Carbon Cycling Linkages of Permafrost Systems (CYCLOPS)

目前，陆地生态系统吸收了化石燃料燃烧释放到大气中的二氧化碳的四分之一，从而减缓了气候变化的速度。随着条件变得更有利于植物生长，大多数模型预测，高纬度地区将在世纪吸收更多的碳。然而，大量的碳储存被冻结在北方和北极的永久冻土中，气候变暖可能会导致其中一些碳被释放到大气中。最近在大尺度模式模拟中纳入了冻土融化，这表明冻土反馈可能非常重要，以至于它可能会大大减少21世纪陆地生态系统对碳的预测净吸收，并对气候变化的速度产生重大影响。碳气候模型中缺少许多关键过程。首先，不同植物群落在隔离土壤和保护永久冻土方面的作用缺乏量化，大多数模型中缺少苔藓等关键群体。此外，火灾干扰可以大大加速冻土融化，因此，保护冻土的植物群落从火灾中恢复的能力可能在确定冻土恢复力方面发挥关键作用。其次，不同的生态系统可能会对解冻作出不同的反应，对温室气体的释放产生不同的影响。在自由排水的生态系统中，解冻可能会导致碳的净释放，这是由于先前冻结的有机物分解增加。另一方面，当泥炭地发生解冻时，土壤沉降可以有效地提高地下水位，这可能导致碳积累。然而，这种潜在的负反馈可能会被更强大的温室气体甲烷的增加释放所抵消。重要的是，在这些对比鲜明的生态系统中，冻土融化的全方位反馈目前还没有反映在基于过程的模型中。为了解决这些问题，我们将进行定向实地考察活动，以确定（1）不同的植物群落在保护不同土壤类型的永冻土中发挥的作用，以及在未燃烧和火灾干扰的生态系统中，以及（2）永冻土融化对自由排水与泥炭地系统中二氧化碳和甲烷通量的影响。通过与加拿大伙伴的链接，将从正在进行永冻层监测的一系列实地地点收集数据，包括：㈠永冻层范围不同的两个对比鲜明的北方泥炭地，以及永冻层退化的地方; ㈡加拿大北方三种重要森林类型内的烧毁和未烧毁地点。数据将由我们的美国合作伙伴提供，来自阿拉斯加连续永久冻土带内燃烧和未燃烧的潮湿酸性苔原。在火灾现场植被恢复的空间变化允许植被和永冻层之间的关系进行详细测试，而苔原，森林和泥炭地网站之间的比较提供了深入了解永冻层融化的影响，在对比ecosystem.Critically，这些数据将被用来开发，参数化和评估一个详细的基于过程的模型植被-土壤-永冻层相互作用。植被-冻土联系的深入表达将改善冻土融化速率的预测。该模型将是第一个模拟自由排水与湿地生态系统中全方位生物地球化学反馈（甲烷和二氧化碳）的模型。此外，通过与英国气象局科学家的联系，我们的模型将与英国联合陆地环境模拟器（JULES）耦合，允许区域模拟运行，并与气候模型耦合。最终，我们的项目将改善对冻土融化速率和后果的预测，并帮助确定对21世纪世纪气候变化的潜在影响。

Terrestrial ecosystems currently absorb one quarter of the carbon dioxide released by fossil fuel burning into the atmosphere, and thus reduce the rate of climate change. As conditions become more favourable for plant growth, most models predict that high latitudes will take up more carbon during the 21st century. However, vast stores of carbon are frozen in boreal and arctic permafrost, and warming may result in some of this carbon being released to the atmosphere. The recent inclusion of permafrost thaw in large-scale model simulations has suggested that the permafrost feedback is potentially so significant that it could reduce substantially the predicted global net uptake of carbon by terrestrial ecosystems during the 21st century, with major implications for the rate of climate change.Large uncertainties remain in predicting rates of permafrost thaw and in determining the impacts of thaw in contrasting ecosystems, with many of the key processes missing from carbon-climate models. Firstly, the role that different plant communities play in insulating soils and protecting permafrost is poorly quantified, with key groups such as mosses absent in most models. In addition, fire disturbance can substantially accelerate permafrost thaw, and hence the ability of permafrost-protecting plant communities to recover from fire may play a key role in determining permafrost resilience. Secondly, different ecosystems may respond differently to thaw with contrasting effects on release of greenhouse gasses. In free-draining ecosystems, thaw may result in the net release of carbon due to increased decomposition of previously frozen organic matter. On the other hand, when thawing takes place in peatlands, soil subsidence can effectively raise the water table, which could result in carbon accumulation. However, this potential negative feedback may be offset by enhanced release of the more powerful greenhouse gas, methane. Importantly, the full range of feedbacks to permafrost thaw in these contrasting ecosystems is not currently reflected in process-based models. To address these issues, we will undertake directed fieldwork campaigns to determine (1) the role that different plant communities play in protecting permafrost within different soil types, and in unburned and fire-disturbed ecosystems, and (2) the impacts of permafrost thaw on fluxes of carbon dioxide and methane in free-draining versus peatland systems. Through links to Canadian partners, data will be collected from a range of field sites where permafrost monitoring is ongoing, including: (i) two contrasting boreal peatlands differing in permafrost extent, and where there is permafrost degradation; (ii) burnt and unburned sites within three important forest types in boreal Canada. Data will be provided from burnt and unburned moist acidic tundra within the continuous permafrost zone in Alaska by our US partners. The spatially variable vegetation recovery at the fire sites allows relationships between vegetation and permafrost to be tested in detail, while comparisons between the tundra, forest and peatland sites provide insights into the impacts of permafrost thaw in contrasting ecosystems.Critically, these data will be used to develop, parameterise and evaluate a detailed process-based model of vegetation-soil-permafrost interactions. The in-depth representation of vegetation-permafrost linkages will improve predictions of rates of permafrost thaw. The model will be the first to simulate the full range of biogeochemical feedbacks (methane and carbon dioxide) in free-draining versus wetland ecosystems. Furthermore, through links with Met Office scientists, our model will be coupled to the Joint UK Land Environment Simulator (JULES), allowing regional simulations to be run, coupled to a climate model. Ultimately, our project will improve predictions of both the rates and consequences of permafrost thaw, and help determine the potential impacts on 21st century climate change.