Neodenticula kamtschatica (Zabelina) Akiba and Yanagisawa, an extinct late Neogene planktonic diatom has been very first observed in the middle Quaternary submarine deposit in the northeastern North Atlantic. The species has been considered for a long time to be limited within the high-to-middle latitudinal North Pacific. In the North Pacific region, this species appeared in the geologic record approx. at 6.4 Ma as “first common occurrence”, and became extinct at 2.65 Ma occurrence. On the other hand, no record of the Atlantic specimens has been presented. Thus, its fossil imprint in the North Atlantic of our investigation implies that at least single episode of the trans-ocean migration (=floral interchange of North Pacific and North Atlantic via the Arctic) of the species occurred during the latest Miocene through Pliocene epoch, considering the tectonic and hydrographic backgrounds such as the initial opening of the Bering Strait (5.5 Ma~) and the final closure of the Panamanian Isthmus (~2.76 Ma). Our evidence is significant to give a further insight on the relationship between the process to establish biogeography of planktonic micro-organisms and the paleoenvironmental change in the Northtern Hemisphere.

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The results of research on marine contamination in the regional areas (the Kara and Barents Seas) in the Arctic Ocean were reported at the Journal of the Japan Society for Marine Survey and Technology, Vol. 15(2).
In the present research, the authors carried out flow analysis and concentration analysis of radioactive materials in the whole region of the Arctic Ocean, based on the release scenario.
A numerical hybrid box model was developed. The results obtained agreed with the observed features in many respects. Especially, stream flows in Norwegian, Barents Sea and Kara Sea showed fairly realistic features. The flow field in the surface layer in the central Arctic Ocean agreed with that in previously known data.
In nuclide dispersion model, nuclide decay, mixing, scavenging and interaction between seawater and bottom sediment layers were taken into consideration in order to improve accuracy of the dosage estimate.
Based on nuclide (Pu-239 and Cs-137) release scenarios, the whole Arctic Ocean was subjected to analysis.
A clear difference was recognized in the diffusion distribution according to the properties of nuclides, and concentration in the sediment is one or two orders higher than that in the seawater when the distribution factor of K_d value is large as in Pu-239.

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地質年代決定精度の高さで注目されている石灰質ナンノ化石層序に基づいて，パナマ地峡の成立と地球の寒冷化との関連について概説した．高緯度海域—北極海域での石灰質ナンノ化石調査結果は，2.75 Maのパナマ地峡の成立とともに北極海域の急激な氷床拡大が発生したことを示唆し，そのタイミングで，寒流系種Coccolithus pelagicusの現在の分布様式が確立する．また，ベーリング海を介した太平洋海水の北極海，東グリーンランド海への流入も，このタイミングで発生し，いわゆるQuaternary-style climateが2.75 Maに開始したことを示唆する．

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第四紀の始まりの改定に関する諸問題を石灰質ナンノ化石層序の観点から総括した．微化石による地質年代決定精度の向上は，温暖化／寒冷化の問題を汎世界的な詳細な対比に基づいて議論することを可能にしたばかりでなく，寒冷化と第四紀の始まりに関する問題を極めて具体的に明らかにすることを可能にした．結果として，汎世界的な寒冷化は，その直前の温暖期に引き続く事件であり，いずれもパナマ地峡の成立による海洋システムの変化が“Climate Crash”を引き起こし，石灰質ナンノプランクトンや浮遊性有孔虫の地理分布の完成と現在の海洋システム，すなわち“Quaternary style Climate”が成立したことを示している．その観点からすると，第四紀の始まりを， Climate Crashに最も近いジェラシアン階基底で第四紀の始まりを定義することは，極めて妥当であると言える．

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Activities by man-kind are limited in the Arctic, high latitude place more than North 66°33′, because of its hostile environment. Only military base, scientific observation station, resources production sites and ethnic community exist. Oil and gas E&P activities have been made in limited area such as Timan-Pechora area and Yamal peninsula in Russia, Mackenzie delta in Canada, North-Lope in Alaska and Barents Sea. Especially for offshore exploration activities in Arctic, it is highly affected by sea ice. As observed by satellite image in Arctic, no or less ice affected areas are defined such as Barents Sea and Norwegian Sea. Ice covered area in the Arctic and near of the Arctic requires serious counter measures against sea ice for putting oil and gas exploration into execution. In this lecture, recent oil and gas exploration activities in the ice covered Arctic offshore area are reviewed. In addition, history and challenge for future on new exploration license area in northeast offshore Greenland, where Greenland Petroleum Development Ltd. (GPX), Japanese Joint Venture Company established by JOGMEC, INPEX, JX, JAPEX and MOECO, are discussed. Although increase of exploration activities in Arctic is expected in the days to come, there are several technical challenges and difficulties for matter of environmental protection. It is an important mission for E&P companies to overcome those challenges and difficulties and to promote frontier oil and gas exploration in the Arctic area.

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