Past methane from lakes in Alaska: integrating proxy records and models

阿拉斯加湖泊过去的甲烷：整合代理记录和模型

• 批准号: NE/T007109/1
• 负责人: Maarten Van Hardenbroek
• 金额: $ 66.24万
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FT007109%2F1
• 关键词: Past; methane; lakes; Alaska; integrating

Increasing concentrations of greenhouse gases in the atmosphere trap heat and cause global warming. Methane is key, as it is 28 times more potent than carbon dioxide in trapping heat. Unfortunately, there is great uncertainty in how the amount of methane in the atmosphere will change under future conditions, so we urgently need more accurate numbers for future methane emissions as the Earth continues to warm. This proposal will make a radical new contribution by providing much better constrained estimates of methane contributions from lakes in Alaska, as an example of a high-latitude region susceptible to global warming. The high northern latitudes are particularly important to climate change effects because climatic warming is accentuated toward the poles, which will accelerate biological processing of carbon, including the production of methane.The uncertainty in future atmospheric methane content reflects the fact that emissions are caused by human actions and natural processes that are themselves affected by climate change. Lakes form one of the largest natural sources of methane. Lake methane production strongly increases in warmer and wetter conditions, leading to more methane entering the atmosphere, where it contributes to further warming. This is an important positive feedback mechanism that could have large impacts on future global climate. This climate-methane feedback is strongest at high latitudes, where lakes are very abundant and recent warming is most severe. However, because temperature is only one of several factors that are likely to affect methane release from lakes and wetlands, the extent of the methane feedback can only be understood through careful numerical modelling.In the past, warmer-than-present climatic conditions prevailed in interior Alaska between 11,000-6,000 years ago. If we can understand how methane behaved under these conditions, we will be in a better position to anticipate future change. We can do this by deriving data directly from lake sediment records coupled with a model to simulate the processes of methane generation and emission. Comparison of model output and observed data forms a powerful hypothesis-testing system that we can use to ascertain how much methane emissions have changed in the past, and why they changed. This study's observed record comes from dated lake sediments. Lake sediments accumulate continuously and preserve records of chemical and biological processes plus information about past climate. Studying these records will allow us to reconstruct information on past methane emissions. Key factors for methane emissions (temperature, water level, organic matter availability, oxygen regime) will also be reconstructed and modelled, which allows us to understand the processes behind lake methane emissions.Our study focuses on lakes in Alaska because this region is well-studied compared with other high-latitude areas, with extensive background information about past climate and carbon cycling. We will reconstruct methane emissions from lakes that were 2-5 degrees warmer 11,000-6,000 years ago, compared with today. We will use a new, quantitative tool for estimating past methane emissions from lakes based on the chemical composition of fossils in sediment records. We will also adapt an existing numerical model that simulates present-day methane emissions to estimate past and future methane emissions. Our integrated approach, combining geochemical measurements and modelling, will allow us to: (1) assess the magnitude of methane emissions through time, (2) identify the key factors driving methane emissions, (3) find critical values for these factors that lead to change, and (4) understand how factors interact to produce observed methane emissions. Our numerical methane model, refined through comparison with empirical observations, will then allow us to make robust estimates for how much greater a contribution lakes may have to atmospheric methane in the future.

大气中温室气体浓度的增加会吸收热量，导致全球变暖。甲烷是关键，因为它吸收热量的能力是二氧化碳的28倍。不幸的是，在未来的条件下，大气中甲烷的数量将如何变化还存在很大的不确定性，因此，随着地球继续变暖，我们迫切需要更准确的未来甲烷排放量数字。该提案将为阿拉斯加湖泊的甲烷排放量提供更好的约束估计，从而做出全新的贡献。阿拉斯加是一个高纬度地区易受全球变暖影响的例子。北纬高纬度地区对气候变化的影响尤其重要，因为气候变暖在两极地区加剧，这将加速碳的生物处理，包括甲烷的产生。未来大气甲烷含量的不确定性反映了这样一个事实，即排放是由人类活动和自然过程引起的，而这些活动和自然过程本身又受气候变化的影响。湖泊是甲烷最大的天然来源之一。在温暖和潮湿的条件下，湖泊甲烷产量会大幅增加，导致更多的甲烷进入大气，从而导致进一步变暖。这是一个重要的正反馈机制，可能对未来的全球气候产生重大影响。这种气候-甲烷反馈在高纬度地区最为强烈，那里湖泊非常丰富，最近的变暖最为严重。然而，由于温度只是可能影响湖泊和湿地甲烷释放的几个因素之一，甲烷反馈的程度只能通过仔细的数值模拟来理解。在过去，11000 - 6000年前，阿拉斯加内陆的气候条件比现在要温暖。如果我们能了解甲烷在这些条件下的表现，我们就能更好地预测未来的变化。我们可以通过直接从湖泊沉积物记录中获得数据，并结合一个模型来模拟甲烷产生和排放的过程。模型输出和观测数据的比较形成了一个强大的假设检验系统，我们可以用它来确定过去甲烷排放量的变化程度，以及变化的原因。这项研究观察到的记录来自于年代久远的湖泊沉积物。湖泊沉积物不断积累，保存了化学和生物过程的记录以及过去气候的信息。研究这些记录将使我们能够重建过去甲烷排放的信息。甲烷排放的关键因素（温度、水位、有机物可利用性、氧气状态）也将被重建和建模，这使我们能够了解湖泊甲烷排放背后的过程。我们的研究重点是阿拉斯加的湖泊，因为与其他高纬度地区相比，这个地区得到了很好的研究，有关于过去气候和碳循环的广泛背景信息。我们将重建11,000-6,000年前湖泊的甲烷排放量，与今天相比，湖泊的温度要高2-5度。我们将使用一种新的定量工具，根据沉积物记录中化石的化学成分来估计湖泊过去的甲烷排放。我们还将采用模拟当前甲烷排放的现有数值模型来估计过去和未来的甲烷排放。我们的综合方法，结合地球化学测量和建模，将使我们能够：(1)评估随时间变化的甲烷排放幅度，(2)确定驱动甲烷排放的关键因素，(3)找到导致变化的这些因素的临界值，以及(4)了解因素如何相互作用以产生观测到的甲烷排放。我们的数值甲烷模型，经过与经验观测的比较，将使我们能够对未来湖泊对大气甲烷的贡献做出可靠的估计。