Deep Water Research Articles

Vodní měkkýši lomů ČSA a Vršany – počátek kolonizace [Aquatic molluscs of the quarries ČSA and Vršany – the beginning of colonization

In 2022 and 2023, aquatic molluscs were surveyed in brown coal quarries ČSA and Vršany, northwestern Bohemia, where mining is ending and reclamation is in progress. Most water bodies were artificially created and relatively young, though some older habitats were present at the quarry edges. In the quarry ČSA, 20 species (17 gastropods, 3 bivalves) were recorded at 40 sites, while 13 species (10 gastropods, 3 bivalves) were found at 39 sites in Vršany. Molluscan communities were generally species-poor, particularly in deeper waters without shallows or with dense reed growth. Shallow, vegetated areas were more favorable. Physa acuta was the most frequent species. Three non-native species (Physa acuta, Potamopyrgus antipodarum, Ferrissia californica) were confirmed, and no protected or endangered species were found.

Gas hydrate stability for CO2-methane gas mixes in the Pegasus Basin, New Zealand: A geological control for potential gas production using methane-CO2 exchange in hydrates

Gas hydrate is an ice-like form of water containing gas, in nature mostly methane (CH4), which requires moderate pressures and low temperatures. The replacement of CH4 by CO2, which also forms a hydrate, could allow CH4 production from hydrate while sequestering CO2. A number of recent studies have focused on theoretical background, experimental simulations, and engineering approaches related to CH4-CO2 exchange in hydrates. We here investigate a key geologic constraint for possible CH4-CO2 exchange in sub-seafloor reservoirs, hydrate stability. We analyze seismic data and gas hydrate system models from the Pegasus Basin east of New Zealand, a region with evidence for abundant gas hydrates. Pressure-temperature conditions beneath the seafloor need to be within the stability fields for both CH4 hydrate and hydrate from the resulting gas mix after CO2 injection. Based on experimental and theoretical studies, we consider 64% a benchmark for maximum achievable CH4 replacement by CO2, resulting in a mix of 64% CO2 – 36% CH4, in hydrate. Down to a water depth of 1087 m, hydrate from this gas mix is stable within the entire CH4 hydrate stability field. A gap develops in deeper water with the base of gas hydrate stability (BGHS) for CH4 being deeper than for the 64% CO2 – 36% CH4 mix. In nature, most mechanisms for CH4 hydrate formation favor high saturation near the BGHS. For an evaluation of possible CH4-CO2 exchange, it is therefore important to investigate mixed-gas hydrate stability near the CH4-BGHS and to identify CH4 hydrates closer to the seafloor.

Assessment of the inundation probability caused by tsunamis along the eastern coast of Hainan Island

ABSTRACT Coastal areas around the South China Sea are threatened by potential tsunamis triggered by large earthquakes in the Manila Trench. To quantitively assess the inundation probability caused by tsunamis is crucial for coastal disaster prevention and mitigation. This study focuses on the eastern coast of Hainan Island, which is located to the west of the Manila Trench and may directly face tsunami impact. More than one million tsunami scenarios are simulated considering the randomness of earthquake magnitude, epicenter location, and focal depth. The simulation of numerous tsunami scenarios is based on the unit source superposition method in deep water, which provides boundary conditions for the local model with high spatial resolution for nearshore wave propagation and inundation. Representative waves with different heights and periods are adopted as incident waves in the local model. By involving the joint probability density of incident wave height and period, the spatial distribution of inundation probability is given along the eastern coast of Hainan Island. This study provided an assessment method for the inundation probability, which can more comprehensively consider the uncertainty of earthquakes and provide a more reliable assessment result than that based on refined simulation of several typical scenarios.

Sources and transport pathways of trace metals to the outer continental shelf off South Carolina and Georgia, USA revealed from the otoliths of moray eels

Trace metal concentrations in otoliths of spotted moray eels (Gymnothorax moringa), non-migratory residents of hard bottom reefs at depths of ∼30–70m along the outer shelf adjacent to South Carolina and Georgia, were analyzed to determine if results provide insights into trace metal sources and transport processes in this dynamic region of the shelf. Li and Mg appear to reflect exposure to local sea water circulated through adjacent porous rock outcrops where the eels reside. Concentrations of Mn, V, Cu, and Zn in otoliths appear to be associated with deep water upwelled along the shelf break. Based on 30 years of water temperature data from fishery surveys, Scamp Ridge, located at 32.30 N at a depth of ∼50m, has significantly lower summertime bottom temperature than elsewhere along the shelf edge, indicating locally enhanced upwelling at that location. The highest levels of Cu and Zn and the lowest of Mn and V were also found in otoliths of eels collected in the vicinity of Scamp Ridge. These results indicate that otolith chemistry in eels can reveal fine-scale structure of water mass inputs to the outer shelf of the southeastern US coast.

The study of radionuclide activities in the sediments of deep areas of Skagerrak and Southern Baltic

This study investigates the activities of radionuclides (137Cs, 210Pb, 214Pb, 239,240Pu, and 40K), carbon isotopes (δ13C and 14C), and grain size compositions in surface bottom sediments across the southern Baltic and Skagerrak Strait. Our findings reveal significant connections between these parameters and their dependence on sediment transport dynamics. The distribution patterns of natural and artificial radionuclides were studied to understand the factors influencing their transport to the deep areas. The results show that 137Cs activity in surface bottom sediments (0–5 cm) ranges from 8 to 11 Bq/kg in the Skagerrak area and reaches 220 Bq/kg in the southern Baltic, closer to the vicinity of river discharges. The activity ranges of 239,240Pu are similar between the study areas, but the mean value at the Skagerrak site is higher at 1.6 Bq/kg. The transport of 210Pbex to the bottom is mainly dependent on the number of fine particles (0–20 μm) in the water column, while the transport of 137Cs primarily driven by scavenging by marine organics from the water column. In the southern Baltic, a strong correlation indicates that a significant share of 137Cs most likely originates from fluvial input. The particle size distribution reflects calm conditions in the deep waters, while in the Curonian Lagoon reference areas there are pronounced contrasts between stations with strong and calm hydrodynamic conditions. The δ13C values in the surface bottom sediments decrease towards river discharge areas, reflecting an increased terrestrial component of the organic fraction, and the number of coarse particles also increases.

Hybrid group opportunistic maintenance strategy for offshore wind turbines considering maintenance resource allocation in harsh working environments

The intelligent maintenance of offshore wind turbines (OWTs) is vital for sustainable energy generation and utilization, as harsh working environments generally limit their application. As offshore wind farms expand into deeper waters, operational and maintenance costs continue to increase. Therefore, devising targeted maintenance strategies for offshore wind farms is crucial. Existing strategies often overlook the role of maintenance resources in controlling the operational and maintenance costs. To address this problem, this study proposes a hybrid group opportunistic maintenance strategy to implement resource allocation-based maintenance for OWTs under dynamic conditions. First, a failure rate model based on the life decline and system coupling is proposed to capture the evolution of failures in OWTs in harsh working environments, thereby enhancing the accuracy of fault maintenance. Subsequently, a hybrid linear and nonlinear deterioration model is proposed to identify the different deterioration trends owing to the various sensitivities of diverse components to harsh working environments, which enhances the precision of degradation maintenance. In addition, a maintenance resource allocation model is proposed to allocate resources in advance, thereby increasing resource utilization and reducing maintenance costs. A multi-objective optimization approach is proposed to maximize the mean maintenance level (MML) and minimize the per unit cycle expected maintenance cost rate (PECR) by considering harsh working environments. Finally, the nutcracker optimization algorithm is introduced into the maintenance model to generate the optimal solution in a multi-objective manner. The results show that the maintenance model is feasible and effective for practical adaptive maintenance applications of OWTs in harsh working environments in practical applications.

Description of new species of deep water Sthenolepis Willey, 1905 and Neoleanira Pettibone, 1970 (Annelida, Sigalionidae) from off Northern California, with the redescription of Sthenolepis spargens Fauchald, 1972

Description of new species of deep water Sthenolepis Willey, 1905 and Neoleanira Pettibone, 1970 (Annelida, Sigalionidae) from off Northern California, with the redescription of Sthenolepis spargens Fauchald, 1972

Assessments of multiple metocean forecasts in the North Atlantic Ocean

Accurate wind and wave forecasts are crucial for a variety of marine operations, including ship design, navigation safety, and engineering. This study evaluates the predictability of wind and wave conditions in the North Atlantic Ocean using both deterministic and ensemble forecast models. A dataset of 29 deep water buoys was used to validate deterministic and ensemble forecasts from the National Centres for Environmental Prediction (NCEP), the Canadian Meteorological Centre (CMC), the European Centre for Medium-Range Weather Forecasts (ECMWF), and the German Weather Service (DWD). A comparison of deterministic and ensemble forecast performance was conducted using eight statistical metrics focusing on the significant wave heights associated with 10-m wind speed. The results indicate that ensemble models exhibit higher correlation coefficients and lower scatter root mean square error especially beyond the 7th forecast day, outperforming deterministic models. The findings suggest that ensemble forecasts offer a more reliable estimation of forecast, enhancing predictability for marine operations.

Process-based forecasts of lake water temperature and dissolved oxygen outperform null models, with variability over time and depth

Near-term iterative ecological forecasting has great potential for providing new insights into our ability to predict multiple ecological variables. However, true, out-of-sample probabilistic forecasts remain rare, and variability in forecast performance has largely been unexamined in process-based forecasts which predict multiple ecosystem variables. To explore how forecast performance varies for water temperature and dissolved oxygen, two freshwater variables important for lake ecosystem functioning, we produced probabilistic forecasts at multiple depths over two open-water seasons in Lake Sunapee, NH, USA. Our forecasting system, FLARE (Forecasting Lake And Reservoir Ecosystems), uses a 1-D coupled hydrodynamic-biogeochemical process model, which we assessed relative to both climatology and persistence null models to quantify how much information process-based FLARE forecasts provide over null models across varying environmental conditions. We found that FLARE water temperature forecasts were always more skillful than FLARE oxygen forecasts. Specifically, temperature forecasts outperformed both null models up to 11 days into the future, as compared to only two days for oxygen. Across different years, we observed variable forecast skill, with performance generally decreasing with depth for both variables. Overall, all temperature forecasts and surface oxygen, but not deep oxygen, forecasts were more skillful than at least one null model >80 % of the forecasted period, indicating that our process-based model was able to reproduce the dynamics of these two variables with greater reliability than the null models. However, process-based oxygen forecasts from deeper waters were less skillful than both null models during a majority of the forecasted period, which suggests that deep-water oxygen dynamics are dominated by autocorrelation and seasonal change, which are inherently captured by the null forecasts. Our results highlight that forecast performance varies among lake water quality metrics and that process-based forecasts can provide important information in conjunction with null models in varying environmental conditions. Altogether, these process-based forecasts can be used to develop quantitative tools which inform our understanding of future ecosystem change.

Exploring the role of microtopography in the spatial pattern of soil water at the hillslope scale based on high-resolution observation

Terraces have consistently been regarded as crucial measures for water conservation and vegetation restoration, particularly in mountainous environments. However, the hydrological effects of terraces in artificial forests have been rarely studied. In this study, detailed topography, soil properties and high-resolution (30 sites) soil water data (0–70 cm) observed from March 2015 to March 2016 were collected at hillslope scale (0.2 ha). The effects of static (soil properties and topography) and dynamic factors (precipitation) on the dynamics and variability of soil water content (SWC) were studied based on statistical methods, temporal stability and variance decomposition methods. The results showed that slope, topographic wetness index (TWI) and microtopography were the main control factors of different soil layers (shallow, middle and deep layer), which explained 37.2 %, 48.6 % and 47.3 % of the total variance of corresponding soil layers, respectively. Microtopography primarily affects deep layer soil water (40–70 cm). Level terraces show significantly higher soil water content (SWC) (30.89 ± 5.28 %) compared to gentle slopes (25.40 ± 5.33 %), steep slopes (27.05 ± 5.74 %), and scarps (19.71 ± 4.43 %) (P<0.05). Temporal stability of soil water varied across different depths, with shallow layer soil water exhibiting significantly weaker stability compared to other depths, the most representative point of different soil layers was located on relatively flat terraces. Decomposition of spatial variance revealed that the time-invariant component was the primary contributor to the total spatial variance, with a mean value over 70 %. These results highlight that microtopography could weaken the influence of soil-terrain factors on soil water, and the implementation of level terraces can enhance hillslope hydrological conditions in the Rocky Mountain area.

Hydrogeochemical and isotopic investigations of groundwater in the reclaimed desert located between EL Nasr canal and Mariut Tableland, NW Coast, Egypt

A complete understanding of groundwater dynamics and its interaction with surface water under the impact of agricultural activities is vital for local agriculture, ecology, and residents of dry regions, which is not commonly recognized in arid areas. This research outlines the geochemical characteristics, recharge sources, and potential factors impacting groundwater quality in a new land reclamation located in the small basin of Abu Mina, which is part of the Western Nile Delta region.1 Thirty-one groundwater samples and two surface water samples were collected in 2021 to represent the Pleistocene aquifer and were subjected to multivariate statistical, hydrochemical, and stable isotope analyses. Data analysis demonstrates that Na+ > Ca2+ > Mg2+ > K+ and SO42– > Cl– > HCO3– > NO3– are the predominant cations and anions, respectively. Groundwater salinity ranged from 465.60 to 6455.18 mg/l, with slightly alkaline. Most of the water samples fall into one of three types of facies: Ca–Cl, Na–Cl, and Mixed Ca–Mg–Cl, in decreasing order. The meteoric genesis index (r2) indicates that deep meteoric water percolation dominates the Pleistocene aquifer. The aquiline diagrams, correlation matrix, and different ionic ratios indicate that evaporation, reverse ion exchange reactions, and the dissolution of carbonate and silicate minerals are the main processes governing groundwater chemistry. Factor analysis (FA) indicated that three factors explain groundwater hydrochemistry, accounting for 71.98% of the total variance. According to the rotating components matrix (F1–F3), the chemistry of the Quaternary aquifer is principally affected by evaporation, ion exchange reactions, and anthropogenic influences. Additionally, salinity increases due to the return flow of irrigation activities and mixing between old and recent water. The stable isotopes (δ18O and δ2H) indicate that the Quaternary aquifer receives groundwater recharge through the return flow of excess irrigation and canal seepage. Under desert reclamation conditions, groundwater salinization processes should be given special consideration. All groundwater samples are appropriate for agricultural irrigation based on the Sodium Adsorption Ratio (SAR), Permeability Index (PI), Percent Sodium (%Na), and Residual Sodium Carbonate (RSC).

Potential effects of the Emeishan large igneous province on Capitanian marine anoxia in the Upper Yangtze region

The widespread Capitanian (late Guadalupian) marine anoxia/euxinia has long been regarded as a key driver of the end-Guadalupian (middle Permian) biotic crisis. However, the cause of this marine anoxia is debated, particularly regarding the influence of the Emeishan large igneous province (ELIP). To investigate the contribution of the ELIP to marine anoxia and the possible causal mechanisms, we undertook a conodont biostratigraphic and geochemical study of the middle Permian Maokou Formation in a platform-to-trough transect in the Upper Yangtze region, South China. Our results show that the depositional facies of the Maokou Formation changed from a carbonate ramp to an intra-platform trough within the Jinogondolella (J.) altudaensis zone in the northwestern Yangtze region, which can be attributed to the initial activity of the ELIP. Mantle-derived Sr inputs in the initial and main stages of the ELIP led to two decreases in 87Sr/86Sr during the Capitanian, in the J. shannoni–J. altudaensis and J. prexuanhanensis–J. xuanhanensis zones. The elevated 87Sr/86Sr values during the late Capitanian may have been due to enhanced continental weathering caused by rapid climate warming in response to subaerial eruptions of the ELIP. The deep-water anoxia–euxinia expanded during the middle Capitanian, as indicated by increased MoEF/UEF and V/(V + Ni) values, along with the disappearance of burrows and appearance of small pyrite framboids in the J. altudaensis zone in the Cheng 20 well. However, shallow-water anoxia occurred during the late Capitanian (i.e., J. prexuanhanensis–J. xuanhanensis zone), as evidenced by positive Ce anomalies and losses of aerobic benthic species in the Erya section. Importantly, marine anoxia and negative δ13Ccarb excursions occurred synchronously, but earlier in deep water than in shallow water, potentially indicating an expansion of the oxygen minimum zone (OMZ). The deep-water anoxia corresponded to a decrease in 87Sr/86Sr ratios and the appearance of an intra-platform trough in the J. altudaensis zone, whereas the shallow-water anoxia in the late Capitanian coincided with elevated 87Sr/86Sr ratios. This suggests that the initial activity of the ELIP promoted the development of the OMZ in deep waters during the middle Capitanian, while the subaerial eruptions of the ELIP drove climate warming that led to the expansion of the OMZ into shallow-water platforms during the late Capitanian.

Revisiting Thorpe scale analysis and diapycnal diffusivities in Drake Passage

Ship heave effects in the swell-prevalent Southern Ocean induce frequent false overturns in density profiles, and conventional Thorpe scale analysis leads to unrealistically large diapycnal diffusivities. Another critical factor causing large positive biases in Thorpe scale analysis concerns the Ozmidov to Thorpe scales ratio α often considered constant and equal to 0.8. A revised Thorpe scale analysis is proposed with an innovative segment-by-segment approach to circumvent heave-induced false overturns together with best-fitting α functions to Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) data, which yields realistic diffusivities in the Drake Passage region. The revised Thorpe scale method applied to a finely-resolved CTD section across the Drake Passage yields typical diffusivities of O (10-5-10-3 m2 s-1), with the largest values being preferentially concentrated close to the bottom at major circumpolar fronts, consistent with nearby DIMES microstructure observations. In the southern Drake Passage the method highlights a middepth (500-1500 m) mixing maximum of 10-4-10-3 m2 s-1 in the Lower Circumpolar Deep Water (LCDW) layer due to large intrusions of Warm Deep Water (a cold/fresh variety of LCDW) of Weddell Gyre origin. The inferred middepth mixing maximum in intrusive regions, which is associated with isopycnal eddy stirring rather than caused by internal waves or double diffusive mixing, supports the short-circuiting paradigm of meridional overturning circulation in the southwestern Scotia Sea region and has important climatic implications in a warming climate.

Deep water contour detection in the visible spectrum

Deep water contour detection in the visible spectrum

Late Pleistocene–Holocene palynology and paleoceanography of İmralı Basin, Marmara Sea: Pollen-spore, dinoflagellate cyst and other NPP zonations

The Marmara Sea is the oceanographic gateway that links the hypersaline Eastern Mediterranean Sea with the hyposaline Black Sea via Straits of Dardanelles and Bosphorus, respectively, and also occupies a transitional vegetation and climatic regime between the Mediterranean and Euxinic phytogeographic ecosystems. Recent palynological studies of long cores from the shallow İmralı Basin perched on the southeastern slope of the Marmara Sea reveal that major paleoecological changes accompanied the isolation and reconnection of the Marmara Sea during the last two Pleistocene glacial–interglacial cycles. Here, we use data primarily from two İmralı Basin cores to determine new quantitative zonations for the pollen-spore, dinoflagellate cyst (dinocyst) and other non-pollen palynomorph (NPP) assemblages in sediments representing the last ∼30 cal ka. A gap in one core is closed using data from three short gravity cores. Twenty-four radiocarbon ages and 20 correlation-ties for sapropel and ash layers from these five cores provide an essentially complete record for the past 30 cal ka. Use of a full suite of palynomorph data (pollen and spores, fungal spores, dinocysts and other phytoplankton, aquatic parasites/saprophytes, zoo-planktonic and zoo-benthic NPPs) shows for the first time that fluctuations in aquatic palynoassemblages during the glacial periods are more complex than simple salinity or temperature responses. The changes involve food web-level turnovers in trait- and size-based food web components in which potential parasites/saprophytes appear critically important.Pollen stratigraphies reveal a significant loss of Euxinic tree taxa by MIS 3c, with only partial recovery in MIS 1. The Euxinic forest elements are replaced by cultivars and other indicators of anthropogenic influences during the MIS 1 that is also marked by a dry interval and corresponding in part with the 4.2 cal ka Eastern Mediterranean Drought Event. The dinocyst zones for the last ∼30 cal ka show a clear turnover from assemblages dominated by brackish Ponto–Caspian taxa to marine assemblages at ∼11.7 cal ka. This phytoplanktonic signal lags slightly behind (a) the vegetation and shift in the other NPP commencing ∼13.2 cal ka, the initial marine incursion at 13.8 cal ka, and the arrival of coccolithophores at ∼13 cal ka. Comparison to published MIS 6 and 5 data reveals higher MIS 2–1 species diversity, reappearance of the MIS 6 marker Impagidinium inaequalis, and the emergences of Pyxidinopsis psilata f. quadrata, cf. Boreadinium breve, and Peridinium spp. of Brenner 2005. The pre-reconnection microbiota is dominated by the unicellular alga Sigmopollis, spikes of colonial Pediastrum algae, the saprophytes/parasites cf. Multiplicisphaeridium and Chytridiomycota. This microbiota is displaced by the post-reconnection assemblage dominated by Botryococcus coenobia, various Platyhelminth egg capsules and ostracod lining-types that persist through the Holocene. A distinctive transitional microbiota with Discocotyle-type turbellarian egg capsules marks the Bølling–Allerød warming, followed at ∼13.3 ka by a marine assemblage with micro-foraminiferal linings and crustacean eggs. The interglacial marine phase of MIS 1 in İmralı Basin has much higher dinocyst species diversity than MIS 5e, reflecting Neolithic impacts (agriculture, land clearance) and expanded shipping trade. Initial marine flooding in the Marmara Sea during both interglacials are marked by sapropel deposition but variations of ravinement surface erosion, and marine deep water residence time in a stratified Marmara Sea are potentially important factors underlying hypoxia/anoxia and sapropel deposition.

Metrics for quantifying the efficiency of atmospheric CO2 reduction by marine carbon dioxide removal (mCDR)

Abstract Marine carbon dioxide removal (mCDR) is gaining interest as a tool to meet global climate goals. Because the response of the ocean–atmosphere system to mCDR takes years to centuries, modeling is required to assess the impact of mCDR on atmospheric CO2 reduction. Here, we use a coupled ocean–atmosphere model to quantify the atmospheric CO2 reduction in response to a CDR perturbation. We define two metrics to characterize the atmospheric CO2 response to both instantaneous ocean alkalinity enhancement (OAE) and direct air capture (DAC): the cumulative additionality (α) measures the reduction in atmospheric CO2 relative to the magnitude of the CDR perturbation, while the relative efficiency (ϵ) quantifies the cumulative additionality of mCDR relative to that of DAC. For DAC, α is 100% immediately following CDR deployment, but declines to roughly 50% by 100 years post-deployment as the ocean degasses CO2 in response to the removal of carbon from the atmosphere. For instantaneous OAE, α is zero initially and reaches a maximum of 40%–90% several years to decades later, depending on regional CO2 equilibration rates and ocean circulation processes. The global mean ϵ approaches 100% after 40 years, showing that instantaneous OAE is nearly as effective as DAC after several decades. However, there are significant geographic variations, with ϵ approaching 100% most rapidly in the low latitudes while ϵ stays well under 100% for decades to centuries near deep and intermediate water formation sites. These metrics provide a quantitative framework for evaluating sequestration timescales and carbon market valuation that can be applied to any mCDR strategy.

Current Loads on a Horizontal Floating Flexible Membrane in a 3D Channel

A 3D analytical model is formulated based on linearised small-amplitude wave theory to analyse the behaviour of a horizontal, flexible membrane subject to wave–current interaction. The membrane is connected to spring moorings for stability. Green’s function approach is used to obtain the dispersion relation and is utilised in the solution by applying the velocity decomposition method. On the other hand, a brief description of the experiment is presented. The accuracy level of the analytical results is checked by comparing the results of reflection and the transmission coefficients against experimental data sets. Several numerical results on the displacements of the membrane and the vertical forces are studied thoroughly to examine the impact of current loads, spring stiffness, membrane tension, modes of oscillations, and water depths. It is observed that as the value of the current speed (CS) rises, the deflection also increases, whereas it declines in deeper water. On the other hand, the spring stiffness has minimal effect on the vibrations of the flexible membrane. When vertical force is considered, higher oscillation modes increase the vertical loads on the membrane, and for a mid-range wavelength, the vertical wave loads on the membrane grow as the CS increases. Further, the influence of the phase and group velocities are presented. The influences of CS and comparisons between them in terms of water depth are presented and analysed. This analysis will inform the design of membrane-based wave energy converters and breakwaters by clarifying how current loads affect the dynamics of floating membranes at various water depths.

Impact of seasonal variations in fronts on suspended sediments transport off the coastal area of Fujian Province

The Zhejiang-Fujian (Zhe-Min) coastal muddy area plays a crucial role in facilitating sediment exchange through a cross-front. The mud depocenter off the Zhe-Min coastal area is a source of suspended sediment that can be transported to the continental shelf of the East China Sea (ECS). Although the front of the inner shelf of the ECS has been extensively reported, the cross-front material transport off the coastal area of Zhe-Min in summer has not been well studied, especially using measured data. To reveal how the front controls the transport of suspended sediment, this study focuses on the impact of fronts on the dispersion of suspended sediment off the coastal area of Fujian Province in different seasons. The results indicate that the front acts as a barrier, inhibiting the dispersion of suspended sediment into the sea. The high-concentration suspended sediment is mainly found to the northwest of the front, with an average SSC of 8.5 mg/L in winter and 3.1 mg/L in summer. The suspended sediment concentration (SSC) follows a V-shaped distribution along the cross-isobath transects, with lower SSC observed at the 50-m isobath compared with the shallow water area and the deep water area. The SSC at the front was the lowest, with an average concentration of 2.3 mg/L in winter and 1.9 mg/L in summer. The front is crucial for the development of the Zhe-Min coastal muddy area. The winter monsoon is strong, resulting in a sufficient supply of suspended sediments in the muddy area and a high transport flux of suspended sediments in the nearshore. The front hinders the dispersion of high-concentrated sediment from the nearshore to the offshore, resulting in the deposition of fine-grained sediments in the nearshore and the formation of an inner shelf muddy sedimentary zone. The findings of this study will help improve our understanding of the sediment source-to-sink processes in the ECS and land–sea interactions.

Matched cross‐spectrum phase processing for source depth estimation in deep water

AbstractZhou et al. (2022) proposed a method for instantaneous source depth estimation in deep water using matched beam intensity processing (MBIP) that leverages depth‐related oscillatory features arising from Lloyd's mirror interference in the frequency domain (Appl. Acoust., 2022, 186, 108493). However, the efficacy of MBIP diminishes with a random source spectrum. To counteract the effect of a random source spectrum, a vertical line array (VLA) positioned near the sea bottom is employed and a cross‐spectrum is generated from the conventional beamforming output, which is achieved by dividing the VLA into upper‐half and lower‐half arrays. The authors find that the cross‐spectrum phase interference pattern is determined by the source depth and is unaffected by the source spectrum. Consequently, a matched cross‐spectrum phase processing method is proposed, which demonstrates appreciable depth estimation accuracy compared to that of the existing techniques, as evidenced by the results from both simulated and experimental data.

Temporal and oceanographic factors differentially affect two size classes of white shark at a Southern California aggregation site

Ontogenetic habitat shifts are a common feature of many marine species, including sharks, which face conservation threats when their distributions overlap with human resource extraction and habitat modification. White sharks Carcharodon carcharias, for example, exhibit a distinctly coastal phase as juveniles, with a limited distribution compared to the basin-scale range of adults. Using an unoccupied aerial vehicle (UAV), we studied a coastal aggregation site within a Southern California Bight nursery area to determine how fine-scale temporal and oceanographic factors affect white sharks at different developmental stages. White shark density, as measured via UAV, was highly variable across time of day and day of year, with modest variation across years. Typically, more sharks were observed in the late afternoon hours. Sharks, especially those &lt;3 m total length, were observed more often during periods of colder seafloor temperatures, potentially reflecting avoidance of these colder, deeper waters by more cold-intolerant smaller white sharks. Alternate models incorporating sea surface temperature showed a very small but significant association between surface temperatures and &lt;3 m total length white sharks for the months we surveyed, but no such association for larger sharks. There were no or only modest effects of visibility, swell height, chl a levels, sea state, and tidal height on UAV-observed shark density. Understanding how temporal patterns and oceanographic predictors of density change over time as well as how shark ontogeny interacts with these factors can help us to better understand how this species uses coastal habitats and predict when they may be more likely to share marine space with humans.