Bathymetry Datasets Research Articles

Effect of bathymetry data on tsunami wave ray tracing in the western Banten sea

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

Nearshore tsunami amplitudes across the Maldives archipelago due to worst-case seismic scenarios in the Indian Ocean

Abstract. The Maldives face the threat of tsunamis from a multitude of sources. However, the limited availability of critical data, such as bathymetry (a recurrent problem for many island nations), has meant that the impact of these threats has not been studied at an island scale. Conducting studies of tsunami propagation at the island scale but across multiple atolls is also a challenging task due to the large domain and high resolution required for modelling. Here we use a high-resolution bathymetry dataset of the Maldives archipelago, as well as corresponding high numerical model resolution, to carry out a scenario-based tsunami hazard assessment for the entire Maldives archipelago to investigate the potential impact of plausible far-field tsunamis across the Indian Ocean at the nearshore island scales across the atolls. The results indicate that the bathymetry of the atolls, which are characterized by very steep boundaries offshore, is extremely efficient in absorbing and redirecting incoming tsunami waves. Results also highlight the importance that local effects have in modulating tsunami amplitude nearshore, including the location of the atoll in question, the location of a given island within the atoll, and the distance of that island to the reef, as well as a variety of other factors. We also find that the refraction and diffraction of tsunami waves within individual atolls contribute to the maximum tsunami amplitude patterns observed across the islands in the atolls. The findings from this study contribute to a better understanding of tsunamis across complex atoll systems and will help decision and policy makers in the Maldives assess the potential impact of tsunamis across individual islands. An online tool is provided which presents users with a simple interface, allowing the wider community to browse the simulation results presented here and assess the potential impact of tsunamis at the local scale.

Detailed Bathymetry and Seafloor Backscatter Image Dataset for Monitoring Ecosystem Environment: Southern Ulleungdo

We obtained a detailed bathymetry dataset using multi-beam echo sounder around Neunggeol located at Southern part in Ulleungdo. The survey period was from September 1, 2019 and the bathymetry survey was carried out by RV Jangmok No2 of Korea Institute of Ocean Science and Technology. The instrument equipment used for the survey were Kongsbergs’s EM2040 (multi-beam echo sounder). The detailed bathymetry of the study area shows gradually depth change from about 4 to 190 m. The study area has relatively gentle slopes from the coast to 25 m and below about 125 m in depth, but a steep slope from about 25 to 125 m. The rocky bottom zones identified from detailed bathymetry and backscattered seafloor images are distributed in the northeastern sea of the coastal area, the central sea, and around Neunggeol. In particular, Neunggeol and the near large outcropping rock are tumulus-like submarine landforms, forming big vertical walls. The submarine cable buried between Ulleungdo and the Korean mainland appears in the northern seafloor of the survey area. Stopper stones and gravels sediment are distributed around it. The rocky bottom zone has a strong and irregular reflection intensity in the seafloor backscattered image and the sandy sediment zone has a relatively weak reflection intensity and a uniform pattern, so the two zones are well divided. We classified the sediment zones into fine-grained sediments, sandy sediments, and gravel-like sediments by using the different reflection intensities due to differences in sediment particle size in the seafloor image. Detailed bathymetry and seafloor backscattered image dataset around Neunggeol can be used as a basic data for habitat environment mapping.

Observing the full ocean volume using Deep Argo floats

The ocean is the main heat reservoir in Earth’s climate system, absorbing most of the top-of-the-atmosphere excess radiation. As the climate warms, anomalously warm and fresh ocean waters in the densest layers formed near Antarctica spread northward through the abyssal ocean, while successions of warming and cooling events are seen in the deep-ocean layers formed near Greenland. The abyssal warming and freshening expands the ocean volume and raises sea level. While temperature and salinity characteristics and large-scale circulation of upper 2000 m ocean waters are well monitored, the present ocean observing network is limited by sparse sampling of the deep ocean below 2000 m. Recently developed autonomous robotic platforms, Deep Argo floats, collect profiles from the surface to the seafloor. These instruments supplement satellite, Core Argo float, and ship-based observations to measure heat and freshwater content in the full ocean volume and close the sea level budget. Here, the value of Deep Argo and planned strategy to implement the global array are described. Additional objectives of Deep Argo may include dissolved oxygen measurements, and testing of ocean mixing and optical scattering sensors. The development of an emerging ocean bathymetry dataset using Deep Argo measurements is also described.

EVALUATION OF A GNSS/IMU/LIDAR-INTEGRATION FOR AIRBORNE LASER SCANNING USING RTKLIB PPK AND PPP GNSS SOLUTIONS

Abstract. Airborne laser scanning allows for efficient acquisition of accurate 3D data for large areas. Because georeferencing of the LiDAR data requires knowledge of the platform trajectory, the laser scanner system commonly comprises a global navigation satellite system (GNSS) receiver/antenna and an inertial measurement unit (IMU). The standard processing pipeline consists of GNSS/IMU integration, georeferencing, and subsequent adjustment of the laser data. Here, we consider a holistic GNSS/IMU/LiDAR-integration approach based on least-squares adjustment. The GNSS is loosely coupled, and the GNSS positions are obtained using either postprocessing kinematic or precise point positioning GNSS processing strategies using the open-source software RTKLib. In this contribution, we compare the resulting point clouds to those of a standard processing workflow and evaluate the impact of the different processing strategies on point cloud quality in terms of internal consistency and absolute accuracy for a airborne laser bathymetry (ALB) dataset. Although the GNSS solutions themselves differ strongly, both the PPK- and the PPP-derived point clouds show better strip differences (below 2.5 cm) and similar absolute accuracy (<4 cm RMSE w.r.t. reference targets after correction of constant datum shift) compared to the reference solution.

Gateway to the arctic: Defining the eastern channel of the Bering Strait

The Bering Strait is the sole gateway and an oceanographic bottleneck for the seasonally warm and comparatively fresh and nutrient-rich Pacific waters to flow into the Arctic, melting ice, lowering salinity, and feeding bird, mammal, and fish populations. The Diomede Islands split this small strait into two main channels, both with northward flow (in the annual mean). The eastern channel, in U.S. waters, also seasonally carries the warmer, fresher Alaskan Coastal Current. Year-round in situ mooring observations (in place since 1990 with annual servicing) show a significant flow increase in the (northward) throughflow, along with seasonal and annual fluctuations. To help with measuring and modelling water flow estimates, we created the first detailed shore-to-shore bathymetric surface of the Bering Strait’s eastern channel, located its narrowest cross-section (1.8 km2) as occurring 5–10 km south of the moorings, and quantified the cross-section across the moorings (2.0 km2), both slightly larger than previously estimated (1.6 km2). Overlaps between older (∼1950) and newer (∼2010) bathymetry data sets identified clear areas of erosion and deposition, with much of the eastern channel having eroded by > 1 m. Since the depth is uniformly ∼ 50 m across much of the eastern channel, the 1 m of erosion that we quantified would only slightly (2 %) increase the sizes of the cross-sections. Much of the seafloor is hard substrate and probably composed of cobbles, but we hypothesize that friction from strong (∼1 + knot) seafloor currents is the most likely explanation for the erosion that we observed. In softer and siltier areas, the bathymetry showed additional evidence of potential current impacts in the form of small seafloor waves (∼0.5 to ∼ 1.0 m tall) and a shore-parallel bar offshore of Cape Prince of Wales Spit. There are large (∼2 m tall) seafloor waves seaward of Cape Prince of Wales Shoal. A previously undescribed (∼1 to 2 km wide, ∼4 m deep) seafloor channel of unknown origin occurred along a linear north/south axis for the full 75 km extent of the bathymetric surface. The southern end of this seafloor channel was near the end of three larger seafloor channels extending westerly out of nearby Norton Sound, suggesting a common origin. These Norton Sound channels may be paleodrainages, as their eastern ends point toward Seward Peninsula inlets with large drainages where paleoglaciers were reported to have existed, but the morphology of these channels is also consistent with tidal channels.

Bathymetry Refinement over Seamount Regions from SAR Altimetric Gravity Data through a Kalman Fusion Method

Seafloor topography over seamount areas is crucial for studying plate motions, seafloor seismicity, and seamount ecosystems. However, seamount bathymetry modeling is difficult due to the complex hydrodynamic environment, biodiversity, and scarcity of shipborne echo sounding data. The use of satellite altimeter-derived gravity data is a complementary way of bathymetry computation; in particular, the incorporation of synthetic aperture radar (SAR) altimeter data may be useful for seamount bathymetry modeling. Moreover, the widely used filtering method may have difficulty in combing different bathymetry data sets and may affect the quality of the computed bathymetry. To mitigate this issue, we introduce a Kalman fusion method for weighting and combining gravity-derived bathymetry data and the reference bathymetry model. Numerical experiments in the seamount regions over the Molloy Ridge show that the use of SAR-based altimetric gravity data improves the local bathymetry model, by a magnitude of 14.27 m, compared to the result without SAR data. In addition, the developed Kalman fusion method outperforms the traditionally used filtering method, and the bathymetry computed from the Kalman fusion method is improved by a magnitude of 9.34 m. Further comparison shows that our solution has improved quality compared to a recently released global bathymetry model, namely, GEBCO 2022 (GEBCO: General Bathymetric Chart of the Oceans), by a magnitude of 34.34 m. The bathymetry model in this study may be substituted for existing global bathymetry models for geophysical investigations over the target area.

From basalt to biosphere: Early non-vent community succession on the erupting Vailulu’u deep seamount

Volcanic eruptions provide rare opportunities to witness the biological recolonization of areas covered by new lava flows by effectively resetting the ecological succession clock to zero. The role of submarine volcanic eruptions as disturbance events and the resulting patterns of ecological succession have mainly been studied in hydrothermal vent ecosystems. However, the effects of submarine volcanic eruptions as disturbance forces have rarely been studied in non-vent ecosystems, particularly on seamounts. Here, we document the early stages of ecological succession of non-vent benthic communities inhabiting the summit caldera of the active Vailulu’u submarine volcano in American Samoa. Sitting above the Samoan volcanic hotspot, Vailulu’u is the youngest volcano of the Samoan chain. Repeated mapping of Vailulu’u in 1999, 2005, 2006, 2012, and 2017 revealed the progressive growth of a new cone named Nafanua. In 18 years, the cone grew >300 meters in height from a starting depth of ~1000 meters below sea level (mbsl). The differential analyses of this time-series bathymetry dataset enabled the assignment of maximum age ranges to different portions of the new cone. High-definition ROV imagery collected in 2017 revealed patterns of community structuring consistent with ecological succession: newly erupted seafloor contained a subset of the benthic species found on older seafloor. Furthermore, individual animal sizes in the younger seafloor zones were smaller than in the older zones. This unusual interdisciplinary combination of geological and biological observations provides constraints on which deep-sea animals recolonize new seafloor after a major disturbance event and how quickly. This knowledge could be applied to identify signs and states of recovery from anthropogenic disturbances by a deep seamount ecosystem.

Channel Bed Adjustment of the Lowermost Yangtze River Estuary from 1983 to 2018: Causes and Implications

Deltaic channels are significant landforms at the interface of sediment transfer from land to oceanic realms. Understanding the dynamics of these channels is urgent because delta processes are sensitive to climate change and adjustments in human activity. To obtain a better understanding of the morphological processes of large deltaic channels, this study assessed the evolution and response mechanism of the South Channel and South Passage (SCSP) in the Yangtze Estuary between 1983 to 2018 using hydrology, multibeam echo sounding and historical bathymetry datasets. Decadal changes in riverbed volume and erosion/deposition patterns in the SCSP were assessed. The results showed that the SCSP experienced substantial deposition with a total volume of 26.90 × 107 m3 during 1983–2002, but significant bed erosion with a total volume of 26.04 ×107 m3 during 2003–2010. From 2011 to 2018, the estuarine riverbeds shifted from erosive to depositional, even though the deposition was relatively marginal (0.76 ×107 m3). We inferred that the SCSP have most likely changed from a net erosion phase to a deposition stage in response to local human activities including sand mining, river regulation project, and Deep Water Channel Regulation Project). The channel aggradation will possibly continue considering sea level rise and the ongoing anthropogenic impacts. This is the first field evidence reporting that the lowermost Yangtze River is reaching an equilibrium state in terms of channel erosion and, in fact, the Yangtze River Estuary channels are beginning to aggrade. The findings have relevant implications for the management of the Yangtze River and other lowland alluvial rivers in the world as global sea level continues rising and human intervention on estuarine systems persists.

Development and Dynamics of Sediment Waves in a Complex Morphological and Tidal Dominant System: Southern Irish Sea

With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamically and morphodynamically complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer–Blackwater Bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, which also exerts a strong influence on the adjacent banner bank. Furthermore, a new sediment transfer system is defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. These new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas, which has direct implications for offshore renewable developments and long-term marine spatial planning.

Energy balance and momentum budgets due to the internal tides generated by a group of submarine canyons

A field multibeam survey discovered a group of regularly-spaced submarine canyons on the continental shelf in the northern South China Sea. However, they are not included in the bathymetry datasets commonly used by the oceanographic community. In this study, we employ a very-high-resolution (as fine as 54 m) numerical model that resolves these submarine canyons to investigate their impacts on the local internal tide generation and propagation. Results show that the barotropic to internal tidal conversion rate exhibits an alternating distribution on each flank of submarine canyons. Rotational direction of the tidal flow determines a positive conversion rate on the west flank and a negative rate on the east flank. The rough seafloor due to the submarine canyons does not appreciably change the dissipation of barotropic tides, but significantly affects the dissipation of internal tides, leading to an averaged dissipation rate of 1.2 × 10−9 W kg −1. Internal tides also induce a bottom intensified mean flow, which causes westward mean transport on the continental slope and a clockwise circulation inside each submarine canyon. The mean flow satisfies a momentum budget between the Coriolis force, pressure gradient and divergence of momentum flux of barotropic and internal tides. We highlight that the divergence of the pseudo-momentum flux of internal tides acts as a stress and is especially reinforced near the sea bottom and surface. Its effect on the sea surface is even comparable with moderate winds (∼13 m s−1).

Seafloor habitats across geological boundaries in Disko Bay, central West Greenland

In this paper we describe seafloor terrain of nearly the entire Disko Bay region and provide scientific baseline information about surface geology and sedimentary environments that can support the seafloor management plan in Greenland. Our study utilized multiple datasets of multibeam bathymetry and backscatter, seismic profiles and ground-truthing consisting of video footage from drop camera and benthic video sled, as well as sediment samples from grab and corers. Our results revealed that the key geological units in Disko Bay characterize the scale of geomorphic features, which in turn affects the distribution and complexity of habitat zones. The NE sub-region is underlain by Cretaceous sandstone and characterized by large-scale landforms, mainly vast flat areas draped by glacial lineations, bedrock ridges and pockmark fields. This setting promotes less topographically complex habitats, i.e. coarse plain, muddy/sandy plain with dropstones, and muddy plain. The SW sub-region is characterized by Precambrian Gneiss and Paleoproterozoic metasedimentary rocks with complex system of small-scale geomorphic features, such as cross-cutting channels. This results in topographically complex habitats in the area, such as rocky bank, coarse rugged terrain, and rocky slopes. Two distinctive habitat areas, associated with potential gas seeps, i) southern pockmark field and ii) western zoanthid-sponge wall, were discovered at the geological boundary separating the two sub-regions. Our study highlights the importance of seafloor habitat mapping and analyses by providing fundamental geophysical knowledge necessary to comply with long-term sustainable use of marine resources in Greenland.

LR B-splines to approximate bathymetry datasets: An improved statistical criterion to judge the goodness of fit

• We introduce Locally Refined B-splines to approximate scattered point clouds. • The local approximation is performed iteratively when the error exceeds a certain threshold. • We investigate the choice of the refinement method with statistical criterion. • We apply our method to fit a small and a large bathymetry dataset. The task of representing remotely sensed scattered point clouds with mathematical surfaces is ubiquitous to reduce a high number of observations to a compact description with as few coefficients as possible. To reach that goal, locally refined B-splines provide a simple framework to perform surface approximation by allowing an iterative local refinement. Different setups exist (bidegree of the splines, tolerance, refinement strategies) and the choice is often made heuristically, depending on the applications and observations at hand. In this article, we introduce a statistical information criterion based on the t-distribution to judge the goodness of fit of the surface approximation for remote sensing data with outliers. We use a real bathymetry dataset and illustrate how concepts from model selection can be used to select the most adequate refinement strategy of the LR B-splines.

Assessing DEM quality and minimizing registration error in repeated geomorphic surveys with multi‐temporal ground truths of invariant features: Application to a long‐term dataset of beach topography and nearshore bathymetry

AbstractRemotely sensed digital elevation models (DEMs) and uncertainty‐based geomorphic change detection have become very practical tools for geoscientists, including for coastal research. Through the analysis of DEMs of differences (DoDs) and the provision of DEM quality, it allows monitoring complex landforms and confidently relating the changes observed to environmental forcing conditions.With continuing remote sensing advances, and as some monitoring programmes are reaching several decades of repeated data collection, it is timely to consider approaches that enable the reconciliation of DEMs of variable and potentially unknown quality before their subsequent geomorphic analyses. In this paper, we present an original workflow whereby composite data formed by fusing available measurements over invariant features serve as multi‐temporal ground truths for assessing repeated DEMs. Results of the evaluation enable identification of DEMs of lower quality (bias and precision) and correction of registration error (horizontal and vertical bias), and thus offer the in‐built capacity for estimating and improving change detection levels afforded by the data.The workflow was applied to a freely accessible multi‐sensor: RTK‐GNSS, terrestrial laser‐scanning, drone photogrammetry and multibeam echo‐sounding dataset of high‐resolution topographic and nearshore bathymetric DEMs collected at the macrotidal pocket beach of Porsmilin (France) over the period 2003–2019. Our results show that consistently high DEM precision can be achieved in a long‐term multi‐sensor dataset, but registration errors may be present and can be minimized through co‐registration with the purpose‐built ground truths. Although the study focuses primarily on measuring height discrepancies, which is directly relevant for DoD analysis, we show that the methods can also be used for dealing with horizontal error when high‐resolution imagery is available. Finally, the detailed DEM evaluations presented, in application to a rare dataset documenting beach and shoreface change for nearly two decades, provide original insights on the performance of usual topo‐bathymetric surveying techniques.

Improving the accuracy of glacial lake volume estimation: A case study in the Poiqu basin, central Himalayas

• We present a new volume-scaling law specific to moraine-dammed lakes. • The new equation shows a more robust performance than other published formulas. • The total lake volume in the Poiqu basin has increased by 148% from 1974 to 2020. Lake volume is a critical parameter in the prediction of potential flood volume and peak discharge in the risk assessment of glacial lake outburst flood (GLOF). As existing volume–area scaling relationships often blur the complexity of lake geometry, we presented a new volume-scaling law specific to moraine-dammed lakes, derived from a large lake bathymetry dataset. The relationship was based on the premise that lake geometry parameters (i.e., area, volume, width/length ratio) scale predictably. We then critically evaluated the performance of the new approach and compared it with 19 existing empirical relationships by examining a database of glacial lake bathymetry obtained without repeated measurements. Overall, the new volume-scaling relationship showed a more robust performance than other published formulas. In addition, an intriguing result was that regional differences were not always controlled by the predictability of lake volumes, that is, there were no regional restrictions on the use of the new method, at least not in the Himalayas. Finally, using the new approach and high-resolution Landsat imagery, our results of sequential mapping of all lakes in the Poiqu basin indicated that the total lake volume has increased by 148% from 1974 to 2020. Compared with other formulas, the lake volume estimation approach proposed in this paper provides an approximate mean value, which provides a key input parameter for flood simulation and a new alternative for estimating lake volume.

Tectonic Influence on the Geomorphology of Submarine Canyons: Implications for Deep-Water Sedimentary Systems

A database-informed metastudy of 294 globally distributed submarine canyons has been conducted with the aim of elucidating the role of tectonic setting on submarine-canyon geomorphology. To achieve this, data from seafloor and subsurface studies derived from 136 peer-reviewed publications and from open-source worldwide bathymetry datasets have been statistically analyzed. In particular, relationships between margin type (active vs. passive) or plate-boundary type (convergent vs. transform vs. complex) have been assessed for key morphometric parameters of submarine canyons, including: streamwise length, maximum and average width and depth, canyon sinuosity, average canyon thalweg gradient, and maximum canyon sidewall steepness. In addition, possible scaling relationships between canyon morphometric parameters and characteristics of the associated terrestrial catchment, continental shelf and slope, and of the broader physiographic setting for canyons along both active and passive margins have been evaluated. The following principal findings arise: 1) overall canyon geomorphology is not markedly different across tectonic settings; 2) slope failure might be more important in passive-margin canyons compared to active ones, possibly due to seismic strengthening in the latter; 3) some aspects of canyon geomorphology scale with attributes of the source-to-sink system and environmental setting, but the strength and sign in scaling might differ between active and passive margins, suggesting that the extent to which canyon geomorphology can be predicted depends on the tectonic setting. Insights from our analysis augment and improve conceptual, experimental and numerical models of slope systems at the scale of individual canyons and source-to-sink systems, and increase our understanding of the complex role played by tectonic setting in shaping deep-water systems.

Eastern Lomonosov Ridge: Constraints for a variable ice mass thickness during former glaciations

Here we present dense acoustic and swath bathymetry data sets as well as geological age constraints that allow a new view on past glacial processes at the Siberian termination of Lomonosov Ridge in the Arctic Ocean between 81° and 84° 20′ N. Here, the seabed is marked by three sets of streamlined glacial lineations observed at present water depths of ~760 m to 1250 m. The shallower streamlined glacial lineations were likely formed during MIS 6 and the deeper ones during MIS 12. Other observations include recessional moraines and pockmarks on a flattened ridge crest. In the subsurface, an acoustically transparent unit above well stratified strata is interpreted as subglacial diamicton overlying pre-glacial sediments at an erosional contact. Furthermore, the diamicton is interpreted to have been deposited as lenses in glacially-eroded proximal settings. In contrast, some parts of the seafloor and subsurface show no glacial overprint in water depths as shallow as 819 m. To explain these findings, we propose that the Siberian termination of Lomonosov Ridge was covered by an ice mass of spatial and temporal variable thickness between ~780 to ~1250 m, that was likely composed of sea ice and thick icebergs calved from ice shelves.

Depth‐limiting resistant layers restrict dimensions and positions of estuarine channels and bars

AbstractEstuaries comprise channels vital for economic activity and bars as valuable habitats. They are increasingly under human‐induced pressures (e.g. sea‐level rise and dredging), resulting in morphological changes that affect navigability, flood safety and ecology. Antecedent geology may strongly steer how estuary channels will adapt to these pressures, but is surprisingly absent in most models. Here geological data and a unique bathymetry dataset covering 200 years from the Ems‐Dollard estuary (Netherlands/Germany) were used to demonstrate how local resistant layers force the position and dimensions of confluences and bars on the scale of an entire estuary. These layers limit channel depth and consequently cause widening, resulting in mid‐channel bar formation and increased channel curvature. This could lead to unexpected estuary widening and may cause land loss in densely populated areas. With increasing channel volume (as may happen again under future sea‐level rise), resistant layers in the estuary's substrate become more exposed, which enhances their effects. Many systems around the world contain shallow resistant layers that potentially constrain estuary channel dimensions and steer bank erosion. This highlights that resistant layer effects are important to consider as part of mixed depositional processes in coastal environments. It is therefore necessary to globally account for the effects of inherited resistant layers in the possible response of estuaries to sea‐level rise and increased tidal penetration.

High-resolution calibration of seismically-induced lacustrine deposits with historical earthquake data in the Eastern Alps (Carinthia, Austria)

Lake sediments are increasingly used to reconstruct recurrence intervals of large earthquakes - a prerequisite for the establishment of accurate seismic hazard models - because they can record strong seismic shaking as mass-transport deposits (MTDs), turbidites or sediment deformations and often reach back several thousands of years. To derive quantitative information on paleo-earthquake size, the sedimentary imprints need to be thoroughly calibrated with independent information on seismic shaking strength. A few calibration studies proposed scaling relationships between the shaking strength of historical earthquakes and the type and size of lacustrine sedimentary imprints. Due to incomprehensive lacustrine mapping or an insufficient record of documented earthquakes, however, rigorous testing of these scaling relationships is lacking. Here, we study the sedimentary infill of the past ∼800 years in Wörthersee and Millstättersee, two large lakes in the Eastern Alps (Carinthia, Austria). These lakes have experienced five well-documented historical earthquakes with local seismic intensities ranging from V – IX (EMS-98 scale). We trace the sedimentary signatures (MTDs and turbidites) of these earthquakes based on a vast dataset of multibeam bathymetry, reflection seismic profiles and numerous precisely dated sediment cores. Seismic intensities as low as V½ are recorded as turbidites originating from deltaic slopes, while hemipelagic slopes can fail from intensities of VI onwards. In Wörthersee, earthquake-recording thresholds are highly dependent on the specific core locations due to local variations in slope characteristics (composition, length, and gradient) and transport distance to the core site. This highlights the potential for establishing multi-threshold paleoseismic records based on multiple coring sites in a single basin. In both lakes, exponential size-scaling relationships are inferred between seismic intensity and i) number or volume of mass-transport deposits and ii) the cumulative thickness of turbidites. Moreover, the relative turbidite presence increases linearly with seismic intensity, confirming the results from a previous study in Chilean lakes. Application of the obtained size-scaling relationships on the first major earthquake documented for Austria (1201 CE) suggests a magnitude of ∼6.4 and an epicentre close to Millstätter See. This demonstrates that lake paleoseismology is a powerful tool to obtain quantitative information on the seismic intensity distribution of paleo-earthquakes.

Hydrodynamic modeling of a complex salt marsh system: Importance of channel shoreline and bathymetric resolution

Modeling hydrodynamics and sediment transport inside a multi-inlet wetland system is a challenging task due to constraints on model efficiency, accuracy and representation of physics, the scarcity of field data for model validation, and more importantly, the availability of high-resolution data sets of channel bathymetry. Lack of field data sets, model assumptions, and limitations often lead to wrong interpretation of the system’s nature. To correctly predict the changes in governing hydrodynamics and morphology of shallow wetland environments, it is essential to resolve the channel properties with the best possible accuracy. In this study, we consider the importance of two factors, numerical model grid resolution around channel shorelines, and bathymetry surveys, in improving the interior channel and mudflat hydrodynamics. Channel shoreline element size is observed to be an essential factor in time-varying channel volume estimation. Lower model resolution in channels inside a marsh can provide good agreement with in-situ surface elevation data, even though the channel surface-velocity phase lag, and velocity magnitude and asymmetry are inaccurate. A higher grid resolution at the channel berms and the high-density channel survey help define the time-varying lateral shoaling bathymetry, cross-section area, and bottom friction, and improve the corresponding model skill and tidal wave properties significantly. We have selected Bombay Hook National Wildlife Refuge, a rapidly eroding salt-marsh system in Delaware Bay, to compare model skills for different hypsometric conditions. Model performance is evaluated during two storm conditions; Hurricane Sandy (2012) and Hurricane Joaquin (2015), using tide gauges located on the marsh interior channels. • Poor grid resolution around marsh-channel berm creates artificial channel convergence and inaccurate tidal wave characteristics. • Topo-bathymetry field survey and bias correction improves channel hypsometry and numerical model reliability significantly. • Inaccurate channel bathymetry and inadequate resolution might lead to acceptable surface elevation but poor tidal velocity field. • The conventional grid generation methods based on sparse cross channel surveys is not sufficient for wetland models.