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Arctic Biosphere Atmosphere Coupling at Multiple Scales

A research consortium linking the Universities of Edinburgh, Durham, Stirling, Sheffield, York, and UCL, CEH and the Macaulay Institute.

The ABACUS consortium is funded by NERC, and is part of IPY, the International Polar Year, the largest international polar science project ever conducted.

How vulnerable are Arctic carbon stores to global warming?

How will changes in Arctic regions affect the rest of the planet?

Our objective is to improve understanding of the controls on carbon, water and energy exchange between arctic terrestrial ecosystems and the atmosphere. ABACUS is 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.

Climate warming is resulting from disruption of the global C cycle (JSA, 2005). The Arctic is already warming significantly, and warming is expected to be fastest and greatest at high latitudes, 4-7ºC over the next century (ACIA, 2004). However, complex linkages between climate, C cycle, energy balance, and hydrology mean that the details of such changes and the response of arctic ecosystems remain poorly understood (Oechel et al, 2000). The Arctic governs some critical feedbacks in global change: (i) the release by warming of considerable but poorly quantified C stores from high latitude soils (20-60% of the global soil C pool, (Hobbie et al., 2000)) could accelerate the build-up of atmospheric CO2, (ii) a shift in albedo from vegetation changes and altered snow dynamics may affect the global energy balance (Betts, 1997), (iii) alterations in river discharge into the Arctic Ocean, due to changes in arctic hydrology, may affect the thermohaline circulation (Peterson et al., 2002). Our proposed research will resolve critical unknowns related to these potential feedbacks in the arctic C, energy and water cycles.

To improve our understanding of the C, water and energy cycles, we will:

• quantify the turnover of soil organic matter (SOM), particularly of contrasting age;
• quantify the differences in C uptake, respiration and allocation among key arctic vegetation types and their responses to drivers: snow, soil temperature (and freezing) and soil moisture);
• test whether regional estimates of the C cycle derived from atmospheric sampling by aircraft are consistent with upscaled measurements from the land surface;
• determine regional budgets of net CH4 emissions and their repose to the hydrological drivers;
• generate improved estimates of the total C stocks of arctic systems in soils and vegetation, with a detailed estimate of errors;
• investigate the strength of coupling between land-atmosphere energy exchanges and local snow cover and soil moisture;
• test the accuracy of snow melt, soil moisture and thaw predictions; and determine how to better represent sub-grid scale hydrological processes in regional and global climate models;
• determine how the interactions of topography with seasonal changes in hydrology govern the strength of C sources and sinks over the arctic landscape.

Our approach is based on linking multi-scale measurements with models representing our best current understanding. We will determine C, water and energy fluxes at a range of scales using small chambers, eddy flux towers, and aircraft. We will monitor C allocation and turnover in vegetation and soils using direct sampling, but also isotopic analyses and labelling experiments. We will determine landscape patterns of vegetation C, soil C and moisture, and snow-cover with a mix of field surveys, aircraft and satellite imagery. We will use a mix of simple empirical models, ecophysiological models, C turnover models and a land surface scheme from a climate model. Our multi-scale measurements, extensive surveys and process investigations will help to determine the errors in current model characterisations of the behaviour and state of the Arctic, which are reliant on relatively coarse resolution data on soils and vegetation, and simple descriptions of key processes. Close integration of models with data from the start of the consortium will allow us to modify the fieldwork in the light of identified model-data inconsistencies. We will also attempt some innovative experiments, for instance using aircraft to sample the atmosphere for determination of ¹⁴C content, a key indicator of soil C turnover.

The project addresses several key themes identified for the NERC Arctic IPY science plan: (1) It will quantify the present state of the arctic environment, particularly soil C and vegetation cover via surveys and remote sensing. (2) It will improve understanding of coupled processes involving the arctic system by studying land-atmosphere exchanges of CO2, water and energy, and processes affecting C cycling. (3) Through a focus on SOM age and turnover rates our study will contribute towards improved understanding of past and present arctic change. (4) We will upgrade predictions of the future state of the Arctic, by improving the modelling of critical processes in global climate and vegetation models. This proposal thus links strongly to IPY themes 1, 2, 3 and 4.

For more information contact Mat Williams (mat.williams@ed.ac.uk; +44 131 650 7776) or Stephan Matthiesen (stephan.matthiesen@ed.ac.uk).