Response of pan-Arctic permafrost peatlands to rapid climate warming

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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.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.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. 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 model of permafrost peatland response to climate warming will be informed by the new palaeo-data sets and future climate-model predictions.