Distance Offshore Research Articles

Mesoscale Variability of Surface Ducts During Santa Ana Wind Episodes

AbstractMesoscale variability of the marine boundary layer characteristics and the corresponding radio wave ducting conditions over the Southern California Bight (SCB) during three Santa Ana wind events have been examined based on the analysis of field observations and diagnosis of mesoscale model simulations. Under the influence of a dry and the stably stratified airflow from inland, a shallow moist internal boundary layer (MIBL) develops over the coastal waters. The MIBL consists of a thin well‐mixed moist layer capped by an inversion layer where the specific humidity decreases with height sharply. Accordingly, a surface duct (SD) is virtually ubiquitous with its depth compared with the MIBL depth. The wind direction and the SD characteristics exhibit diurnal variations over the SCB area associated with land and sea breezes. In addition, the MIBL interacts with the coastal topography, Channel Islands, and sea surface temperature gradients, resulting in spatial mesoscale variabilities in SD characteristics. Specifically, the SD height and strength grow with the offshore distance owing to the surface latent heat flux over sea, and in the meantime, exhibit substantial along‐shore variations. The shallow MIBL tends to split and flow around the higher elevation of the islands, leading to the formation of wakes with reduced modified refractivity. These island wakes may extend dozens of kilometers downstream with the SD height and strength growing accordingly.

Sea Surface Temperature Trends in the Coastal Zone of Southern England

Kassem, H.; Amos, C.L., and Thompson, C.E.L., 2023. Sea surface temperature trends in the coastal zone of southern England. Journal of Coastal Research, 39(1), 18–31. Charlotte (North Carolina), ISSN 0749-0208. Sea surface temperature (SST) trends along the south coast of England (northern English Channel) were examined based on data from systematic buoy measurements deployed by the National Network of Regional Coastal Monitoring Programmes of England (NNRCMP) since 2003. These data were supplemented with: (1) long-term, coastal SST measurements by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS); (2) global data sets compiled by the Hadley Centre since 1900, and (3) satellite-derived observations from Moderate Resolution Imaging Spectroradiometer (MODIS) (Aqua) since 2002. These data sets were used to evaluate de-seasoned nearshore trends in SST along the south coast of England and examine links to regional ocean-atmosphere teleconnections. The analyses of long-term, CEFAS data support the proposal that prior to the mid-1980s there were no de-seasoned trends in SST and conditions from year to year were relatively stable. Subsequently, interannual fluctuations appear to have increased, associated with a period of warming between 1985 and 2003 (0.28 °C/decade). Post 2003, interannual fluctuations in SST monitored by the NNRCMP buoys continued, and the warming trend appears to be greater (0.42 °C/decade). This trend in SST is greatest in the nearshore and decreases with distance offshore. The warming in SST also varied greatly from month to month. The greatest warming took place from December to March, whilst the least heating (and sometimes cooling) occurred between September and November. Analysis of Hadley (HadSST1.1) and MODIS data sets substantiated these trends. The greatest warming (post 2003) was found west of Portland Bill (up to 0.76 °C/decade) and decreased towards the Strait of Dover. Despite this west-to-east trend, all 12 NNRCMP stations between Penzance and Folkestone showed remarkably similar results, suggesting regional and global sources of heat rather than local sources. This is corroborated through wavelet coherence analysis linking SST anomalies to regional/global ocean-atmosphere teleconnection indices at seasonal scales.

Distribution of organophosphate ester fractions in sediment of the Eastern China Marginal Seas and the influencing factors.

Organic pollutant fractions should be closely investigated because of their different ecological risks. In this study, we examined the distribution of organophosphate ester (OPE) fractions (labile, stable-adsorbed, and tight-adsorbed fractions) in sediments from Eastern China Marginal Seas (ECMSs) and assessed the influencing factor of the fractions. The mean values of total OPEs in ECMSs are 13.70 ± 6.16μg L-1 in seawater and 32.04 ± 14.31μgkg-1 in sediment. The results showed that OPE concentration decreased from the northern to the southern ECMSs, and tris(1-chloro-2-propyl) phosphate and tris(1,3-dichloro-2-propyl) phosphate were the primary OPEs. The mean contents of labile, stable-adsorbed, and tight-adsorbed fractions in the ECMSs were 9.50, 11.29, and 11.71μgkg-1, respectively. Labile OPEs were predominant in offshore waters; the percentage of stable- and tight-adsorbed fractions increased progressively with offshore distance in ECMSs. The specific surface area and surface functional groups of sediment were not consistent with the fraction concentrations from the correlation coefficient, but the gross domestic product per coastline agreed well with the fraction distribution. Based on this, we conclude that human activity, rather than physicochemical characteristics of sediments, may be the primary influencing factor of the relative distribution of different OPE concentration fractions in ECMSs.

Assessing a model of Pacific Northwest harmful algal bloom transport as a decision-support tool

In the Pacific Northwest, blooms of the diatom Pseudo-nitzschia (PN) sometimes produce domoic acid, a neurotoxin that causes amnesic shellfish poisoning, leading to a Harmful Algal Bloom (HAB) event. The Pacific Northwest (PNW) HAB Bulletin project, a partnership between academic, government, and tribal stakeholders, uses a combination of beach and offshore monitoring data and ocean forecast modeling to better understand the formation, evolution, and transport of HABs in this region. This project produces periodic Bulletins to inform local stakeholders of current and forecasted conditions. The goal of this study was to help improve how the forecast model is used in the Bulletin's preparation through a retrospective particle-tracking experiment. Using past observations of beach PN cell counts, events were identified that likely originated in the Juan de Fuca eddy, a known PN hotspot, and then particle tracks were used in the model to simulate these events. A variety of “beaching definitions” were tested, based on both water depth and distance offshore, to define when a particle in the model was close enough to the coast that it was likely to correspond to cells appearing in the intertidal zone and in shellfish diets, as well as a variety of observed PN cell thresholds to determine what cell count should be used to describe an event that would warrant further action. The skill of these criteria was assessed by determining the fraction of true positives, true negatives, false positives, and false negatives within the model in comparison with observations, as well as a variety of derived model performance metrics. This analysis suggested that for our stakeholders’ purposes, the most useful beaching definition is the 30 m isobath and the most useful PN cell threshold for coincident field-based sample PN density estimates is 10,000 PN cells/L. Lastly, the performance of a medium-resolution (1.5 km horizontal resolution) version of the model was compared with that of a high-resolution (0.5 km horizontal resolution) version, the latter currently used in forecasting for the PNW HAB Bulletin project. This analysis includes a direct comparison of the two model resolutions for one overlapping year (2017). These results suggested that a narrower, more realistic beaching definition is most useful in a high-resolution model, while a wider beaching definition is more appropriate in a lower resolution model like the medium-resolution version used in this analysis. Overall, this analysis demonstrated the importance of incorporating stakeholder needs into the statistical approach in order to generate the most effective decision-support information from oceanographic modeling.

Experimental investigations on the hydrodynamics of a multi-body floating aquaculture platform exposed to sloping seabed environment

The coastal area near islands has become a key area for aquaculture because of the long offshore distance and suitable wave conditions. There is a topographic change near the islands, and the reflected waves generated by the topography modify the wave field in the aquaculture area, which may cause structural damage to the offshore net cage. Most studies on the hydrodynamic characteristics of aquaculture structures do not consider the effects of topography. Therefore, we investigated the hydrodynamic characteristics and wave field of a multi-body floating aquaculture platform under the influence of sloping seabed by leveraging a physical model approach. The results show that the low-frequency component of the surge motion of the cage on the weather side increases significantly under the influence of sloping seabed. However, the heave and pitch motions change slightly. Considering the presence of the sloping seabed, the wave elevations inside cages have been changed too., The wave breaking inside the cage on the weather side becomes more evident when the incident wavelength is equal to the width of the cage. And its wave response gradually shifts from wave frequency to high frequency. Regarding the cage on the lee side, the wave response inside it is positively correlated with the incident wavelength. The results of this study provide a reference for the design and optimization of aquaculture structures anchored near islands.

Groundwater Response to Tide Fluctuation and Rainfall in Coastal Reclamation Area

Abstract Land reclamation not only provides valuable space for urban development, but also creates an upper aquifer in fill materials. Analysis of groundwater level (GWL) fluctuations in coastal aquifer formed due to land reclamation can provide important insight into the groundwater system (GWS) evolution, including the connectivity between the GWL and influencing variables (ocean tide and rainfall). This study presents wavelet analysis, multichannel SSA-wavelet analysis (MSSA-WA), and lag correlations to analyze the response of GWL to ocean tide and rainfall in the reclamation area of Zhoushan Island, China. The MSSA-WA results and the lag correlations show that the MSSA-WA provides better analysis results, specifically, clay layer and rainfall filtered information. The influence of the influencing variables on the upper GWL is relatively greater than the clay layer, and rainfall has a relatively stronger impact on GWLs than tides. The GWLs of the upper layer, SW18 and SW21, which are heavily influenced by influencing variables, can be predicted through variations in influencing variables. Finally, the analysis of the results shows that the lithology of different aquifers, offshore distance, preferential flow path, and pressure load can be factors between tides and GWLs. For rainfall and GWLs, different lithology of aquifers, properties of vadose zone, and topography can be influential factors. The combination method provides an optimization method for GWL fluctuations in coastal reclamation area with combined MSSA and wavelet analysis for correlation analysis between GWL and influencing variables (ocean tide and rainfall) and analysis of corresponding causes and influencing factors.

Wave energy assessment in the China East Adjacent Seas based on a 25-year wave-current interaction numerical simulation

This study evaluates the wave energy in the China East Adjacent Seas based on a 25-year high temporal and spatial resolution wave-current interaction wave hindcast dataset from 1996 to 2020. The spatial distribution characteristics of the multi-year and monthly average wave energy flux in the China East Adjacent Seas are analyzed. The temporal variability characteristics of wave energy flux are quantified and analyzed by using a coefficient of variation, a seasonal variability index and a monthly variability index. The exploitable wave energy flux was assessed by excluding the waves with energy flux less than 2 kW/m and setting different significant wave height upper thresholds. Then, after considering factors such as wave energy resource abundance, temporal variability, offshore distance and water depth, 12 hotspots in the China East Adjacent Seas are believed relatively suitable for wave energy development. Four types of wave energy converters with different power capacities are selected to analyze their performance in different hotspots to provide a basis for design and selection of wave energy converters suitable to the China East Adjacent Seas. Due to the higher conversion efficiency when the significant wave height is small, Oyster performs best among the four selected wave energy converters.

Spatiotemporal variations of heavy metal historical accumulation records and their influencing mechanisms in the Yangtze River Estuary

Complex transformations of heavy metals in the mega-river-estuary continuum limit our understanding of their pollution history. This study investigated sedimentary compositions of heavy metals, major elements, total organic carbon, grain size, and radionuclides to study spatiotemporal variations in heavy metal accumulation patterns and their controlling mechanisms in four sediment cores (E1-E4) from the Yangtze River Estuary (YRE). Results show that only E3 in the distal YRE front mirrors well the heavy metal pollution history due to its continuous deposition in a stable sedimentary environment, while E1 and E2 record the influence of riverine and estuarine projects and processes apparently. E1 in the proximal YRE front registers intense human disturbance through sediment dredging and dumping activities to produce a thick layer of abnormal low 210Pbex and minor heavy metal concentrations. E2 in the intermediate YRE front demonstrates the recently increasing influence of reduced sediment discharge by its upcore coarsening trend with decreased heavy metal concentrations. Flood and storm events left different imprints in core sediments of E2 and E3 by their coarse stratal units with fewer heavy metal concentrations. The source analysis indicates that heavy metals in estuarine sediments mainly come from natural processes but are significantly affected by human activities. A direct linkage of the heavy metal accumulation history with the socioeconomic development in recent decades is found by a comparison study of core data from the tidal river to the estuary, albeit with a remarkable spatiotemporal difference, which is jointly determined by grain size, offshore distance, hydrodynamic condition, depositional status, and sedimentation rate besides estuarine processes. This warns us to carefully interpret the heavy metal history from single or sparse core data in a mega estuary system with intense natural forces and human disturbances analogous to the YRE.

Spatio‐Temporal Variability of Suspended Sediment Fronts (SSFs) on the Inner Shelf of the East China Sea: The Contribution of Multiple Factors

AbstractModulated by a host of complex processes, suspended sediment fronts (SSFs) on the inner shelf of the East China Sea persist strongly and vary notably. Using hourly suspended sediment concentration data collected by the Geostationary Ocean Color Imager over the period 2011–2021, a gradient‐based edge detection algorithm was implemented to extract SSFs; the frontal probability (FP) and seasonal and interannual variability were identified and interpreted. Pronounced frontal activity is principally confined to the nearshore waters within the 60‐m isobaths and decreases with increasing offshore distance. Frontogenesis is mainly determined by the bottom topography and tide‐induced mixing. Empirical orthogonal function decompositions reveal that the seasonal cycle dominates the variability of SSFs, which responds to the cycles of winds and related changes in coastal currents and upwelling. The highest FPs are identified in winter when wind‐induced suspended sediment transport and resuspension reach their annual maxima. In summer, stratification and the intrusion of Kuroshio subsurface water are not conducive to frontogenesis. Furthermore, the discharge of the Yangtze River has a certain influence on the frontal variability in the waters around the Zhoushan Archipelago. Notably, the interannual variability of SSFs is modulated by the El Niño‐Southern Oscillation. These findings, based on a comprehensive dataset of SSFs over 10 years, can usefully inform the studies of marine pollutant transport, sedimentary dynamics, fisheries, and wider ecological processes in the study area.

An Improved Coastal Marine Gravity Field Based on the Mean Sea Surface Height Constraint Factor Method

Construction of a high spatial resolution and high precision marine gravity field in coastal areas is constrained by the low quality and sparse coverage of altimetry data, except for limited shipborne and airborne gravity surveys. To address this problem, a mean sea surface height constraint factor (MSSHCF) method based on the ordinary kriging method and the remove-restore technique is proposed from the perspective of interpolation. In this method, the data is standardized during the interpolation process to reduce the error and mean sea surface as variables related to the marine gravity field are added to the semi-variance function in ordinary kriging to obtain a marine gravity field with a spatial resolution of 1′ × 1′. Validation experiments show that the MSSHCF method more closely agrees with the referenced SS V28, DTU17 global marine gravity models than the ordinary kriging method. Our results were further validated against shipborne data; the accuracy of the MSSHCF method is 0.13 and 0.33 mGal higher than that of the ordinary kriging method in two experimental areas. The effects of ocean depth and offshore distance on the results were also assessed. These results show that the proposed method is more accurate than the ordinary kriging method, when the distance and depth varied. Therefore, our study demonstrates that the MSSHCF method is an innovative and feasible tool for extracting gravity fields along coastal, beach, and island areas.

Occurrence, spatial distribution, and partitioning behavior of marine lipophilic phycotoxins in the Pearl River Estuary, South China

The occurrence, spatial distribution, and partitioning behavior of 17 marine lipophilic phycotoxins (MLPs) in surface and bottom seawater, particulate organic matter (POM), and surface sediment from the Pearl River Estuary (PRE) were investigated to understand current contamination and the potential risks to marine ecosystems in this region. Nine MLPs were detected, including azaspiracid1−3, gymnodimine, okadaic acid, dinophysistoxin 1−2, pectenotoxin2 (PTX2), and homoyessotoxin, with Σ17MLP concentrations ranging 545–12,600 pg L−1 and 619−8,800 pg L−1 in surface and bottom seawater, respectively; 0–294 ng g−1 and 0.307–300 ng g−1 dry weight (dw) in surface and bottom POM, respectively; and 3.90–982 pg g−1 dw in surface sediment. Lower Σ17MLP levels in the seawater were found at the mouth of the PRE, and gradually increased with increasing distance offshore. According to the calculated partition coefficient, the affinity of MLPs for the aquatic environment components was as follows (from highest to lowest): POM > seawater > sediment. Overall, the distribution and migration of MLPs in the PRE may depend on partition coefficients, the organic carbon fraction, and environmental factors.

Growth heterogeneity of Larimichthys polyactis in spring and autumn along the coast of Zhejiang, China

In order to understand the growth dynamics of Larimichthys polyactis in spring and autumn along the coast of Zhejiang Province, we used the survey data of bottom trawlers in spring (April) and autumn (November) from 2014 to 2019 along the coast of Zhejiang Province to examine the heterogeneity of L. polyactis growth by constructing a generalized linear model (GLM) and nine linear mixed effect models (LMEM). The results showed that body length of L. polyactis ranged from 15 mm to 210 mm, with an average of 124.12 mm. The dominant body length group ranged from 110 mm to 140 mm. The body weight ranged from 0.04 g to 156.2 g, with an average of 33.28 g. The dominant body weight group ranged from 30 to 50 g. According to the AIC minimum criterion, the LMEM model with the random effects of seasons and water zones on growth parameters a and b was the best. The results of cross validation also showed that the prediction of this model was the best. In the optimal model, the fixed value of growth parameter a was 0.61×10-4, which ranged in (0.32-1.91)×10-4 after adding season and water random effect. The fixed value of parameter b was 2.73, and ranged from 2.49 to 2.86 after adding the random effects of season and water area, indicating that small yellow croaker was under negative allometric growth. Season and water zone had significant effects on the relationship between body length and body weight of small yellow croaker. From a seasonal perspective, the growth rate of small yellow croaker in spring was higher than that in autumn. From water zone perspective, the closer the offshore distance, the faster the growth rate of small yellow croaker.

Lagrangian Observation of the Kuroshio Current by Surface Drifters in 2019

In this research, the features of the Kuroshio Current in 2019 were studied based on the observations of 29 self-developed surface current experiment drifters deployed in the western Pacific Ocean and the East China Sea. The Kuroshio flow pattern and velocity magnitude observed in 2019 were largely consistent with the climatology based on the historical drifter dataset, but they still exhibited distinctive characteristics. The intrusion of the Kuroshio into the South China Sea in the spring was observed by a group of drifters crossing the Luzon Strait from east to west, which is a notable departure from the non-intrusion pattern noted to occur in the spring in most of the historical records. A strong intrusion of the Kuroshio into the East China Sea was also observed, taking an anti-cyclonic turn in the northeast of Taiwan Island. Both the drifter trajectories and altimeter-derived dynamical topography captured the large meander pattern of the Kuroshio south of Japan in 2019, with the flow path having a maximum offshore distance of 470 km. In addition, Lagrangian statistics (lateral diffusivity, integral time scale, and integral space scale) were estimated for four selected regions with adequate drifter samplings. The lateral diffusivity had large values along the Kuroshio segment in the East China Sea and small values on the continental shelf of the East China Sea. The integral time scales for the four regions ranged from 0.8 to 3.7 days, with a corresponding integral space scale of 19~128 km.

Spatiotemporal Characteristics of Fish Larvae and Juveniles in the Waters around Taiwan from 2007 to 2019.

Simple SummaryFish larvae and juveniles are necessary fishery recruitment resources. As climate change and natural climate events continue to impact marine ecology, it may become difficult to determine the characteristics of changes in fish larvae and juveniles. Using samples and data from long-term marine experimental monitoring, we found a high diversity of fish larvae and juveniles in the waters around Taiwan, and the abundance of different fish species varied spatially and seasonally. We also found that distance from the coastline and topography were the key factors affecting the community of fish larvae and juveniles. By presenting these data as times series, we confirmed that 2009 was a critical year for regime change between fish larvae and juveniles in different depth zones. The year also happened to include Taiwan’s worst typhoon on record. These results emphasize the need to conduct more detailed research to prevent predictable and unpredictable shocks.Taiwan is located at the intersection of tropical and subtropical islands in the western Pacific Ocean. This area is an important spawning and breeding ground for many economic and noneconomic species; however, little is known about the long-term dynamics of fish larvae and juveniles in these waters. In this study, we conducted an in-depth exploration of their spatial characteristics using 2007–2019 field survey samples. Our results demonstrated the seasonality and spatiality of the larvae and juveniles of different fish species. We also found that the continental shelf and offshore distance were key factors affecting fish larvae and juveniles. Changes in community structure were temporally correlated with the extreme rainfall of Typhoon Morakot (the worst typhoon ever recorded in Taiwan). These data can be used as a management reference for fisheries’ policymaking and provide key insights into nearby marine ecosystems and the early life history of fish.

System topologies, key operation and control technologies for offshore wind power transmission based on HVDC

Offshore wind power (OWF) is considered a perfect energy source for the future low-carbon power system. However, the growing offshore distance and water depth would require more cost-efficiency and reliable techniques than the HVAC solution, which indicates the OWF HVDC transmission technique will be a promising solution. In this paper, the current situation of OWF-HVDC projects is introduced at first. Then, despite the most popular topology-modular multilevel converter, other alternative converters and system topologies with higher power density and cost-efficiency are presented, including the hybrid modular multilevel converter, alternative arm converter, and diode rectifier. Next, several multi-terminal topologies are introduced, which synthesize the advantages of different converters. Finally, the key technologies for OWF HVDC operation and control are summarized, including grid-forming control strategy for offshore wind turbine, harmonic instability suppression, and frequency regulation participation strategy design.

Changes in the burial efficiency and composition of terrestrial organic carbon along the Mackenzie Trough in the Beaufort Sea

In this study, we investigated surface sediments collected along a Mackenzie Trough transect during the R/V Araon expeditions (ARA04C, ARA05C, and ARA08C) in the Beaufort Sea in 2013, 2014, and 2017. We applied various inorganic and organic geochemical tools (major elements, carbon and nitrogen contents, stable carbon and radiocarbon isotope compositions, and molecular biomarkers) in combination with sedimentological measurements (mineral surface area (SA) and grain size) to assess the source and burial characteristics of organic carbon (OC). In general, the sediment mean grain size decreased with water depth whereas the SA increased, resulting in a decrease in the OC loading and the burial efficiency of terrestrial OC. The sedimentary OC was further influenced by the loss of terrestrial OC and replacement with marine OC with increasing water depth. Accordingly, our results suggest that hydrodynamic sorting and degradation of terrestrial OC co-occurred together with the enrichment of marine OC with distance offshore. Such processes controlled the burial and reactivity of terrestrial OC along the Mackenzie Trough transect.

Nesting habits of grey crowned craneBalearica regulorumin Lake Ol’ Bolossat basin, Kenya

AbstractInformation on breeding habits of grey crowned crane (Balearica regulorum) in Kenya is currently lacking. Investigations were therefore carried out between 2017 and 2020 to determine its nesting habits in Lake Ol’ Bolossat basin including nest‐site features, number and distribution of territorial pairs, clutch size, eggs, and duration of breeding cycle. While 103 pairs were observed in the lake marshlands (mean density 5.00 pairs/km2), only 20 were found in upland wetlands. The number of pairs and densities (pairs/km2) in each of the lake's sections were as follows: north (24; 3.23), middle (47; 5.42), and south (32; 6.24). During this study, 61% (n = 63) of the lake marshland pairs attempted to breed compared to 80% (n = 16) in the upland wetlands. A mean of 2.23 eggs/clutch and a modal clutch of three eggs was recorded in 33 accessible nests. The range of influential factors in nest‐site selection were as follows: water depth (50–100 cm), vegetation height around the nest (60–90 cm), and an offshore distance of >100 m. Breeding cycle showed phenotypic plasticity in response to variations in local weather conditions. The number and density of cranes in this study area show its importance in the recovery and survival of the species, and which should subsequently be accorded effective protection.

Distribution pattern and influencing factors for the microplastics in continental shelf, slope, and deep-sea surface sediments from the South China Sea

Marine microplastic pollution has become a major global concern in recent years and the fate of microplastics in the ocean is a hot issue of research. We investigated microplastic pollution in surface sediments in the northern South China Sea to explore its distribution characteristics and influencing factors across the continental shelf, continental slope, and deep-sea environments. It was found that the microplastic abundance of surface sediments was 130.56 ± 40.48 items/kg. The average abundance of microplastics in all three topographic areas gradually decreased with increasing distance offshore. However, the differences in microplastic diversity indices between the three areas were not significant and were higher than those in other seas of the world, indicating that the waters of the northern South China Sea are rich in microplastics from complex sources, with more pollution input channels. In the continental shelf, fibrous and low density microplastics accounted for the largest amount, with a low degree of microplastic aging, and were mostly transported by suspended-load. These microplastics were mainly influenced by human activities. In the deep sea, microplastics with higher density were the most abundant and the number of fibrous microplastics was fewer, while the average size was larger, mainly influenced by the bottom currents. These microplastics underwent long-term bedload transport. In the continental slope, the main factors affecting the distribution of microplastics were more complex. In addition to pollution by human activities, the slope also receives microplastic materials carried by bottom currents; therefore, the composition of microplastics in the slope combines those characteristics of microplastics in both the continental shelf and deep-sea areas. The findings of this study indicate that the South China Sea is affected by complex pollution sources under the dual effects of human activities and natural conditions; in particular, the pollution situation in the deep-sea area needs extensive attention.

Public's preference for the treatment of Ulva prolifera blooms: A choice experiment study in China

The continuous outbreak of Ulva prolifera green tide has brought many negative effects on economy and ecological environment in Qingdao, China. In this paper, we use the Random Parameters Logit and Multinomial Logit models to estimate residents' preference for Ulva prolifera treatment attributes based on a choice experiment survey. Additionally, we distinguish residents' free-riding beliefs in the provision and price to test the heterogeneous effects of free-riding beliefs on the stated preferences. The results reveal that Qingdao residents show the strongest preference for the reducing of the cover area of Ulva prolifera, followed by offshore distance, maximum density, and duration times. The annual willingness to pay is 61.68 CNY, 48.3 CNY, 34.8 CNY, and 29.1 CNY per person on average, respectively. In addition, we find that people with weaker belief in free-riding concerning provision show stronger preference on the Ulva prolifera treatment and higher sensitivity of governance costs than people with stronger belief. However, free-riders who want to influence price do not show any different preferences on the treatment of Ulva prolifera with other people. This study is conducted to help make a benefit-cost analysis of the treatment of Ulva prolifera blooms, and can provide theoretical references for designing an incentive-compatible questionnaire.

Deposition records of persistent organic pollutants and black carbon in dated sediment cores from China marginal seas: Implications for terrestrial sources and transport processes

Black carbon (BC) and persistent organic pollutants (POPs) were analyzed from three sediment cores collected offshore in the East China Marginal Seas. The results showed steadily increasing or stable BC concentrations and fluxes. By contrast, time trends of POPs fluxes were consistent with historical records of commercial production and use in China. Although the POP inventories decreased significantly with increase in offshore distance, the relatively consistent trends for individual POPs in different sea areas confirmed that the main sources are derived from mainland China and that atmospheric input was an important contribution. POPs inventories decreased by 59–91 % during transport from the Yellow Sea to the remote East China Sea and deposition to the sediment. This suggests that the source signal for POPs may be preserved under stable depositional environments, even though only a fraction of those pollutants are buried in open sea sediments.