’s ongoing experiment; there’s only one more time point to go in that study. Then we went to help Lollie pack her bags and get checked in for her flight home.

Because the airport here is so small but still requires the TSA agents to screen all bags, travelers are encouraged to check in early. This greatly reduces the check in wait times and relieves congestion in the very small arrival/departure area.  After Lollie checked in she went back home and finished preparing a fabulous Mexican dinner for the whole team.

Alas all good things must come to an end and finally it was time for Lollie, Adriane, and Debbie to head back to the airport to start their long journeys home.  We miss them already.

Skidaway Institute scientists study Arctic climate change

Climate change will have profound effects on the Arctic ecosystem, and those effects may be felt around the world. Skidaway Institute of Oceanography professor Marc Frischer is launching a three-year project to examine the effects of rising temperatures in the Arctic and how those changes will impact the marine food web.

The project is funded by a $356,139 grant from the National Science Foundation (NSF).

“We know global climate change is impacting the fragile Arctic environment,” said Frischer. “Atmospheric concentrations of heat absorbing greenhouse gases including carbon dioxide are rising; the Arctic sea ice and permafrost are melting; and models are predicting significant changes in precipitation patterns in the Arctic.

“What we don’t know is how living systems will respond or adapt to those changes and how, ultimately we as humans will have to adapt to those changes.”

The work will be conducted in Point Barrow, the northernmost location in the US, at a NSF supported research station operated by the Barrow Arctic Science Consortium.

Pt. Barrow, Alaska, in winter

The landscape at Point Barrow is tundra that sits on top of as much as 1,300 feet of permanently frozen soil called “permafrost.” The concern is that with climate warming this permafrost will begin to melt and release an enormous amount of organic material into the coastal ocean.

“What you have now is have is up to 1,300 ft deep frozen soils consisting of ancient forest peat locked in the permafrost,” said Frischer. “What will happen when the permafrost starts to melt and that material, called humic acid, is released into groundwater, streams, rivers and ultimately into the ocean? That is what we want to know.”

Frischer’s focus will be on the microscopic organisms that comprise the very bottom of the Arctic Ocean food web. They include a wide variety of tiny organisms. On one end are the autotrophs, organisms that consume inorganic material and produce energy through photosynthesis, like plants. At the other end are the heterotrophs that consume organic material and obtain their energy from what they eat, like animals.

The humic acid material is rich in carbon, but lacks nitrogen, a key element that both autotrophs and heterotrophs need to make use of the carbon in the humic material. For every carbon molecule an organism uses, it will also need nitrogen.

“If you are going to grow more things, then that nitrogen has to come from somewhere,” said Frischer. “Our hypothesis is that as this humic material enters the coastal Arctic, there will be a greater demand for nitrogen at the base of the food web.”

Whoever gets that nitrogen, whether it will be the plant-like autotrophs or the animal-like heterotrophs, will determine how much organic production ends up farther up the food web in larger marine animals and eventually humans.

“This will all be set by whoever wins the war for nitrogen,” said Frischer.

Over the course of the project, Frischer and his team will travel to the Arctic several times a year. While in the Arctic, Frischer’s team will focus on making observations of the system and conducing experiments to determine what organisms are growing, which organisms are using the humic material, and determining where they are getting their nitrogen from and how they are doing it.

“We will manipulate the nutrients in the water samples and see how the different micro-organisms react,” said Frischer. “From that we should be able to project how the natural environment will react and ultimately contribute new data that help us understand and predict the biological effects of climate warming in the Arctic.”

Frischer will be working with two collaborators on the project, Patricia Yager from the University of Georgia, and Deborah Bronk from the Virginia Institute of Marine Science. Both Yager and Bronk received independent grants from NSF to participate in the study.

Skidaway Institute awarded NSF grants

The Skidaway Institute of Oceanography has received two research grants from the National Science Foundation totaling more than $761,000. The awards are being funded under the American Recovery and Reinvestment Act of 2009.

Dr. Marc Frischer

The first grant for $356,139 was awarded to Skidaway Institute scientist Marc Frischer to investigate how a warming climate will affect the food web dynamics in the Arctic Ocean.

“We are most appreciative to the National Science Foundation for funding this significant research,” said Skidaway Institute Director James Sanders. “A warming climate is causing significant changes in the Arctic marine environment, including reduced sea ice and increased terrestrial discharge from rivers of nutrients such as carbon and nitrogen. It is very important that we understand the way these changes will affect food web dynamics and, ultimately, the entire Arctic marine ecosystem.”

Frischer will work with collaborators Deborah Bronk from the Virginia Institute of Marine Science and Patricia Yager from the University of Georgia Research Foundation on the project.

Dr. Elizabeth Mann

The second grant for $404,833 was awarded to Elizabeth Mann of Skidaway Institute, along with collaborators Eric Stabb of the University of Georgia and Hongwei Wu of Georgia Tech. They will investigate the way some marine bacteria obtain and utilize the key nutrient iron in environments where this metal is scarce.

According to Mann, it is important to understand how organisms produce the compounds that help keep iron in solution in the surface ocean. Iron is a key nutrient for the growth of microscopic algae, known as phytoplankton, which absorb large amounts of carbon dioxide from the atmosphere.

“In many areas of the world’s ocean, iron concentrations are so low that phytoplankton growth is reduced,” Mann said. “An increase in iron availability will lead to the removal of more carbon dioxide from the atmosphere through photosynthesis.”