DNA barcoding technology is a tool for rapid and accurate species identification using short orthologous DNA sequence. In this study, both traditional morphology and DNA barcoding technology was used to accurately identify ichthyoplankton species in the Changjiang River Estuary and its adjacent waters. Morphological description was carried out at the same time. The results showed that in spring and summer of 2016 and summer of 2017, 55 species of ichthyoplankton were obtained, belonging to 9 orders and 19 families. Among them, there were 35 species of Perciformes at most. The seasonal variation of ichthyoplankton in fish group was not obvious, while there was significant seasonal variation in species. Only Coilia mystus, Engraulis japonius and Larimichthys polyactis appeared both in spring and summer. It was the first time to describe the morphological characteristics of Harpadon nehereus larva and juvenile. In addition, the quantifiable characters, fin development and melanin distribution of larvae and juvenile of Harpadon nehereus, Chelon affinis, Eleutheronema tetradactylum, Sillago japonica and Paraplagusia japonica, were described and drew. The research could provide a scientific basis for the study of fish nursery in estuaries, and also provide a new way for the accumulation of taxonomic data in the early stage of fish development.

The radial sand ridges is a typical sedimentary accumulation body distributed off the coast of Jiangsu Province. Under the influence of the sediment supply of the Changjiang River and the Huanghe River as well as the coastal tidal current, the typical silty-muddy tidal flats are developed, and the sediment elements can record the important information of the environmental changes of the tidal flats. Three short core samples were collected in the tidal flat of radial sand ridges to establish a reliable chronological framework and geochemical element testing, and 14 elements with high X-ray fluorescence (XRF) core scanner analysis signal strength were selected for clustering and correlation method to extract environmental information. The sedimentary environment changes of the northern Jiangsu radial sand ridges under the influence of human activities and coastal environment changes in the past 100 years were studied. The results indicate that the contents of Si, Ca and Fe in the core sediments of typical tidal flat profile in this area are relatively high, and the contents of Si, Ca and Fe increasing from north to south, while the contents of Mn, Ba, Cu and Zn are low, and the little changes in contents at all profiles changes. In terms of vertical change, Si, Ca and Fe have the same vertical change trend, while Ni, Zn and S have the opposite change trend with Si, Ca and Fe in different sediment cores. Correlation and clustering analysis show that Si, Ca and Fe have high correlation, that is, they have similar geochemical behavior and consistent material source. In addition, it is negatively correlated with elements Ni, Cu and Zn, suggesting that these elements have different geochemical behaviors with the former. The sedimentary environment changes of the tidal flat are obvious and show different patterns in different regions in the northern Jiangsu radial sand ridges, and the material source, hydrodynamic environment and human activities are the main reasons leading to the change of the sedimentary environment.

Based on the analysis of the rare earth element (REE) geochemical characteristics and clay mineral assemblages of Core TS6 sediment samples in the southern area of Southwest Taiwan Basin, South China Sea, the provenance and characteristics of its changes, material transport mechanism of sediments in the study area over the last 19 ka (the last deglaciation) are discussed. The comprehensive analysis of provenance shows that the rivers in Taiwan are the main provenance of sediments in the study area. The rivers in the west of Taiwan contribute more than the rivers in the east, and the Zhujiang River also transports part of sediments to the study area. Due to the large differences on the types and contents of the main clay minerals in different provenance areas, it is judged that the illite and chlorite of the clay minerals in the study area are mainly provided by the rivers in Taiwan; the kaolinite is mainly provided by the Zhujiang River and the less content of montmorillonite is provided by Luzon Island in the southeast. Since the last deglacial period, the input of terrigenous materials in the study area has been gradually reduced under the control of sea level changes. The provenance changes reflected by the combination of clay minerals are mainly controlled by changes in climate and ocean currents, and the influence of multiple factors may be superimposed.

To investigate the changes in mercury (Hg) speciation in vegetated sediments of the wetlands in Changjiang River Estuary, China, following the invasion of Spartina alterniflora, we determined total mercury (THg), methylmercury (MeHg), toatal organic carbon (TOC), reduced sulfur (S) and grain size in core sediments (0−40 cm) vegetated with different plants in wetlands. The results showed that: (1) the mean concentrations of THg were 49.9−100.9 μg/kg in sediments vegetated by S. alterniflora, Phragmites communis, Scirpus mariqueter and Scirpus tabernaemontani had a significant positive correlation with the fraction of fine particles (<16 µm) and TOC content (r²=0.85, p<0.01; r² =0.58, p<0.01), indicating that the distribution of Hg levels in sediments could be dominated by the spatial differentiation of the mineral-organic complexes in fine particles. The invasion of S. alterniflora promoted the deposition of fine particles, and thus could facilitate Hg storage indirectly in wetland sediments. (2) The mean concentrations MeHg and average values of MeHg/THg (%) in vegetated sediments were 0.3−1.4 μg/kg and 0.4%−1.4%, respectively. The profiles of MeHg and MeHg/THg exhibited decrease with increasing depth across all sites. There was no significant difference in the content of MeHg and the values of MeHg/THg in vegetated sediments dominated by S. alterniflora, P. australis and S. mariqueter, indicating that the impact of S. alterniflora invasion on Hg methylation may be limited. In addition, there was no significant positive correlation between MeHg/THg and THg, TOC and acid volatile sulfur (AVS). S-K edge XANES further revealed that the reduced sulfur (S) (e. g., thoil and sulfide) changed greatly in depth profiles. These results suggested that the changes in reduced sulfur could have limited impacts on MeHg production. The values of MeHg/THg was higher in surface horizon (0～8 cm) than in deeper horizon, indicating that the higher rates of Hg methylation in surface sediments and the degradation of fresh organic matter (e. g., algae and plant litter) could be the key biogeochemical process on controlling MeHg production in surface sediments of wetland in Changjiang River Estuary.

The submarine topographic features and distribution types of the Xuande atoll in the Xisha Islands have important indications for the influence of regional geological structure, sea level rise and fall, and ocean hydrodynamics. In order to study the submarine topography and geomorphology of the Xuande atoll, we detailed survey in the Xuande atoll of the Xisha Islands, including side scan sonar, single-beam sounding, and surface sediment sampling. The results show that: (1) Xuande atoll is a type of incomplete atoll, with lagoon deposits in the middle, and four water channels with a water depth of about 60 m had been divided, namely, the gate of the Xishazhou at the northwest of the atoll, the “Red Grass Gate” of the Nanshazhou-Yongxing, the gap on the west side of the atoll, and the gap on the south side of the atoll; (2) according to the geomorphic features, the underwater geomorphic types of the Xuande atoll are divided into 3 grades and 11 types of grades classification systems. The dynamic geomorphology units such as sand waves and grooves in the study area show that the submarine features in the shallow water area of Xuande atoll are controlled by prevailing monsoons and wave sites. The tidal channel water body formed by the deep water entrance is the main factor shaping the dynamic geomorphology of the Xuande atoll lagoon area. There are six levels of underwater terraces on the seaward slope in the southeastern part of the study area. By comparing the characteristics of the coral reef terraces in the South China Sea, the genesis of the seaward slope terraces on the Xuande atoll is likely to be a combination of global sea level changes and crustal subsidence.

The melting of sea ice affects the ocean heat absorption in the form of positive feedback, and plays an important role in the changes of the Arctic environment and economic activities in the Arctic region. Based on the daily sea ice concentration data of the Arctic Ocean from 1979 to 2018, the estimation method of sea ice retreat onset dates in the Arctic marginal sea was improved by comprehensively considering the factors such as sea ice conditions and so on in different seas. Comparative analyses of different methods show that this improved method can reflect the changes of ice conditions in different sea areas and different years, and can eliminate some influences of weather disturbance on the estimation of retreat onset, so as to avoid premature estimation results. By using this method, it is found that the retreat onset dates of every Arctic marginal sea are generally advanced. The advanced trends of retreat onset dates are generally the same as advanced trends of melt onset dates. However, different sea areas have different degrees of advancement. The Kara Sea and the Chukchi Sea have the strongest trend of early retreating, reaching 9 d/（10 a）, while the East Siberian Sea has the weakest trend, only 4 d/（10 a）. The difference of retreat onset dates gradually increases between these regions. There are significant interannual variations in the retreat onset dates, the standard deviations of each marginal sea are about 15 d. In the past decade, the difference between the earliest and the latest retreating reaches 50 d, which appeared in the Beaufort Sea.

Antarctic sea ice plays an important role in the global climate system. In contrast to the rapid decrease in Arctic sea ice extent, Antarctic sea ice extent exhibits a gradually increasing trend before 2014, followed by an abrupt decline in the last four decades. A single large-scale atmospheric circulation cannot fully explain the long-term trend of Antarctic sea ice, and the coupling influence of ocean-atmosphere interactions has not been sufficiently investigated. Limited by the capabilities of remote sensing and numerical simulation, the Antarctic sea ice thickness and volume variations in the context of global change cannot be quantified precisely with currently available sea ice thickness and volume data. Moreover, the climate effects of Antarctic sea ice change require further investigation. Hence it is strongly urgent to develop a long-term and reliable Antarctic sea ice thickness data set to quantify the Antarctic sea ice volume change. Meanwhile, the influences of multi-climate modes and ocean-atmosphere coupling system on the Antarctic sea ice changes should be considered comprehensively.

Using archived data from Chinese Polar Numerical Weather Forecasting System (PNWFS) and America Antarctic Mesoscale Prediction System, the spatial and temporal distribution of katabatic winds and air mass flux from Dome A to the coast of Prydz Bay are analyzed, and basic characteristics of katabatic winds in the region are depicted. It is found that the katabatic winds in this area is strongly affected by the terrain of the Antarctica ice sheet. Steep terrain such as the western side of the Amery Ice Shelf sees stronger katabatic winds than smooth terrain does; and the katabatic winds vary greatly with the season for temporal distribution with stronger winds in winter. Adiabatic warming, which can be found in the area where strong katabatic winds flow, causes increasing of near surface temperature at the Amery Ice Shelf. The maximum katabatic wind speed zone is located at a height of about 100 m to 200 m above the ground. Katabatic winds extents to higher altitudes while surface winds are stronger. The surface air mass flux of the katabatic winds along the coast of the Prydz Bay is extremely uneven in spatial and temporal distribution. Strong katabatic winds in the Amery Ice Shelf are linked to more mesoscale cyclone activities in the Prydz Bay waters. The process of mesoscale cyclones induced by katabatic winds in the Prydz Bay is worthy of attention, thus the mechanism of cyclogenesis forced by katabatic winds needs further notice.

The extreme cyclones in the Arctic can reflect the characteristics of climate change in the Arctic and have important influence on the regulation of hydrometeorological elements in the Arctic. The characteristics of their activities and atmospheric circulation situation deserve attention. Using the daily reanalysis data provided by National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) defines the Arctic Super Cyclone (ASC) processes. Then analyze the activity characteristics of the ASCs and their atmospheric circulation characteristics based on the NCEP/NCAR reanalysis data of the National Snow and Ice Data Center (NSIDC). The results show that the 5% threshold of the minimum pressure in the Arctic for identifying ASCs have a significant unimodal seasonal variation characteristic that is low in winter and high in summer, which means the intensity of ASC in winter is much stronger than that in summer. Most of the ASCs are imported from the Atlantic sector to the polar region via the Nordic Sea, Barents Sea and the Kara Sea. Besides, a small part of the ASCs are imported from the original or Pacific sector. Most ASCs are generated on the north side of the jet axis or outlet area of the jet stream on two oceans. A minimal number of ASCs are generated in the continent or the middle and low latitudes. And the vast majority of ASCs disappear in the polar region and cannot return to the middle latitudes. The frequency of polar native ASC accounted for about one-third of the total, and there was no significant trend of increase or decrease overall. However, the frequency of long-life ASCs increased with a 0.49 times/decade trend, indicating their duration increased. There is a strong correlation between ASCs frequency and the Arctic Oscillation (AO) in winter. There are low-temperature and low-pressure anomalies in the polar region of the regression of the atmospheric circulation pattern. The upper polar vortex deepens and the two ocean jets turn northward, while the central axis of the mid-latitude jet stream is weak. The formation and development of ASCs are not only conducive to the transition of AO to the positive phase, but also conducive to the enhancement of ASC activity under the positive phase of AO, which is a potential indicator of AO phase change.

During the ice melting season, the surface, bottom and lateral melting of natural ice floes coexist, and the melting rate of the three is that the melting rate of the bottom is greater than the lateral, and the lateral is greater than the surface. And the smaller the ice floe size, the higher the proportion of lateral velocity. In order to solve the problem of including the small-scale ice floe scale indicators into the melting parameterization plan, in the low-temperature environment laboratory without radiation, no flow rate, controlled air temperature and water temperature, the disk samples of natural sea ice and artificially frozen fresh water ice were carried out. Experiments on the melting process of disc samples with different initial water temperatures and different initial diameters were carried out. Obtain the disc sample diameter, thickness and mass melting process. Based on these experimental data, a new indicator of sample diameter-to-thickness ratio was constructed. Through physical analysis and mathematical statistics, the melting rate of the surface and bottom surface of the sea ice and freshwater ice sample was established with the temperature gradient, the lateral melting rate, temperature difference, and diameter. The relationship between the thickness ratio. These relationships can be applied to the melting parameterization scheme of floating ice within a natural diameter range of 100 m. It is expected to solve the demand for numerical simulation of the energy and mass balance of the summer melting season of Arctic sea ice and coastal freshwater ice at the sea estuary.