An Analysis of the Carbon Balance of the Arctic Basin from 1997 to 2006

These data sets are the results of a model-data analysis of the contemporary C balance of the Arctic system in which the land and ocean area of the Arctic Basin is treated as a linked system of CO2 and CH4 exchange across terrestrial, marine and atmospheric components. The study area for the terrestrial component of the Arctic Basin is defined as the land area within the watersheds of the major rivers that drain into the Arctic Ocean (Lammers et al., 2001). Several process-based tools were used to conduct this analysis of C dynamics across the Arctic Basin between years 1997 and 2006 through simulations of land atmosphere CO2 and CH4 exchange, the transfer of land-based C to the Arctic Ocean, and ocean-atmosphere CO2 exchange. CO2 and CH4 exchange between the terrestrial ecosystems of the basin and the atmosphere, along with the export of dissolved organic C (DOC) to the Arctic Ocean, were estimated using the Terrestrial Ecosystem Model (TEM). The TEM considers the effects of a number of factors on its simulations of C dynamics including changes in atmospheric CO2, tropospheric ozone, nitrogen deposition, climate, and disturbance/land use including fire, forest harvest, and agricultural establishment/abandonment. TEM also calculates pyrogenic emissions of CO2, CH4, and CO from the combustion of vegetation and soil carbon in wildfires. The DOC leaching dynamics of TEM are a function of soil C decomposition rate, soil DOC concentration and water flux through the soil. We used the methane dynamics module of TEM (MDM-TEM) to estimate the exchange of CH4 with atmosphere of both wetlands, which generally emit CH4 to the atmosphere, and uplands, which generally consume CH4 from the atmosphere. The MDM-TEM considers the effects of a number of factors on its simulations of CH4 dynamics including the area of wetlands, fluctuations in the water table of wetlands, temperature, and labile carbon inputs into the soil solution derived from the net primary production (NPP) estimates of TEM. The MIT ocean biogeochemistry model simulated the net exchange of CO2 with the atmosphere as driven by changes in sea ice, water temperature, ocean circulation, and DOC inputs from TEM. The results of these simulations were compared with estimates of CO2 and CH4 exchange from atmospheric inversion models and with observations of terrestrial C export from Arctic watersheds. The simulated transfer of land-based C to the Arctic Ocean was compared against estimates based on a sampling of DOC export from major Arctic rivers (McClelland et al., 2008). The land-atmosphere CO2 exchange estimate was compared with results from the TransCom3 atmospheric inversion model inter-comparison project (Gurney et al., 2008), and CH4 to results from atmospheric inversion-estimated surface emissions (Chen and Prinn, 2006). To compare the "bottom-up" results from our model simulations with the "top down" estimates from these inversion studies, we summarize our estimates of surface-atmosphere CO2 and CH4 exchange for the land and ocean area matching the three high-latitude regions defined in the Transcom 3 model experiments (Gurney et al., 2002), namely the Boreal North America, Boreal Asia and Northern Ocean regions.本数据集为北极系统当代碳（carbon, C）平衡的模型-数据分析成果，研究中将北极盆地的陆地与海洋区域视为连接陆地、海洋与大气各组分的二氧化碳（CO₂）和甲烷（CH₄）交换耦合系统。北极盆地陆地组分的研究范围定义为：所有注入北冰洋的主要河流流域范围内的陆地区域（Lammers等，2001）。本研究采用多款基于过程的模型工具，对1997至2006年间北极盆地的碳动态开展分析，模拟内容涵盖陆地-大气间的CO₂与CH₄交换、陆地碳向北冰洋的输运，以及海洋-大气间的CO₂交换过程。盆地陆地生态系统与大气间的CO₂、CH₄交换，以及溶解有机碳（dissolved organic C, DOC）向北冰洋的输出量，均通过陆地生态系统模型（Terrestrial Ecosystem Model, TEM）估算得到。TEM在碳动态模拟中考虑了多种因素的影响，包括大气CO₂浓度变化、对流层臭氧、氮沉降、气候条件，以及干扰/土地利用活动（如野火、森林采伐、农业开垦与撂荒等）。此外，TEM还可计算野火中植被与土壤碳燃烧产生的CO₂、CH₄及一氧化碳（CO）的燃烧排放通量。TEM中的DOC淋溶动态由土壤碳分解速率、土壤DOC浓度及土壤水分通量共同决定。本研究采用TEM的甲烷动态模块（methane dynamics module of TEM, MDM-TEM），估算湿地与高地生态系统与大气间的CH₄交换通量：湿地通常向大气排放CH₄，而高地则通常从大气中吸收CH₄。MDM-TEM在CH₄动态模拟中考虑了多种因素的影响，包括湿地面积、湿地地下水位波动、温度，以及由TEM的净初级生产力（net primary production, NPP）估算结果推导得到的输入至土壤溶液中的活性碳含量。麻省理工学院海洋生物地球化学模型（MIT ocean biogeochemistry model）则模拟了由海冰变化、海水温度、海洋环流以及TEM输入的DOC共同驱动的海洋-大气CO₂净交换过程。 将上述模拟结果与大气反演模型得到的CO₂、CH₄交换通量估算值，以及北极流域陆地碳输出的观测数据进行对比。模拟得到的陆地碳向北冰洋的输运量，则与基于北极主要河流DOC输出采样数据得到的估算值进行对比（McClelland等，2008）。陆地-大气CO₂交换通量的估算结果与TransCom3大气反演模型比对项目的结果进行对比（Gurney等，2008），CH₄交换通量则与大气反演得到的地表排放估算结果进行对比（Chen和Prinn，2006）。为将本研究模型模拟得到的“自下而上（bottom-up）”结果与上述反演研究得到的“自上而下（top-down）”估算结果进行对比，本研究针对TransCom3模型试验中定义的三个高纬度区域（Gurney等，2002）——即寒温带北美、寒温带亚洲与北部海洋区域——对应的陆地与海洋范围，汇总了其地表-大气CO₂与CH₄交换通量的估算值。