Abstract Infragravity (IG) waves (periods nominally 25–250 s) are generated in shallow water by nonlinear difference‐frequency interactions between shorter period (nominally 4–25 s) incident sea‐swell waves. Previous studies show strong IG reflection from the beach face and detectable IG energy in alongshore‐propagating edge waves. Here, a linear wave model is developed to invert observed pressure (P) and velocity (cross‐shore and alongshore, U, V) cross‐spectra (including sensors separated in both the alongshore and cross‐shore directions) into cross‐shore standing and alongshore progressive linear shallow‐water modes. This inversion uses the Bayesian maximum a posteriori method (MAP). Infragravity edge waves on a moderately sloped ocean beach are characterized using 60 days of observations with low‐to‐moderate energy incident waves. Colocated P and UV sensors were deployed from the shoreline to 30 m depth, with an eight‐element PUV array in 7 m depth spanning 1.5 km alongshore. MAP estimates qualitatively agree with previous results obtained using the maximum likelihood estimator and smaller arrays. Edge waves average (28%, 14%, 43%) of the IG (P, U, V) variances in 7 m depth. Edge waves are most energetic at high tide when the shoreline slope is largest, possibly because the steep beach supports the multiple constructively interfering shoreline reflections required to form edge waves. The numerical wave model SWASH 1D assumes normally incident waves and neglects edge waves, but reproduces approximately the energy and cross‐shore structure of P and U.
Abstract Sea ice plays a critical role in the Southern Ocean freshwater budget and influences water mass transformation (WMT) by redistributing freshwater across density classes. However, the mechanisms driving inter‐model spread in this process remain poorly understood. Here, we analyze 18 climate models from the Coupled Model Intercomparison Project Phase 6 to identify the processes controlling sea ice–driven WMT. We show that the inter‐model spread is governed by three factors: sea ice production, sea ice spatial redistribution, and ocean density‐driven redistribution. Sea ice production is the dominant contributor, as it sets the total freshwater flux available for redistribution. Sea ice spatial redistribution controls how efficiently freshwater is transported across the Southern Ocean and across surface density classes, making it the main pathway through which sea‐ice freshwater forcing contributes to cross‐isopycnal transformation and ventilation in most models. In contrast, ocean density‐driven redistribution, arising from seasonal surface density changes, determines the density classes interacting with freezing and melting and dominates in low‐ventilation models. Together, sea ice production sets the freshwater input and the two redistribution processes control its transfer across density classes. Among these, sea ice production shows the strongest correlation with inter‐model spread. We further show that differences in sea ice production are closely linked to surface ocean temperature through differences in air–sea heat flux. Overall, sea ice–driven WMT emerges from tightly coupled ocean–atmosphere–sea ice interactions. Reducing model uncertainty therefore requires improved representation of air–sea heat exchange, sea ice thermodynamics, and their coupling with ocean density structure.
Abstract This study develops a three‐dimensional model to describe wave–current interactions over a seabed featuring a porous layer with spatially varying thickness. A previous approach (Hsu et al., 2018, https://doi.org/10.1016/j.coastaleng.2018.06.003 ) addressed energy dissipation within the porous medium by introducing a complex‐valued group velocity and representing energy transport through its real part; however, this treatment lacked solid physical justification and relied on an empirical damping coefficient within the phase‐averaged wave model. The present work extends Mellor's (2008, https://doi.org/10.1175/2008jpo3971.1 ) depth‐resolved formulation, originally devised for impermeable seabeds, to incorporate the effects of a porous layer. The solution is explicitly decomposed into wave and current components. For the wave part, eigenfunctions based on linear wave theory are used to characterize wave motion in both the fluid and porous regions. By applying a phase‐averaging technique, analytical expressions are derived for essential quantities such as the real‐valued dynamic and kinematic group velocities, radiation stresses, drift velocity, and energy dissipation within the porous medium. This theoretical foundation is suitable for integration into existing numerical models that simulate wave–current interactions over porous seabeds and reef environments. Several numerical results are presented and discussed for the dynamic and kinematic group velocities, as well as for the temporal modification factor of wave energy under various porous parameters. The numerical evidence shows that the proposed theory can contribute up to for shallow water waves propagating over a thick porous layer of high porosity. In addition, the formulations of the energy sinks are implemented to simulate wave damping over porous breakwaters.
Abstract Bottom‐water oxygen (O 2 ) possibly constitutes the strongest regulating factor on ecosystem function of the seafloor environment. The conventional view of bottom‐water O 2 regulation in temperate regions is a strong seasonal variability imposed by deposition of fresh, labile organic carbon following the spring and fall plankton bloom generating changing sediment O 2 demand. The supply of O 2 is considered mainly regulated by seasonally‐varying thermal stratification or large‐scale lateral advection of water masses. However, benthic O 2 also varies over much shorter timescales, but the spatiotemporal regulation of this O 2 variability is not well resolved. We conducted a 10‐month‐long in situ study (2022–2023) of bottom‐water O 2 dynamics at a 40‐m‐deep coastal site in the Baltic Sea. Following the spring bloom and the onset of thermal stratification, the gradual decline in O 2 was regularly interrupted by rapid (<24 hr) oxygenation events in which O 2 levels spiked, subsided, but remained elevated by between 25 and 180 μmol L −1 relative to conditions before the event. Without these events, extrapolation of the observed O 2 decline implied hypoxic or anoxic bottom‐water conditions by mid‐May. Similarly, reoxygenation of the lower water column in the late fall was controlled by a few rapid and strong reoxygenation events. These events are consistent with regional‐scale ocean circulation and mixing processes, potentially involving a downwelling mixing front and/or coastal trapped/internal waves. However, we lack data to unambiguously distinguish between these mechanisms. We suggest that rapid benthic oxygenation events are likely a common characteristic of coastal seafloors and critical for benthic ecosystem functioning.
Abstract Local surface heat flux feedback plays a critical role in modulating sea surface temperature (SST) variability. Here we estimate local surface heat flux feedbacks using an observational and a reanalysis data set, and outputs from 27 CMIP6 models. We find that CMIP6 models systematically overestimate the magnitude of negative net surface heat flux feedback by 22%–27% globally. This excessive damping mainly arises from overly strong latent heat flux feedback globally, with an additional contribution from stronger shortwave feedback in the tropics. Despite these strong negative feedbacks, SST variability in CMIP6 models does not show clear signs of excessive overdamping, as both SST variance and persistence are broadly consistent with observations. This apparent inconsistency suggests compensating oceanic processes, potentially related to underestimated ocean damping or biases toward overly deep mixed layer depths.
Abstract The dynamics of cross‐shelf transport in the northern South China Sea (NSCS) are critical to regional material transport, whereas the quantities and governing mechanisms, particularly under the monsoon‐driven seasonal reversals, remain incompletely explored. This study investigates the dynamics and seasonal variability of cross‐isobath volume transport over the NSCS shelf using high‐resolution numerical simulations. Results indicate pronounced seasonal reversals in shelf circulation: during the summer southwesterly monsoon, the combined Guangdong Coastal Current and South China Sea Western Boundary Current (SCSWBC) drive northeastward flow, yielding net onshore transport at the 50‐m and 100‐m isobaths. In contrast, the winter northeasterly monsoon reverses the circulation, resulting in offshore transport at the same isobaths. Conversely, the 200‐m isobath exhibits opposing dynamics, with offshore transport in summer and onshore transport in winter. Dynamical diagnosis shows that transport on inner and middle shelves is influenced by the bottom pressure torque, driven by the along‐shelf sea‐level gradients resulting from water accumulation or depletion against the western boundary formed by Hainan Island and Leizhou Peninsula. In summer, the strong horizontal density gradient enhances the significance of the joint effect of baroclinicity and relief ( Q JEBAR ) in the cross‐shelf transport balance, while strong winter mixing weakens this effect. On the outer shelf, Q JEBAR and surface wind stress‐induced transport governs transport variability through baroclinic adjustments influenced by SCSWBC, Slope Current, and Kuroshio interactions, and wind‐induced Ekman transport. These findings highlight distinct dynamical regimes across different shelf zones, providing a mechanistic framework for understanding seasonal cross‐shelf carbon and nutrient fluxes in the NSCS.
Abstract The California Current System (CCS) is a globally recognized source of nitrous oxide (N 2 O), a potent greenhouse gas to the atmosphere; however, little is known about the underlying sources of N 2 O within the CCS. During the 2021 NOAA West Coast Ocean Acidification cruise, we collected samples for N 2 O and nitrate (NO 3 − ) concentration and isotope ratio measurements–from Dana Point, California (31.78°N) to Haida Gwaii, Canada (52.40°N)–to understand what processes shape the distribution of N 2 O in the CCS and subsequent emissions. Throughout the primary range of the subsurface California Undercurrent (CUC), with potential density anomalies of 26–27 kg m −3 , we observed elevated 15 N/ 14 N in both NO 3 − and N 2 O, corresponding with negative N*. These signals of nitrogen loss and N 2 O production from denitrification are indicative of northward transport of waters from eastern tropical North Pacific oxygen deficient zone throughout the CUC. Together with contemporaneous data from an underwater glider network, we observed strong upwelling of CUC waters between Pt. Conception and Cape Mendocino in California, corresponding with high surface density and excess N 2 O concentrations, leading to large N 2 O fluxes to the atmosphere (as high as 48 μmol m −2 d −1 ). Thus, the tracers employed in this study link CUC transport to N 2 O emissions to the atmosphere during the summer upwelling season. Because the CUC is projected to expand and shoal in response to climate change, this source of N 2 O could be enhanced under these conditions.
Abstract Nonlinear high‐frequency internal waves (HIWs) can occur at oceanic frontal interfaces but are rarely observed directly. This study presents field observations of HIWs near submesoscale fronts (SFs) in the northern Gulf of Mexico. A marine X‐band radar detected a series of organized bands, with a spacing of 50 ∼ 300 m, near SFs. The bands propagate toward SFs at speeds of 0.10–0.40 m/s, derived from consecutive radar backscatter intensity images. These fortuitous bands were identified as the surface expression of HIWs. This identification is supported by corresponding temperature undulations from a thermistor chain below a wave glider. The ship‐based observations provided vertical density and current (buoyancy and shear) profiles at a large frontal scale. These profiles, taken beneath and upstream of the HIW signature, are employed in the Taylor‐Goldstein equation using the mixed layer depth as a surrogate bottom, which predicts the shear instability growth rate at different wavelengths and corresponding phase speeds. The theoretically predicted fastest‐growing mode wavelength and its phase speed closely align with the observed HIWs after adjustments to the background shear and buoyancy uncertainty ranges. These findings support a shear–stratification instability framework for HIW generation along the shoaling thermohaline front. As HIWs influence local mixing and energy dissipation, they may bear the significance of the frontal energy budget and forward energy cascade from the submesoscale currents to isotropic turbulence in the upper ocean.
Abstract Marine heatwaves (MHWs) exert profound impacts on marine ecosystems and socio‐economic systems. Although individual extreme events have been widely investigated, the mechanisms underlying decadal‐scale abrupt shifts in MHW regimes under global warming remain poorly understood. Here, we identify a pronounced abrupt change in MHW accumulated days over the Gulf Stream (GS) extension around 2013, marked by a stepwise increase of 8.75 days substantially exceeding the long‐term linear trend. Using a random forest framework, we show that a rapid buildup of subsurface ocean heat content (OHC), rather than anomalous surface heat fluxes, is the dominant contributor to this abrupt change. Mechanistic analyses further indicate that this subsurface heat accumulation is dynamically associated with a northward displacement of the Gulf Stream, driven by anomalous southerly winds. By combining observations with CESM2 pacemaker experiments and targeted AGCM sensitivity simulations, we trace the origin of these atmospheric anomalies to an abrupt warming in the subtropical eastern Pacific. This remote forcing excites a transcontinental, quasi‐stationary Rossby wave train, which sustains a deep, equivalent‐barotropic anticyclonic circulation over the GS Extension. Our results identify a previously underappreciated teleconnection linking Pacific climate variability to Atlantic subsurface heat redistribution, underscoring the capacity of remote atmospheric forcing to induce abrupt MHWs abrupt changes in western boundary current regions.
Abstract Submarine canyons and trenches are the main pathways for transport of water, sediments, and nutrients across the continental slope. In the North Sea, transport across the slope and into the Norwegian Sea is confined to the Norwegian Trench (NT). From June 2023 to May 2024, we recorded time series data in the middle of the NT (272 m) and close to the Atlantic continental slope (363 m) using moored ADCPs to investigate the hydrodynamic variability. We identified semi‐diurnal and diurnal tidal influence explaining 19% of the variance in the flow in the middle of the NT, and 10% of the variance at the continental slope, respectively. The deep currents respond to local winds and to coastal‐trapped waves (CTWs) on time scales of 1–10 days. Significant correlations between increased water temperature and along‐slope winds from the Southwest show that CTWs enable strong inflows of Atlantic Water, whereas winds from the Northeast favor upwelling of Arctic waters. In the central trench, seasonal signals in velocity, backscatter, and temperature are related to the North Atlantic Oscillation, highlighting the connectivity of the NT to the North Sea. The interactions of remotely forced CTWs and the up‐and downwelling of water masses are typically observed in submarine canyons. With this study we add to a new understanding of the hydrodynamics in the NT, which are comparable to the dynamics observed in canyons around the world.
Abstract Volcanic islands are prone to flank instabilities that can generate tsunamis even when mobilized volumes are moderate. This study investigates submarine collapses during the 2011–2012 eruption south of El Hierro, which built the Tagoro submarine volcano. Repeated multibeam bathymetric surveys captured the rapid growth, collapse, and reconstruction of the edifice, providing an exceptional record of seafloor change during an active submarine eruption. This record is used to develop a hybrid survey‐modeling methodology that links observed collapse morphology to scenario‐based estimates of the near‐field wave response. First, two OpenFOAM‐based approaches are benchmarked against laboratory experiments of submerged landslide‐tsunami generation: a computationally efficient viscoplastic mixture model and a more detailed Eulerian‐Eulerian two‐phase model. The two‐phase model is included as a reference to help assess the simplified mixture approach in the laboratory benchmark. The mixture model is then applied at field scale to simulate the largest Tagoro collapse. In the absence of tide gauge records, the numerical parameter set for the field scale simulations is selected based on its agreement with the erosion and deposition patterns inferred from bathymetric differencing. The resulting simulations reproduce the main landslide pathway and predict a strongly directional near‐field wave field, with local amplification over the island shelf controlled by bathymetry. The results show that repeated bathymetric monitoring, combined with physics‐based 3D modeling, can bridge observed volcanic seafloor change and plausible landslide‐tsunami scenarios. This approach is not intended for real‐time warning, but provides a transferable framework for local hazard assessment during prolonged submarine eruptions.
Abstract The geological record indicates that Earth experienced several global glaciations—so‐called “snowball Earth” events—the most recent of which shortly preceded the emergence of complex life. These are usually attributed to a runaway ice‐albedo feedback triggered by solar or atmospheric radiative forcing crossing a critical threshold. In this study, we use the Budyko‐Sellers energy‐balance model to demonstrate that such events can also be initiated by changes in the efficiency of meridional heat transport, potentially driven by tidal resonances with the Sun or Moon or by continental reconfiguration. We identify two special points associated with this mechanism—the neutral point, where the heat transport efficiency does not affect the ice coverage, and the transcritical point, where the snowball transition occurs precisely at the neutral point. We find that these points correspond to special climate states characterized by maximal meridional heat transfer, entropy production, and sensitivity to perturbations. Moreover, we show that when the climate is marginally baroclinically stable, the transport efficiency is near the value that maximizes the rate of entropy production, so that any mechanism pushing the climate toward marginal baroclinic stability also pushes it toward a state of maximum entropy production. Finally, by partitioning the model into an ocean and an atmosphere, we show that destabilization into a snowball state can result either from increased atmospheric or decreased oceanic transport efficiency. Our findings suggest a novel mechanism for snowball initiation and the organization of global climate that should be further investigated with large‐scale models and geological tests.
Abstract Wind forcing plays a central role in oceanic circulation, including circulation in small bays where complex coastal orography modulates local winds both in time and space. However, their role in the circulation of such bays remains unclear because local winds are difficult to observe directly over the sea. Here, we used oceanic and atmospheric simulations with 100 m horizontal grid spacing, together with observations, to investigate wind‐driven circulation under time‐ and spatially varying wind forcing in Otsuchi Bay. The simulation forced by time‐ and spatially varying winds reproduced the observed SSS distribution more closely than the simulation forced by time‐varying but spatially uniform wind, which is a common simplification in coastal oceanic simulations. This improvement was explained by bay interior upwelling away from the coastline, which was not evident under spatially uniform wind forcing. This upwelling was driven by wind stress divergence rather than by wind stress curl. Spectral analysis showed that the relative importance of two mechanisms varied across timescales. Divergence‐driven vertical motion was strongest at periods shorter than the local inertial period, but it became relatively weaker than curl‐driven motion at longer periods. This study demonstrates that short‐timescale wind stress divergence can drive bay interior upwelling and modify the SSS distribution in small bays. This finding further suggests that upwelling in small bays is not limited to coastline‐confined upwelling or curl‐driven Ekman upwelling. Accounting for divergence‐driven upwelling is therefore important for understanding and modeling coastal circulation in small bays, with potential implications for the vertical transport of biogeochemical materials.
Abstract Ocean alkalinity enhancement (OAE) aims to mitigate climate change by increasing the chemical capacity of seawater to store anthropogenic CO 2 . OAE can be implemented through multiple pathways, each of which intentionally modifies marine carbonate chemistry through increases in total alkalinity (TA). Experimental research has only recently begun to assess how such TA perturbations (ΔTA) and associated carbonate chemistry changes affect ocean ecosystems. Meaningful assessments need context on how ΔTA‐induced by different OAE pathways would evolve over time and in magnitude. Here, we use a dilution equation, a regional model, and a global model to explore how marine organisms would be exposed to ΔTA under realistic constraints. We find that a more extreme ΔTA of>1,000 μmol kg −1 , a perturbation common in OAE experiments, only occurs for minutes in a minuscule fraction of the OAE‐perturbed seawater volume. In contrast, ΔTA between 1 and 100 μmol kg −1 is a ubiquitous perturbation range for OAE under real‐world constraints, yet are not commonly in focus of environmental OAE assessments. These results suggest that there is a disconnect between real‐world ΔTA that can plausibly be invoked by OAE and the experimental ΔTA range frequently used in the environmental OAE assessment. While “unrealistic” ΔTA can provide mechanistic insights into an organism or ecosystem response to carbonate chemistry changes, they can also cause overestimation of OAE effects, if the unrealistic ΔTA is not contextualized appropriately. Our results can be used to improve the contextualization of OAE studies, thereby making the interpretation of ΔTA effects on the environment more robust.
Abstract Ageostrophic velocities at ocean fronts play a key role in ventilating the upper ocean. The overturning circulation driven by cross‐front ageostrophic flow is widely recognized as the major mechanism of vertical transport, but the role of along‐front ageostrophic velocities remains underrepresented in existing theory. Here, we recast the quasigeostrophic (QG) momentum equations in a reference frame that follows the local geostrophic flow (a front‐following coordinate system) and show that the along‐front and cross‐front ageostrophic flows originate from distinct underlying dynamics. To maintain the leading‐order geostrophic balance of the front, the next‐order Coriolis force acting on supplies the tangential acceleration of the geostrophic flow in the along‐front direction. In the cross‐front momentum balance, by contrast, the Coriolis force acting on acts as the centripetal acceleration of , yielding , where the curvature number Cu is defined by the local radius of curvature and the Coriolis frequency . For curved fronts where Cu varies rapidly, adjustments of generate horizontal divergence and drive overturning circulations along the frontal axis. Idealized simulations of curved fronts confirm that ageostrophic motions can be successfully reconstructed from geostrophic fields. These results suggest an underappreciated role of front curvature in modulating vertical velocity at ocean fronts, with implications for identifying curvature‐induced hotspots of vertical transport from satellite sea surface height observations.
Abstract Submarine Groundwater Discharge (SGD) is often omitted from estuarine circulation modeling systems despite its potential to alter salinity, density, and stratification. So, this study employed a one‐way coupled PARallel Flow (ParFlow)–Finite Volume Community Ocean Model (FVCOM) framework to investigate the hydrodynamic influence of terrestrially derived meteoric groundwater discharge on the Chesapeake Bay. The results show that SGD effects vary spatially and seasonally, whereas the groundwater recharge/discharge is more likely to echo the precipitation events. Submarine Groundwater Discharge effects become more significant during the low river flow conditions, especially in summer and in Middle Bay due to the high SGD to river discharge ratio. Under baseline conditions, SGD slowly enhances stratification (0%–2%) by freshening the bottom layer and sharpening the adjacent halocline where river discharges being trapped above the pycnocline barely modifies the deeper and denser layers. During Hurricane Ida, prolonged period of precipitation elevated the SGD, which resulted in a 20% salinity reduction, however, wind driven mixing dominated stratification during the storm peak and SGD‐driven bottom freshening re‐establishes stratification during post‐storm recovery. Sensitivity experiments addressing uncertainties in SGD volume show that an ideal tenfold SGD intensification produces an 8% salinity reduction and a 10% (30%) stratification enhancement (reduction) throughout the bay (shallow Upper Bay). While river discharge dominates the estuarine freshwater budget, SGD exerts a physically distinct and disproportionate secondary influence on deep‐layer density, salt intrusion, exchange circulation, and stratification, with implications for oxygen dynamics and biogeochemical cycling in this vulnerable estuary.
Abstract Greenland's ice loss is increasing across the ice sheet due to enhanced surface melting and accelerated glacier discharge, contributing to sea level rise and potentially altering ocean circulation and marine ecosystems. Fjords play a key role in this process by linking the ocean and ice sheet, but currently a limitation is that most fjords in Greenland lack observational data, especially seasonal data sets. Using glacier‐to‐coast hydrographic sections from the Ella Ø fjord complex in East Greenland, we document strong seasonal variability. Summer conditions are characterized by ice‐free, warmer, and fresher surface waters, with clear glacier meltwater and precipitation signals confined to the upper 50 m and primarily to the inner fjord. In winter, the fjord is ice covered, with colder and saltier surface waters, weaker turbidity that is dominated by basal melt at depth, and only small fractions of glacier meltwater and local meteoric water. The Polar Water layer is warmer close to the marine‐terminating glacier during both seasons, without corresponding change in salinity. The observed seasonal change in Polar Water thickness of 40 m is consistent with the proposed thinning of the Polar Water layer along the Northeast Greenland shelf since the 2000s, suggesting that longer‐term changes are superimposed on a strong seasonal variability. Given that most freshwater from the Arctic Ocean flows southward along the East Greenland coast, influencing regional and potentially large‐scale ocean circulation, it is important to gain more insight into its seasonal variability across multiple locations to evaluate the robustness of reported longer‐term changes.
Abstract Antarctic open‐ocean polynyas trigger vigorous wintertime convection, influencing ocean circulation and atmospheric processes. In the Weddell Sea, interaction between the Weddell Gyre and the Maud Rise seamount generates a Taylor column that favors polynya formation. However, owing to limited observations, the dynamics of such polynya formation remain partially understood, particularly the long‐term preconditioning that sets the stage for polynya occurrence. We use glider observations from late austral summer 2022 to investigate the role of mixing in preconditioning, focusing on the interior layer below the pycnocline, which stores heat that melts sea ice and regulates deep convection. We show that multiple mixing processes contribute to the preconditioning. Widespread interleaving structures along the northwestern flank of Maud Rise are identified, indicating that warm, salty water intrudes into the Taylor column along isopycnals. This intrusion is likely driven by lateral shear and eddies, both arising from the flank's anticyclonic circulation. Moreover, eddy shedding, cabbeling, and diffusive convection jointly enhance lateral homogenization and destratification of the Taylor column interior below the pycnocline. Using the large eddy method and a triple decomposition of the tracer variance equation, we calculate snapshot‐based along‐isopycnal heat and salt transports from the Rise flanks into the Taylor column as ∼0.18 TW and ∼, respectively. At these rates, idealized estimates suggest that polynya‐favorable conditions could develop within 2–6 years of the observations. Our results highlight the role of mixing in polynya formation and the need to realistically represent these processes in climate‐scale ocean models.
Abstract We present a bidirectional coupling between a nonlinear kinematic depth inversion method and a phase‐averaged spectral wave model to evaluate the influence of wave nonlinearity over gently sloping nearshore bathymetry. Time‐resolved wave imagery provides spatially varying frequency–wavenumber fields, whereas the simulated significant wave height field supplies a measure of amplitude dispersion. These data are integrated to quantify an effective nonlinearity parameter across contrasting wave energy conditions, encompassing both calm and energetic states. Particular attention is given to the shoaling region and the inner surf zone under spilling type breaking, where amplitude effects and depth‐induced dissipation significantly modify the dispersion characteristics. Comparisons between the proposed nonlinear depth inversion and independently surveyed bathymetry show that neglecting nonlinearity produces a systematic depth overestimation that scales with the local nonlinearity, whereas addressing nonlinearity reduces this bias by as much as 90%. Video‐derived surface motion retains identifiable dispersive signatures after the onset of spilling type breaking, enabling depth inversion when wave nonlinearity is addressed. This remains valid until breaking‐generated foam becomes sufficiently dense that the resulting noise level becomes comparable to the wave signal. The analysis shows that video‐derived wave kinematics and bathymetry, when interpreted with a calibrated spectral wave model, provide a consistent description of the nonlinear transformation of shoaling and breaking waves. It also identifies the parameter ranges in which linear depth inversion becomes less reliable under field conditions.
Abstract Algal bloom predictions remain challenging in coastal regions such as the East China Sea (ECS) because of limited in situ observations and inaccurate chlorophyll– a numerical predictions. Along tide–dominated coasts, phytoplankton growth is primarily light limited in summer because of tide–induced high turbidity. Satellite observations reveal that the optimal phytoplankton growth conditions occur exactly at the outer edges of turbidity fronts where light availability and nutrients converge, facilitating the formation of bloom initiation zones. Algal blooms generally expand coastward with the shoreward movement of turbidity fronts and dissipate as these fronts recede offshore. A U–Net based turbidity prediction model for ECS coasts was developed via numerical modeling of tidal data and satellite–derived turbidity data. This model could accurately predict the movements and offshore distances of turbidity fronts and could provide algal bloom dynamics 1–2 days in advance. This study provides new insights for early warning of algal blooms along tidal–dominated coasts.
