The temporal and spatial variation characteristics and influencing factors of euphotic depth and primary productivity in the Zhanjiang Bay were studied by applying voyage data of four seasons from 2016 to 2017．The results showed that the average value of euphotic depth was (6.95±3.17) m, and the spatial variations were more obvious than the seasonal variations. There was a significant positive correlation between K_d (PAR) and turbidity, as the R² of established linear regression model was 0.73 (p<0.01), indicating that suspended particles on euphotic depth was the dominant attenuation factor in the Zhanjiang Bay. The average value of primary productivity obtained by VGPM model was (639.53±427.95) mg/(m²·d), and its temporal and spatial characteristics were basically consistent with euphotic depth, which mean euphotic depth explained the temporal and spatial distribution pattern of primary productivity better than chlorophyll a concentration.

In order to improve the study of the interaction between internal solitary waves and submarine slope sediments, the stage of continued motion on the slope after internal solitary waves fragmentation is focused on in this paper, and conducts physical simulation experiments to analyse the changes in earth pressure and super-pore water pressure in response to the slope to reveal the process of internal wave action. The results show that the sediment particles on the slope are resuspended under the combined action of vortex and seepage caused by the internal solitary waves fragmentation, and the change in slope gradient does not change the dominant dynamic role of the sediment in generating the dynamic response; the amplitude of the internal solitary waves affect the ratio between vortex and seepage, i.e. the vortex is dominant under small amplitude conditions and the seepage is dominant under large amplitude conditions; the fragmented fluid forms a new dynamic role when it rushes out along the slope. The dynamic response of the sediment to the new vorticity is influenced by the slope of the slope. The results of this paper are useful for the study of internal solitary waves resuspension transporting seafloor sediments and modifying seafloor topography.

The applicability of environmental DNA (eDNA) metabarcoding fragments to relative fish species had not been compared. There was a risk of “species loss” in diversity surveys. In order to screen out the best fragments, we compared the resolution rate differences of 15 eDNA metabarcoding fragments in 106 genera (a total of 935 species). The results were as follows: (1) the protein-coding gene (COI, fragment 15) had the highest resolution rate, but the universality of its corresponding primer pairs was the worst; the overall mean distance based on primer pair sequence of fragment 09, fragment 11, fragment 07, fragment 03 and fragment 12 were obviously large, suggesting their eDNA amplification efficiency were possibly low. (2) The resolution rates were significantly affected by the length of fragments, and the fragment 05, fragment 06, fragment 01, fragment 02 and fragment 13 of ribosomal genes had a higher resolution rate except fragment 15. (3) Non-metric multidimensional scaling analysis (NMDS) showed that there were great differences among different genes and different fragments belonging to the same gene. Therefore, the combination application of multi-fragment and multi-gene should be considered; besides, fragment 01 and fragment 02, and fragment 05 and fragment 06 were close to each other in the NMDS plot. They function of fish resolution were overlapped. (4) Species groups affected the resolution results, and eDNA studies stilled need to develop fragments with higher resolution rates. Based on the resolution rate of relative species, the universality of primer pairs and NMDS analysis, this study recommended fragment 01 (Mifish-U) for 2×150 bp sequencing platform and fragment 05 (Ac12S) for 2×250 bp sequencing platform, supplemented by fragment 13 (Vert-16S-eDNA) to investigate the diversity of relative fish. This study provided some support for improving the accuracy of fish eDNA survey results.

The Yellow Sea presents unique topographic conditions, and the tidal wave movement in this area has unique characteristics. In this paper, Geostationary Ocean Color Imager (GOCI) inversion and Oregon State University (OSU) tidal current model are used to obtain the sea surface currents field in the Yellow Sea. Based on the unique tidal wave system in the sea area, the tidal wave interference area is proposed and identified, and then the currents field of GOCI inversion is extracted. And partition of two kinds of trend data usability evaluation, through the validation of the drifting buoy data evaluation. The results show that the sea surface currents field obtained by GOCI inversion and OSU tidal current model has a certain degree of reliability. The AME value of sea surface currents field velocity obtained by GOCI inversion is 0.77, and that obtained by OSU tidal model is 0.49. On the whole, the currents field data obtained by GOCI inversion and OSU tide model are reliable to a certain extent. In the central area of the Yellow Sea near the tidal wave interference area, the consistency between GOCI tidal currents data and OSU tidal currents data is better than that of OSU tidal currents data, and their AAE values are 48.45° and 63.10°, respectively. In the coastal area of the Yellow Sea far from the tidal wave interference area, the consistency between the OSU tidal currents data and the measured data is better than that of the GOCI tidal currents data in terms of velocity magnitude and direction.

The loading tides in the South China Sea and adjacent straits are calculated by means of the Green’s function method based on a high-resolution regional ocean tide model for the South China Sea, the DTU10 global ocean tide model, and the Gutenberg-Bullen A Earth model. The results show that the maximum amplitude of M₂ vertical displacement loading (VDL) tide exceeding 18 mm appears in the Taiwan Strait; the second maximum exceeding 14 mm appears off the north-west coast of Kalimantan. The maximum amplitudes of the K₁ and O₁ VDL tides, exceeding 18 mm and 14 mm respectively, appear near the southern South China Sea; the second maximum exceeding 8 mm, appears in the Beibu Gulf. The distribution patterns of self-attraction and loading (SAL) tides are very similar to those of VDL tides in that the SAL tides have amplitudes about 1.2 times to 1.7 times the corresponding VDL tides and have phases basically opposite to corresponding VDL tides. The maximum amplitude of M₂ SAL tide also appears in the Taiwan Strait and off the north-west coast of Kalimantan, with a magnitude exceeding 24 mm and 18 mm respectively.

The changes of shoreline caused by human activities affect the kinematic characteristics of tidal wave in the propagation process. Based on the hourly tidal level data from five tidal stations in the Wenzhou Bay from 1984 to 2019, the temporal and spatial variation of tidal wave patterns in this area and deconstructed the contribution of major tidal clusters to the tidal asymmetry is analyzed in this study . The results show that the tidal patterns in Oujiang Estuary and Yueqing Bay, two semi-enclosed embayments of the Wenzhou Bay, are obviously different. The tidal symmetry of Oujiang Estuary is flood-dominant tide and the tidal asymmetry increases continuously in the upstream direction, whilst tide is ebb-dominant in Yueqing Bay. Moreover, the tidal asymmetry shows distinct seasonal variation. The skewness ($ \gamma $) reaches maximum in June to July and December to January in the Wenzhou Bay. The tidal asymmetry in this area is mainly controlled by the component groups such as M₂/M₄, M₂/S₂/MS₄ and M₂/N₂/MN₄. The skewness caused by nonlinear interactions from M₂/S₂/MS₄, M₂/N₂/MN₄, O₁/K₁/M₂ shows obvious seasonal variation. Since 2000, the tidal asymmetry of Wenzhou Bay has been decreasing, which is related to the frequent reclamation surrounding the Oujiang Estuary.

Estuarine morphologies play an important role on tidal asymmetry. A two-dimensional numerical model is established with the Humber Estuary, UK as a reference site. A series of simulations are designed to examine the effects of the estuary cross-section shape, planform and convergence on the development of tidal asymmetry, whilst maintaining the same tidal prism. Model results show that deeper channels result in the lag and enhancement of phase difference whilst shallower channels result in a decline in the maximum ebb-tide velocity and longer period of ebb tide, and the estuary tends to be flood-dominated; narrow tidal flat tends to favour ebb dominance while broad tidal flat tends to favour flood dominance. Flood dominance is strongest in the convergent and long estuary. In addition, narrowing the estuary width will enhance the residual flow velocity of the main channel but weaken the residual flow velocity of the tidal flat. With the increase in estuary convergence, the residual flow velocity of the main channel increases but decreases on the tidal flat, and strengthen the flood dominance of the tidal flat. This paper further improves the research on the influence of estuary landforms on tidal asymmetry, which has certain guiding significance for reclamation and coastal engineering.

Current CMIP6 climate models (such as CESM2 and NESM3) use constant snow density, while those models that focus on snow depth and density changes (such as SnowModel-LG) use empirical snow density formulas. Comparing the modeled snow depth with those observed by the CryoSat-2 satellite, it is found that from the perspective of the spatial distribution and average value of the snow depth, it is difficult to detect the effects of varying snow density on the simulation of snow depth in the Arctic Ocean. The model improvement and its mechanism from varying snow depth is still to be further studied. Here an empirical snow density model considering meteorological factors such as air temperature, wind etc., is applied to the SNOTEL observational site to carry out the following sensitivity experiments for different factors: A. snow density model considering all meteorological factors; B. constant snow density model; C. same as A but the influence of wind on the densification is not considered and D. same as A but the influence of temperature on the densification is not considered. The root mean square error of snow depth simulated by experiments A, B, C and D from November 1, 2018 to May 10, 2019 are 4.2 cm, 4.8 cm, 25.9 cm, and 4.2 cm, respectively. The results show that the mean snow density and depth simulated by the varying snow density model are close to the results using constant snow density, but the root mean square error of the simulated snow depth from Case A is the smallest, and the Case A simulation can reproduce the high frequency variations of snow depth on the time scale of several days to ten days. In the meantime, the relative errors in the period with high-frequency snow depth variations are also reduced as they are found to be related. In addition, it is also found that the influence of temperature on snow densification is much smaller than that of wind.

With the intensification of global warming, the source sink process of carbon in the Arctic shelf-edge sea is becoming more and more important in the study of global carbon cycle. As a typical continental shelf marginal sea in the Arctic Ocean, the source, transportation and burial of sedimentary organic carbon in this area are unique under the influence of rivers, sea ice, marine primary productivity and coastal erosion. Based on the sampling of suspended particulate matter (SPM) and hydrological data obtained from the second Sino-Russian Arctic joint expedition during late summer and early fall in 2018, we foucus on the distribution characteristics, sources and influencing factors of particulate organic carbon (POC) in the Laptev Sea. The results show that POC ranges from 35.27 μg/L to 1 185.58 μg/L, with an average of 172.65 μg/L. Under the effect of river input, coastal erosion and marine primary productivity, the distribution of surface POC shows a decreased trend from near shore towards offshore; the bottom POC is mainly controlled by sediments resuspension, and the high content of POC appears in the east of Lena River Delta. There was a significant positive correlation between SPM concentration and POC concentration, indicating its direct impact on the occurrence of POC; a more positive relation is found among the bottom layer samples, which may indicate the varied origin of POC in different layers. The value of δ¹³C_POC in study area value is between −31.03‰ and −25.79‰, and the value of δ¹³C in surface layers is obviously depleted compared with the bottom layer, which is even lower than the end-member of the surrounding terrestrial contributor, suggesting that these POC is not derived from land-based origin. The utilization of the terrestrial POC degraded dissolved inorganic carbon by offshore phytoplankton maybe responsible for this depletion of δ¹³C offshore, which could also be an important process on the supply and source apportionment of POC in this Arctic coastal area.

The change of fluvial suspended sediment concentration (SSC) to the sea directly reflects the effects of riverine anthropogenic activities and natural force. Based on long-term hydrological data at Tarbert Landing Station of the Mississippi River (MR), statistical means, such as percentile method and Mann-Kendall method are used to detect change process of SSC from the MR entering the Gulf of Mexico in recent 40 years, and associated possible influencing factors. The results show that: (1) SSC from the MR entering the Gulf of Mexico is characterized by a staged decline from 1976 to 2015, in the first stage from 1976 to 1987, the SSC is relatively high with an average value of 0.33 kg/m³; in the second stage from 1988 to 2015, the SSC is much lower with a mean value of 0.25 kg/m³. (2) The relationship between daily SSC and runoff of MR follows Gaussian distribution. Compared with the first stage (1976−1987), the rating curve between SSC and runoff in the second stage (1988−2015) is relatively flat, when the number of high daily SSC event over 0.60 kg/m³ reduces significantly. SSC increases with the runoff in low-action flows and reaches the maximum when the runoff approaches 20 000 m³/s, but decreases with the runoff thereafter. The rating curve between monthly SSC and water discharge of the MR exhibits “double-loop” shape during 1976−1987, but presents clockwise “single loop” with “sediment before water” during 1988−2015. (3) Flood diversion project construction and soil conservation measures dominate the fluvial SSC from the MR into the Gulf of Mexico. The construction of flood diversion engineering reduces the sediment source along the river channel, and the soil conservation measures repress the land erosion, which have combined to keep the SSC at a relatively low level. In addition, SSC in the MR presents minor response to extreme hydrological events.