Study On Long-Term Turbulence Monitoring Technique And Its Application In Deep-Sea Mixing Research

In the ocean, energy of meso-scale or large-scale motions eventually cascade tosmall scale motions and dissipated as heat through micro-scale turbulence andassociated mixing. Ocean turbulent mixing, not only plays an important role intransporting momentum, mass and nutrient, but also is a key factor in modifying andmaintaining meso-scale to large-scale kinematic motions in the ocean, such as thethermohaline circulation. Therefore, quantifying the ocean turbulence and mixingintensity, generally represented by dissipation rate of turbulent kinematic energy(TKE), is essentially important, and it is usually fulfilled by in situmeasurement.To reach the requirement of long-term observation of ocean turbulence andmixing, this work focuses on measuring techniques of deep-sea turbulence and mixing.Configuration and manufacture of shear probe and corresponding calibration methodwas first accomplished. In order to promote ocean turbulence measuring techniques inChina, enlarge our knowledge about long-term mixing variability in the abyssal ocean,and improve the understanding of deep ocean kinematic motions and associatedmechanism, the Moored Turbulence Measuring Instrument (MTMI) was developedand then integrated it to a mooring system in order to measure ocean turbulence andmixing long-termly, continuously and steadily. Based on comparative examination ina tank, and ocean field experiments in coastal sea and the deep South China Sea(SCS), the MTMI was validated to work well and could measure ocean turbulenceand mixing effectively. The dissipation rates estimated by MTMI agreed well withthat by ADV and MSS60Profiler.The MTMI was first designed and developed in China, and its maximumworking depth is4000m. The MTMI was intended for monitoring the deep-seaturbulence and mixing process long-termly, continuously and steadily. Its externalmechanical and internal electronically design was introduced in detail, and laboratoryexperiment showed that MTMI has a noise level as small as the MSS60Profiler.An effective calibration method was introduced, and then a suitable instrument toshear probe sensitivity calibration was designed, developed and applied, Thesubsequent calibration experiment indicated that the calibration system was effective.Two methods for estimating dissipation rate of TKE were summarized, whichwere based on the diffusive and inertial-convective subrange of turbulence kinematicenergy spectrum, respectively. A compensation method, which could efficaciously eliminate the contamination signal induced by the observing platform oscillations,was proposed, applied and validated in the ocean field experiment.A long-term mooring system was designed and developed in this work formonitoring ocean mixing process continuously and steadily. The comparativeexperiment in coastal region indicated that the mooring system worked well and theobserved dissipation rate of TKE by MTMI agreed well with that by MSS60profiler.Furthermore, an observing experiment aiming to examine the long-term oceanturbulence and mixing process was conducted in the SCS. The mooring systemworked well and steadily in the abyssal ocean with obtaining batch data, whichsignificantly facilitate the effort in understanding the abyssal mixing process and deepcirculation dynamics.