Search

Reports on developments about geological studies as of September 2003. Recovery of Fossil Nessie, a plesiosaur from the waters of Loch Ness, Scotland. Plan of the Tuvalu government to evacuate its 9,300 inhabitants because of the rise in sea levels in the Island of Tuvalu in the Pacific; Threat of the loss of peat Ireland due to the demand for peat by British gardeners.

The Limnology & Oceanography Bulletin has published a list of the top three accessed articles for each issue in the second quarter of 2023. The articles cover a range of topics including nitrogen patterns in a eutrophic lake during an algal bloom, prey selection in copepods, and the effects of ocean acidification on marine phytoplankton. Other articles explore the interactive effects of nitrogen and phosphorus on lake phytoplankton, the contribution of migrating copepods to the carbon pump, and the response of under-ice plankton communities to a snow removal experiment. The final set of articles investigate the unique carbon isotope fingerprints of microalgal taxonomic groups, the control of bottom hypoxia in alpine lakes, and the implications of sea-level rise on intertidal primary production. The authors are commended for their contributions to the journal. [Extracted from the article]

Coral reef islands are amongst the most vulnerable environments to sea‐level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variability. Comparison with carbonate sediment production rates from census‐based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR. Plain Language Summary: Low‐lying coral reef islands are under threat of sea‐level rise (SLR). However, when these islands are flooded, ocean waves can bring in sediment that can increase the island elevation. This would enable coral reef islands to better withstand flooding in the future. Knowing how much sediment is brought in will help in our understanding of future changes to these islands due to SLR. In this paper, we use data from 28 Indo‐Pacific coral reef islands to compute sediment supply to the islands. We find that on average 0.1 m3 of sediment (roughly 100 kg) is delivered each year for every meter of island shoreline. We further suggest that this implies that only one quarter of the sediments produced by the coral reef system is delivered to the island shoreline. Most of the sediment produced remains on the reef flat or is exported to the ocean or the lagoon. Our results will help future studies to predict more accurately how coral reef islands will adjust to SLR. Key Points: We provide the first estimates of carbonate sediment delivery rates to 28 coral reef islands using all data available from the literatureSediment delivery to the reef islands occurs at a rate of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variabilityWhere island building has been continuous through island history, long‐term delivery rates provide valuable estimates for contemporary rates [ABSTRACT FROM AUTHOR]

Developed barrier systems (barrier islands and spits) are lowering and narrowing with sea‐level rise (SLR) such that habitation will eventually become infeasible or prohibitively expensive for most communities in its current form. Before reaching this state, choices will be made to modify the natural and built environment to reduce relatively short‐term risk. These choices will likely vary substantially even along the same developed barrier system as these landscapes are rarely uniformly managed alongshore. Building on the results from a companion paper, here we use a new modeling framework to investigate the complexities in barrier system dynamics that emerge as a function of alongshore variability in management strategies, accelerations in SLR, and changes in storm intensity and frequency. Model results suggest that when connected through alongshore sediment transport, barriers with alongshore variable management strategies—here, the construction of dunes and wide beaches to protect either roadways or communities—evolve differently than they would in the absence of alongshore connections. Shoreline stabilization by communities in one location influences neighboring areas managed solely for roadways, inducing long‐term system‐wide lags in shoreline retreat. Conversely, when barrier segments managed for roadways are allowed to overwash, this induces shoreline curvature system‐wide, thus enhancing erosion on nearby stabilized segments. Feedbacks between dunes, storms, overwash flux, and alongshore sediment transport also affect outcomes of climate adaptation measures. In the case of partial, early abandonment of roadway management, we find that system‐wide transitions to less vulnerable landscape states are possible, even under accelerated SLR and increased storminess. Plain Language Summary: Because humans inhabit barrier islands and spits (collectively referred to as "barriers") these landscapes, that would otherwise naturally change shape in response to storms and sea‐level rise (SLR), are influenced by efforts to protect development with wide beaches and tall dunes. These features interfere with a process called overwash, which transports sand landward during storms, building barrier elevation relative to sea level. Here, we use a new model to better understand how these interactions influence the habitability of barriers over time. Our simulations show that different management decisions made for adjacent coastal segments affect each other in positive and negative ways. When communities nourish beaches, adjacent to segments managed for roadways, some nourished sand reaches the adjacent segments, reducing shoreline erosion there. Conversely, portions of barriers that are managed only for roadways allow some overwash to reach the barrier interior; this negatively affects neighboring communities by enhancing their shoreline erosion rates. We find that early abandonment of dune management along portions of barriers may prevent highly vulnerable future states, such as barrier drowning. As communities explore choices for climate adaptation, our findings reveal the importance of coordination among decision makers in adjacent communities to avoid undesirable outcomes. Key Points: When management strategies vary alongshore, their effects are coupled via alongshore sediment redistribution, influencing barrier evolutionBeach nourishment (along portions of barriers) induces system‐wide lags in shoreline retreat, even decades after nourishment practices ceaseMore overwash (due to lower dunes or increased storminess) can prolong habitability, but drives increased nourishment frequency elsewhere [ABSTRACT FROM AUTHOR]

This paper summarizes the forest dynamics and carbon sequestration abilities of, as well as the influences of sea‐level rise on, Micronesian mangrove forests as revealed from long‐term studies (more than 25 years). Monitoring surveys of the permanent plots in the area's major mangrove communities revealed that the tree density decreased, while aboveground biomass increased. However, in the Rhizophora stylosa community characterized by densely developed stilt roots, the aboveground biomass temporarily decreased due to a decrease in old stilt roots, but it increased again by generating a large amount of new stilt roots. The highest aboveground biomass was estimated to be 895 Mg ha−1, which is the highest value of all the existing ground survey data from the tropics. Mangrove peat was deposited in the entire mangrove area, but its thickness differed according to the forest community, which indicated that the belowground stored carbon also differed depending on the community. In recent years, a rise in sea level exceeding 5 mm year−1 was observed in this region, and surface erosion occurred in the Bruguiera gymnorrhiza and Sonneratia alba communities. On the other hand, in the R. stylosa and Rhizophora apiculata communities, the ground level rose due to the accumulation of mangrove peat. The temporal decrease in old stilt roots and the accelerated increase in new stilt roots observed in the R. stylosa community may also be an effect of sea‐level rise. Long‐term monitoring surveys in mangrove forests are thus effective in quickly catching the effects of sea‐level rise. [ABSTRACT FROM AUTHOR]

The immense impacts of tsunamis can inflict substantial damage on coastal infrastructure systems during their lifetime and lead to considerable economic loss. However, with the increasing intensity and variability of sea‐level rise due to climate change, evaluations of the life‐cycle tsunami risk associated with cumulative loss have become increasingly complex since tsunami hazards are time‐dependent. In addition, the number of earthquake events and the corresponding arrival times are substantially uncertain. Therefore, an accurate life‐cycle tsunami risk assessment methodology should be established to appropriately develop disaster mitigation measures. This paper provides a novel life‐cycle risk assessment of building portfolios subjected to tsunami hazards under non‐stationary sea‐level rise effects due to climate change. The cumulative loss of a building portfolio is evaluated through a compound renewal process based on earthquake interarrival time uncertainties and time‐dependent risk. The earthquake interarrival times are modeled using a non‐Poisson process based on historical data. Tsunami hazard curves that consider the effects of sea‐level rise, estimated based on climate models, are obtained with tsunami propagation analysis. The time‐variant annual risk is estimated based on reliability and building unit loss. Finally, a numerical procedure is proposed to estimate the life‐cycle tsunami risk of building portfolios. An illustrative example is provided by applying the framework to several municipalities in the Kochi Prefecture of Japan to assess the effects of climate change on the life‐cycle tsunami risk. [ABSTRACT FROM AUTHOR]

Global coastal flood exposure (population and assets) has been growing since the beginning of the industrial age and is likely to continue to grow through 21st century. Three main drivers are responsible: (a) climate‐related mean sea‐level change, (b) vertical land movement contributing to relative sea‐level rise, and (c) socio‐economic development. This paper attributes growing coastal exposure and flood risk from 1860 to 2100 to these three drivers. For historic flood exposure (1860–2005) we find that the roughly six‐fold increase in population exposure and 53‐fold increase in asset exposure are almost completely explained by socio‐economic development (>97% for population and >99% for assets). For future exposure (2005–2100), assuming a middle‐of‐the‐road regionalized socio‐economic scenario (SSP2) without coastal migration and sea‐level rise according to RCP2.6 and RCP6.0, climate‐change induced sea‐level rise will become the most important driver for the growth in population exposure, while growth in asset exposure will still be mainly determined by socio‐economic development. Plain Language Summary: This study provides the first analysis of historical (1860–2005) and future (2005–2100) coastal flood exposure and flood risk and the attribution of both to the three main drivers: socio‐economic development, climate‐related sea‐level change and geologic sea‐level change. From 1860 to 2005 coastal population has grown roughly by factor 6 and coastal assets roughly by factor 53 and this growth has almost completely be driven by socio‐economic development. From 2005 to 2100 further growth is expected, where the actual factor depend on the chosen scenario. However, this future growth is much more driven by climate‐induced sea‐level rise then the historical growth. For coastal risk adaptation measures have to be taken into account and it shows that adaptation is a crucial factor. With adaptation taken into account the increase in coastal risk is lower than the increase in coastal exposure, in general with higher attribution to the climate driver. Key Points: 20th century coastal exposure and risk is almost completely attributable to socie‐econmoic developmentFor 21st century this changes: climate induced sea‐level rise can become the main driver of coastal exposure and risk in the 21st centuryCoastal adaptation is a crucial driver for coastal risk ‐ global mitigation policy needs to be complemented by local coastal management [ABSTRACT FROM AUTHOR]

Satellite imagery is widely used to study beach changes. Studies based on satellite‐derived results predict that by 2100, half of the world's beaches will disappear. Although previous studies have been productive and alarming, the reliability of these findings has not been validated. This study presents an initial comprehensive assessment of the reliability of satellite‐derived beach shoreline changes and concludes that despite the use of state‐of‐the‐art subpixel shoreline identification technologies and water‐level correction methods based on beach profile shapes, the errors in satellite‐derived shoreline positions remain significant. Thus, adequate satellite imagery is crucial for enhancing the reliability of satellite‐derived beach changes. Furthermore, the historical water levels when the Landsat and Sentinel‐2 images were taken exhibited significant systematic deviations and both long‐term and short‐term changes. Consequently, the beach changes obtained through the direct statistics obtained from satellite imagery based on big‐data platforms such as the Google Earth Engine (GEE) are susceptible to systematic biases. The study also concluded that satellite‐derived beach changes based on adequate satellite imagery have distinct, significant, and diverse responses to human activities. Given the current context of intensified human activities and notable inaccuracies in satellite‐derived shoreline positions, fully utilizing satellite imagery to study beach changes can help establish stronger connections between beach changes and human activities. This contributes to a better understanding of beach evolution mechanisms and the need for beach restoration and protection, with multiple scientific, engineering, and social implications. Plain Language Summary: Beaches around the globe are currently facing significant threats due to the combined influence of rapid sea‐level rise and intensified human activities. Researchers have used satellite images to study beach changes, and the results are alarming. Some researchers even predict that by 2100, half of the world's beaches will have disappeared. However, the existing research has mainly evaluated the precision of satellite‐derived shoreline position data rather than satellite‐derived beach changes. Moreover, the identified beach changes are not clear enough to determine the links between beach changes and human activities. Based on all available Landsat and Sentinel‐2 images, this study presents the first comprehensive assessment of the reliability of satellite‐derived beach shoreline changes and demonstrates the distinct, remarkable, and diverse responses of a typical beach to human activities. The study revealed that the water levels when the satellite images were taken exhibited systematic deviations and both long‐term and short‐term changes. Consequently, water‐level corrections to the shoreline positions that were obtained through direct statistical analyses of satellite imagery are essential for reliably studying both global and local beach changes. Finally, adequate satellite imagery is recommended for identifying high‐precision beach changes. Key Points: This paper presents an initial comprehensive assessment of the reliability of satellite‐derived beach shoreline changesBeach changes obtained through the direct statistics obtained from satellite imagery on big‐data platforms are prone to systematic biasesAdequate satellite imagery is crucial for enhancing the reliability and revealing the impact of human activities [ABSTRACT FROM AUTHOR]

The Bering‐Bagley Glacier System (BBGS), Alaska, Earth's largest temperate surging glacier, surged in 2008–2013. We use numerical modeling and satellite observations to investigate how surging in a large and complex glacier system differs from surging in smaller glaciers for which our current understanding of the surge phenomenon is based. With numerical simulations of a long quiescent phase and a short surge phase in the BBGS, we show that surging is more spatiotemporally complex in larger glaciers with multiple reservoir areas forming during quiescence which interact in a cascading manner when ice accelerates during the surge phase. For each phase, we analyze the simulated elevation‐change and ice‐velocity pattern, infer information on the evolving basal drainage system through hydropotential analysis, and supplement these findings with observational data such as CryoSat‐2 digital elevation maps. During the quiescent simulation, water drainage paths become increasingly lateral and hydropotential wells form indicating an expanding storage capacity of subglacial water. These results are attributed to local bedrock topography characterized by large subglacial ridges that dam the down‐glacier flow of ice and water. In the surge simulation, we model surge evolution through Bering Glacier's trunk by imposing a basal friction representation that mimics a propagating surge wave. As the surge progresses, drainage efficiency further degrades in the active surging‐zone from its already inefficient, end‐of‐quiescence state. Results from this study improve our knowledge of surging in large and complex systems which generalizes to glacial accelerations observed in outlet glaciers of Greenland, thus reducing uncertainty in modeling sea‐level rise. Plain Language Summary: The Bering‐Bagley Glacier System (BBGS), Alaska, Earth's largest temperate surging glacier, recently surged in 2008–2013. A surge glacier cycles between a long period of normal flow and a short period of accelerated flow where large‐scale deformations, such as crevasses, occur. This paper focuses on investigating a surge in a large and complex system rather than a small glacier where most studies on surges have been conducted. We use a numerical model to simulate glacier evolution for both the quiescent phase and the initial surge phase of the BBGS. For each phase, we analyze the simulated elevation‐change and ice‐velocity, and infer information on the evolving hydrologic drainage system. During the quiescent phase, ice‐mass builds up at locations consistent with those observed and water drainage paths become longer with expanding capacity to store subglacial water. These results are attributed to local bedrock topography characterized by large subglacial ridges that act to dam the down‐glacier flow of ice and water. In the surge simulation, we model surge evolution through Bering Glacier by implementing a new friction representation that mimics a propagating wave. As the surge progresses through the glacier, drainage efficiency further degrades in the areas of fast‐moving ice. Key Points: Using a full‐Stokes approach informed by satellite observations, a quiescent and surge phase of the Bering‐Bagley Glacier System (BBGS) are simulatedLocal bed topography controls the formation of several reservoir areas, which lengthen down‐glacier drainage paths during quiescenceA friction representation for the surge phase is implemented based on observed properties of kinematic surge waves in the BBGS [ABSTRACT FROM AUTHOR]

Little is known about the effect of tidal changes on minor flooding in most lagoonal estuaries, often due to a paucity of historical records that predate landscape changes. In this contribution, we recover and apply archival tidal range data to show that the mean tidal range in Miami, Florida, has almost doubled since 1900, from 0.32 to 0.61 m today. A likely cause is the dredging of a ∼15 m deep, 150 m wide harbor entrance channel beginning in the early 20th century, which changed northern Biscayne Bay from a choked inlet system to one with a tidal range close to coastal conditions. To investigate the implications for high‐tide flooding, we develop and validate a tidal‐inference based methodology that leverages estimates of pre‐1900 tidal range to obtain historical tidal predictions and constituents. Next, water level predictions that represent historical and modern water level variations are projected forward in time using different sea level rise scenarios. Results show that the historical increase in tidal range hastened the occurrence of present‐day flooding, and that the total integrated number of days with high‐tide floods in the 2020–2100 period will be approximately O(103) more under present day tides compared to pre‐development conditions. These results suggest that tidal change may be a previously under‐appreciated factor in the increasing prevalence of high‐tide flooding in lagoonal estuaries, and our methods open the door to improving our understanding of other heavily‐altered systems. Plain Language Summary: Tabulations of historical tidal range indicate that tidal range in Miami (Florida) has approximately doubled since the 19th century, from 0.32 to 0.61 m. The likely cause appears to be the construction and dredging of the shipping channel to the Port of Miami, though historical land‐reclamation may also play a role. In this paper, we show that the increase in tidal range significantly exacerbates the number of minor flood events that are occurring throughout the Biscayne Bay region. As sea‐level rise continues, tidal changes will cause high‐tide flood impacts to be felt about a decade earlier than would have occurred under historical tidal conditions. Key Points: Tidal range in the Miami downtown area almost doubled over the past century due to human‐induced bathymetric change and wetland reclamationPre‐1900 tidal predictions are estimated from historical tidal range using a tidal‐constituent inference based methodIncreased tidal range increases the probability of high‐tide flooding and shortens the time to when sea‐level rise will cause chronic flooding [ABSTRACT FROM AUTHOR]

Extensive research into the evolution of wave‐dominated estuaries has been documented since the 1960s. However, there has only been limited research on the prograding bay‐head deltas that are the primary drivers for the rate and stage of estuary evolution. This paper presents the findings of a high‐resolution spatial study into the evolution of the Macquarie Rivulet bayhead delta in the Lake Illawarra barrier estuary. The delta's evolution has been established based on sedimentological analysis of 74 cores, two 14C ages and 45 amino acid racemization ages. This study intersected two Pleistocene and 10 Holocene sedimentary facies associations representing both the retrogradational and progradational phases of delta development. The distribution of bayhead delta facies associations in shallow barrier estuaries is initially controlled by the antecedent morphology, but, in contrast to deeper estuaries, this influence decreases as sedimentation proceeds. Changing relative sea level also has a major control on facies distribution with transgressive facies deposited as relative sea‐level rises being replaced by prograding deltaic facies during the highstand and subsequent minor relative sea‐level fall. Fluvial sediment supply and river flood events affect the rate of delta progradation, and produce low and high flow sediment deposits within the overall deltaic sequence. The low tidal flux in barrier estuaries, the muddy cohesive nature of the sediments and the prevalence of bioturbation means that primary sedimentary structures are rarely preserved in these bayhead delta facies. The depositional model of bayhead delta evolution shown by the Macquarie Rivulet delta would be widely applicable to other similar barrier estuary settings. [ABSTRACT FROM AUTHOR]

The Miocene sequences in the north‐west of the Gulf of Suez represent transition zones between carbonate‐dominated and siliciclastic‐dominated strata. These rocks were greatly influenced by the Gulf of Suez rifting, which resulted in lateral variations of facies and hence presented a complicated stratigraphic setting. Here, we interpret the sequence stratigraphy of the Sadat Area to the north‐west of the Gulf of Suez by integrating biostratigraphic data and microfacies analysis to contribute primarily to the geology of the studied successions and incorporate the existing knowledge of syn‐rift deposition. We determined the ages of the studied formations by biostratigraphic examination of the integrated calcareous nannoplankton, planktic, and benthic foraminifera. Our results distinguish four genetic Miocene sequences. These sequences are defined by four major sequence boundaries that outline sedimentation cycles and were chiefly deposited in a lagoon to outer‐shelf settings. The proposed Miocene eustacy is well‐correlated with global curves, implying a rise in sea level in the lower parts of Zones M4, M5, and M8. In contrast, the reduction of sea‐level rise resulted in the decrease of accommodation space in the upper part of Zone M5. The studied Miocene deposits mainly formed in a shallower marine environment, as shown by a comparison between data from the eastern side of the Gulf of Suez and the data presented in this paper. Furthermore, we demonstrate that the local tectonic activity linked with the Gulf of Suez rifting and the eustatic sea‐level changes were significant factors in the deposition of the Miocene in the studied successions. [ABSTRACT FROM AUTHOR]

Sea‐level rise is a "nascent subsystem" with policy actors actively developing initial policy preferences through participation across multiple policy forums in a polycentric system. This paper uses item‐response models to empirically analyze how actors, perceived problems, and preferred policy solutions are related in a latent "policy space". We focus on California's San Francisco Bay region, where in the last decade, sea‐level rise emerged to become one of the most salient climate adaptation issues. We find that actors and policy preferences are arranged in a two‐dimensional space, with highly engaged actors more likely to consider environmental justice and ecological aspects of sea level rise. Our findings have implications for theories of nascent subsystems within the Advocacy Coalition Framework, and for understanding how a local policy subsystem develops to address and prioritize the multi‐faceted impacts of climate change. [ABSTRACT FROM AUTHOR]

The Pearl River Delta is a complex ecological‐artificial system. The low‐elevation landform and land subsidence make the Guangdong‐Hong Kong‐Macao Greater Bay Area (GBA) more vulnerable to heavy rainstorms with sea‐level rise in the future. Therefore, this study discussed how to optimize the delta‐related built environment based on locality via cooperation between urban designers and hydrology researchers so that urban development in the GBA can adapt to water disasters. First, this study proposed three adaptive spatial strategies for urban design to improve flood resilience: (a) adding more sunken space and rearranging the locations of manholes; (b) adding more retention space to the waterway system; and (c) improving foundation elevation for suitable development intensity. With the prediction of sea‐level rise and land subsidence, four different scenarios were defined. Second, a coupled 1D/2D hydrodynamic model was built for scenario‐based urban inundation simulations. Third, a Python workflow was developed to reveal the water volume exchange, and an ArcMap workflow to realize the impact of inundation. The simulation results show that (a) more sunken space can lower the peak runoff discharges and decrease the runoff coefficient; (b) more retention space can extend the capacity of the urban drainage system and adapt to the rise of sea level; and (c) improving foundation elevation and more sunken green space can direct the surface water to submerge urban land in reasonable order, which can protect the significant infrastructures and development lands. This paper suggests that these adaptive spatial strategies can serve as solutions for resilience development. [ABSTRACT FROM AUTHOR]

The ambition and architecture of the post-2012 climate change regime will be critical to the survival of many small island developing nations, many of which are low-lying, vulnerable to the impacts of sea-level rise and exposed to increasingly frequent and severe extreme weather events. This paper highlights the key outcomes sought by the Alliance of Small Island States in the international negotiating process on the post-2012 regime and compares these calls with what has been achieved thus far. The paper concludes that while little progress has been made to date, useful avenues for progress do exist if only the political will can be found. [ABSTRACT FROM AUTHOR]

One of the largest sources of uncertainty in sea level rise prediction is glacial acceleration, of which the surge phenomenon is the least understood type. The surge of the Bering Bagley Glacier System (BBGS), Alaska, in 2011–2013 has provided a rare opportunity to study the surge phenomenon in a large and complex glacier system. A surge results in widespread crevassing throughout the glacier system complicating many traditional techniques used to study glacier dynamics. In this paper, we utilize crevassing as a means to investigate the recent BBGS surge through numerical modeling and geostatistical data analysis. Following the principles of structural glaciology, image‐based crevasse characterizations are obtained through geostatistical methods applied to Landsat‐7 data, supplemented by airborne field observations. On the modeling side, a 3‐D full‐Stokes finite element model of the BBGS is developed and applied to investigate ice dynamics and surface structures during the recent surge. A von Mises criterion is adopted to simulate crevassing at the glacier surface, oriented along the axes of maximum principal tensile stress. To facilitate evaluation of model‐ and data‐derived crevasse characteristics, three different comparison methods are introduced. General agreement in the model‐data comparisons indicates that the model has the ability to represent the BBGS system during peak acceleration. The crevasse‐based approach is also employed to optimize the basal sliding parameter and the von Mises stress threshold in the model. Results further indicate that bed topography is an important constraint in modeling the surge process. [ABSTRACT FROM AUTHOR]

Abstract: Reserves of fresh groundwater on atoll islands are extremely fragile due to climatic and anthropogenic stresses. Of major concern is the quantity of water to be available in the coming decades under the influence of variable rainfall patterns, rising sea level, environmental conditions, and expected population growth that depends on groundwater resources. In this study, a 3‐dimensional numerical modelling approach using the SEAWAT modelling code is used to estimate freshwater lens volume fluctuation for 4 representative islands in the Republic of Maldives in response to long‐term changes in rainfall, sea‐level rise (SLR), and anthropogenic stresses such as groundwater pumping and short‐term impacts from tsunami‐induced marine overwash events. This work is divided into 2 papers. This first paper presents numerical model set‐up and calibration, and the effect of future rainfall patterns and SLR on fresh groundwater reserves. The second paper focuses on marine overwash events. The results of simulated future freshwater lens volume presented in the first study contribute to efficient groundwater resources planning and management for the Maldives in the upcoming decades. Freshwater lenses in small atoll islands (area < 0.6 km2) are shown to have a strong variability trends in the upcoming decades with expected reduction in lens volume between 11% and 36% due to SLR. In contrast, freshwater lenses in larger atoll islands (area > 1.0 km2) are shown to have less variability to changing patterns with expected reduction in lens volume between 8% and 26% due to SLR. Study results can provide water resource managers with valuable findings for consideration in water security measures. [ABSTRACT FROM AUTHOR]

Gravitationally consistent solutions of the Sea Level Equation from leakage‐corrected monthly‐mean GFZ RL06 Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On (GRACE‐FO) Stokes coefficients reveal that barystatic sea level averaged over the whole global ocean was rising by 1.72 mm a−1 during the period April 2002 until August 2016. This rate refers to a truely global ocean averaging domain that includes all polar and semienclosed seas. The result corresponds to 2.02 mm a−1 mean barystatic sea level rise in the open ocean with a 1,000 km coastal buffer zone as obtained from a direct spatial integration of monthly GRACE data. The bias of +0.3 mm a−1 is caused by below‐average barystatic sea level rise in close proximity to coastal mass losses induced by the smaller gravitational attraction of the remaining continental ice and water masses. Alternative spherical harmonics solutions from CSR, JPL, and TU Graz reveal open‐ocean rates between 1.94 and 2.08 mm a−1, thereby demonstrating that systematic differences among the processing centers are much reduced in the latest release. We introduce in this paper a new method to approximate spatial leakage from the differences of two differently filtered global gravity fields. A globally constant and time‐invariant scale factor required to obtain full leakage from those filter differences is found to be 3.9 for GFZ RL06 when filtered with DDK3, and lies between 3.9 and 4.4 for other processing centers. Spatial leakage is estimated for every month in terms of global grids, thereby providing also valuable information of intrabasin leakage that is potentially relevant for hydrologic and hydrometeorological applications. Plain Language Summary: Satellite gravimetry as realized with the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On (GRACE‐FO) missions is measuring tiny variations in the Earth's gravity field that are directly caused by divergent horizontal mass transports such as the melting of ice sheets and the corresponding discharge of melt water into the ocean basins. Between April 2002 and August 2016, this mass inflow caused sea level to rise by 1.72 mm each year as quantified from the latest GRACE reprocessing performed at our institute. The indirect observation principle of GRACE limits the spatial resolution so that highly localized mass loss signals are smeared out into the larger surrounding area, and possibly even from land into the ocean. We propose here a new method to quantify this so‐called spatial leakage from the difference of gravity fields smoothed with slightly different spatial filters. A scale factor is obtained from exploiting the availability of two independent methods to estimate the mass component of sea level rise: The first method spatially integrates over the global gravity fields in all regions away from the coasts, and the second method utilizes a (leakage‐corrected) mass distribution over the continents to calculate the gravitationally consistent distribution of water masses in all ocean basins. We estimate this scale factor as 3.9. Key Points: Mean barystatic sea level rise is biased high by 0.3 mm a−1 when estimated with a 1,000 km coastal buffer zoneFractional spatial leakage in monthly GRACE gravity fields is quantified with two differently strong DDK filtersFractional leakage is scaled by a factor of 3.9 to make results from the Sea Level Equation consistent with open‐ocean integrations [ABSTRACT FROM AUTHOR]

We develop idealized analytical and numerical models to study how storm surge amplitudes vary within frictional, weakly convergent, nonreflective estuaries. Friction is treated using Chebyshev polynomials. Storm surge is represented as the sum of two sinusoidal components, and a third constituent represents the semidiurnal tide (D2). An empirical fit of storm surge shows that two sinusoidal components adequately represent storm surge above a baseline value (R2 = 0.97). We find that the spatial transformation of surge amplitudes depends on the depth of the estuary, and characteristics of the surge wave including time scale, amplitude, asymmetry, and surge‐tide relative phase. Analytical model results indicate that surge amplitude decays more slowly (larger e‐folding) in a deeper channel for all surge time scales (12–72 hr). Deepening of an estuary results in larger surge amplitudes. Sensitivity studies show that surges with larger primary amplitudes (or shorter time scales) damp faster than those with smaller amplitudes (or larger time scales). Moreover, results imply that there is a location with maximum sensitivity to altered depth, offshore surge amplitude, and time scale and that the location of observed maximum change in surge amplitude along an estuary of simple form moves upstream when depth is increased. Further, the relative phase of surge to tide and surge asymmetry can change the spatial location of maximum change in surge. The largest change due to increased depth occurs for a large surge with a short time scale. The results suggest that both sea level rise and channel deepening may also alter surge amplitudes. Plain Language Summary: Many estuaries around the world are heavily altered from their natural state. Wetlands have been reclaimed, and shipping channels widened and deepened to accommodate large container ships. The effects on storm surge and flood risk are just beginning to be explored. In this paper we employ a theoretical approach to understand how the characteristics of a storm surge—such as how fast it is moving, how big it is, and whether it happens on flood or ebb tide—change how it behaves in an estuary. Our results show that storm surge generally gets larger when channels are dredged and deepened; the largest amplification is observed for fast‐moving storms with a short time scale, within estuaries that are highly frictional. Other characteristics—such as the timing relative to the tide and the shape of the estuary—also impact the amplitude and the amount of sensitivity to changing conditions. We find that channel deepening effects are negligible at the coast and far upstream. In between, a region of maximum sensitivity to dredging occurs. Thus, changes in flood risk due to channel deepening and sea level rise can be spatially variable, even within a single estuary. Key Points: An idealized model shows that channel deepening increases surge amplitude and moves the location of maximum change in surge landwardThe damping in storm surge varies spatially and depends on surge time scale, amplitude, asymmetry, and timing relative to tidesThe largest amplification in surge due to channel deepening occurs in strongly frictional estuaries for large amplitude fast moving events [ABSTRACT FROM AUTHOR]

Sea‐level change threatens the U.S. East Coast. Thus, it is important to understand the underlying causes, including ocean dynamics. Most past studies emphasized links between coastal sea level and local atmospheric variability or large‐scale circulation and climate, but possible relationships with local ocean currents over the shelf and slope remain largely unexplored. Here we use 7 years of in situ velocity and sea‐level data to quantify the relationship between northeastern U.S. coastal sea level and variable Shelfbreak Jet transport south of Nantucket Island. At timescales of 1–15 days, southern New England coastal sea level and transport vary in anti‐phase, with magnitude‐squared coherences of ∼0.5 and admittance amplitudes of ∼0.3 m Sv−1. These results are consistent with a dominant geostrophic balance between along‐shelf transport and coastal sea level, corroborating a hypothesis made decades ago that was not tested due to the lack of transport data. Plain Language Summary: Sea‐level rise is an imminent threat to coastal communities worldwide, including the U.S. East Coast. Therefore, it is crucial to understand the processes driving regional sea‐level change. While past studies documented how coastal sea level may be influenced by large‐scale ocean circulation, less attention has been paid to the role of more local currents over the shelf and slope. Here we explore the relationship between coastal sea level along the northeastern U.S. and the Shelfbreak Jet, a current that flows along the shelfbreak from the Labrador Sea to Cape Hatteras (North Carolina). From 7 years of in situ data of both current velocities and water levels, we see that as coastal sea level rises, Shelfbreak Jet transport increases westward (and vice versa) on timescales of days to weeks. Our results lay the groundwork for understanding relationships between coastal sea level and local ocean dynamics elsewhere. Key Points: Daily Shelfbreak Jet transports and Southern New England coastal sea levels are anti‐correlated during 2014–2022The observed relationship between these two variables is consistent with geostrophic balanceFor this region, coastal sea levels are more sensitive to local ocean dynamics than to large‐scale circulation [ABSTRACT FROM AUTHOR]

Anticipating and managing the impacts of sea‐level rise for nations astride active tectonic margins requires understanding of rates of sea surface elevation change in relation to coastal land elevation. Vertical land motion (VLM) can either exacerbate or reduce sea‐level changes with impacts varying significantly along a coastline. Determining rate, pattern, and variability of VLM near coasts leads to a direct improvement of location‐specific relative sea level (RSL) estimates for coastal hazard risk assessment. Here, we utilize vertical velocity field from interferometric synthetic aperture radar (InSAR) data, calibrated with campaign and continuous Global Navigation Satellite System data, to determine the VLM for the entire coastline of New Zealand. Guided by available knowledge of the seismic cycle, the VLM data infer secular, interseismic rates of land surface deformation. Using the Framework for Assessing Changes to Sea‐level (FACTS), we build probabilistic RSL projections using the same emissions scenarios employed in IPCC Assessment Report 6 and local VLM data at 8,179 sites, thereby enhancing spatial coverage that was previously limited to four tide gauges. We present ensembles of probability distributions of RSL for each scenario to 2150, and for low confidence sea‐level processes to 2300. Where land subsidence is occurring at rates >2 mm/y VLM makes a significant contribution to RSL projections for all scenarios out to 2150. Our approach can be applied to similar locations across the world and has significant implications for adaptation planning, as timing of threshold exceedance for coastal inundation can be brought forward (or delayed) by decades. Plain Language Summary: This study outlines an approach for deriving probabilistic projections of relative sea‐level change that account for changes in land surface elevation continuously along a coastline. Previous sea‐level projections that included vertical land movements (VLMs) were restricted to tide gauge locations. To provide spatial‐resolution required by practitioners for effective adaptation planning, we have combined elevations measured using satellite radar data with measurements from land‐based Global Navigation Satellite System (GNSS) receivers to build a continuous VLM database showing land uplift and subsidence (sinking) for the entire coastline of New Zealand. We integrate these data into probabilistic sea‐level projection methodology used in Intergovernmental Panel on Climate Change (IPCC) Assessment Report 6 (AR6) for the range of future climate scenarios. Our approach could be applied to any region of the world where the coastline is affected by VLM due to secular tectonic deformation. Downward land movement >2 mm/y makes a significant contribution in sea‐level projections for all climate scenarios out to the end of this century. This means that adaptation planning decision thresholds, such as those linked to the impacts of coastal flooding and inundation, may be brought forward by decades. Key Points: Anticipating impacts of sea‐level rise for active tectonic margins requires location‐specific knowledge of vertical land movement (VLM)VLM from geodetic measurements integrated with IPCC AR6 projections to provide probabilistic RSL estimates for dynamic coastlinesDownward VLM > 2 mm/y makes a significant contribution to RSL projections bringing forward adaptation decision thresholds by decades [ABSTRACT FROM AUTHOR]

In this paper we present new proxy‐based sea‐level reconstructions for southern New Zealand spanning the last millennium. These palaeo sea‐level records usefully complement sparse Southern Hemisphere proxy and tide‐gauge sea‐level datasets and, in combination with instrumental observations, can test hypotheses about the drivers of 20th century global sea‐level change, including land‐based ice melt and regional sterodynamics. We develop sea‐level transfer functions from regional datasets of salt‐marsh foraminifera to establish a new proxy‐based sea‐level record at Mokomoko Inlet, at the southern tip of the South Island, and to improve the previously published sea‐level reconstruction at Pounawea, located about 110 km to the east. Chronologies are based on radiocarbon, radiocaesium, stable lead isotope and pollen analyses. Both records are in good agreement and show a rapid sea‐level rise in the first half of the 20th century that peaked in the 1940s. Previously reported discrepancies between proxy‐based sea‐level records and tide‐gauge records are partially reconciled by accounting for barystatic and sterodynamic components of regional sea‐level rise. We conclude that the rapid sea‐level rise during the mid‐20th century along the coast of southern New Zealand was primarily driven by regional thermal expansion and ocean dynamics. [ABSTRACT FROM AUTHOR]

We use the results of a one‐dimensional morphodynamic model and the basis of the "Lagrangian equilibrium state" (Maan et al., 2015, https://doi.org/10.1002/2014JF003311) to derive a quantitative relationship between the progradation speed of tidal flats and the suspended sediment concentration in their adjacent waters and show that the speed increases more than linearly with the concentration. We also show that horizontally prograding flats rise vertically with sea level rise at the expense of their horizontal speed via a linear relationship. If accretion rates are insufficient to keep up with sea level rise, however, the intertidal flat submerges and retreats landward at the same time. We apply the obtained relationships to the Yangtze Estuary to estimate the critical sediment concentration level below which a shift from progradation to retreat can be expected. Plain Language Summary: The combination of sea level rise, decreasing sediment availability, and human fixation of the coastline results in large stresses on coastal areas worldwide. Extremely sensitive are the intertidal wetlands, lying in‐between the low and the high water line. Loss of coastal wetlands increases the coastal vulnerability to extreme events and sea level rise and undermines the coastal defense. We need a better understanding of the complex dynamics of the seabed to effectively interfere and stimulate its rise. System theory can be used to express system variables in terms of external system drivers. In this paper, the basis of the "Lagrangian equilibrium state" (Maan et al., 2015, https://doi.org/10.1002/2014JF003311) is used to derive quantitative relationships between the expansion rate of intertidal flats and three external drivers: the suspended sediment concentration in their adjacent waters (i.e., in the tidal channels), the "wave‐induced erosion," and the rate of sea level rise. Wave‐induced erosion and sea level rise lead to the existence of a critical sediment concentration level below which the intertidal system shifts from expansion to retreat. We apply the obtained relationships on the expanding flats in the Yangtze Estuary to estimate the critical shrinkage factor for the suspended sediment concentration in the estuary. Key Points: The progradation speed of tidal flats increases stronger than linearly with the suspended sediment concentration in their adjacent watersA critical suspended sediment concentration can be determined below which the system shifts from progradation to retreatAn estimate of the "wave‐induced erosion" is thereby needed, which can be obtained from in situ measurements [ABSTRACT FROM AUTHOR]

After the Last Glacial Maximum (LGM) global mean sea level (GMSL) rise was characterized by rapid increases over short (decadal to centennial) timescales superimposed on a longer term secular rise and these have been termed meltwater pulses (MWPs). In this paper we review the timing, impact and nature of these and the effects of rapid drainage of large post‐glacial MWPs into the world's oceans. We identify nine MWPs, four of which occurred in three periods of rapid sea level rise (19.5–18.8, 14.8–13.0 and 11.5–11.1 ka BP). The rest are dated to the period during the Early Holocene sea level rise after 11 ka BP. We show that drainage of the known post‐glacial lakes in total produced less than around 1.2 m of the 125 m of GMSLR since the LGM. [ABSTRACT FROM AUTHOR]

The vulnerability of tourism-dependent communities, coastal tourism facilities, and beaches to climate change demands the use of measures that can urgently minimise vulnerability and in the long term achieve sustainable development. This paper makes policy recommendations to address climate change and sea level rise challenges in small island developing states. Using Barbados as a case study, the paper found that innovations in policies and projects have offset the past ills of mass tourism and fortuitously now serve as pre-emptive measures in adapting to climate change. The array of methods for combating these changes includes physical planning policies, integrated coastal zone management, and infrastructure projects. Among the key areas for policy innovation are the adoption of protection, accommodation, and retreat strategies, which are informed by rigorous cost-benefit analysis and stakeholder consultation. Ecosystem-based adaptation to climate change is also necessary, especially for islands where coral reef protection is urgent. Moreover, policy adjustments are required on building construction, water resources management, sewage treatment, coastal zone management, physical planning, and land management. Institutional constraints, including the lack of capacity to implement, monitor, and enforce measures, must also be addressed if progress is to be made in adapting to climate change. A major conclusion is that the severity of coastal damage, the importance of tourism to sustainable development, and the country's adaptive capacity play a key part in the selection and implementation of climate change adaptation measures. [ABSTRACT FROM AUTHOR]

We show that steric sea‐level varies with a period of 18.6 years along the western European coast. We hypothesize that this variation originates from the modulation of semidiurnal tides by the lunar nodal cycle and associated changes in ocean mixing. Accounting for the steric sea level changes in the upper 400 m of the ocean solves the discrepancy between the nodal cycle in mean sea level observed by tide gauges and the theoretical equilibrium nodal tide. Namely, by combining the equilibrium tide with the nodal modulation of steric sea level, we close the gap with the observations. This result supports earlier findings that the observed phase and amplitude of the 18.6‐year cycle do not always correspond to the equilibrium nodal tide. Plain Language Summary: The orbital position of the moon and the gravity pull it exerts on the earth varies with a period of 18.6 years. This cycle is called the lunar nodal cycle and it results in small variations of yearly averaged sea level (∼1–2 cm). Understanding this variability is important because it allows, for example, to quickly detect an acceleration in local sea‐level rise due to global warming. Here we show that the lunar nodal cycle also has an influence on the temperature and salinity in the surface 400m of the ocean. As a result, the ocean density changes and amplifies sea level variations along the western European coast. We make the hypothesis that since the lunar nodal cycle also influences the amplitude of the semidiurnal tides, and since those tides are known to be responsible for a large part of ocean mixing, a change in ocean mixing could be the cause of the ocean density variability that we observe. Key Points: Steric sea level changes are influenced by the 18.6‐year lunar nodal cycle along the western European coastThis influence could result from the modulation of semidiurnal tides by the lunar nodal cycle and the associated change in ocean mixingThis finding is a step toward resolving the long‐standing discrepancy between the theoretical long‐period nodal tide and observed signal [ABSTRACT FROM AUTHOR]

Many barrier islands and spits (collectively, "barriers") throughout the world are highly developed. As low‐lying, sandy coastal landforms, barrier systems are naturally reshaped by processes associated with storms and sea‐level rise (SLR). The resulting landscape changes threaten development, and in response, humans employ defensive measures that physically modify barrier geometry to reduce relatively short‐term risk. These measures include the construction of large dunes, emplacement of beach nourishment, and removal of washover. Simulations conducted using a new coupled modeling framework show that, over decades to centuries, measures to protect roadways and communities alter the physical characteristics of barrier systems in ways that ultimately limit their habitability. We find that the pathway toward uninhabitability (via roadway drowning or community narrowing) and future system states (drowning or rebound) depends largely on dune management—because building dunes blocks overwash delivery to the barrier interior—and on initial conditions (barrier elevation and width). In the model, barriers can become lower and narrower with SLR to the point of drowning. The timing and occurrence of barrier drowning depends on randomness in the timing and intensity of storms and dune recovery processes. We find that under a constant rate of SLR, negative feedbacks involving storms can allow barriers that do not drown to rebound toward steady‐state geometries within decades after management practices cease. Plain Language Summary: Barrier islands and spits (collectively referred to as "barriers") can naturally keep up with sea‐level rise primarily through a process called overwash. During overwash, sand from the beach is washed landward past the dunes by storm waves, leading to increases in barrier height (elevation) and width. Tall dunes, built to protect roadways and oceanfront properties, prevent overwash from elevating the existing barrier landscape. Here we use a new model to show that over many decades to centuries, an unintended consequence of rebuilding tall dunes in the aftermath of storms, which then block future overwash, is the narrowing and lowering of barriers relative to sea level. In some cases, this leads to complete drowning of the barrier interior. In other cases, once humans stop rebuilding dunes, the landscape recovers in as little as a few decades. Key Points: Counterintuitively, with higher dune design heights and lower/wider initial barrier geometries, barriers become uninhabitable soonerRandomness in dune‐storm interactions dictates whether or not a barrier drowns after management ceasesSimulations suggest barrier systems can recover in height, width, and cross‐shore position quickly (within decades) after management ceases [ABSTRACT FROM AUTHOR]

Detecting and attributing sea‐level rise over different spatiotemporal scales is essential for low‐lying and highly populated coastal regions. Using the Detection and Attribution Model Intercomparison Project (DAMIP) from the Coupled Model Intercomparison Project Phase 6, we evaluate the role of anthropogenic forcing in sea‐level change in the historical (1950–2014) period in the Indo‐Pacific warm pool region. We use three models that have at least 10 ensemble members, corresponding to different DAMIP simulations. We determined the changes in regional sea level from both natural and anthropogenic forcings. Our results demonstrate: (a) the emergence of an anthropogenic footprint on regional sterodynamic sea‐level change has a large spatiotemporal diversity over the Indo‐Pacific warm pool region with the earliest emergence in the western Indian Ocean; (b) a significant rise in dynamic sea level (DSL) (up to 25 mm) and thermosteric (up to 40 mm) sea level over the western Indian Ocean due to greenhouse gas forcing; (c) a positive Indian Ocean Dipole‐like pattern in the DSL changes over the tropical Indian Ocean; (d) a significant increase in the halosteric contribution to sea‐level rise in the Indo‐Pacific warm pool region, and (e) a pronounced rise of manometric sea level (up to 20 mm) over shallow oceans and coastal regions in recent decades. These results provide a comprehensive spatiotemporal analysis of the attribution of anthropogenic factors to sea‐level changes in the Indo‐Pacific warm pool region. Plain Language Summary: Various natural and human‐induced factors contribute to sea‐level change, but separating their distinct impacts on a regional to local scale remains challenging. Here we use computer model simulations of global climate to detect and attribute historical sea‐level changes (1950–2014) in the Indo‐Pacific warm pool region to anthropogenic greenhouse gas and aerosol forcing versus natural forcing. We discovered that the historical rise in sea level is predominantly driven by the influence of greenhouse gases, although aerosols tend to moderate the rate of rise. Notably, the rate of sea‐level rise and the time of emergence of anthropogenic signals vary spatially in the region. As an example, anthropogenic signals emerged earlier in the western Indian Ocean in the twentieth century than in the eastern Indian Ocean. Sea‐level rise in the deeper oceans of the Indo‐Pacific warm pool region is primarily governed by changes in ocean temperature (termed thermosteric) and salinity (halosteric). Conversely, in shallow regions such as over the maritime continent and continental shelves, sea‐level rise is primarily a consequence of a local increase in ocean mass (manometric). Our study provides a better understanding of the attribution of regional sea‐level changes in the recent past and their possible implications for the future. Key Points: Historical sea‐level changes in the Indo‐Pacific warm pool region are attributed using large‐ensemble climate model simulationsThe role of greenhouse gas forcing on historical sea‐level changes is dominant, but the time of emergence varies regionallyTropical Indian Ocean dynamics played a key role in controlling historical sea‐level changes in the Indo‐Pacific warm pool region [ABSTRACT FROM AUTHOR]

India has good reasons to be concerned about climate change as it could adversely affect the achievement of vital national development goals related to socio-economic development, human welfare, health, energy availability and use, and infrastructure. The paper attempts to develop a framework for integrated impact assessment and adaptation responses, using a recently built railroad coastal infrastructure asset in India as an example. The framework links climate change variables — temperature, rainfall, sea level rise, extreme events, and other secondary variables — and sustainable development variables — technology, institutions, economic, and other policies. The study indicates that sustainable development variables generally reduce the adverse impacts on the system due to climate change alone, except when they are inadequately applied. The paper concludes that development is a vital variable for integrated impact assessment. Well crafted developmental policies could result in a less-GHG intensive future, enhanced adaptive capacities of communities and systems, and lower impacts due to climate change. [ABSTRACT FROM AUTHOR]

Evaluating shoreline retreat rate (SRR) on different spatial‐temporal scales is critical for effective coastal management. Large‐scale evaluations typically rely on data‐driven methods such as Discrete Bayesian networks (BNs). However, these BNs require discretization of continuous variables which can lead to information loss. Here, we propose a new method, the Hybrid BN to incorporate continuous variables without discretization. Both Discrete and Hybrid BNs were developed and compared to evaluate large‐scale (continental scale) SRR in Australia, using Digital Earth Australia data set. These BNs used forcing parameters (e.g., waves, tide, sediment sink/source, and sea level rise [SLR]) and geomorphic settings (e.g., geomorphology, backshore profile, and surfzone slope) to predict SRR. Validation of the BNs showed that Hybrid BNs, which provide a more realistic assessment of the range of SRR, outperform in predicting continuous variables, when compared with Discrete BNs. However, Discrete and Hybrid BNs provide consistent qualitative findings for the SRR of Australia. Among forcing parameters, the sediment sink/source was found to be the most informative variable to indicate the shoreline retreat, followed by tide, SLR rate, and wave processes. In the scenario of an increased SLR rate, tropical tidal flats were predicted as the most at risk coasts in Australia. We found that BNs can reflect the impact of different factors on coastal evolution, and predict future shoreline change by exploring historical data. The performance of these models can be further improved when more data sets become available. Key Points: Hybrid Bayesian networks outperform discrete ones in predicting continuous shoreline retreatThe distance to inlets is the most significant in determining shoreline retreat rate, followed by tidal impacts and sea level rise (SLR)In Australia, tropical tidal flats are the most sensitive coasts to the increase in SLR rate [ABSTRACT FROM AUTHOR]

Denmark has been subject to complex interactions of isostatic uplift and eustatic sea level changes since the last deglaciation. Prominent coastal beach ridges as well as lagoonal and lake deposits from this period have been investigated at a number of sites in the region to constrain the relative sea level (RSL) changes. However, despite the common occurrence of former coastal lagoons and lakes in proximity to raised beach ridges, they have rarely been studied in combination. In this study, we use a multiproxy approach including geospatial data, lake sediment coring, ground penetrating radar and optically stimulated luminescence dating to investigate the Holocene coastal evolution and RSL history at Rugård in Mols Bjerge National Park, on the east coast of the Jutland Peninsula. Our results show that the coastal area at Rugård was transgressed between c. 7.6 and 7.0 cal. ka BP and that RSL was ~4.5 m higher than present between c. 6.6 and 5.9 ka ago, when the highest section of the beach ridge plain was deposited. The elevation and timing of this relative highstand are in good agreement with previous estimates of the Littorina transgression and contribute to our combined knowledge about RSL history and coastal evolution in the southern Kattegat. Subsequently, isostatic adjustment has caused uplift and erosion of the beach ridge plain, but renewed progradation and deposition of a lower beach plain have taken place since c. 1740 CE. Our results demonstrate the value of using a multiproxy approach to study RSL changes and coastal evolution. [ABSTRACT FROM AUTHOR]

The Hirnantian period, making the end of the Ordovician with significant mass extinctions and large ice‐sheets, is a critical interval for studying paleoclimate variations. This research represents the first cyclostratigraphic study of this period, utilizing high‐resolution (1 mm sampling rate) geochemical data from the ∼7‐m thick SH‐1 drill core, capturing the latest Ordovician glaciation. Our analysis identifies the presence of Milankovitch cycles with periods of 17–21, ∼33, and ∼100‐kyr, suggesting an optimal sedimentation rate of 3.1 m/Myr. Notably, we detected signals of millennial‐scale variability, aligning with the ∼1.5‐kyr Dansgaard‐Oeschger and ∼2.4‐kyr Hallstatt heliomagnetic cycles, even in deposits lacking visible laminae alternation. This finding bolsters the hypothesis of an external origin for these millennial‐scale features. Additionally, our reconstruction of sea‐level variations, using principal component analysis and sedimentary noise modeling, reveals two intervals of sea‐level fall and one sea‐level rise, linked to an astronomical forcing cycle of ∼1.2‐Myr. The obliquity band power‐total power ratios correspond to ∼1.2‐Myr periodicities for s4‐s3 term. The synchronization of ∼1.2‐Myr cycle minimum with a sea‐level drop (low PC1 value) suggests that glacio‐eustatic variations were influenced by ∼1.2‐Myr obliquity modulation cycles. This research enhances our understanding of glacio‐eustasy during the latest Ordovician from an astronomical perspective, offering valuable insights into the interplay between orbital cycles and Earth's paleoclimate. Key Points: Millennial‐scale cycles have been detected based on five high‐resolution proxy seriesMillennial‐scale cycle preserved in the Hirnantian was linked to the D‐O and Hallstatt cycle∼1.2‐Myr PC1 filter revealed one rise and two falls of sea‐level during Hirnantian [ABSTRACT FROM AUTHOR]

Melt rates at the base of Antarctic ice shelves are needed to drive projections of the Antarctic ice sheet mass loss. Current basal melt parameterizations struggle to link open ocean properties to ice‐shelf basal melt rates for the range of current sub‐shelf cavity geometries around Antarctica. We present a proof of concept exploring the potential of simple deep learning techniques to parameterize basal melt. We train a simple feedforward neural network, or multilayer perceptron, acting on each grid cell separately, to emulate the behavior of circum‐Antarctic cavity‐resolving ocean simulations. We find that this kind of emulator produces reasonable basal melt rates for our training ensemble, at least as close as or closer to the reference than traditional parameterizations. On an independent ensemble of simulations that was produced with the same ocean model but with different model parameters, cavity geometries and forcing, the neural network yields similar results to traditional parameterizations on present conditions. In much warmer conditions, both traditional parameterizations and neural network struggle, but the neural network tends to produce basal melt rates closer to the reference than a majority of traditional parameterizations. While this shows that such a neural network is at least as suitable for century‐scale Antarctic ice‐sheet projections as traditional parameterizations, it also highlights that tuning any parameterization on present‐like conditions can introduce biases and should be used with care. Nevertheless, this proof of concept is promising and provides a basis for further development of a deep learning basal melt parameterization. Plain Language Summary: A warmer ocean around Antarctica leads to higher melting of the floating ice shelves, which influence the ice loss from the Antarctic ice sheet and therefore sea‐level rise. In computer simulations of the ocean, these ice shelves are often not represented. For simulations of the ice sheet, so‐called parameterizations are used to link the oceanic properties in front of the shelf and the melt at their base. We show that this link can be emulated with a simple neural network, which performs at least as well as traditional physical parameterizations both for present and much warmer conditions. This study also proposes several potential ways of further improving the use of deep learning to parameterize basal melt. Key Points: We show that simple neural networks produce reasonable basal melt rates by emulating circum‐Antarctic cavity‐resolving ocean simulationsPredicted melt rates for present and warmer conditions are similar or closer to the reference simulation than traditional parameterizationsWe show that neural networks are suited to be used as basal melt parameterizations for century‐scale ice‐sheet projections [ABSTRACT FROM AUTHOR]

We produce projections of global mean sea‐level rise to 2500 for low and medium emissions scenarios (Shared Socioeconomic Pathways SSP1‐2.6 and SSP2‐4.5) relative to 2020, based on extending and combining model ensemble data from current literature. We find that emissions have a large effect on sea‐level rise on these long timescales, with [5, 95]% intervals of [0.3, 4.3]m and [1.0, 7.6]m under SSP1‐2.6 and SSP2‐4.5 respectively, and a difference in the 95% quantile of 1.6 m at 2300 and 3.3 m at 2500 for the two scenarios. The largest and most uncertain component is the Antarctic ice sheet, projected to contribute 5%–95% intervals of [−0.1, 2.3]m by 2500 under SSP1‐2.6 and [0.0, 3.8]m under SSP2‐4.5. We discuss how the simple statistical extensions used here could be replaced with more physically based methods for more robust predictions. We show that, despite their uncertainties, current multi‐centennial projections combined into multi‐study projections as presented here can be used to avoid future "lock‐ins" in terms of risk and adaptation needs to sea‐level rise. Plain Language Summary: Sea levels are predicted to rise for hundreds to thousands of years, even if emissions are reduced. Decisions about how to adapt to more frequent and severe coastal flooding need predictions showing a range of possible futures. However, few computer modeling studies of the contributing factors to sea level rise extend as far as the year 2300, and few to 2500. We present illustrative predictions of global mean sea level rise for low and medium emissions scenarios to 2500 by combining previous modeling studies and extending them where necessary. We take the widest possible range when combining studies, to show many possible futures. Predictions for global average sea level rise are 0.3–4.3 m at 2500 for the low emissions scenario, where global warming stays below around 2°C. Under medium emissions, where long‐term warming is predicted to be around 2–5°C, the predictions are around double this: from 1.0 to 7.6 m. Our aim is to outline possible long‐term futures based on physical understanding, so decision‐makers can analyze potential implications for society and avoid making decisions that are difficult to change later. We describe some potential applications of our projections, as well as key knowledge gaps and future research directions. Key Points: Projections of global mean sea‐level rise to 2500 have [5, 95]% intervals of [0.3, 4.3]m under SSP1‐2.6 and [1.0, 7.6]m under SSP2‐4.5The most uncertain sea‐level contributor continues to be the Antarctic ice sheet, with multiple studies considered to build a projectionDespite the uncertainties, our projections can be used to analyze their societal implications and recognize and potentially avoid lock‐ins [ABSTRACT FROM AUTHOR]

The impacts on the Australian coast of a changing climate include environmental and property damage arising from increased frequency and severity of coastal weather events, storm surge, coastal erosion, and coastal flooding. Coastal management policies and planning laws are often relied upon to manage both the impacts and competing interests in the coast. The existence of these policies and laws, and their interpretation by the courts, bears a weight of expectation upon them to deliver in the face of climate change which merits further consideration. Indeed, a rich field is open from which to consider the constitution and construction of law in and across different places, in the context of climate change adaptation. The Australian coast is a unique and locally specific context from which to explore the relationship between law and place as performed in the Vaughan litigation, and this paper considers such important potential as it gains expression in the Vaughan litigation. © 2016 Institute of Australian Geographers [ABSTRACT FROM AUTHOR]

Using high‐frequency tide gauge observations from 1980 to 2017, we analyzed changes in extreme sea levels (ESLs) along the Chinese coast to examine whether extreme sea‐level rise acceleration could be observed. The results indicated that the ESL has risen with fluctuations along the Chinese coast. The ESL also featured significant decadal variabilities. The ESL rise was accelerated at most tide gauges throughout the whole study period, especially after the 1980s, while the acceleration patterns varied with station location. The mean sea level (MSL) change was confirmed as the major driver of the ESL change according to the analysis. However, the skew surge may also have affected the extremes at many of the tide gauges, which was observed after detrending. The extreme/MSL had a significant positive correlation with the Atlantic Multidecadal Oscillation, which is supposed to affect the MSL through a combination of variation in sea surface temperature, pressure system, and wind. That sea level oscillation is dominated by Atlantic Multidecadal Oscillation should be taken into consideration when studying accelerations in the rate of ESLs and of MSLs along the Chinese coast. Key Points: The acceraction of the extreme sea level along the Chinese coast is analyzed in the paper for the first timeWe found that the Atlantic Multidecadal Oscillation (AMO) significantly affect the mean sea levels and extreme sea levels along the Chinese coast [ABSTRACT FROM AUTHOR]

Due to their choked geometry, coastal lagoons can attenuate extreme water levels compared to the open sea. However, this protective property is expected to decrease due to sea‐level rise. By studying idealized lagoons in a non‐dimensional parameter space, this study describes non‐linear interactions between tides, storm surges, freshwater fluxes into the lagoon, and sea‐level rise. The non‐dimensional numbers include lagoon geometry and forcing scales. The main objective is to provide an overview of potentially affected lagoons and to highlight the importance of attenuation changes due to sea‐level rise. Tidal and storm surge induced maximum water levels inside lagoons rise faster than sea‐level rise for most of the parameter space. Maximum water levels due to freshwater fluxes rise slower than sea‐level rise for strongly choked lagoons. For compound events, the response between rising faster or slower than sea‐level rise depends strongly on the lagoon geometry. Plain Language Summary: Coastal lagoons are known to reduce extreme water levels compared to the open sea due to their narrow and shallow connections to the ocean. However, the rising mean sea level will decrease this protective property. In this study, we investigate lagoons using a simple box model to explore how combinations of tides, storm surges, river discharge, and sea‐level rise will change water levels inside lagoons. The study aims to provide an overview of potentially affected lagoons and to highlight the importance of these processes. Due to sea‐level rise, water from the ocean can more easily flow into the lagoon. Therefore, our results show that maximum water levels inside a lagoon can rise faster than sea‐level rise. On the other hand, river discharge can exit the lagoon more easily at the same time. For this case, water levels inside a lagoon rise slower than sea‐level rise. For events where tides, storm surges, and river discharge are all present, the maximum water level may rise either slower or faster than sea‐level rise, depending on the properties of the lagoon. Further studies are needed to understand the implications for coastal communities. Key Points: Tides, storm surges, freshwater fluxes, and sea‐level rise interact non‐linearly on the water level in choked coastal lagoonsMaximum water levels inside choked lagoons can increase faster than sea‐level rise due to non‐linear attenuation changesMaximum water levels due to freshwater fluxes increase slower than sea‐level rise [ABSTRACT FROM AUTHOR]

Eustatic sea level changes and vertical tectonic movements are producing uplifted paleoshorelines. Along subduction zones, uplifted terraces are used to study fault activities and, overall, allow to interpret the tectonic history of plate convergence. Northeastern Oman is experiencing plate convergence following the late Cretaceous obduction of the Semail Ophiolite. Post-obduction shallow-marine carbonates have been uplifted to different elevations from 133 to >2,000 m. The present study employs a multidisciplinary approach to elucidate the variability in relief and to introduce a geodynamic model that extends beyond the temporal constraints imposed by the late Quaternary age of the sediments found on the uplifted terraces. Stratigraphic and fault analyses produced a post-obductional geodynamic model to advance the existing regional models in the framework of the subduction of the Arabian Plate in the Makran Zone. In addition, we rely on imaging geodesy, geomorphology and dating to explain the late Quaternary uplift scenario. Overall, analyses of geomorphology, stratigraphy, and fault patterns reveal spatially heterogeneous post-late Cretaceous uplift in the region. Compartmentalization by major faults created individual blocks and relief variability. Within the timeframe of marine terrace formation (late Quaternary), we also observed spatially varied displacements. Ground displacements by Interferometric Synthetic Aperture Radar document an ongoing spatial heterogenous uplift at approximately 1.3 mm/a. Finally, temporal variability was evident during the late Quaternary by unusually high late Pleistocene (<40 ka) uplift rates averaging ≥2 mm/a in younger terraces, while for older terraces (>40 ka) the uplift rate is distinctly lower (<1 mm/a). [ABSTRACT FROM AUTHOR]

Earthquake‐driven subsidence can cause cascading hazards at the coast by exacerbating relative sea level rise, storm surges, tsunami, and tidal flooding. At Ahuriri Lagoon near Napier, Aotearoa New Zealand, paleoseismic uplift and subsidence are typically attributed to upper plate faults and subduction interface earthquakes, respectively. We test this assumption with elastic dislocation models of upper plate and subduction interface earthquakes informed by historical events, seismic surveys, and modern interface coupling data. We compared our surface deformation results to paleoseismic records preserved at Ahuriri Lagoon, which includes eight rapid subsidence (c. 0.5–1.2 m) and two rapid uplift events over the last c. 7 kyr. Our models demonstrate that offshore upper plate faults could cause subsidence of c. 0.5–1 m at Ahuriri Lagoon at recurrence intervals of c. 2 kyr. A range of subduction interface earthquakes can also produce subsidence at Ahuriri Lagoon, and may explain larger (>1 m) subsidence, but must rupture the currently creeping (i.e., aseismic) portions of the interface. We demonstrate that both upper plate fault and subduction interface earthquakes may have contributed to the Ahuriri Lagoon records, and that interface coupling may be more spatially or temporally heterogeneous than modern geodetic data suggest. Models of sea‐level rise and earthquake multi‐hazards that do not include the effects of upper plate faulting may mischaracterize risk at the coast. Plain Language Summary: Earthquakes can cause land to uplift or subside. If land subsides along the coastline, it becomes more susceptible to flooding, storm waves, tsunami, and ongoing sea level rise. The geologic record at Ahuriri Lagoon near Napier, New Zealand, shows that earthquakes have caused subsidence of at least 0.5 m many times over the last 7,000 years. We modeled how earthquakes on different faults, such as the subduction zone or smaller crustal faults above it, would vertically move the coastline. We found that both types of earthquakes have likely caused subsidence at Ahuriri Lagoon, which differs from past interpretations that focus mainly on subduction zone earthquakes. Additionally, the subduction earthquakes that cause subsidence at Ahuriri Lagoon are not in the expected location based on modern instrumental data. Therefore, future hazard models may need to take into account a broader range of earthquake source faults and more complex earthquake scenarios. Key Points: Elastic dislocation modeling shows that listric upper plate faults can cause coastal coseismic subsidence above the down‐dip rupture limitCoseismic subsidence at a key site (Ahuriri Lagoon, central Hikurangi margin) can be caused by both upper‐plate and subduction earthquakesSubduction seismic cycle interpretations using coseismic uplift and subsidence records should consider the influence of upper plate faults [ABSTRACT FROM AUTHOR]

In the coming decades, coastal flooding will become more frequent due to sea‐level rise and potential changes in storms. To produce global storm surge projections from 1950 to 2050, we force the Global Tide and Surge Model with a ∼25‐km resolution climate model ensemble from the Coupled Model Intercomparison Project Phase 6 High Resolution Model Intercomparison Project (HighResMIP). This is the first time that such a high‐resolution ensemble is used to assess changes in future storm surges across the globe. We validate the present epoch (1985–2014) against the ERA5 climate reanalysis, which shows a good overall agreement. However, there is a clear spatial bias with generally a positive bias in coastal areas along semi‐enclosed seas and negative bias in equatorial regions. Comparing the future epoch (2021–2050) against the historical epoch (1951–1980), we project ensemble‐median changes up to 0.1 (or 20%) in the 1 in 10‐year storm surge levels. These changes are not uniform across the globe with decreases along the coast of Mediterranean and northern Africa and southern Australia and increases along the south coast of Australia and Alaska. There are also increases along (parts) of the coasts of northern Caribbean, eastern Africa, China and the Korean peninsula, but with less agreement among the HighResMIP ensemble. Information resulting from this study can be used to inform broad‐scale assessment of coastal impacts under future climate change. Plain Language Summary: In the next few decades, coastal flooding is expected to become more frequent due to rising sea levels and changes in storms. To understand and prepare for these changes, we use a global hydrodynamic and multiple climate models to investigate how storm surges (a temporarily rise in water level during a storm) will respond to a warmer climate. These are the first global projections of storm surges based on highly detailed climate models (25–50 km). We compare the model output for recent years (1985–2014) with real‐world weather data, known as reanalysis data, and find a good overall agreement. However, the comparison also shows relatively large differences with larger or smaller values in certain areas. For the future (2021–2050), results show storm surge changes up to 20%. These changes vary around the world. Some areas (Mediterranean, northern Africa, and southern Australia) might experience lower storm surges, whereas other areas (South Australia, Alaska, the northern Caribbean, eastern Africa, China, and the Korean Peninsula) might experience higher storm surges. By using advanced computer models as done here, we are able to better understand how climate change could impact coastal area and thus make informed decisions for the future. Key Points: Storm surge projections from 1950 to 2050 based on the Global Tide and Surge Model and a ∼25 km‐resolution High Resolution Model Intercomparison Project climate model ensembleValidation against ERA5 reanalysis (1985–2014) shows that the model performs well globally, but also reveals a clear spatial biasThe median‐ensemble change of the 1 in 10‐year storm surge levels from 2021–2050 compared to 1951–1980 shows changes up to 0.1 m or 20% [ABSTRACT FROM AUTHOR]

Most of the US Gulf Coast is composed of barrier islands, peninsulas, chenier plains, and mainland beaches that are the main line of defense for wetlands, estuaries, and urban and industrial centers from rising sea level and severe storms. These wave‐dominated shorelines are currently experiencing widespread erosion. Using newly acquired and existing results from 13 sites spanning south Florida to south Texas, we compare shoreline migration rates during the late Holocene (∼−4000 to 1850 CE) with historical changes since the mid‐19th century. The records show an overall trend of seaward growth during the late Holocene followed by landward migration or a decrease in the rate of growth during historical time. Diminishing offshore sand supply, human alteration of rivers and coastal sand transport, and severe storms have contributed to this change in shoreline trajectory, but their influence has been mostly limited in extent. The most likely cause of this reversal from coastal stability and growth to widespread shoreline retreat is the dramatic historical increase in the rate of sea‐level rise over the past century. Plain Language Summary: Future shoreline positions are difficult to predict because of the many natural and anthropogenic stressors that influence erosion and accretion over various spatial and temporal scales. This study provides documentation of a regime shift in coastal barrier evolution from stability or growth over the previous few thousand years to nearly ubiquitous erosion in historical time. Declining sediment supply, severe storms, and human alterations to the coast contributed to this change, but the Gulf‐wide extent of coastal change is mainly a result of historical acceleration of sea‐level rise. Management practices will need to adapt to this new state of continuous coastal retreat as the rate of sea‐level rise will continue to increase in the future. Key Points: Data from 13 sites across the Gulf Coast quantify shoreline migration rates during the late Holocene relative to historical timeShoreline growth during the late Holocene transitioned to landward migration or a decrease in the rate of growth during historical timeThis reversal from coastal stability and growth to widespread shoreline retreat is likely due to historical accelerated sea‐level rise [ABSTRACT FROM AUTHOR]

Sea‐level rise (SLR) will cause coastal groundwater to rise in many coastal urban environments. Inundation of contaminated soils by groundwater rise (GWR) will alter the physical, biological, and geochemical conditions that influence the fate and transport of existing contaminants. These transformed products can be more toxic and/or more mobile under future conditions driven by SLR and GWR. We reviewed the vulnerability of contaminated sites to GWR in a US national database and in a case comparison with the San Francisco Bay region to estimate the risk of rising groundwater to human and ecosystem health. The results show that 326 sites in the US Superfund program may be vulnerable to changes in groundwater depth or flow direction as a result of SLR, representing 18.1 million hectares of contaminated land. In the San Francisco Bay Area, we found that GWR is predicted to impact twice as much land area as inundation from SLR, and 5,282 additional state‐managed sites of contamination may be vulnerable to inundation from GWR in a 1.0 m SLR scenario. Increases of only a few centimeters of elevation can mobilize soil contaminants, alter flow directions in a heterogeneous urban environment with underground pipes and utility trenches, and result in new exposure pathways. Pumping for flood protection will elevate the saltwater interface, changing groundwater salinity and mobilizing metals in soil. Socially vulnerable communities are disproportionately exposed to this risk at both the national scale and in a regional comparison with the San Francisco Bay Area. Plain Language Summary: We estimated the number of sites with known contamination in the US Superfund program at the national scale and found 326 Superfund sites that may be exposed to inundation from below as rising sea levels push groundwater higher along the coast. California, North Carolina, Virginia, and New York have the largest area of federally managed contaminated land that may be exposed. Thousands of additional sites are managed by state agencies. We conducted a comparison in the San Francisco Bay Area that included state‐managed sites. We found that more than 5,000 sites in the San Francisco region may be exposed to rising groundwater with sea‐level rise (SLR) of 1.0 m, including 1,480 open sites, and an additional 3,817 closed sites that may contain residual contaminants. If the ratio of Superfund to state‐managed sites in this region (1:406) holds, the number of at‐risk contaminated sites nationally may be more than 132,000. Low‐income residents and people of color are disproportionately represented near these sites and therefore may face higher risks. Additional sub‐regional research is urgently needed to understand these exposures. Interactions will occur between the salinity of rising coastal groundwater and shallow pumping, affecting infrastructure and building foundations. Adaptation plans must consider rising groundwater to avoid widespread failures. Key Points: Rising sea levels will cause rising groundwater to inundate some coastal contaminated sites, mobilizing pollutants and causing corrosionWe found 326 Superfund sites that may be at risk nationally, and more than 5,000 state managed sites in a San Francisco Bay area comparisonSocially vulnerable communities are disproportionately exposed to this hazard, with potential impacts on indoor air, foundations and infrastructure [ABSTRACT FROM AUTHOR]

Globally, sea-level rise is expected to impact on many coastal regions and settlements. While mitigation of global greenhouse gas emissions remains an important task, adaptation is now seen as a critical component of the policy equation. Local government is a key player in adaptation planning and managing risk through their mandated role in land use planning and development control. Yet, managing the predicted impacts of climate change is proving to be a complex and difficult task for planners and policy makers. This paper reports on a case of local government deliberation on possible planning responses to address future sea-level rise impacts in New South Wales, Australia. Using structured, expert opinion of planners and other technical experts engaged in a collaborative network in the Sydney region, we explore the feasibility of implementing planning and policy measures at the local and regional scales to respond to inundation risk as a result of sea-level rise and storm surge events. Our research shows how local governments employ specific scale-oriented strategies to engage private and public actors at different scales to manage legal, financial, and technical risks in coastal adaptation. [ABSTRACT FROM AUTHOR]

Baeteman, C., Waller, M. & Kiden, P. 2011: Reconstructing middle to late Holocene sea-level change: A methodological review with particular reference to 'A new Holocene sea-level curve for the southern North Sea' presented by K.-E. Behre. Boreas, 10.1111/j.1502-3885.2011.00207.x. ISSN 0300-9483. A number of disciplines are involved in the collection and interpretation of Holocene palaeoenvironmental data from coastal lowlands. For stratigraphic frameworks and the assessment of relative sea-level (RSL) change, many non-specialists rely on existing regional models. It is, however, important that they are aware of major developments in our understanding of the factors controlling coastal change and of the potential sources of error in sea-level reconstructions. These issues are explored through a critical evaluation of a new sea-level curve presented by for the southern North Sea. In contrast to most sea-level curves published from this region over the last 20 years, the curve shows strong fluctuations that are interpreted as representing vertical movements of sea level. We present a detailed examination of the data used by Behre. From this analysis it is clear that many of the data points used are unsuitable for high-resolution (centimetre or decimetre) sea-level reconstruction. This paper also gives an overview of possible sources of error with respect to the age and altitude of sea-level index points and of changes in our understanding of the processes that underpin the interpretation of the organic and occupation levels used as index points. The constraints on the spatial scale over which sea-level reconstructions can be applied (changes in palaeotidal range and crustal movements) are also considered. Finally, we discuss whether the large-amplitude centennial-scale sea-level fluctuations proposed by Behre can be reconciled with the known mechanisms of sea-level change and other recent high-resolution studies from this region. We conclude that such fluctuations are highly unlikely to be real features of the sea-level history of the southern North Sea. [ABSTRACT FROM AUTHOR]

Understanding past sea levels is essential to respond to the challenges of climate change. In the Pacific and Tasman, sea level has been up to 1.5 m higher during the mid-Holocene, similar to the predictions of some global warming models. Within New Zealand the knowledge of sea-level movements, especially during the recent past is poor, with the last major investigation being conducted 20 years ago. This paper reviews the state of local understanding of higher sea levels and suggests regions for further study and new methods of analysis to understand the nature of sea-level change in New Zealand. [ABSTRACT FROM AUTHOR]

Recent research suggests that over 75% of resources extracted globally now go toward creating, maintaining, or operating material stocks (MS) to provide societal services like housing, transport, education, and health. However, the integrity of current and future built environments, and the capacity of the system to continue providing services, are threatened by extreme events and sea‐level rise (SLR). This is especially significant for the most disaster‐prone countries in the world: Small Island Developing States. In the aftermath of disasters, complex rebuilding efforts require substantial material and economic resources, oftentimes incurring massive debt. Understanding the composition and dynamics of MS and environmental threats is essential for current and future sustainable development. Drawing on open‐source OpenStreetMap (OSM) data, we conducted a spatially explicit material stock analysis (MSA) for The Bahamas for 2021, where we included buildings and transport MS, and SLR exposure scenarios. Total MS was estimated at 76 million tonnes (Mt) or 191 tonnes per capita (t/cap) of which transport comprises 43%. These MS are likely to increase by 36 Mt in the future. Simulations show that under 1‐, 2‐, or 3‐m SLR scenarios, around 4, 6, and 9 Mt of current MS will be exposed, with transport MS at greatest risk, with over 80% of total exposure in each scenario. Our findings highlight the critical role that key MS play in sustainability and resilience, contributing to the emphasis on effective development planning and climate change adaptation strategies, and to the exploration of the use of OSM data for studying these objectives. [ABSTRACT FROM AUTHOR]

This study presents the first detailed description of the upper sedimentary succession of the late Pleistocene and Holocene deposits in the Gulf of San Jorge (Patagonia) based on several hundred kilometers of high‐resolution seismic (sparker) profiles and numerous sediment cores. High‐resolution seismic stratigraphy confirms the existence of a paleo‐fluvial network formed during sea‐level lowstands and buried by central basin estuarine deposits during the last marine transgression. Analyses of lithostratigraphy and radiocarbon ages indicate the onset of subtidal sedimentation at ~14 cal ka bp. Before the onset of subtidal conditions, the first steps of marine incursion seem to have led to the development of lagoonal/wind–tidal flat environments, advocating for a sea‐level stillstand. An abrupt increase in the log(Ti/Ca) ratio in a distinct multi‐centimeter‐thick layer and the identification of a wave‐ravinement surface suggest rapid sea‐level rise in the gulf prior to ~14 cal ka bp, consistent with Meltwater Pulse 1A. Overall, this study highlights the significant impact of sea‐level rise on sedimentation in the gulf from the onset of marine incursions to the mid‐Holocene, as well as the reduced contribution, as currently observed, of riverine inputs due to the progressive diminution and withdrawal of glacial drainage starting before the Holocene. [ABSTRACT FROM AUTHOR]

Satellite‐derived shoreline observations combined with dynamic shoreline models enable fine‐scale predictions of coastal change across large spatiotemporal scales. Here, we present a satellite‐data‐assimilated, "littoral‐cell"‐based, ensemble Kalman‐filter shoreline model to predict coastal change and uncertainty due to waves, sea‐level rise (SLR), and other natural and anthropogenic processes. We apply the developed ensemble model to the entire California coastline (approximately 1,760 km), much of which is sparsely monitored with traditional survey methods (e.g., Lidar/GPS). Water‐level‐corrected, satellite‐derived shoreline observations (obtained from the CoastSat toolbox) offer a nearly unbiased representation of in situ surveyed shorelines (e.g., mean sea‐level elevation contours) at Ocean Beach, San Francisco. We demonstrate that model calibration with satellite observations during a 20‐year hindcast period (1995–2015) provides nearly equivalent model forecast accuracy during a validation period (2015–2020) compared to model calibration with monthly in situ observations at Ocean Beach. When comparing model‐predicted shoreline positions to satellite‐derived observations, the model achieves an accuracy of <10 m RMSE for nearly half of the entire California coastline for the validation period. The calibrated/validated model is then applied for multi‐decadal simulations of shoreline change due to projected wave and sea‐level conditions, while holding the model parameters fixed. By 2100, the model estimates that 24%–75% of California's beaches may become completely eroded due to SLR scenarios of 1.0–3.0 m, respectively. The satellite‐data‐assimilated modeling system presented here is generally applicable to a variety of coastal settings around the world owing to the global coverage of satellite imagery. Plain Language Summary: We present a computer model to predict shoreline change due to waves, sea‐level rise (SLR), and other local processes. We apply the model to the entire California coastline (approximately 1,760 km), much of which is not well monitored using traditional survey methods. Observations of historical shoreline position obtained from satellite images can be used in lieu of traditional shoreline survey data to estimate erosion/accretion trends as well as to calibrate and validate models. By 2100, the model estimates that 24%–75% of California's beaches may become completely eroded due to SLR scenarios of 1.0–3.0 m, respectively. Key Points: We assimilate a large‐scale, ensemble shoreline‐change model with observations of shoreline position derived from Landsat satellitesSatellite‐derived shoreline observations perform similarly to in situ observations for calibrating and validating shoreline modelsThe model estimates that, without interventions, 24%–75% of California's beaches may be completely eroded by 2100 due to future sea‐level rise [ABSTRACT FROM AUTHOR]

High‐quality subsurface data provide new insights into the formation of Oak Ridges Moraine (ORM), an ~80 km3 sequence of stratified meltwater deposits resting >200 m above adjacent Lake Ontario. The ORM sedimentary succession comprises a three‐part regional architecture: (i) ~north–south channel sand–gravel; (ii) channel‐capping rhythmites; and (iii) east–west ridge sediments. The ORM depositional sequence overlies a regional unconformity with a cross‐cutting channel network resulting from ~north–south meltwater floods that transitioned progressively (falling stage) from a ~NNE to ENE flow direction (parallels Lake Ontario depression). Seismic profiles delineate the channels and channel fill characteristics of bank‐to‐bank channel sedimentation of thick gradational gravel–sand–mud sequences. Channel‐capping mud (~100–236 rhythmites) within multiple channels beneath the ORM landform mark a widespread interval of low‐energy, seasonally controlled subglacial pond deposition. During this quiescent period ice‐sheet thickness adjusted to flood‐induced stretching/thinning and re‐profiled slopes. New ice gradients led to east–west flow and deposition of the overlying third element, a sequence of high‐energy confined esker–fan sediments along ORM ridge. Close, sequential timing (~329 varve years) of channel, basin and ridge‐forming architectural elements supports naming this assemblage the ORM formation. Proposed ORM floods are analogous to Icelandic jökulhlaups based on the size, geometry and sedimentology. The observed rhythmite interval between flood events represents a short period (~236 years) of regional meltwater storage prior to east–west ORM flooding. The ORM channel and overlying esker‐fan sediment ridge represent two closely timed meltwater drainage events rather than formation by coalescing ice streams. The scale and timing of the ORM flood events are linked to rapid sea‐level rise, ~13.5 ka BP. This high‐resolution ORM sedimentological record may provide insights into depositional and glaciogenic controls of other large, stratified moraines. The ORM data indicate deposition in response to hydrodynamic events (outbreak floods, re‐profiled ice) rather than direct climate forcing. [ABSTRACT FROM AUTHOR]

Barataria Estuary is an economically and ecologically important estuary in coastal Louisiana, USA. Due to rapid wetland loss, extreme Mississippi River flood and drought events (e.g., the flood of 2019 and the drought of 2022), devastating storm events (e.g., Hurricane Ida in 2021), eustatic sea‐level rise (SLR), high subsidence rates, and human activities, temporal and spatial variability of salinity and temperature in the estuary is highly complex. This study comprehensively investigates environmental drivers that govern salinity and temperature dynamics, as well as the effects of a proposed large‐scale, land‐building diversion of Mississippi River water. A three‐dimensional (3D), process‐based hydrodynamic, salinity and temperature transport model system is formulated and implemented. Three different modeling domains are set up for nested computations. The model system is validated for the year 2018 against measurements of water level, salinity, and temperature. A series of numerical experiments are then carried out to quantitatively examine impacts of various environmental drivers, as well as nearshore density stratification and local baroclinic forcing. The drivers include wind, rainfall, freshwater point‐source diversion, SLR, and Mississippi River discharge. Interestingly, the analysis shows that the proposed Mid‐Barataria diversion and rainfall can cause a reduction of annual salinity up to 14 and 10 ppt, respectively. Neglecting the effect of nearshore density stratification could underestimate salinity by up to 9 ppt. The well‐mixed estuary can be adequately modeled using depth‐averaged models. However, to adequately capture proper salinity and temperature stratification, it is necessary to use 3D models for the coastal regional domain. Plain Language Summary: Salinity and temperature are essential factors for coastal ecosystems. Barataria Estuary in coastal Louisiana is a semi‐enclosed shallow estuary influenced by natural processes and human activities, which we call drivers. To investigate how various drivers affect salinity and temperature in the estuary, we developed a numerical model. Drivers considered in this study include wind, rainfall, river discharge, sea‐level rise, and diversion projects that introduce freshwater from the Mississippi River. To be sure the model performed well, we compared the model output to observed measurements of water level, salinity, and temperature in Barataria Estuary. Next, we looked at the model results with and without each driver to see how it impacted the results. We found that the most significant drivers are the proposed Mid‐Barataria diversion and rainfall. Both can cause huge salinity reductions in the middle and lower regions of the estuary. This research also showed the importance of using a three‐dimensional model, rather than a horizontal two‐dimensional model in which no changes are allowed in the water column, to capture salinity and temperature behavior in deep areas outside of barrier islands of Barataria Estuary. Key Points: Barataria salinity can be heavily influenced by the Mid‐Barataria diversion and rainfall, reduced up to 14 and 10 ppt, respectivelyNeglecting the effect of nearshore density stratification underestimates salinity in Barataria Estuary by up to 9 pptThe well‐mixed Barataria Estuary can be adequately modeled using a 2D local model, but offshore conditions need to be provided by a 3D model [ABSTRACT FROM AUTHOR]