Variations of atmospheric components and their isotopes over the glacial-interglacial cycles

为了阐明过去三个冰期-间冰期大气组分及其同位素的时间变化，从南极全长2504m的圆顶富士冰芯提取空气样品，分析了CH4、N2O、CO2、δ^&lt；15&gt；N和O_2的δ^&lt；18&gt；O的浓度。还对钻探现场采集的同一物种的空气样品进行了分析，并通过数值模式模拟结果，定量地研究了冰与空气之间的年龄差异和空气进入冰层的过程。研究结果表明：(1)大气组分在降雪中以分子扩散的方式运动，并纠正其对被冰遮挡的空气组分的影响，建立了N_2的δ^&lt；15&gt；N的计算程序。还发现在冰川-间冰期循环中，冰和空气之间的年龄差在2000年到5000年之间变化。(2)CH_4浓缩物…More在从冰期向间冰期过渡的过程中迅速增加，在间冰期结束时迅速下降，然后在冰期最大时逐渐下降到最小值，并伴随着较大的波动。(3)冰期N_2O浓度普遍较低，间冰期N_2O浓度较高，但冰盛期N_2O浓度极高，这可能是由于暴露在陆架上的细菌活动所致。(4)CO_2浓度变化在190~300ppmv之间，与冰期-间冰期旋回有很好的相关性，其中11.5kr左右的周期尤为明显。(5)δ^&lt；18&gt；大气中的O主要随着海平面的变化而变化，但从间冰期到冰期，这种关系发生了逆转，这表明陆地生物圈的贡献增加了。较少

In order to elucidate temporal variations of atmospheric components and their isotopes over the last three glacial-interglacial cycles, air samples were extracted from an Antarctic deep ice core with a full length of 2504 m. Dome Fuji, and analyzed for the concentrations of CH_4, N_2O and CO_2, δ^<15>N of N_2 and δ^<18>O of O_2. Air samples collected from firn at the drilling site were also analyzed for the same species, and by simulating the results using numerical models, age differences between ice and air and trapping processes of air into ice were investigated quantitatively. The results obtained from this study summarized as follows :(1) It was found that air components moved by molecular diffusion in firn, and to correct its influence on air components occluded in ice, the procedure has been established using δ^<15>N of N_2. It was also found that the age differences between ice and air varied between 2000 and 5000 years over the glacial-interglacial cycle.(2) The CH_4 concentra … More tion increased rapidly during the transition from the glacial period to the interglacial period, decreased rapidly at the end of the interglacial period, and then decreased gradually toward the minimum value at the glacial maximum, accompanying large fluctuations. This variation was correlated well with those of temperature, and its cause was attributable to changes in CH_4 emission affected by climate change.(3) The N_2O concentration generally showed low values during the glacial period and higher values during the interglacial period, but extremely high values were ofter found at the glacial maximum, due probably to bacterial activities on the exposed continental shelves.(4) The CO_2 concentration varied between 190 and 300 ppmv, showing a good correlation with the glacial-interglacial cycle, and the period of about 11.5 kyrs was especially predominant in this concentration variation.(5) The value of δ^<18>O in atmospheric principally followed the variation of sea level, but the relationship was reversed during the period from the interglacial to the glacial, suggesting enhanced contribution of the terrestrial biosphere. Less