Paleolimnological perspectives on the shifting geographic template of permafrost landscapes and its implications for Arctic freshwater biodiversity

Geographic context matters when trying to understand how permafrost thaw impacts northern freshwater biodiversity in a warming climate. Most risk to freshwater from thawing permafrost is associated with abrupt thaw processes known as thermokarst. Lake sediments can provide a record of thermokarst landscape development and associated biogeochemical and biodiversity trends over long timescales, providing a tool to link thermokarst geomorphology with freshwater biodiversity. We describe how paleolimnology, with its inherent emphasis on long-term perspectives, can characterize the shifting geographic template of warming thermokarst landscapes and its implications for biodiversity. We suggest aligning thermokarst lake paleolimnological research with hypothesis-testing frameworks used by permafrost hydrologists and biogeochemists and by the Freshwater Circumpolar Biodiversity Monitoring Program, and advocate for knowledge co-production with northern Indigenous communities. Lastly, we stress the importance of considering geographic context in the choice of study sites to ensure that diverse thermokarst landscapes are represented (especially those most vulnerable to warming) and that the fine-scale differences in limnological settings that influence ecosystem response to thermokarst stressors are accounted for.

7. The Arctic carbon vault

‘The Arctic carbon vault’ describes the large share of Earth's organic carbon sequestered in the frozen ground and within the shelf sea sediments of the Arctic Ocean. The organic carbon stock of the permafrost is roughly equivalent to half of total global soil carbon. A cold Arctic with extensive permafrost is an effective long-term carbon sink as carbon is safely locked away as long as permafrost is maintained. Giant craters appeared on the Yamal peninsula. The thawing permafrost leads to the formation of thermokarst lakes, which are frozen bodies of water held in subsidence depressions created by the thawing of ground ice. Well-preserved carcasses of extinct ice age beasts, including woolly mammoths and cave bears, have been recovered from the thawing permafrost.

Ice and Ivory: the cryopolitics of mammoth de-extinction

Woolly mammoth tusk hunting has become a black-market industry in the Siberian region of Yakutia, where thawing permafrost due to climate change is revealing the bodies of thousands of mammoths. They are often in a state of incredible preservation, and their accompanying tusks can be sold to China where they are carved into ornaments as a marker of status. Alongside tusk hunting, another potential industry has emerged: de-extinction. Many of the mammoths found on the tundra have potentially viable DNA that might be used to resurrect a mammoth through genetic technology. Mammoth de-extinction is a cryopolitical process – a focus on the preservation and production of life at a genetic level through cold storage. 'Cryobanks' have emerged as a way to safeguard endangered and extinct species' genetic material, and forms part of a turn towards pre-empting conservation crises during what some scholars are calling the 'sixth great extinction.' The mammoth's body is broken down into pieces – tusks form luxury commodity chains, whilst flesh and blood is parceled into frozen genes and cells. The mammoth in the freezer is indicative of a reorganization of cold life in a warming world, with the specific cryopolitics found in the cryobank an attempt at extending human control over planetary processes that are now seemingly out of control. Drawing on fieldwork undertaken at the Mammoth Museum in Yakutsk, Siberia, and at the Natural History Museum's cryobank in London, I follow the mammoth from permafrost, to freezer, to back outside, and consider how her de-extinction is a response to a particular sort of future crisis –that of our own extinction.

Sources, fate and distribution of inorganic contaminants in the Svalbard area, representative of a typical Arctic critical environment–a review

Global environmental changes not only contribute to the modification of global pollution transport pathways but can also alter contaminant fate within the Arctic. Recent reports underline the importance of secondary sources of pollution, e.g. melting glaciers, thawing permafrost or increased riverine run-off. This article reviews reports on the European Arctic–we concentrate on the Svalbard region–and environmental contamination by inorganic pollutants (heavy metals and artificial radionuclides), including their transport pathways, their fate in the Arctic environment and the concentrations of individual elements in the ecosystem. This review presents in detail the secondary contaminant sources and tries to identify knowledge gaps, as well as indicate needs for further research. Concentrations of heavy metals and radionuclides in Svalbard have been studied, in various environmental elements since the beginning of the twentieth century. In the last 5 years, the highest concentrations of Cd (13 mg kg−1) and As (28 mg kg−1) were recorded for organic-rich soils, while levels of Pb (99 mg kg−1), Hg (1 mg kg−1), Zn (496 mg kg−1) and Cu (688 mg kg−1) were recorded for marine sediments. Increased heavy metal concentrations were also recorded in some flora and fauna species. For radionuclides in the last 5 years, the highest concentrations of 137Cs (4500 Bq kg−1), 238Pu (2 Bq kg−1) and 239 + 240Pu (43 Bq kg−1) were recorded for cryoconites, and the highest concentration of 241Am (570 Bq kg−1) was recorded in surface sediments. However, no contamination of flora and fauna with radionuclides was observed.

Nutrient Inputs Stimulate Mercury Methylation by Syntrophs in a Subarctic Peatland

Climate change dramatically impacts Arctic and subarctic regions, inducing shifts in wetland nutrient regimes as a consequence of thawing permafrost. Altered hydrological regimes may drive changes in the dynamics of microbial mercury (Hg) methylation and bioavailability. Important knowledge gaps remain on the contribution of specific microbial groups to methylmercury (MeHg) production in wetlands of various trophic status. Here, we measured aqueous chemistry, potential methylation rates (kmeth), volatile fatty acid (VFA) dynamics in peat-soil incubations, and genetic potential for Hg methylation across a groundwater-driven nutrient gradient in an interior Alaskan fen. We tested the hypotheses that (1) nutrient inputs will result in increased methylation potentials, and (2) syntrophic interactions contribute to methylation in subarctic wetlands. We observed that concentrations of nutrients, total Hg, and MeHg, abundance of hgcA genes, and rates of methylation in peat incubations (kmeth) were highest near the groundwater input and declined downgradient. hgcA sequences near the input were closely related to those from sulfate-reducing bacteria (SRB), methanogens, and syntrophs. Hg methylation in peat incubations collected near the input source (FPF2) were impacted by the addition of sulfate and some metabolic inhibitors while those down-gradient (FPF5) were not. Sulfate amendment to FPF2 incubations had higher kmeth relative to unamended controls despite no effect on kmeth from addition of the sulfate reduction inhibitor molybdate. The addition of the methanogenic inhibitor BES (25 mM) led to the accumulation of VFAs, but unlike molybdate, it did not affect Hg methylation rates. Rather, the concurrent additions of BES and molybdate significantly decreased kmeth, suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in kmeth with combined addition of BES and molybdate, and accumulation of VFA in peat incubations containing BES, and a high abundance of syntroph-related hgcA sequences in peat metagenomes provide evidence for MeHg production by microorganisms growing in syntrophy. Collectively the results suggest that wetland nutrient regimes influence the activity of Hg methylating microorganisms and, consequently, Hg methylation rates. Our results provide key information about microbial Hg methylation and methylating communities under nutrient conditions that are expected to become more common as permafrost soils thaw.

The Changing Climate's Snowball Effect

Shrinking snowpack, thawing permafrost, and shifting precipitation patterns have widespread consequences. Can new technologies—and public policies—help communities adapt?