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

气候变暖是全球碳循环中断的结果。北极已经在显著变暖，预计高纬度地区的变暖速度最快、幅度最大，下个世纪将上升4-7摄氏度。然而，气候、碳循环和全球能源平衡之间存在着复杂的联系，这意味着人们对这种全球变化的细节仍然知之甚少。北极也有可能加速或减缓气候变化：(1)北极土壤中大量碳储量的变暖释放可能加速温室气体的积累；(2)树木覆盖的增加可能改变太阳光对空间的反射，从而影响全球能量平衡；(3)流入北冰洋的河流流量的变化可能影响海洋环流，从而影响西欧和北欧的气候。目前，主要的未知因素意味着对未来北极系统的预测仍然高度不确定。关键的不确定性涉及(i)土壤有机质（SOM）的动态，这是大量碳的储存，（ii）北极景观的斑块性，（iii）北极植被中碳的分配和周转，（iv）地形、植被和土壤之间的相互作用，(v)植物生长与土壤条件之间的联系，以及（vi）春季和秋季在控制植物和土壤活动方面的重要性。我们提出了一个主要的、相互关联的项目，包括植物和土壤研究、大气测量、飞机和卫星观测以及建模，以解决北极陆地生物圈对全球变化响应的不确定性。总的问题是“是什么控制了北极生态系统与大气之间碳和能量交换的年际和空间变异性？”我们的实地站点位于瑞典阿比斯库（一个重点区域在干冻土带，另一个在树线附近）和芬兰凯沃（一个重点在湿冻土带，另一个在干冻土带）。在凯沃和阿比斯库，卫星图像和飞机飞行将覆盖10公里× 10公里的区域，包括两个重点区域。该项目有八个工作包：WP1植物分配和物候学研究，主要群落类型的呼吸产量比研究（通过收获、根系测量和同位素示踪试验）。WP2凋落物的周转，SOM，土壤的景观分布（通过土壤调查，同位素标记的凋落物，炸弹C测年来确定SOM年龄）。WP3室测量土壤和植被在精细尺度上的CO2和水分交换（分辨率~1m）。WP4 ~100 m尺度上土壤/植被与大气之间CO2和水分交换的连续塔测量。WP5在两个研究区域的飞机测量，记录二氧化碳和水的交换以及陆地表面的图像。这些测量将扩展到许多平方公里的区域。WP6卫星对地观测。我们将把若干卫星仪器的观测结果与相关野外活动中记录的植物覆盖测量结果联系起来。WP7我们使用模型将不同时间和空间尺度上连接的信息连接起来。这些模型代表了我们对该系统的最佳理解，我们通过独立的观察来检查和改进我们的理解，无论是从室内，塔，飞机还是卫星。我们通过WP1和WP2实验来测试我们是否能够理解卫星和飞机在舱室和塔上记录的细节数据。WP8我们将举办一个国际研讨会，与来自世界各地的同事分享我们的想法。建立以实地测量为基础的暑期学校，培养研究生，为本科生提供暑期实地体验。

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.