Continental Shelf Research最新文献

De-reclamation is a common strategy used for the restoration of tidal flats. In this study, we investigate the morphodynamic response of tidal channel networks and tidal flats after de-reclamation initiatives using the Delft3D numerical model. We find that tidal channel networks that have undergone reclamation and retreat projects have a lower drainage density (8.95 km⁻¹) than that of channel networks that formed naturally (11.33 km⁻¹), and the drainage efficiency of natural formed channel networks is almost three times greater than restored channel networks. These findings indicate that de-reclamation alone cannot fully erase the imprinting of the previous reclamation. We also find that the ultimate effectiveness of de-reclamation is affected by the geographical layout and unchanneled path length of the inchoate main creek system. In addition, following the implementation of de-reclamation, the immediate opening of previously enclosed areas amplifies the tidal prism, thereby intensifying tidal scouring and resulting in significant erosion, with erosion rate reaching hundreds of millimeters per day. Such losses can be remediated under sufficient sediment supply and prevented through the construction of artificial channels. However, this severe erosion may escalate under an insufficient sediment supply or a heightened tidal prism, potentially leading to permanent loss. These findings constitute an important reference for future engineering practices that support the safety and sustainability of coastal resources.

A three-dimensional numerical model, based on Delft3D code, has been implemented and calibrated in the mesotidal Guadalquivir Estuary (Spain), a tidally-driven estuary due to the reduced freshwater discharges (25 m³s^-1 year-round average), which are subject to human regulation at the dam located at its head. The model has been applied to study in detail some estuarine features for low freshwater discharges: the first one is the non-linear interaction of semidiurnal constituents, which results in a tidal amplification factor (ratio of local amplitude to the amplitude at the mouth) that depends on the spring-neap tidal cycle, with markedly larger values during neap tides. The second one is the analysis of tidal resonance in the estuary, extending previous studies on the topic, which shows that resonance occurs at near-diurnal frequencies. The peak of resonance decreases in magnitude and shifts towards lower frequencies as friction increases, either by increasing the friction coefficient itself or the amplitude of the tide.

The southern sector of the Malin Shelf, a subregion of the NW European Shelf, is noted for episodic and unimpeded incursions of oceanic water onto the shelf in an area where the northward flowing European slope current interacts with steep bathymetry, yet the in-situ biological consequences of these incursions are largely unexplored. In this study phytoplankton productivity, nitrate assimilation and community growth rates are presented to characterise in-situ biological conditions during a prominent chlorophyll bloom that occurred at the shelf break in July 2013. Surface waters were replete with nitrate (2–7 μmol L⁻¹) and phosphate (0.1–0.4 μmol L⁻¹) but deficient in silicate (Si < 1 μmol L⁻¹). Chlorophyll concentrations were significantly negatively correlated with phosphate concentrations but not correlated with nitrate or silicate. High variability between stations in productivity, nitrate assimilation, and depth averaged phytoplankton community growth rates, which ranged from <0.01 to 0.14 d⁻¹, could be attributed to subsurface gradients in production and biomass distributions. Though variable the magnitude of productivity rates in this sector of the Malin Shelf environment do not appear unusual relative to comparable observations suggesting that despite the uncommon physical conditions of the study site phytoplankton productivity was not significantly modified by proximity to oceanic influences.

The response of tintinnids to frontal processes and to strong gradients of salinity and suspended particulate matter was studied in the Río de la Plata estuary, one of the widest and most turbid in the world, and characterized by a quasi-permanent salt wedge regime. The tintinnid community was explored at different depths under strong stratification conditions along the main axis of the estuary, covering from fluvial to marine coastal waters. A total of 21 taxa belonging to 10 genera (Amphorides, Climacocylis, Codonellopsis, Eutintinnus, Luminella, Nolaclusilis, Salpingella, Stylicauda, Tintinnidium and Tintinnopsis) were identified. The highest number of species was found at polyhaline waters. Species abundances varied within 4 orders of magnitude and allowed differentiating the tintinnid community into three main assemblages, Riverine, Mid-estuary and Marine Coastal, with highest, intermediate and lowest mean abundances, respectively. Discrepancies between ordination analyses based on environmental variables and species abundances were found in locations associated with salinity fronts. The Estuarine Turbidity Maximum matched with the highest tintinnid abundances, while the halocline hosted the highest number of species. A small variability of β-diversity and its components (Abundance Difference and Abundance Replacement) were explained by salinity, temperature and Suspended Particulate Matter. A significant correlation was found between species contributions to β-diversity and the mean Lorica Oral diameter of taxa, probably due to the influence of prey size on the spatial distribution of tintinnids. General results emphasize the importance of site-to-site physical and biological conditions in the distribution of tintinnids within the Rio de la Plata estuary.

This study employs a fully coupled physical-biological model to explore the oceanic dynamics and phytoplankton production in one of Australia's most prominent coastal upwelling systems, the Bonney Coast Upwelling, that has barely been studied before. The study focusses on how physical processes provide two different food sources for blue whales (Balaenoptera musculus), namely, phytoplankton and krill (treated as nonbuoyant particles). While phytoplankton multiplies and grows rapidly within weeks in the euphotic zone in response to nutrient enrichment, krill can only be transported into the region via ambient currents. Findings of this study suggest that phytoplankton blooms appear slowly in the main upwelling plume on timescales of 4–8 weeks. Dynamical influences from incoming coastal Kelvin waves significantly weaken or strengthen this classical upwelling plume and its phytoplankton productivity. On the other hand, the upwelling-favorable wind induces a continuous coastal current that also extends eastward past the Bonney Coast. This current operates to transport and distribute krill (that cannot swim horizontally) westward along the shelf, which explains the apparent conundrum why blue whales also feed on the upstream side of the upwelling plume. The author postulates that the variability of both plankton production and the intensity of the upwelling flow (passing krill swarms along the shelf) control the feeding locations of blue whales and other baleen whales on Australia's southern shelves.

Bays in coastal upwelling regions often serve as larvae retention zones underpinning functioning of marine ecosystems. Using a three-dimensional hydrodynamic model, this process-oriented study explores the ocean dynamics that follow from the relaxation of a spatially-uniform, upwelling-favourable wind field behind a headland. Findings reveal that wind relaxation leads to the appearance of a swift coastal countercurrent (CCC) as the inshore retroflection of the coastal upwelling jet. The analysis reveals that the CCC starts to form along the downwind coast of the headland where the upwelling-induced onshore barotropic pressure gradient opposes the wind stress. Here, wind relaxation indirectly induces a flow convergence that reverses the barotropic pressure gradient within ∼5 km from the coast which geostrophically drives the CCC. Once generated, this inshore barotropic pressure anomaly propagates along the coast as a coastal Kelvin wave to form an inshore retroflection of the upwelling jet. On the other hand, the upwelling creates a plume of denser water on the shelf behind the headland. After wind relaxation, the rotational-gravitational adjustment of this dense-water plume marks the front of the retroflection zone as a cyclonic baroclinic feature with a diameter of the baroclinic deformation radius (∼10 km). Findings show that this rotational-gravitational adjustment intensifies the pressure-gradient forcing of the CCC. Overall, the findings demonstrate that the retroflecting coastal current can traps both upwelled water and particles in vicinity of the headland, which is clearly of relevance to marine productivity.

For isolated oceanic structures above sea level in synoptic-scale wind fields, shielding causes a wind wake with reduced wind intensity on the lee side of the structure. This generates a wind-stress curl that may act as a source term for continental shelf waves (CSWs) propagating around the structure, if the bottom is sloping. We investigate CSW propagation in the case where the structure (a wind farm or an island) is circular and the depth over the shelf slope increases exponentially with radial distance. For free waves, the wave number, and hence the frequency, is quantized. We demonstrate that for circular banks with narrow continental margins, the resulting eigenfrequencies are close to those obtained for a straight shelf. Modelling the stress in the wind wake as a solitary pulse that moves along a straight shelf, we find, in the absence of friction, a forced solution that increases linearly in time when the pulse moves with the same speed as the free wave speed. For strong winds over longer periods of time, the along-shore wave velocity in the case of resonance may be of the order $m/s$ for topographic parameters characteristic of the Taiwan Bank. Velocities of this magnitude could potentially cause harmful erosion as well as affect the ecosystem on the bank slopes.

By using multisource reanalysis datasets, satellite data, etc., the influences of Typhoon Soulik on the upper ocean of two cold eddies off northeastern Taiwan Island (hereafter referred to as the P-Cold Eddy and D-Cold Eddy), which are distributed around Pengjia Islet and northeastern Diaoyu Island, respectively, were investigated. The results showed that the P-Cold Eddy was strengthened, and the D-Cold Eddy, which was previously invisible in the surface layer, began to appear. The seawater temperatures in the upper mixed layer of the two cold eddies decreased the most on 13 July, with the sea surface temperatures (SSTs) decreasing by 1.16 °C and 0.97 °C and the mixed layer temperatures decreasing by 1.23 °C and 1.06 °C, respectively. The upper ocean cooling of the P-Cold Eddy was mainly caused by upwelling, whose formation was related to the climb of more Kuroshio subsurface cold water northward forced by the typhoon. The upwelling of the D-Cold Eddy was weak, and the warming effect of the heat pump could be observed at the bottom of its mixed layer. The process of cooling and increasing salinity in the mixed layer of the D-Cold Eddy was mainly associated with the inflow of the upper cooler and saltier seawater from the P-Cold Eddy. The air–sea exchange term was not the main factor in the cooling of the seawater in the mixed layer during the forced stage, but it became dominant during the relaxation stage, and the latent heat flux (Q_LH) contributed significantly to its change.

Variability in supply of terrestrial sediments to the coastal zone impacts sediment transport processes and ecological dependencies. This study investigated surface sediment distribution and transportation within a 2020 km² shallow embayment following a period of flood induced sediment supply. Extensive field sampling of 221 common sites between 2015 and the 2019 follow-up survey presented, identified significant reduction in fine sediment fractions, evident through a 367 km² decrease in surface mud coverage. Wind-wave sediment transport processes controlled the spatial distribution of fine sediments, exporting 23 million tonnes of mud from the shallow sedimentation zones. In a broader context, sensitive benthic habitats such as seagrass meadows exhibited signs habitat recolonisation coinciding with areas of reduced mud content. Despite these promising short-term outlooks, the developed fine sediment budget suggests ongoing terrestrial sedimentation will exhaust key sediment sinks within Moreton Bay, effectively reducing the system's ability to buffer future sedimentation events.

The present study was carried out to investigate the phytoplankton distribution in tropical waters and its implication for establishing land-based ballast water treatment technology and test facility (BWTT-TF) as per the International Maritime Organization (IMO) guidelines. Samples were collected from the Swarnamukhi estuary (SE) and coastal locations on the east and west coast of India. The maximum phytoplankton density in the size group of ≥10 and < 50 μm was recorded as 3002 cells/mL in estuarine waters and 172 cells/mL in coastal waters. Among the phytoplankton, Bacillariophyta and Pyrrophyta were observed at all locations, whereas Ochrophyta and Chlorophyta were found only at specific locations or during specific periods. According to IMO guidelines, the minimum required number of species (5) was observed at all the locations, but the minimum number of phyla (3) was not found at some locations. The IMO minimum required phytoplankton density (>1000 cells/mL) was observed only during the bloom period, whereas it was about 5–50 times lower during other periods. Taxonomic distinctness indices were used to examine the diversity beyond the conventional species count. The study found that the Buckingham Canal and Swarnamuki River upstream among the SE locations, and coastal stations of Pamanji and Tirunelveli among the coastal locations, are suitable sites to establish land-based BWTT-TF. Since the results indicate that achieving the IMO specified size group of ≥10 and < 50 μm density in tropical waters was possible only during the bloom period, culturing phytoplankton surrogates and concentrating naturally available phytoplankton are recommended as alternate methods for establishing land-based ballast water treatment technology and test facilities.