Methane in NEEM-2011-S1 ice core from North Greenland, 1800 years continuous record: outliers removed, v2

Description and Notes
Description: Methane concentration from the Greenland NEEM-2011-S1 Ice Core from 71 to 408m depth (~270-1961 CE).
Methane concentrations analysed online by laser spectrometer (SARA, Spectroscopy by Amplified Resonant Absorption, developed at Laboratoire Interdisciplinaire de Physique, Grenoble, France) on gas extracted from an ice core processed using a continuous melter system (Desert Research Institute). Methane data have a 5 second integration time (raw data acquisition rate 0.6 Hz). Analytical precision, from Allan Variance test, is 0.9 ppb (2 sigma). Long-term reproducibility is 2.6% (2 sigma). Gaps in the record are due to problems during online analysis. Online analysis conducted August-September 2011.
Note: Lat-Long provided is for main NEEM borehole. The NEEM-2011-S1 core was drilled 200 m distance away in 2011 to 410 m depth.

Methane concentrations are reported on NOAA2004 scale (instrument calibrated on dry synthetic air standards).
A correction factor of 1.079 has been applied to all data to correct for methane dissolution in melted ice core sample prior to gas extraction. Correction factor calculated using empirical data (concentrations not aligned/tied to existing discrete methane measurements).

Additional methods description provided in:
* Stowasser, C., Buizert, C., Gkinis, V., Chappellaz, J., Schupbach, S., Bigler, M., Fain, X., Sperlich, P., Baumgartner, M., Schilt, A., Blunier, T., 2012. Continuous measurements of methane mixing ratios from ice cores. Atmos. Meas. Tech. 5, 999-1013.
* Morville, J., Kassi, S., Chenevier, M., Romanini, D., 2005. Fast, low-noise, mode bymode, cavity-enhanced absorption spectroscopy by diode-laser self-locking. Appl. Phys. B Lasers Opt. 80, 1027-01038.
* NEEM (North Greenland Eemian Ice Drilling) project information http://neem.dk/

数据集描述与附注

## 数据集描述
本数据集收录格陵兰NEEM（North Greenland Eemian Ice Drilling，北格陵兰埃姆间冰期冰钻项目）-2011-S1冰芯71至408米深度（对应公元270年至1961年）的甲烷浓度数据。
甲烷浓度通过激光光谱仪（SARA，全称放大谐振吸收光谱法（Spectroscopy by Amplified Resonant Absorption））在线分析得到，该仪器由法国格勒诺布尔跨学科物理实验室开发，气体样品取自美国沙漠研究所研发的连续熔融系统处理的冰芯样品。甲烷数据的积分时长为5秒（原始数据采集速率为0.6 Hz）。经阿伦方差（Allan Variance）测试，其分析精度为0.9 ppb（2σ），长期重现性为2.6%（2σ）。数据记录中的间隙源于在线分析过程中出现的故障。本次在线分析于2011年8月至9月开展。

## 附注
本次提供的经纬度坐标对应NEEM主钻孔位置。NEEM-2011-S1冰芯于2011年在主钻孔200米外处钻探，钻探深度达410米。
本数据集的甲烷浓度采用NOAA2004标准刻度（仪器使用干燥合成空气标准品进行校准）。所有数据均已应用1.079的校正因子，以校正气体提取前熔融冰芯样品中甲烷的溶解损失。该校正因子基于实验数据计算得到（本次浓度数据未与已公开的离散甲烷测量值进行校准对齐）。

更多方法学细节可参考以下文献：
* Stowasser, C., Buizert, C., Gkinis, V., Chappellaz, J., Schupbach, S., Bigler, M., Fain, X., Sperlich, P., Baumgartner, M., Schilt, A., Blunier, T., 2012. 冰芯甲烷混合比的连续测量. 《Atmos. Meas. Tech.》, 5, 999-1013.
* Morville, J., Kassi, S., Chenevier, M., Romanini, D., 2005. 基于二极管激光自锁的快速低噪声逐模腔增强吸收光谱法. 《Appl. Phys. B Lasers Opt.》, 80, 1027-1038.
* NEEM（北格陵兰埃姆间冰期冰钻项目）项目信息：http://neem.dk/