This report describes surface water temperature measurements obtained by an autonomous observing instrument “UpTempO” as a part of RV Mirai Arctic cruise in 2014, MR14-05. The UpTempO is a drifting buoy consisting of an underwater thermistor chain, carrying 16 thermistors and 3 pressure sensors, and a surface floating unit for Iridium satellite communication with sensors of sea surface temperature and sea level pressure. Three UpTempOs have been deployed from RV Mirai in the ice-free Chuckhi Plateau. UpTempOs have successfully collected the near-surface temperature data to reveal seasonal change of surface layer heat content during a transition from late summer to mid-winter. The past Mirai expeditions, aiming to reveal the yearlong air-sea heat exchange in the Arctic, has faced difficulties to continue the observation after the surface freezing onsets since RV Mirai is not designed to sufficiently resist pressures from surrounding ice floes. Then, deploying the autonomous instrument such as UpTempO from the ship could make it possible to carry out the prolonged observation even the freezing onset onward.

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海洋観測機器の製作コストやランニングコストを下げるため，プリント基板をエポキシ樹脂に直接固定し，水中や海底で使用するLED光源とチャージポンプを開発，それぞれ耐圧試験や実海域での作動を確認した．LED光源は水深約9200 mの海底に5回投入したが，物理的な破損もLEDの故障も生じなかった．この光源を基に製作したものをトンガ海溝，ホライゾン海淵（水深10800 m）の海底で使用，堆積物直上の様子や底生生物活動のハイビジョン撮影に成功した．チャージポンプには圧力に弱い電解コンデンサが必要なため，樹脂で固定する前にコンデンサをカプセルで覆い，人工的な気泡の中に配置することで圧力から保護する手法を開発した．この手法で樹脂固定して製作したチャージポンプと赤色LEDを，伊平屋北熱水フィールド（水深1053 m）内の人工熱水噴出孔における深海電池の発電実験に供した．結果，LEDの点灯により発電が確認された．エポキシ樹脂は海水，温度，圧力，光などによって劣化することが知られているが，深海環境における強度や透明度の変化についての知見はいまだ乏しいため，長期設置と強度試験による寿命の推定が今後の課題となろう．

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A sediment squeezing tool for use in interstitial water extraction at the onboard laboratory of D/V Chikyu was modified for use at pressures up to 112.3 MPa. A pair of titanium water-gathering plate originally developed by Central Research Institute of Electric Power Industry (CRIEPI) replaces a thin mesh to allow squeezing of sediment at a higher pressure without jamming of sediments. The modified tool endured a longer period of squeezing at high pressure, and yielded greater volume of interstitial water in test experiments. The acquired fluid sample composition showed no major changes even at the pressure of 112.3 MPa, although further tests must be conducted to assess the potential dehydration of clay mineral at high pressures. However, squeezing of sandstone of approximately 12％ porosity yielded no interstitial water at all, showing system limitations for low-porosity samples. The improved tool and the data from these experiments are expected to be useful when low-porosity sediments from a deep hole are obtained.

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