Atmospheric methane interpolar difference, four-box troposphere modeled sources, last glacial maximum and deglaciation, Greenland and Antarctica

This dataset includes estimates of the atmospheric methane relative interpolar difference (rIPD) across the Last Glacial Maximum and Deglaciation. The rIPD was calculated using discrete, high-resolution methane measurements from the Western Antarctic Ice Sheet (WAIS) Divide, Northern Greenland Eemian (NEEM) and Greenland Ice Sheet Project Two (GISP2) ice cores. Two independent interpolar difference (IPD) records were determined: One using NEEM and WAIS and one using GISP2 and WAIS. The dataset includes rIPD values calculated using both Greenland methane data both corrected and uncorrected for excess methane (Lee et al., 2020). The rIPD was calculated by smoothing each methane record and synchronizing them to the WD2014 gas age scale. 1-sigma rIPD uncertainties are included. This dataset also includes the output of the four-box troposphere model used to interpret the rIPD. For both excess methane-corrected records, the model output and 1-sigma uncertainty is provided for northern extratropical (30N - 90N) and total tropical (30S - 30N) sources in teragrams per year (Tg yr-1). For the NEEM-derived rIPD, sections of the rIPD where atmospheric methane changed rapidly were deemed untrustworthy were removed from the dataset. Lee, J. E. et al. Excess methane in Greenland ice cores associated with high dust concentrations. Geochimica et cosmochimica acta 270, 409-430 (2020).

本数据集包含末次冰盛期（Last Glacial Maximum）与冰消期（Deglaciation）大气甲烷相对极间差（relative interpolar difference, rIPD）的估算结果。该数据集的rIPD基于南极西部冰盖（Western Antarctic Ice Sheet, WAIS）分水岭冰芯站点、北格陵兰Eemian冰芯（Northern Greenland Eemian, NEEM）以及格陵兰冰芯计划二号（Greenland Ice Sheet Project Two, GISP2）的离散高分辨率甲烷观测数据计算得到。研究构建了两组独立的极间差（interpolar difference, IPD）记录：一组依托NEEM与WAIS数据，另一组依托GISP2与WAIS数据。本数据集涵盖了针对过量甲烷（excess methane）进行校正与未校正的两类格陵兰甲烷数据计算得到的rIPD值（Lee等，2020）。rIPD的计算步骤为：先对每条甲烷记录进行平滑处理，再将其同步至WD2014气体年代标尺。数据集同时提供1σ置信度下的rIPD不确定度。此外，本数据集还包含用于阐释rIPD结果的四箱对流层模型输出结果。针对两组经过量甲烷校正的记录，模型分别给出了北温带（30°N - 90°N）与全球热带（30°S - 30°N）甲烷源的排放量估算值及1σ不确定度，单位为太克每年（teragrams per year, Tg yr⁻¹）。针对基于NEEM数据推导得到的rIPD序列，研究人员剔除了其中大气甲烷快速变化的不可信区段。参考文献：Lee, J. E. 等. 与高粉尘浓度相关的格陵兰冰芯过量甲烷. 地球化学与宇宙化学学报, 270卷, 409-430页 (2020).