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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A high power LED light and a charge pump with a LED indicator fixed with epoxy resin were developed in order to demonstrate reducing the cost of the deep-sea instruments. The LED light was brought at ca. 9200 m depth for five times. The light had no deformation and no crackes, and it worked after the deployents. It was also used to record the bottom at Tonga trench, where the world second deepest site (10800 m), and the video recording was succeeded. The charge pump was applied to confirm the electricity generation at the artificial hydrothermal vent in Iheya North hydrothermal field (1053 m). To protect electrolytic capacitors from pressure, they insulated from the resin with medicine capsules before fixing. The LED indicator was lighted on when the electrode of the fuel cell battery was inserted into the hydrothermal water. However, the degradation process of the epoxy resin under the deep-sea environments attributing high pressure and low temperature environments is still unknown. The guaranteed time of the instruments constructed with epoxy resin should be investigated throughout long term in situ exposure and the strength tests.

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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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