Field observation at South China Sea

The observation site is located on the northern slope of the South China Sea (20.08°N, 115.2°E), with a water depth of 659 m. A bottom landing frame was deployed at the site from 13:00 on August 20, 2020 to 17:00 on September 2, with an observation duration of 316 h. The frame was equipped with velocity profilers (75 kHz-ADCP and 2 MHz-ADCP) and an Acoustic Doppler velocimetry (ADV). The 75 kHz-ADCP measured full-depth velocity profiles with data interval of 1 min (75kHzADCP.mat). The 2 MHz-ADCP measured fine-scale (vertical resolution: 0.007 m) bottom boundary layer velocity profiles with data interval of 1 min (2MHzADCP.mat). The ADV measured velocity at 0.6 mab with data interval of 1 min (ADV.mat). Owing to insufficient battery power, 12 days of effective data were obtained by the ADV during the observation period. The bottom shear stress was calculated using covariance method (tau_adv_3hz.mat) and logarithmic velocity profile fitting method (tau_log.mat) with data interval of 1 min, 10 min, respectively. The inversion of SSC (SSC.mat) was based on the echo intensity of 2 MHz-ADCP with data interval of 1 min. At the last stage of observation, 16 cast profile measurements were carried out over 27 h (2020.09.01, 08:00:00 to 2020.09.02, 10:00:00) (Figure 1c) using a backscattering meter (Wetlabs BB) and an optical laser diffraction instrument (LISST-100X). Wetlabs BB measured the backscattering intensity profiles (Wetlabs BB.mat) and LISST measured the SPM volume concentration profiles (Lisst.mat).