Samples of Jumbo flying squid (Dosidicus gigas) were collected from Chinese squid jigging vessels in the high seas of Ecuador, Peru and Chile in the southeast Pacific Ocean in 2015 and 2017. The trace elements in the eye lenses of D. gigas were measured to study the geographical differences and their relationship with sea surface temperature. The results showed that elements such as Mg²⁵, Ni⁶⁰, Cu⁶³, Sr⁸⁸ and Ba¹³⁷ in the peripheral part of eye lenses of D. gigas in the high seas of Ecuador, Peru and Chile were significant difference, while there were no significant differences between each two sea areas in the elements of Na²³, Al²⁷, Si²⁹, P³¹, Ca⁴³, Mn⁵⁵, Zn⁶⁶ and Pb. Except for Sr⁸⁸, Ba¹³⁷, Fe⁵⁷ and Ni⁶⁰, which showed significantly linear negative correlations with SST (p<0.05), there were no significant correlations with SST in the other elements (p>0.05). Sr⁸⁸, Ba¹³⁷, Fe⁵⁷ and Ni⁶⁰ could be regarded as indicator elements of the ambient temperature of D. gigas, and Ba¹³⁷ could also be regarded as indicator element of the water depth and upwelling. Consequently, trace elements in eye lenses could be used to reconstruct the habitat environment of cephalopod.

There is little information about the relationship between aerobic anoxygenic photoheterotrophic bacteria (AAPB) and upwelling. In this work, the response of AAPB to upwelling in the southern Taiwan Strait was examined, using the “Time-series observation-based cyanobacteria-calibrated InfraRed Epifluorescence Microscopy, TIREM”. The results showed that in the initial stage of upwelling, the abundances of AAPB and total heterotrophic bacteria were low; with the development, their abundances both increased and reached the highest value at the mature stage of upwelling; notably, when the upwelling declined, they began to decrease. During the developmental process of upwelling, AAPB abundance was positively correlated with chlorophyll a concentration in a certain range, and limited by low phosphorus concentration, while total heterotrophic bacteria abundance was positively correlated with nitrogen, phosphorus and silicon nutrients concentration, suggesting that dissolved organic carbon released by phytoplankton and phosphorus limitation might play a more direct and important role in AAPB, while nutrients probably acted as an important role in the response of total heterotrophic bacteria to upwelling. This study will help to better understand the unique role of AAPB in the biogeochemical cycle of carbon and other biogenic elements.

Dimethylsulfoniopropionate (DMSP) is one of the most abundant organic sulfur molecules on earth, and plays an important role in global sulfur cycle and climate regulation. DMSP is the principal precursor of dimethyl sulfide (DMS), which can be degraded through many ways in the ocean, and microbial degradation is one of the most important ways. Coral reef is one of the major sources of marine DMS, and coral-associated DMSP degrading bacteria play an important role in the process of DMS production. In the present study, 39 strains of DMSP degrading bacteria were isolated from six reef building corals, including Acropora millepora, Acropora formosa, Acropora echinata, Acropora digitifera, Pocillopora damicornis, and Galaxea fascicularis. The phylogenetic analysis of DMSP degrading bacteria was performed based on 16S rRNA gene sequence, 39 strains of DMSP degrading bacteria belonged to 4 phyla, 6 classes, and 19 genera, the dominant genus was Bacillus. The DMS production efficiency of DMSP degrading bacteria were analyzed by GC-FPD detection of DMSP products, the results showed that 9 strains had the ability of high DMS production. The probiotic effects of bacteria with high DMS production on corals in response to climate warming need to be further studied.

The instabilities of longshore currents are the far infragravity band waves. The study of its propagation characteristics will help us to understand its influence on the evolution of coastal beach and the transport and migration of pollutants, fish eggs and other organisms. Based on the wavelet coherence spectrum, this paper analyzes the propagation characteristics of the unsteady motion under regular and random waves, and discusses the influence of the wave height, period and slope on it. The results show that the irregular wave is easier to induce the unsteady motion, and the positive or negative phase difference of the unsteady motion is about 30° in the case of irregular waves, which is similar to the incident angle of waves; with the increase of the incident wave height, nonlinear effects become stronger and the period range of the unsteady motion will be wider, that is to say, it is easier to induce the unsteady motion; the incident wave period has a little effect on the propagation; the steeper the slope is, the more likely it is to induce the instabilities of longshore currents.

As a common submarine geological disaster, wave-induced seabed liquefaction seriously threatens the safety of subsea engineering facilities in the Huanghe River Delta. The structure, physical and mechanical properties of seabed soil after wave-induced liquefaction all have changed, so it has important theoretical significance and practical value to study on the evaluation of potential possibility of re-liquefaction of seabed soil after previous liquefaction. In this paper, a series of cyclic triaxial liquefaction tests were conducted on core samples collected from submarine non-liquefied and liquefied zone in the Huanghe River Delta, respectively. The differences between non-liquefied and liquefied seabed soil in the developing trends of pore pressure and axial dynamic strain with cycles were analyzed and discussed, and the corresponding liquefaction potentials were also comparatively evaluated. The test results show that compared to pore pressure, the strain standard is more suitable to evaluate the liquefaction potential of the seabed silt in the Huanghe River Delta. The pore pressure and dynamic axial strain development characteristics indicate that the re-liquefaction resistance of the liquefied seabed silt is improved to some extent compared with the non-liquefied silt. Furthermore, the correlations between the normalized pore pressure ratio u_d/σ₃ and the normalized cycle ratio N/N_f could be described quantitatively by the hyperbolic or exponential functions for liquefied and non-liquefied seabed silts. Finally, the critical cyclic stress ratio for the non-liquefied seabed silt is around 0.20 compared to 0.35 for the liquefied one in the Huanghe River Delta. The research findings will contribute to deepening the understanding of the wave-induced liquefaction mechanism of seabed silt, and also provide an example reference for the study of the mechanical properties of soil subjected to previous cyclic stress history.

After the launch of China’s HY-2B altimeter in October 2018, NSOAS (National Satellite Ocean Application Service) conducted a HY-2B altimetry calibration experiment in Wanshan, Zhuhai. The experiment used the tide gauge along the coast to conduct the calibration experiment from November 3, 2018 to December 12, 2018, near the sub-satellite point of the HY-2B transit orbit 375 on Zhiwan Island. During the experiment period, HY-2B revisited the calibration point three times, and the results showed that the three-period HY-2B altimetry calibration bias were (3.06±3.48) cm, (2.85±1.03) cm, −7.41 cm; there was a certain drift in the calibration bias in the first three cycles, and subsequent calibration work was required to determine the cause of the drift.

It is crucial to evaluate seafloor massive sulfides (SMS) in terms of their special distribution. Transient electromagnetic method (TEM) is ideal for land mineral deposits prospecting, but the complicated seafloor topography, inner structure of sulfide deposits and measuring conditions in the hydrothermal field pose a great challenge to its application in the ocean. In order to verify the application potential of TEM in deep-sea exploration, a 3D forward modeling scheme was developed with finite element method, combining with bathymetry data and drilling results. The method was then applied to the TAG hydrothermal field, Mid-Atlantic Ridge, and the result was well fitted with acquired TEM data. By comparing the forward simulation results under different instrument positions, attitudes and altitude, we found that the coincident loop system could effectively detect the active TAG mound ore body when the altitude was less than 60 meters. Complex seafloor topography and how the instrument was being towed could significantly disturb the early time response, while the instrument attitude also made an influence on the detected signal. Therefore, it was necessary to combine the bathymetry data, instrument positioning data and attitude data in the research area to better interpret the measured TEM responses.

The Bohai Sea is an important economic zone of China. Sea ice has been a significant threat to the human activities around the Bohai Sea. As the imaging capability of synthetic aperture radar (SAR) is independent of sun illumination and cloud condition, it is of great significance to detect the sea ice of the Bohai Sea from SAR images. Due to the limitation of the feature extraction mechanism, the accuracies of traditional sea ice detection methods need to be improved. Deep learning has a strong self-learning ability and is suitable for image detection. Here, we employ the well-known deep learning framework, U-Net, as the basic structure, and design a hybrid loss function to optimize the U-Net model, forming a hybrid loss U-Net model for sea ice detection in the Bohai Sea. The Sentinel-1 dual-polarization (VV and VH) SAR images are the inputs of the model. We compare the hybrid loss U-Net model with several traditional methods (Pulse Coupled Neural Network, Markov Random Field and Watershed Algorithm) and deep learning method based on CNN. Experiments show that the hybrid loss U-Net-based model achieves 97.567%, 98.769%, 98.767% and 98.771% in IoU, F1_Score, Precision and Recall respectively, outperforming the other methods. Compared with VV single-polarized input, the detection results of dual-polarized information input are 0.375%, 0.111%, 0.639% and 0.740% higher in F1_Score, Precision, Recall and IoU respectively. The detection results of the hybrid loss model are 1.129%, 0.947%, 1.794% and 2.231% higher than those of the non-hybrid loss function in F1_Score, Precision, Recall and IoU respectively. The model could effectively detect details such as ice water line, inter-ice water and ice gap. Our model is applied to detect the sea ice of a whole SAR image in the Bohai Sea, which can provide technical supports for sea ice monitoring, sea ice change analysis and sea ice prediction.

The seasonal variability of M₂ constituent exerts a major influence on the coastal ocean environment. The enhanced harmonic analysis (EHA) can synchronously extract the temporally varying amplitudes and phase lags of significant constituent and the constant values of the other constituents. In this study, the seasonal variability of the M₂ constituent in the Bohai Bay, China, is investigated by analyzing one-year sea level observations at two stations with EHA. In order to evaluate the accuracy of EHA, artificial "sea level" is designed in the ideal experiment. Both the estimated temporally varying amplitude and phase lag of the M₂ constituent and constant values of the S₂, K₁ and O₁ constituents using EHA were much closer to the prescribed values than those obtained using the other methods, indicating the capability and efficacy of EHA. When the real sea level observations were analyzed using EHA, the estimated M₂ constituent amplitude has significant seasonal variability, with large values in summer and small values in winter. The sensitivity experiments show that the trend of seasonal variation of M₂ amplitude in Bohai Bay is not affected by the experimental settings, and it is robust and can reflect the real seasonal variation of M₂ constituent. The seasonal variations in the M₂ amplitude is possibly induced by the seasonally alternating Asia monsoon, as the Asia monsoon dominates the seasonality of mean sea level, stratification and eddy viscosity, which are main influence factors summarized in the previous studies.

Sea level rise, strong typhoon and storm surge have increasingly serious impacts on coastal flood disasters in the southeastern China in the context of climate change. To address the climate change and estimate the hazard of extreme sea level in the future, based on the multiple data of oceanographic and atmospheric observation and methods of mathematical statistics, the impact of historical strong typhoon No.9914 (Dan) and No.1614 (Meranti) on the extreme sea level in coastal waters of Xiamen and estimates the changes and return of extreme sea level at scenarios of future sea level rise under RCP4.5 and RCP8.5 was analyzed in this paper. The results show that: (1) astronomical tide, storm surges and heavy precipitation induced the extreme sea level event (732 cm) during the period of strong typhoon No.9914; (2) the combined impacts of multiple hazards such as wind (ashore gale), rainfall (heavy precipitation), waves (giant waves), tides (high tide) and current (torrents) is an important cause of serious disasters in coastland of Xiamen; (3) under the medium and high greenhouse gas emission scenarios (RCP4.5 and RCP8.5), by 2050 and 2100, recent 1-in-100-year extreme sea level event will become 1-in-30-year (1-in-2-year) and 1-in-25-year (1-in-less than 1-year). It shows that the hazards of extreme sea level on coastland of Xiamen will increase significantly, and high adaptation measures in Xiamen should be taken to reduce the risk on coastal flood hazards in the future.