IAP-25-044

Characterising methane productivity during the Late Holocene in Arctic Sweden

Arctic regions are warming up to four times faster than the global average. As temperatures rise, the Arctic is becoming greener, with expanding vegetation on land and increased productivity of macrophytes and algae in lakes and ponds. This enhanced productivity supplies more organic matter for decomposition, fuelling microbial activity and increasing methane production in lakes. Arctic lakes are therefore key hotspots for methane emissions, with potentially significant feedbacks to global climate.

This project will investigate both the modern and long-term sensitivity of methane cycling in Arctic lakes to environmental change. Focusing on sites in Arctic Sweden, it will (i) characterise the age and source of contemporary methane emissions and (ii) reconstruct centennial-scale records of methane production and consumption (methanogenesis and methanotrophy) during the late Holocene, a period of dynamic climate and land-use change. Naturally accumulating lake sediments will provide well-dated archives for reconstructing changes in lake productivity, microbial communities, climate, and anthropogenic activity and contemporary methane dated using novel methane collection and radiocarbon (14C) methods.

Shaped by student interests, the project combines geochemical and geochronological analyses with historical and contemporary records of land use, climate, and methane emissions to provide a unique, multi-scale perspective on methane cycling. This multi-proxy and interdisciplinary approach will provide critical insights into how Arctic lakes have responded to past environmental pressures, and what this means for future methane emissions in a rapidly changing Arctic.

The specific objectives of the PhD are to:
• Characterise the age and source of contemporary lake methane emissions using 14C analyses.
• Develop centennial-scale records of methane production across the late Holocene.
• Reconstruct climate and land use in the study region.
• Integrate modern and palaeo records to evaluate the long-term sensitivity of Arctic lake methane cycling to climate change and anthropogenic impact.

This project uses different complementary techniques to characterise lake productivity and reconstruct methane cycling. Some of these techniques are not commonly taught at undergraduate and/or masters level so the supervisory team will provide full training in all methods. We are looking for a student with interests in palaeoclimate and/or human-environment interactions, and who enjoys lab work.

The student will begin by working on existing sediment cores, ensuring a strong foundation for the project. Arctic fieldwork will be conducted to collect samples for dating contemporary methane emissions and, if desirable, to survey lake study sites, measure water-column physiochemistry, and recover additional sediment cores.

Contemporary methane emissions will be collected using newly developed point and time-integration sampling approaches and dated using 14C (Garnett and Dean, 2024). 14C measurements of aquatic methane are limited globally, therefore these data will be novel and potentially transformative for understanding lake methane cycling.

Core sediments will be analysed using lithostratigraphic techniques including loss-on-ignition (LOI), mineral magnetics, and XRF core scanning. Chronological control will be established using 210Pb dating for recent sediments and 14C dating for longer records.

Methane cycling will be reconstructed using lipid biomarkers sensitive to methanogenesis and methanotrophy, including hopanoids and glycerol dialkyl tetraethers (GDGTs) (Naeher et al., 2015; Davies et al., 2015).

Environmental conditions in the lake catchments will be reconstructed using leaf-wax lipid biomarkers (n-alkanes as records of vegetation inputs) and elemental geochemistry (e.g., XRF as erosional indicators). Precipitation reconstructions will be developed using compound-specific hydrogen isotopes (McClymont, Mackay et al., 2023). Depending on student interests and project development, additional lipid biomarker approaches could be applied, such as GDGT distributions to reconstruct past temperature. The project lends itself well to complementary palaeoecological analyses to reconstruct such as pollen, diatoms or sedaDNA to reconstruct changes in vegetation and aquatic productivity.

Year 1

– Review existing literature on methane production in lake systems, long-term environmental change, and methodological development.
– Subsample existing lake sediment cores.
– Start laboratory analysis on sediment cores, which will include sediment descriptions, physical properties analysis (elemental chemistry (XRF) and carbon analysis), sub-sampling the core for lipid biomarker analyses and conducting initial radiocarbon dating of the cores.
– Plan and conduct Arctic fieldwork (e.g., Sweden) to extract collect contemporary methane samples, with the option of collecting additional lake sediment cores.
– Complete first year progression paper to detail the project overview, research questions and methodology.

Year 2

– Continue and expand laboratory analysis, focusing on lipid biomarkers and 14C measurements.
– Attend national conference to share emerging results (e.g., British Organic Geochemistry Society or Quaternary Research Association).
– Begin writing of thesis and papers

Year 3

– Finalise laboratory work. Complete radiocarbon analysis and produce final core chronologies.
– Data analysis and interpretation.
– Present results at a national and international conference (e.g., International Union for Quaternary Research/International Paleolimnological Association/International Meeting of Organic Geochemistry).
– Continue writing of thesis and papers.

Year 3.5

– Complete thesis writing and submission

This project will develop cross-disciplinary, transferable skills in problem solving, project management, experimental design, data analysis and visualisation and report writing.

Specialist skills will be developed in:
• Laboratory analyses: training will be provided on sediment core logging, 14C and 210Pb dating, XRF scanning and lipid biomarker extraction, processing and analysis at Durham University state-of-the-art research laboratories. The analyses can be tailored to student’s interest (e.g., to include sedimentary ancient DNA/palaeoecology).
• Computational/statistical analyses: Training in computer programming in R for data visualisation and statistical analyses is provided at Durham and Nottingham Universities.
• Field techniques: training in methane sampling, lake surveying and coring with opportunities for Arctic fieldwork experience depending on student interest. The project success does not depend on fieldwork since cores are already available for analysis.

The candidate will also benefit from broad skills training provided in-house at Durham (e.g. science communication, thesis writing, writing for grants and publications, presentation skills) via the Geography Department and the award-winning Career and Research Development (CAROD) group. Furthermore, a broad range of cohort-based training in environmental science and science communication is provided within the IAPETUS2 Doctoral Training Partnership. Training requirements of the individual will be identified and met through the development of a personal training plan.

Regular participation in Durham’s Physical Geography weekly research group meetings and seminar series will further support the student’s development as an independent, well-connected researcher.