Beneath the Surface

Fig.1. Permafrost thaw ponds in Northern Canada are formed when collapse of ground levels associated with permafrost occurs and creates depressions. Such land surfaces are called thermokarst. (Credit: Steve Jurvetson via Flickr, 2008)

Editors Note: This article is the first in a series that focuses on the International Year of Soils, a global effort that aims to increase the awareness of the importance of soil for food security and the environment. Future articles of ours will address the role soil plays in these areas and why soil repositories matter.

The frozen tundra of northern Alaska may not seem like a hotbed of life on Earth, but it is actually teeming with communities of microorganisms. These microbes currently live within the frozen soil, or permafrost, of Arctic regions and will soon play a very important role in environmental change. Increased temperatures have started to thaw permafrost soils, which cover 24% of the exposed land surface in the Northern Hemisphere. As the soil thaws, microbes metabolize ancient litter and animal remains trapped underground, releasing carbon dioxide and methane gas into the atmosphere. These greenhouse gases can accelerate climate change and contribute to the vicious cycle of warming and carbon release.

The latest estimate for stored carbon in permafrost is 1,700 gigatons of carbon -- double what is currently in the atmosphere -- but scientists agree that the total magnitude, timing, and mechanisms of carbon release are largely unknown. In order to understand the role of permafrost during climate change and how exactly carbon will be released, some researchers are scaling down and analyzing the genetics of the situation.

Bacteria Beneath Us

Janet Jansson, a scientist at the Pacific Northwest National Laboratory, and her colleagues recently published an article in the journal Nature, aiming to characterize microbial communities in permafrost. They compared cores of various Alaskan soils, from the frozen permafrost and the seasonally frozen active layer to thermokarst bog samples that represent a permanent state of thaw. Instead of remaining dormant in sub-zero temperatures, many microbes were actively producing methane. Permafrost species had proteins specifically for cold tolerance, as well as the ability to move through permafrost and easily adapt their nutrition needs. The active layer contained the most diverse makeup, while bog samples revealed many new species that are methane-producers. Although these results do not give the complete story of what microbes experience during a thaw, it supports the idea that increased temperatures mean more methane in the atmosphere.

Fig.2. Permafrost thawing in Gates of the Arctic National Park caused the bank of this lake to thaw and Okokmilaga River to cut through and drain to sea. (Credit: NPS via Flickr, 2014)

Caught in a Loop

As Jansson and her colleagues sought to understand the mechanisms of temperature change on a small scale, a slew of other studies questioned the timing and magnitude of the thaw. Robert Spencer, with Florida State University, and an international team of researchers reported in Geophysical Research Letters that thawing permafrost will catalyze an extremely rapid release of greenhouse gases. A separate study in Nature by NAU professor Ted Schuur and his colleagues suggested that a sudden release was unlikely, but the amount of carbon seeping into the atmosphere over the next century would still be around 130 to 160 gigatons. They also believe that further deep-core sampling and studying permafrost regions below the sea could increase the estimate of frozen carbon sources.

While there is plenty of worry about methane-producing microorganisms (methanogens), scientists are also interested in methanotrophs. These methane-munching microorganisms have been shown to offset methane production from the seabed and are important when considering permafrost activity. Such microbes might actually serve to take in some of the released greenhouse gases, which is useful in the Arctic where temperatures increase nearly twice as fast as the global average.

A Need for Soil Collections

Ultimately new climate change models must address permafrost soil thermodynamics and how the environment will forecast potential release. Unfortunately, there is a lack of data on subsea or even deeper terrestrial soils. More samples are needed to augment those cores in facilities like the National Lacustrine Core Repository in Minnesota and data records for groups like Canadian Geothermal Data Collection, which documents permafrost in Northern Canada. These collections are vital for research, such as that done by Jansson’s team, as well as for monitoring purposes. Such repositories may hold the key to mitigating climate change in Earth’s most vulnerable areas.



References:

Hultman, J., et al. (2015, May 14). Multi-omics of permafrost, active layer and thermokarst bog soil microbiomes. Nature, 521: 208-212. doi:10.1038/nature14238

Schuur, E. A. G., et al. (2015, April 09). Climate change and the permafrost carbon feedback. Nature, 520: 171-179. doi: 10.1038/nature14338

Spencer, R. G. M., et al. (2015, April 27). Detecting the signature of permafrost thaw in Arctic rivers. Geophysical Research Letters, 42 (8): 2830-2835. doi: 10.1002/2015GL063498

Glossary

permafrost
A subsurface layer of soil that has been frozen for at least two years. Most permafrost regions exist in the Arctic, Antarctic, and sub-Arctic zones, although some high-altitude locations exist.
greenhouse gases
Gases in Earth’s atmosphere which absorb and emit thermal radiation and can cause Earth’s surface temperature to increase. Such gases include carbon dioxide, methane, and ozone.
active layer
The top layer of soil in permafrost regions that thaws and refreezes each year.
thermokarst bog
A type of bog (wetland terrain dominated by peat accumulation) that exists in thermokarst regions in Arctic and sub-Arctic areas. Thermokarst is a land surface that is pitted due to thawing permafrost which can lead to the collapse of ground levels.
methanotroph
Microorganisms which are able to use methane as their only source of carbon and energy.