Continental Shelf Research最新文献

Over the period 2016–2022 environmental data were obtained at four points in the northern section of the tropical Estero Salado (ES), the inner coastal lagoon that flows through Guayaquil, the largest city in Ecuador. Surface water from the more remote southern limit of the ES, El Morro was also sampled in 2022. The study shows that waters of the northern part of this low salinity (<12) coastal lagoon were often hypoxic, occasionally approached anoxia, and were slightly acidic (6.86 ± 0.67). The same waters contained extremely high concentrations of dissolved inorganic nitrogen which averaged between 2.00 and 16.3 μM for nitrite, 89.8–238 μM for nitrate and 35.0–758 μM for ammonium whilst dissolved inorganic phosphorus averaged 21.3–381 μM. Dissolved oxygen was between 22.4 and 129 μM, and all samples were <50% saturated. Additionally, remarkably high concentrations of total and fecal coliforms and Escherichia coli were measured in this northern section, which are well above national and international standards. A trophic state index strongly indicates that northern part of the ES is hyper-eutrophic. Whilst nutrients were at lower concentrations at El Morro, they still exceeded those expected for typical natural and balanced estuaries, thus showing signs of eutrophication. Two major drivers for these hyper-eutrophic conditions in the north are effectively no riverine inputs to flush the system, and nutrient inputs being dominated by run off from the city as industrial, wastewater and sewage discharges, together with pulses associated with the seasonal rainfall. Based on comparison of nutrient data given here with the same parameters from several decades ago, the situation has become worse over this timescale. This trend follows the dramatic increase in population of the city of Guayaquil, and associated increase in discharges of polluted waters. The ES needs major improvements in environmental quality if it is to avoid further deleterious impacts for local populations. The ES thus fits into the global trend of increasing eutrophication in estuarine and coastal waters. Estimates using the new nutrient measurements indicate that the ES is exporting significant amounts of DIN and DIP into coastal waters of the Gulf of Guayaquil and then the Eastern South Pacific.

The behavioral characteristics of internal solitary waves (ISWs) in the central Andaman Sea were revealed by analyzing multisource satellite remote sensing images combined with synchronous mooring data. The relationship between the generation time and tides of ISWs in the central Andaman Sea was analyzed and discussed. The ISWs in the central Andaman Sea exhibit a notable semidiurnal tidal cycle, primarily occurring during the spring tide. Additionally, it was observed that larger currents can generate ISWs with larger amplitudes. The propagation velocity of the ISWs initially increases and then decreases from the source, with no significant overall change in the deep areas. Based on the analysis of satellite remote sensing images that cover the source of ISWs in the central Andaman Sea, the generation time of ISWs was estimated. A comparison was made between the estimated generation time and the tidal flow predicted from the TPXO 9 global tidal model at the location of the ISW source. It was found that ISWs are generated when the westward tidal flow reaches its maximum. The ISWs in the central Andaman Sea are generated between the islands of Car Nicobar and Teresa Island. They propagate eastward into the Andaman Sea, grow in amplitude, split into multiple waves, dissipate, and vanish in the waters near the Danao Islands. The entire life cycle of these waves lasts for approximately 3∼4 days.

The process of flocculation in dredge plumes was investigated by field measurements using Laser In-Situ Scattering and Transmissometry (LISST), Optical Back Scatter (OBS) sensors and an Acoustic Current Doppler Profiler (ADCP) during dredging campaigns in Port Curtis, Queensland (Australia). Suspended sediment characteristics differed significantly between natural ambient suspended sediment and sediment suspended by dredging as well as between sediment suspended by mechanical and hydraulic dredgers. LISST measurements enabled distinction of the suspended sediment by origin and showed that the majority of sediment particles naturally in suspension were aggregated flocs made up of multiple smaller particles. Primary particles in natural suspended sediment had a median particle size (d₅₀) of 8 to 14 μm, while in-situ flocs had a d₅₀ of 52 to 99 μm. There were both microflocs and macroflocs present in the natural suspended sediment, with the microflocs being dominant (representing 67%–80% of the flocs). Mechanical dredging resulted in the release of individual particles, microflocs and macroflocs, with the potential for a comparable percentage of macroflocs as in natural suspended sediment (11%–27% compared to 20%–33% in natural suspended sediment). Macroflocs released by mechanical dredging were likely to have originated from the seabed. During overflow from the hopper, the suspended sediment released from the hydraulic dredger had smaller flocs compared to the natural suspended sediment, with a reduction in the d₅₀ of in-situ flocs from 91 to 67 μm and a reduction in the proportion of macroflocs from 32% to 24%. These results indicate that larger macroflocs present on the seabed had been broken up by the hydraulic dredging, with most of the suspended sediment remaining in the form of smaller microflocs, suggesting that the flocs were not completely disaggregated by the shear-stress generated during hydraulic dredging. Ongoing aggregation of suspended sediment was shown to occur in the sediment suspended by both dredging methods within 20–25 min of the plumes being generated. This study demonstrates the importance of considering flocculation in predictive dredge plume modelling studies to prevent significantly underestimating the settling velocity and substantially over-estimating the extent and intensity of dredge plumes if flocculation is not accounted for.

Despite few pioneering works in the late XIX and early XX century, the poriferan fauna of Madeira has remained mostly unexplored until today, Madeira being one of the least studied eastern Atlantic archipelagos in terms of its sponge diversity. After a thorough analysis of both new material collected by SCUBA diving as well as a literature research, 140 sponge species are known to occur in the Madeira archipelago. From the 56 species identified by both collected material and pictures, approximately 60% (34 species) are new records for the Archipelago. These 34 new records were found associated with littoral rocky substrates and, to a lesser extent, caves, rhodolith beds and wrecks, within a depth range of 10–35 m depth. Our records also contain several Mediterranean species that have not been previously recorded in the North Atlantic, several North-east Atlantic species whose presence in Madeira marks their southernmost limit of occurrence, as well as elements from the subtropical West African fauna. Amongst the new additions to its sponge fauna there are the first records of Homomscleromorpha, with at least three Oscarella species noted, as well as a new species of Hemimycale (Demospongiae, Poecilosclerida). Yet, this is still an underestimation of Madeira's real sponge diversity. Data on Madeiran sponge fauna is still skewed towards shallow and littoral habitats, with other less accessible environments, such as caves, rhodolith beds or the deep sea, remaining largely unexplored. Similarly, complex poriferan groups (e.g. calcareans, haplosclerids, tetractinellids, hymedesmids) have only been partially studied, and their true diversity remains unknown. Finally, due to a lack of prior baseline it is difficult to conclude if some newly recorded species are non-indigenous, range-expanding or simply previously overlooked native species. However, it is now clear that two previously thought non-indigenous species, Mycale (Carmia) senegalensis and Prosuberites longispinus are in fact native to the Archipelago, their prior status as non-indigenous arising from the lack of prior confirmation of their presence outside of port facilities.

The main physical processes affecting the circulation variability in Halifax Harbour (HH), including the intense lateral intrusion of offshore sub-surface waters into Bedford Basin (BB), are studied using a nested-grid modelling system (NGMS). The annual and monthly mean circulation in HH are characterized by a typical two-layer estuarine circulation, with seaward currents in the upper layer and landward currents in the lower layer, both showing strong temporal and spatial variability. The intense lateral intrusion of offshore sub-surface waters into BB occurs at time scales of a few days. The intense intrusion, in combination with winter connection, is important for the renewal of deep waters in BB. The model sensitivity experiments suggest that the persistent northwesterly winds strengthen the near-surface seaward currents and the lateral intrusion of offshore sub-surface waters into BB. The persistent southwesterly winds can also trigger the lateral intrusion, but are less effective than the northwesterly winds. The southeasterly winds, on the contrary, reduce significantly the seaward currents in the surface layer and prevent the lateral intrusion. The accumulative effects of winds and tides on the 3D hydrodynamics in HH are also examined. Local winds have dominant effects on the 3D currents and temperature/salinity, through driving vertical mixing and coastal upwelling. By comparison, tides play a secondly role in affecting the currents and temperature/salinity in BB but are important in the Narrows.

In this study, the storm-tide and waves associated with Hurricanes Irma and Maria that struck Puerto Rico (PR) successively in 2017 were simulated using a coupled circulation and spectral wave model (TELEMAC2D + TOMAWAC), and validated against water level and wave measurements from gauges deployed around the island. Particular emphasis was placed on the storm-tide and wave interaction in the coastal area of San Juan, the capital of PR. At the San Juan coast, Irma caused a maximum of $\sim$0.2 m surge and 0.2–0.3 m wave setup, while Maria induced a larger maximum surge of nearly 1.0 m but a smaller wave setup at 0.1 - 0.2 m. Meanwhile, Irma-induced waves caused a strong westward longshore current ($\sim$2 m/s), which interacted with the storm-tide associated eastward current ($\sim$0.5 m/s) and led to small-scale gyres (several hundred meters in diameter) and rip currents formed near the coast, that in turn affected the significant wave height (SWH) locally. In contrast, during the passage of Maria, the wave- and storm-tide-induced longshore currents were in the same westward direction (maximum at $\sim$1 m/s and $\sim$3 m/s respectively); the strong current first refracted the waves towards the following current status (wave and current propagating in the same direction) and then decreased the significant wave height by nearly 2 m in a relatively large area ($\sim$2 km wide band along the coastline) off the coastal shelf.

The Primary Productivity of an ecosystem is an indicator of the health of the marine ecosystem and fishing yield. Primary productivity across the continental sea of the North Indian Ocean (NIO) basin was estimated using two vertically generalised production models. We examine the productivity using two non-parametric tests and present the changes using a gridded basin map. In the Behrenfeld and Falkowski (BF) approach, estimated primary productivity shows a significant decline of over 6550 km² from 2003 to 2020, recorded spatially 100 km² adjacent to the coastline. However, an area of 825 km² across the exclusive economic zone of the Indian sub-continent has seen a significant rise in primary productivity. The Kameda and Ishizaka (KI) model limits productivity reduction to 2500 km² across the NIO basin. The seasonal trends indicate reduced summer productivity across the basin. Both models point towards a significant reduction of productivity observed across the Bay of Bengal (BoB) and Arabian Sea (ARS) coastal regions owing to the damaging effects of anthropogenic-induced global warming. Secondly, simultaneous regression analysis using climate-based indicators and satellite-based NPP and Chlr-a data shows a significant reduction with high magnitude in the levels of NPP across the BoB and ARS between 1997 and 2020 due to rising sea surface temperature and a reduction of 9% and 6% in chlorophyll-a levels, respectively. These results point towards the inverse linkage between the rising SST on the primary productivity of the NIO basin and its devastating impacts on marine fisheries, especially in the BoB. These findings underscore the need for urgent action to mitigate the impacts of climate change and promote sustainable management of marine resources.

Mesozooplankton (MSP) are significant primary and secondary consumers in aquatic ecosystems that influence biogeochemical cycles and are considered important bioindicators of ecosystem functioning. Data on the spatio-temporal variability of the MSP population from the estuarine and coastal waters of northwestern Bay of Bengal (BoB) is scarce. The present study is the first detailed investigation on the spatio-temporal dynamics of MSP along the estuarine and coastal waters of northwestern BoB from two contrasting seasons over a period of three years based on univariate and multivariate statistical analyses. The crucial drivers for spatio-temporal variability in the MSP community were water temperature, salinity, dissolved oxygen (DO) concentration, nutrient (nitrate, phosphate, silicate) concentrations, and Chlorophyll (Chl) a concentration. The highest mean MSP abundance was obtained during summer monsoon (SM). The results of this study state that there is a significant seasonal difference in the hydrographical parameters that change the community dynamics of MSP inhabiting the estuarine and coastal waters of BoB. The MSP species assemblages during winter monsoon (WM) were governed by high salinity and DO levels while those during SM were associated with high water temperature, nutrients, and Chl a concentration. A clear seasonal shift from the gelatinous community in WM to the crustacean community in SM was documented. A total of 172 MSP species were identified during WM, and 200 MSP species during SM, with 37 species being exclusively detected during WM and 65 species being exclusively recorded during SM. The most abundant species during WM were Chrysaora caliparea, Cyanea nozakii, Sagitta bipunctata, Pleurobrachia pileus, and Acromitus flagellatus to name a few and those during SM consisted of Undinula vulgaris, Acartia (Odontacartia) spinicauda, Oithona simplex, Oithona similis, and Oncaea venusta. Copepoda was the most dominant taxa during all sampling seasons, while ichthyoplankton and meroplankton fauna were low during WM and comparatively higher during SM, indicating the top-down control of their population by gelatinous taxa. Biodiversity indices reflected well to excellent diversity patterns of MSP. In the current scenario of global warming and climate change, our research highlights the need for comprehensive long-term monitoring of estuarine and coastal waters of western BoB, which harbour a rich marine faunal diversity, to identify the bioindicators of seasonal variability among major MSP groups.

The lack of tsunami wave warning during the Anak Krakatau collapse in 2018 resulted in devastating damage to coastal areas. The tsunami wave arrived in the coastal areas approximately half an hour after the collapse. As a tsunami wave can travel abruptly, an early warning system should warn faster. However, a warning system based on a sophisticated hydrodynamic model in real-time would take time to conduct the numerical tsunami wave simulation. Hence, this study proposes a fast and reliable estimation of tsunami wave propagation through a classic ray tracing analysis. We use two ray-tracing methods to investigate the tsunami wave propagation from Anak Krakatau to the western Banten Sea. The first method follows Snell’s law, considering dispersive waves, and the second assumes non-dispersive waves based on the ray tracing equations, considering the Earth’s sphericity. Both methods are quantitatively evaluated by comparing the travel time measured at Anyer and Marina Jambu. This study finds that non-dispersive wave tracing performs a shorter computational time and slightly better prediction of tsunami wave propagation than dispersive-based wave tracing, with a relative absolute difference of the travel time of 17.9–26.7% in Anyer and 3.6–5.2% in Marina Jambu. This study also confirms the importance of bathymetry validity in wave ray tracing. Two regional bathymetry datasets with a mean difference of less than 5 m result in different wave ray tracing, in which one dataset does not produce the wave ray path towards the Panaitan Island. Based on bathymetric surveys in Anyer and Marina Jambu, the national bathymetry data (BATNAS) has shown its superiority to being used as a bathymetry in the ray-tracing process, with correlations of 81% and 93% in both areas compared to other available bathymetry datasets. We summarize that reliable bathymetry data and the non-dispersive ray tracing method can be used as an initial estimation of tsunami wave propagation efficiently.