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The southeastern United States Coastal Plain ecosystem contains baldcypress (Taxodium distichum) swamps and grass‐dominated marshes. These ecosystems also occurred on the exposed continental shelf during lower sea levels but are rarely preserved due to the mechanically erosive nature of transgression and regression. Two presently marine sites on the northeastern Gulf of Mexico's continental shelf contain well‐preserved woody terrestrial sediments that were the subject of previous studies. This study continues the investigation using geochemical (δ13C, δ15N, δ34S) and palynological characteristics of these formerly terrestrial sediments to determine if swamps and/or marshes existed at the time of deposition. The first site is located ∼20 km southeast of Horn Island, Mississippi (MS) and the core has terrestrial sediments radiocarbon dated to 11,066–10,228 (2σ) calibrated years BP (early Holocene). The second site is the "Alabama Underwater Forest" located ∼13 km south of Gulf Shores, Alabama (AL) and the cores have terrestrial sediments optically stimulated luminescence dated to 63 ka (±10 ka, 2σ) to 72 ka (±16 ka, 2σ) (late Pleistocene). Geochemical results for the MS sediments indicate a swamp‐to‐freshwater marsh transitional series, whereas the AL sediments indicate a swamp‐to‐saltwater marsh transitional series, both supported by palynological results. Further exploration of the geochemical results using linear discriminant analysis, trained with published geochemical data, supports the swamp and marsh interpretations. We conclude that the near‐pristine preservation of these woody deposits is not solely due to physical mechanisms, such as rapid burial, but is also coupled with anoxia‐ and euxinia‐driven biogeochemical reactions promoting wood and woody debris preservation in swamp and marsh environments. Plain Language Summary: Scientists have studied unique sites offshore of Alabama and Mississippi that contain soils, peat, wood, and tree stumps. Scientists have determined that the trees from the Alabama site are between 42,000 and 72,000 years old and were alive during the last ice age when sea levels were much lower than today. The Mississippi site contains woody peat sediments about 11,000 years old and occurred when sea levels were rapidly rising globally. These types of formally land‐based sediments are eroded as the sea level rises at the end of the glacial periods. Furthermore, wood and plant matter decay after the plant dies and become part of the soil. We investigated the chemistry of the preserved soils to understand the conditions that lead to their preservation. Chemical and pollen analyses found that these deposits are past swamp and marsh ecosystems that occurred on land similar to those occurring along the United States Gulf Coast today. Swamps and marshes have still waters with little oxygen that stop decay leading to the preservation of the wood and tree stumps. Swamps occur in depressions where water can collect and over time they fill with sediments. These preserved swamp deposits are time capsules from the past. Key Points: Multiple paleo‐terrestrial deposits containing wood and peat are preserved offshore in the northeastern Gulf of MexicoGeochemical and microfossil analyses find that these deposits are past swamp and marsh ecosystemsSwamps and marshes that are anoxic and/or euxinic promote the biogeochemical preservation of woody and organic matter [ABSTRACT FROM AUTHOR]

Numerical modeling of wave transformation, hydrodynamics, and morphodynamics in coastal regions holds paramount significance for combating coastal erosion by evaluating and optimizing various coastal protection structures. This study aims to present an integration of numerical models to accurately simulate the coastal processes with the presence of coastal and harbor structures. Specifically, integrated modeling employs an advanced mild slope model as the main driver, which is capable of describing all the wave transformation phenomena, including wave reflection. This model provides radiation stresses as inputs to a hydrodynamic model based on Reynolds-averaged Navier–Stokes equations to simulate nearshore currents. Ultimately, these models feed an additional model that can simulate longshore sediment transport and bed level changes. The models are validated against experimental measurements, including energy dissipation due to bottom friction and wave breaking; combined refraction, diffraction, and breaking over a submerged shoal; wave transformation and wave-generated currents over submerged breakwaters; and wave, currents, and sediment transport fields over a varying bathymetry. The models exhibit satisfactory performance in simulating all considered cases, establishing them as efficient and reliable integrated tools for engineering applications in real coastal areas. Moreover, leveraging the validated models, a numerical investigation is undertaken to assess the effects of wave reflection on a seawall on coastal processes for two ideal beach configurations—one with a steeper slope of 1:10 and another with a milder slope of 1:50. The numerical investigation reveals that the presence of reflected waves, particularly in milder bed slopes, significantly influences sediment transport, emphasizing the importance of employing a wave model that takes into account wave reflection as the primary driver for integrated modeling of coastal processes.

Numerical modeling of wave transformation, hydrodynamics, and morphodynamics in coastal regions holds paramount significance for combating coastal erosion by evaluating and optimizing various coastal protection structures. This study aims to present an integration of numerical models to accurately simulate the coastal processes with the presence of coastal and harbor structures. Specifically, integrated modeling employs an advanced mild slope model as the main driver, which is capable of describing all the wave transformation phenomena, including wave reflection. This model provides radiation stresses as inputs to a hydrodynamic model based on Reynolds-averaged Navier–Stokes equations to simulate nearshore currents. Ultimately, these models feed an additional model that can simulate longshore sediment transport and bed level changes. The models are validated against experimental measurements, including energy dissipation due to bottom friction and wave breaking; combined refraction, diffraction, and breaking over a submerged shoal; wave transformation and wave-generated currents over submerged breakwaters; and wave, currents, and sediment transport fields over a varying bathymetry. The models exhibit satisfactory performance in simulating all considered cases, establishing them as efficient and reliable integrated tools for engineering applications in real coastal areas. Moreover, leveraging the validated models, a numerical investigation is undertaken to assess the effects of wave reflection on a seawall on coastal processes for two ideal beach configurations—one with a steeper slope of 1:10 and another with a milder slope of 1:50. The numerical investigation reveals that the presence of reflected waves, particularly in milder bed slopes, significantly influences sediment transport, emphasizing the importance of employing a wave model that takes into account wave reflection as the primary driver for integrated modeling of coastal processes. [ABSTRACT FROM AUTHOR]

AlMashan, N.; Al-Attar, I., and Neelamani, S., 2024. Assessment of annual sedimentation into Failaka Marina (Kuwait) and possible solutions for reduction of siltation. Journal of Coastal Research, 40(3), 527–553. Charlotte (North Carolina), ISSN 0749-0208. Sedimentation is critical for ports, harbors, and marinas, requiring accurate assessment. Failaka Marina in Kuwait is experiencing a severe noncohesive sedimentation problem. The samples collected at the seven locations along the beach showed that the beach has a uniform grain-size diameter, meaning it is poorly graded sand. The sampling at the tip of the southern breakwater showed that the shoaling is mainly sand. The suspended-sediment concentration varies from 0.025 kg m–3 to 1.2 kg m–3, whereas the mean concentration at the marina entrance is 0.85 kg m–3. The time series of the suspended solids over a year in the seawater surrounding Failaka Island shows a range of 8 to 48,069 ppm. Such a considerable variation in suspended load is due to the massive amounts of dredging and spoil disposal at Boubyan Island and Basra Port (Iraq) when a high sediment load moves around Failaka Island with a concentration of more than 40,000 mg L–1. Annual sedimentation is about 2.35 m y–1, which is responsible for blocking the main entrance for navigation. Kuwait's Ministry of Communication allocates $4 to $6 million annually for dredging and disposal activities. This study evaluates the six marina entrance modification scenarios to determine the best scenario that achieves a measurable reduction in sedimentation rate in the Marina. Six marina breakwater modifications were studied, and annual sedimentation rates were numerically computed. The study use Coupled MIKE 21/3 to simulate hydrodynamic conditions for cohesive sediment transport in a problem area. Field data from 2015 calibrated and validated the model. The primary sediment-moving force is SE wind and sea-swell waves. Littoral drift along Failaka Island's southern coastline and high suspended-sediment concentration result in littoral drift and settling. The best scenario showed a 28% sedimentation reduction and a 26% reduction in maintenance dredging costs from the six studied scenarios. [ABSTRACT FROM AUTHOR]

Coastal erosion is a pervasive global phenomenon, exemplified by the Hel Peninsula situated in the Gulf of Gdańsk, the southern Baltic Sea. The geological constitution of the Hel Peninsula, characterized by sandy and loosely consolidated material, predisposes its coastal zones to continual morphological changes. The peninsula's limited width and elevation exacerbate shoreline erosion, particularly during periods of heightened storm activity. This study scrutinizes the effectiveness of coastal nourishment interventions, with a specific focus on segments influenced by the Władysławowo port and the Kuźnica vicinity, over several years. This specific section of the coast serves as a significant case study due to its role as a transit zone for sand transport along the whole peninsula. Protective measures, including shore nourishments and coastal groynes, aim to mitigate erosion impacts. Utilizing Airborne Laser Scanning (ALS) data spanning from 2008 to 2022, erosion dynamics were analyzed. The analysis reveals significant erosion patterns coinciding with the frequency and volume of nourishment material deposition, particularly evident in heavily nourished areas proximate to Władysławowo and Kuźnica. Despite persistent monitoring endeavors, persistent erosive trends pose imminent threats to Kuźnica's infrastructure, necessitating further research into the efficacy of implemented coastal protection measures. [ABSTRACT FROM AUTHOR]

The integration of machine learning (ML) techniques in coastal engineering marks a paradigm shift in how coastal processes are modeled and understood. While traditional empirical and numerical models have been stalwarts in simulating coastal phenomena, the burgeoning complexity and computational demands have paved the way for data-driven approaches to take center stage. This review underscores the increasing preference for ML methods in coastal engineering, particularly in predictive tasks like wave pattern prediction, water level fluctuation, and morphology change. Although the scope of this review is not exhaustive, it aims to spotlight recent advancements and the capacity of ML techniques to harness vast datasets for more efficient and cost-effective simulations of coastal dynamics. However, challenges persist, including issues related to data availability and quality, algorithm selection, and model generalization. This entails addressing fundamental questions about data quantity and quality, determining optimal methodologies for specific problems, and refining techniques for model training and validation. The reviewed literature paints a promising picture of a future where ML not only complements but significantly enhances our ability to predict and manage the intricate dynamics of coastal environments. [ABSTRACT FROM AUTHOR]

Global concern on extreme events is increasing the need for real timemonitoring of the wave fields in coastal areas. High Frequency (HF) radars, a remote sensing technology widely applied to measure near real time surface coastal currents with demonstrated accuracy, can also play a major role in the operational monitoring of waves height, period and direction. However, the ability of HF radar to measure waves can be jeopardized by specific ocean-meteorological and environmental conditions. Thus, a case-to-case analysis and parameterization is necessary to ensure the best data in each study area. In the southeastern (SE) Bay of Biscay, the EuskOOS HF radar network, composed by two compact HF radar stations provides hourly surface waves data in near real time. In this work, we analyze the effects of wind and noise levels on the radar skills for wave measurement, compared with existing in-situ data obtained by an offshore buoy. Then, the HF radar wave measurements for 2022 are analyzed with special focus on the most energetic observed wave events. The analysis performed versus in-situ data shows that both stations present reliable and accurate data for waves over 1.5 m, in agreement to what can be expected for a 4.46 MHz radar. The highest correlations are observed for waves > 4 m significant wave height, which demonstrates the capabilities for monitoring highly energetic events. Interference and noise detected on very precise time slots significantly reduced the availability and reliability of the measurements. Also, local winds blowing from land direction were found to affect the agreement between radar and in-situ measurements. Recommendations extracted from the analysis are provided, with the aim that they can be extended to other HF networks for more accurate wave monitoring. [ABSTRACT FROM AUTHOR]

Andrade, H.A.A.; Rodrigues, F.C.G.; Fletcher, C.H.; Casey, G., and Giannini, P.C.F., 2024. Winter sedimentology and morphology of the Maçambaba beach–foredune system, SE Brazil. Journal of Coastal Research, 40(2), 338–352. Charlotte (North Carolina), ISSN 0749-0208. The Maçambaba Holocene coastal barrier and dune system in Rio de Janeiro state, Brazil, is located immediately west of an abrupt orientation change from SW-NE to W-E on the SE Brazilian coastline. The eolian deposits are formed by winds from the SW, associated with polar air masses advancing in austral winter, and winds from the NE, associated with summer monsoon and upwelling intensification. The active beach–foredune system consists of intermediate reflective beaches and ramp incipient foredunes in the western (km 0–km 14) and central (km 15–km 35) sectors of the barrier and intermediate to dissipative beaches with more common ridge incipient foredunes in the eastern sector (km 36–km 48). This pattern from W to E indicates a change in the beach–foredune system from a more erosional regime with lower sand supply in the west to a more depositional setting in the east. Measured at the swash line, winter mean grain size fines and granulometric sorting increases from W to E, evidence of a net longshore drift in this direction. The increase in eolian sand supply toward the east favors sand reworking by SW (onshore) winds in the winter; consequently, coastal dunes are well developed in this sector. Overwash processes frequently develop where eolian deflation favors marine inundation during winter swell events. After their formation, washover fans are typically reworked by reverse winds from the NE (offshore) in austral summer. Throughout the entire barrier system, seasonal shifts in both swell orientation and wind direction are dominant climatic factors determining the development of washover fans, blowouts, and parabolic dunes with opposing migration directions. Investigating the effect of this climatic seasonality on the beach–foredune system is critical to understanding coastal response to storm events and climatic variations on longer timescales. A barreira costeira holocênica de Maçambaba localiza-se no estado do Rio de Janeiro, Sudeste do Brasil, imediatamente a oeste de uma mudança abrupta de orientação na costa, de sudoeste-nordeste para oeste-leste. Os depósitos eólicos são formados pelos ventos de sudoeste, associados às massas de ar polar que avançam no inverno austral, e pelos ventos de nordeste, associados à monção de verão e à intensificação da ressurgência. Nos setores central e oeste da barreira, o sistema praia-duna ativo consiste em praias intermediárias refletivas e dunas frontais incipientes em rampa. No setor leste, ele é composto por praias intermediárias dissipativas e dunas frontais incipientes em cordão. A passagem de dunas frontais em rampa, na parte oeste da barreira, para dunas frontais dominantemente em cordão, na parte leste, indicam que o aporte de areia eólica é maior a leste que a oeste. Nas amostras coletadas no espraiamento, a seleção granulométrica melhora e o tamanho médio de grão diminui de oeste para leste, o que é sugestivo de transporte longitudinal de sedimentos nesse rumo. O crescimento do aporte sedimentar para leste aumenta o retrabalhamento eólico pelos ventos de sudoeste (onshore) no inverno, e consequentemente as dunas costeiras são melhor desenvolvidas no setor leste, incluindo a formação de rupturas de deflação (blowouts). Neste setor, processos de sobrelavagem costeira frequentemente se desenvolvem onde a deflação eólica favorece a inundação marinha durante eventos de swell no inverno. Após sua formação, os leques de sobrelavagem são geralmente retrabalhados pelos ventos reversos de nordeste (offshore) no verão austral. Na barreira como todo, mudanças sazonais na orientação do swell e na direção do vento são fatores climáticos dominantes que determinam o desenvolvimento e deposição de leques de sobrelavagem, blowouts e dunas parabólicas com direções de migração opostas. Investigar o efeito dessa sazonalidade climática no sistema praia-duna ativo é fundamental para entender a resposta costeira a eventos de tempestade e variações climáticas em escalas de tempo mais longas. [ABSTRACT FROM AUTHOR]

The study presents a multi-proxy archive from hypersaline coastal Lake Chokrak in eastern Crimea, a steppe region which is particularly susceptible to moisture fluctuations. XRF, organic carbon and nitrogen, and palynological analyses are used to reconstruct the evolution of the lake and landscape development around it and to provide information about the driving forces behind those changes, such as climate and human impact. The findings show that the basin was an open marine bay between 7640 and 5500 cal. yr BP. After 5500 cal. yr BP, the low rates of sea-level rise led to gradual infilling of the basin. The prevalence of mesic herb-grass steppe around the site, as well as the expansion of broad-leaved trees in the Crimean mountains, indicate relatively warm and humid climate conditions during the Mid-Holocene. Elemental proxies and marine NPPs point to a transition to lagoonal conditions from 4270 cal. yr BP. The progressive shallowing of the basin was accompanied by the spread of more xeric Artemisia -grass steppe, which suggests a shift to arid conditions. The occurrence of cereal pollen from 3660 cal. yr BP may indicate the first signs of cultivation in the study area. The active build-up of a sand barrier from 3000 cal. yr BP led to a gradual separation of the basin from the sea. By 900 cal. yr BP, the fully-formed sand barrier resulted in a transformation of the lagoon into a hypersaline lake. The closing of the lagoon was accompanied by an expansion of halophytic communities around the site. Human-induced vegetation changes became more pronounced with the development of agrarian and pastoral activities around the site from ca. 750 cal. yr BP. [ABSTRACT FROM AUTHOR]

A field assessment was carried out in May 2023 in a natural protected area in South Italy to investigate the real-time behavior and fate of common marine litter items at different depths at the nearshore and foreshore under low energetic conditions. The field data were also compared with theoretical values calculated using theoretical formulations considering the Stokes drift current, wind-induced current, and current at breaking position. The wind approached from N to W, with values ranging from 2.4 to 3.8 m/s. The propagated significant wave height ranged from 14 to 21 cm, with an associated period of 3 s. Items with a positive buoyancy recorded different velocities. Very protruding (above water surface) items were greatly affected by windage and recorded velocities from 0.23 to 0.33 m/s; higher than the theoretical values that do not take into account windage. Theoretical values correctly predicted the velocity of other less-protruding items but slightly underestimated the velocity of neutral buoyancy items, evidencing in both cases the low relevance of the Stokes drift current. Items with a negative buoyancy moved (or not) in the bottom with different velocities. Different behaviors were observed at the breaking point, where items surfed (or not) spilling breaking waves, and at the foreshore, where items moved along the plunge step or in a "zig–zag" movement due to a swash–backwash process. [ABSTRACT FROM AUTHOR]

Coastlines globally are sensitive to the effects of sea-level rise, increased coastal storminess and changes in coastal sediment supply and sediment dynamics in the Anthropocene. Coastlines are also influenced by land use change, urbanization and development of built infrastructure. These changes can affect the dynamics of coastal landforms, weaken coastal resilience and make coasts more sensitive to climate hazards. This study critically examines the properties of coastlines that contribute to coastal biophysical resilience in South Africa, highlighting their relativerates of change and dynamic behaviour in response to physical and human forcing factors. Coastal landforms can be considered as 'green infrastructure' that can buffer the effects of climate change as well as providing ecosystem and environmental services in their own right. Viewing coastal landforms as green infrastructure provides a 'nature-based solution' to mitigate against climate change impacts that can work with – not against – the natural geomorphic, sedimentary and ecological processes of coastlines. Coastal landforms can also contribute to socioecological resilience, where they provide environmental and ecosystem services. The green infrastructure approach to coastal resilience has not been well developed in South Africa but is more effective in supporting coastal sustainable development. [ABSTRACT FROM AUTHOR]

Sandy beaches have different shoreline change rates (i.e., erosion/accretion rates). An erosive process on beaches poses risks for human-occupied areas. One example is Matinhos Beach (state of Paraná - Brazil), which has an average annual erosion rate of around 1.5 m yr-1 This study applied a methodology that combines in situ measurements and numerical modeling to simulate the physical processes in the coastal area of Matinhos during the 2018 Austral winter. Monthly DGPS surveys were carried out in the study area from June to September. The MOHID modeling system was applied to simulate hydrodynamics and sediment transport, considering waves and tidal forcing validated with in situ data. The WAVEWATCH III and SWAN models were applied in a nesting approach to simulate the waves at Matinhos Beach. The GFS was used to assess the wind conditions. The study period showed a dynamic evolution of accretion and erosion between monthly measurements with no clear pattern in most profiles. Significant sand accumulation was observed near the headland. Morphological changes were minor due to the predominance of low energy without significant storm events. The measured morphological changes are in line with the residual littoral drift obtained from the modeling results for the period. The residual current velocities were towards the southwest, with magnitudes ranging from 0.15 m s-1 to 0.2 m s-1. A slight variation in the angle of wave incidence (10°) may change the direction (southwest or northeast) and intensity of the littoral drift. The applied methodology can reduce uncertainty and support effective coastal management. However, the seasonal scales of wave climate cannot be disregarded, nor can the need for coastal oceanographic data. [ABSTRACT FROM AUTHOR]

Despite considerable differences in local conditions, the average air flow parameters at coastal stations had similar seasonal and interannual patterns. The decreasing trends in average wind speeds were not reliable due to inhomogeneity in the long-term series. Being less sensitive to inhomogeneities, both the zonal and meridional components and the average air flow estimates increased in 1966â2021. The changes in flow direction and in other wind characteristics were better described as quasi-cyclic rather than using a linear trend. In the Sõrve coastal case study, the wind velocity components were separated into opposite subsets, which were one-sidedly analysed by ignoring the other direction. Both westerly and easterly sub-components increased by 0.5 m/s in 2004â2021. Regarding wind-driven coastal processes along the peninsula, the changes in the westerly component, but not in the easterly component, are important on the western coast, and vice versa for the eastern coast. Assuming the potential impacts of winds via waves and currents, the influence of long-term changes in sea ice conditions were considered. Although the forcing load was more than twice as high on the western coast, the relative effect of the âice maskâ was smaller, as ice conditions were milder there. Along the eastern coast of the Sõrve Peninsula, the prevalence of SW-directed forcing can be expected, because the westerly forcing is shaded there by land. The SW-directed flow has strengthened over the study period because of an increase in the easterly and northerly wind speed subset and a decrease in the ice cover on the Gulf of Riga.

Small rivers that flow into the sea often terminate in estuaries or lagoons that may be separated from the sea by a sandy beach barrier. As a result of variations in barrier width and river discharge, these river mouths can be variously open, closed or partly open at different times. This behaviour reflects the interplay between the processes and properties of river systems (discharge, sediment supply, channel width, water velocity) and beach systems (beach width and height, grain size, wave regime, longshore processes). This study examines the dynamic behaviour of 32 river mouths located along 238 km of the coastline of Eastern Cape Province, South Africa, between 2000 and 2021 using Google Earth imagery. At each available time snapshot, individual river mouths were classified along a continuum as open, partly open or closed. Results show that nine river mouths were permanently open whereas 22 varied between the three states. Only one river mouth was partly open and none was closed for the entire period. Some spatial and temporal patterns were also identified. Commonly, adjacent river mouths may show the same patterns of opening/closing, which may reflect regional climate forcing. Fewer river mouths are open during winter/autumn compared to summer, likely reflecting rainfall seasonality. Thus, regional climate is considered to be the major control on river mouth dynamics, likely in combination with human activities that impact on river discharge, although the role of coastal sediment dynamics is significantly less well understood. The interplay between these different forcing factors requires further investigation. [ABSTRACT FROM AUTHOR]

The integration of machine learning (ML) techniques in coastal engineering marks a paradigm shift in how coastal processes are modeled and understood. While traditional empirical and numerical models have been stalwarts in simulating coastal phenomena, the burgeoning complexity and computational demands have paved the way for data-driven approaches to take center stage. This review underscores the increasing preference for ML methods in coastal engineering, particularly in predictive tasks like wave pattern prediction, water level fluctuation, and morphology change. Although the scope of this review is not exhaustive, it aims to spotlight recent advancements and the capacity of ML techniques to harness vast datasets for more efficient and cost-effective simulations of coastal dynamics. However, challenges persist, including issues related to data availability and quality, algorithm selection, and model generalization. This entails addressing fundamental questions about data quantity and quality, determining optimal methodologies for specific problems, and refining techniques for model training and validation. The reviewed literature paints a promising picture of a future where ML not only complements but significantly enhances our ability to predict and manage the intricate dynamics of coastal environments.

Coastal nutrient loading has been linked to a decline in the capacity of seagrass ecosystems to sequester carbon (‘blue carbon’); however, the mechanisms are unclear. Here we investigated how nutrient loading can affect the contribution that seagrass plant material makes to blue carbon stocks by investigating plant quality-decomposition dynamics. Specifically, we used a combination of laboratory and field experiments to account for various changes in biogeochemical cycling from seagrass meadows, ranging from changes in leaf quality to CO2 fluxes. It was found that nutrient loading increased the ‘labile’ content of seagrass (i.e. increased levels of leaf nitrogen, phosphorus and soluble organic carbon (amino acid and soluble sugar content), and at the same time decreased levels of ‘recalcitrant’ carbon (i.e. materials that are harder for microbes to break down, such hemicellulose, cellulose and lignin contents). Nutrient-enriched leaves decomposed ∼ 18 % faster than non-enriched leaves (i.e. greater biomass loss from nutrient-affected seagrass), resulting in ∼ 80 % more CO2 emissions from nutrient-enriched seagrass. We also found that seagrass that naturally contained high levels of labile carbon at the start of the experiment were affected to a greater degree (i.e. higher CO2 emissions) by nutrients addition than seagrass that had high proportions of recalcitrant carbon to begin with. Overall, these findings suggest that nutrient loading can weaken the capacity of seagrass ecosystems to act as blue carbon sinks through its effect on seagrass leaf decomposability.

Grain size affects the rates of aeolian sediment transport on beaches. Sediment in coastal environments typically consists of multiple grain‐size fractions and exhibits spatiotemporal variations. Still, conceptual and numerical aeolian transport models are simplified and often only include a single fraction that is constant over the model domain. It is unclear to what extent this simplification is valid and if the inclusion of multi‐fraction transport and spatial grain‐size variations affects aeolian sediment transport simulations and predictions of coastal dune development. This study applies the numerical aeolian sediment transport model AeoLiS to compare single‐fraction to multi‐fraction approaches for a range of grain‐size distributions and spatial grain‐size scenarios. The results show that on timescales of days to years, single‐fraction simulations with the median grain size, D50, often give similar results to multi‐fraction simulations, provided the wind is able to mobilize all fractions within that time frame. On these timescales, vertical variability in grain size has a limited effect on total transport rates, but it does influence the simulation results on minute timescales. Horizontal grain‐size variability influences both the total transport rates and the downwind bed grain‐size composition. The results provide new insights into the influence of beach sediment composition and spatial variability on total transport rates toward the dunes. The findings of this study can guide the implementation of grain‐size variability in numerical aeolian sediment transport models. Plain Language Summary: The growth of coastal dunes is caused by the wind, which moves sand from the beach to the dunes. The sand grains on the beach have different sizes. For instance, the size of the sand grains can vary from the waterline to the start of the dunes. Small sand grains are more easily picked up by the wind than larger, heavier grains. Thus, the size of sand grains and how they are spread over the beach can impact how much sand is moved by the wind. We use computer simulations to calculate how much sand is moved by the wind under different conditions. We investigate how different assumptions about the grain size on the beach influence these calculations. The results show that the calculations with one single sand size, in most cases, give comparable results to simulations with more complicated sand size variations. The simplified approach is beneficial because it reduces the need for detailed field data of grain sizes for future calculations. Key Points: The effects of multi‐fraction transport and spatial grain‐size variations were examined with the numerical aeolian transport model AeoLiSThe D50 can be used as a representative grain size in aeolian sediment transport modeling on a time scale of days to yearsThe bed surface grain size in the upwind source area might be the most relevant to include in aeolian sediment transport models [ABSTRACT FROM AUTHOR]

High latitude mountain environments are experiencing disproportionately adverse effects from climate change. The Gulf of Alaska (GoA) region is an embodiment of this change, particularly concerning a shifting hydrologic balance. Even so, the magnitude and contribution of fresh submarine groundwater discharge (fresh SGD) remains virtually unexplored within the region, though it has gained increasing attention globally due to its chemical significance and influence on coastal ecosystems. Here we provide the first regional estimates of fresh SGD to the GoA using two established water balance approaches. This is an effective way to distinguish the contribution of terrestrially derived fresh SGD, rather than the more commonly quantified total SGD which includes discharge that is driven by marine forces such as sea‐level oscillations and density gradients. We compare the approaches and assess their capabilities in computing the magnitude of fresh SGD over a large regional scale. Mean annual fresh SGD flux ranges between 26.5 and 86.8 km3 yr−1 to the GoA, equivalent to 3.5%–11.4% of the total freshwater discharge. Contributions are highest in the Southeastern panhandle and lowest in the Cook Inlet basin, with the highest area normalized contribution occurring in the Prince William Sound. Fresh SGD exhibits high spatial and temporal variability throughout the region. Although freshwater discharge to the GoA is investigated considerably, the importance of fresh SGD has, thus far, been overlooked. Plain Language Summary: Mountainous regions are highly susceptible to the impacts of climate change. This is especially evident in the Gulf of Alaska (GoA), where freshwater systems flowing from mountainous coastlines are experiencing a rapid shift in the timing, quantity, and chemical composition of their waters as they outflow to the ocean. Fresh submarine groundwater discharge (fresh SGD) is one such pathway that water travels where water below the ground surface empties into the ocean underneath the ocean's surface. This type of water flow is known to have elevated nutrients and solutes, thus making it important for near shore marine life. We estimate fresh SGD to the GoA using two mathematical models and compare the results from each. We find that fresh SGD is between 3.5% and 11.4% of the total amount of freshwater that flows to the ocean from the GoA, which is a significant portion. Key Points: We compare two water balance approaches to estimate fresh submarine groundwater discharge to the Gulf of AlaskaMean annual flux of fresh, terrestrial groundwater ranges from 26.5 to 86.8 km3, or 3.5%–11.4% of the total annual freshwater dischargeWe identify fresh submarine groundwater discharge hotspots from an extensive remote high‐latitude coastline [ABSTRACT FROM AUTHOR]

A field assessment was carried out in May 2023 in a natural protected area in South Italy to investigate the real-time behavior and fate of common marine litter items at different depths at the nearshore and foreshore under low energetic conditions. The field data were also compared with theoretical values calculated using theoretical formulations considering the Stokes drift current, wind-induced current, and current at breaking position. The wind approached from N to W, with values ranging from 2.4 to 3.8 m/s. The propagated significant wave height ranged from 14 to 21 cm, with an associated period of 3 s. Items with a positive buoyancy recorded different velocities. Very protruding (above water surface) items were greatly affected by windage and recorded velocities from 0.23 to 0.33 m/s; higher than the theoretical values that do not take into account windage. Theoretical values correctly predicted the velocity of other less-protruding items but slightly underestimated the velocity of neutral buoyancy items, evidencing in both cases the low relevance of the Stokes drift current. Items with a negative buoyancy moved (or not) in the bottom with different velocities. Different behaviors were observed at the breaking point, where items surfed (or not) spilling breaking waves, and at the foreshore, where items moved along the plunge step or in a “zig–zag” movement due to a swash–backwash process.

The acceleration of coastal processes is manifested in the form of coastal erosion, average sea level rise, drastic changes in coastlines, and more turbulent ocean waters. In this study, the coasts of Kerala and Tamil Nadu, India, were selected to identify the effects of increasing coastal processes. Therefore, it is necessary to identify and map vulnerable areas by taking into account the key parameters, such as topographical and socio-economic factors, to relate to coastal processes. The fuzzy Analytical Hierarchy Process (AHP) method was employed to identify the most vulnerable zones. The key findings revealed that about 14% and 2% of the coast of Tamil Nadu and Kerala, respectively, are classified under the physically highly vulnerable category. Similarly, ~17% and ~30% of coastal Tamil Nadu and Kerala, respectively, are highly socially vulnerable. The overall vulnerability assessment showed that 7–8% of both coastal areas were highly vulnerable. We concluded that the Thiruvallur, Chennai, Kanchipuram, Cuddalore, and Nagapattinam coasts on the east coast and the Malappuram, Thrissur, Ernakulam, Alappuzha, and Kollam coasts on the west coast were very highly vulnerable to coastal processes. Identifying vulnerable zones helps to better understand the impacts of rapid coastal processes and, with this prior estimation, the policymakers can take necessary actions to mitigate the irreversible impacts of coastal processes. [ABSTRACT FROM AUTHOR]

The advances in morphodynamics numerical modelling and the free availability of such updated models have made XBeach a powerful tool to predict the hydrodynamic and morphologic processes on sandy coasts. This paper addresses the impact of the sea-structure-sediments interactions in the morphological evolution of a coastal stretch which undergoes erosion and overtopping despite having a combined groyne field-dune-seawall defence scheme. Preliminary tests, tailored to conclude on the model mode-version to be applied in the case study, evidence the importance of considering the NH mode. After calibrated and validated, the model was applied for a set of cases to compute and discuss the effect of the individual defence scheme structural elements and the hydrodynamic driving factors, namely the wave energy and obliquity and the tidal range, on the morphodynamics. The results revealed that the seawall aggravates the erosion of the beach, despite being essential in the protection against overtopping and coastline retreat, and that the present configuration of the groyne field does not provide enough protection at the downdrift part of the stretch. The knowledge acquired can support the interpretation of the topo-bathymetric behaviour in similar coastal defence schemes existent worldwide. [ABSTRACT FROM AUTHOR]

In coastal environments, strong feedback can exist between benthic fauna and sediment dynamics. Benthic populations can modify sediment dynamics through biofiltration and bioturbation, while hydro- and sediment dynamics directly determine local environmental conditions for benthic organisms. However, these complex feedbacks are difficult to study in situ. Here, we carried out mesocosm experiments to characterize the effects of a benthic species (the gastropod Crepidula fornicata) on mud dynamics under hydrodynamic conditions representative of their natural habitat. Different experimental tests related to the inclusion (or not) of dead or live crepidula reveal that biofiltration can increase particle settling up to 40%. Flocculation, which is strengthened by organic matter enrichment in shell beds, also substantially increases particle settling. Thus, both processes enhance sedimentation above live crepidula habitats. Furthermore, these experiments highlight serious technical, physical and biological challenges that have to be tackled for properly investigating bio-physical interactions. [ABSTRACT FROM AUTHOR]

This paper reports the water temperature structure and associated coastal processes in the NE part of the Black Sea. In situ temperature was measured in the water area of the Utrish Nature Reserve. The thermistor chain was moored in 2020 and included 6–10 temperature sensors with an accuracy of ±0.025 °C and time step of one minute. The seasonal variations in the water temperature, upwelling events, internal waves and diurnal cycle were analyzed. The maximum value of SST (28.6 °C) was registered in the subsurface layer in August 2021; the minimum (7.7 °C) was registered in March 2022. Estimates of the diurnal temperature cycle were obtained according to spectral analysis. Summer months show the diurnal cycle more than 60% of the time, and the cold period shows it less than 10% of the time. Internal waves appeared in thermocline with periods from 5 min to 20 h. The strongest Ekman upwelling was registered in September 2021. The water temperature dropped from 26 °C to 16 °C in 10 h. Additionally, quality assessments of two hydrodynamic models were made. The models showed a good correlation (0.9) with water temperature measurements, but RMSE could reach 1–1.8 °C for subsurface layers. Temperature variability and its characteristics are an important basis for future coastal ecosystem studies in the Utrish. [ABSTRACT FROM AUTHOR]

In sandy beach systems, the aeolian sediment transport can be governed by the vertical structure of the sediment layers at the bed surface. Here, data collected with a newly developed sand scraper is presented to determine high‐resolution vertical grain size variability and how it is affected by marine and aeolian processes. Sediment samples at up to 2 mm vertical resolution down to 50 mm depth were collected at three beaches: Waldport (Oregon, USA), Noordwijk (the Netherlands) and Duck (North Carolina, USA). The results revealed that the grain size in individual layers can differ considerably from the median grain size of the total sample. The most distinct temporal variability occurred due to marine processes that resulted in significant morphological changes in the intertidal zone. The marine processes during high water resulted both in fining and coarsening of the surface sediment. Especially near the upper limit of wave runup, the formation of a veneer of coarse sediment was observed. Although the expected coarsening of the near‐surface grain size during aeolian transport events was observed at times, the opposite trend also occurred. The latter could be explained by the formation and propagation of aeolian bedforms within the intertidal zone locally resulting in sediment fining at the bed surface. The presented data lays the basis for future sediment sampling strategies and sediment transport models that investigate the feedbacks between marine and aeolian transport, and the vertical variability of the grain size distribution. [ABSTRACT FROM AUTHOR]

The coastline of Morocco extends across the northwest Maghreb region of Africa, from the western Mediterranean to the eastern Atlantic. Cultural heritage resources include archaeological remains that reveal a myriad of past human activities in the country's coastal zone, from Middle Paleolithic habitation sites to historical large-scale port infrastructure. As also experienced globally, natural and anthropogenic factors are affecting the stability and morphology of Morocco's coastal zone and impacting the archaeological sites therein. Recently, Morocco ratified the UN Integrated Coastal Zone Management (ICZM) Protocol and enacted a national ICZM law that include frameworks for management plans to include cultural heritage resources. One of the main challenges to developing ICZM plans in Morocco, however, is a gap in knowledge: there has been no baseline assessment of how all the factors at play impact cultural heritage assets. By focusing on northern Morocco as a case study, I identify six factors that specifically affect the coastline with examples of documented and potential impacts on archaeological sites. This is intended as a preliminary assessment that also aims to contribute to the development and content of potential management plans with recommendations for next steps. [ABSTRACT FROM AUTHOR]

We used the observations from the east coast of the USA and model simulations to elicit marine atmospheric surface layer (MASL) processes that controlled the spatial variability of electromagnetic ducting conditions in the near‐shore (60 km) marine environment during CASPER‐East field campaign. The estimated evaporation duct height (EDH) showed an average decrease of ∼2.5 m over every 10 km distance from the shore. The surface layer stability conditions chiefly determined the duct heights. While the mean duct height remained ∼10 m under unstable conditions, deeper (>20 m) evaporation ducts were frequently evident (∼40% of the time) during stable MASL conditions, which were responsible for the observed near‐shore EDH variability. Episodes of warm offshore flow and advection of hot and humid air from the Gulfstream region created ideal environmental conditions for stable MASL development and thus deeper ducts over the coastal ocean. A detailed case study of warm and humid Gulfstream air advection over the cooler coastal ocean is presented to elucidate the temporal evolution of the surface layer stability and associated changes in the spatial distribution of the evaporation duct height. Key Points: Stable conditions in the nearshore CASPER‐East region can be caused by both offshore flow and flow from the Gulf StreamThe near‐shore region of Duck, North Carolina, showed a gradual decrease of evaporation duct height from the shore ∼2.5 m for every 10 kmHigh‐evaporation ducts are associated with stable stratifications in the coastal marine atmospheric surface layer [ABSTRACT FROM AUTHOR]

The Shore Temple in Mahabalipuram (Tamil Nadu, Southern India) exists since the late 7th century. Historical sources suggest that it was built on an island in honour of the gods Vishnu and Shiva. A former bridge over the canal, which separated the island from the mainland, and a seawall, which protected the shore from the waves are dysfunctional now, as they are located too high above the present day sea level. A holy well, part of the temple complex, reaches down to the modern freshwater lens. We suggest that about 1 m uplift occurred after the construction of the temple, the canal and the seawall, but before the construction of the well. This event during the reign of King Rajasimhan in the early 8th century most likely was caused by an earthquake of magnitude M > 6.5 that led to the uplift of the island. There are thick walls of a ruined masonry building in the former, sand-filled canal, tilted in various directions. These are evidence for liquefaction of subsoil, caused by a second earthquake of intensity IX-X. The east coast of India has remained prone to destructive earthquakes: archaeoseismology proves to be useful tool which can help to identify these areas. [ABSTRACT FROM AUTHOR]

Effective coastal management requires an understanding of sediment dynamics. This study examines the distribution of heavy minerals (HMs) in two distinct coastal regions: the mainland and spit, each with unique sediment deposition patterns. The spit accumulates sediment through alongshore sediment transport (AST), while the mainland experiences erosive processes and significant human impacts. The hydrodynamic behaviour and weathering resistance of HMs enables source identification. This has helped to reveal differences between the two regions, with apatite being characteristic of spit sediments and garnet of mainland beaches. Coastal processes, such as erosion, sediment transport, and accumulation, significantly shape the distribution of the HMs, with garnets dominating erosive shores and amphiboles dominating accumulative shores. Furthermore, the study found that human-made coastal infrastructure also affects the composition of HMs and the sediment distribution through AST. This research has implications beyond the local level, providing global insights into the complexities of coastal dynamics. The study emphasises the importance of using HM analysis in conjunction with grain size analysis to understand the distribution of beach sediment composition. It also highlights the significant role of coastal processes, including anthropogenic impacts such as jetty construction or deepening port entrance canals on AST. • Heavy mineral analysis complements grain size analysis to study coastal sediment dynamics. • Heavy mineral composition in beach sediments aided in excluding three coastal areas along the studied sea coast. • Heavy mineral distribution patterns revealed disruptions in alongshore sediment transport due to coastal infrastructure. • Heavy mineral composition depends on coastal processes: garnets dominate on eroding, and amphiboles on accumulative shores. [ABSTRACT FROM AUTHOR]

Coastal pelagic ecosystems are highly variable in space and time, with environmental conditions and the distribution of biomass being driven by complex processes operating at multiple scales. The emergent properties of these processes and their interactive effects result in complex and dynamic environmental mosaics referred to as “seascapes”. Mechanisms that link large-scale oceanographic processes and ecological variability in coastal environments remain poorly understood, despite their importance for predicting how ecosystems will respond to climate change. Here we assessed seascape variability along the path of the rapidly intensifying East Australian Current (EAC) Southern Extension in southeast Australia, a hotspot of ocean warming and ecosystem tropicalisation. Using satellite and in situ measures of temperature, salinity and current velocity coupled with contemporaneous measurements of pelagic biomass distribution from nine boat-based active acoustic surveys in five consecutive years, we investigated relationships between the physical environment and the distribution of pelagic biomass (zooplankton and fish) at multiple timescales. Survey periods were characterised by high variability in oceanographic conditions, with variation in coastal conditions influenced by meso-to-large scale processes occurring offshore, including the position and strength of eddies. Intra-annual variability was often of a similar or greater magnitude to inter-annual variability, suggesting highly dynamic conditions with important variation occurring at scales of days to weeks. Two seascape categories were identified being characterised by (A) warmer, less saline water and (B) cooler, more saline water, with the former indicating greater influence of the EAC on coastal processes. Warmer waters were also associated with fewer, deeper and less dense biological aggregations. As the EAC continues to warm and penetrate further south, it is likely that this will have substantial effects on biological activity in coastal pelagic ecosystems, including a potential reduction in the accessibility of prey aggregations to surface-feeding predators and to fisheries. These results highlight the import role of offshore oceanographic processes in driving coastal seascape variability and biological activity in a region undergoing rapid oceanic warming and ecological change.

This paper reports the water temperature structure and associated coastal processes in the NE part of the Black Sea. In situ temperature was measured in the water area of the Utrish Nature Reserve. The thermistor chain was moored in 2020 and included 6–10 temperature sensors with an accuracy of ±0.025 °C and time step of one minute. The seasonal variations in the water temperature, upwelling events, internal waves and diurnal cycle were analyzed. The maximum value of SST (28.6 °C) was registered in the subsurface layer in August 2021; the minimum (7.7 °C) was registered in March 2022. Estimates of the diurnal temperature cycle were obtained according to spectral analysis. Summer months show the diurnal cycle more than 60% of the time, and the cold period shows it less than 10% of the time. Internal waves appeared in thermocline with periods from 5 min to 20 h. The strongest Ekman upwelling was registered in September 2021. The water temperature dropped from 26 °C to 16 °C in 10 h. Additionally, quality assessments of two hydrodynamic models were made. The models showed a good correlation (0.9) with water temperature measurements, but RMSE could reach 1–1.8 °C for subsurface layers. Temperature variability and its characteristics are an important basis for future coastal ecosystem studies in the Utrish.

Coastal plastic debris is a major problem affecting both sandy beaches and nearshore environments. Over several decades, plastic debris has become a global threat to the natural environment due in part to single-use culture, pervasiveness and accumulation following years of improper disposal. Despite the global research effort, in the Caribbean region, only a few studies attempt to quantify the amount and sources of debris. This paper combines coastal geomorphology and plastic debris collection with GIS spatial analysis at Maracas Beach, Trinidad between 2015 and 2016. Overall, 567 separate plastic items were captured and classified from within two 30 m wide zones at the central and eastern portions of the microtidal sandy beach. Macro- and meso-plastic debris associated with beach activity (n=233) and single use waste (n=215) were the most abundant debris. Microplastic debris (n=94) consists mainly of polystyrene granules and unidentifiable fragments from larger recreational debris that are readily lost to the environment. Using manufacturer’s information, polystyrene (n=206) was the most dominant debris. Regression models were also conducted using the average beach size and average beach angles where a weak positive linear relationship was found. Kernel density estimation was used to geovisualize the distribution of plastic items per square metre to develop a plastic debris signature. Despite current beach management activities, a large proportion of macro- and meso-sized debris can enter the environment. Studies such as these are invaluable for the Caribbean region where attempts to manage the pollution caused by plastic are limited by data. [ABSTRACT FROM AUTHOR]

From 2013 to 2020, water levels in Lake Michigan rose from an all-time low to the highest levels observed in nearly four decades, causing shoreline changes throughout the Great Lakes. These changes are particularly noticeable at North Avenue Beach in Chicago, an artificial beach where federal, state, and city agencies have mitigated rising waters by importing sand and constructing groins. Using spring season aerial imagery from 2012 to 2020, we calculated beach area for each year and compared sand cover loss between years to water level change per the USGS station located just south of the study area. Analysis reveals year-to-year loss in sand cover since 2013, with the largest single-year change occurring between 2018 and 2019. An inverse relationship with a slight lag exists between water level and these beach area changes. We calculated sand-groin distances from 2000 to 2020 to identify north–south effects. Of the six beach cells separated by groins, the northernmost two cells failed over the study period, and experienced the largest individual sand-groin distance losses. We modeled inundation to investigate whether the sand loss was explainable by lake level change alone, with particular attention given to hardened shoreline implemented north of the beach in 2015. Observed sand cover loss markedly exceeded predictions from the inundation modeling. In addition to water level changes, a local response to shoreline modification and obstruction of sediment transport at this site may influence sand cover. [ABSTRACT FROM AUTHOR]

The launch of the first Indian Remote Sensing Satellite in 1988 ushered in a new era of utilization of satellite data and technology in natural resources monitoring, coastal area management, disaster mitigation, weather and climate change studies. India with its very long coast line, areal extent, resources and population would have been a huge challenge to the coastal researchers and administrators if not for the Indian Remote Sensing satellite data that provided the much needed temporal, thematic information for effective mapping, monitoring and management of the coastal areas. The country's large and diverse coastal regions are economically important and ecologically rich but also extremely vulnerable and highly prone to natural and anthropogenic hazards. Through the last three decades, the Indian remote sensing programme has contributed immensely to our understanding of the coast and ocean processes, coastal ecosystems, habitats, marine pollution and the vulnerability of the coast to natural hazards. IRS-1C with its improved spatial resolutions, additional spectral band, improved repetitively ushered in a new era of research specifically in the management of coastal areas and resources. Availability of spatial data at various resolutions, low cost, advances in technology resulted in new applications for management coastal areas. IRS-1C also can be aptly termed as the precursor for thematic satellite series such as OCEANSAT, RESOURCESAT and CARTOSAT, thereby setting the environs for thematic research in coastal areas. Integrated utilization of remote sensing data, numerical models, GIS and GPS has paved the way for the development of operation systems for management of coastal areas, thereby realizing the vision of Dr. Vikram Sarabhai, the father of Indian Space Programme, of building a self-reliant and indigenous Space Programme for the betterment of quality of life of the common people. [ABSTRACT FROM AUTHOR]

• Sand sources for San Francisco bay changed during holocene transgression. • The San Francisco estuary is likely an importer of sand from the pacific coast. • Pacific coast is cut-off from central valley fluvial sources in modern conditions. • Most sand in San Francisco bay is likely relic from low stand fluvial transport. • Transgressive sand sourcing reversals may be abrupt in large structural estuaries. Coastal sand supply is a critical component of shoreline stability in the face of modern threats to coastal zones such as sea level rise or anthropogenic sediment extraction. Understanding the natural and anthropogenically perturbed dynamics of coastal systems has become a pressing challenge for coastal communities, such as the San Francisco Bay area in the United Sates, a large structurally controlled estuary system where stakeholders seek to balance the extraction of coastal sand resources for economic use and ensure sufficient sand supply for sustaining natural coastal environments. Developing accurate and comprehensive models of sand inputs and transport pathways in different types of coastal systems is imperative to balancing these competing needs. While estuarine sediment transport has been well-studied in many systems globally, structurally controlled estuaries in tectonically active settings have received relatively less attention. The prevailing hypothesis for sediment transport through San Francisco Bay describes active input and transport of sand from a large integrated regional catchment, through multiple subembayments, and out to Pacific coast beaches; a model contrary to prevailing understanding of highstand estuarine sediment transport in most settings. We test this model by applying comprehensive sand provenance analysis to surface and near-surface sand deposits in and around San Francisco Bay coupled with sand residence time data from optically stimulated luminescence (OSL) dating. New provenance results include sand petrography modal abundances, bulk geochemistry, and U-Pb detrital zircon geochronology from 27 Holocene samples throughout the San Francisco Bay region. Collectively, these new results highlight marked sediment provenance and residence time differences between San Francisco Bay structural subembayments. In particular, distinct compositional differences and OSL ages exist between sand in the bayhead region of the estuary (OSL ages ca. 4 ka; Sacramento River/local provenance) and sand from the more distal bay regions and the Pacific coast (OSL ages ca. 1 ka; integrated Sierra Nevada provenance). These provenance differences better support a revised sand input and transport model with disconnected depocenters across three structurally restricted subembayments from bayhead to the Pacific coast. New data suggest that at present the bayhead region receives limited supply from the Sacramento-San Joaquin Delta drainage with subsidiary supply from local circum-bay drainages. Sand deposited in the region from the Pacific coast through the inlet (Golden Gate) and into the estuary consists of a combination of tidal winnowing and reworking of "relic" sand from lowstand periods combined with sand eroded from Pacific coast sea cliffs, and sand supply from local Coast Range drainages. These results suggest that sand is likely not transported directly to the Pacific coast from the Sacramento-San Joaquin Delta under modern conditions. Moreover, it is likely that structural constrictions between the main estuary and outer coast and between estuary subembayments cause abrupt cessation of sediment input from the main regional drainage during marine flooding, a feature likely common to large structurally controlled estuaries globally. This revised model for San Francisco Bay sand transport illustrates the need for research targeted at interpreting natural sand transport pathways in coastal systems where coarse sediment supply is a sustainability concern. [ABSTRACT FROM AUTHOR]

Simultaneous determination of dissolved silver (dAg) with other key GEOTRACES trace metals is difficult because dAg in seawater tends to form negatively charged chloride species that result in only 75% recovery efficiency with commonly used NOBIAS PA-1 chelating resins. In this study, we developed a method using solid phase extraction coupled with isotope dilution that enables full quantification (97.9 ± 2.1%) of dAg along with other major trace metals including cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), and lead (Pb) (recovery efficiency = 100% to 102%) in seawater samples. Seawater samples were first spiked with Ag-109 and allowed to reach isotopic equilibrium before extraction using NOBIAS PA-1 chelating resin. Then, dAg isotope ratios (Ag-109/Ag-107) before and after solid phase extraction were determined and used to quantify dAg. Determination of dAg with dissolved Cd, Cu. Mn, Ni, and Pb in reference seawater material CASS-6 resulted in deviations of between 1.0% and 8.8% from the consensus values, which are well within the standard error of measurement. We then successfully determined the concentrations of dissolved Cd (0.05–0.2 nM), Cu (0.5–13 nM), Mn (10–140 nM), Ni (2–12 nM), Pb (5–110 nM), and Ag (10–40 pM) in Otsuchi Bay, Japan and its surrounding rivers. Evaluation of the behavior of dAg under a salinity gradient using estuarine samples collected from Samunsam River, Malaysia shows increasing dAg concentration with salinity (R2 = 0.68), which suggests release of sedimental Ag under high ambient chloride concentrations. Our new method enables rapid and simultaneous measurements of dAg with other key GEOTRACES trace metals in a single analysis, which is expected to expedite analysis and increase availability of oceanic dAg data globally. • Solid phase extraction enabled rapid extraction of silver from seawater matrix. • Use of isotope dilution enabled full quantification of silver in seawater. • Simultaneous determination of silver with other key trace metals achieved. [ABSTRACT FROM AUTHOR]