Watermass properties and deep currents in the northern Yap Trench observed by the Submersible Jiaolong system

According to the field experiment implemented by the cruise with the observation by Submersible Jiaolong in No. 37 and 38 Cruise of China Ocean Mineral Resources R&D Association, detailed investigations about northern Yap Trench, including the water properties, bottom currents, turbulent mixing were presented. The deep watermass properties indicate that the deep water originates from East Mariana Basin (EMB) and East Caroline Basin (ECB), as part of the west propagating Lower Circumpolar Deep Water (LCPW). The volume transport results further prove it. The variability of salinity, potential temperature presents semidiurnal variations. The isothermal level variations indicate the existence of semidiurnal internal tide. The phase of salinity lags about 12 h than that of potential temperature. The salinity serves as the compensation on the isopycnal. The bottom currents mainly consist of the low frequency motions, near inertial motions, semidiurnal and diurnal motions. The strong semidiurnal motions derived by Lanczos band-pass filter and reconstructed current indicate the existence of internal tide in the western side of Yap Trench. Enhanced turbulent mixing is observed at the central part and slope of the northern Yap Trench, and weakens the stratification. The strong mixing seems to be caused by internal tides dissipation. Though mesoscale eddies are active around the Yap Trench, the bottom currents are not directly associated with mesoscale eddies.