Multiple studies have confirmed the long-term property modification of water columns from the bottom to the sea surface at the Southern Ocean and pointed out that it is closely related to the changes of large-scale external forcing. However, the higher frequency interannual variability of the water masses and its causes are still poorly understood, including the winter water (WW), which is the most vulnerable to external forcing near the sea surface. Based on repeated hydrographic observations along 110°E in Januaries 2011 to 2020 and meteorological reanalysis datasets, this study estimated interannual variability of the WW layer in the seasonal ice zone (SIZ) and its possible causes over ten years. Results show that WW properties have significant temporal and spatial variability in this region. A significant positive correlation between the WW core temperature anomaly and the previous-year Antarctic Oscillation (AAO) index anomaly (R = 0.69) and a negative correlation between the AAO index and the turning latitude of the local zonal wind component (R = −0.61), indicate that a larger (smaller) AAO index corresponds to a southward (northward) shift of the divergence zone, and the increase (decrease) of the WW core temperature in the SIZ. A negative correspondence between the local net precipitation anomaly and the WW core salinity anomaly indicates the negative net precipitation anomaly (less freshwater transport to the ocean) after 2016 contributes to an increase in the WW core salinity anomaly. Meanwhile, the local eddy kinetic energy anomaly is negatively correlated with the WW thickness anomaly (R = −0.70), which supports the idea that the enhancement (decrease) in the intensity of persistent cyclonic eddies in this region may strengthen (weaken) the upward pumping to shoal the depth of the circumpolar deep water, and further affect the WW thickness. This study contributes to an in-depth understanding of the specific response of water columns in the Southern Ocean to the high-frequency variability of external forcing.

Early diagenesis in marginal sea sediments is an important process that affects carbon cycling and burial. Early diagenetic processes and influencing factors, however, remains poorly constrained. Dissolved inorganic carbon (DIC), dissolved inorganic nitrogen (DIN), Fe²⁺, Mn²⁺, sulfate and other parameters in sediment porewaters of five short cores collected in August 2018 from the Changjiang River Estuary and East China Sea inner-shelf were analyzed. In combination with grain size composition, specific surface area, organic carbon concentrations and stable carbon isotopic composition in surface sediments and bottom water parameters, the early diagenetic processes and influencing factors in sediments under different sedimentary regimes were studied. Concentrations of DIC and ${{\rm {NH}}_4^+} $ in sediment porewaters in the mud area gradually increase with depth, and relatively high production fluxes of DIC and ${{\rm {NH}}_4^+} $ (4.03 mmol/(m²·d) and 0.57 mmol/(m²·d), respectively) and consumption fluxes of ${{\rm {SO}}_4^{2-}} $ (−4.56 mmol/(m²·d)) are observed at the center of the mud area, while in the sandy area, there are no obvious variations of these solutes, and the fluxes are lower compared with those in muddy sediments. According to the vertical distributions of these solutes in the sediment porewaters, the sediment disturbance depth in the mud area varies at 20−40 cm, and gradually decreases from the Changjiang River Estuary mud area to the Zhe-Min coast mud area, whereas in the sandy area, no sediment disturbance is found. The thickness of sediment disturbed layer is positively correlated with solute fluxes (e.g., DIC and ${{\rm {NH}}_4^+} $) in sediment porewaters, indicating that the physical reworking of sediments is an important factor affecting the remineralization of sedimentary organic carbon in the mud area. In general, the main decomposition pathway of the sedimentary organic carbon in the disturbed layer of the mud area is iron/manganese reduction, and below the disturbed layer the main pathway is the sulfate reduction, while in the sandy area, the main degradation pathway is aerobic respiration. This study enriches the understanding of the impact of sedimentary dynamic processes on early diagenesis in the Changjiang River Estuary and adjacent sea areas, and contributes to better understand the cycling and burial of organic carbon in the large-river estuary and adjacent sea areas.

Two single-scene SAR images observed by Radarsat-2 and Sentinel-1A were decomposed to obtain a pair of SAR sub-aperture images at different azimuth-angles, respectively. Doppler centroid anomaly method was used to invert the sea surface current of two sub-aperture images with different azimuth angles. The current field was obtained by vector synthesis. The inversion results were verified by the HYCOM model data with spatio-temporal matching. The results show that the root mean square (RMS) of the current velocity between the synthesized result by two sub-aperture images of Radarsat-2 and the HYCOM model data is 0.09 m/s, and the correlation coefficient is 0.64. The RMS of current direction is 10.49° and the correlation coefficient is 0.78 of this group data. As for the results of the Sentinel-1A image, the RMS of the current velocity is 0.06 m/s, and the correlation coefficient is 0.82. The RMS of the current direction is 2.85°, and the correlation coefficient is 0.86. It can be seen that the two-dimensional ocean currents field can be effectively inverted based on the two sub-aperture SAR images that decomposed from single-scene SAR image. The inversion accuracy is related to the relative direction of the radar’s looking direction and the real current vector. The inversion accuracy of the sea surface current field can be higher when the relative angle is small.

Most of the small rivers in the Shandong Peninsula have clear sediment sources and relatively small mineral deposition differentiation, and their study can provide regional similarities for the analysis of the sources of large rivers into the sea, as well as the characteristics of the material sources in the Shandong Peninsula for the deposition of the Yellow Sea shelf and Bohai Sea shelf. In this paper, the distribution patterns of detrital minerals in surface sediment samples taken from riverbeds, estuaries and beaches were analysed at multiple grain levels, taking the Xin’an River, a small short-source river in the northeastern part of the Shandong Peninsula, as an example. The study shows that the Xin’an River basin and beach sediments are mostly medium and fine sands, with moderate heavy mineral content in the whole sample, ranging from 1.47% to 8.19%. Twenty-seven heavy minerals and eight light minerals occur, with the main heavy minerals hornblende (41.7%), chlorite (16.7%), actinolite (10.6%) and limonite (6.7%) and the main light minerals quartz (49.0%), plagioclase (26.5%) and potassium feldspar (20.7%), which are much more abundant than the other detrital minerals in the riverbed, estuary and beach, and the mineral assemblage remains constant, with less significant variation in relative content between them, while there is a significant non-linear correlation between non-dominant mineral species and clastic grain size. Mineral species and content in the Xin’an River are controlled by the regional lithological sources, i.e. acidic and moderately acidic intrusive rocks and regional metamorphic rocks, and the relatively stable output of amphibole group minerals across the different features of the Xin’an River is responsible for their homogeneity. The short source rivers of the Shandong Peninsula are derived from similar geological features and rock types, although the types and content of detrital minerals vary. The main controlling factors for mineral composition variation are regional sources and particle size sorting, followed by sedimentary environmental differences. In contrast, the high content of mica group and carbonate minerals in a specific grain size and the low content of amphibole group minerals are the aspects that distinguish the Huanghe River from the river source materials in the northern and southern coastal waters of the Shandong Peninsula.

Red tide is a major marine ecological disaster in China. Effectively monitoring the occurrence and spatial distribution of red tide is of great significance for their prevention and control. Traditional red tide monitoring is mainly conducted by watercolor satellites with low spatial resolution. However, there are monitoring blind areas for frequent small-scale red tides. GF-1 WFV remote sensing images, featuring high spatial resolution and a wide imaging range, can be used to monitor small-scale red tides. However, the traditional method for watercolor satellites cannot be used for GF-1 WFV satellite data as GF-1 WFV remote sensing images are characterized by low spectral resolution and few bands. And it is hard to extract the information about red tide as they differ in both shape and scale. Due to diverse shapes of the red tide distribution, this paper proposes a scale-adaptive red tide detection network (SARTNet) for GF-1 WFV sensing images. This network adopts a two-layer backbone structure to integrate the shape and detail features of red tide and introduces an attention mechanism to model the correlation between features of red tides at different scales, thereby improving its performance in detecting red tides that are complexly distributed. The experimental results show that the red tide detection performance of SARTNet is better than that of the existing methods, with an F1 score above 0.89; and it is less affected by environmental factors, with few missing and misstated pixels for red tide information at different scales.

Fully integrating the use of satellite remote sensing and in-situ observation information to build a high-quality underwater temperature and salinity fields is a frontier topic in the development of marine scientific research. Currently, the vast majority of assimilation systems use assimilation schemes that require the assumption that elements have some artificially predetermined relationship between the surface and underwater. As a result, the temperature and salinity analysis field was more man-made and could not objectively reflect the real state of the ocean. This paper proposed a scheme that did not make any relationship assumptions, only relied on the complementary effects of different types of observation data in time and space, and combined the satellite remote sensing and in-situ observations for spatio-temporal four-dimensional multiscale objective analysis. Compared with the experimental results of assimilating these two types of observation data separately, it was found that the method could not only obtain more accurate temperature and salinity profile structure characteristics, but also reflect the detailed information of the mesoscale changes in the sea surface, the multi-scale information in the observation data was extracted to the maximum, and the effect of “1 + 1 > 2” was realized, and constructed a completely objective temperature and salinity analysis field. The results also showed that assimilating satellite remote sensing sea surface salinity data can effectively improve the analysis of temperature and salinity, which proved that the role of satellite remote sensing sea surface salinity observation on temperature and salinity assimilation could not be ignored.

Phytoplankton blooms in polar regions with seasonal sea ice cover show a unimodal seasonality. However, the bloom processes are controlled by multiple physical and biogeochemical factors, including sea ice, light availability, mixed layer depth, and nutrients; those may result in great uncertainties in simulating phytoplankton bloom by the Earth System Models (ESMs). In this study, the results of 11 Coupled Model Intercomparison Phase-6 (CMIP6) ESMs were analyzed and evaluated with various types of observational products in order to determine whether those ESMs can correctly model the phytoplankton blooms in three Arctic shelf seas, Barents Sea, Chukchi Sea, and Bering Sea. By calculating multiple indices that represent light and nutrient limitations, the error sources of simulated surface chlorophyll a concentrations were comprehensively analyzed. Our results show that the 11 ESMs can be divided into three groups based on ice-adjusted photoperiod, rate of change of mixed layer depth, and surface nitrate concentration. Some groups are characterized by the smallest bias between modeled indices and observation-based reference, and those ESMs perform best in simulating phytoplankton bloom characteristics. The other groups of ESMs differ significantly from the reference values in terms of surface nitrate and/or rate of change of mixed layer depth, resulting in delayed occurrences of annual chlorophyll a peak concentration and greater differences in corresponding peak values. In general, in addition to the two primary constraints of light and nutrients, the ESMs should also well represent the upper mixed layer controlled by temperature and salinity distributions, so as to accurately simulate the seasonal variation of surface chlorophyll a concentration. The above analyses indicate ESMs can be used in assessing polar planktonic ecosystems, and there is room for improving ecosystem-related parametrization in future ESM development.

Seagrass coverage ratio is an important indicator reflecting the ecological status of seagrass beds. In this paper, through the design of aerial photography scheme and flight condition test, the high-resolution seagrass image map of the Dongjiao Coconut Forest sea area was obtained by using UAV aerial photography. Combined with the image classification tools of ArcGIS software and 3D tools, a new method for calculating the coverage ratio of seagrass were obtained and the coverage of seagrass was calculated. The station location of simulating survey method of the traditional seagrass coverage ratio was compared and discussed. Seagrasses in the coastal sea bed of the Dongjiao Coconut Forest are distributed on the coral reefs within 300 m from the shore with patches and intervals. Using the new method, the concentrated distribution area of seagrass at sea bed of the Dongjiao Coconut Forest is about 23 221 m², and average concentration distribution ratio is 17.79%. The distribution area of seagrass in this study area is about 16 423 m², and the coverage ratio of seagrass is 12.58%. The coverage ratio of seagrass is higher, and the ecological condition of seagrass bed is good. Sargassum is densely distributed in the southeast area of the study area, with a distribution area of 755.6 m² and a coverage of 0.5%, and grows as a single cylinder floating. By simulating the investigation station location of the sample frame method and sample line method of traditional seagrass coverage survey, seagrass coverage ratio changes with different stations, sample frame, and sample line positions changing randomly, which is the reason for the representativeness and comparability of the traditional survey results. The research results of this project have the promotion and application value in the investigation of seagrass ecological monitoring area.

In the real sea state, the differences in directions of component waves result in three-dimensional short-crested waves, which have many different characteristics compared to two-dimensional long-crested waves. Therefore, in present study, the whole generation and evolution processes of short-crested freak waves are experimentally simulated by dispersive and directional focusing of component waves, in order to examine the external features and relationship of the abnormal large waves occurring during the processes. The results indicate that the abnormal large wave evolves symmetrically along the peak wave direction and undergoes a three- or four-stage process, each stage is indicated by the characteristic parameters of the abnormal large wave, it implies that the characteristic parameters can be used to identify the stage which the large abnormal wave is in and predict the variation tendency; and that compared to the two-dimensional cases, the “wave group” and “deep trough” stages are likely to be skipped, as a result, the spatio-temporal spans of the generation and evolution processes are smaller for the three-dimensional cases, it implies that in three-dimensional wave fields, the deep troughs and successive large waves (wave group) associated with freak waves may have a low probability of occurrence.

Polar ships always collide with various types of sea ice in varying degrees during their voyages in ice-covered regions, so sufficient fatigue strength reserves are essential. This paper proposes a cumulative damage analysis method for ice-induced fatigue on polar ship structures based on field measured ice loads. Firstly, according to the statistical analysis of the field data of ice thickness and sailing speed of RV Xue Long during the China’s 8th Arctic Scientific Expedition, ice-induced fatigue conditions are constructed within the ice thickness range of 0.5−2.5 m and the sailing speed range of 2−12 kn. The joint probability distribution of the two parameters is taken as the occurrence probability of fatigue conditions. Then, the time histories of ice loads under typical conditions are identified based on the support vector machine method. The key positions and corresponding hot spot stresses are determined by dynamic analysis. The rainflow counting algorithm is adopted to count the number of stress cycles. Finally, the fatigue damage during the voyage is further calculated by S-N curve and Miner linear cumulative damage theory, which verifies the ice navigation safety of RV Xue Long. This paper has certain reference significance for the ice-resistant design and safety evaluation of polar ship structures.