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A new gravity sensor based on electromagnetic damping for the JMGrav marine gravimeter is presented. The new gravity sensor considered the advanced construction methods of the electromagnetic damping system of the gravimeter. The design features of the new system are discussed and the research survey data in the South China Sea are shown. Numerical simulations are applied to model the magnetic and mechanical characteristics of the system using finite element analysis and to evaluate the force distribution and the resulting damping effects. The performance characteristics of the system were tested on a motion simulator in laboratory, and the gravimeter was subjected to vertical accelerations of up to 100 Gal in 1–1 000 s. It was found that the amplitude reduction of vertical accelerations in 3–15 s is 30–45 dB, with a time lag of 2–5 s, while the effect on gravity in period greater than 600 s is less than 0.5 dB, with a time lag of less than 100 s. The accelerations cause discrepancies of approximately only 1 mGal between the static value and the mean dynamic value. The sea tests were conducted in September 2020. Gravity measurements were taken with a JMGrav marine gravimeter onboard the R/V Dongfanghong 3, and the effective survey line exceeded 2 000 km. Completely irregular accelerations with peaks up to 100 Gal yielded a reduction of approximately 40 dB in amplitude. The survey data were evaluated using ocean gravity field models and grid line tests. The results show that the accuracy of the gravity measurements is better than 2 mGal. [ABSTRACT FROM AUTHOR]

Submarine seep plumes are a natural phenomenon in which different types of gases migrate through deep or shallow subsurface sediments and leak into seawater in pressure gradient. When detected using acoustic data, the leaked gases frequently exhibit a flame-like structure. We numerically modelled the relationship between the seismic response characteristic and bubble volume fraction to establish the bubble volume fraction in the submarine seep plume. Results show that our models are able to invert and predict the bubble volume fraction from field seismic oceanography data, by which synthetic seismic sections in different dominant frequencies could be numerically simulated, seismic attribute sections (e.g., instantaneous amplitude, instantaneous frequency, and instantaneous phase) extracted, and the correlation between the seismic attributes and bubble volume fraction be quantitatively determined with functional equations. The instantaneous amplitude is positively correlated with bubble volume fraction, while the instantaneous frequency and bubble volume fraction are negatively correlated. In addition, information entropy is introduced as a proxy to quantify the relationship between the instantaneous phase and bubble volume fraction. As the bubble volume fraction increases, the information entropy of the instantaneous phase increases rapidly at the beginning, followed by a slight upward trend, and finally stabilizes. Therefore, under optimal noise conditions, the bubble volume fraction of submarine seep plumes can be inverted and predicted based on seismic response characteristics in terms of seismic attributes. [ABSTRACT FROM AUTHOR]

Satellite records show that the extent and thickness of sea ice in the Arctic Ocean have significantly decreased since the early 1970s. The prediction of sea ice is highly important, but accurate simulation of sea ice variations remains highly challenging. For improving model performance, sensitivity experiments were conducted using the coupled ocean and sea ice model (NEMO-LIM), and the simulation results were compared against satellite observations. Moreover, the contribution ratios of dynamic and thermodynamic processes to sea ice variations were analyzed. The results show that the performance of the model in reconstructing the spatial distribution of Arctic sea ice is highly sensitive to ice strength decay constant (Crhg). By reducing the Crhg constant, the sea ice compressive strength increases, leading to improved simulated sea ice states. The contribution of thermodynamic processes to sea ice melting was reduced due to less deformation and fracture of sea ice with increased compressive strength. Meanwhile, dynamic processes constrained more sea ice to the central Arctic Ocean and contributed to the increases in ice concentration, reducing the simulation bias in the central Arctic Ocean in summer. The root mean square error (RMSE) between modeled and the CryoSat-2/SMOS satellite observed ice thickness was reduced in the compressive strength-enhanced model solution. The ice thickness, especially of multiyear thick ice, was also reduced and matched with the satellite observation better in the freezing season. These provide an essential foundation on exploring the response of the marine ecosystem and biogeochemical cycling to sea ice changes. [ABSTRACT FROM AUTHOR]

The main goal of the work is to study the spatiotemporal structure of sea currents in the shelf–slope zone of the northeastern part of the Black Sea. The studies were carried out by numerical simulation methods using the combined hydrodynamic and spectral wave models incorporated in the DHI MIKE computational complex. The model has been verified based on the data of field observations performed by means of the hydrophysical test site of the Institute of Oceanology, Russian Academy of Sciences (Gelendzhik test site). As a result of calculations with a discreteness of half an hour, the fields of velocities and directions of currents for the period from January 2016 to December 2020 were obtained. Despite the fact that the total length of the massif is insufficient for climatic generalizations, analysis of the data obtained from the numerical experiment makes it possible to judge some general features of the seasonal dynamics of waters. As a result of the work that was carried out, the features of current velocity fluctuations in the frequency domain were revealed, and, based on the averaged current fields, the main seasonal features of water circulation in the shelf zone of the northeastern Black Sea coast were estimated. [ABSTRACT FROM AUTHOR]