Changes In Bathymetry Research Articles

Implementing the iCORAL (version 1.0) coral reef CaCO3 production module in the iLOVECLIM climate model

Abstract. Coral reef development is intricately linked to both climate and the concentration of atmospheric CO2, specifically through temperature and carbonate chemistry in the upper ocean. In turn, the calcification of corals modifies the concentration of dissolved inorganic carbon (DIC) and total alkalinity in the ocean, impacting air–sea gas exchange, atmospheric CO2 concentration, and ultimately the climate. This feedback between atmospheric conditions and coral biogeochemistry can only be accounted for with a coupled coral–carbon–climate model. Here we present the implementation of a coral reef calcification module into an Earth system model. Simulated coral reef production of the calcium carbonate mineral aragonite depends on photosynthetically active radiation, nutrient concentrations, salinity, temperature, and the aragonite saturation state. An ensemble of 210 parameter perturbation simulations was performed to identify carbonate production parameter values that optimize the simulated distribution of coral reefs and associated carbonate production. The tuned model simulates the presence of coral reefs and regional-to-global carbonate production values in good agreement with data-based estimates, despite some limitations due to the imperfect simulation of climatic and biogeochemical fields driving the simulation of coral reef development. When used in association with methods accounting for bathymetry changes resulting from different sea levels, the model enables assessment of past and future coral–climate coupling on seasonal to millennial timescales, highlighting how climatic trends and variability may affect reef development and the resulting climate–carbon feedback.

Modelling Mediterranean ocean biogeochemistry of the Last Glacial Maximum

Abstract. We present results of simulations performed with a physical–biogeochemical ocean model of the Mediterranean Sea for the Last Glacial Maximum (LGM) and analyse the differences in physical and biochemical states between the historical period and the LGM. Long-term simulations with an Earth system model based on ice sheet reconstructions provide the necessary atmospheric forcing data, oceanic boundary conditions at the entrance to the Mediterranean Sea, and river discharge to the entire basin. Our regional model accounts for changes in bathymetry due to ice sheet volume changes, reduction in atmospheric CO2 concentration, and an adjusted aeolian dust and iron deposition. The physical ocean state of the Mediterranean during the LGM shows a reduced baroclinic water exchange at the Strait of Gibraltar, a more sluggish zonal overturning circulation, and the relocation of intermediate and deep-water-formation areas – all in line with estimates from palaeo-sediment records or previous modelling efforts. Most striking features of the biogeochemical realm are a reduction in the net primary production, an accumulation of nutrients below the euphotic zone, and an increase in the organic matter deposition at the seafloor. This seeming contradiction of increased organic matter deposition and decreased net primary production challenges our view of possible changes in surface biological processes during the LGM. We attribute the origin of a reduced net primary production to the interplay of increased stability of the upper water column, changed zonal water transport at intermediate depths, and lower water temperatures, which slow down all biological processes during the LGM. Cold water temperatures also affect the remineralisation rates of organic material, which explains the simulated increase in the organic matter deposition, which is in good agreement with sediment proxy records. In addition, we discuss changes in an artificial tracer which captures the surface ocean temperature signal during organic matter production. A shifted seasonality of the biological production in the LGM leads to a difference in the recording of the climate signal by this artificial tracer of up to 1 K. This could be of relevance for the interpretation of proxy records like, e.g., alkenones. Our study not only provides the first consistent insights into the biogeochemistry of the glacial Mediterranean Sea but will also serve as the starting point for transient simulations of the last deglaciation.

Multidimensional Evaluation of Altimetry Marine Gravity Models with Shipborne Gravity Data from a New Platform Marine Gravimeter

With the development of satellite altimetry technology and the application of new altimetry satellites, the accuracy and resolution of altimeter-derived gravity field models have improved over the last decades. Nowadays, they are close enough to shipborne gravimetry. In this paper, multi-source shipborne gravity data in the South China Sea were taken to evaluate the accuracies of two high-precision altimeter-derived marine gravity field models (SS V30.1, DTU17). In these shipborne gravity data, there are dozens of routes’ ship gravimetry data, obtained from the National Geophysical Data Center (NGDC); data were tracked from a marine survey with a commercial marine gravimeter (type KSS31M), and data were tracked from a marine gravimetry campaign that was conducted with a newly developed platform gravimeter (type JMG) in the South China Sea in September 2020. After various data filtering, processing, and calibrations, the shipborne gravity data were validated with crossover points analysis. Then, the processed shipborne data were employed to evaluate the accuracy of the altimeter-derived marine gravity field models. During this procedure, the quality of JMG shipborne gravity data was compared with the results of KSS31M and NGDC data. Analysis and evaluation results show that the crossover points verification accuracies of KSS31M and JMG are 0.70 mGal and 1.61 mGal, which are much better than the accuracy of NGDC, which is larger than 8.0 mGal. In the area where the bathymetry changes slowly, the root mean square error values between altimetry gravity models and KSS31M data are respectively 3.28 mGal and 4.54 mGal, and those of the JMG data are respectively 2.94 mGal and 2.60 mGal. According to the above results, we can conclude that the JMG has the same 1–2 mGal accuracy level as KSS31M and can meet the measurement requirements of marine gravity.

Evaluation of ecosystem services vis-à-vis perceptions and attitudes of local communities towards Wetland conservation in Kashmir Himalaya

Valuation of ecosystem services along with the perceptions and attitudes of local communities is crucial for sustainable management of wetlands. This study assesses changes in wetland area and bathymetry, and provides insights into local community's perceptions of ecosystem services, and attitudes towards wetland conservation in Kashmir Himalaya, India. High-resolution satellite data was used to assess land use land cover (LULC) changes within the wetland. The bathymetry changes were assessed by performing depth measurements before and after dredging in 2019 and 2022, respectively. Perceptions of ecosystem services and attitudes of residents towards wetland management were examined through surveys in 182 households from the target population of 334 families. The findings reveal that Khushalsar wetland provides important provisioning (food, fodder, thatching mats, fish, vegetables), regulating (flood control, carbon sequestration, water quality improvement), supporting (habitat, biomass and oxygen production, water and nutrient cycling), and cultural services (aesthetic, education, spiritual). The economic benefits from provisioning services range from 240 USD/yr for minor vegetables to 1201–1802 USD/0.05 ha/yr for Nelumbo nucifera. The analysis of LULC changes indicates a ∼16.5% reduction in wetland area from 1980 to 2017, with a further ∼10% decrease from 2017 to 2021, resulting in an overall loss of ∼25% (27.1 ha) in wetland area from 1980 to 2021. Bathymetric assessments reveal an increase in maximum depth from 427 cm in 2019 to 547 cm in 2022 following dredging activities. Socioeconomic analysis showed the significance of Khushalsar wetland as an important source of livelihood for local communities. Survey results indicate that all the respondents have positive attitudes towards the protection and management of the Khushalsar wetland. The study demonstrates that human conservation activities have significantly contributed to positive changes in the wetland such as increase in depth and flood storage capacity. The study concludes that government protection along with active participation of local communities is indispensable for sustainable management of wetlands.

Submesoscale features of coastal upwellings in the Black Sea: Observations and modeling

Coastal upwellings significantly affect the thermohaline structure, gas exchange and the fluxes of nutrients in the upper layers. They are often characterized by complex spatial structure, which is related to impact of different factors – changes of bathymetry, impact of background currents, baroclinic instability and others. In this study, we use high-resolution NEMO numerical model-ling and satellite data to study in details several physical causes of the observed submesoscale features of the Black Sea coastal upwellings: . 1) the influence of capes on the separation of coastal upwelling from the coast and its further transformation into submesoscale eddies; 2) the influence of mesoscale eddies on the structure of coastal upwellings; 3) the role of river plumes and haline fronts in the transport of upwellings. Comparison of model and satellite data shows that the numerical calculations reasonably well reproduce the onset time, intensity and areas of upwellings. Further, we show that the discussed processes can significantly affect the intensity, evolution and propagation of coastal upwellings in the Black sea.

Potential Sunda Strait tsunami hazard due to the current deformation of Anak Krakatau

Abstract The tsunami Sunda Strait event at 2018 is a prove that volcanic activity may trigger a devastating and unpredictable tsunami. Several findings indicate that this catasrophe generated by flank collapse caused by the instability of Gunung Anak Krakatau (AK). Other processes of volcanic activity that cause tsunamis include pyroclastic flows, subaerial and submarine landslides, underwater explosions, blasts, and caldera collapse. In the 1883, Krakatau Mount produced the largest tsunami event, and it is apparent that AK is one of threats in Sunda Strait that may potentially produce tsunami in the future since it is still active until now. Some latest research shows there are two submarine landslide threats near Gunung Anak Krakatau; in the northeast part of AK and an elliptical landslide source in the west part of AK with the estimated landslide volume about 0.014 km3 and 0.6 km3, respectively. Those threats will be simulated by shallow water equation model to obtain the tsunami wave height near the source and at crucial areas along Sunda Strait as well as its tsunami time arrival. The first scenario is sourced from a new deposit from the 2018 eruption, and the latter is a change of slopes bathymetry due to volcanic or seismic activity. It is observed that the highest elevation of tsunami from the first scenario reached only 2.5 cm at Tanjung Lesung, Banten and 80 cm at the nearest island, Panjang Island. The second scenario has the height of 50 cm at Labuan, Banten and 70 cm at Panjang Island. The tsunami time travel at the surrounding islands is ranging between 0.6 - 5.8 minutes (scenario 1) and 0.7-4.9 minutes (scenario 2). Both scenario reached the inexpensive device of sea level monitoring at the east side of Rakata after 5 minutes and the height is 30 cm and 1.6 cm respectively for scenario 1 and 2.

The effects of bathymetry on the long-term carbon cycle and CCD

The shape of the ocean floor (bathymetry) and the overlaying sediments provide the largest carbon sink throughout Earth's history, supporting ~one to two orders of magnitude more carbon storage than the oceans and atmosphere combined. While accumulation and erosion of these sediments are bathymetry dependent (e.g., due to pressure, temperature, salinity, ion concentration, and available productivity), no systemic study has quantified how global and basin scale bathymetry, controlled by the evolution of tectonics and mantle convection, affects the long-term carbon cycle. We reconstruct bathymetry spanning the last 80 Myr to describe steady-state changes in ocean chemistry within the Earth system model LOSCAR. We find that both bathymetry reconstructions and representative synthetic tests show that ocean alkalinity, calcite saturation state, and the carbonate compensation depth (CCD) are strongly dependent on changes in shallow bathymetry (ocean floor ≤600 m) and on the distribution of the deep marine regions (>1,000 m). Limiting Cenozoic evolution to bathymetry alone leads to predicted CCD variations spanning 500 m, 33 to 50% of the total observed variations in the paleoproxy records. Our results suggest that neglecting bathymetric changes leads to significant misattribution to uncertain carbon cycle parameters (e.g., atmospheric CO2 and water column temperature) and processes (e.g., biological pump efficiency and silicate-carbonate riverine flux). To illustrate this point, we use our updated bathymetry for an Early Paleogene C cycle case study. We obtain carbonate riverine flux estimates that suggest a reversal of the weathering trend with respect to present-day, contrasting with previous studies, but consistent with proxy records and tectonic reconstructions.

Deep sediment characterization from very low-frequency features from merchant ships

The very low-frequency noise from merchant ships provides a good wideband source to study the deep layers of the seabed. The nested striations which characterize ship spectrograms contain unique acoustic features where the waveguide invariant (β) becomes infinite. This occurs at frequencies between 20 and 80 Hz where pairs of modal group velocities are equal. The goal of this project was to identify the β = ∞ frequencies in ship noise spectrograms and use these frequencies to perform statistical inference for the deep layer sound speeds and thicknesses. The Seabed Characterization Experiment of 2022 on the New England continental shelf had three vertical line arrays strategically placed between two shipping lanes. The average water depth was 75 meters with less than one meter bathymetry change between the arrays. The results of this study are based primarily on five ships. There was a gradual shift in the β = ∞ frequencies between the three arrays, suggesting a gradual change in the deep sediment layers. [Work supported by Office of Naval Research.]

Effect of wave motion on the scouring caused by a marine propeller jet: An experimental and numerical study

Bathymetry changes induced by marine propeller jets on movable beds are a crucial issue in harbors, especially in the maneuvering zone. The knowledge of the scour hole and deposition mound dimensions, due to propeller jets, is important in the context of sediment management.Although the presence of waves is well known in harbor environments, propeller jet scours are usually investigated under still water conditions neglecting the effect of wave interaction. Moreover, the interaction between waves and propeller jets can also occur in mooring out of harbors. For these cases, the interaction of wave induced hydrodynamics and propeller jets is a crucial issue that is still an open and challenging problem. This paper aims to address, for the first time, the knowledge gap by investigating the influence of waves on propeller jets in unconfined conditions, which in turn can lead to alterations in scour and deposition patterns. The study relies on a specific experimental investigation. The selection of the parameters of the experimental tests is based on the results of prior analyses aimed to investigate the propeller jets induced scour and deposition in still water conditions and in the presence of a current. Hence, regular waves with different parameters (i.e. wave height and wave period) have been then reproduced in a wave flume where a propeller jet has been installed. The experimental tests aimed to get insight on the scour profiles as well as scour hole bathymetry induced by propeller jets under the influence of regular wave propagation. Numerical simulations have been also performed to investigate the effects of the wave-induced velocity acting on the propeller jets hydrodynamics. Spectral analysis has been then applied to characterize the complex scoured form and bedforms on the bathymetry configuration induced by the tested propeller jet and waves.

Late Pleistocene Evolution of Tides and Tidal Dissipation

AbstractStudies of the Last Glacial Maximum (LGM; 26.5–19 ka) tides showed strong enhancements in open ocean tidal amplitudes and dissipation rates; however, changes prior to the LGM remain largely unexplored. Using two different ice sheet and sea level reconstructions, we explicitly simulate the evolution of the leading semi‐diurnal and diurnal tidal constituents (M2, S2, K1, and O1) over the last glacial cycle with a global tide model. Both sets of simulations show that global changes, dominated by the Atlantic, take place for the semi‐diurnal constituents, while changes for the diurnal constituents are mainly regional. Irrespective of the reconstruction, open ocean dissipation peaks during the sea level lowstands of MIS 2 (∼20 ka) and MIS 4 (∼60 ka), although dissipation values prior to MIS 2 are sensitive to differences in reconstructed ice sheet extent. Using the statistically significant relationship between global mean sea level and dissipation, we apply regression analysis to infer open ocean and shelf dissipation, respectively, over the last four glacial cycles back to 430 ka. Our analysis shows that open ocean tidal energy was probably increased for most of this period, peaking during glacial maxima, and returning to near‐present‐day values during interglacials. Due to tidal resonance during glacial phases, small changes in bathymetry could have caused large changes in tidal amplitudes and dissipation, emphasizing the need for accurate ice margin reconstructions. During glacial phases, once global mean sea level decreased by more than ∼100 m, the amount of open ocean tidal energy available for ocean mixing approximately doubled.

Monitoring of Bathymetry Changes in the Coastal Area of Dokdo, East Sea

Monitoring of Bathymetry Changes in the Coastal Area of Dokdo, East Sea

The Impact of Coastline and Bathymetry Changes on the Storm Tides in Zhejiang Coasts

Coastal evolutions are expected to have a significant impact on storm tides, disproportionately aggravating coastal flooding. In this study, we utilize a nested storm tide model to provide an integrated investigation of storm tide responses to changes in coastline and bathymetry along the Zhejiang coasts. We selected coastline and bathymetry data from 1980 and 2016, as well as data from three typical typhoon events (i.e., Winnie, Haikui, and Chan-hom) for simulating the storm surge processes. The results indicate that changes in the coastline and bathymetry from 1980 to 2016 have resulted in an increase in storm tides in the northern part and a decrease in the central part of Zhejiang. Specifically, storm tides in Hangzhou Bay have increased significantly, with an average increase of about 0.3 m in the maximum storm tides primarily attributed to coastline changes. On the contrary, in smaller basins like Sanmen Bay, while reclamation itself has reduced peak storm surges, rapid siltation has consequently exacerbated the storm surge. By decomposing storm tides into astronomical tides and storm surges, we discovered that the change in tidal levels was twice as significant as the surge change. Moreover, the nonlinear tide–surge interaction was nearly four times that of the pure surge, significantly contributing to storm surge variation. Alterations in the momentum balance reveal that the water depth-induced bottom friction and wind stress increase contributes to the local enlargement of storm tides at the bay head, while the coastline changes exaggerate nearshore storm tides through an increase in the advection term.

Mapping the Unresolved Tidal Resource in Estuaries

Estuaries are ideal locations for extracting tidal energy and yet the global resource appears poorly mapped. Estuaries typically have high tidal ranges and strong tidal currents, due to amplification processes; and this resource is juxtaposed to industrial/residential areas with electricity demand [1]. For example, 22 of the 32 largest cities in the world are adjacent to estuaries [2], and UK estuaries collectively worth over £5.5b to UK economy with >1/6th of the population and ~1b tonnes of cargo traded at their ports [3]. 
 Mapping the tidal energy resource is challenging due to the sensitivity of ocean-model simulated currents to the model resolution [4]. Both tidal amplitude and currents are heavily modified in estuaries [5]. Whilst many estuary-specific resource modelling studies have been achieved (e.g. [6]), no large-scale future tidal energy resource mapping project has been undertaken – likely due to computational cost (e.g. [4]). It is therefore unrealistic to hydrodynamically model all global estuarine systems, to resolve current and future changes to the tidal energy resource; instead we aim to apply a simplified analytical technique that could be calibrated and validated by the new NASA SWOT satellite mission (https://swot.jpl.nasa.gov/), as well as citizen science. Estuarine tidal dynamics have been observed to change rapidly due to changes in river-flow climatology and bathymetry (e,g. dredging); see [7]. Indeed, climate change driven impacts to tidal dynamics (sea-level rise and altered riverine climatology), alongside anthropogenic driven morphodynamical changes and interactions with future tidal dynamics, could increase the future estuary tidal resource [1].
 Three physical processes drive mean tidal amplification excluding over-tides): (1) Funnelling - concentration of the tidal energy flux with reducing width; (2) Resonance - when estuary length-scales are close to the natural period of the basin; and (3) Shoaling (reduction in the propagation speed of the tidal wave resulting in an increase in amplitude). Each of these three processes are analytical solved, and a 1D analytical model applied to demonstrate the resource. Sea-Level Rise (SLR) scenarios are included to show SLR can modify estuarine tidal dynamics through both estuarine geometry (e.g. increasing resonance) and boundary conditions (global mean sea-level rise increasing boundary conditions). A normalised result of the analytical approach is shown in Figure 1, which demonstrates a computationally efficient analytical solution that includes future changes to tidal dynamics. 
 Our research will apply this analytical solution to the Bristol Channel, a region soon-to-be heavily instrumented as part of the “Cal-Val phase of the NASA SWOT project (https://projects.noc.ac.uk/swot-uk/swot-uk-bristol-channel). Finally, we will develop a technique to bring together digital observations from citizens and sensor networks (see https://digitalenvironment.org/), to validate our simplified approach and resolve the tidal energy resource.

Impacts of a Cascadia Subduction Zone Earthquake on Water Levels and Wetlands of the Lower Columbia River and Estuary

AbstractSubsidence after a subduction zone earthquake can cause major changes in estuarine bathymetry. Here, we quantify the impacts of earthquake‐induced subsidence on hydrodynamics and habitat distributions in a major system, the lower Columbia River Estuary, using a hydrodynamic and habitat model. Model results indicate that coseismic subsidence increases tidal range, with the smallest changes at the coast and a maximum increase of ∼10% in a region of topographic convergence. All modeled scenarios reduce intertidal habitat by 24%–25% and shifts ∼93% of estuarine wetlands to lower‐elevation habitat bands. Incorporating dynamic effects of tidal change from subsidence yields higher estimates of remaining habitat by multiples of 0–3.7, dependent on the habitat type. The persistent tidal change and chronic habitat disturbance after an earthquake poses strong challenges for estuarine management and wetland restoration planning, particularly when coupled with future sea‐level rise effects.

Deglacial climate changes as forced by different ice sheet reconstructions

Abstract. During the last deglaciation, the climate evolves from a cold state at the Last Glacial Maximum (LGM) at 21 ka (thousand years ago) with large ice sheets to the warm Holocene at ∼9 ka with reduced ice sheets. The deglacial ice sheet melt can impact the climate through multiple ways: changes of topography and albedo, bathymetry and coastlines, and freshwater fluxes (FWFs). In the PMIP4 (Paleoclimate Modelling Intercomparison Project – Phase 4) protocol for deglacial simulations, these changes can be accounted for or not depending on the modelling group choices. In addition, two ice sheet reconstructions are available (ICE-6G_C and GLAC-1D). In this study, we evaluate all these effects related to ice sheet changes on the climate using the iLOVECLIM model of intermediate complexity. We show that the two reconstructions yield the same warming to a first order but with a different amplitude (global mean temperature of 3.9 ∘C with ICE-6G_C and 3.8 ∘C with GLAC-1D) and evolution. We obtain a stalling of temperature rise during the Antarctic Cold Reversal (ACR, from ∼14 to ∼12 ka) similar to proxy data only with the GLAC-1D ice sheet reconstruction. Accounting for changes in bathymetry in the simulations results in a cooling due to a larger sea ice extent and higher surface albedo. Finally, freshwater fluxes result in Atlantic meridional overturning circulation (AMOC) drawdown, but the timing in the simulations disagrees with proxy data of ocean circulation changes. This questions the causal link between reconstructed freshwater fluxes from ice sheet melt and recorded AMOC weakening.

Evolution of Global Ocean Tide Levels Since the Last Glacial Maximum

AbstractThis study addresses the evolution of global tidal dynamics since the Last Glacial Maximum focusing on the extraction of tidal levels that are vital for the interpretation of geologic sea‐level markers. For this purpose, we employ a truly‐global barotropic ocean tide model which considers the non‐local effect of Self‐Attraction and Loading. A comparison to a global tide gauge data set for modern conditions yields agreement levels of 65%–70%. As the chosen model is data‐unconstrained, and the considered dissipation mechanisms are well understood, it does not have to be re‐tuned for altered paleoceanographic conditions. In agreement with prior studies, we find that changes in bathymetry during glaciation and deglaciation do exert critical control over the modeling results with minor impact by ocean stratification and sea ice friction. Simulations of 4 major partial tides are repeated in time steps of 0.5–1 ka and augmented by 4 additional partial tides estimated via linear admittance. These are then used to derive time series from which the tidal levels are determined and provided as a global data set conforming to the HOLSEA format. The modeling results indicate a strengthened tidal resonance by M2, but also by O1, under glacial conditions, in accordance with prior studies. Especially, a number of prominent changes in local resonance conditions are identified, that impact the tidal levels up to several meters difference. Among other regions, resonant features are predicted for the North Atlantic, the South China Sea, and the Arctic Ocean.

Study on effects of complex bathymetry on the deep acoustic field in Western Pacific Ocean

Seafloor bathymetry has an important effect on acoustic propagation. In a deep water experiment in the Western Pacific in 2020, acoustic field in the reliable acoustic path (RAP) zone, the shadow zone, and the refracted zones were measured with shallow sources and deep receivers. Two important phenomena were observed. First, in the first shadow zone, the signal level (S) changing with source range presents a “W” shape: it sharply decreases by 19 dB after the source just pass the RAP boundary and then increases by 11 dB immediately, which produces the first S trough; after remaining stable for a range interval of 29 km, it drops again by 12 dB and then soars by 16 dB, which produces the second S trough. Secondly, the range spans of refracted zones that expected to be 29 km narrows down to only 13 km. Based on the precisely measured bathymetry and the range-dependent acoustic model-parabolic equation (RAM-PE), the S distribution were reproduced and its characteristics were explained. It was found that rather than the large-scale bathymetry change (e.g, large seamount or break shelf), it is the local bathymetry change that have significant effects on the S distribution.

Fully nonlinear phase-resolved wave modelling in the Norwegian fjords for floating bridges along the E39 coastal highway

Coastal wave conditions are highly influenced by bathymetry variations and coastlines. The Norwegian fjords present large gradients of bathymetry changes and irregular coastline geometries that make the understanding of the near-coast wave conditions a challenging task. The proposed floating bridges for permanent fjord-crossings along the Norwegian E39 coastal highway require reliable and efficient numerical simulations of a large domain at the fjords. In this manuscript, a phase-resolving fully non-linear potential flow (FNPF) model is used to investigate wave propagations with the presence of complex bathymetry and coastlines at two fjords along the path of the highway. The FNPF model is equipped with a robust coastline algorithm, flexible wave breaking algorithms, a free-surface and bathymetry-following sigma -grid and parallel high-performance computation capability. Both long-crested and short-crested offshore swell wave conditions are simulated at the two fjords, Sulafjord and Bjørnafjord. Sulafjord is more exposed to the offshore swell while Bjørnafjord is more sheltered. The phase-averaging spectral wave models are also applied for both fjords and compared with the phase-resolving FNPF model. The significance of applying phase-resolving model for strongly nonlinear wave transformations in the fjords is demonstrated. The wave transformations and the wave field inhomogeneity and incoherence are captured using the phase-resolving time domain simulation results, which reveal significant engineering considerations for floating bridge design. The presented numerical approach is seen to be able to simulate the complex transformations of irregular waves and identify key wave field characteristics with the presence of irregular bathymetry and coastlines such as the Norwegian fjords.

Biogeographic provinces and genomically delineated stocks are congruent in snapper (Chrysophrys auratus) from southeastern Australia

AbstractMarine species often exhibit genetic discontinuities concordant with biogeographic boundaries, frequently occurring due to changes in ocean circulation, bathymetry, coastline topography, and temperature. Here, we used 10 916 single nucleotide polymorphisms (SNPs) to assess the concordance between population genomic differentiation and coastal biogeography in the fishery-important snapper (Chrysophrys auratus) across southeastern Australia. Additionally, we investigated whether spatial scales of assessment and management of snapper align with evidence from population genomics. We detected genomic structure concordant with the region's three biogeographic provinces across snapper from 11 localities (n = 488) between the west coast of South Australia and the south coast of New South Wales. We also detected fine-scale genetic structuring relating to spatial variation in spawning and recruitment dynamics, as well as temporal stability in the genomic signal associated with two important spawning areas. The current management boundaries in the region coincided with either the genetic breaks at bioregional boundaries or with local-scale variation. Our study highlights the value of population genomic surveys in species with high dispersal potential for uncovering stock boundaries and demographic variation related to spawning and recruitment. It also illustrates the importance of marine biogeography in shaping population structure in commercial species with high dispersal potential.

Estimating Earthquake-Induced Tsunami Height Probabilities without Sampling

Given a distribution of earthquake-induced seafloor elevations, we present a method to compute the probability of the resulting tsunamis reaching a certain size on shore. Instead of sampling, the proposed method relies on optimization to compute the most likely fault slips that result in a seafloor deformation inducing a large tsunami wave. We model tsunamis induced by bathymetry change using the shallow water equations on an idealized slice through the sea. The earthquake slip model is based on a sum of multivariate log-normal distributions, and follows the Gutenberg-Richter law for seismic moment magnitudes ranging from 7 to 9. For a model problem inspired by the Tohoku-Oki 2011 earthquake and tsunami, we quantify annual probabilities of differently sized tsunami waves. Our method also identifies the most effective tsunami mechanisms. These mechanisms have smoothly varying fault slip patches that lead to an expansive but moderately large bathymetry change. The resulting tsunami waves are compressed as they approach shore and reach close-to-vertical leading wave edge close to shore.