Sunlight, not microbes, key to carbon dioxide in Arctic

Terrestrial organic matter is shown spilling into a lake. Credit: Image courtesy of Oregon State University

The vast reservoir of carbon stored in Arctic permafrost is gradually being converted to carbon dioxide (CO2) after entering the freshwater system in a process thought to be controlled largely by microbial activity.

However, a new study -- funded by the National Science Foundation and published this week in the journal Science -- concludes that sunlight and not bacteria is the key to triggering the production of CO2 from material released by Arctic soils.

The finding is particularly important, scientists say, because climate change could affect when and how permafrost is thawed, which begins the process of converting the organic carbon into CO2.

"Arctic permafrost contains about half of all the organic carbon trapped in soil on the entire Earth -- and equals an amount twice of that in the atmosphere," said Byron Crump, an Oregon State University microbial ecologist and co-author on the Science study. "This represents a major change in thinking about how the carbon cycle works in the Arctic."

Converting soil carbon to carbon dioxide is a two-step process, notes Rose Cory, an assistant professor of earth and environmental sciences at the University of Michigan, and lead author on the study. First, the permafrost soil has to thaw and then bacteria must turn the carbon into greenhouse gases -- carbon dioxide or methane. While much of this conversion process takes place in the soil, a large amount of carbon is washed out of the soils and into rivers and lakes, she said.

"It turns out, that in Arctic rivers and lakes, sunlight is faster than bacteria at turning organic carbon into CO2," Cory said. "This new understanding is really critical because if we want to get the right answer about how the warming Arctic may feedback to influence the rest of the world, we have to understand the controls on carbon cycling.

"In other words, if we only consider what the bacteria are doing, we'll get the wrong answer about how much CO2 may eventually be released from Arctic soils," Cory added.

The research team measured the speed at which both bacteria and sunlight converted dissolved organic carbon into carbon dioxide in all types of rivers and lakes in the Alaskan Arctic, from glacial-fed rivers draining the Brooks Range to tannin-stained lakes on the coastal plain. Measuring these processes is important, the scientists noted, because bacteria types and activities are variable and the amount of sunlight that reaches the carbon sources can differ by body of water.

In virtually all of the freshwater systems they measured, however, sunlight was always faster than bacteria at converting the organic carbon into CO2.

"This is because most of the fresh water in the Arctic is shallow, meaning sunlight can reach the bottom of any river -- and most lakes -- so that no dissolved organic carbon is kept in the dark," said Crump, an associate professor in Oregon State's College of Earth, Ocean, and Atmospheric Sciences. "Also, there is little shading of rivers and lakes in the Arctic because there are no trees."

Another factor limiting the microbial contribution is that bacteria grow more slowly in these cold, nutrient-rich waters.

"Light, therefore, can have a tremendous effect on organic matter," University of Michigan's Cory pointed out.

The source of all of this organic carbon is primarily tundra plants -- and it has been building up for hundreds of thousands of years, but doesn't completely break down immediately because of the Arctic's cold temperatures. Once the plant material gets deep enough into the soil, the degradation stops and it becomes preserved, much like peat.

"The level of thawing only gets to be a foot deep or so, even in the summer," Crump said. "Right now, the thaw begins not long before the summer solstice. If the seasons begin to shift with climate change -- and the thaw begins earlier, exposing the organic carbon from permafrost to more sunlight -- it could potentially trigger the release of more CO2."

The science community has not yet been able to accurately calculate how much organic carbon from the permafrost is being converted into CO2, and thus it will be difficult to monitor potential changes because of climate change, they acknowledge.

"We have to assume that as more material thaws and enters Arctic lakes and rivers, more will be converted to CO2," Crump said. "The challenge is how to quantify that."

Some of the data for the study was made available through the National Science Foundation's Arctic Long-Term Ecological Research project, which has operated in the Arctic for nearly 30 years.

Source:  Oregon State University

Wild weather in the Arctic causes problems for people and wildlife

Svalbard's reindeer population can be severely affected by winter icing.
Credit: Brage Bremset Hansen

The residents of Longyearbyen, the largest town on the Norwegian Arctic island archipelago of Svalbard, remember it as the week that the weather gods caused trouble. Temperatures were ridiculously warm -- and reached a maximum of nearly +8 degrees C in one location at a time when mean temperatures are normally -15 degrees C. It rained in record amounts.

Snow packs became so saturated that slushy snow avalanches from the mountains surrounding Longyearbyen covered roads and took out a major pedestrian bridge. Snowy streets and the tundra were transformed into icy, rain-covered skating rinks that were difficult to navigate with snowmobiles. Flights were cancelled, the airport closed, and travel around town was tricky.

The situation was particularly problematic out on the Arctic tundra. Rain falling on snow can percolate to the base of a snowpack where it can pool at the soil surface and subsequently freeze. That makes it impossible for grazing reindeer to get at their food, for example, and extreme warm spells can even affect temperatures in the permanently frozen ground found throughout the archipelago.

But the extreme event also offered an interdisciplinary group of scientists, from climatologists to biologists to snow geophysicists and structural engineers, a chance to document the event and learn from it. Their cross-disciplinary report, "Warmer and wetter winters: characteristics and implications of an extreme weather event in the High Arctic," was published on 20 November in Environmental Research Letters.

"We had a unique opportunity to document what happened, and we did," said Brage Bremset Hansen, the first author on the paper, and co-author Øystein Varpe. "This was a case study from one event…but since it was an extreme event, and with all of our contacts in the different disciplines, we were able to compile this information into one story, which is quite rare."

Hansen is a biologist at the Norwegian University of Science and Technology's Centre for Biodiversity Dynamics, and Varpe is an associate professor at the University Centre in Svalbard.

Just a 0.2 percent chance of happening

Co-author Ketil Isaksen, a climatologist from the Norwegian Meteorological Institute, said that such an extreme event has a 500-year return period, which means that the probability of it happening in any one year is just 0.2 percent.

At the same time, climatologists say that Svalbard has seen the greatest increase in temperatures of any place in Europe over the last three decades.

And while no one can attribute the event directly to global warming, virtually all climate studies show that the High Arctic, including Svalbard, will become increasingly warmer and wetter over time.

"We expect this to be more likely to happen," Isaksen said.

Reindeer mortality up

As a biologist, Hansen was very interested in how the extreme weather would affect the archipelago's natural communities. Only four vertebrate species overwinter on Svalbard -- the wild Svalbard reindeer (Rangifer tarandus platyrhynchus), the Svalbard rock ptarmigan (Lagopus muta hyperborea), and the sibling vole (Microtus levis), and one animal that eats them all, the Arctic fox (Vulpes lagopus).

When Hansen and his colleagues compared summer population counts of reindeer after the January 2012 event to counts conducted for the previous summer, they found that the number of reindeer carcasses in many populations was among the highest ever recorded.
But it could have been worse, he said, in part because recent increases in summer temperatures have made for better foraging conditions for Svalbard reindeer overall.

"It wasn't like there were dead reindeer all over the tundra," he said. "If this had happened in the colder 1980s, it could have been much worse. …They had a nice winter up to this event, which occurred rather late."

Rain and permafrost

Hansen and colleagues have previously published research on the overwintering animal community on Svalbard, suggesting that such extreme events can affect all species. But what makes the new findings unique is the collaboration between different disciplines that enabled researchers to assemble a picture of what happened to Svalbard's physical environment, and to people living in the outposts of Longyearbyen and Ny-Ålesund, a tiny community with a winter population of about 30 people.

In Ny-Ålesund, for example, it rained nearly 100 mm in one day -- which would be more typical of the Norwegian coastal town of Bergen, renowned for its heavy rains. That one-day amount represented a quarter of the precipitation that Ny-Ålesund typically gets in a year.

Isaksen documented a significant increase in ground temperatures in permafrost as deep as 5 metres below the surface as a result of the extreme warming. This temperature increase came on top of a decades-long larger trend of warming of the permafrost on Svalbard, the researchers said. Permafrost is permanently frozen ground that is found throughout the archipelago and the High Arctic. In regions in the Northern Hemisphere where permafrost is found, it occupies approximately 25% (23 million km²) of the land area.

Tourism and infrastructure

And for Svalbard residents, who are some of the most northerly inhabitants on the globe, there were significant socioeconomic effects. During and after the event, it was difficult for snowmobiles to travel out on the tundra on the thick layer of ice, Varpe said.

This thick layer, averaging 15.3 cm, persisted out on the tundra well after the event was over, said Jack Kohler, senior research scientist, glaciology, at the Norwegian Polar Institute.
"The winter rain event leads to the ground-ice formation, and the ice lasts the remainder of the melt season, until it melts, and that is what I would call the significant happening," Kohler said. "The rain is an event, for sure, but the ice is actually the (big) event."

The result was a strong decrease in tourism for the rest of the winter, specifically for activities such as guided snowmobile and dogsled tours. Tour numbers dropped by 28 percent compared to the previous winter, and were the lowest ever since 2001, which is when statistics were first continuously kept. The researchers also believe that had a ripple effect on hotel stays and other tourist activities.

Another potential problem exposed by the extreme event was the vulnerability of the town's infrastructure to avalanches. A major avalanche in June 1953 destroyed the town's hospital and other buildings, killing three people, but since then, many buildings have been constructed without regard to potential avalanche risks. If Svalbard's climate continues to warm as our downscaled climate scenarios predict, the likelihood of damaging avalanches will only increase, Hansen and colleagues say.

Hansen is continuing to investigate the consequences of a warmer Arctic on Svalbard's natural communities and human population with a research project called VINTERREGN (Winter rain). Of particular interest is whether or not plants, which usually do not grow taller than a couple of inches at this latitude, can withstand being completely covered in ice for several months.

Source:  The Norwegian University of Science and Technology (NTNU)

Permafrost soil: Possible source of abrupt rise in greenhouse gases at end of last ice age

Pleistocene Ice Complex cliff: 35 meters high Pleistocene Ice Complex cliff at Sobo Sise Island (Lena Delta), Siberian Arctic. Credit: Alfred-Wegener-Institut / Thomas Opel

Scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have identified a possible source of carbon dioxide (CO2) and other greenhouse gases that were abruptly released to the atmosphere in large quantities around 14,600 years ago. According to this new interpretation, the CO2 -- released during the onset of the Bølling/Allerød warm period -- presumably had their origin in thawing Arctic permafrost soil and amplified the initial warming through positive feedback. The study now appears online in the journal Nature Communications.

One of the most abrupt rises in the carbon dioxide concentration in the atmosphere at the end of the last ice age took place about 14,600 years ago. Ice core data show that the CO2 concentration at that time increased by more than 10 ppm (parts per million, unit of measure for the composition of gases) within 200 years. This CO2 increase, i.e. approx. 0.05 ppm per year, was significantly less than the current rise in atmospheric CO2 of 2-3 ppm in the last decade caused by fossil fuels. These data describe an abrupt change in the global carbon cycle during the transition from the last ice age to the present-day warm interglacial and allow conclusions to be drawn about similar processes that could play a role in the future.

To determine the origin of the greenhouse gas, a team around by the geoscientists and climate researchers Dr. Peter Köhler and Dr. Gregor Knorr from the Alfred Wegener Institute has carried out computer simulations focusing on the new interpretation of these CO2 data. These calculations were motivated by new radiocarbon data (14C) that provide information on the age of the CO2 released to the atmosphere. The age of the carbon then allows conclusions to be drawn about the carbon source.

"The virtual lack of radiocarbon in the CO2 that was released into the atmosphere shows us that the carbon must have been very old," says Köhler. The carbon therefore cannot be originated from the deep ocean, Köhler adds: "The carbon stored in the deep ocean has been subject to exchange with the atmosphere over a period of millennia. In the atmosphere 14C has its only source. It is produced through the impact of galactic cosmic rays on molecules in the atmosphere." However, radiocarbon is unstable and decays with a half-life of around 5,700 years. The atmospheric data of CO2 and 14C can only be explained if a carbon source is assumed that contains virtually no 14C any more -- thus the greenhouse gases must have had another source than the deep ocean.

Permafrost soil contains, to some extent, very old organic material, which is released in the form of the greenhouse gases CO2 and methane when the soil thaws. Permafrost soil thus might be a possible source of old carbon. The thawing of Arctic permafrost soil might have been caused by a sudden resumption of large-scale Atlantic heat transport in the ocean that initiated the Bølling/Allerød warm period in the high northern hemisphere.

The scientists were able to estimate the amount of the carbon dioxide released to the atmosphere by applying a computer model that simulates the global carbon cycle. The simulation results indicate that the input of more than half a gigaton of carbon per year (1 gigaton = 1 petagram) over a period of two centuries is necessary to explain the observed data. This corresponds to a total amount of more than 100 gigatons of carbon. Present-day anthropogenic CO2 emissions due to fossil fuels, at approx. ten gigatons of carbon a year, are greater than the release rates of this natural process by a factor of at least ten.

According to the study, the proposed thawing of large areas of permafrost, followed by the rise in greenhouse gases, occurred at the same time as the warming in the northern hemisphere at the beginning of the Bølling warm period. The released greenhouse gases may amplify the initial warming through feedback effects.

A similar effect is also predicted for the future in the current IPCC report. Warming in Siberia, for instance, is already leading to thawing of permafrost soil: outgassing of CO2 and methane takes place. The same processes observed today -- and are expected to an even greater extent in the coming decades -- presumably occurred in a similar manner 14,600 years ago. "However, the state of the climate on Earth today has already been changed by anthropogenically emitted greenhouse gases. Future CO2 release due to the proposed thawing of permafrost will be substantially less than the input due to fossil fuels. However, these emissions from permafrost soil are additional greenhouse gas sources that further amplify the anthropogenically induced effect," says Köhler.

Source:  Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

Emergence of modern sea ice in Arctic Ocean, 2.6 million years ago

Field Work in the Arctic sea ice. Credit: Thomas A. Brown and Simon T. Belt

"We have not seen an ice free period in the Arctic Ocean for 2,6 million years. However, we may see it in our lifetime." says marine geologist Jochen Knies. In an international collaborative project, Knies has studied the historic emergence of the ice in the Arctic Ocean. The results are published in Nature Communications.

The extent of sea ice cover in Arctic was much less than it is today between four and five million years ago. The maximum winter extent did not reaching its current location until around 2.6 million years ago. This new knowledge can now be used to improve future climate models.

"We have not seen an ice free period in the Arctic Ocean for 2,6 million years. However, we may see it in our lifetime. The new IPCC report shows that the expanse of the Arctic ice cover has been quickly shrinking since the 70-ies, with 2012 being the year of the sea ice minimum," Jochen Knies.

He is marine geologist at the Geological Survey of Norway (NGU) and Centre for Arctic Gas Hydrate, Climate and Environment, UiT The Arctic Univeristy of Norway.

In an international collaborative project, Jochen Knies has studied the trend in the sea ice extent in the Arctic Ocean from 5.3 to 2.6 million years ago. That was the last time Earth experienced a long period with a climate that, on average, was warm before cold ice ages began to alternate with mild interglacials.

Fossils reveal past sea ice extent

"When we studied molecules from certain plant fossils preserved in sediments at the bottom of the ocean, we found that large expanses of the Arctic Ocean were free of sea ice until four million years ago," Knies tells us.

"Later, the sea ice gradually expanded from the very high Arctic before reaching, for the first time, what we now see as the boundary of the winter ice around 2.6 million years ago ," says Jochen Knies, who is also attached to CAGE, the Centre for Arctic Gas Hydrate, 

Environment and Climate at the University of Tromsø, the Arctic University of Norway.

Arctic Ocean likely to be completely free of sea ice

The research is of great interest on the international stage because present-day global warming is strongly tied to a shrinking ice cover in the Arctic Ocean. By the end of the present century, the Arctic Ocean seems likely to be completely free of sea ice, especially in summer.

This may have major significance for the entire planet 's climate system. Polar oceans , their temperature and salinity, are important drivers for world ocean circulation that distributes heat in the oceans. It also affects the heat distribution in the atmosphere. Trying to anticipate future changes in this finely tuned system, is a priority for climate researchers. For that they use climate modeling , which relies on good data.

"Our results can be used as a tool in climate modelling to show us what kind of climate we can expect at the turn of the next century. There is no doubt that this will be one of many tools the UN Climate Panel will make use of, too. The extent of the ice in the Arctic has always been very uncertain but, through this work, we show how the sea ice in the Arctic Ocean developed before all the land-based ice masses in the Northern Hemisphere were established," Jochen Knies explains.

Seabed samples from Spitsbergen

A deep well into the ocean floor northwest of Spitsbergen was the basis for this research. It was drilled as part of the International Ocean Drilling Programme, (IODP), to determine the age of the ocean-floor sediments in the area. Then, by analysing the sediments for chemical fossils made by certain microscopic plants that live in sea ice and the surrounding oceans, Knies and his co-workers were able to fingerprint the environmental conditions as they changed through time.

"One thing these layers of sediment enable us to do is to "read" when the sea ice reached that precise point," Jochen Knies tells us.

The scientists believe that the growth of sea ice until 2.6 million years ago was partly due to the considerable exhumation of the land masses in the circum-Arctic that occurred during this period. "Significant changes in altitudes above sea level in several parts of the Arctic, including Svalbard and Greenland, with build-up of ice on land, stimulated the distribution of the sea ice," Jochen Knies says.

"In addition, the opening of the Bering Strait between America and Russia and the closure of the Panama Cannel in central America at the same time resulted in a huge supply of fresh water to the Arctic, which also led to the formation of more sea ice in the Arctic Ocean," Jochen Knies adds.

All the large ice sheets in the Northern Hemisphere existed around 2.6 million years ago.

Scientists at Norwegian Geological Survey (NGU), CAGE, UiT The Arctic University of Norway,University of Plymouth, Universitat Autònoma de Barcelona, Stellenbosch University in South Africa and Institució Catalana de Recerca i Estudis Avançats in Barcelona have collaborated in this work.

Source:  University of Tromso (Universitetet i Tromsø - UiT)

Satellites measure increase of Sun's energy absorbed in the Arctic

The Arctic Ocean is absorbing more of the sun's energy in recent years as white, reflective sea ice melts and darker ocean waters are exposed. The increased darker surface area during the Arctic summer is responsible for a 5 percent increase in absorbed solar radiation since 2000.
Credit: NASA Goddard's Scientific Visualization Studio/Lori Perkins

NASA satellite instruments have observed a marked increase in solar radiation absorbed in the Arctic since the year 2000 -- a trend that aligns with the steady decrease in Arctic sea ice during the same period.

While sea ice is mostly white and reflects the sun's rays, ocean water is dark and absorbs the sun's energy at a higher rate. A decline in the region's albedo -- its reflectivity, in effect -- has been a key concern among scientists since the summer Arctic sea ice cover began shrinking in recent decades. As more of the sun's energy is absorbed by the climate system, it enhances ongoing warming in the region, which is more pronounced than anywhere else on the planet.

Since the year 2000, the rate of absorbed solar radiation in the Arctic in June, July and August has increased by five percent, said Norman Loeb, of NASA's Langley Research Center, Hampton, Virginia. The measurement is made by NASA's Clouds and the Earth's Radiant Energy System (CERES) instruments, which fly on multiple satellites.

While a five percent increase may not seem like much, consider that the rate globally has remained essentially flat during that same time. No other region on Earth shows a trend of potential long-term change.

When averaged over the entire Arctic Ocean, the increase in the rate of absorbed solar radiation is about 10 Watts per square meter. This is equivalent to an extra 10-watt light bulb shining continuously over every 10.76 square feet of Arctic Ocean for the entire summer.

Regionally, the increase is even greater, Loeb said. Areas such as the Beaufort Sea, which has experienced the some of the most pronounced decreases in sea-ice coverage, show a 50 watts per square meter increase in the rate of absorbed solar radiation.

"Advances in our understanding of Arctic climate change and the underlying processes that influence it will depend critically upon high quality observations like these from CERES," Loeb said.

As a region, the Arctic is showing more dramatic signs of climate change than any other spot on the planet. These include a warming of air temperatures at a rate two to three times greater than the rest of the planet and the loss of September sea ice extent at a rate of 13 percent per decade.

While these CERES measurements could ultimately become another of those signs of dramatic climate change, right now scientists say they have obtained the bare minimum of a data record needed to discern what's happening over the long term.

Getting data beyond 15 years will allow scientists to better assess if recent trend falls outside the realm of natural variability, said Jennifer Kay, an atmospheric scientist at the Cooperative Institute for Research and Environmental Science at the University of Colorado.

"We need long time series to detect climate change signals over the internal variability. For example, observed sea ice loss over the last 30 years cannot be explained by natural variability alone." Kay said. "Fifteen years is long, but climate is often defined as the average over 30 years -- so we are only half-way there with the CERES observations."

Kay and colleagues have also analyzed satellite observations of Arctic clouds during this same 15-year period. Kay's research shows summer cloud amounts and vertical structure are not being affected by summer sea ice loss. While surprising, the observations show that the bright sea ice surface is not automatically replaced by bright clouds. Indeed, sea ice loss, not clouds, explain the increases in absorbed solar radiation measured by CERES.

Increasing absorbed solar radiation is causing multiple changes in the sea ice cover, said Walt Meier, a sea ice scientist from NASA's Goddard Space Flight Center, Greenbelt, Maryland. Two of those changes include the timing of the beginning of the melt season each year and the loss of older, thicker sea ice.

The onset of the melt season in the high Arctic is now on average seven days earlier than it was in 1982, Meier said. Earlier melting can lead to increased solar radiation absorption. This is one step in a potential feedback cycle of warming leading to melting, melting leading to increased solar radiation absorption, and increased absorption leading to enhanced warming.

Since 2000, the Arctic has lost 1.4 million square kilometers (541,000 square miles) of older ice that is more than 3 meters thick, which during winter has essentially been replaced by ice that is less than 2 meters thick, according to data provided by Mark Tschudi at the University of Colorado. Once again, Meier said, this trend is a step in a feedback cycle.

"Having younger and thus thinner ice during winter makes the system more vulnerable to ice loss during the summer melt season," Meier said.

CERES instruments are currently flying on the Terra, Aqua and Suomi-NPP satellites. The Terra satellite launched Dec. 18, 1999, and CERES first started collecting Arctic data in 2000 so 2015 will mark 15 continuous years of CERES measurements over the Arctic.

The instruments include three radiometers -- one measuring solar radiation reflected by Earth (shortwave), one measuring thermal infrared radiation emitted by Earth (longwave), and one measuring all outgoing radiation, whether emitted or reflected.

Source:  NASA/Goddard Space Flight Center