Arctic Biosphere-Atmosphere Coupling across multiple Scales (ABACUS).

Climate warming is resulting from disruption of the global carbon cycle. The Arctic is already warming significantly, and warming is expected to be fastest and greatest at high latitudes, 4-7 degreesC over the next century. However, there are complex links among climate, the carbon cycle and the global energy balance which mean that the details of such global changes remain poorly understood. The Arctic also has the potential to speed up or slow down climate change: (i) the release by warming of considerable C stores held in arctic soils may accelerate the build-up of greenhouse gases, (ii) an increase in tree-cover may alter the reflection of sunlight to space and thus affect the global energy balance, (iii) alterations in river discharge into the arctic ocean may impact on the ocean circulation and thus the climate of western and northern Europe. Currently, there are major unknowns that mean predictions of the future arctic system remain highly uncertain. The key uncertainties relate to (i) the dynamics of soil organic matter (SOM), which is a large store of C, (ii) the patchiness of the arctic landscape, (iii) the allocation and turnover of carbon in arctic vegetation, (iv) the interactions between topography, vegetation and soils, (v) the links between plant growth and soil conditions, and (vi) the importance of spring and autumn in controlling plant and soil activity. We propose a major, linked programme of plant and soil studies, atmospheric measurements, aircraft and satellite observations, and modelling, to tackle the uncertainties in the response of the arctic terrestrial biosphere to global change. The overall question is 'what controls the interannual and spatial variability of carbon and energy exchange between arctic ecosystems and the atmosphere?' Our field sites are based at Abisko, Sweden (with one focus area in dry tundra, the other just below the tree-line nearby), and Kevo, Finland (with one focus on wet tundra, the other on dry tundra). At Kevo and Abisko both satellite imagery and aircraft flights will encompass an area of 10 km x 10 km, including both focus areas. The project has eight work-packages: WP1 Studies on plant allocation and phenology, and respiration-production ratios for major community types (via harvests, root measurement and isotope tracer experiments). WP2 Turnover of litter, SOM, landscape distribution of soils (via soil surveys, isotope labelled litter, bomb C dating to determine SOM age). WP3 Chamber measurements of CO2 and water exchanges from soils and vegetation at fine scales (a resolution of ~1m). WP4 Continuous tower measurements of CO2 and water exchange between the soils/vegetation and the atmosphere at scales of ~100 m. WP5 Aircraft measurements over the two study regions, recording CO2 and water exchanges and images of the land surface. These measurements will extend over areas of many km squared. WP6 Earth Observation via satellites. We will link observations from several satellite instruments to measurements of plant cover recorded in associated field campaigns. WP7 We use models to connect the information connected at different time and space scales. The models represent our best understanding of the system, and we check and improve our understanding against independent observations, whether from chambers, towers, aircraft or satellites. We test whether we can understand the data from satellites and aircraft in terms of the detail recorded at the chambers and towers and with the WP1 and WP2 experiments. WP8 We will run an international workshop to share our ideas with colleagues from around the world. We will train post-graduates with a summer-school based around field measurement, and provide undergraduates with summer field experience.