IAP2-22-409

Constraining the conditions for greenhouse gas release from permafrost soils

Permafrost is the rock, sediment or soil that remains at or below 0oC for more than two consecutive years. The permafrost zone occupies 24% of the exposed land area in the Northern Hemisphere (Zhang et al., 2000). This high latitude region is warming twice as fast as the rest of Earth surface (Cohen et al., 2014) and amplified polar warming is thawing permafrost soils. These soils store a vast amount of organic carbon (OC) that has been locked away for thousands of years. Upon thaw, a portion of this carbon is released to the atmosphere as carbon dioxide (CO2) and methane (CH4), which threatens to further amplify Arctic warming – this is called the permafrost carbon feedback loop (Schuur et al., 2015). Permafrost thaw and carbon release is of major concern for climate change mitigation (Natali et al., 2021) as outlined in the Special Report of the Intergovernmental Panel on Climate Change report in 2019 (Pörtner et al., 2019).

Upon permafrost thaw, the form of greenhouse gas released (CO2 or CH4) from soils is dependent on their redox conditions. In dry, oxygenated soils (high O2), aerobic respiration occurs driving the release of OC as CO2. In wet, poorly oxygenated soils (low O2), anaerobic respiration can occur driving the release of OC as CH4, a more potent greenhouse gas than CO2. Across an O2 gradient lies a cascade of alternative electron acceptors (e.g. iron) that when in operation, prevent the release of CH4 to the atmosphere.

Identifying the redox conditions in permafrost soils, thus the form and amount of greenhouse gas released, is an area of significant ongoing research helping to understanding the effect global warming has on soil GHG emissions. In this project, the student will use natural abundance vanadium (V) isotopes, to understand the role that a changing water table depth has on greenhouse gas release from high latitude soils. V is a redox sensitive element, and we hypothesise that i) under oxic conditions above the soil water table, V occurs as the V(V) vanadate oxyanion. and ii) under poorly oxic conditions beneath the soil water table, V is a mixture of V(III) and V(IV) species. This change in V speciation as a result of a change in soil water table depth can be mapped using V isotopes (Prytulak et al., 2016). The student will combine V isotope data with long-term water table depth and greenhouse gas measurements to understand the role that water table depth plays on greenhouse gas emissions from permafrost soils. This project will involve fieldwork in the UK and Alaska.

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Image Captions

The Arctic tundra (Healy, Alaska. Photo Credit: C Hirst)

Methodology

To achieve the overarching aim, the project is constructed of the following stages:

Stage 1: Preliminary fieldwork will be carried out in high latitude, non-permafrost soils with contrasting long term-water table depths (Moor House, Upper Teesdale, UK) in order to calibrate V isotopes to changes in water table depth. At all locations, soil pore waters will be collected on a decimeter-scale resolution from soils above and below the water table. The CO2 and CH4 fluxes will be measured from the same site.

Stage 2: Fieldwork will be carried out at sites of minimal long-term water table fluctuation and extensive long-term water table fluctuation (Eight Mile Lake, Alaska) in permafrost soils. At all locations, soil pore waters will be collected on a decimeter-scale resolution from soils above and below the water table. The CO2 and CH4 fluxes will be measured from the same site.

Stage 3: V concentrations and V isotope compositions will be determined on the soil pore waters. δ51V compositions will be measured using multi-collector inductively coupled mass spectrometry (MC-ICPMS, Neptune®) at Durham University.

Stage 4: The V isotope data interpretation will be coupled with long term water table depth measurements and greenhouse gas measurements, alongside dissolved organic carbon (DOC) and major cation data on the soil pore waters.

Project Timeline

Year 1

Literature review, fieldwork preparation, field work to Moor House, UK; introduction to V isotope analysis

Year 2

V isotope analysis on UK soil pore waters, fieldwork preparation, field work to Eight Mile Lake, Alaska, conference in the UK

Year 3

V isotope analysis on Alaskan soil pore waters; international conference

Year 3.5

Manuscript and thesis writing, submission and examination

Training
& Skills

This project will provide a fantastic platform to gain multidisciplinary training, including in experiment development and isotope geochemistry. Dr Catherine Hirst will oversee the direction, development and progress of the project and will provide expertise in experiment design and isotope geochemistry. In addition, Dr Catherine Hirst will be a close mentor for the candidate’s career development. Dr Sabine Reinsch will provide valuable expertise on the effect of climate change on soil properties. Dr Julie Prytulak will provide expert knowledge on vanadium isotope systematics and measurements. Professor Fred Worrall will provide a wealth of knowledge on carbon processing in peatlands. Dr Geoff Nowell will provide important expertise on isotope geochemistry – the candidate will have tailored training on all instruments and become a proficient user of the multi collector-inductively coupled plasma mass spectrometer. Professor Sophie Opfergelt will provide key support regarding processes occurring in permafrost soils. The candidate will additionally have access to extensive IAPETUS2-cohort and NERC training workshops.

The candidate will join vibrant research communities at Durham University and Université Catholique de Louvain, where they will be welcomed and encouraged to network with colleagues and their collaborators. The candidate will have the opportunity to present their results to at least one research conference. Furthermore, they will be encouraged to disseminate their result to the general public at school and community events. Together, these interactions will provide the candidate with opportunities to learn and practice skills in dissemination, networking and different styles of research communication.

References & further reading

Cohen, J., Screen, J.A., Furtado, J.C., Barlow, M., Whittleston, D., Coumou, D., Francis, J., Dethloff, K., Entekhabi, D., Overland, J. and Jones, J., 2014. Recent Arctic amplification and extreme mid-latitude weather. Nature geoscience, 7(9), pp.627-637.

Zhang, T., Heginbottom, J.A., Barry, R.G. and Brown, J., 2000. Further statistics on the distribution of permafrost and ground ice in the Northern Hemisphere. Polar geography, 24(2), pp.126-131.

Pörtner, H.O., Roberts, D.C., Masson-Delmotte, V., Zhai, P., Tignor, M., Poloczanska, E. and Weyer, N.M., 2019. The ocean and cryosphere in a changing climate. IPCC Special Report on the Ocean and Cryosphere in a Changing Climate.

Lenton, T.M., 2012. Arctic climate tipping points. Ambio, 41(1), pp.10-22.

Schuur, E.A., McGuire, A.D., Schädel, C., Grosse, G., Harden, J.W., Hayes, D.J., Hugelius, G., Koven, C.D., Kuhry, P., Lawrence, D.M. and Natali, S.M., 2015. Climate change and the permafrost carbon feedback. Nature, 520(7546), pp.171-179.

Natali, S.M., Holdren, J.P., Rogers, B.M., Treharne, R., Duffy, P.B., Pomerance, R. and MacDonald, E., 2021. Permafrost carbon feedbacks threaten global climate goals. Proceedings of the National Academy of Sciences, 118(21), p.e2100163118.

Gustafsson, J.P., 2019. Vanadium geochemistry in the biogeosphere–speciation, solid-solution interactions, and ecotoxicity. Applied geochemistry, 102, pp.1-25.

Wu, F., Qi, Y., Yu, H., Tian, S., Hou, Z. and Huang, F., 2016. Vanadium isotope measurement by MC-ICP-MS. Chemical Geology, 421, pp.17-25.

Prytulak, J., Sossi, P.A., Halliday, A.N., Plank, T., Savage, P.S. and Woodhead, J.D., 2016. Stable vanadium isotopes as a redox proxy in magmatic systems. Geochemical Perspectives Letters.

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