The Oceanic Temperature Variance near the Bottom of the Southern Mariana Trench

In December 2016, an ocean-bottom seismometers (OBS) array was deployed across the southern Mariana Trench. The observation stations were aligned in the SE-NW direction from 140º 55'E, 10º 43' N to 142º 43'E, 12º 42'N, passing the Challenger Deep. At each station, one or two high-sensitivity temperature loggers were attached upon OBS to record the temperature at about 0.5 m above the sea floor with sampling rate from 1 to 16 Hz. Within the station depth range from 1,665 to 7,520 m, it was found that the bottom temperature decreases with increasing depth until at depth around 4,800 m. At stations of greater depth, the temperature was then found to increase with a rate of 11.95 mK/MPa, which is consistent with the estimated adiabatic pressure derivative of temperature in abyssal ocean. Moreover, the temperature fluctuation (root mean square) decreases from 4.5 × 10-2 to 7.6 × 10-4 ºC with increasing depth. In the temperature spectrum analysis, the diurnal and semidiurnal tides were well identified in all stations, and their relationship with depth is being investigated.