Volume articles

Mangroves, coastal salt marshes and seagrass beds, as the typical coastal blue carbon ecosystems, have been widely recognized for their remarkable capacity in carbon storage. Vegetation carbon pool and sediment (or soil) carbon pool were considered to be the major carbon pools within the coastal blue ecosystems and their variations determined the overall carbon sequestration of the ecosystems. From a perspective of carbon pool interactions, this study summarized the previous research work based on literature review, including the interactions within various vegetation carbon pools and within various sediment carbon pools, as well as the interactions between vegetation and sediment carbon pools. Interspecific competition, allochthonous carbon input and biogeomorphology were found to be the key to understand the carbon pool interactions. Finally, a perspective on the current state-of-the-art of blue carbon pool study is offered, with challenges and suggestions for future directions.

Costal ocean receives a bunch of carbon materials and nutrients from terrestrial sources, relates a lot of carbon-involving interactions. Meanwhile, it is normal that sedimentary reservoir-cap systems with good trap conditions beneath coastal ocean, these entrapments have potentials to storage CO₂. This review focuses on the coastal ocean as the research object, and introduces the carbon cycle processes in coastal ocean, their factors which could influence CO₂ fluxes in the carbon cycle processes, and the potential carbon storage mechanisms of the coastal marine sedimentary basins. From the perspective of “carbon peaking and carbon neutrality”, the significance of coastal oceans for “Ocean Negative Carbon Emission (ONCE)”, its potential promotion paths, carbon storage potentials in sedimentary basins and the problems faced by coastal oceans are discussed. Overall, the costal ocean is one of the important blue carbon sink areas. In the coastal marine seawater system, improving the reaction efficiency of microbial carbon pump and carbonate carbon pump have positive significance for CO₂ negative emissions; The suitable reservoir-cap systems for CO₂ storage beneath coastal ocean can not only provide extra spaces, but also guarantee the safety for CO₂ storage. In the future, the main research directions should be to inhibit the conversion process of carbon materials to CO₂ in coastal oceans and ensure the safety of CO₂ storage in sedimentary reservoirs, these could provide theoretical basis and technical guarantee for CO₂ negative emissions.

Marine gas hydrate deposits are significant temporal reservoirs for hydrocarbons migrating from deep sources. This is crucial to our understanding of ocean carbon cycling. The cold seep, a geological process regarding gas leakage from deep or shallow sources, is usually linked with gas hydrate decomposition. In this thesis, we reviewed the latest applications of in situ monitoring and detecting methods regarding the leakage plumes, migration pathways, and seafloor geomorphologies associated with gas hydrate and cold seep systems, primarily including vessel-and land-based gas plume measurements, surface ocean-lower atmosphere hydrocarbon emission detections, seafloor visualization techniques, and in situ observation networks. The integrated applications of these in situ observation methods provide a nuanced view of the temporal and spatial variability of hydrate and cold seep systems, facilitate understanding of the fate of hydrocarbons, and expand our knowledge of cold-seep biota in a watery desert.

As the second largest river in Zhejiang Province, Oujiang River has about 20 billion cubic meters of water flowing into the East China Sea every year. In order to explore the COD_Mn flux of Oujiang River into the sea and its characteristics of long-term changes based on the correlation between the measured data and the spectral information of Landsat-8 remote sensing image, the Oujiang River COD_Mn remote sensing inversion model was constructed (the average relative error is 28%) and the inversion results of COD_Mn in the middle and lower reaches of Oujiang River in 1986-2020 were obtained. In addition, based on rainfall data, the runoff and COD_Mn flux into the sea was further estimated and then remote sensing monitoring of long-term changes of Oujiang COD_Mn flux into the sea was realized. The results show that the difference of COD_Mn between dry and wet seasons in the Oujiang River Estuary is not obvious, but in general, the COD_Mn in wet season was slightly higher than that in dry season. From 1986 to 2020, the COD_Mn flux of Oujiang River into the sea fluctuated greatly, with a slight downward trend.

Carbon stock variation observation forms the basis for coastal saltmarsh blue carbon sink accounting. In order to accurately estimate the carbon sequestration rate of coastal saltmarshes over a short-term scale (seasonal to annual), this study carried out field observations and sample collections within a coastal saltmarsh on the south bank of Hangzhou Bay, covering different seasons of 2022. This study was primarily based on high-resolution surface monitoring by Surface Elevation Table (SET) systems. The results revealed a seasonal plant growth pattern between March and September for both the native species Scirpus mariqueter and the exotic species Spartina alterniflora. In terms of belowground biotic carbon stock changes, over the growing season, the carbon stock increase for Scirpus mariqueter reached 11 g C·m^-2 whilst this value was 56 g C·m^-2 for Spartina alterniflora. The SET data indicated a sedimentation rate of 13.02 cm·a^-1 within the Spartina alterniflora saltmarsh, higher than that of the Scirpus mariqueter saltmarsh, 12.30 cm·a^-1. Calculating the sedimentation rate data with sediment bulk density and organic carbon content, the sediment carbon accumulation rate of Scirpus mariqueter saltmarsh was estimated to be 460 g C·m^-2·a^-1, lower than 588 g C·m^-2·a^-1 of the Spartina alterniflora saltmarsh. Combining the biotic carbon stock increase and sediment carbon stock increase, the carbon sequestration rate for the Spartina alterniflora saltmarsh was found to be 644 g C·m^-2·a^-1, higher than the value of Scirpus mariqueter saltmarsh, 471 g C·m^-2·a^-1. Thus, the difference in carbon sequestration abilities of native and exotic species should be considered for future coastal blue carbon management.

Tidal flat is an important part of coastal wetland, and is of great significance for blue carbon. Remote sensing is the most widely used method for tidal flat monitoring, but due to the influence of tides, the area of tidal flat extracted by remote sensing is often greatly underestimated. In this study, Sentinel-2 satellite images from 2016 to 2021 were used to extract the instantaneous area of tidal flats in Yueqing Bay, and the quantitative relationship between tidal flats area and tidal level or the tidal level correction model for tidal flats area was established. On this basis, Landsat satellite images in 7 years from 1988 to 2020 were selected to extract the instantaneous tidal flat area, and the established correction model was used to obtain the corrected multi-year tidal flat area at low tide level, and the change of tidal flat area in Yueqing Bay in recent 30 years and the main driving factors were analyzed. In recent 30 years, the tidal flat area of Yueqing Bay showed a trend of significant increase from 1988 to 1994, sharp decrease from 1994 to 2010, slight increase from 2010 to 2015, and decrease again from 2015 to 2020. The development and utilization of tidal flat by human activities is the main driving factor of tidal flat area change in Yueqing Bay.

Coastal bays are greatly affected by human activities and natural changes, and the influence mechanism of variation in seawater carbon source and sink patterns is extremely complex. Due to the small spatial scale of the bay, it is necessary to use wide-bands high-spatial resolution satellite remote sensing for monitoring the air-sea CO₂ flux. Compared with the traditional kilometer-level ocean color satellite data, the retrieval of the sea surface partial pressure of CO₂ (pCO₂), the key parameter to calculate air-sea CO₂ flux, is extremely challenging in small-scale bays. Taking Xiangshan Bay in Zhejiang Province in autumn as an example, a satellite retrieval algorithm for sea surface pCO₂ was proposed based on the in situ pCO₂ data and Sentinel-2 satellite images in the past five years, using the machine learning method of support vector machine (SVM). The algorithm validation results showed a good performance with R² of 0.92 and RMSE of 23.23 μatm, and the satellite-derived results were consistent with the in situ values. On this basis, the satellite products of pCO₂ in Xiangshan Bay in autumn from 2017 to 2021 (September to November) were produced. The results revealed that the pCO₂ of Xiangshan Bay showed a decreasing trend from the top of the bay to the mouth of the bay, with an average value of 514.56 μatm, of which the average pCO₂ in the inner bay was 551.94 μatm and the average pCO₂ in the outer bay was 477.19 μatm, which implied that Xiangshan Bay was a source of atmospheric CO₂ as a whole. There was no significant trend change of pCO₂ in autumn in the past five years. Combined with the analysis of in situ data of multiple parameters, it was found that the sea surface pCO₂ of autumn in Xiangshan Bay in 2021 was jointly regulated by physical mixing and biological activities. Sea surface temperature (SST) had a good positive correlation with pCO₂, which was mainly reflected by the thermodynamic equilibrium of carbonate system. In addition, the normalized pCO₂(NpCO₂) with average temperature had a good negative correlation with seawater salinity and dissolved oxygen saturation. The relationship between NpCO₂ and salinity resulted from the exchange of sea water inside the bay and offshore coastal water under tidal effect. Long-time series satellite data analysis also confirmed that sea surface pCO₂ had a relatively consistent trend with the average tide height inside and outside the bay, and this trend was stronger in the outside bay than that in the inner bay. In this study, a set of pCO₂ remote sensing retrieval methods in the small-scale bay was constructed, which laid a good foundation for the subsequent long-time series satellite monitoring of sea-air CO₂ fluxes.

The monitoring of carbon flux dynamics and assessment of carbon sink functions of island forest ecosystems are rarely reported due to their special geographical location and few data sources. In this study, the forest ecosystem of the Nanji Island was used as the research object, the carbon sink potential of island forests and their driving factors were assessed. Based on eddy correlation techniques, the temporal variation characteristics and driving factors of net ecosystem productivity (NEP), gross primary productivity (GPP), and ecosystem respiration (Reco) from 2020 to 2021 were explored. Results showed that the forest ecosystem of Nanji Island was carbon sink. Net CO₂ uptake in 2020 and 2021 were 516 g C·m^-2·a^-1 and 598 g C·m^-2·a^-1, Reco were 1 037 g C·m^-2·a^-1 and 1 646 g C·m^-2·a^-1, and GPP were 1 552 g C·m^-2·a^-1 and 2 244 g C·m^-2·a^-1, respectively. Total solar radiation (Rg), photosynthetically active radiation (PAR), net radiation (Rn) and sensible heat (H) were significantly and positively correlated with NEP and GPP (p≤0.001); air temperature (Tair) and soil temperature (Tsoil) were significantly and positively correlated with Reco(p≤0.001). The photosynthesis time of Nanji Island forest was longer than the carbon sink time on the daily scale. When Tair reached 10.05-27.76 ℃ and PAR reached 110.47-429.44 μmol·m^-2·s^-1, the photosynthesis intensity of island forest was higher than that of ecosystem respiration, which showed CO₂ absorption. The monitoring and assessment of carbon fluxes in the forest ecosystems of Nanji Island will provide an important theoretical support for the establishment of a dynamic monitoring and assessment management system for blue carbon in China.

Mangroves, salt marshes, and seagrass beds are known as the three major coastal blue carbon ecosystems (CBCEs), which play important roles in marine biodiversity maintenance, water purification, nutrient recycling, carbon sequestration and storage. Guangdong Province and Guangxi Zhuang Autonomous Region in China, where the CBCEs are widely distributed, were selected as the research areas, to investigate the spatial relationship between CBCEs and the marine ecological redlines (MERs). The CBCE conservation gap was analyzed, and the recommended priority conservation areas outside the MERs were proposed. The CBCE distribution data obtained from the satellite images in 2019, combined with field survey and UAV remote sensing data collected during 2020 and 2021 showed that the CBCEs in Guangdong totaled 14 481.39 hm² (mangroves 11 928.87 hm², salt marshes 1 258.00 hm², seagrass beds 1 294.52 hm²), whereas the CBCEs in Guangxi totaled 11 751.30 hm² (mangroves 10 171.70 hm², salt marshes 1 450.36 hm², seagrass beds 129.24 hm²). 62.13% of the CBCEs in Guangdong and 59.88% in Guangxi were covered by the MERs. The distribution areas and protection ratios of mangroves and seagrass beds in Guangdong were both larger than those in Guangxi, while the distribution area and protection ratio of salt marshes in Guangxi were larger than that in Guangdong. As to the 3 types of CBCEs in Guangdong, 62.13% of the mangroves, 38.16% of the salt marshes and 85.41% of the seagrass beds were under protection. For the CBCEs in Guangxi, 61.44% of the mangroves, 49.58% of the salt marshes and 52.99% of the seagrass beds were protected. This research suggests the coast from Rongmujiang Bay to Maowei Sea, the areas of Tieshan Bay, Leizhou Bay, Zhelin Bay and other related locations as the recommended priority conservation areas outside the MERs.

The multiple indices of n-alkanes including ∑oddC_25-33, CPI, ACL, C₃₁/C₂₇ and P_mar-aq from a sediment core HKUV16 retrieved in the Pearl River Estuary were analyzed to explore their sources and environmental changes since the mid-Holocene. The distribution features of n-alkanes of core HKUV16 indicated that they were mainly from terrestrial higher vegetation. From 8.0 to 7.0 ka BP, ∑oddC_25-33, CPI, and P_mar-aq increased, while ACL and C₃₁/C₂₇ were low, which showed that terrestrial organic matter input increased and woody vegetation increased. The decrease of ∑oddC_25-33 during 7.0~3.2 ka BP indicated that the input of terrestrial organic matter decreased, while the ACL and C₃₁/C₂₇ showed an increase-decrease-increase trend, suggesting that the Pearl River Basin might have experienced dry-wet-dry climate change. From 3.2 to 2.2 ka BP, high ACL and C₃₁/C₂₇ indicated that herbaceous plants expanded and the climate was relatively arid. The multi-indices showed that the input of n-alkanes to the Pearl River Estuary before 2.2 ka BP was mainly affected by East Asian summer monsoon. However, increasing human activities since 2.2 ka BP might have become the dominant factor for the ecological environment of the Pearl River Basin.

Subaqueous debris flows are widely developed on polar continental margins, many of which are glacigenic, representing the products of ice sheets reaching the shelf edge. In the western Arctic Ocean, a large number of debris flows have been identified at the continental margin west of the Northwind Basin, however research on debris flows within this basin has hardly been carried out. In this study, the distribution of debris flows was outlined and their formation ages were determined using the high-resolution sub-bottom profiler data. Then the mega-scale glacial lineations (MSGL) was used as the judgment indicators to infer the origin of these debris flows. It is found that the debris flows in the study area are mainly distributed on the southwestern and northern-central slope of the western sub-basin, in the southeastern part of the eastern sub-basin, and on the slopes of some seamounts and cliffs. They are from the surrounding continental shelf, ridges and seamounts. Most debris flows coexist with MSGL and are presumed to be glacigenic. More than 9 glacigenic debris flows have been found on the southwestern slope, which may indicate more than 9 ice streams advances through the Broad Bathymetric Trough. The number of ice streams advances are much more than the previous speculation (3-5). There are also some debris flows with no ice-grounding landforms (e.g. MSGL) have been found in the nearby seamounts and are presumed to be non-glacigenic. The shock caused by the grounding of the ice sheets/shelves in the nearby area or tectonic movement may be the trigger factors for this kind of debris flows.

Using Argo measured data combined with satellite remote sensing data and moored buoy data, the upper ocean temperature and salinity response caused by super typhoon Rammasun in 2014 was analyzed and studied. The result shows that super typhoon Rammasun resulted in cooling of sea surface temperature and deepening of mixing layer. Meanwhile, mixing length and vertical velocity induced by typhoon were calculated in this research, which explained the causes of temperature changes in the subsurface layer. Strong mixing and weak upwelling led to warming of the subsurface layer, whereas weak mixing and strong upwelling led to cooling of the subsurface layer. Compared with the change of temperature, the response of salinity was more complex. Precipitation first caused the decrease of surface salinity, and then vertical mixing led to a large increase of surface salinity. However, the effect of precipitation could greatly inhibit this process. After the typhoon departed, the vertical mixing was weakened, and the salinity was greatly reduced because of the heavy precipitation, it was even lower than that before the typhoon.

Wave is an important factor to shape the dynamic geomorphology of the open tidal flat, but researches on tidal-flat wave characteristics are still limited. Taking Nanhui tidal flats in the Changjiang Estuary as an example, the wave characteristic parameters and wave spectrum parameters were obtained by inverting flow-velocity and water-pressure data from the Acoustic Doppler Velocimeters (ADVs) at some fixed platforms, and their changes over tidal cycles and associated influence mechanisms were discussed. The results show that both normal wave direction and prominent wave direction at three stations of Nanhui tidal flats are mainly southeast during the observation period, with long-period swells dominating. The effective wave height of the three stations is positively correlated with the water depth, but the fitting coefficients of each station are different over flood and ebb periods. Wave orbital velocities are obviously modulated by the shallow water effect and the flow directions, and their maximum values usually occur at the early flooding stage, while minimum values can be observed to occur during the current transition periods. The wave energy spectrum during ebb tides is featured by the bimodal pattern because of high influence by tidal levels and coastal topography, and the peak energy is continuously attenuated and gradually dispersed with the concurrent shift of peak frequencies.

With the advancement of observation technology and the improvement of ocean numerical simulation capabilities, some stable subsurface coherent vortices have been widely observed in the ocean, which far from the formation source area. These vortices possess distinctive dynamic characteristics, such as a low potential vorticity center, lens-like structure of isopycnals, weak stratification, and anomalous temperature, salinity, or other tracer properties compared to the surrounding water mass. Their core flow is relatively stronger. These subsurface coherent vortices significantly impact ocean water mass transport, thermohaline circulation and marine biological environment. This paper comprehensively summarizes researches on subsurface coherent vortices in the ocean, including their structure, hydrological characteristics, identifying methods, global distribution, dynamic mechanisms and their important effects on ocean environment. Furthermore, the research perspectives are discussed, such as the difficulties in the research and the issues that need to be solved to comprehensively understand subsurface coherent vortices in the ocean.

Oujiang River is a typical mountain river whose water and sediment fluxes are characterized by a great disparity between flood and dry seasons. Based on the measured data of water discharge and sediment load at the mainstream control hydrological station of Oujiang River in the past 71 years (1950—2020) and 43 years (1956—1998), respectively, the coefficient of nonuniformity, Mann-Kendall non-parametric statistical test and double mass curve were used to analyze the variations of runoff and sediment load during the flood seasons (including plum rain season from April to June and typhoon season from July to September) and dry seasons (non-flooding season from October to March in next year) in the Oujiang River. The results showed that: (1) The peak and valley month of runoff were the same as sediment load. The peak month of both runoff and sediment load appeared in June, while their valley month appeared in December. The plum rain season was the most important period of water and sediment transporting to sea from Oujiang River. (2) The runoff showed significant decreasing trend in the plum rain season, significant increasing trend in non-flooding season, and non-significant trend in typhoon season during 1950—2020 in Oujiang River. The nonuniformity of intra-annual distribution for runoff had become more uniform obviously, resulting from the regulation of reservoirs. (3) The sediment load showed significant decreasing trend in the plum rain season due to the interception of reservoirs, and no significant trend in typhoon season and non-flooding season during 1956—1998 in Oujiang River. The nonuniformity of intra-annual distribution for sediment load showed little change, which might relate to the nonuniformity of intra-annual distribution for precipitation. (4) The relationship between sediment load and runoff during typhoon and non-flooding season changed in 1975 and 1959, respectively, both of which were related to the heavy rainfall within the river basins.

Coastline is one of the important geographical elements to describe the boundary between land and sea. Under the dual influence of natural factors and socio-economic factors, coastline dynamic evolution of different intensities continues to occur. Based on Landsat series satellite remote sensing images, the spatial and temporal evolution of the coastline of Nan’ao Island from 1976 to 2021 was analyzed by RS and GIS technology combined with field investigation, and the driving factors were analyzed by grey correlation analysis. The results show that : (1)In the past 45 years, the coastline of Nan’ao Island has changed significantly. The coastline length has increased by 11.06 km, and the fractal dimension have generally increased.(2)During the study period, the type of coastline changed from natural coastline dominated by bedrock to artificial coastline, the comprehensive index of coastline utilization show an increasing trend, and the main structure of coastline development and utilization show a form of single to multiple.(3)The evolution of the coastline of Nan’ao Island has obvious regional differences. That of Houzhai Town is greatly affected by human factors, and its evolution is more significant. The coastlines of Yun’ao and Shen’ao Towns are mainly affected by natural factors, and their evolutions are relatively slow.(4)Typhoon(natural disasters) and population are the main driving factors of the coastline evolution of Nan’ao Island.

Two-phase leaching method can separate hydrogenetic and residual mineral phases of ferromanganese nodules, which will provide valuable information with the research of ferromanganese nodule mineralization and pale-environment. In order to study the applicability of the two-phase leaching method in the nodule mineralization research for different types of nodules compared to the bulk sample results, the ferromanganese nodules samples from six stations were selected, which were collected on the seamounts area of western Pacific Ocean and CC Zone of eastern Pacific Ocean, respectively. Geochemical and mineralogical compositions of the bulk samples were analyzed, and elements compositions of the hydrogenetic and residual mineral phases were analyzed, which were obtained using the two-phase leaching method. The results indicated that the mass ration variation of the residual mineral phases was not obvious with about 14.0%-17.6%, which had high contents of Nb, Rb, Ta, Ti, Zr. Contents and relevant rations of elements such as Co, Ni, Cu, Zn, Sr, REY in the hydrogenetic mineral phase showed similar features with those in the bulk samples. Proportion of elements contents like Ti, Nb, Sr between hydrogenetic and residual mineral phases showed well negative correlation with Mn/Fe values, which probably could be regarded as index for ferromanganese nodule mineralized environment research in the future.

The radioactive isotope radon-222(²²²Rn) is an inert element derived from the decay of uranium in the earth’s strata. Due to its stability, ease of measurement and significant difference in activity between groundwater and surface water, it has been widely used as a tracer in the study of submarine groundwater discharge (SGD) in recent years. In this study, the ²²²Rn activity of seawater was selected as the object of study, and the spatial and temporal characteristics of ²²²Rn were analyzed, and the SGD flux was estimated through a ²²²Rn mass balance model, based on two cruises of August-September, 2021 and December, 2021-January, 2022 from the northern Beibu Gulf. The results show a spatial and temporal variation of ²²²Rn distribution which was significantly affected by the terrestrial SGD process. The mean ²²²Rn activity decreased by about 40% in winter compared with that in summer. In summer, there show high ²²²Rn activity in bottom water especially from the northern part of the research area with a strong SGD process, but with low ²²²Rn activity in winter with weak SGD process. Based on the ²²²Rn mass balance model, the SGD fluxes of 4.16 cm·d^-1 in summer and 2.88 cm·d^-1 in winter were calculated from the research area, which shows significantly high SGD flux in summer dominant with nearshore SGD and low SGD flux in winter dominant with offshore SGD. Since the research area is surrounded by land and islands, the SGD processes were likely to be an important natural pathway for the terrestrial sources transporting to the nearshore waters.

The diversity and geographical distribution pattern of deep-sea polychaete animals have been a research focus of deep-sea biodiversity science. Data from the Ocean Biogeographic Information System (OBIS) were used to analyze the characters of deep-sea benthic polychaetes diversity and distribution in the western Pacific. The results show that the collection data mainly distributed in the distinctive geographic units (e.g. seamounts and trench) near coastal countries. A total of 318 species from 51 families were recorded in the study area. Polynoidae has the highest species diversity and the largest depth distribution. The number of species decreases with depth, but increases at 2 500-3 000 m and 4 000-4 500 m. The deep-sea polychaetes exhibit high levels of endemism. Many species are endemic to hydrothermal vents. For deep-sea benthic polychaetes in the western Pacific, four biogeographical areas are recognized: Sea of Japan, biogeographic area near the continent represented by Sagami Bay, region characterized by hydrothermal vents (Okinawa Trough, Manus Basin, Fiji Basin) and regions characterized by trenches or plains (Japan Trench, Kuril-Kamchatka Trench, eastern Australia and New Zealand area).

Micropropagules with rapid growth and reproduction are an important seed sources for the early outbreak of the green tide. In this study, the micropropagule seedlings of Ulva prolifera were collected as experimental materials, and two CO₂ levels (LC, 400 μatm; HC, 1 000 μatm) and three dissolved inorganic phoshphate (DIP) concentrations (LP, 0.32 μmol/L; MP, 3.62 μmol/L; HP, 36.2 μmol/L) were set to analyze the effects of CO₂, DIP and their interaction on its growth and photophysiological performance. The results of the growth indexes including relative growth rate (RGR), net photosynthetic rate (P_n) and respiration rate (R_d) showed that CO₂ significantly affected on the RGR and P_n (p<0.05). DIP significantly affected on the RGR, P_n and R_d (p<0.05). Specifically, RGR and P_n were significantly positively correlated with DIP concentration (p<0.05), while R_d was significantly negatively correlated with DIP concentration (p<0.05). However, their interaction had no significant effect on RGR, P_n and R_d (p>0.05). The results of fluorescence parameters including effective quantum yield [Y(II)], maximum relative electron transfer rate (rETR_max), saturation light intensity (E_k) and light utilization efficiency indicated (α) reveal that CO₂ significantly affected on the rETR_max and E_k (p<0.05), but had no significant effect on the Y(II) and α (p>0.05). DIP significantly affected all the fluorescence parameters, which were significantly promoted by the DIP concentration increase (p<0.05). And their interaction had significant effect on the rETR_max and Y(II) (p<0.05), but had no significant effect on the E_k and α (p>0.05). Pigments of Chl a, Chl b and carotenoid results showed that CO₂, DIP and their interaction significantly affected the pigments contents (p<0.05). Evelated-CO₂ significantly inhibited pigment synthesis (p<0.05), and the inhibitory effect was enhanced with the increasing of DIP concentration. The pigments contents were significantly positively correlated with DIP concentration (p<0.05). Our findings suggested that evelated-CO₂ and higher DIP concentration obviously promoted the growth of U.prolifera seedlings, which was favorable for the green tide outbreak.

Ship meteorological instrument is an important part of marine hydrometeorological observation technology, which is a key process to realize global synchronous ocean observation. Leading the development of consensus-based international standards will effectively promote the market standardization and product internationalization of China’s marine meteorological instrument manufacturing industry. The paper starts with the importance of ship meteorological instrument, analyzes the development process of marine meteorological instrument standards, and summarizes the current status of relevant standardization organizations. Also, it discusses how to promote the international standardization of marine meteorological instruments: (1) optimize key technical indicators; (2) cooperate with the international standardization platform of marine technology.

Nitrate is the main nitrogen form available for phytoplankton life activities in the ocean, and its nitracline depth (Z_N) directly affects the vertical transport of nitrate and the ocean primary productivity, and then further influences the carbon cycle. With the advancement of ocean observation technologies, the profile data of nitrate have been collected in diversified ways, such as ship-based CTD observations and BGC-Argo automatic observations. The vertical sampling resolution of these techniques varies significantly (the vertical sampling resolution of CTD is lower than that of BGC-Argo). In view of different sampling data, it is urgent to conduct systematic and quantitative comparative analysis and study on the computing methods of Z_N. In this study, three different methods: difference method, gradient method and threshold method, are adopted to compute the corresponding Z_N by using the historical ship-based CTD data and BGC-Argo buoy data in the Northwest Pacific Ocean. The results show that in the case of single nitrate profile, based on BGC-Argo data, the difference between observed Z_N and the Z_N calculated by difference method is only 0.2 m, followed by threshold method is 20.0 m and gradient method is 202.8 m at most. Based on CTD data, the difference between observed Z_N and Z_N calculated by difference method is 2.0 m, the threshold method is 49.0 m, and the gradient method is 155.0 m. Compared with the gradient method and threshold method, the difference between the Z_N calculated by the difference method and the observed Z_N is the smallest. According to the results of statistical error analysis, it is found that the Z_N calculated by the three methods based on BGC-Argo data show a good correlation with the observed Z_N. Among them, the error of difference method is the smallest (R²=0.77, RMSE=28.48 m). The R² and RMSE of threshold method are 0.64 and 34.85 m, and the R² and RMSE of gradient method are 0.52 and 53.80 m. For CTD data, due to its low vertical sampling resolution, the Z_N calculated by the three methods is quite different from the observed Z_N. However, compared with the gradient method and threshold method, the error of the difference method is still the smallest (R²=0.81, RMSE =16.13 m). The R² and RMSE of threshold method are 0.47 and 27.65 m, and the R² and RMSE of gradient method are 0.42 and 36.41 m. The applicability of each method is preliminarily explored through comparing and analyzing the characteristics and differences of them so as to provide some scientific reference for the in-depth research on the vertical distribution characteristics and upward transport process of nitrate.

Based on the high frequency data of sea-air interface buoys, the variation pattern and driving factors of sea-air partial pressure of carbon dioxide (pCO₂) were analyzed and the sea-air CO₂ flux in the coastal waters of Qingdao in spring was estimated. During the observation period, the sea area changed from a carbon sink of atmospheric CO₂ to a carbon source, which was mainly caused by the continuous increase of sea surface pCO₂. By analyzing the controlling factors of pCO₂, it was found that temperature was the main driving factor of pCO₂ growth, and biological processes played a certain inhibiting role. The sea surface pCO₂ showed a diurnal variation. The effects of temperature and biological factors on the diurnal variation of pCO₂ were related to solar radiation, but they had opposite effects. In addition, the analysis showed that different sampling frequencies of buoys affected the estimation of sea-air CO₂ flux and shortening the sampling interval could effectively reduce the deviation of CO₂ flux estimation and improve the accuracy of estimation.

The spatiotemporal variation of surface eddy kinetic energy (EKE) in the South Australian Basin was studied using sea level anomaly during 1993-2019. The results show that in spatial scale there are two regions of high EKE: one to the west, and one to the east. On the seasonal scale, surface EKE is the strongest in austral winter with a maximum (57±9 cm²/s²) in July and the weakest in autumn with a minimum (40±5 cm²/s²) in March. On the interannual scale, surface EKE is related to El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM). Partial correlation analysis indicates that surface EKE shows negative correlations with ENSO, lagging the Niño3.4 index by 9 months, and EKE is significantly weakened (strengthened) in the decaying year of El Niño (La Niña). Meanwhile, surface EKE shows positive correlations with SAM, lagging SAM index by 14 months, and EKE is significantly strengthened (weakened) in the next year of the positive (negative) SAM phases.

Tidal current energy is the kinetic energy carried in the horizontal movement of tidal water, which has great development prospects. Accurate simulation and characterization of regional tidal currents can help to efficiently evaluate the spatial and temporal distribution of tidal energy resources, which is the key to the development and utilization of tidal current energy resources. In this paper, a high-resolution numerical model of tidal currents is constructed by applying FVCOM ocean model in Zhoushan sea area where has rich tidal current energy, and the reliability of the model is confirmed by tidal level and current verification. According to the simulation results, six waterways with dense tidal current energy resources in the Zhoushan sea area were identified, among which the average energy density of Xihoumen waterway, Cezi waterway and Taohuagang waterway exceeds 2.0 kW/m², and the maximum energy density exceeds 20 kW/m², and the flow speed over 1.0 m/s of the whole month is more than 80%. During tidal current ebb and flow, the reflow is dominant, while the asymmetry and rotation of tidal current are low. The flow stability coefficient is more than 0.98, so it is more suitable for the development and utilization of tidal current energy than other three waterways. The best location for tidal current energy development in these three waterways was then determined by calculating the significant hours and available hours, and the corresponding exploitable tidal current energy resources were evaluated using the Farm method, which were 27.53 MW, 39.96 MW, and 130.26 MW, respectively.

Based on the one-year measured wave data in the coastal area of Cangnan, Zhejiang Province, the characteristics of wave parameters were statistically analyzed, the correlation between wave parameters was analyzed by using the least square method, the relationship between the average wave duration and wave height was studied, the wave energy was estimated, and the characteristics of typical typhoon waves during typhoon “Lekima” were analyzed.The results show that the study area is mainly composed of light waves with spectral peak period of 5-9 s, the annual average significant wave height of 1.22 m, the normal wave direction is E, the strong wave direction is ENE.There is a significant linear relationship between the characteristic wave heights, which conforms to the typical Rayleigh Distribution.In typhoon free period and cold wave free period with significant wave height below 2.7 m and typhoon period with significant wave height above 4.1 m, the average duration of wave decreases exponential decays with the increase of wave height, and the attenuation rate of typhoon period with significant wave height above 4.1 m is higher than that of typhoon free period and cold wave free period with significant wave height below 2.7 m.During the impact of typhoon “Lekima”, the maximum wave height, spectral peak period, and spectral peak density show a basically synchronous process of first increasing and then decreasing, with a maximum spectral peak density of 55.10 m²/Hz;the typhoon wave spectrum before and after the impact of the typhoon show a bimodal spectrum, while the wave spectrum during the most significant period of typhoon impact show a unimodal spectrum.

The clay mineral assemblage in abyssal sediments can reflect the paleoclimate and paleoenvironment changes of the provenance area. Predecessors have many studies about the characteristics of clay mineral assemblages in the Pacific sediments west of the Mariana Trench, but the less research on the characteristics of clay mineral assemblages in the east of the Mariana Trench limits a deeper understanding of the relationship between the Asian aeolian dust input and the Pacific deep-sea sedimentary environment. In this study, 31 surface samples and 1 core sample collected in the Malkus-Wake Seamount area of the Western Pacific during the 2019 DY54 cruise were analyzed for clay minerals, combined with the data collected in the Western Pacific and nearby areas, we discussed the characteristics of composition, distribution and the provenance of clay minerals. The results showed that illite was the main clay mineral in surface sediments of the study area, with an average value of 69%; the content of chlorite and kaolinite were the second, with an average of 16% and 11% respectively; that of smectite was the least, with an average of 3%. In the core P04, the assemblage of the clay mineral was basically the same as surface samples, but below 250 cm depth, the content of smectite increased significantly, while the content of illite decreased relatively. Provenance analysis showed that Asian aeolian dust was the main source of illite in the study area, and kaolinite and chlorite might also be from Asian aeolian dust, and the East Asian winter monsoon was the main transport force of these clay minerals. The smectite in sediments could be mainly formed by weathering of submarine volcanic materials. The increase of illite content while the decrease of smectite content in the upper layer of core P04 sediment was responded to the increase of Asian aeolian dust input since the Middle Pleistocene.

The selection of extreme value samples and the determination of distribution models are two crucial aspects when calculating the design wave height. When selecting extreme value samples using the peaks over threshold method, the standard storm length method is commonly used to “de-cluster” the exceedances in order to make the samples conform to independence standards. However, the crucial parameter in the standard storm length method needs to be manually selected which increases the uncertainty of samples. In this paper, an automatic standard storm length estimation method is proposed, then the wave height peaks over threshold sample in the western Guangdong sea area is selected based on this method. To accurately fit the sharp peak and heavy tail of the wave height peaks over threshold sample, the combined distribution method is used to construct a new model: Gumbel-Pareto distribution model. Based on this model, the design wave height calculation is carried out in the western Guangdong sea area. The result shows that the goodness of fit for the Gumbel-Pareto distribution model to the wave height peaks over threshold sample is higher than that of Gumbel distribution and Generalized Pareto distribution, which can offer a reasonable reference for the design of large offshore engineering.

To evaluate the environmental changes before and after the operation of the green petrochemical project, polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the adjacent sea area of Yushan Island where the project is located, were investigated and monitored for four consecutive years from 2018 to 2021. The results showed the total PAHs contents ranged from 16.9 to 178.0 μg·kg^-1 with the average content of 75.9±24.0-102.6±41.4 μg·kg^-1, showing an overall downward trend over the past four years, with a lower overall concentration compared to other sea areas in China. The average content of different PAHs components in the investigated surface sediments from high to low were: 4 rings PAHs, 5 rings PAHs, 3 rings PAHs, 6 rings PAHs and 2 rings PAHs. The surface sediments of the surveyed sea area was mainly composed of silt, and the spatial distribution of PAHs was influenced by various factors. The sources of PAHs in the surveyed sea area were relatively stable, with small interannual differences, mainly originating from the long-distance migration of combustion products of substances such as oil, firewood, and coal. According to the sediments quality baseline method evaluation, the ecological risk level of PAHs in the surveyed sea area sediments was relatively low. The green petrochemical project did not cause an increase in PAHs of sediments in adjacent sea areas during the construction and production periods. However, as the project continues to operate, its impact on the surrounding ecological environment still needs to be continuously monitored.

Based on Western Pacific surface seawater as matrix, a series of reactive phosphorus reference materials with the concentration of 0.5-4.0 μmol/L were prepared. By investigating the uniformity and stability of the 4 batches of samples, it was confirmed that the performance met the needs of requirements. For the determination of reactive phosphorus in aqueous sample, segmented continuous flow analysis system with UV detector was used. The experimental conditions were optimized, the limit of detection(LOD) of the method was 0.03 μmol/L, and the relative standard deviation (RSD) of 4 different concentration batches was 0.37%-2.45%. The reliability of the method was verified by testing a CRM. The error was not more than 0.05 μmol/L. The concentration standard value of the series of reference substances was determined by 6 laboratories, and the relative expended uncertainty of characterization was evaluated, which was 2%-10%.

The unique geographical features of the island countries in South Pacific, which are surrounded by sea and small in size, make most of the island countries in this region "ecologically fragile areas". Based on this, multi-source satellite data were used to monitor the marine ecological environment of Nauru, Palau, Tuvalu, and the Marshall Islands. It was also focused on whether there have been significant changes in the ecological environment of various countries before and after the Tonga volcanic eruption, to help to understand the impact of the Tonga volcanic eruption. The results show that: (1) In terms of temporal and spatial distribution of climatic states, the sea surface temperature and transparency of the surrounding waters of the South Pacific island countries maintain a relatively high level, while chlorophyll and net primary productivity decrease rapidly with the increase of offshore distance. (2) Warming, acidification and sea level rising are common problems faced by the sea areas of the four island countries. (3) The eruption of the Tonga Volcano has no significant impact on the coastal TSM mass concentration and SST. (4) The phenomenon of abnormally rising surface temperature and changed suspended matter mass concentration of the island in the first half month of the volcanic eruption has implications for disaster warning and forecasting using remote sensing methods.

The waters surrounding South Georgia Island are one of the highest primary productivity regions in the Southern Ocean with enormous carbon sequestration potential. However, the strength of the biological pump efficiency in this area is still uncertain due to the lack of continuous upper ocean observation data.In this study, the hydrological and biogeochemical parameters obtained from the Biogeochemical Argo (BGC-Argo) floats deployed in the South Georgia Island vicinity during the period of 2017-2020 were utilized to investigate the impacts of physical processes on biogeochemical processes and to estimate the carbon export flux in the Antarctic summer. Results indicated that both upstream (northeast of the Antarctic Peninsula) and downstream (Georgia Basin) regions of South Georgia Island exhibited strong seasonal characteristics in Chl-a, with the latter area having a 4-month sustained period of phytoplankton bloom, suggesting a stable and continuous supply of iron. Using the temporal variability of the seasonal particulate organic carbon (POC) export, the summer POC export fluxes of the upstream and downstream regions were estimated to be 7.12±3.90 mmol·m^-2·d^-1 and 45.29±5.40 mmol·m^-2·d^-1, respectively, indicating that the difference might be due to enhanced downward export of organic carbon after the deepening of the mixed layer. The study found that the region maintained a high biological pump efficiency, contrary to the previous conclusion that the Georgia Basin had “high productivity low export efficiency”, which might have been caused by the limited “real-time” representation of the entire seasonal characteristics during ship-based surveys. BGC-Argo provides high spatiotemporal resolution of multi-parameter observation data, and this study demonstrates that it can more accurately quantify and evaluate marine biogeochemical processes and carbon sequestration potential.

Near-inertial waves (NIWs) play an important role in the response of ocean to typhoon. Their frequency varies with the depth and is the main factor in determining the propagation rate of near-inertial energy to the ocean interior. Based on the observation data from mooring, the factors affecting the blue-shift frequency of NIWs excited by typhoon were investigated in northwestern South China Sea. By analyzing the vorticity effect and Doppler effect caused by background currents, this study suggests that the Doppler effect of background currents was the main factor in the blue-shift frequency of NIWs. As depth increased, inertial wave frequencies increased. Quantitative calculations further demonstrated that within the upper 200 meters, the Doppler effect of the background currents was negative, approaching zero in depth around 200 meters. However, in the depth range of 230 to 400 meters, the Doppler effect became positive. This depth range exhibited the maximum strength of the background currents, with their direction aligned with the propagation direction of inertial waves. Consequently, the positive Doppler shift induced by the background currents was most pronounced. The results of this study are important for improving the understanding of the ocean response to typhoons, especially the propagation of near-inertial waves in areas with complex background current structure (e.g., the western boundary current region).

Based on the mesoscale atmospheric model WRF and the regional ocean model ROMS, a two-way coupled WRF-ROMS air-sea model was constructed to simulate the super typhoon Mangkhut in 2018. The results showed that the simulation results of the coupled air-sea model were better than those of the only atmospheric or ocean model, and the error of the typhoon track obtained from the coupled model was within 60 km, which was in good agreement with the best track. Compared with the observation results, the simulation results of wind speed and sea level pressure in the coupled model were better than others model. Based on the simulation results of the coupled air-sea model, the spatial and temporal distribution of the wind field, pressure field, sea surface flow field, and storm surge under the super typhoon Mangkhut were further analyzed. The results showed that: (1) In terms of spatial distribution, after the typhoon entered the South China Sea, the radius of the seven-level wind circle was larger behind the right side of the typhoon; the cyclonic flow field showed a significant Ekman effect with the typhoon wind field, and the flow direction was 45° from the wind direction. The wind field, pressure field, wind-generated flow field and water gain distribution all had obvious asymmetry, and the typhoon intensity, flow velocity and water gain were greater on the right side of the typhoon path than on the left side. (2) In terms of time distribution, the distribution of the wind field and the pressure field were similar and synchronized with the typhoon center, while the wind-driven flow field and storm surge were three hours behind the typhoon track.

Seawalls play an important role in protecting coastal towns from extreme waves damage. Based on two-dimensional incompressible two-phase flow numerical model, the influences of onshore wind on overtopping characteristics of solitary wave under coastal seawall were systematically studied in this paper. The reliability of the numerical model was verified by comparing the numerical results with experimental data, and the influencing factors such as onshore wind speed, incident wave height, crest freeboards of the coastal seawall, beach slope and seawall slope on the hydrodynamic process of solitary wave overtopping of coastal seawalls were discussed in detail. The research results show that with the increase of onshore wind speed, incident wave height and the decrease of crest freeboards of the coastal seawall, the maximum overtopping volume, maximum runup height and spatial distributions of the maximum water elevation gradually increase. With the increase of beach slope and seawall slope, the maximum overtopping volume increase and decrease, respectively, while the maximum runup height gradually increase. Onshore wind can affect the hydrodynamic characteristics of solitary wave overtopping of coastal seawall, increase the wave steepness and the wave crest propagation speed and cause the wave breaking earlier. Compared with the windless condition, the maximum wave overtopping volume, maximum runup height, maximum hydrodynamic forces and spatial distributions of the maximum water elevation are increased under onshore wind. The results of this study can provide a reference for the design of coastal engineering.

Deep-sea sediments have attracted much more attention in recent years because of their potential resources for rare earth elements plus Yttrium (REY). However, the host minerals and enrichment mechanism of REY in deep-sea sediments, and the spatial distribution characteristics and metallogenic regularity of the REY-rich sediments are still unclear. The Clarion-Clipperton Fracture Zone (CCZ) in the East Pacific is the most important polymetallic nodule metallogenic belt, and its potential of REY resources has not been well evaluated. In this study, the whole-rock geochemistry (728 groups of major elements and 625 groups of trace elements) of sediments from 125 stations in the west CCZ over an area of 27 800 km² was analyzed. The results show that the sediments in the study area are significantly rich in MnO, P₂O₅ and REY than those from Australian shales and global subducting sediments. Spatially, ∑REY has a positive correlation with P₂O₅, CaO, and Ce negative anomalies, indicating that calcium apatite is the main host minerals of REY. The average value of ∑REY in the sediments over the study area is 470±202 μg/g, some samples meet the criteria of REY-rich sediments (∑REY>700 μg/g), indicating that the study area has a certain potential of REY resources. Spatial interpolation analysis shows that REY-rich sediments are mainly distributed in the northern area characterized by hilly terrain, while they are poorer in the southern basin with flat terrain. The difference of geomorphology in the study area affects the regional deposition rate and the hydrodynamic sorting of calcium apatite, leading to the north-south zoning of REY resources distribution in the study area.

Acoustic characteristics of seafloor sediments are the basic elements of marine sound field calculation and engineering geological evaluation. In situ measurement is an effective means to accurately obtain acoustic characteristic parameters. The structure stratification characteristics and the existence of geological anomalies such as boulders lead to vertical and lateral heterogeneity, and the existing acoustic in situ measurement system is difficult to detect and recognize the nonuniform features, and there is a lack of discrimination reference for the identification of stratigraphic non-uniformity. In this study, an oblique acoustic in situ longitudinal wave measurement method based on the heterogeneity of seafloor deposition was proposed, and a simulation study on the oblique acoustic in situ measurement of sediments within a hundred meters was carried out by using the finite element method. According to the data of regional geological engineering exploration data in the East China Sea, three models of uniform sedimentary layer, stratified sedimentary layer, and a sedimentary layer containing the boulder were constructed, and a simulation of acoustic velocity measurement in the sedimentary layer was carried out based on oblique in situ measurement method. The results show that the oblique in situ measurement method was effective in identifying the inhomogeneity in the large-depth sedimentary layer. By introducing the concept of equivalent offset, the original acoustic velocity calculation formula was improved, effectively improving anomaly identification accuracy. The oblique acoustic in situ measurement method proposed in this study was an effective extension of the existing in situ measurement methods of sedimentary layers, which will help to promote the further application of in situ measurement in marine engineering surveys.

Coastal erosion leads to land loss and seriously threatens people’s life and property safety. It is great significant to identify coastal erosion vulnerability for disaster prevention and mitigation. The evaluation index system was constructed from three aspects: coastal dynamics, coastal morphology and social economy. Using the DSAS model and remote sensing data, the coast was discretized into equally spaced units based on section method, the weight and grade of the evaluation index were determined based on the entropy weight method, the coastal erosion vulnerability in the study area was calculated, and the spatial differentiation and influencing factors of coastal erosion vulnerability were identified by geographic detector. The results showed that the proportions of coastal erosion vulnerability for extremely high vulnerability, high vulnerability, medium vulnerability, low vulnerability and extremely low vulnerability in central coast of Jiangsu were 5.60%, 15.80%, 30.93%, 24.21%, and 23.46%, respectively, that showed a decreasing trend from north to south. The extremely vulnerable areas of coastal erosion were mainly located in the coastal area between the Zhongshan Estuary and the Sheyang Estuary. The spatial differentiation of coastal erosion vulnerability in central Jiangsu was the result of the synergistic effect of multiple factors such as coastal dynamics, coastal morphology, and economic and social activities. Among them, tidal slope, land cover, average tidal range, and coastline change rate were the dominant factors for the spatial differentiation of coastal erosion vulnerability.