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

为了阐明近3个冰期-间冰期旋回大气成分及其同位素的时间变化，对南极深冰芯（全长2504 m）进行了大气采样。结果表明：（1）富士山顶大气中CH_4、N_2O、CO_2的浓度以及N_2的δ^<15>N和O_2的δ^<18>O浓度均高于富士山顶大气中的浓度。从钻场的积雪采集的空气样品也分析了相同的物种，并通过数值模式模拟的结果，冰和空气之间的年龄差异和捕获空气到冰的过程进行了定量研究。（1）研究发现，空气组分在积雪中的运动是由分子扩散引起的，为了校正分子扩散对空气组分的影响，本文建立了用N_2的δ^ N来修正分子扩散的方法<15>。研究还发现，在冰川-间冰期循环中，冰和空气之间的年龄差异在2000年至5000年之间变化。(2)CH_4浓度 关于我们 在冰期向间冰期的过渡期内，盐度迅速升高，间冰期末期盐度迅速降低，最高冰期时盐度逐渐降低至最低值，并伴随着较大的波动。这种变化与温度变化有很好的相关性，其原因是气候变化影响CH_4排放的变化。(3)N_2O浓度在冰期普遍偏低，间冰期偏高，但在极盛期常出现极高值，这可能与暴露大陆架上的细菌活动有关。(4)CO_2浓度变化在190 ~ 300 ppmv之间，与冰期-间冰期旋回有较好的相关性，其中11.5 kyr左右的周期在该浓度变化中占主导地位。(5)大气δ^ O值<18>主要随海平面的变化而变化，但在间冰期至冰期，这种关系发生了逆转，表明陆地生物圈的贡献增强。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