| Co-Investigator(Kenkyū-buntansha) |
MACHIDA Toshinobu Nat.Inst.Envirn.Stud., Asso.Prof., 主任研究員 (20260185)
SAEKI Tazu Tohoku Univ., Computer Center, Assist.Prof., 大型計算機センター, 助手 (30302243)
AOKI Shuji Tohoku Univ., Grad.School of Sci., Asso.Prof., 大学院・理学研究科, 助教授 (00183129)
WATANABE Okitsugu Nat.Inst.Pol.Res., Prof., 教授 (60111861)
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| Research Abstract |
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
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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
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