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

Lead Research Organisation: University of Sheffield
Department Name: Animal and Plant Sciences


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 degrees C 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. We propose a major, linked programme of plant and soil studies, atmospheric measurements, aircraft and satellite observations, and modelling, to improve our understanding of the response of the arctic terrestrial biosphere to climate change. Our overall aim is to determine what controls the temporal and spatial variability of carbon, water 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 in birch forest), 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, soil organic matter (SOM), landscape distribution of soils (via soil surveys, isotope labelled litter, bomb C dating to determine SOM age), CH4 emissions. WP3 Chamber measurements of C 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, and records of snow depth, soil moisture and climate. WP5 Aircraft measurements over the two study regions, recording CO2 and water exchanges and images of the land surface and profiles of CH4. 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 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.


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Description Objective: To quantify the differences in C uptake, respiration and allocation among key arctic vegetation types.
We tested the hypothesis that "Productive ecosystems in fertile sites (high available N) allocate relatively fewer resources to nutrient uptake, so fine root:foliage ratios are negatively correlated with LAI." Extensive sampling across multiple and contrasting vegetation types in two study regions (Abisko, Sweden and Kevo, Finland) have shown this hypothesis to be true, with root:shoot ratios declining with increasing LAI. Furthermore, root biomass, carbon and length increase linearly with LAI up to LAI = 1, with constant root biomass at LAI>1. Minirhizotron imaging approaches have also shown that root turnover rates increase linearly with LAI. These relationships occur irrespective of vegetation type allowing root biomass, C, length and turnover rates to be estimated from the single remotely sensed parameter of LAI. The relationships described above now allow root biomass, C, length and turnover data to be quantified from remotely sensed estimates of LAI, significantly facilitating estimates of these at landscape and regional scales across the pan-arctic and providing much needed data for model parameterization. Models need to be able to explain emergent ecosystem properties such as this, in order to provide increased confidence among model projections. A paper describing these emergent relationships has been submitted to Nature.
The partitioning of fixed C into biomass or autotrophic respiration is a critical determinant of ecosystem C balance, often assumed ~50% but rarely measured. 13C pulse-labelling in a range of moss communities provided a means to quantify the fate of fixed C. Measurements of 13CO2 gaseous return from Sphagnum confirmed the expected 50% partitioning over a period of ~14 days. But in Polytrichum, a more productive moss, autotrophic respiration was ~80% of fixed photosynthetic C. These results indicate very different patterns of C dynamics among moss species, with implications for total ecosystem budgets. We also undertook measurements of C exchange from these moss communities before and after snow melt. We found that Polytrichum communities were active under snow during the spring, while Sphagnum and vascular plants were inactive. We used models combined with phenology data to estimate annual gross primary production for mosses and vascular plants. While vascular plants had a higher overall capacity for C uptake, mosses had the greatest capacity during the shoulder seasons of thaw and freeze.
Outcome: new emergent ecosystem properties to test models and use for upscaling with earth observations; quantification of plant C stocks and turnover, and of moss vs vascular production over extended growing season.
Exploitation Route Improvements to models of Arctic vegetation response to global change.
Sectors Environment

Description To support public outreach activities, with exhibits at festivals and museums on Arctic vulnerability to climate change
First Year Of Impact 2007
Sector Education
Impact Types Societal