Anthropogenic global warming threatens the stability of Siberian permafrost, with the potential to release vast amounts of greenhouse gases into the atmosphere, further exacerbating climate change.
This project aims to reconstruct historical temperatures, seasonal characteristics, and permafrost extent — thus establishing critical thresholds for permafrost thaw that can inform predictions of permafrost dynamics in near future.
What controls permafrost?
Permafrost formation is traditionally associated with cold glacial intervals. Degredation is associated with warmer interglacials. However, recent studies have suggested the formation of permafrost may be driven by more than just temperature. Seasonal characteristics such as the length of the frost period, snow depth, and summer rainfall may also play an important role. Continentality, the distance from oceanic heat and moisture sources, is known to have a strong influence on these characteristics. This raises the question of how shifting atmospheric teleconnections in response to anthropogenic climate change, such as reduced Arctic sea ice or shifted westerly winds, will influence permafrost formation and degradation in the future.
Understanding the complex interplay between these seasonal characteristics and permafrost stability is vital for informing predictions of permafrost thawing thresholds as the world warms over the coming decades and centuries. Thawing permafrost has been identified as a key climate tipping point with the potential to release vast quantities of carbon into the atmosphere, as well as having severe impacts for local communities by damaging infrastructure and threatening ecosystems.
Image: Sebastian Breitenbach
Clumped isotope temperatures
Clumped isotopes measurement of calcium carbonate offer a means to infer historical temperatures based on the isotopic configuration of the carbonate lattice. Clumped isotope measurements look at the degree to which ‘heavy’ isotopes, 18O and 13C, are bonded (or clumped) together within the carbonate lattice, with an increasing level of clumping occurring at lower temperatures.
Clumped isotope measurements offer a definitive means of deducing palaeotemperatures without knowledge of the isotopic composition of carbonate precipitation waters.
ISOPERM will conduct clumped isotope analysis on speleothems and ostracods.
Formation of speleothems relies on carbonate deposition from liquid water. Thus, speleothem formation only occurs during permafrost free periods. Formation periods can be precisely dated using U-series techniques, and multiannual mean temperatures deduced from clumped isotope measurements. Thus, it is possible to reconstruct temperature thresholds under which permafrost thaw has occurred in the past.
This project will rely on slowly precipitated subaqueous samples including cave pearls, cave pool rim crusts, and geodes, rather than stalagmites and cryogenic carbonates which have been shown to be sensitive to kinetic fractionation processes. High resolution stable isotope and trace element measurements will complement clumped isotope temperatures to give multi-proxy records of environmental changes.
Ostracod samples will be obtained from fossil permafrost deposits. Ostracods grow in polygonal pools, shallow pools that form in summer and can be found across vast stretched of northern Eurasia. Since these pools freeze in winter, ostracods can only grow in summer and hence their clumped isotope signature reflects summer temperatures.
Stable isotope measurements of relict ground ice will allow inferences of glacial and interglacial climate during phases of permafrost formation. Ground ice forms from freezing precipitation, forming predominantly in glacial episodes, however sporadic interglacial formation can also be found. Measurements will be made predominantly from two sources: ice wedges which form from meltwater entering thermal contraction cracks in spring and therefore preserve a record of cold season precipitation, and intra-sedimental ice which originates in soil moisture and preserves a record of summer precipitation. These two archives can be utilised to obtain records of historical seasonality.
Image: Thomas Opel
Key sites have been identified along a North-South transect in East Siberia from the Arctic Ocean to Lake Baikal, allowing us to map spatial extent of permafrost in response to changes in seasonality, continentality and hydrology.
Botovskaya Cave is the most southerly site, 58 km north-northeast of the town of Zhigalovo. It is the longest known cave system in Russia, stretching over 69km in a horizontal maze of thousands of passages criss-crossing long tectonic fissures. The site has been extensively studied, with multiannual ground monitoring data, and an existing repository of samples covering the last ~1.1 Ma. Today permafrost is largely absent from the Botovskaya Cave region. Rain and snowmelt seep into the cave causing extensive speleothem formation.
The Kirensk karst region, some 450 km northeast of Botovskaya is a largely unstudied region that has been identified as a fieldwork target due to its position on the boundary between continuous to non-continuous permafrost. The region is thought to be highly sensitive to future anthropogenic warming and could represent an important tipping point.
Mamontova Gora has been identified as a new study site for permafrost measurements. The site sits within the modern day continuous permafrost region and features extensive ice wedge formation.
Further relic permafrost samples will be analysed from northerly study sites at the Batagay Megaslump (pictured, with people for scale), a 1 km wide depression formed by thawing permafrost, as well as Bykovky Peninsula and the Dmitry Laptev Strait, which are both in close proximity to the Arctic Ocean.
Image: Thomas Opel