Lakes and the Arctic Carbon Cycle

北极正在迅速变化，据预测，随着气候变暖，今天的苔原地区将被树木覆盖，例如，到2100年，森林将向北扩展到俄罗斯的北欧海岸。在北极的一些地区，如阿拉斯加，这个过程，通常被称为“绿化”，在过去的几十年里已经被观察到；木本灌木的分布向北扩展到冻土带。这种植被变化影响土壤中的养分循环，包括碳循环，但它们将在多大程度上改变景观尺度上的碳储存或释放仍存在争议。我们也不完全了解湖泊在这个系统中所起的作用，尽管我们知道，苔原和北部森林中的许多湖泊今天正在向大气中释放大量的二氧化碳和甲烷，其中一部分碳是从周围景观的植被和土壤中进入湖泊的。湖泊是北极景观的重要组成部分：我们在俄罗斯和西格陵兰岛的研究区域有成千上万的湖泊，它们是更广泛景观中碳循环的焦点。了解植物、土壤、营养物和湖泊之间的相互作用是至关重要的，因为在北纬高纬度地区，特别是在冻土中，有大量的碳储存，如果这些碳被转移到大气中（以二氧化碳或甲烷的形式），它将产生正反馈，进一步推动全球变暖。因此，北极是地球系统的一个重要组成部分，了解它将如何应对全球环境变化是至关重要的。湖泊是这一过程中的关键环节。由于湖泊与陆地碳循环紧密相连，湖泊沉积物记录忠实地记录了流入湖泊的碳的变化，以及湖泊内碳的生物处理过程的变化。我们还知道，与今天观测到的或预测到的类似的植被变化发生在气候比今天温暖的过去，因此过去的事件可以为未来的变化提供类似的模拟。该项目将检查湖泊沉积物记录，使用提取一系列化学信号和微观植物和动物遗骸的技术，以了解植被变化如何与过去的自然气候变暖相关，例如树木线向北迁移，影响湖泊的整体生物生产力、物种组成和占主导地位的碳处理类型。取决于不同生物过程之间的平衡，而这些过程又与周围的植被和土壤有关，湖泊可能主要是碳储存，还是主要是碳排放？在景观尺度上。植被类型的变化也影响植物残骸的分解和土壤发育，这与氮循环和可利用性有关。氮是控制生产力和碳固定和储存的重要因素，因此研究氮和碳的动态具有重要意义。由于气候和地质的空间变异性，北极周围植被发展（以及物种迁移）的速度和涉及的植物类型并不统一。通过检查三个地区（阿拉斯加、格陵兰岛、俄罗斯）中的几个湖泊，我们将能够描述一系列不同的植被转变和湖泊的相关反应。我们的结果可以用来告知我们对最近开始和未来变化的可能途径的理解。它们也可以扩大到整个北极，从而有助于理解全球变暖的反馈这一更广泛的科学目标。

The Arctic is changing rapidly, and it is predicted that areas which are today tundra will become tree-covered as warming progresses, with, for example, forest spreading northwards to the coast of northern European Russia by 2100. In some parts of the Arctic, such as Alaska, this process, commonly referred to as "greening", has already been observed over the past few decades; woody shrubs are expanding their distribution northwards into tundra. Such vegetation changes influence nutrient cycling in soils, including carbon cycling, but the extent to which they will change the storage or release of carbon at a landscape scale is debated. Nor do we fully understand the role that lakes play in this system although it is known that many lakes in the tundra and northern forests are today releasing carbon dioxide and methane into the atmosphere in significant amounts, and a proportion of this carbon comes into the lake from the vegetation and soils of the surrounding landscape. Lakes form an important part of arctic landscapes: there are many thousands of them in our study areas in Russia and west Greenland, and they act as focal points for carbon cycling within in the wider landscape.It is vital that we understand the interactions between plants, soils, nutrients, and lakes because there are massive carbon stores in the high northern latitudes, particularly in frozen soils, and if this carbon is transferred into the atmosphere (as carbon dioxide (CO2) or methane) it will create a positive feedback, driving further global warming. For this reason, the Arctic represents a critical component of the Earth System, and understanding how it will it respond to global environmental change is crucial. Lakes are a key link in this process.As lakes are tightly coupled with terrestrial carbon cycling, changes in the flows of carbon to a lake are faithfully recorded in lake sediment records, as are changes in the biological processing of that carbon within the lake. We also know that similar vegetation changes to those observed or predicted today occurred in the past when climate was warmer than today, and thus past events can provide an analogue for future changes. This project will examine lake sediment records, using techniques that extract a range of chemical signals and microscopic plant and animal remains, to see how vegetation changes associated with past natural climate warming, such as migration of the tree-line northwards, affected lake functioning in terms of the overall biological productivity, the species composition, and the types of carbon processing that were dominant. Depending upon the balance between different biological processes, which in turn are linked to surrounding vegetation and soils, lakes may have contributed mostly to carbon storage or mostly to carbon emissions ?at a landscape scale. Changes in vegetation type also influence decomposition of plant remains and soil development, and this is linked to nitrogen cycling and availability. Nitrogen is an important control over productivity and hence of carbon fixation and storage, and thus it is important to study the dynamics of nitrogen along with those of carbon. Due to the spatial variability of climate and geology, the pace of vegetation development (and of species immigration) and the types of plants involved have not been uniform around the Arctic. By examining several lakes in each of three regions (Alaska, Greenland, Russia) we will be able to describe a broad range of different vegetation transitions and the associated responses of the lakes. Our results can be used to inform our understanding of the likely pathways of recently initiated and future changes. They can also be up-scaled to the whole Arctic and so contribute to the broader scientific goal of understanding feedbacks to global warming.