Arctic Research:

CYCLOPS: Carbon Cycle Linkages in Permafrost Systems (NERC Arctic thematic programme, 2012-2015).

Many of the key biological processes influencing the rates and biogeochemical

consequences of permafrost thaw are missing from coupled carbon-climate models, making predictions of the magnitude and sign of the permafrost feedback to climate in contrasting ecosystems highly uncertain. The overall aim of CYCLOPS is to develop, parameterise and evaluate a detailed process-based model of vegetation-soil-permafrost interactions using data collected through directed field campaigns in the discontinuous and sporadic permafrost zones of western Canada, and data available from Alaskan tundra in the continuous permafrost zone. The project brings together teams from the Universities of Sheffield, Edinburgh (Mat Williams, project lead), Exeter (Iain Hartley) and Sussex (Julian Murton) as well as Canadian and US partners. The University of Sheffield

component focusses on gaining better understanding of the relationships between plant communities (including their biodiversity and traits) and their ability to protect (insulate) permafrost and control active layer depth. We also aim to understand how these plant-permafrost interactions control ecosystem carbon balance, and how ecosystem carbon balance is modified by key changes in vegetation and active layer depth such as during post-fire succession or wetland development following permafrost thaw. We also play a key role in the provision of field data for modelling.

Lab member: Dr James Fisher (post-doctoral researcher)

NSINK: Sources, sinks and impacts of atmospheric nitrogen deposition in the Arctic (EU Marie Curie ITN, 2008-2012)

NSINK (http://nsinkproject.group.shef.ac.uk/NSINK/Home.html) is an EU funded consortium investigating the enrichment of Arctic terrestrial and aquatic ecosystems by reactive atmospheric nitrogen from low latitude emission centres. Our component has focussed on the impacts of acute atmospheric nitrogen deposition events on high arctic tundra. These events results from polluted air masses that originate in industrialised countries, and where the air mass travels to the high arctic with minimal dispersal. From these, extreme and acute nitrogen pollution events can result where up to 80% of the total annual nitrogen deposition may be deposited in just a few days (less than a week) rainfall. We have used field plot manipulation approaches to study the plant, soil and microbial responses to such extreme N deposition events as well as tracing the deposited pollutant N into the plant, soil, microbial and leachate pools to understand the fate of the pollutant. Our field work is based at Ny-Ålesund in Svalbard.

Lab members:

Sonal Choudhary, PhD student (now completed), Fate and impacts of extreme N deposition in high arctic tundra.

Dr Aimeric Blaud, PhD student (now completed), Responses of soil microbial communities of extreme N deposition events.

Extreme Winter Warming in the European sub-arctic (Leverhulme trust funded, 2007-2010)

Lab members:

Dr Stef Bokhorst (post-doctoral researcher, extreme winter warming)

Dr Catherine Preece (PhD, now completed, studying the impacts of ice encasement, hypoxia and high CO2)

ABACUS: Arctic atmosphere biosphere coupling at multiple scales (NERC funded 2006-2009)

As a result of global warming and increased frequency of climatic extremes, the Arctic is experiencing an increased frequency of extreme and sudden winter warming events in some regions. During these events, temperatures increase rapidly to well above freezing and may remain so for typically a week. Such warming events can result in near complete snow melt across whole landscapes exposing ecosystems to warm temperatures, and then the returning extreme cold. Consequences include extensive damage to plants which lose their freeze tolerance (winter hardening) during the warming event and are therefore damaged by the returning extreme cold. This can then impact on ecosystem structure (due to inter-specific differences in sensitivity between species) and reduced carbon sequestration by the ecosystem. It is also of interest that these events are damaging to shrubs, and so may act against the “greening” of the Arctic that is resulting from increased shrub cover due to summer warming. Other concerns include the impacts of ice encasement, where snow only partially melts and the re-freezes around the plant canopy, leading to hypoxic and high CO₂ conditions). This work (funded by the Leverhulme Trust UK, and the NERC UK, and including support from Norwegian collaborators) uses a combination of unique field simulation studies (of extreme winter warming, ice encasement and hypoxia/high CO₂) to determine the impacts of extreme winter warming and ice enhancement on sub-Arctic heathland.

ABACUS (http://www.geos.ed.ac.uk/abacus) is a UK consortium (lead by Mat Williams, University of Edinburgh) that was formed to improve understanding of the controls on carbon, water and energy exchange between arctic terrestrial ecosystems and the atmosphere. Research was undertaken as a linked programme of plant and soil process studies, isotope analyses, flux measurements, micro-meteorology, process modelling, and aircraft and satellite observations designed to improve predictions of the response of the arctic terrestrial biosphere to global change. The University of Sheffield lead the plant-scale work package, that sort to understand plant community controls on ecosystem carbon budgets, including seasonal dynamics of fluxes linked to phenology, spatial distribution of vegetation in heterogeneous arctic landscapes, the importance of transition zones between vegetation types, and consequences for landscape carbon budgets, as well as how leaf and root processes drive vegetation and ecosystem carbon cycling, and the links between above and below ground carbon stocks.

Lab members:

Dr Ben Fletcher (post-doctoral researcher)

Victoria Sloan (PhD student, now completed)

MULTIARC: Multi-scale approaches to understanding carbon dynamics in Arctic and upland systems (2006-2010)

MultiArc (http://aps.group.shef.ac.uk/multiarc/index.html) was a EU funded Marie Curie ITN with the overarching objective to

understand the plant, soil and freshwater driven processes that define carbon dynamics at the plot and ecosystem scale and to understand how these processes scale up to drive the catchment-scale carbon dynamics. It trained 6 PhD students in a partnership on the University of Sheffield (UK), Vrije Universiteit Amsterdam (The Netherlands) and the Abisko Scientific Research Station (Sweden). Its key objectives were to (a) quantify carbon fluxes in catchments representing different stages of development from systems of low carbon storage to those with significant carbon pools; (b) compare these carbon dynamics along multiple transitions (glacial - non-glacial / alpine - sub-alpine / sub-Arctic); (c) understand how “up-stream” components of carbon cycling (e.g. plant traits, microbial functioning, soil processes) drive downstream changes in the organic and inorganic carbon dynamics of catchments; (d) provide a much needed understanding of their sensitivity to future environmental perturbations. The University of Sheffield's work focussed on the controls and changes in vegetation and freshwater carbon dynamics both spatially along a sub-arctic catchment (from birch forest a low altitude to alpine tundra at high altitude), and temporally throughout the year and annual water cycle.

Lab members:

Eva Koller (PhD student, now completed)

Nils Ohlanders (PhD student, now completed)