Coastal salt marsh margin, as the transition zone between salt marsh and tidal flat, presents three types of three-dimensional form: smooth, transition and cliff. And it shows different curvilinear features in the planar shape. As a high dynamic bio-geomorphic system, marsh margin changes rapidly due to the influence of natural processes and human activities. But the lack of high-resolution observational data makes further understanding of this change difficult. Here, we address this challenge using UAV-based Structure-from-Motion (UAV-SfM) photogrammetry which has the advantages of high resolution, non-invasive, repeatability, and low cost. We conducted two aerial surveys of salt marsh on Jiangsu coast, to obtain orthophotographs and Digital Surface Model (DSM) with cm-level pixel resolutions. And it supports us to determine the location of marsh margin, classify the type of the margin, and quantitatively describe the topography changes. We found the smooth and cliff margin are stable and dominant. The smooth margin has complex planar shape and retreats slowly. And the transition and cliff margin have regular shape and retreat fast. The transition margin changes drastically and turns to the cliff margin. This work proves that UAV-SfM photogrammetry is suitable for efficient and accurate quantification of the topography of marsh margin, and provides a new perspective for understanding the evolution process of marsh margin.

We can discover that there exist storm currents along Yangjiang sea area of western Guangdong waters in spring and summer of 2019 by analyzing materials which measure hydrologic and hydrometeorological along west coast of Guangdong flow Yangjiang sea area from 2018 to 2019. The result of research shows: Firstly, the velocity of 2 m water depth at the observation site reached 164.7 cm/s and 9 m water depth at the observation site reached 127.6 cm/s at 6:00 a.m. on May 5, 2019. The velocity of Yangjiang Shapa sea area 2 m water depth at the observation site reached 161.8 cm/s and 9 m water depth at the observation site reached 156.6 cm/s at 4:00 to 5:00 a.m. on August 1, 2019. Secondly, the suddenly strong currents in spring and summer have typically shock current trait in the Yangjiang 20 m to 30 m sea area along the shore current area of western Guangdong. The strong current happens at the surface of the ocean during the time of rising tide for 2 h to 4 h. Thirdly, during the transition period of southwest wind and northeast wind, the coastal sea area of western Guangdong is prone to form a water convergence zone. The sea level of the coastal sea area rises, and the sea level of the offshore sea area drops. The strong horizontal pressure gradient force from the shore to the outside causes the coastal water to strengthen the westward movement, resulting in shock current.

Based on the ERA5 reanalysis data and the meteorological observation data obtained during Chinese Arctic Research Expeditions, the temporal and spatial variation characteristics of the key near-surface meteorological parameters that influence ship navigation in the Arctic passages in summer are analyzed. The results show that the weather conditions in July and August are the most suitable for ship navigation in the Arctic passages. The low temperature, strong wind and huge wave weather increase significantly in September, which impacts ship navigation greatly. The weather in October is even worse, posing a quit challenge to ship navigation. Low temperature mainly occurs in the middle of each passage, and strong wind and huge wave are concentrated in the areas at both ends of the passages. Both the strong wind probability and huge wave probability show a decreasing tendency in the entire Arctic passages in summer with large interannual changes except for the Norwegian Sea and Barents Sea in October and the central Arctic in summer. According to the observation data, it is found that the northeast passage has the poorest visibility, the northwest passage has the best visibility, and the trans-Arctic passage has moderate visibility.

The Bering Sea is one of the most obvious areas with reduced winter sea ice in Arctic region. The seasonal and long-term variations of sea ice in this region are closely related to the local climate, hydrological environment and ecosystem, as well as to Chinese weather and climate. In order to identify the long-term variation of winter sea ice in this region, the trend and spatial difference of sea ice extent in Bering Sea from 1960 to 2020 were analyzed by using the sliding t-test and linear regression analysis method based on Hadley Center data, and the effects of atmospheric forcing, such as general circulation, on sea ice change were analyzed. The results showed that the winter sea ice extent of the Bering Sea decreased significantly from 1960 to 2020, and there were significant abrupt changes in the 1970s and around 2000. During these processes, the Aleutian low pressure center and low pressure were strengthened, the core position shifted to the west of Bering Sea and the corresponding wind field distribution changes. Such process has a nearly 20-year cycle of oscillation. At the same time, the phase change of the Pacific Decadal Oscillation can regulate the meridional wind by changing the sea level pressure, and alter the thermal advection into the Bering Sea, thus affecting the winter sea ice extent. Therefore, winter sea ice in the Bering Sea is mainly controlled both by the Aleutian low pressure system and the North Pacific decadal oscillation, as well as the gerneral climate warming.

In this paper, sediment smear observations, X-ray diffraction analyses, major, trace and rare earth elements analyses, and in situ micro zone geochemical analyses of single minerals were carried out on samples of core GC02 and GC06 from the rare earth-rich deep-sea sediments in the Central Indian Ocean Basin to explore their geochemical characteristics, material sources and enrichment mechanisms of rare earth elements (REY). The results show that the sediment types of core GC02 are calcareous clay and zeolitic clay, and the sediment types of core GC06 are calcareous clay, zeolite-bearing clay and zeolitic clay. Rare earth elements are enriched in zeolite-bearing clays and zeolitic clays. The North American Shale Composite (NASC) Standardized patterns of REY in the sediments indicate a possible seawater origin. Mineralogical and geochemical signatures indicate that the terrestrial fraction of these sediments in the study area should be the eolian dust material originated primarily from Australian. Elemental correlations and CaO/P₂O₅ ratios indicate that the main host mineral of REY in REY-rich deep-sea sediments is bioapatite (fish teeth/bone), followed by Fe-Mn micronodule. This study summarizes and discusses the formation mechanism of REY-rich sediments and improves a conceptual model for the formation process of REY-rich sediments.

The Yap Trench is an important part of the trench-arc-basin system in the western Pacific Ocean. In the northern part of the Yap Trench, the Yap Trench and the Mariana Trench are typically vertically intersected. The geomorphology of the sea area was studied in detail. The results show that the water depth, morphology and profile of the trenches change obviously near the junction of the two trenches, and have segmented. The slopes on both sides have uplift, depression and fault geomorphology, which are closely related to the special subduction position at the junction of the trenches. In addition, according to the geomorphic characteristics and plate spreading rate, the spreading center of the Parece Vera Basin should be located near 137°35'34''E before 20 Ma, and the Yap Trench is likely to be transformed from the spreading center exposed by the Parece Vera Basin.

This study compiled the data of ^239+240Pu specific activity, ²⁴⁰Pu/²³⁹Pu atom ratio and ^239+240Pu flux or inventory in the East China Sea and adjacent waters. Based on the ^239+240Pu concentration in atmospheric fallout, ^239+240Pu in seawater, ^239+240Pu in organisms, ^239+240Pu in sediment trap and ^239+240Pu in sediment, the geochemical behavior of ^239+240Pu were explained in the East China Sea and adjacent waters. The results showed that global fallout and Pacific proving grounds close-in fallout were the two major sources of ^239+240Pu. Under the influence of water masses such as the Changjing River diluted water, Zhejiang-Fujian Coastal Current, Taiwan Warm Current, Kuroshio Current and upwelling current, mixing effect and removal effect, the concentration of ^239+240Pu in coastal waters of the East China Sea showed a trend of removal over time, the burial depth of ^239+240Pu in the near shore sediments was deeper than that in the far sea area. In the northeast of Taiwan Island of China, the ^239+240Pu specific activity and ^239+240Pu inventory in Okinawa Trough increased significantly under the influence of Kuroshio current intrusion and upwelling current. At the same time, this study found that the relationship between ^239+240Pu specific activity and ²⁴⁰Pu/²³⁹Pu atom ratio in surface sediments of the East China Sea, and confirmed the existence of a tributary of the Kuroshio bottom in northeastern Taiwan, and indicated the location where the Taiwan Warm Current and a tributary of the Kuroshio bottom may intersect.

The purpose of this paper is to clarify the genesis of natural gas of Y gas field, and establish accumulation model to guide the next exploration deployment in X Sag, East China Sea Basin. Based on the analyses of natural gas composition, carbon isotope of alkane gas, light hydrocarbon and biomarker compound of condensate oil, this paper systematically studies the genetic types and sources of oil and gas, establishes the reservoir accumulation model of Y large and medium-sized gas field, and puts forward the exploration direction of large and medium-sized gas field. The analyses of carbon isotope, light hydrocarbon and burial history show that the natural gas in Y gas field is highly mature coal type gas generated by the source rocks of middle Eocene Pinghu formation in the sag during the Longjing movement period (13 Ma BP). The characteristics of pristane/phytane and regular sterane of condensate oil reflect that the source rocks of middle Eocene Pinghu formation in the central sag are developed in tidal flat and lagoon sedimentary environment with weak oxidation weak reduction, and there are a certain number of lower aquatic organisms in the hydrocarbon generating parent material. Y gas field has a spatiotemporal coupling reservoir accumulation model of “Pinghu formation source rock, Huagang formation large channel sand reservoir and Mid-Miocene compressional tectonism” in the central sag. It is clear that the compressional anticline belt in the central sag is the main exploration direction of large and medium-sized gas fields in X Sag.

Based on the field data of floc size, suspended sediment concentration and hydrodynamic data, the flocculation characteristics of tidal flat in the south of the Huanghe River Estuary are studied. The results show that the floc size of Huanghe River Estuary tidal flat range is 25.42–264.44 μm, and the average diameter is 95.20 μm. The effect of water turbulence on the flocculation of tidal flat at the Huanghe River Estuary is different, and the upper limit of turbulence on flocculation promotion is about G_l=3.76 s^–1. While the turbulence intensity of water is lower than G_l, turbulence promotes sediment flocculation, and the particle size of floc increases with the strengthen of turbulence intensity, whereas the turbulence mainly inhibits flocculation, the particle size of floc decreases with the attenuate of turbulence intensity. The suspended sediment concentration inhibits the flocculation, particle size of floc corresponding to high sediment content under the same turbulent conditions is smaller. There is a negative correlation between the effective density and the particle size of the floc, and the settling speed of the floc is mainly affected by the particle size. This study complements the understanding of sediment flocculation characteristics in tidal flat of weak tidal estuary.

To analyze the effects of wave height, vegetation density, submerged height of vegetation and current on the bed shear stress at vegetation zones, a three-dimensional wave-current numerical flume is established based on OpenFOAM in this study. The results show that the bed shear stress attenuates along the vegetation zones because of the blocking effect of vegetation, and the decay rate is positively correlated with the wave height, vegetation density and submerged height of vegetation. Compared with pure wave, the amplitude of positive bed shear stress increases and the amplitude of negative bed shear stress decreases under the condition of combined wave-current flows. The weak current has no obvious effect on the size and distribution of the bed shear stress at vegetation zones. In the case of strong current, the bed shear stress increases at vegetation zones and suddenly decreases after the vegetation zones.