The outbreak of crown-of-thorns starfish has seriously threatened the ecological health of coral reefs, and the supplement of nutrients in seawater may be a key factor leading to the outbreak of starfish. Sandy sediments play a key role in regulating the nutrient concentration and structure in coral reefs. Therefore, crown-of-thorns starfish and sandy sediments were incubated using flow-through reactor, to analyze the effects of crown-of-thorns starfish excretion and dead body degradation on nutrient concentration and structure, and to explore the role of sandy sediments under activities of crown-of-thorns starfish. The results were as followed: (1) crown-of-thorns starfish excreted dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) at rates of (83.55±4.74) μmol/(ind.·h) and (2.53±0.03) μmol/(ind.·h), respectively, which maight provide nutritional conditions for the continuous outbreak of starfish; (2) sandy sediments could regulate the nutrient concentration changed by the excretion of starfish, about 70.7% of DIN and 91.4% of DIP were trapped in the sediments, but the increase of DIN/DIP caused by nutrient exchange at the sediment-seawater interface may be detrimental to coral growth; (3) the degradation of starfish organisms could promote the release of nutrients at the sediment-seawater interface. Based on the density of starfish, the released nutrients could cause the concentrations of DIN and DIP in the overlying water to increase by 0.32 μmol/L and 0.01 μmol/L, respectively, which maight promote the rapid growth of macroalgae and hinder the self-restoration of corals.

The temporal and spatial variation characteristics and influencing factors of euphotic depth and primary productivity in the Zhanjiang Bay were studied by applying voyage data of four seasons from 2016 to 2017．The results showed that the average value of euphotic depth was (6.95±3.17) m, and the spatial variations were more obvious than the seasonal variations. There was a significant positive correlation between K_d (PAR) and turbidity, as the R² of established linear regression model was 0.73 (p<0.01), indicating that suspended particles on euphotic depth was the dominant attenuation factor in the Zhanjiang Bay. The average value of primary productivity obtained by VGPM model was (639.53±427.95) mg/(m²·d), and its temporal and spatial characteristics were basically consistent with euphotic depth, which mean euphotic depth explained the temporal and spatial distribution pattern of primary productivity better than chlorophyll a concentration.

In order to understand the distribution characteristics, relationships and diffusion fluxes of nutrients and metal elements across the sediment-water interface, we investigated the vertical profiles of nutrients and metal elements through the diffusive gradient in thin-films (DGT) technology in Shenzhen Bay (SZB) and Maozhou River (MZR). The two-dimensional high-resolution available sulfur (DGT-labile S) distributions were also synchronously measured. The results showed that the mean concentrations of ${\rm{NH}}_4^+ $, P and S²⁻ and heavy metals of Cd, Co, Cu, Fe, Ni, Pb and Zn in porewater of MZR were significantly higher than those in the overlying water and the SZB, except for ${\rm{NO}}_3^- $ and Mo. The pollution degree of nutrients and metal elements in porewater of MZR was generally higher than that in SZB, but the pollutants of nutrients and metal elements in SZB were more than those in MZR. The spatial distribution of DGT-labile S in MZR indicated the distinguish bioturbation-induced tubes, which enhanced the spatial heterogeneity and led the increasing of solute concentrations with sediment depths. The diffusion fluxes of nutrients and metal elements ranged from −0.27 μg/(cm²·d) to 0.0065 μg/(cm²·d) in SZB, and from −0.061μg/(cm²·d) to 0.069 μg/(cm²·d) in MZR.

Atmospheric correction (AC) is the basis and premise of quantitative remote sensing of water column. The effects of different AC models on water depth inversion from the four aspects of AC model, AC model parameters, water component differences, and water depth inversion band combination are discussed in this paper. The research uses 6S, FLAASH, ACOLITE and QUAC four AC models, select continental, marine and urban aerosol patterns, and the shallow waters around the northwest side of Oahu Island and Shemya Island are used as the study area of clean water, while the shallow waters around Liaodong Shoal and Penang Strait are used as the study area of turbid water. AC is performed based on Landsat-8 multispectral images, and eight wavebands are used for bathymetric remote sensing inversion. The results show that: (1) all the four AC models can weaken the atmospheric influence on the water signal to some extent; the correction results of different models are somewhat different depending on the parameter selection and the components of the water column. And the peak reflectance of the two types of water column occurs in the blue and green bands, respectively. (2) The 6S model is more robust, and the bathymetric inversion results of this model are less volatile than the rest of the models due to the changes in the components of the water column. The water depth inversion results of the two aerosol models of the FLAASH have more obvious differences in turbid water, and the difference of MRE in shallow water of Liaodong Shoal is 7.9%; the ACOLITE model is significantly influenced by the water column type and has superiority and stability for turbid water, and the MRE is 5.6% lower than that of FLAASH. (3) The accuracy of multi-band water depth inversion is generally better than that of single-band, but there is no significant correlation between the accuracy of inversion and however, there is no significant correlation between the inversion accuracy and the number of bands; the combination of bathymetric inversion bands has different sensitivity to different study areas, the inversion accuracy of the three-band model is better in clean water, and the inversion accuracy of the four-band model is optimal in turbid water, and the MRE is reduced by 5.6% compared with the three-band model.

Estuarine morphologies play an important role on tidal asymmetry. A two-dimensional numerical model is established with the Humber Estuary, UK as a reference site. A series of simulations are designed to examine the effects of the estuary cross-section shape, planform and convergence on the development of tidal asymmetry, whilst maintaining the same tidal prism. Model results show that deeper channels result in the lag and enhancement of phase difference whilst shallower channels result in a decline in the maximum ebb-tide velocity and longer period of ebb tide, and the estuary tends to be flood-dominated; narrow tidal flat tends to favour ebb dominance while broad tidal flat tends to favour flood dominance. Flood dominance is strongest in the convergent and long estuary. In addition, narrowing the estuary width will enhance the residual flow velocity of the main channel but weaken the residual flow velocity of the tidal flat. With the increase in estuary convergence, the residual flow velocity of the main channel increases but decreases on the tidal flat, and strengthen the flood dominance of the tidal flat. This paper further improves the research on the influence of estuary landforms on tidal asymmetry, which has certain guiding significance for reclamation and coastal engineering.

Sea ice thickness is one of the main sea ice parameters. Automatic recognition of sea ice thickness in video is a significant component of sea ice parameters extraction. In this paper, the machine vision method based on Hough transform is used to recognize the surface contour of sea ice, so as to obtain the sea ice thickness parameters. According to the characteristics of sea ice image, the overall recognition process is divide into image edge recognition, approximate line segment recognition and sea ice contour segment group recognition. In the process of line segment identification, three parameters of line segment group including angle, length and spacing are established based on the geometric characteristics of sea ice. In order to verify the reliability of the method, this method is applied to analysis the field survey data of Xuelong icebreaker’s eighth Arctic expedition. The results show that the three parameters have the optimal threshold value. When it is lower than this value, increasing the threshold will increase the effective recognition rate; when it is higher than this value, increasing the threshold will increase the false recognition rate. The ice thickness recognition rate can reach more than 90% by using the optimal threshold. Therefore, the ice thickness identification method based on Hough transform can realize the real-time monitoring of sea ice thickness.

The change of fluvial suspended sediment concentration (SSC) to the sea directly reflects the effects of riverine anthropogenic activities and natural force. Based on long-term hydrological data at Tarbert Landing Station of the Mississippi River (MR), statistical means, such as percentile method and Mann-Kendall method are used to detect change process of SSC from the MR entering the Gulf of Mexico in recent 40 years, and associated possible influencing factors. The results show that: (1) SSC from the MR entering the Gulf of Mexico is characterized by a staged decline from 1976 to 2015, in the first stage from 1976 to 1987, the SSC is relatively high with an average value of 0.33 kg/m³; in the second stage from 1988 to 2015, the SSC is much lower with a mean value of 0.25 kg/m³. (2) The relationship between daily SSC and runoff of MR follows Gaussian distribution. Compared with the first stage (1976−1987), the rating curve between SSC and runoff in the second stage (1988−2015) is relatively flat, when the number of high daily SSC event over 0.60 kg/m³ reduces significantly. SSC increases with the runoff in low-action flows and reaches the maximum when the runoff approaches 20 000 m³/s, but decreases with the runoff thereafter. The rating curve between monthly SSC and water discharge of the MR exhibits “double-loop” shape during 1976−1987, but presents clockwise “single loop” with “sediment before water” during 1988−2015. (3) Flood diversion project construction and soil conservation measures dominate the fluvial SSC from the MR into the Gulf of Mexico. The construction of flood diversion engineering reduces the sediment source along the river channel, and the soil conservation measures repress the land erosion, which have combined to keep the SSC at a relatively low level. In addition, SSC in the MR presents minor response to extreme hydrological events.

The Yellow Sea presents unique topographic conditions, and the tidal wave movement in this area has unique characteristics. In this paper, Geostationary Ocean Color Imager (GOCI) inversion and Oregon State University (OSU) tidal current model are used to obtain the sea surface currents field in the Yellow Sea. Based on the unique tidal wave system in the sea area, the tidal wave interference area is proposed and identified, and then the currents field of GOCI inversion is extracted. And partition of two kinds of trend data usability evaluation, through the validation of the drifting buoy data evaluation. The results show that the sea surface currents field obtained by GOCI inversion and OSU tidal current model has a certain degree of reliability. The AME value of sea surface currents field velocity obtained by GOCI inversion is 0.77, and that obtained by OSU tidal model is 0.49. On the whole, the currents field data obtained by GOCI inversion and OSU tide model are reliable to a certain extent. In the central area of the Yellow Sea near the tidal wave interference area, the consistency between GOCI tidal currents data and OSU tidal currents data is better than that of OSU tidal currents data, and their AAE values are 48.45° and 63.10°, respectively. In the coastal area of the Yellow Sea far from the tidal wave interference area, the consistency between the OSU tidal currents data and the measured data is better than that of the GOCI tidal currents data in terms of velocity magnitude and direction.

The loading tides in the South China Sea and adjacent straits are calculated by means of the Green’s function method based on a high-resolution regional ocean tide model for the South China Sea, the DTU10 global ocean tide model, and the Gutenberg-Bullen A Earth model. The results show that the maximum amplitude of M₂ vertical displacement loading (VDL) tide exceeding 18 mm appears in the Taiwan Strait; the second maximum exceeding 14 mm appears off the north-west coast of Kalimantan. The maximum amplitudes of the K₁ and O₁ VDL tides, exceeding 18 mm and 14 mm respectively, appear near the southern South China Sea; the second maximum exceeding 8 mm, appears in the Beibu Gulf. The distribution patterns of self-attraction and loading (SAL) tides are very similar to those of VDL tides in that the SAL tides have amplitudes about 1.2 times to 1.7 times the corresponding VDL tides and have phases basically opposite to corresponding VDL tides. The maximum amplitude of M₂ SAL tide also appears in the Taiwan Strait and off the north-west coast of Kalimantan, with a magnitude exceeding 24 mm and 18 mm respectively.

Tsunami is one of the disasters that seriously endanger the safety of human life and property among natural disasters. In the context of global warming and increasing economic development, more and more people, infrastructure and wealth are exposed to tsunami disasters, greatly increasing the risk and vulnerability of personal and property safety in coastal and delta areas. The analysis of temporal and spatial variation of historical tsunami disasters can help us understand the evolutionary laws of tsunami disasters, and provides a useful reference for more accurate disaster warning, disaster prevention and control, etc. A study on the temporal and spatial variation of global tsunami by extracting complete and homogeneous data is conducted in this paper. The results show that: (1) for 0.1 m≤RH<0.5 m, 0.5 m≤RH<1 m, 1 m≤RH<5 m, 5 m≤RH<10 m, 10 m≤RH<20 m and 20 m≤RH intervals, the tsunami catalogues can be considered complete since 1963, 1940, 1950, 1946, 1922 and 1885 respectively; (2) from time changes it can be seen that there is a certain increasing trend in the occurrence of global tsunamis. Approximately 7 more wave runup events are observed every year. At the same time, in different intensity intervals, the frequency of tsunamis has different changes. In the intervals of 0.1 m≤RH<0.5 m, 0.5 m≤RH<1 m, and 1 m≤RH<5 m, the tsunami have a certain periodicity, showing two obvious peaks, but when the RH is greater than 5 m, the periodicity of the tsunami is no longer obvious, and it shows a clear increasing trend at this time; (3) there is a certain increasing trend in the occurrence of tsunamis in East Asia, South Pacific, South America, and Indian Ocean. However, in North America, there is a decreasing trend, and there is no significant change in Europe; (4) except for North America, tsunami events in other regions show a good power law distribution relationship, indicating that the occurrence of tsunamis follows certain self-organized critical behavior. In comparison, small tsunami events are more likely to occur in Europe, while tsunami events in East Asia and the Indian Ocean are more prone to various types of tsunami events, of which large tsunami events occupy a larger portion.