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Global vulnerability of permafrost peatlands to rapid climate warming

Dr Graeme Swindles (SOG), Dr Paul Morris (SoG), Professor Andy Baird (SoG), Dr Jennifer Galloway (Geological Survey of Canada)

Project partner(s): Geological Survey of Canada (Potential CASE)

Contact email: g.t.swindles@leeds.ac.uk

Despite their relatively small global areal extent (3% of the earth’s land surface), peatlands are disproportionately important to the future of global-scale ecosystem-climate feedbacks. Organic-rich permafrost peat stores approximately 277 Pg of carbon (C), equivalent to 14 % of the global soil C store (Tarnocai et al., 2009). Until recently this huge soil C store has been rendered effectively inert, protected from decomposition by lethargic microbial activity in frozen soil conditions. However, twenty-first century climatic warming is projected to be greatest in high-latitude areas of the Northern Hemisphere, where the majority of permafrost peatlands occur (Christensen et al., 2013).  Widespread permafrost thaw exposes this C store to rapid rates of decay which leads to increased emissions of greenhouse gases to the atmosphere and further global warming (Hartmann et al., 2013). However, recent research indicates that this global warming effect may be partially compensated by increased C sequestration through newly invigorated ecosystem productivity and peat accumulation under warmer conditions (Swindles et al., 2015a). The project aims to evaluate whether this compensation mechanism is occurring in permafrost peatlands at a hemispheric scale and whether it has the potential to impact on future climate.

Zones of permafrost have retreated rapidly poleward in recent decades, evidenced by the widespread development of degradation features such as thaw lakes (Jorgenson and Osterkamp, 2005), increased active layer thickness (Åkerman and Johansson, 2008) and in some locations the complete disappearance of permafrost (Sollid and Sørbel, 1998; Johansson et al., 2006). Timescales of field monitoring campaigns (greenhouse gas flux rates, water-table and temperature measurements) are limited to the last two to three decades and in spatial scale, and thus provide only a partial record of the response of permafrost peatlands to recent warming. Palaeoecological approaches can provide important baseline information over much longer timescales, necessary for a fuller understanding of the fate of degrading permafrost peatlands. A dearth of palaeoecological studies into the response of permafrost peatlands to climatic change during the instrumental period (the last 100-150 years) leaves the future of degrading permafrost peatlands, and their likely feedbacks to the global climate system, highly unclear.

Swindles et al. (2015a) used a novel high-resolution palaeoecological approach to understand changes in three permafrost peatlands (Abisko region, Arctic Sweden) over the last ~200 years. The region experienced rapid warming during the twentieth century (Callaghan et al., 2010); mean annual air temperature exceeded the 0°C threshold around AD 2000, pushing the area beyond the climatic threshold at which permafrost can be sustained. As predicted, a drying trend was identified in the three Swedish peatland sites until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes.  Based on these data, Swindles et al. proposed a five-phase model for permafrost peatland response to climatic warming that showed a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. This final stage has the potential for enhanced carbon sequestration through newly invigorated productivity and rapid peat accumulation. The findings indicate that the buffering capacity of permafrost peatlands to future climate change may be greater than previously thought and are in contrast to the paradigm that catastrophic loss of peatland C stock, and subsequent accelerated climate warming under future climate change is the only trajectory.

Figure 1: Peat plateau collapsing and becoming fen: evidence of permafrost degradation from Stordalen mire, Abisko, Northern Sweden.

Objectives

Will carbon release from permafrost peatlands at high latitudes lead to the much discussed “carbon bomb” and further warming of climate through positive feedback mechanisms? Or, alternatively, will the peatlands act as climate buffers through invigorated carbon sequestration driven by increased productivity under a warmer climate and/or suppressed decomposition in newly saturated conditions from thawing permafrost? These are pressing questions with important global implications for the future of climate-biosphere interactions.

The objective of this project is to test a five-phase model of permafrost peatland degradation from Swindles et al. (2015a) at a hemispheric scale. Currently, our model is based on a small number of peatlands in subarctic Sweden. However, the majority (by area) of permafrost peatlands occur in the continental regions of Canada and Siberia. To assess potential feedbacks from permafrost peatlands on a hemispheric scale a broader range of permafrost peatlands must be subject to rigorous palaeoenvironmental investigation. We will focus on regions characterised by recent rapid climate warming using the high-resolution multi-proxy palaeoecological approach developed in Swindles et al. (2015a). We will test the following key hypotheses: permafrost peatlands have undergone a (i) rapid shift in hydrology to wetter conditions and; (ii) increased carbon accumulation during the twentieth century in response to rapid climate warming.

Figure 2: A permafrost peatland losing carbon. Desiccation and cracking of a peatland’s surface near Toolik, Alaska, USA.

We have identified a number of key regions characterised by rapid climate warming that contain a significant area of permafrost peatland, including: Arctic Canada, Alaska, Russia and Sweden (Figures 1 and 2).  In the laboratory we will carry out bulk density and loss-on-ignition analyses following standard methods (Chambers et al., 2011). Carbon accumulation will be calculated following Tolonen and Turunen (1996). We will analyse for testate amoebae in cores from each location and apply statistical transfer functions to develop a water-table depth reconstruction (Swindles et al., 2015b). We will develop an accurate, precise chronology for each core using 210Pb, AMS radiocarbon, spheroidal carbonaceous particles and tephrochronology. We will compile available data on active layer thickness and instrumental climate data to compare with the peat-based data. In addition, we will use freely-available remote-sensed images to investigate whether there has been changing wetness (e.g. increase in open water areas) in the study sites over the last few decades. A new conceptual model of permafrost peatland response to climate warming will be informed by the new palaeo-data sets and future climate-model predictions.

Potential for high impact outcome

Climate change and planet earth’s changing carbon cycle are two of the most pressing issues facing society. We are in a unique position at Leeds to answer important unresolved questions about the dynamics of peatlands under a changing climate. The research topic has immediate policy-relevant findings, and we therefore anticipate the project generating several papers with at least one being suitable for submission to a high impact journal.

Training

The student will work under the supervision of Drs Swindles, Morris and Baird within the River Basins and Processes and Ecology and Global Change research groups.  Students will be trained in a variety of laboratory techniques as well as receiving training in field-based methods. Training in statistical analysis and modelling can be provided in-house. The successful PhD student will have access to a broad spectrum of training provided by the Faculty that include an extensive range of training workshops in numerical analysis, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). Supervision will involve regular meetings between all supervisors and the CASE partner.

Student profile

Applicants should have an undergraduate degree in physical geography, environmental science, earth science, geology, biology or ecology. The minimum requirement for entry is a good upper second class degree. Candidates with first class degrees and masters qualifications in relevant subjects are particularly encouraged to apply. A background in palaeoecology, Quaternary science or environmental change studies would be highly advantageous. Some understanding of statistics or modelling would also be an advantage (although not essential). A strong interest in global environmental problems and a willingness to travel to high-latitude environments is essential. Informal enquires should be directed to Graeme Swindles g.t.swindles@leeds.ac.uk

CASE Partner

The proposal has been agreed as a “Partnership Project” (a potential CASE project), with the Geological Survey of Canada providing extra funding additional to the NERC student stipend. The project aligns with an existing collaboration between Leeds and the Geological Survey of Canada to understand environmental change at high latitudes. The project includes a visit to the CASE partner in Canada.

References

Åkerman, H. J., Johansson, M. Thawing permafrost and thicker active layers in sub-arctic Sweden. Permafr. Periglac. Process. 19, 279–292 (2008).

Callaghan, T. V., Bergholm, F., Christensen, T. R., Jonasson, C., Kokfelt, U., Johansson, M. A new climate era in the sub-Arctic: Accelerating climate changes and multiple impacts. Geophys. Res. Lett. 37 (2010).

Chambers, F. M., Beilman, D. W., Yu, Z. Methods for determining peat humification and for quantifying peat bulk density , organic matter and carbon content for palaeostudies of climate and peatland carbon dynamics. Mires Peat 7, 1–10 (2011).

Christensen, J. H. et al. Climate Phenomena and their Relevance for Future Regional Climate Change in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to IPCC AR5, 1–6, 1217–1308, doi: 10.1017/CBO9781107415324 (2013).

Hartmann, D. L., Tank, a. M. G. K., Rusticucci, M. IPCC Fifth Assessment Report, Climate Change 2013: The Physical Science Basis. IPCC AR5, 31–39 (2013).

Johansson, M., Christensen, T. R., Akerman, H. J., Callaghan, T. V. What determines the current presence or absence of permafrost in the Torneträsk region, a sub-arctic landscape in northern Sweden? Ambio 35, 190–197 (2006)

Jorgenson, M. T., Osterkamp, T. E. Response of boreal ecosystems to varying modes of permafrost degradation. Canadian J. of Forest Res. 35, 2100–2111 (2005).

Sollid, J. L., Sørbel, L. Palsa bogs as a climate indicator: examples from Dovrefjell, southern Norway. Ambio 27, 287–291 (1998).

Swindles, G. T., Morris, P. J., Mullan, D., Watson, E. J., Turner, T. E., Roland, T. P., Amesbury, M. J., Kokfelt, U., Schoning, K., Pratte, S., Gallego-Sala, A., Charman, D. J., Sanderson, N., Garneau, M., Carrivick, J. L., Woulds, C., Holden, J., Parry, L., Galloway, J. M. The long-term fate of permafrost peatlands under rapid climate warming. Sci.Rep. 5, 17951 (2015a).

Swindles, G. T., Amesbury, M. J., Turner, T. E., Carrivick, J. L., Woulds, C., Raby, C., Mullan D., Roland, T. P., Galloway, J. M., Parry, L., Kokfelt, U., Garneau, M., Charman, D. J., Holden, J. Evaluating the use of testate amoebae for palaeohydrological reconstruction in permafrost peatlands. Palaeogeog., Palaeoclim., Palaeoecol . 424, 111-122 (2015b). 

Tarnocai, C., Canadell, J. G., Schuur, E. A. G., Kuhry, P., Mazhitova, G., Zimov, S. Soil organic carbon pools in the northern circumpolar permafrost region. Global Biogeochem.Cy. 23 (2009).

Tolonen, K., Turunen, J. Accumulation rates of carbon in mires in Finland and implications for climate change. The Holocene 6, 171–178 (1996).

Related undergraduate subjects:

  • Biology
  • Earth science
  • Ecology
  • Environmental science
  • Geology
  • Physical geography