Greenhouse gas flux measurements at the zero curtain, North Slope, Alaska, 2012-2025

Overview- This project proposes to create a long-term, year-round field observations to better understand the controls on greenhouse gas (GHG) emissions from the Arctic at time scales that will encompass significant climate change and variability. Research over decadal time frames is critical for understanding the effect of climate variability and change on carbon dioxide (CO2) and methane (CH4) fluxes and to provide the baseline needed to evaluate temporal changes. This is particularly relevant in arctic ecosystems where the large spatial heterogeneity prevents using nearby stations to build a time series in the GHG emissions, given that fluxes can vary substantially over the meter scale. This project will allow creating the longest running year-round Arctic eddy covariance network, and to standardize, upgrade, and apply the network to improve understanding of the long-term effects of climate variability and change on trace gas feedbacks from the Arctic. This project will make existing data more useful and relevant and will expand an already large user base. A special emphasis will be on the fall zero curtain period when an unfrozen soil layer hovers around 0°Celsius (C) supporting significant CO2 and CH4 releases to the atmosphere, and the entire cold season (Zona et al., 2016). Zero curtain processes plausibly explain how upland tundra can be a larger emitter of CH4 than low-lying, wet tundra, and how the cold seasons might emit more CH4 than the summer season (Zona et al., 2016, Commane et al., 2017). At present, however, cold season observations are too short to adequately test hypotheses concerning the controlling mechanisms or to develop understanding that allows us to predict, with confidence, future CO2 and CH4 fluxes form the Arctic. Five Arctic eddy covariance flux towers will be used to evaluate the long term changes in the CO2 and CH4 fluxes across three moisture environments in Barrow (recently renamed as Utqiaġvik) (CMDL (Climate Monitoring and Diagnostics Laboratory), BEO (Barrow Environmental Observatory), and BES (Biocomplexity Experiment South) towers) and a ~300km latitudinal gradient passing through Atqasuk (ATQ) and culminating in Ivotuk (IVO). These measurements are intended to be of sufficient duration and breadth to capture and interpret the effect of extreme and/or unexpected events on GHG fluxes in the Arctic. The support from this grant would allow expansion of the time series to a more than 20-year record of CO2 and 11-year record of CH4 fluxes, resulting in an unprecedented dataset, critical to refining our analytical and predictive ability of the controls of CH4 loss from the Arctic.

项目概述：本项目拟构建长期、全年连续的野外观测体系，以在涵盖显著气候变化与气候变率的时间尺度上，深入解析北极温室气体（GHG）排放的控制机制。基于十年尺度的研究对于理解气候变率与变化对二氧化碳（CO₂）、甲烷（CH₄）通量的影响至关重要，同时可为评估时间尺度上的变化提供必要的基准。这一点在北极生态系统中尤为关键：由于通量在米级尺度上可发生显著变化，空间异质性极强的北极区域无法通过邻近站点构建温室气体排放的时间序列。本项目将建成全球持续时长最长的北极全年涡度相关（eddy covariance）观测网络，并通过标准化、升级与应用该网络，深化对气候变率与变化如何影响北极痕量气体反馈的认知。本项目将提升现有数据的实用性与相关性，并扩大已颇具规模的用户群体。本项目将重点聚焦秋季零幕期与整个寒冷季：其中秋季零幕期指未冻结土层温度维持在0℃左右、向大气释放显著量CO₂与CH₄的阶段（Zona等，2016）。零幕过程可合理解释：为何高地苔原的CH₄排放量高于低洼湿地苔原，以及为何寒冷季的CH₄排放量可能高于夏季（Zona等，2016；Commane等，2017）。然而目前，寒冷季的观测时长过短，既无法充分验证与控制机制相关的假说，也无法形成可靠认知以精准预测北极未来的CO₂与CH₄通量。本项目将采用5座北极涡度相关通量塔，开展以下观测：一是在巴罗（现已更名为乌特恰维克/Utqiaġvik）区域内的三种水分环境中，评估CO₂与CH₄通量的长期变化，该区域的观测塔包含CMDL（气候监测与诊断实验室/Climate Monitoring and Diagnostics Laboratory）塔、BEO（巴罗环境观测站/Barrow Environmental Observatory）塔以及BES（南部生物复杂性实验/Biocomplexity Experiment South）塔；二是沿贯穿阿特卡斯克（ATQ）并终止于伊沃图克（IVO）的约300公里纬度梯度开展观测。本观测体系的时长与覆盖范围均足以捕捉并解析极端或突发事件对北极温室气体通量的影响。本次资助将推动观测时间序列的扩展，最终形成超过20年的CO₂通量记录与11年的CH₄通量记录，构建出前所未有的数据集，这对于优化我们解析与预测北极CH₄排放控制机制的能力至关重要。