Due to its high surface albedo, snow plays an important role in the air-ice-ocean interaction in high-latitude regions. Accurate snow mass balance calculations are needed to understand the evolution of sea ice and interaction between snow-ice and atmosphere better. One of the factors affecting snow mass balance is snow density. Constant mean snow bulk density is used to convert snow water equivalent to snow depth in the present 1-D high-resolution thermodynamic snow-ice model (such as HIGHTSI). Simplified to 2 snow layers, being fresh and old, algorithm reference to Lagrangian snow-evolution model (SnowModel-LG) used to treat layered snow compaction is introduced into HIGHTSI to reproduce the physical process of compacting in both the fresh and old layer and affecting the snow depth following the principle of mass conservation. Forced by ERA-Interim reanalysis data, modified HIGHTSI was applied to investigate the impact of snow density on snow depth along drift trajectories of 15 sea ice mass balance buoys (IMB) during snow accumulation period and assess the model results against observation. In contrast to the previous bulk snow density setting, with a constant density of 330 kg/m³ (T1) or 200 kg/m³ (T2), our new algorithm calculates snow depth by considering both the fresh and old snow densifying over time (T3). The simulations indicate that the improved algorithm is more reasonable to deal with the density evolution, and can reproduced the snow depth well. The overaccumulation caused by heaping continuously at the lower density of new snowfall can be avoided by considering the response of both the fresh and old snow depth to compaction. The absolute error calculated by layered snow compaction is reduced by 5 cm by setting the observation as a reference of both the fresh and old snow depth to compaction. The absolute error calculated by layered snow compaction in T2 is reduced by 5 cm by setting the observation as a reference.

In the Canadian Circumpolar Flaw Lead System Study, the physical and optical properties of first-year ice during the freezing season were observed at the Amundsen Gulf from November 24th, 2007 to January 26th, 2008. The results show that the thickness of sea ice during this period ranged from 27 cm to 108 cm, while the snow depth varied between 0 cm and 6 cm. The changes of temperature, salinity and density in the interior of sea ice are respectively: temperature within the sea ice rose monotonically along with the increasing of depth, reaching a maximum of −2.2℃ at the surface and a minimum of −22.4℃ at the bottom; the salinity ranged from 3.30 to 11.70 with a C-shaped pattern in its vertical section, which means that the salinity of upper surface and bottom layer is larger than that in the middle part; the average density of the sea ice was slightly larger, which is (0.91±0.03) g/cm³. With the special designing of artificial light source and in-situ instrumentation, an obvious two-peek structure at 490 nm and 589 nm was found in the spectral distribution of the transmitted radiation through the first-year ice. The two-peak structure weakens as the thickness of sea ice increases, indicating the spectrum dependence of the attenuation. In the visible band, the spectral absorbance of both bare ice and snow-covered ice reaches its minimum at 490 nm, and rises as the wavelength moves towards 443 nm or 683 nm. However, for snow-covered ice, the variation of absorption rate is little enough to present a spectral independence. In addition, the spectral distribution of the attenuation coefficient was U-shaped in the visible band, with a minimum of 1.7 m⁻¹ at 589 nm. The integral diffuse attenuation coefficient of the first-year ice in visible band was about 2.3 m⁻¹, which was slightly higher than 1.5 m⁻¹, the diffuse attenuation coefficient of multi-year floe ice. The difference of the optical properties between first-year ice in the Amundsen Gulf and multi-year ice in the north of Canada Basin is mainly attributed to various components of the sea ice inclusions caused by the input of terrestrial materials with different absorption and scattering properties.

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.

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.

Marine heatwave, considered as events with prolonged anomalously high sea surface temperature in certain sea areas. The occurrence of marine heatwave could impact the function and service of marine ecosystem. In recent years, the marine heatwave in the China offshore become more frequent, and attract considerable attention. Used a range of ocean temperature data including daily satellite observations and daily in situ measurements, we analysised the characteristics of marine heatwave in the China offshore in 2019. Results show that in 2019, the frequency of marine heatwave is higher in the sea areas around Hainan Island, the Changjiang River Estuary, the Bohai Sea and the sea areas off Jiangsu Province, with the frequency of 7−12 times. The marine heatwave duration in the Beibu Gulf lasts the longest, more than 150 days. In addition, took the classical marine heatwave that last from February to April in Beibu Gulf as an example, anomaly characteristics of air temperature, sea level pressure and wind during the event period were investigated specifically and the corresponding relationships between the marine heatwave and meteorological background fields in different seasons in Beibu Gulf was further studied. On the whole, the higher air temperature, weaker East Asian winter monsoon, larger area and the northward and westward extension of subtropical high are the important factors for the occurrence and maintenance of the marine heatwave in the Beibu Gulf in the early 2019.

Based on tropical cyclone (TC) disaster data and the best-track database from Shanghai Typhoon Institute of China Meteorological Administration (CMA-STI) during 1984 to 2017, this study analyzed the spatial-temporal characteristics of TC disaster in China and their differences for the three prevailing tracks, along with the discussion of the overland duration and its potential risk. Main results of this study were summarized as follows: (1) There was a significant upward trend with direct TC-associated economic losses, while the proportion of losses to Gross Domestic Product (GDP) and the deaths showed a downward trend. (2) TC-associated economic losses accompanied with the three prevailing TC tracks showed a substantial difference. The recurving TCs tended to be less and lower impact, while westward and west-northward TCs appeared to be more and higher impact in China. Particularly, more frequent TCs with westward movement affected the Guangdong, Guangxi and Hainan provinces. TCs tending to west-northward tracks mainly caused a serious TC-associated disaster in Guangdong, Fujian, and Zhejiang provinces. (3) The average overland duration, as a potential index for TC-associated disaster, showed an upward trend. Note that the reasons on the changes of TC overland duration for the three prevailing tracks appeared to be different. The increased average overland duration for recurving TCs were likely to relate to the decreased in TC average overland translation speed. In contrast, the increased average overland duration of westward and west-northward moving TCs were possibly due to the increased average distance that TCs traveled over land.

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.

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 study of tidal changes is of great significance in marine engineering, marine mapping as well as marine transportation. Because nearly all tide gauges are located in the coastal waters, previous studies mainly focus on tidal changes in the shallow waters. In the deep sea, due to the lack of long-term high-frequency sea level observations, tidal changes are remained unclear. Based on the tide gauge observations and satellite altimeter data, non-stationary tidal harmonic analysis toolbox S_TIDE to extract the long-term trend of amplitudes of four major constituents in the South China Sea is first used in this paper. Results show that in most areas of the South China Sea, the amplitudes of four major constituents are stable and have no significant positive or negative trends. In minor areas of the South China Sea, the amplitudes of four major constituents have significant trends. The largest positive trends can reach 2.91 mm/a and the largest negative trends can reach 3.50 mm/a. The long-term trends of tidal amplitudes in this area may be related to the change of the surface expression of internal tides. The tides observed by satellite contain not only barotropic tides but also the surface expression of internal tides. The internal tides as well as their surface expression in the South China Sea are strongest in the world. The changes of ocean stratification can influence the generation, propagation and dissipation of internal tides as well as their surface expression and eventually induce the long-term trends of tidal amplitudes in the South China Sea.

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.