Discussion of the reliability of CO2, CH4 and N2O records from polar ice cores (scientific paper)

Air in polar ice has about the same composition as atmospheric air at the time of ice formation. This allows to determine the composition, especially the concentration of greenhouse gases, in the past. However, the air composition in the ice can be slightly altered by chemical and biological processes in the ice. The reliability of long term trends can be determined by comparing records from different ice cores. For short duration details and time lags such comparisons are not possible due to uncertainties of the age scales of records from different cores. In this case very detailed records along sections of ice cores show whether the scatter of the results is larger than the theoretical expected one. A larger scatter is assumed to be caused by reactions between impurities in the ice which show generally short term variations. A low scatter of detailed high resolution records is therefore, a prerequisite for reliable records

Reconstruction of past atmospheric CH4 concentration from the firn air data at Dome Fuji (scientific note)

Air samples were collected from different depths of the firn layer at Dome Fuji in December 1998 and analyzed for CH4 concentrations. The age distribution of CH4 in the firn was calculated by using a one-dimensional numerical model, and then the inverse method was applied to reconstruct variations of atmospheric CH4 in the past. The age distribution function was calculated by including processes of molecular diffusion, downward air advection and bubble trapping in the snow-ice transition zone. Once the age distribution function is calculated, the vertical distribution of CH4 in the firn layer can be reconstructed by a linear combination of the age distribution functions weighted by the atmospheric CH4 concentrations in the past. Therefore, the most plausible past atmospheric record of CH4 can be derived iteratively so that its observed profile in the firn layer was reproduced well. In order to check the calculation scheme, the estimated variation of atmospheric CH4 was compared with direct measurements in the Antarctic region. They were in good agreement with each other, even for rapid slowing down of the secular increase observed in the 1990\u27s

Reconstruction of the atmospheric CO2 concentration history from an Antarctic deep ice core, Dome Fuji using a wet extraction technique: analysis procedures,dating of air in ice and concentration variations (scientific paper)

In order to deduce the atmospheric CO2 concentration variations over the past 320 kyr, air samples were extracted from the Dome Fuji deep ice core using a wet extraction method, and their CO2 concentration values were determined with a reproducibility of 1.0 ppmv. By measuring the CO2 concentrations of firn air samples collected at Dome Fuji, it was found that the effective bubble close-off depth can be defined by the mid-point of the close-off zone. For dating the air in the ice core, the age difference between ice and air (Δage) was estimated by using a densification model to be between 1000 and 5000 years, showing small and large values during the interglacial and glacial periods, respectively, due primarily to variations of precipitation. The CO2 concentration variations with a mean time resolution of about 1.1 kyr over the last three glacial-interglacial cycles showed a good correlation with those of δ18O, which suggests that the Southern Ocean played an important role in the variation of the atmospheric CO2 concentration during the last three glacial-interglacial cycles

In-situ measurement of the atmospheric CO concentration at Syowa Station, Antarctica

A high-precision measurement system for the atmospheric CO concentration was developed. With some modifications to a gas chromatograph CO analyzer, instrumental reproducibility of 0.5 ppbv was achieved. This could be sufficient for detection of short-term, seasonal and long-term variations of the atmospheric CO concentration in the Antarctic region. A standard gas system to maintain a consistent calibration scale for the CO measurements was also prepared. The measurement system was installed at Syowa Station in March 2000 and has been maintained up to the present. The first-year\u27s observation showed a clear seasonal cycle of CO concentration

Climatic and atmospheric histories over the past 700,000 years from the Dome Fuji deep ice core, Antarctica

第3回極域科学シンポジウム　横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日（月） 国立国語研究所 ２階講

Accurate chronology of the Dome Fuji deep ice core based on O2/N2 ratio of trapped air

第2回極域科学シンポジウム　氷床コアセッション 11月16日（水） 国立極地研究所 2階大会議

レンゾク フロー シキ シツリョウ ブンセキケイ ヲ モチイタ タイキチュウ メタン ノ タンソ ドウイタイ ヒ ノ コウセイド ソクテイ

メタン(CH_4)濃縮装置とガスクロマトグラフ-燃焼炉-同位体比質量分析計を用いた大気中メタンの炭素同位体比(δ^(13)CH_4)分析システムを開発した.本システムは,100 mlの大気試料(標準状態で0.18μlのCH_4)を用いて0.07‰の再現性でδ^(13)CH_4を分析することが可能である.2002年から2008年にかけて,空気ベースCH4標準ガスのδ^(13)CH_4を繰り返し分析することにより,δ^(13)CH_4分析値の信頼性を確認した.国立極地研究所において大気中のCH_4濃度とδ1^(13)CH_4の日変化を観測し,両者の関係からCH4 濃度の変動原因について情報が得られることを確認した.A high-precision measurement system for the carbon isotope ratio of atmospheric CH4 (δ^(13)CH_4) was developed using a pre-concentration device for CH4 and a gas chromatograph-combustion-isotope ratio mass spectrometer (GC-C-IRMS). The measurement system required 100 mlSTP of an atmospheric air sample, corresponding to approximately 0.18μlSTP of CH_4, to determine the δ^(13)CH_4 value with a reproducibility of 0.07‰. Replicated analyses of a CH_4-in-air standard gas during the period from 2002 to 2008 indicated that the value of δ^(13)CH_4 measured by this system was consistent within the measurement reproducibility. To evaluate the δ^(13)CH_4 measurement system, thus developed, diurnal variations of the atmospheric CH_4 concentration and δ^(13)CH_4 were observed in the northern part of the Tokyo metropolitan area. From the relationship between the CH_4 concentration and δ^(13)CH_4, dominant sources of the observed CH4 fluctuations were identified