Based on the CryoSat-2 L1B data for April 2017−2019, this study compares and analyzes the multi temporal and spatial scale differences of UCL13, DTU10, DTU13, DTU15 and DTU18 mean sea surface height (MSS) models and the Arctic sea ice freeboard retrieval. The differences of various mean sea surface height models and the sea ice freeboard retrieval are compared with UCL13. The experimental results show that the average absolute deviation range between different MSS models is 0.19−0.26 m as well as the standard deviation range is 0.55−0.57 m, among which the difference between DTU18 and UCL13 is the smallest. The mean absolute deviation range of sea ice freeboard retrieved by the other four MSS models is 0.50−0.79 cm with the standard deviation range is 1.17−1.74 cm. Compared to airborne Operation IceBridge (OIB) data, the correlation coefficients of sea ice freeboard retrieved by the five MSS models range from 0.70 to 0.71 with the root mean square error range is 7.7−7.8 cm. Therefore, the biases between various MSS models have little influence on sea ice freeboard retrievals in the entire Arctic region, since biases impact both the lead and ice floe height measurements in the same way, and thus cancel out. However, in the areas with sparse leads, such as the northern Canadian Islands and the Laptev Sea, the sea ice freeboard retrieved by different MSS models varies greatly.

The Nares Strait, located between Ellesmere Island, Canada and Greenland, is one of the important channels for the export of Arctic sea ice. The surface fresh water brought by the melting of these sea ice has a vital impact on the formation of deep water in the Baffin Bay and the Labrador Sea. However, due to its relatively narrow structure, there is no detailed study on the sea ice motion in this area. In this study, the daily Sentinel-1 images were used to extract the information of sea ice motion in the northern region of Nares Strait from September 2016 to August 2017, to show the motion process of ice floes in the strait, and to analyze the characteristics and influencing factors of ice floe motion combined with wind speed, current speed and other data. The results show that wind and current jointly dominate the motion of sea ice, with the correlation coefficients are 0.767 and 0.709, respectively. The multiple linear regression model established by wind speed, current speed and sea ice concentration with ice speed also has the complex determination coefficient reaching 0.727. Further analysis shows that both wind and sea current have relatively less influence on sea ice speed when their speed is relatively stable. The results of this study on the influence of wind and ocean currents on the process of sea ice motion can provide references for the study of ocean-atmospheric dynamics models.

Funded by the National Key Basic Research Development Program, a multi-vessel oceanography survey was conducted synoptically in the South China Sea (SCS) in August 2000, which appeared to be the unique, available synoptic survey that covered the entire SCS basin in deep summer. A number of difficulties were encountered during the survey that affected the quality of observation, even though they were resolved underway. Although some related research works were previously published, no carefully quality control of the data and a comprehensive analyses had ever appeared before. In this work, the original CTD and shipboard ADCP data were carefully calibrated in the first place, and the hydrography and circulation features were then analyzed and discussed to leave a record of the cruises as complete as possible. The results indicate that, in deep summer, the basin shows different physical characteristics on both sides of its SW–NE oriented axis of the basin. The circulation is generally anticyclonic southeast of the axis, in which the Nansha anticyclonic gyre (NSAG) is especially powerful; the area northwest of the axis, in contrast, appears to be dominated by mesoscale features of different categories, where no obvious structure of large scale circulation is found. The analyses confirm that the scales of the NSAG are over 400 km horizontally and nearly 1000 m vertically, with a maximal swirling speed close to 1 m/s, which appears to be the most remarkable circulation feature of the SCS. Moreover, its position and strength are subject to significant interannual variation. In the Mindoro Strait, the exchange flow showes a sandwich structure during the observation period. This is different from our previous understanding and suggests that the strait exchange may have different modes varying with the forcing condition.

The asymmetry of flood and ebb plays an important role in the process of sediment transport and geomorphological evolution, which is a significant feature of the flow field in estuaries. The erosion and accumulation, sediment transport and sediment characteristics in the Huanghe River Estuary based on the measured topography, sediment particle size, hydrological and sediment observation data were analyzed in this paper. The Delft 3D model was used to simulate the flow field in the Huanghe River Estuary, and the spatial distribution of magnitude differences between flood and ebb velocities under different conditions were calculated. Combining the above, the dynamic mechanism of erosion and accretion in coastal area of the Huanghe River Estuary was discussed. The results show that there are multiple siltation and erosion centers distributed between the active river mouth and the Laizhou Bay. There is a noticeable asymmetry of flood and ebb velocities in the area, and there is the flood dominant area off the active river mouth, extending the Laizhou Bay southward in a tongue shape, while the near shore and the Laizhou Bay are dominated by ebb. The erosion and deposition in the Huanghe River Estuary are largely controlled by the spatial distribution of flow velocity asymmetry and the conversion of dominant flow. The strong north wind strengthens and expands flood-dominance, and promotes siltation and coarsening of sediment in the Laizhou Bay.

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.

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.

Online monitoring of pollutants exporting into coastal waters is one of the key technique to realize marine pollution control and coordination of monitoring and management. In this study, based on salinity and fluorescence dissolved organic matter (FDOM) sensor data between 2014−2018 from a multi-parameter buoy deployed in Jiulong River Estuary, a rapid inversion model of chemical oxygen demand (COD) was established. Daily river end member COD concentrations were then extrapolated by effective concentration method. Combined with daily runoff data, daily estuarine export fluxes of COD between 2014 and 2017 were estimated. The factors controlling the flux variations were quantified by flux decomposition model. The results indicated: (1) The average concentration deviation of the inversion was (10.4±8.8)%, indicating the good reliability and stability of inversion model. (2) On seasonal scale, COD concentration in dry season of 2016 was lower than the other dry seasons, which was regulated by 2015−2016 super El Niño events. However, the sharp increase of runoff still significantly increased the COD export flux. (3) On annual scale, the COD export flux in 2016 from the Jiulong River 4.4 ×10⁴ t/a was significantly higher than the other three years (3.0−3.2)×10⁴ t/a. The abnormal precipitation in 2016 caused by 2015−2016 El Niño event was the major reason for such yearly variation. This study highlighted the application of online FDOM sensor system for high frequency monitoring of COD export. This would help to achieve long-term continuous high-frequency monitoring of land-based pollutants and their fluxes into the sea and their regulatory factors. This would provide important technical support for marine ecological environmental protection and management.

Trophic level among main organisms in costal water of Lüsi fishing ground in summer, 2018, were analyzed in this study by stable isotope method. Using IsoSource model, we calculated potential carbon source contribution of the phytoplankton, POM and SOM of consumers, and then compared the former and latter TLs variation of main organisms by overlapping potential carbon source influence. Results showed that phytoplankton and SOM were main potential carbon source of main organisms in costal water of Lüsi fishing ground in summer. Two trophic level spectrums were constructed by overlapping three potential carbon sources and a single species as the baseline organisms, respectively. The trophic level of the right trophic level spectrum ranged from 1.74 to 3.92, which was averagely 0.19 lower than that of the left trophic level spectrum. Although the overall trend was unchanged, the trophic positions of some fish and most shrimps were changed in two spectrums. The baseline organisms in the right trophic level spectrum changed with the different stacking ratio of potential carbon sources, which could reflect the trophic level more effectively and was more suitable for organisms at low trophic levels, such as shrimp and crabs. However, this had little impact on fish in the position of middle and advanced consumers.

Ommastrephes bartramii is an economically important species for Chinese squid jigging fleet. Understanding the spatio-temporal distribution on fishing ground is crucial to the sustainable utilization of fish resources. The study constructed BP (back propagation) neural network models with different scenarios to speculate the dynamics of O. bartramii abundance based on fishery data in the months of July to October during 2000 to 2015. The model with year, month, longitude, latitude, sea surface temperature (SST), and sea surface salinity (SSS) as independent variables, 8 neurons in hidden layers, had the smallest mean square error, and thus selected as optimal model. The results showed that the significant fluctuation in CPUE between years, the local abundance was low and scattered in July and October, whereas was high and concentrated at 41.5°−43.5°N, 155°−160°E in August and September. Environmental factors, including SST and SSS affect the spatio-temporal distribution of local abundance, and should be considered in stock assessment and management.