Response of pan-Arctic permafrost peatlands to rapid climate warming

尽管泥炭地的全球面积相对较小（仅占地球陆地面积的3%），但它们对未来全球尺度的生态系统-气候反馈有着不成比例的重要意义。富含有机物的永久冻土泥炭储存了大约277 Pg的碳(C)，相当于全球土壤碳储量的14% （Tarnocai et al., 2009）。直到最近，这个巨大的土壤C库一直处于有效的惰性状态，在冻土条件下，休眠的微生物活动保护着它不被分解。然而，21世纪的气候变暖预计将在北半球高纬度地区最为严重，那里是大部分永久冻土泥炭地的所在地（Christensen et al., 2013）。广泛的永久冻土解冻使这种碳储存暴露于快速衰减的速度，导致温室气体排放到大气中增加，进一步导致全球变暖（Hartmann et al., 2013）。然而，最近的研究表明，在更温暖的条件下，通过生态系统生产力的新激活和泥炭积累，增加的碳固存可能部分补偿了这种全球变暖效应（Swindles等，2015）。该项目旨在评估这种补偿机制是否在半球范围内发生在永久冻土泥炭地，以及它是否有可能影响未来的气候。高纬度地区永久冻土泥炭地的碳释放是否会导致人们热议的“碳炸弹”，并通过正反馈机制导致气候进一步变暖？或者，在气候变暖的情况下，由于生产力的提高和/或永久冻土融化在新饱和条件下抑制分解，泥炭地是否会通过加强碳封存而起到气候缓冲作用？这些紧迫的问题对气候-生物圈相互作用的未来具有重要的全球影响。该项目的目标是在半球尺度上测试Swindles等人（2015a）的永久冻土泥炭地退化的五阶段模型。目前，我们的模型是基于瑞典亚北极地区的一小部分泥炭地。然而，永久冻土泥炭地的大部分（按面积计算）发生在加拿大和西伯利亚的大陆地区。为了在半球范围内评估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Swindles等人（2015a）开发的高分辨率多代理古生态方法，重点关注近期气候快速变暖的地区。我们将测试以下关键假设：永久冻土泥炭地经历了(i)水文向湿润条件的快速转变；（ii） 20世纪因气候迅速变暖而增加的碳积累。我们已经确定了一些以快速气候变暖为特征的关键地区，这些地区包含大量的永久冻土泥炭地，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着火损失分析（Chambers et al., 2011）。碳积累将在Tolonen和Turunen（1996）之后计算。我们将分析每个位置岩心中的遗骨变形虫，并应用统计传递函数来开发地下水位重建（Swindles等人，2015b）。我们将利用210Pb、AMS放射性碳、球状碳质颗粒和温度年代学，为每个岩心制定准确的年代学。我们将收集有关活动层厚度的现有数据和仪器气候数据，与基于泥炭的数据进行比较。此外，我们将使用免费的遥感图像来调查在过去的几十年里，研究地点的湿度是否发生了变化（例如开阔水域的增加）。新的古数据集和未来气候模式预测将为永久冻土泥炭地对气候变暖的响应提供信息。

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.