The Arctic is Collapsing
Article II: Explain “thermokarst” and one of the main consequences of Arctic warming.
The Arctic is both figuratively and literally collapsing. Melting of the permafrost does not always occur uniformly across the Arctic surface; local destabilisation of the soil can cause it to collapse in certain areas. This is referred to as a thermokarst failure. It occurs when a very ice-rich, constantly frozen soil is locally thawed. The ice melting causes the soil to collapse and form a hollow that is eventually filled with water from the melted ice in the surrounding permafrost. These thermokarst failures lead to the release of even more soil carbon because they allow the thawing to reach deeper into the ground.
Water originating from a thermokarst failure generally has a very high concentration of dissolved organic carbon. This is likely due to the fact that a thermokarst failure affects frozen soils at a depth much deeper than the active layer, which only reaches about twenty to forty centimetres below the surface (Cory, R. et al.). Thermokarst failures scar the Arctic landscape, leaving behind deep hollows where the ground has collapsed. In this article, we are only discussing the effects this will have on climate change, but this is also having detrimental effects on the whole Arctic ecosystem.
Sunlight amplifies the CO2 release from Arctic permafrost soil carbon.
The carbon that is stored in the Arctic is at risk of being released. It is yet not determined if this carbon will be released as carbon dioxide (CO2), released as methane (CH4), or remain in the water streams and end up in the oceans. All of these scenarios would make drastic changes to the environment. Let us look at the first scenario, how CO2 would be released from the thawing Arctic permafrost.
Climate change is thawing Arctic permafrost, and this allows for microbial respiration of previously frozen carbon. As a result, the loss of CO2 into the atmosphere is on the rise. Microbial conversion is the process that converts the carbon into a greenhouse gas. One study revealed that newly exposed dissolved carbon is over 40% more likely to undergo microbial conversion when exposed to UV light than when kept in the dark (Cory, R., et al.).
The carbon is exposed to light when the melt water enters a water stream at the surface. Once at the surface, microbes will be able to covert this dissolved carbon into CO2 and release it to the atmosphere. Unfortunately, that is not the only gas that could be released. Methane, a more powerful greenhouse gas, can also be released via a process called microbial decomposition, but that’s the topic for another article. For now, let’s turn our attention back to the release of CO2.
Thermokarst failures expose very deep Arctic mineral soil that generally has a very high carbon concentration. It is therefore not surprising that water draining from a thermokarst failure contain high levels of permafrost carbon. Previous studies have suggested that it is not the total amount of carbon in the water that controls its susceptibility to undergo a chemical alteration, therefore other factors must control how much of the dissolved carbon in the melt water that will be converted into CO2 (Cory, R. et al.).
Sunlight acts as the spark that lights the flame, figuratively. Sunlight initiates the breakdown of this carbon by bacteria in waters coming from thermokarst failures. After breakdown has begun, bacteria then convert this carbon into a greenhouse gas. This breakdown process was also studied in waters that were not from permafrost. It was discovered that in those waters, light only inhibited the bacterial production of carbon dioxide. Therefore, waters that have melted out of the permafrost are much more reactive, which means that a lot of the carbon in these waters is at risk of turning into a gas. On average, production of CO2 was increased by about 47% in thermokarst waters after exposure to light. Contrastingly, CO2 production was decreased by about 14% in non-thermokarst waters after exposure to light (Cory, R. et al.).
This is consistent with the theory that bacterial production is often times hindered by light exposure in naturally occurring Arctic waters. Water released from thermokarst failures is not considered to be naturally occurring because this increased thawing is a direct result of climate change. As predicted earlier, these differences had nothing to do with the total amount of dissolved organic carbon available to the bacteria in each type of water analysed (Cory, R. et al.).
We now know that sunlight affects how bacteria can convert the carbon into a gas. When the water has little to no prior light exposure, up to 90% of the dissolved organic carbon can be converted into CO2 (Cory, R., et al.). Since this carbon was kept in the dark soil for millennia and is now exposed to UV light, it is therefore extremely likely that most of it will be released into the air. The carbon that is not converted into CO2 will remain in the water stream and eventually be dumped into the ocean. This could eventually amplify our human induced on-going ocean acidification.
Sunlight is amplifying the conversion from dissolved carbon into carbon gases in the atmosphere and this means that the thawing of arctic permafrost could accelerate global warming. With the Arctic permafrost soils containing twice the amount of carbon that currently sits in the atmosphere, it is safe to say that the Arctic future is looking grim.
Cory, R., Crump, B., Dobkowski, J. and Kling, G. (2013). Surface exposure to sunlight stimulates CO2 release from permafrost soil carbon in the Arctic. Proceedings of the National Academy of Sciences, 110(9), pp.3429-3434.
Hannah is studying Applied Climatology Masters programme at Birmingham University, after having completed an undergraduate degree in Earth Sciences at the University of Michigan. Hannah is also the creator of the Instagram account @theclimatediaries.