Response of pan-Arctic permafrost peatlands to rapid climate warming

尽管泥炭地的全球面积相对较小(占地球陆地表面的3%)，但对于全球规模的生态系统-气候反馈的未来来说，泥炭地具有不成比例的重要性。富含有机的永久冻土泥炭储存了大约277pg的碳(C)，相当于全球土壤碳储存的14%(Tarnocai等人，2009年)。直到最近，这一巨大的土壤碳库一直处于有效的惰性状态，在冰冻土壤条件下，由于微生物活动迟缓，它不会被分解。然而，21世纪的气候变暖预计将在北半球高纬度地区最严重，那里是大多数永久冻土泥炭地的发源地(Christensen等人，2013年)。大范围的永久冻土融化使这个C库暴露在快速腐烂的环境中，这会导致温室气体排放到大气中的增加和进一步的全球变暖(Hartmann等人，2013年)。然而，最近的研究表明，这种全球变暖效应可以通过在更温暖的条件下新恢复的生态系统生产力和泥炭积累而增加的碳固存来部分补偿(Swinles等人，2015a)。该项目旨在评估这种补偿机制是否正在半球尺度上发生在永久冻土泥炭地中，以及它是否有可能影响未来的气候。高纬度永久冻土泥炭地的碳释放是否会导致人们热议的“碳弹”，并通过正反馈机制进一步变暖？或者，泥炭地是否会通过在气候变暖时提高生产力和/或在新饱和的条件下抑制融化的永久冻土的分解来促进碳固存，从而起到气候缓冲的作用？这些都是对气候-生物圈相互作用的未来具有重要全球影响的紧迫问题。该项目的目标是测试Swinles等人提出的永久冻土泥炭地退化的五阶段模型。(2015A)在半球尺度上。目前，我们的模型是基于瑞典亚北极的一小部分泥炭地。然而，大部分(按面积计算)永久冻土泥炭地位于加拿大和西伯利亚大陆地区。为了在半球尺度上评估来自永久冻土泥炭地的潜在反馈，必须对更大范围的永久冻土泥炭地进行严格的古环境调查。我们将使用Swinles等人开发的高分辨率多代理古生态方法，重点关注以最近快速气候变暖为特征的地区。(2015A)。我们将检验以下关键假设：(I)多年冻土泥炭地经历了(I)水文学向更潮湿条件的快速转变；(Ii)在20世纪，由于快速气候变暖，碳积累增加。我们已经确定了一些以快速气候变暖为特征的关键地区，其中包括：加拿大北极、阿拉斯加、俄罗斯和瑞典。在实验室中，我们将按照标准方法进行体积密度和点火损失分析(Chambers等人，2011年)。碳积累将根据Tolonen和Turunen(1996)计算。我们将分析每个地点岩心中的遗体阿米巴虫，并应用统计传递函数来开发地下水位深度重建(Swinles等人，2015b)。我们将使用210Pb、AMS放射性碳、球状碳质颗粒和延时年代学为每个岩心制定准确、精确的年代学。我们将汇编现有的活动层厚度数据和仪器气候数据，以与基于泥炭的数据进行比较。此外，我们将使用免费提供的遥感图像来调查研究地点在过去几十年中是否发生了湿度变化(例如，开放水域区域的增加)。新的古数据集和未来的气候模型预测将为永久冻土泥炭地对气候变暖的反应提供新的模型。

Despite their relatively small global areal extent (3% of the earth's land surface), peatlands are disproportionately important to the future of global-scale ecosystem-climate feedbacks. Organic-rich permafrost peat stores approximately 277 Pg of carbon (C), equivalent to 14 % of the global soil C store (Tarnocai et al., 2009). Until recently this huge soil C store has been rendered effectively inert, protected from decomposition by lethargic microbial activity in frozen soil conditions. However, twenty-first century climatic warming is projected to be greatest in high-latitude areas of the Northern Hemisphere, where the majority of permafrost peatlands occur (Christensen et al., 2013). Widespread permafrost thaw exposes this C store to rapid rates of decay which leads to increased emissions of greenhouse gases to the atmosphere and further global warming (Hartmann et al., 2013). However, recent research indicates that this global warming effect may be partially compensated by increased C sequestration through newly invigorated ecosystem productivity and peat accumulation under warmer conditions (Swindles et al., 2015a). The project aims to evaluate whether this compensation mechanism is occurring in permafrost peatlands at a hemispheric scale and whether it has the potential to impact on future climate.Will carbon release from permafrost peatlands at high latitudes lead to the much discussed "carbon bomb" and further warming of climate through positive feedback mechanisms? Or, alternatively, will the peatlands act as climate buffers through invigorated carbon sequestration driven by increased productivity under a warmer climate and/or suppressed decomposition in newly saturated conditions from thawing permafrost? These are pressing questions with important global implications for the future of climate-biosphere interactions. The objective of this project is to test a five-phase model of permafrost peatland degradation from Swindles et al. (2015a) at a hemispheric scale. Currently, our model is based on a small number of peatlands in subarctic Sweden. However, the majority (by area) of permafrost peatlands occur in the continental regions of Canada and Siberia. To assess potential feedbacks from permafrost peatlands on a hemispheric scale a broader range of permafrost peatlands must be subject to rigorous palaeoenvironmental investigation. We will focus on regions characterised by recent rapid climate warming using the high-resolution multi-proxy palaeoecological approach developed in Swindles et al. (2015a). We will test the following key hypotheses: permafrost peatlands have undergone a (i) rapid shift in hydrology to wetter conditions and; (ii) increased carbon accumulation during the twentieth century in response to rapid climate warming.We have identified a number of key regions characterised by rapid climate warming that contain a significant area of permafrost peatland, including: Arctic Canada, Alaska, Russia and Sweden. In the laboratory we will carry out bulk density and loss-on-ignition analyses following standard methods (Chambers et al., 2011). Carbon accumulation will be calculated following Tolonen and Turunen (1996). We will analyse for testate amoebae in cores from each location and apply statistical transfer functions to develop a water-table depth reconstruction (Swindles et al., 2015b). We will develop an accurate, precise chronology for each core using 210Pb, AMS radiocarbon, spheroidal carbonaceous particles and tephrochronology. We will compile available data on active layer thickness and instrumental climate data to compare with the peat-based data. In addition, we will use freely-available remote-sensed images to investigate whether there has been changing wetness (e.g. increase in open water areas) in the study sites over the last few decades. A new model of permafrost peatland response to climate warming will be informed by the new palaeo-data sets and future climate-model predictions.