奈良岡 浩

PAHsに関する最新の研究の提言として、炭素・水素安定同位体比を用いた研究の可能性について論述している。

We established a separation procedure of sedimentary straight-chain and cyclic fatty acids by urea adduction to facilitate GC/C/IRMS analysis. The procedure involves a mixing of the monocarboxylic methyl ester fraction with 15% (w/v) urea in MeOH (200μl), ethyl acetate (300μl) and n-pentane (500μl) at room temperature. After drying the solvents under N₂ flow, the non-adduct fraction (cyclic compounds) is washed with n-hexane (3×1.5ml) (mean recovery: 91%). The residue is dissolved in water (4ml) and the adduct fraction (straight-chain compounds) is subsequently extracted with n-hexane/ether (9:1v/v; 3×1.5ml) (mean recovery: 87%). The separation we apply here was confirmed not to affect the isotopic composition of the straight-chain and the cyclic fatty acids.

Compound-specific isotope analysis has been developed recently using gas chromatography/combustion/mass spectrometry (GC/C/IRMS). This paper summarizes principles and progress of GC/C/IRMS, and reviews recent some important works using this new method. GC/C/IRMS is a novel tool for (i) biomarker analysis in sediments and living matter, (ii) paleoenvironment analysis including reconstruction of ancient biogeochemical processes, (iii) geochemical cycle study of organic compounds in a terrestrial-marine system, (iv) evaluation of maturity and diagenesis of organic matter including petroleum formation, (v) ecological analysis, (vi) evaluation of anthropologenic pollution in environment, (vii) detection of extraterrestrial organic compounds and the formation mechanism study, (viii) tracer studies in environment.

An isolation procedure of microgram amounts of long-chain n-alkanes from crude oil using molecular sieve was examined for its applicability to stable carbon isotope analysis by gas chromatography/isotope ratio mass spectrometry (GC/IRMS).<br>The procedure examined is as follows: molecular sieve (type 5A, 200 mg) in 1 ml of isooctane solvent are mixed with a saturated hydrocarbon fraction extracted from an appropriate amount (approx. 20 mg) of crude oil and stayed at room temperatures for more than 3 hours. Long-chain n-alkanes are isolated by extraction with n-hexane after dissolution of the resulting molecular sieve with 47% hydrofluoric acid solution. The recoveries were 90±6% for C₁₅~C₃₄ n-alkanes when their total amounts applied do not exceed 1.4 mg. No effect of the isolation procedure on carbon isotope ratios of n-alkanes was observed.

Over 2400 pieces were collected by the Asuka wintering party of the 29th Japanese Antarctic Research Expedition (JARE-29,1987-89) on the bare icefields around the S&emptyv;r Rondane Mountains in Queen Maud Land, East Antarctica. The Asuka party searched almost all of the bare icefields around the mountains in the 1987-88 and 1988-89 field seasons. About 110 pieces (Asuka-87) of meteorites were collected on the bare ice around Mt. Balchen in the eastern part of the mountains in January and February 1988. In the first reconnaissance, about 240 pieces of meteorites (also Asuka-87) were recovered from the Nansenisen Icefield in February and March 1988. The Asuka-88 meteorites, over 2100 pieces, were found during the systematic search of this icefield during November 1988 and January 1989. The specimens were named officially the Asuka (A)-87001 to A-87352,and A-880001 to A-882124,in order of discovery. The Asuka-87 and Asuka-88 meteorite collections were filed as the National Institute of Polar Research (NIPR) meteorites with details of date of find, weight, dimensions and comments. According to the initial processing, the Asuka-87 meteorites comprise one iron, one stony-iron, 9 achondrites, 3 carbonaceous chondrites and over 300 ordinary chondrites, the total weight being 120kg. The largest specimen in the Asuka-87 collections is an LL-group chondrite of about 46kg. The Asuka-88 meteorites comprise 7 irons, 5 stony-irons, over 50 achondrites, 31 carbonaceous chondrites and over 2000 ordinary chondirtes. The total weight is about 400kg. Two specimens in the Asuka-88 collection were tentatively identified as a very coarse-grained and unbrecciated gabbroic meteorite and an olivine-fassaite-plagioclase achondrite with crystalline texture.

第29次南極地域観測隊のあすか越冬隊はセールロンダーネ山地周辺の裸氷域における隕石探査の際に, 同じ裸氷上において汚れ層を発見採集した。汚れ層は山地周辺の裸氷域に多く存在していたが, ナンセン氷原においてその存在数が多いことが特徴であった。ろ過された試料は大部分が火山ガラスであり, 粒径や色から予備的に5種類に区分することができた。EPMA化学分析によると, 火山ガラスのSiO_2は50-70%に分布し, SiO_2-(Na_2O+K_2O)比から分析した火山ガラスの大部分は非アルカリ質であることが明らかとなった。Dirt bands were observed on the surface of the bare ice fields around the SΦr Rondane Mountains during the search for Antarctic meteorites in 1988-1989. Dirt bands were commonly distributed on the bare ice around the mountains, especially in Nansenisen. Dirt bands were collected and filtered after melting. Microscopic observation revealed that dust materials were composed mainly of volcanic glass shards. Five types of volcanic ash were preliminarily clarified with respect to the colors (black, dark gray, gray, reddish brown and pale gray) and sizes (5-50μm) of the particles. The EPMA chemical analyses indicated that the volcanic glass shards contained 50-70% SiO_2 and belonged to the nonalkaline region considering from the SiO_2-(Na_2O+K_2O) diagram.

第29次南極地域観測隊のあすか越冬隊は, セールロンダーネ山地周辺の裸氷域において1988年1月から1989年1月までの間に5回にわたる隕石探査を実施した。その結果, 主に3つの裸氷域から約2000個の隕石を発見, 採集した。総重量はおそらく400kgを越えるであろう。これらの隕石はAsuka-88およびAsuka-89隕石と命名される予定である。予備的な分類によると普通コンドライトが最も多く, 隕鉄や石鉄隕石, エコンドライト, 炭素質コンドライトおよび珍しい種類の隕石も含まれている。今回採集した最大の隕石は46kgのLLタイプのコンドライトである。A systematic search for Antarctic meteorites was carried out by the Asuka winter party of the 29th Japanese Antarctic Research Expedition on the bare ice field around the Sφr Rondane Mountains in the 1987-1988 and 1988-1989 field seasons. More than 2000 meteorite specimens as individuals or fragments were collected from three main areas around the mountains. Their total weight could be more than 400kg. The collection of these meteorites, which will be named officially Asuka-87 and Asuka-88 meteorites, consist of various types of meteorites, such as irons, stony-irons, chondrites, achondrites and carbonaceous chondrites, including some unique specimens. The largest specimen in this collection is a 46kg LL type ordinary chondrite.

第29次南極地域観測隊の夏季地学調査隊(10名編成)は, 1988年1月6日から2月3日までの29日間, セールロンダーネ山地の中の未調査域である東部地域(バルヒェン地域)を中心に, 地質・地形・測地・隕石の4分野にわたる調査を実施した。またこの調査に先立って, 測地部門の2名は, 1987年12月21日と22日に山地東部および中部地域においてピラタス機による航空写真撮影を行った。好天に恵まれ, 大きな事故のなかったことも幸いして, 各部門ともほぼ計画どおりの調査・作業を終えることができた。本報告では, 今回の調査における設営面を含めた行動の概要を中心に記述し, 併せて各部門の成果も簡単に紹介する。The ten-man summer field party of the 29th Japanese Antarctic Research Expedition (JARE-29) carried out geological, geomorphological and geodetic field work and a meteorite search in the S&emptyv;r Rondane Mountains, mainly east of Byrdbreen (71°40'-72°15'S, 26°30'-28°E) from January 6 to February 3,1988 (29 days). In addition, on December 21 and 22,1987,two surveyors from our party took aerophotographs in the eastern and central parts of the mountains, using a "Pilatus Porter" plane. Being favored by good weather and no serious accident, we were able to complete most of the work that we had planned. This paper is a description of the field operation including logistics and a brief report on the geological, geomorphological and geodetic field work, meteorite search and aerophotography.