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

为了阐明近3个冰期-间冰期旋回的大气成分及其同位素的时间变化，从全长2504 m的南极深冰芯中提取了空气样品。分析了CH_4、N_2O和CO_2的浓度，N_2的δ^<15>N和O_2的δ^<18>O。对钻探现场采集的空气样本进行了相同物种的分析，并通过数值模型模拟结果，定量研究了冰与空气的年龄差异以及空气进入冰的捕获过程。研究结果表明：(1)空气组分在冰中通过分子扩散运动，为纠正分子扩散对冰中空气组分的影响，建立了δ^<15>N of N_2的过程。在冰期-间冰期旋回中，冰与空气的年龄差异在2000年至5000年之间变化。(2) CH_4浓度在冰期向间冰期过渡期间迅速上升，在间冰期结束时迅速下降，在冰期极大期逐渐减小至最小值，并伴有较大波动。这一变化与气温变化具有较好的相关性，其原因与气候变化对CH_4排放的影响有关。(3) N_2O浓度总体上表现为冰期低值，间冰期较高，但在冰期极大期往往出现极高值，这可能与暴露的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-间冰期旋回具有较好的相关性，其中以11.5 kyr左右的周期变化最为显著。(5)大气δ^<18>O值主要随海平面的变化而变化，但在间冰期至冰期期间，δ^<18>O值与海平面的关系相反，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