Large-scaled reclamation modifies the coastal environment dramatically while accelerating the disappearance of salt marshes, which causes the degradation of the coastal ecosystem and the biodiversity function. In this study, we explored the changes of tidal flat and salt marsh coverage in a small-scale tidal flat with an area of ~160 000 m² in the plain coast of Jiangsu Province, China. Human activities (e.g., the construction of dikes) are a crucial contributor that benefits for the tidal flat accretions and the following changes of salt marsh coverage. Located in the front of the man-made “concave coastline”, the study area is suitable for sediment accretion after the dike construction in the end of 2006. On the basis of the annual tidal surface elevation survey from 2007 to 2012, the sedimentation rates in the human influenced tidal flat varied from a few centimeters per year to 23 cm/a. The study area experienced a rapid accretion in the tidal flat and the expansion of the salt marsh, with the formation of a longshore bar, and a subsequent decline of the salt marsh. Breaking waves during the flooding tide brought much sediment from the adjacent tidal flat to the study area, which caused burial and degeneration of the salt marsh. The vertical grain size changes within a 66 cm long core in the study area also demonstrated the above changes in the tidal environment. This study indicates that the responses of small-scale tidal flat changes to reclamation are significant, and the rational reclamation would benefit for the new salt marsh formation in front of the dikes. Further research about the evolution of small scale tidal flat as well as the spatial planning of the polder dike should be strengthened for the purpose to maintain a healthier coastal environment.

A buoy of 10 m in diameter was used to record the current speed and direction in a vertical profile in the offshore area of the Changjiang (Yangtze River) Estuary (with an average water depth of 46.0 m) for one year. The results include: (1) the currents rotate clockwise and the current direction is consistent in a vertical profile without clear seasonal variations. (2) The horizontal current speeds are generally high, with a maximum of 128.5 cm/s occurring in summer and 105.5 cm/s appearing in winter commonly close to the surface. The average current speeds in the vertical profile fall in the same range (the differences are less than 8.0 cm/s), with the maximum of 47.0 cm/s occurring in summer and 40.8 cm/s in winter. The average current speed during spring tides is twice that during neap tides (26.5 cm/s). (3) Significant differences of speeds are observed in the vertical profile. The maximum current speed occurs at either surface (spring and winter) or sub-surface (summer and autumn), with the minimum current speed appearing at the bottom. The maximum average current speed of all layers is 57.9 cm/s, which occurs in the 18-m layer during summer. (4) The average speed of the residual currents ranges from 7.5 cm/s to 11.3 cm/s, with the strongest occurring in spring and weakest in winter. The residual currents of all layers are eastward during spring and winter, whereas northeastward or northward during summer and autumn. (5) The currents in the offshore of Changjiang Estuary are impacted collectively by diluted Changjiang River discharge, the Taiwan Warm Current, monsoon and tides.

The exploration of unconventional and/or new energy resources has become the focus of energy research worldwide, given the shortage of fossil fuels. As a potential energy resource, gas hydrate exists only in the environment of high pressure and low temperature, mainly distributing in the sediments of the seafloor in the continental margins and the permafrost zones in land. The accurate determination of the thickness of gas hydrate stability zone is essential yet challenging in the assessment of the exploitation potential. The majority of previous studies obtain this thickness by detecting the bottom simulating reflectors (BSRs) layer on the seismic profiles. The phase equilibrium between gas hydrate stable state with its temperature and pressure provides an opportunity to derive the thickness with the geothermal method. Based on the latest geothermal dataset, we calculated the thickness of the gas hydrate stability zone (GHSZ) in the north continental margin of the South China Sea. Our results indicate that the thicknesses of gas hydrate stability zone vary greatly in different areas of the northern margin of the South China Sea. The thickness mainly concentrates on 200–300 m and distributes in the southwestern and eastern areas with belt-like shape. We further confirmed a certain relationship between the GHSZ thickness and factors such as heat flow and water depth. The thickness of gas hydrate stability zone is found to be large where the heat flow is relatively low. The GHSZ thickness increases with the increase of the water depth, but it tends to stay steady when the water depth deeper than 3 000 m. The findings would improve the assessment of gas hydrate resource potential in the South China Sea.

According to a series of important historical maps, i.e., the Location Map of the South China Sea Islands, the Nansha Islands, Zhongsha Islands, Xisha Islands, Yongxing Island and Shidao Island, and Taiping Island (archived by the Territorial Administration Division of the Ministry of Interior of Republic of China in 1946), and the Administration District Map of the Republic of China published in 1948, the dashed line surrounding the South China Sea Islands represents China’s sea boundary in the South China Sea at that time. It was both connected with, and an extension of, the land boundary of China. At that time the dashed line was used to represent the waters boundaries while the solid line was used to represent the land boundary—a universal method used in maps that was then recognized internationally. The above observation provides historical and scientific evidence of China’s sea boundary in the South China Sea that is useful for the international maritime delimitation over the South China Sea area.

The invasions of the alien species such as Spartina alterniflora along the northern Jiangsu coastlines have posed a threat to biodiversity and the ecosystem function. Yet, limited attention has been given to their potential influence on greenhouse gas (GHG) emissions, including the diurnal variations of GHG fluxes that are fundamental in estimating the carbon and nitrogen budget. In this study, we examined the diurnal variation in fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) from a S. alterniflora intertidal flat in June, October, and December of 2013 and April of 2014 representing the summer, autumn, winter, and spring seasons, respectively. We found that the average CH₄ fluxes on the diurnal scale were positive during the growing season while negative otherwise. The tidal flat of S. alterniflora acted as a source of CH₄ in summer (June) and a combination of source and sink in other seasons. We observed higher diurnal variations in the CO₂ and N₂O fluxes during the growing season (1 536.5 mg CO₂ m^–2 h^–1 and 25.6 μg N₂O m^–2 h^–1) compared with those measured in the non-growing season (379.1 mg CO₂ m^–2 h^–1 and 16.5 μg N₂O m^–2 h^–1). The mean fluxes of CH₄ were higher at night than that in the daytime during all the seasons but October. The diurnal variation in the fluxes of CO₂ in June and N₂O in December fluctuated more than that in October and April. However, two peak curves in October and April were observed for the diurnal changes in CO₂ and N₂O fluxes (prominent peaks were found in the morning of October and in the afternoon of April, respectively). The highest diurnal variation in the N₂O fluxes took place at 15:00 (86.4 μg N₂O m^–2 h^–1) in June with an unimodal distribution. Water logging in October increased the emission of CO₂ (especially at nighttime), yet decreased N₂O and CH₄ emissions to a different degree on the daily scale because of the restrained diffusion rates of the gases. The seasonal and diurnal variations of CH₄ and CO₂ fluxes did not correlate to the air and soil temperatures, whereas the seasonal and diurnal variation of the fluxes of N₂O in June exhibited a significant correlation with air temperature. When N₂O and CH₄ fluxes were converted to CO₂-e equivalents, the emissions of N₂O had a remarkable potential to impact the global warming. The mean daily flux (MF) and total daily flux (TDF) were higher in the growing season, nevertheless, the MF and TDF of CO₂ were higher in October and those of CH₄ and N₂O were higher in June. In spite of the difference in the optimal sampling times throughout the observation period, our results obtained have implications for sampling and scaling strategies in estimating the GHG fluxes in coastal saline wetlands.

The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores, along with the hydrologic data and human activities in the catchment. The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea, which could be divided into three stages as 1958–1970, 1971–1990 and 1991–2009. Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes. There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010, i.e., 1940–1950, 1951–1980, 1981–1990 and 1991–2010. The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980, whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990. Despite the further reduction of the water and sediment input into the sea from 1990 to 2009, this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly, the significantly increased silt contents of the sensitive component.

This study aims at explaining the relationship between thermodynamic characteristics and direction of rotation of mesoscale eddies (MEs). The geometric characteristics of the MEs are under the following assumptions: the structure of the MEs is symmetrical, and changes of oceanic physical variables are close to linear features in the radial direction in the ME regions. Based on these assumptions, by using primitive equations without friction under a cylindrical coordinate system, the thermodynamic characteristics of the MEs are derived, showing that the conventional relationship of warm anticyclonic eddies with high sea surface height (SSH) and cold cyclonic eddies with low SSH is not consistent with the SSH and sea surface temperature (SST) observations of eddies. The results show that the symmetrical form is an ideal approximation for the geometric characteristics of MEs. In consideration of the above assumptions, there are advantages for derivation of the characteristics of the MEs under a cylindrical coordinate.

In the east of China’s seas, there is a wide range of the continental shelf. The nutrient cycle and the carbon cycle in the east of China’s seas exhibit a strong variability on seasonal to decadal time scales. On the basis of a regional ocean modeling system (ROMS), a three dimensional physical-biogeochemical model including the carbon cycle with the resolution (1/12)°×(1/12)° is established to investigate the physical variations, ecosystem responses and carbon cycle consequences in the east of China’s seas. The ROMS-Nutrient Phytoplankton Zooplankton Detritus (NPZD) model is driven by daily air-sea fluxes (wind stress, long wave radiation, short wave radiation, sensible heat and latent heat, freshwater fluxes) that derived from the National Centers for Environmental Prediction (NCEP) reanalysis2 from 1982 to 2005. The coupled model is capable of reproducing the observed seasonal variation characteristics over the same period in the East China Sea. The integrated air-sea CO₂ flux over the entire east of China’s seas reveals a strong seasonal cycle, functioning as a source of CO₂ to the atmosphere from June to October, while serving as a sink of CO₂ to the atmosphere in the other months. The 24 a mean value of air-sea CO₂ flux over the entire east of China’s seas is about 1.06 mol/(m²·a), which is equivalent to a regional total of 3.22 Mt/a, indicating that in the east of China’s seas there is a sink of CO₂ to the atmosphere. The partial pressure of carbon dioxide in sea water in the east of China’s seas has an increasing rate of 1.15 μatm/a (1μtm/a=0.101 325 Pa), but pH in sea water has an opposite tendency, which decreases with a rate of 0.001 3 a^–1 from 1982 to 2005. Biological activity is a dominant factor that controls the $ {p_{{\rm{C}}{{\rm{O}}_2}{\rm{air}}}} $ in the east of China’s seas, and followed by a temperature. The inverse relationship between the interannual variability of air-sea CO₂ flux averaged from the domain area and Niño3 SST Index indicates that the carbon cycle in the east of China’s seas has a high correlation with El Niño-Southern Oscillation (ENSO).

The major and trace elements in 110 surface sediment samples collected from the middle of the Bay of Bengal (mid-Bay of Bengal) are analyzed to investigate provenance. Si levels are highest, followed by Al, and the distributions of these two elements are identical. The average CIA* (chemical index of alteration) value is 72.07, indicating that the degree of weathering of the sediments in the study area is intermediate between those of sediments of the Himalayan and Indian rivers. Factor analyses and discrimination function analyses imply that the two main provenances are the Himalayan and the Indian continent. The inverse model calculation of the Ti-normalized element ratios of the Bay of Bengal sediments indicate an estimated average contribution of 83.5% and 16.5% from the Himalayan and peninsular Indian rivers to the study area, respectively. The Himalayan source contributes more sediment to the eastern part of the study area, whereas the western part receives more sediment from the Indian Peninsula than did the eastern part. The primary mechanisms for deposition of sediments in the study area are the transport of Himalayan matter by turbidity currents and river-diluted water and the transport of Indian matter to the study area by a surface circulation in the Bay of Bengal, particularly the East India Coastal Current.