Continental Shelf Research最新文献

To evaluate the salinity stress on ecological quality using protozoa, a 1-month baseline study was conducted along a gradient of salinity 9, 19, 29, 39, and 49 PSU (practical salinity unit). Protozoan samples were collected from an intertidal zone of the Yellow Sea, northern China. The findings demonstrated that (1) protozoan species represented different tolerance to scales of salinity stress; (2) the species richness decreased with increase of salinity, while in individual abundances sharply dropped with both increase and decrease of salinity compared to the control (29 PSU); (3) the probit regression revealed the median inhibition concentrations (IC₅₀) values 21.14 and 38.24 PSU for low (<29 PSU) and high (>29 PSU) situations, respectively; and (4) high salinity stress significantly shifted the community pattern of the protozoan fauna. Therefore, it is suggested that periphytic protozoan communities may be used a useful bioindicator of ecological quality under salinity stress in marine ecosystems.

The well-known 2022 Tonga volcanic tsunami event raised worldwide attention and the leading tsunamis induced by the atmospheric disturbance have been found to be small in deep-sea and greatly amplified over the continental slope. It prompted our thoughts what influences the amplification of the forced wave over continental slope. This study focuses on evolution of the forced wave induced by pressure disturbance moving from deep-sea basin to land, and aims to clarify the influences of topographic and barometric factors on the amplification ratio based on numerical experiments of the idealized problem. When a pressure disturbance moves faster than free water waves in deep-sea basin similar with the Tonga event, it is shown that the maximum amplification ratio appears at a slope neither too steep nor too mild. It is found that the relative slope length to the spatial scale of pressure disturbance is a good index for the amplification ratio. As the translational speed of pressure disturbance varies, the nearshore wave is greatly affected by the Froude number Fr in the deep-sea. It should be noted that a huge amplification can happen over the slope when Fr < 1 in deep-sea, and form a more dangerous hazard than Fr > 1.

Mud settling velocity in coastal regions is controlled by flocculation, which in turn strongly depends on turbulence, chemistry, and biology of the water-sediment mixture. As a result, mud settling velocity can be poorly constrained, and vary in space and time by orders of magnitude. Here we quantified mud settling velocity in Barataria Basin, a deltaic estuary in Louisiana (USA), using three independent methods: eddy covariance (one station for 200 days), floc cameras (4 stations at one time), and Rouse profile inversion (14 stations, replicated 10–30 times each). Eddy covariance indicates that settling velocity increases with turbulence, at least within the range experienced at the site (shear rate G up to 10 Hz). Settling velocity increases with salinity (in the 0 to 6 psμ range) for moderate turbulence levels (5 < G < 10 Hz), but it is nearly independent of salinity for low levels of turbulence (G < 5 Hz). Consistent with this finding, floc camera measurements – taken at low turbulence levels – indicate similar floc sizes for salinities from 0.4 to 20 psu. Settling velocity estimated from a Rouse profile inversion also lacks a dependence on salinity, likely because they were taken at low turbulence levels. This study is novel in that it utilizes three methodologies to independently predict the mud settling velocity, with quantified settling velocity values ranging 0.1–1 mm/s, and with most values between 0.2 and 0.5 mm/s. Overall these measurements confirm that mud is flocculated in both the saline and freshwater zones of Barataria Basin, and that turbulence is the largest factor controlling mud settling velocity. Nonetheless, salinity can increase mud settling velocity up to a factor of two. These results could inform the management of sediment imported into estuaries from freshwater sources, such as through natural drainages, crevasse splays, and engineered river diversions.

Unicellular eukaryotes known as benthic foraminifera have sophisticated survival mechanisms and ecological environmental indicators. Ten surface samples from the Yellow River Delta's coastal region were taken for this study to analyze the distribution of foraminifera in relation to environmental factors and to examine their microbial diversity. We looked at the physicochemical aspects of the environment at each sampling site (such as pH, TN, TOC, EC, δ¹³C, δ¹⁵N, PAHs, etc.), and we employed 16S rRNA high-throughput sequencing analysis to look into the interactions between microbial communities and foraminiferal species. The findings demonstrated that the Yellow River Delta's advantage benthic foraminiferal species were Quinqueloculina complanata, Ammonia beccarii, and Ammonia aomoriensis, and that TOC and TN were significant determinants of the distribution of benthic foraminiferal communities. PAH enrichment in the coastal zone effects on microbial communities and benthic foraminifera are not yet readily apparent. Sediment organic carbon and nitrogen isotope analysis revealed that marine plankton may be the dominant source of organic matter in the coastal zone sediments in the research area, which was made up of both land-based and marine organic matter. It implies that foraminifera have some environmental indicators, especially when combined with the distributional traits of the benthic foraminiferal assemblages and their considerable association with environmental parameters. The findings revealed that Q. complanata was found in the Yellow River water-affected estuarine coastal zone, A. aomoriensis was significantly influenced by sediment organic matter content and reflected the estuarine and nearshore environments and the combination of Ammonia beccarii-Ammonia aomoriensis-Elphidium excavatum assemblage indicated a semi-open intertidal shallow marine environment. Additionally, benthic foraminifera showed a responsive association with microorganisms, indicating that microbial diversity may be one of the driving forces behind benthic foraminifera's ability to adjust to environmental changes. The findings of this study will open up new avenues for research into the environmental importance of coastal zone ecosystems and for understanding how benthic foraminiferal communities survive.

Quantification of the vertical distribution of chlorophyll a (Chl-a), as one of characteristics of primary production (PP), is critically important to estimate annual PP in the water column (IPP) using models and remote sensing data. IPP estimation in optically complex and highly variable waters such as the Kara Sea is not a trivial task. In the present study, based on the data obtained during three multidisciplinary cruises to the eastern regions of the Kara Sea in August–October, the differences in the vertical distribution of Chl-a and PP under and without the influence of the river plume (Case II and Case I water types, respectively) are established. In Case I waters in August 2014, under the low values of the diffuse attenuation coefficient (K_d) of downwelling photosynthetically available radiation (PAR) (the median value (Me) K_d = 0.158 m^-1) and the deep euphotic layer (Z_eu) (Me = 30 m), the deep chlorophyll maximum (DCM) was well-pronounced. At the end of September 2015 in Case II waters influenced by the river runoff, when Me K_d increased 1.7-fold and Z_eu decreased 1.3-fold, the DCM was absent. Also, the DCM was not manifested at the end of the growing season, under conditions of extremely low underwater PAR (Me = 0.35 mol quanta m⁻² d⁻¹). In the sampling period, the PP maxima were observed at the surface and the DCM did not influence the vertical PP distribution. The depth of the nitracline was directly associated with the distribution of riverine waters and determined the depth and degree of DCM manifestation. The outcomes of the presented study suggest that a decrease in subsurface PAR influenced by the impact of riverine waters and the total decline of incident radiation from August to October determine the vertical distribution of PP and Chl-a.

Spatial variation and interspecies differences in the trophic position (TP) of copepods were investigated using nitrogen isotope ratios of amino acids. In the summer of 2021, coastal waters and the Changjiang diluted water generated clear seawater temperature and salinity fronts in the South Sea of Korea. Paracalanus parvus s. l. was a dominant species in the copepod community, and the second dominant species differed among inshore, intermediate, and offshore sites. The TP of each copepod species was estimated in two ways, considering only metazoan diets (TP_Glu, based on glutamic acid and phenylalanine nitrogen isotope ratios) and both metazoan and protistan diets (TP_Ala, based on alanine and phenylalanine nitrogen isotope ratios). Both TP_Glu and TP_Ala indicated trophic variability among copepod species and the contribution of protistan diets as a food source in the study area. Calanus sinicus showed a similar herbivorous TP of 2.0 in both TP_Glu and TP_Ala, suggesting little contribution from protistan diets. Two copepod species (P. parvus s. l. and Acartia omorii) exhibited TP_Glu values of approximately 2.0 but their TP_Ala values increased from 0.1 to 0.5, indicating mixed diets of both primary producers and protists. The other three copepods (Pseudocalanus sp., Oithona similis, and O. atlantica) showed a wide range in TP_Glu (2.4–3.1) and TP_Ala (2.7–3.4), suggesting that protistan trophic transfers enhance TP_Ala (by up to 0.5) in omnivorous copepods. We found a spatial variation in the TPs of copepods among water masses by various controlling factors including surface seawater temperature, salinity, and size-fractionated Chl-a. Our findings support that the TP values could be potential indicative of interspecies variability, providing useful information on the composition of the planktonic food web.

Depending on dimensions, orientation and topographic features, the circulation of semi-enclosed seas adjacent to regions of coastal upwelling are strongly influenced by their interaction with a shelf upwelling jet of adjacent waters. A special case are square bays, where opening is about the same size as length, and are bordered by headlands at the entrance. This study analyzed surface currents measured between 2009 and 2020 with high-frequency (HF) radar in Todos Santos Bay, a square bay located in northwestern México, to obtain mean and seasonal surface circulation patterns. HF radar measurements indicate that the average circulation pattern within the bay is cyclonic, with water of the California Current (CC) entering primarily as a coastal jet through the northern mouth of the bay. The similarity of monthly average maps with the long-term average suggests the cyclonic circulation persists year-round. Scale analysis demonstrates that given the size of the bay, only one eddy, primarily controlled by inertia, is dominantly formed inside. The mean cyclonic circulation defines the bay as an upwelling shadow.

Warm ocean temperature extremes, including marine heatwaves, have profound impacts on natural marine systems and aquaculture industries across the globe. In Tasmania, Australia, one aquaculture industry that has been significantly impacted by warm temperatures is Pacific Oyster (Magallana gigas, previously named Crassostrea gigas) farming, due to recurring outbreaks of the virus Ostreid herpesvirus 1. Such viral outbreaks are understood to be driven by high seawater temperatures, but the temperature threshold or duration for triggering disease and mortalities remain unclear. This study investigates the relationship between in-situ farm temperatures and oyster disease and mortality on the southeast coast of Tasmania, Australia using daily observations from three oyster growing areas (Pipe Clay Lagoon, Upper Pittwater, and Lower Pittwater) over three seasons. It is found that a 12-day averaged daily mean temperature is an excellent measure of the occurrence of high mortality. Specifically, a 21-day mean of 23.7 °C resulted in a 70% likelihood of high mortality, which is defined here as oyster losses of >15%. On the other hand, for lower levels of disease and mortality, a 12-day average of daily mean temperature gave the strongest relationship. A 12-day mean of 19.7 °C led to 70% probability of some disease and low mortality. The analysis also found in-situ farm temperature generally correlates well with remotely sourced temperature observations, indicating their potential usability for operational management. This study demonstrates a statistical risk analysis framework for the oyster farming industry, helping to improve the understanding of the detrimental impact of high temperatures on Pacific Oysters.

Microstructure measurements of velocity shear from the continental slope of the northwest coast of India (NWCI) in the eastern Arabian Sea are used to quantify the relative importance of double diffusion and internal tides induced diapycnal mixing in the different depth layers. It is found that the hydrographic conditions in the NWCI are conducive to the formation of moderately strong salt fingering (Turner angle between 55° and 72°). However, salt finger-induced vertical mixing dominates only in the upper 180 m of the water column, below which intense shear-driven turbulent mixing due to internal tide reduces its significance. As a result of this, the staircase structures, a measure of salt finger dominance in the water column, are frequent, and the mean temperature change across the interface (DT_IH; 0.33 °C) is relatively larger in the upper 180 m compared to sporadic occurrence of steps with a small magnitude of DT_IH (0.18 °C) below 180 m. It is also found that in the upper 180 m of the water column in the NWCI, mean diapycnal diffusivity (K_ρ) is approximately a factor of eight larger (8.3 ± 1.3 × 10⁻⁵ m²s⁻¹) than the estimation in the open ocean region of the eastern Arabian sea (5.4 ± 1.1 × 10⁻⁶ m² s⁻¹). However, due to internal tides, the magnitude of K_ρ reaches as large as O (10⁻²) m² s⁻¹ below 180 m in the NWCI. The mean downward heat flux estimated in the salt finger-dominated (upper 180 m) layers is ∼ -6.1 Wm^-2, and the shear-driven mixing-dominated layers (below 180 m) is ∼ -10.2 Wm^-2.