Permafrost catchments in transition: hydrological controls on carbon cycling and greenhouse gas budgets

The Arctic is undergoing rapid climatic change, with dramatic consequences for the 'Frozen World' (the 'cryosphere'), including reductions in the depth, extent and duration of sea ice, and seasonal snow cover on land, retreat of ice sheets/glaciers, and melting of permafrost ("ground that remains at or below 0 degrees C for at least two consecutive years"). This is important not only for local and regional ecosystems and human communities, but also for the functioning of the entire earth system. Evidence is growing that organic matter frozen in permafrost soils (often for many millennia) is now thawing, making it available for decomposition by soil organisms, with the release of carbon dioxide (CO2) and methane (CH4), both greenhouse gases (GHGs), as by-products. A major concern now is that, because permafrost soils contain 1672 petagrams (1 Pg = 1 billion tonnes) of organic carbon (C), which is about 50% of the total global below-ground pool of organic C, and permafrost underlies ~ 25% (23 million km2) of the N hemisphere land surface, a melting-induced release of GHGs to the atmosphere from permafrost soils could result in a major acceleration of global warming. This is called a 'positive biogeochemical feedback' on global change; in other words, an unintentional side-effect in the global C cycle and climate system.

Unfortunately, the interacting biological, chemical and physical controls on CO2 and CH4 emissions from permafrost (and melting permafrost) environments to the atmosphere are the subject of much speculation because the scientific community does not know enough about the interactions between C and water cycling in permafrost systems. Warmer and drier soils may release more CO2, while warmer/wetter soils might release more CH4. Permafrost thawing also causes changes in the way water flows though the landscape (because frozen ground if often impermeable to water), and some areas may become drier, while others wetter. How the relative proportions of CO2 and CH4 emissions change, and their absolute amount, is critical for the overall 'global warming potential' (GWP) because these two gases have different potency as GHGs. Release of C from soils into freshwaters also needs to be taken into account because down-stream 'de-gassing' and decomposition of organic materials also influences releases of CO2 and CH4 from freshwater, or delivery of C to lakes/oceans. All-in-all, predicting the GWP of permafrost regions is scientifically challenging, and the interactions between the water (hydrological) and C cycles are poorly known.

In this project we recognise the key role that hydrological processes play in landscape-scale C fluxes in arctic and boreal regions. In permafrost catchments in NW Canada (including areas where permafrost is known to be thawing) we will measure the capture of C from the atmosphere (through photosynthesis), its distribution in plants and soils, and the biological, physical and chemical controls of C transport and delivery from soils to freshwaters, and ultimately to the atmosphere as CO2 and CH4. In essence we wish to 'close the C cycle'. Field-based measurements of key processes in the water and C cycles, including geochemical tracer and state-of-the-art C, hydrogen and oxygen isotope approaches, will be linked by computer modelling. The project team, together with partners in Canada, the US and UK, is in a unique position to link the water and C cycles in permafrost environments, and we will deliver essential scientific knowledge on the potential consequences of climate warming, and permafrost thawing, for GHG emissions from northern high latitudes. Both for local peoples directly dependent on arctic tundra/boreal forest ecosystems for their livelihoods and cultural identity, and for the global community who must respond to, and anticipate, potential consequences of climate and environmental change, this project will represent a significant step forward in understanding/predictive capacity.

The proposed research will impact directly upon a range of key beneficiaries. We will use our existing contacts to contribute to the development of the stakeholder engagement strategy for the wider NERC Arctic Research Programme. Specifically, we aim to (1) enhance the profile of UK Arctic research through collaboration with the wider scientific/policy-maker communities in both the UK and Canada, (2) support outreach activities on the consequences of change to those dependent on the Arctic environment; in particular, economic and societal impact on the local and regional communities, and (3) promote a wider understanding of the local through to global implications of change in the northern latitudes within schools and the wider public through public engagement in science activities. Specific exemplars of beneficiaries we will actively target include: UK and Canadian government departments and their relevant agencies. The tangible benefits will be improved modelling, and hence more robust outputs and understanding, leading to stronger evidence-based policy decisions. In the UK these stakeholders will include the Met Office and Department for Energy and Climate Change. In Canada the principle beneficiary will be Environment Canada (EC), which is mandated to preserve the natural environment. Internationally the main route to dissemination to other governments is through IPCC and its scientific evidence base. For example, Co-I Smith and the Met Office Hadley Centre are developing the Joint UK Land Environment Simulator (JULES) model, for which the ECOSSE model (used in this project), forms the basis of the modelling of soil C, N and GHG fluxes.

The existing working relationship between Project Partners and the Met Office will ensure that new understanding generated by the project will be incorporated into these models, and provide evidence for further policy development. Key direct benefits, in terms of improvement in models and their parameterisation and development, will accrue over the timescale of the life of the proposed project and ca. 12-24 months following its completion (i.e. direct impacts of very high relevance on a short timescale). For example, the IPCC Fifth Assessment report, for which one of our team members (Smith) is a convening lead author, is currently being drafted and is due for completion in 2014. Work from this project will be of direct relevance to WGI, which addresses the physical science basis of climate change.

Key international beneficiaries (further raising the UK influence in the climate change arena) include Environment Canada and the United States Geological Survey (USGS). For example, we will work with the Great Rivers Observatory Project (USGS) to enhance understanding of circum-arctic and circum-boreal affects of permafrost thaw on terrestrial and aquatic systems. Furthermore, through our contacts with EC we have constructed key parts of our proposal to build on, and extend, EC research. Our project outputs will directly benefit EC, and other national (US, UK) institutions responsible for monitoring and predicting climate change and its effects (US National Centre for Atmospheric Research (NCAR), US National Oceanographic and Atmospheric Administration ( NOAA), UK Met Office).

Our public engagement will help improve awareness and concern for the Arctic and likely impacts of change. Better information to individuals in the general population plays a key role in determining future public policy decisions and outcomes. All the opportunities afforded by the wealth of interactions between the public and statutory bodies detailed above, plus with local communities, schools and colleges, will be a major training component for both the early career researchers (PDRAs) employed on the project, to help broaden and develop their career paths in science. For complete details see the full Pathways to Impact document attached.