Wallenberg Academy Fellows

Thawing permafrost affects our climate

Large amounts of carbon are stored in the frozen ground in the earth’s Polar Regions. Rising temperatures allow the carbon to be released into the atmosphere in the form of greenhouse gases. Ellen Dorrepaal is examining how arctic ecosystems are affected by climate change and what the implications are for our future climate.

Ellen pushes a metal rod into the boggy ground. It goes in just over half a meter before it reaches the permafrost, the level at which the ground is frozen, summer and winter.

Changes in the permafrost, for example here at Abisko, 200 kilometers north of the Arctic Circle, have enormous implications for the global climate.

Carbon from decomposing dead plant tissues has accumulated in the soil in Polar Regions for a very long time, because the low temperatures slow down decomposition. But as the climate warms up, the frozen ground starts thawing. The huge quantities of carbon stored in the soil may then be released and leak into the atmosphere in the form of carbon dioxide and methane, two greenhouse gases. This would further accelerate the warming process. A feedback circle is created in which a warmer climate causes the soil to release more greenhouse gases, which make the climate even warmer.

Ellen’s research examines these processes. She was one of the first people to document how much carbon is released from thawing permafrost, findings that were published in Nature in 2009.

“We have shown that the thaw causes the release of carbon dioxide. Now we are examining the processes involved more closely. We want to see what happens to the ecosystem – plants, microbes and soil fauna – when the permafrost thaws, and how this affects the climate,” she says.

Cameras monitor plant roots

In a bog framed by the majestic Abisko Mountains in the far north of Sweden she presents some of her research team’s field experiments. At a number of sampling sites long, transparent tubes have been inserted in the ground. A camera in the tube enables the researchers to examine the roots of plants living in the soil above the permafrost, the “active layer”, which here is made up of peat.

Snow fences are used to simulate a warmer climate. These are put in position by researchers from Lund University. They catch the snow and create an insulating cover over the sampling sites. When the permafrost is thawed by the warmth, nutrients are released. These enable the plant roots to extend down towards the permafrost layer. The roots in turn give off carbon, which may increase the release of carbon dioxide from the soil into the atmosphere.

“The additional carbon from roots may have a great impact, but to date the role played by plants has not been much examined,” Ellen explains.

Back in the lab the researchers examine soil from the sampling sites. Among other things, they study how thawing affects micro-organisms and nutrients, and also how decomposition of carbon in the soil is affected by the input of new carbon.

The team includes researchers with expertise from different scientific disciplines. They are therefore able to study how the various parts of the ecosystem interact.

Mini-glasshouses used to monitor the tree line

The researchers have placed low glasshouses at selected sites on the mountain slopes around Abisko. They have no roof or floor, but within the walls the temperature is two or three degrees higher than outside. The glasshouses are being used in studies of how a warmer climate affects the tree line, where forest gives way to bare mountain.

“Earlier studies have shown that the tree line is migrating up mountainsides as the climate warms up. But this is not true everywhere. We try to explain this by examining the effect a warmer climate has on the vegetation in which young trees would establish,” Ellen says.

The glasshouses have been placed in areas covered with different types of moss, which is the predominant vegetation above the tree line. Inside the glasshouses birch and pine seedlings have been planted, whose growth is monitored by the researchers. They also study which characteristics of mosses affect how well the seedlings perform.

A long way from Amsterdam

Ellen’s interest in nature began when she grew up in the countryside outside Amsterdam. She studied biology at Utrecht University, spending some months at Abisko even then. As a PhD student and later a post-doctoral student at VU University Amsterdam, she carried out experiments there during the summers.

Ellen has lived year-round at Abisko since 2010. She is conducting her research at the Climate Impacts Research Centre at Umeå University. True, she is far from her family and friend in Amsterdam, but she is happy.

“Abisko is a very dynamic place, considering there are only 120 –150 inhabitants. People from around the world work at the research station and many young people are employed in the tourism sector. There is a welcoming atmosphere and it is easy to meet new people,” she says.

“For research purposes it is also important to live here all year round, not least given the impact of winter on nature – such as when the snow settles for the winter, how icy it is, or whether lemmings dig tunnels in it. These are important factors to bear in mind when interpreting our data. Many people who study how climate change impacts ecosystems pay too little attention to the winter,” Ellen comments.

“Being named a Wallenberg Academy Fellow means I can shape my research team more strategically. I can recruit researchers with expertise in various disciplines to integrate knowledge about different parts of the ecosystems and tackle the issues I want to examine.”

She is not bothered by the length and the darkness of the winters.

“We do a lot of skiing, which I like. And after all, in summer it is light around the clock!”

Text Sara Nilsson
Translation Maxwell Arding
Photo Magnus Bergström