Variation of Suspended Particles in the Bottom Layer of the East China Sea with Data from Seafloor Observatory

Abstract

The in situ scattering and transmissometry laser (LISST-100X), equipped with an acoustic wave and current (AWAC) meter and conductivity, temperature, and depth (CTD) instruments over the seabed in the East China Sea, was used to monitor the variation in suspended particles in the bottom sea layer, including particle size distribution (PSD) and volume concentration. The power law approximation was tested to describe the variability in PSD based on the field data. The results show that the power law was robust in processing continuous data, accompanied with the same optimal reference particle size (~63 μm) and little change in the corresponding exponent (~3.4) in both periods. Suspended particles were divided into three types: macroflocs (>133 μm), microflocs (36–133 μm), and single grains (<36 μm). Particle sizes were coarse during the two seasons, with macroflocs representing more than 60% of all the suspended particles, especially in February, when the particle size spectra were usually open-ended. Results from the harmonic analysis method indicate that tidal-induced resuspension and advection are the major reasons for the diurnal dynamics of sediments. Due to the tidal asymmetry in the region, we only found one mode in volume concentration at the moment of maximum velocity. However, the ratios of macroflocs were bimodal, with maximum floods and ebbs in one tidal cycle in February, when the higher mode at the maximum ebbs may be contributed to by the flocculation of finer particles considering the decreasing ratios of finer particles. Due to the enhanced stratification and the clean barrier built up by the Taiwan Warm Current in the southeast corner, the significant daily variation in suspended particles observed in February weakened in September. The influence of waves was uncertain, although the correlation coefficient between significant wave height and volume concentration was about 64% in February.

An Object Model for Seafloor Observatory Sensor Control in the East China Sea

“…Citing the observatory operation period between February 2018 and August 2018 as an instance, the prototype system acquired 400 thousand pieces of velocity data from AWAC sensor as well as 2 million and over 1.7 million pieces of data, respectively, from LISST-100X sensor and SBE 26 sensor. Observations of the aforementioned three sensors were also used to monitor the variation of suspended particles in the bottom waters in a case study [36]. To be specific, two initial periods of the observatory operation cycles, in 2015 and 2018, were selected to study the diurnal and seasonal variations including particle size distribution (PSD) and volume concentration (Figure 8).…”

Comparative Assessment of Fluvial Suspended Sediment Concentration Analysis Methods

“…Although the monitoring of PSD is usually only of secondary importance, the information content of changes over time in PSD is not negligible. For instance, it may indicate a new source of fluvial sediment and the variation in PSD during flood events [59,60] is also required for the modelling of sediment transport processes. The expeditionary cross-sectional measurements help to explore the spatial distribution of the SSC which is not negligible when selecting the position of a fixed sensor.…”

Optimized Classification of Suspended Particles in Seawater by Dense Sampling of Polarized Light Pulses

“…While the ocean continues to create huge benefits for modern society, its own ecology has also encountered great challenges to human life and production [2][3][4]. As an important and essential component in seawater, the suspended particles significantly influence the optical properties of seawater, as well as the marine ecological environment [5,6]. For example, certain harmful types of microalgae rapidly cause algae blooms in a short period, which is a threat to marine organisms [7][8][9].…”