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A ship sailing along the coastline of Svalbard. Photo: Ekaterina Uryupova

Subsea permafrost (also offshore or submarine permafrost) is a frozen ground occurring beneath the coastal seas in the polar and subpolar regions. Compared to data on the terrestrial part, scientists have not yet collected that much information about subsea permafrost. It is generally accepted that the origin of subsea permafrost is linked to the past as it was formed on land during global cooling events known as Ice Ages and then it was subsequently flooded as sea level rose up. Recently, it has been shown that even now submarine groundwater seepage can preserve this ground ice frozen under the influence of cold currents in the subarctic areas such as the Labrador coast.¹⁾Normandeau A., Eamer J.B.R., Way R.G. et al. Evidence for subsea permafrost in subarctic Canada linked to submarine groundwater discharge. Nat. Geosci. (2024). https://doi.org/10.1038/s41561-024-01497-z This highlights the complex role of the subsea permafrost in the global system.

According to recent research models, the area of submarine permafrost is estimated as 2.5 million square kilometers today.²⁾Overduin P.P., Portnov A., Ruppel C.D. Arctic Report Card 2023. Permafrost beneath Arctic ocean margins. DOI: 10.25923/fzwe-6432. Retrieved on 20 October 2024 from https://arctic.noaa.gov/report-card/report-card-2023/permafrost-beneath-arctic-ocean-margins-2023/ Additionally, subsea permafrost carbon areas in the Arctic shelf zone are considered as one of the least studied characteristics of the sea floor.³⁾Miesner, F., Overduin, P.P., Grosse, G. et al. Subsea permafrost organic carbon stocks are large and of dominantly low reactivity. Scientific Reports 13, 9425 (2023). https://www.nature.com/articles/s41598-023-36471-z At the same time, scientists confirm that it might be a significant contributor in the global carbon cycle, especially under ongoing climate change. Do we know enough about the subsea permafrost to be able to project the impact of climate change on the Arctic region?

Actual knowledge gap

The global data systems on permafrost, which remain sporadic, rarely updated, and with lacking information about the submarine permafrost publicly available.⁴⁾Bouffard, T.J.; Uryupova, E.; Dodds, K.; Romanovsky, V.E.; Bennett, A.P.; Streletskiy, D. Scientific Cooperation: Supporting Circumpolar Permafrost Monitoring and Data Sharing. Land 2021, 10, 590. https://doi.org/10.3390/land10060590 Field and satellite-based observations of the sea bed still show insufficient knowledge about this characteristic of the Earth. In comparison to the extensive borehole network focused on terrestrial permafrost, subsea characteristics remain understudied and appear as a patchy data sampling. Some information on the submarine permafrost is stored in national databases which are sometimess not publicly open or limited to the scientific community.

In relation to the subsea permafrost, scientists agree about poor understanding of the global processes such as the carbon cycle.⁵⁾Schuur E.A.G., et al. (2022). Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic. Annual Review of Environments and Resources 2022. 47:343–71. https://doi.org/10.1146/annurev-environ-012220-011847 It is observed that the seabed slowly thaws and releases methane and carbon which can have significant impacts on climate, but how much organic material it contains and how fast the gasses may be released – this is still unknown.⁶⁾Sayedi S.et al, 2020. Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment. Environmental Research Letters, 2020; 15 (12): 124075 DOI: 10.1088/1748-9326/abcc29

Another challenge related to the subsea permafrost data collection is about extremely high expenses and technological obstacles which are still being explored in the areas – usually the combination of seismic methods with borehole geophysical records is used to observe the distribution of frozen underwater sediment. The most effective way to continue field observations would be possible through international cooperation, however, this option remains limited due to political confrontations between Arctic states.⁷⁾Uryupova E. (2022). Political tensions lead to “gaps” in scientific data in the Arctic region. Polar Journal, 10 September 2022. Retrieved on 20 October 2024 from https://polarjournal.ch/en/2022/09/10/political-tensions-lead-to-gaps-in-scientific-data-in-the-arctic-region/ There are only a few field studies which are focused specifically on the subsea permafrost. Latest changes, related to the suspended joint permafrost and carbon projects between Russia (the world’s longest Arctic coastline and overall area of 11 million square kilometers of frozen ground in total)⁸⁾UNESCO Courier (2022). Sergey Zimov: “Thawing permafrost is a direct threat to the climate”. Retrieved on 2 October 2024 from https://courier.unesco.org/en/articles/sergey-zimov-thawing-permafrost-direct-threat-climate and other countries, definitely contribute negatively to exchange of scientific information.⁹⁾Devyatkin P. (2024). Can Russian-US Scientific Cooperation Be Restored as Arctic Warming and the Ukraine War Intensify? The Nation, 16 April 2024. Retrieved on 1 September 2024 from https://www.thenation.com/article/world/russia-global-warming-science-diplomacy/ And due to a lack of research and uncertainties in this area, determining causes and rates of the release will remain unknown until better empirical and modeling estimates are available, and international scientific cooperation is restored.

Climate change impact

Submarine permafrost degradation is considered to be a part of the climate change process. As a result of the ongoing alterations impacting this characteristic, among others, a significant role is given to the coastal erosion and river heat discharge in the Arctic seas. For instance, satellite-based evaluations focused on the offshore areas of the Laptev Sea have detected high rates of resuspended sediments in the turbid zones, which becomes a new dynamic characteristic of the changing environment resulting in the submarine permafrost erosion.¹⁰⁾Osadchiev A., Adamovskaya P., Myslenkov S., Dudarev O., Semiletov I. Satellite-Based Evaluation of Submarine Permafrost Erosion at Shallow Offshore Areas in the Laptev Sea. Remote Sensing. 2023; 15(20):5065. https://doi.org/10.3390/rs15205065

Containing more organic carbon than its terrestrial counterpart, it is suggested that subsea permafrost might be a major dissolved organic matter source to the Arctic Ocean, which could potentially release extreme amounts of carbon in the water column.¹¹⁾Chen M., et al (2021). Subsea permafrost as a potential major source of dissolved organic matter to the East Siberian Arctic Shelf. Science of The Total Environment, Volume 777, 2021, 146100, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2021.146100 According to the scientific data, it is estimated that permafrost-associated gas hydrates may contain about 20 gigatons of carbon¹²⁾2.7 × 1013 kg CH4, one gigaton equals one billion metric tons, or one trillion kilograms in the form of intra-permafrost, sub-permafrost hydrates, and/or free gasses in the permafrost sediments.¹³⁾Angelopoulos M., Overduin PP., Miesner F., Grigoriev M.N., Vasiliev A.A. (2020). Recent advances in the study of Arctic submarine permafrost. Permafrost and Periglacial Processes, 31: 442–453. https://doi.org/10.1002/ppp.2061

Gas hydrates are predicted on the continental slopes of the Arctic seas such as the Laptev Sea, offshore area of Svalbard, and other areas.¹⁴⁾Bogoyavlensky V., Kishankov A., Kazanin A., Kazanin G. (2022). Distribution of permafrost and gas hydrates in relation to intensive gas emission in the central part of the Laptev Sea (Russian Arctic), Marine and Petroleum Geology, Volume 138, 2022, 105527, ISSN 0264-8172, https://doi.org/10.1016/j.marpetgeo.2022.105527 Permafrost cores from the sea bed of the Laptev Sea showed an annual thaw rate of 1.3 ± 0.6 kg OC m−2 in the area, which exceeds the thaw rates for terrestrial permafrost.¹⁵⁾Wild B., Shakhova N., Dudarev O. et al. Organic matter composition and greenhouse gas production of thawing subsea permafrost in the Laptev Sea. Nature Communications 13, 5057 (2022). https://doi.org/10.1038/s41467-022-32696-0 This makes scientists think that the “frozen seabed” may potentially play a more important role in the future of the Earth linked to climate.

In addition, scientists still do not have enough understanding of mechanisms of stability of different chemical elements stored in the permafrost, and how fast the elements can be released under the impact of climate change. Some of those elements have a potential hazard for human health, and among them, for instance, are mercury and arsenic stored in waterways in the Arctic. Scientific observations have shown that a significant amount of mercury and elevated dissolved arsenic are liberated from permafrost during bank erosion in the USA (Alaska)¹⁶⁾Smith M.I. et al. (2024). Mercury stocks in discontinuous permafrost and their mobilization by river migration in the Yukon River Basin Environ. Res. Lett. 19, 084041. DOI 10.1088/1748-9326/ad536e. Retrieved from https://iopscience.iop.org/article/10.1088/1748-9326/ad536e and Canada.¹⁷⁾Skierszkan E.K. et al. (2024) Arsenic Mobilization from Thawing Permafrost ACS Earth and Space Chemistry 2024 8 (4), 745-759. DOI: 10.1021/acsearthspacechem.3c00355. Retrieved from https://pubs.acs.org/doi/abs/10.1021/acsearthspacechem.3c00355 Compiled observation data from different field research expeditions suggests that subsea permafrost might be a significant source of tremendous amounts of chemicals to the Arctic Ocean and northern rivers.

Impact of drilling and seabed mining on subsea permafrost

The most intense human activity in the Arctic is recorded along shelves and subsea permafrost coasts, which are known as extremely dynamic areas. These locations are affected by offshore explorations and the exploitation of resources such as natural oil and gas. Mining and drilling is required to reach the most ancient organic carbon and methane hydrates which are stored in continental shelf deposits, particularly in the Arctic shelves, where they are sequestered beneath and within the subsea permafrost. Surely, the extraction of mineral resources from the seabed plays a very significant role in development of the Arctic region. However, only few studies are done to observe the industrial safety and impact of drilling activities on the subsea permafrost. Surely, oil and gas extraction are known as contributors of pollution in the ocean and atmosphere.¹⁸⁾Borshchevskaia E., Gorokhovskaya V., Khludova M., Mangutov E., Shapulenko A. (2022). Pollution in the Arctic: Oil and Gas Extraction on the Continental Shelf as a Major Contributor. The Arctic Institute, 28 June 2022. Retrieved on 1 October 2024 from https://www.thearcticinstitute.org/pollution-arctic-oil-gas-extraction-continental-shelf-major-contributor/ Also, scientists have found thawing underwater permafrost during the drilling operations due to the long-term thermal effect of wells on seabed, as well as physical destruction of the frozen layers.¹⁹⁾Dziublo A.D. et al. (2021). Ensuring industrial safety when drilling wells and developing oil and gas field infrastructure on the shelf of the Arctic and Subarctic seas. Minerals and mining engineering 8, DOI: 10.21440/0536-1028-2021-8-24-33. Retrieved on 1 October 2024 from https://www.mining-science.ru/download/2021/8/003.pdf This may also contribute to the increasing rates of released organic and inorganic chemical elements into the water and atmosphere.

Thawing subsea permafrost: challenges in the future

The current state of the subsea permafrost remains understudied, and understandings of the impact of climate change on this characteristic is limited. Moreover, data collection and exchange of information between scientists has become even more challenging under modern political confrontations and strategic decisions in the Arctic region. The impact of climate change and potential release of significant amounts of the organic/inorganic matter from thawing subsea permafrost is considered to be a major dilemma for the research community to understand the global role of the subsea permafrost. More work in this area is needed. Without international cooperation it would not be possible to create international databases and manage effective exchange of information in the framework of Arctic science diplomacy.