Relative Sea-level Rise Research Articles

Florida mangrove dieback on a decadal and centennial timescales

Hurricanes are considered some of the most devastating weather phenomena, causing deaths and destruction along the coast. Mangroves are perceived as natural defenses against coastal hazards. However, mangrove gaps, known as mangrove dieback, have occurred in southwestern Florida. This study implemented a spatial-temporal analysis based on satellite, lidar and unmanned aerial vehicle (UAV) images collected along the southwestern Florida coast between Tampa and Naples from 1994 to 2020 CE, and multi-proxy analyses on sediment cores sampled from two mangrove dieback sites to determine the cause(s) of mangrove death and the implications for the sustainability of these forests. The data indicated that out of the 86 identified dieback, 78 % arose between 2004 and 2017 CE, when one tropical storm and three hurricanes made landfall on the studied coast, suggesting hurricanes as the main driver for this mangrove degradation. Multi-proxy analysis indicated mangrove expansion since ~600 cal yr BP due to relative sea-level (RSL) rise. However, hurricanes caused losses in the mangrove area between 1930 and 1950 CE, and during the last two decades in the studied sites. Ground topographic data and aerophotogrammetry revealed circular dieback with permanent ponds (~30 cm depth) inhibiting mangrove recovery. The mangrove death occurred in <3 years, with a gradual dieback expansion due to positive feedback involving physicochemical processes in the sediments. In addition, recent hurricanes increased pre-existing dieback areas. Therefore, dieback sites are vulnerability hotspots for mangroves in the face of projected RSL rise and higher frequency of intense hurricane strikes. Mangrove dieback should be monitored on a temporal (seasonal - annual) and spatial (cm-m) resolution only possible through the combination of satellite and UAV data. Integrating remote sensing and stratigraphic analysis enabled us to identify mangrove diebacks on a decadal to centennial timescale, improving our comprehension of how catastrophic weather events affect these forests.

Hydrographic restriction conditions in the Middle and Upper Yangtze region during the Early Silurian post-glacial transgression: Constraints from major, trace elemental geochemistry and Mo-TOC relationship

Redox-sensitive trace metals have not only been widely used as the proxy for palaeoredox potential due to the strong enrichments under reducing conditions but also provide critical information into water-mass properties, such as the degree of basin restriction. In order to reveal the Early Silurian post-glacial transgression hydrographic restriction conditions throughout the Middle and Upper Yangtze region, trace metal concentrations and organic geochemical data of the lower Longmaxi Formation were analyzed by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Leco combustion techniques. We analyzed the hydrographic restriction conditions and redox conditions of different depocenters, including the Southern, Eastern, and Northern Sichuan Basin depocenters and the Western Hubei Region depocenter. The sedimentary Mo-TOC relationship, MoEF-UEF covariation, and upwelling intensity suggest that the Southern, Eastern Sichuan Basin depocenters and the Western Hubei Region depocenter were deep water areas with moderate hydrographic restriction, whereas the restriction conditions of Northern Sichuan Basin depocenter was relatively weak. In addition, due to the combined effect of geographical location, connectivity with the open Qinling Ocean, and estuarine circulation, restriction degrees varied in the same depocenter. The redox proxy (Corg/P) indicated that the lower Longmaxi Formation was deposited in an anoxic water column. There are significant spatial differences in redox conditions in different depocenters and different locations within the same depocenter, which may be controlled by relative sea level rise, hydrographic restriction, and upwelling intensity. Anoxic conditions were more likely to occur in areas where water column was relatively deep and restricted. In addition, the anoxic conditions in the Northern Sichuan Basin depocenter may also associated with the strong upwelling intensity and the behavior of P cycling back to water column, which can promote the primary productivity and further maintain persistent anoxic conditions. The correlation between Corg/P and Mo/TOC indicates that, in relatively weak restriction basin, the trace elements enrichment in sediments was controlled by trace elemental concentrations in seawater. In moderate restriction basin, the trace elements enrichment was mainly controlled by redox conditions. Whereas under more reducing conditions, hydrographic restriction may tend to become the dominant factor. The application of sediment Mo-TOC relationship, MoEF-UEF covariation, and upwelling can provide insights into hydrographic restriction conditions, but the Mo/TOC relationship is limited to anoxic facies, as little trace metal accumulation could also be the consequence of oxic conditions.

Difference of Sedimentary Characteristics and Main Controlling Factors Between Platform Margin Shoal and Ramp Shoal in M Formation of A Oilfield in The Middle East

Abstract The bioclastic limestone reservoirs of M Formation in A Oilfield mainly develop in the ramp shoal and platform margin shoal, but the sedimentary characteristics, spatial distribution and main controlling factors of the two types of shoals are significantly different. Based on the data of seismic, well logging, core, casting thin sections and analytical tests, the comparative analyses of lithology, petrophysics and spatial distribution of the two types of shoals are carried out, and the control mechanism of relative sea level rise and fall and paleogeomorphology on their development is clarified. It is showed that the two types of shoals can be subdivided according to hydrodynamic conditions and bioclastic types. The platform margin shoals are dominated by grainstone and gravel limestone, and the bioclastics are mainly rudist and echinoderms. The logging curve is funnel-shaped, and the seismic is patchy distribution. In the vertical direction, the grain size of shoals becomes coarser, and the sedimentary sequence of medium energy shoal—medium-high energy shoal—high energy shoal is developed. In the horizontal direction, the facies belts of different shoals are narrow, and they are distributed quasi-layered semi-continuously around high energy shoals. The ramp shoals are dominated by packstone and grainstone, and the bioclastics are mainly non-fixed bivalves and algae. The logging curve is micro-tooth box-shaped, and the seismic is sheet distribution. In the vertical direction, the grain size change of shoals is not significant, and the sedimentary sequence of medium energy shoal—medium-high energy shoal is developed. In the horizontal direction, the facies belts of different shoals are wide, and they are distributed layered continuously around medium-high energy shoals. Relative sea level change controls the energy of sedimentary environment and the type of shoal facies, and the high position of paleogeomorphology controls the formation and distribution of high energy shoals. When the relative sea level is high and the paleogeomorphology is gentle, the ramp shoal is developed. As the relative sea level drops, the hydrodynamic condition increases, and the difference in the accumulation speed of different shoals enhances the fluctuation of the paleogeomorphology, the ramp shoal gradually transitions to the platform margin shoal. The above research can provide reference for the exploration and development of such reservoirs.

The increase of particle size shifts the biogeochemical cycle functions of mineral-associated microorganisms and weakens the mineral-associated organic carbon sink in mangrove soils.

Carbon with stable forms, such as mineral-associated organic carbon (MOC), is crucial for the sink capabilities in mangrove soils, and mineral-associated microorganisms (MMOs) are important players for the formation and metabolism of MOC. Therefore, the future successions of the MMO functions and MOC contents under the background of climate change are of value for a deeper understanding of mangrove ecology. The relative sea level rise caused by the global warming results in the increase of mangrove soil particle size (PS), which provides distinct microcosms for MMOs and MOC. However, the responses of MMO functions and MOC content to the PS increase of mangrove soils are unknown. The current study aims to reveal the succession regulations of MMO functions and their potential ecological impacts for the storages of MOC in different PS fractions, therefore widening our knowledge of future function migration and promoting the research development of mangrove.

Seasonal Temperature Distributions and Variations in Salt Marshes: Field Investigation and Numerical Simulation

AbstractSoil temperature regulates biogeochemical processes and is a key environmental factor affecting salt marsh ecosystems. Previous studies on soil temperature and heat transport in intertidal marshes predominantly focused on short‐term changes, leaving seasonal variations unclear. This study conducted a yearlong field and modeling investigation to examine temporal and spatial temperature variations in a creek‐marsh section under estuarine and meteorological influences. The results showed that inundating tidal water propagated the seasonal water temperature signal to marsh soils, especially at low elevations, thereby modulating air temperature‐induced soil temperature variations and distributions. The response of soil temperature to air and tidal water temperatures exhibited a damped and delayed pattern. In contrast, tide‐induced porewater circulations near the creek facilitated the temperature responses. A regression model incorporating a Gamma distribution function was developed to quantify the delayed and cumulative thermal effects of tidal water and air on shallow soil temperatures. The model coefficients varied along the creek‐marsh section, capturing the seasonal regulation of periodic tidal inundation on soil temperature in the low‐elevation marsh and near the creek. Sensitivity analyses indicated that relative sea level rise lowered yearly‐averaged temperatures for the marsh platform by enhancing latent heat export. Surface water warming increased the marsh temperatures at lower elevations. This study demonstrates that the creek‐marsh topography, warming, and relative sea level rise jointly affect soil temperature dynamics, advancing our understanding of temperature‐dependent biogeochemical processes in marsh ecosystems.

Assessing Current Coastal Subsidence at Continental Scale: Insights From Europe Using the European Ground Motion Service

AbstractBeside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence.

Development and application of a simplified biophysical model to study deltaic and coastal ecosystems

Many coastal regions around the globe experience land loss due to high relative sea level rise rates, declining sediment supply, and a host of other anthropogenic factors. To evaluate possible restoration strategies, we developed a computationally efficient Simplified Biophysical Model (SBM). The SBM includes hydrodynamic, morphodynamic, and marsh inundation components. The hydrodynamic and mineral sediment processes of the SBM are based on open source Delft3D models. The marsh inundation MATLAB module is a simplified vegetation response to salinity and inundation used to estimate annual organic accretion rates. Organic accretion is added annually to the morphodynamic calculations of mineral sediment. The typical run time for the SBM for an area of 4500 km2 is ∼0.8, 2.5, and 4.7 days real time for one, three, and five decade simulations, respectively which is considered a computationally efficient for modeling decadal landscape evolution. The utility of the SBM was demonstrated through an application to assess the performance of a sediment diversion in the Barataria Basin in Louisiana, USA. The model results demonstrate the importance of incorporating the impact of salinity and inundation effects on the resilience of marshes subjected to high rates of relative sea level rise. Further, the sediment reduction analysis confirms the critical impact of the Mississippi River sediment decline on potential land building from sediment diversions where 1.5%, and 3% annual declining rates show a reduction in net land gain due to Mid-Barataria Sediment Diversion operation of 30% and 50 %, respectively. This highlights the importance of considering the Mississippi River sediment supply decline in restoration projects’ planning and specifically, sediment diversions.

Contrasting organic carbon respiration pathways in coastal wetlands undergoing accelerated sea level changes

Carbon cycling in coastal wetland soil is controlled by a complex interplay between microbial processes and porewater chemistry that are often influenced by various external forcings like wind, river discharge, and sea-level changes, where most of the organic carbon is mineralized to its inorganic form by various aerobic and anaerobic respiration pathways. The export of this inorganic carbon (DIC) from coastal wetlands has long been recognized as a significant component of the global carbon cycle. The major objective of this work is to determine the relative contribution of various respiration pathways to seasonal DIC production in two contrasting marshes (brackish and salt). The DIC fluxes estimates for the brackish and salt marshes were found to range between 36.52 ± 5.81 and 33.98 ± 2.21 mmol m−2 d−1 in winter and 133.10 ± 102.60 and 82.37 ± 30.87 mmol m−2 d−1 during summer of 2020. For the brackish marsh, aerobic respiration and iron reduction were found to be the primary contributors to DIC production representing 17.91–35.21 % and 61.13–81.97 % of total measured organic matter (OM) respiration respectively. On the other hand, aerobic respiration and sulfate reduction were the primary contributors to DIC production in the salt marsh, accounting for 37.91–83.93 % and 15.87–62.04 % of the total measured OM respiration respectively. The Mississippi River Deltaic Plain experiences high relative sea level rise and expected to undergo rapid change in salinity regime in near future from additional changes in river discharge, proposed sediment diversion plans, and storm surge intensities. The current study represents the first attempt to concurrently estimate various respiration pathways in this region and more studies are needed to understand the trajectories of soil OM respiration pathways and its impact on coastal carbon cycling.

Tropical cyclone activity over the past 1200 years at the Pelican Cays, Belize

Tropical cyclone (TC) models indicate that continued planet warming will likely increase the global proportion of powerful TCs (specifically Categories 4 and 5 hurricanes), increasingly jeopardizing low-lying coastal communities and resources such as the Pelican Cays, Belize. The combination of increased coastal development and continued relative sea-level rise puts these communities at even higher risk of damage from TCs. The short TC observational record for the western Caribbean hampers the extensive study of TC activity on centennial timescales, which hinders our ability to fully understand past TC climatology and improve the accuracy of TC models. To better assess TC risk, paleotempestological studies are necessary to put future scenarios in perspective. Here, we present a high-resolution reconstruction of coarser-grained sediment deposits associated with TC (predominately ≥ Category 2 hurricanes) passages over the past 1200 years from Elbow and Lagoon Cays, two coral reef-bounded lagoons at the northern and southern end of the Pelican Cays; the most southern Belizean paleotempestological site to date. Coincident timing of historic storms with statistically significant coarser-grained deposits within cay lagoon sediment cores allows us to determine which historic TCs likely generated event layers (tempestites) archived in the sediment record. Our compilation frequency analysis indicates one active interval (above-normal TC activity) from 1740-1950 CE and one quiet interval (below-normal TC activity) from 850-1018 CE. The active and quiet intervals in the Pelican Cays composite record are anticorrelated with those from nearby and re-analyzed TC records to the north, including the Great Blue Hole (∼100 km north) and the Northeast Yucatan (∼380 km northwest). This site-specific anticorrelation in TC activity along the western Caribbean indicates that we cannot rely on any one single TC record to represent regional TC activity. However, we cannot discount that these anticorrelated periods between the western Caribbean sites are due to randomness. To confirm that the anticorrelation in TC activity among sites from the western Caribbean is indeed a function of climate change and not randomness, an integration of more records and TC model simulations over the past millennium is necessary to assess the significance of centennial-scale variability in TC activity recorded in reconstructions from the western Caribbean.

Rising seas could cross thresholds for initiating coastal wetland drowning within decades across much of the United States

Accelerated sea-level rise is an existential threat to coastal wetlands, but the timing and extent of wetland drowning are debated. Recent data syntheses have clarified future relative sea-level rise exposure and sensitivity thresholds for drowning. Here, we integrate these advances to estimate when and where rising sea levels could cross thresholds for initiating wetland drowning across the conterminous United States. Our results show that there is much spatial variation in relative sea-level rise rates, which impacts the potential timing and extent of wetlands crossing thresholds. High rates of relative sea-level rise along wetland-rich parts of the Gulf of Mexico and Atlantic coasts highlight areas where wetlands are already drowning or could begin to drown within decades, including large wetland landscapes within the Mississippi River delta, Greater Everglades, Chesapeake Bay, Texas, Georgia, and the Carolinas. Collectively, our results underscore the need to prepare for transformative coastal change.

Evaluating flood hazards in data-sparse coastal lowlands: highlighting the Ayeyarwady Delta (Myanmar)

Coastal lowlands and river deltas worldwide are increasingly exposed to coastal, pluvial and fluvial flooding as well as relative sea-level rise (RSLR). However, information about both single and multiple flood-type hazards, their potential impact and the characteristics of areas, population and assets at risk is often still limited as high-quality data either does not exist or is not accessible. This often constitutes a main barrier for generating sound assessments, especially for scientific and public communities in the so-called Global South. We provide a standardised, integrative approach for the first-order assessment of these single and multiple flood-type hazards and show how this can be conducted for data-sparse, hardly accessible and inaccessible coastal lowlands such as the Ayeyarwady Delta in Myanmar by using only open accessible and freely available datasets of satellite imagery, global precipitation estimates, satellite-based river discharge measurements, elevation, land use, and population data. More than 70% of the delta, mainly used for agriculture, and about 40% of its present population are prone to flooding due to either monsoon precipitation and runoff, storm surge, and RSLR, or their combination, jeopardising food security and economic development in the region. The approach allows for the integration and combination of various datasets, combined in a highly flexible workflow that performs at low computational capacities, supporting the evaluation of flood-prone areas on regional and local scale for data-sparse coastal lowlands worldwide. It thereby allows to attribute different types of flood hazards, complements concepts of vulnerability and risk, and supports risk-informed decision making and development of effective multi-flooding adaptation strategies.

Spatial patterns of organic matter content in the surface soil of the salt marshes of the Venice Lagoon (Italy)

Abstract. Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity.

On the Bruun Rule suitability for modelling shoreline change

Modelling and understanding shoreline response to sea-level rise over decadal to centennial timescales is crucial for managing sandy coasts. Globally, the Bruun Rule is one of the most common shoreline model applied to facilitate this. However, there are several limitations to the Bruun Rule, which can compromise coastal management decisions. Here, we provide a novel assessment of the suitability of the Bruun Rule for application in sandy coasts by applying it to hindcast and project shoreline change in three morphologically different sandy beaches over yearly and decadal timescales. We also compare the Bruun Rule predictions against associated observations, published predictions from a hybrid shoreline model, and historical shoreline changes. Results show that the Bruun Rule fails to accurately hindcast and provide realistic projections of future shoreline change in sandy coasts. We attribute this to the Bruun Rule's assumption of linearity between shoreline retreat and relative sea-level rise and its inability to account for nearshore circulation. We, therefore, recommend limiting the use of the Bruun Rule for informing policy and the management of sandy coasts.

Late Pleistocene depositional processes of coastal aeolian deposits and their relationship with environment change on the Changxing Island of Liaodong Peninsula, northeastern China

Coastal aeolian deposits are product of the coupling between aerodynamics and coastal hydrodynamics, which is of great significance for reconstructing aeolian activities and the coastal environmental change. Here, we investigated the coastal aeolian deposits on Changxing Island, northeastern China, using geochemistry and microscopy of the minerals together with the published sedimentological data. The results showed that aeolian deposits are mainly derived from beach sands reworked by wind. Previously published Optically Stimulated Luminescence (OSL) dating results show that the deposition ages of the aeolian deposits are 41 ka, 49 ka, and 67 ka, respectively. The sedimentologic and geochemistry of aeolian deposits are sensitive to climate change. Notably, the micromorphology structure of the surface of quartz sand particles reveals the process of the coastal environment evolution. ∼41 ka, the surface of the grains is characterized by significant subaqueous environments, showing subangular with high relief, large conchoidal fracture, and V-shaped pits. These features correspond to the early sub-interstadial stage of MIS3, characterized by a warm and humid climate and sea level highstand. Under the relative sea level rise, the high rate of sand supply produced by coastal erosion contribute to aeolian deposit formation. In contrast, at 49 ka and 67 ka, the quartz grain exhibits typical aeolian environment features that exhibits subrounded with low relief, upturned plates, and dish-shaped pits, which respond to glacial periods of cold and windy conditions and sea level lowstand. The exposure of abundant sandy material, coupled with lower vegetation cover and strong East Asian winter monsoon (EAWM) contribute to higher sediment availability and sand accumulation. We therefore propose that sediment supply control by sea-level change is the primary reason for coastal aeolian sand deposition under different climatic backgrounds.

Sedimentary record of water-sediment regulation and channel shifts in the Yellow River (Huanghe) Delta

Delta are vital habitats for people and biotic communities. Many of the world's large river deltas are shrinking because of relative sea level rise and intensifying human interventions in the basin. Among these, the Yellow River Delta (hereafter YRD) has been enormously impacted by frequent channel avulsions and a Water-Sediment Regulation Scheme (WSRS) through upstream reservoirs since 2002. However, it remains undisclosed how the YRD responses to these human interventions. Here, modern sedimentation and inter-annual to multi-decadal timescales evolution of the YRD were studied using a dataset including 10 sediment cores collected in the subaqueous delta during the 2014 WSRS, satellite images, hydrographic and bathymetric data from 1976 to 2014. Our results show that the sedimentation of the delta can be divided into three stages: 1976–1995, 1996–2001, and 2002–2014. The area of subaerial delta generally increased from 3884 km2 to 4441 km2 during the whole 1976–2014 period except for a net land loss during 1996–2000. >70% of the delta coastline became artificial after 2000. Bathymetric data reveals that the subaqueous delta was seriously eroded after 1996 due to a shortage of sediment supply, with an estimated 2.3 × 108 t/yr and 1.1 × 108 t/yr of sediment respectively transported to the delta's adjacent sea during 1996–2001 and 2002–2014. The deltaic sediment became coarser due to the impact of the WSRS. Radionuclide 7Be uncovers a rapid sediment accumulation of ∼12 cm at the active delta front during the 2014 WSRS. The evolution of the YRD has become complex under the influence of natural and anthropogenic factors. The YRD thus provides an exemplar shift from natural to human-dominated delta. These results are important for the delta management decision making.

On the contribution of tidal floods on damp walls of Venice

The city of Venice, Italy, has historically coped with tidal flooding and is an example of a resilient system, but today the disruptive effects of relative sea level rise pose even more complex challenges. Some of the most significant damage to the city's historic architectural assets is related to the effects of salty water on masonry due to rising damp and tidal flooding. This paper evaluates the entity and distribution of rising damp in seven Venetian brick masonries by quantifying moisture content, soluble salt content, and ion distribution. The distribution is compared with previous literature data and related to tidal and meteorological data recorded prior to sampling. The results show that frequent tidal flooding exacerbates rising damp phenomena within building masonry, resulting in higher moisture contents both in height and depth. Possible future scenarios of relative sea level based on models and the effects of countermeasures such as the MOSE dam are discussed about the likely damage to masonry exposed to rising damp and tidal flooding.

Exploring the tidal response to bathymetry evolution and present-day sea level rise in a channel–shoal environment

Abstract. Intertidal flats and salt marshes in channel–shoal environments are at severe risk of drowning under sea level rise (SLR) ultimately ceasing their function of coastal defense. Earlier studies indicated that these environments can be resilient against moderate SLR as their mean height is believed to correlate with tidal amplitude and mean sea level. Recent morphological analyses in the German Wadden Sea on the northwestern European continental shelf contradicted this assumption as mean tidal flat accretion surpassed relative SLR, indicating that nonlinear feedback between SLR, coastal morphodynamics, and tidal dynamics played a role. We explored this relationship in the German Wadden Sea's channel–shoal environment by revisiting the sensitivity of tidal dynamics to observed SLR and coastal bathymetry evolution over one nodal cycle (1997 to 2015) with a numerical model. We found a proportional response of tidal high and low water to SLR when the bathymetry was kept constant. In contrast, coastal bathymetry evolution caused a spatially varying hydrodynamic reaction with both increases and decreases in patterns of tidal characteristics within a few kilometers. An explorative assessment of potential mechanisms suggested that energy dissipation declined near the coast, which we related to a decreasing tidal prism and declining tidal energy import. Our study stresses the fact that an accurate representation of coastal morphology in hindcasts, nowcasts, and ensembles for bathymetry evolution to assess the impact of SLR is needed when using numerical models.

Sedimentary and stratigraphic architecture of the Duitschland and Rooihoogte formations (Palaeoproterozoic, South Africa): implications for tempo of the Great Oxidation Event

Abstract Determining the tempo and causality of key palaeoclimate events recorded in sedimentary strata depends on high-resolution numerical ages and well-constrained stratigraphic correlations at regional and global scale. This requirement is not necessarily met in Precambrian strata due to poorer age resolution, limited preservation, and secondary overprints. A good example includes the Palaeoproterozoic Rooihoogte and Duitschland formations in South Africa, which document the disappearance of mass-independent fractionation of sulphur isotopes (MIF-S) and contain glacial diamictites at their base. They are thus key records of Earth’s surface oxygenation during the Great Oxidation Event (GOE). However, previous studies have either correlated these units, resulting in a unidirectional oxidation trend; or have regarded them as successive strata, causing an interpretation of oscillating oxidation. This study uses extensive outcrop and new core material to investigate correlation between these two units, and to establish depositional models. Results show that key stratigraphic markers can be traced around the entire Kaapvaal craton both in outcrop and the subsurface. In particular, the basal Bevets breccia and the top Duitschland breccia are here re-interpreted as two separate units that are present at the base and top of both formations, supporting correlation of the formations. Consequently, the base of both formations records a major craton-wide event of uplift and karstification, leading to carbonate dissolution and chert brecciation. Erosion of older rocks from across the craton also delivered material for the basal glacial diamictite. The majority of mixed siliciclastic-carbonate sediments were deposited on a storm- and/or delta-influenced shelf. Depositional packages in both formations reflect post-glacial relative sea level rise, followed by progradation of a deltaic, storm or shoreline depositional system. There is a relatively short-lived depositional hiatus to overlying shales of the Timeball Hill Formation. Both Rooihoogte and Duitschland formations thus record only a single glacial event at their base, and a unidirectional trend of oxidation.

Combatting Relative Sea-Level Rise at a Global Scale: Presenting the International Panel on Land Subsidence (IPLS)

Land subsidence is increasingly recognized as a critical factor exacerbating relative sea-level rise (SLR), particularly affecting coastal cities and delta regions worldwide. Despite its significance, subsidence is often underrepresented in global SLR assessments. This manuscript introduces the formation of the International Panel on Land Subsidence (IPLS), which aims to unify scientific communities and global research efforts, improve monitoring, modeling, projections and mitigation strategies, and integrate subsidence with global SLR projections. We outline a roadmap for the IPLS to become a pivotal resource in global environmental policy, similar in scope to the IPCC. By fostering intergovernmental collaboration and standardizing responses, IPLS seeks to place land subsidence prominently on international agendas, provide mitigation strategies to reduce coastal land subsidence, and thereby relative SLR, and enhance the resilience of vulnerable coastal populations.

Past and Future Impacts of the Relative Sea Level Rise on the Seafront of Ancient Delos (Cyclades, Greece) and Flooding Scenarios by 2150

Sea level rise due to global warming is a continuing and, disappointingly, accelerating process which has already affected and will further impact coastal lowlands and the social and economic activities in these areas. Delos Island, situated in the middle of the Cyclades in the Aegean Sea, was considered the most sacred of all islands in ancient Greek culture and was a trading hub for the entire eastern Mediterranean. Uninhabited since the 7th century AD, and consistently the focus of research and touristic attention, the island is designated as an archaeological site and inscribed on the UNESCO World Heritage List. Previous studies on the relative sea level (rsl) changes suggest a steadily rising rsl during the last 6300 years, starting from a sea level of −4.80 ± 0.20 m in the Late Neolithic. The seafront of the ancient city of Delos is subject to the effects of rsl rise, which have caused significant coastline retreat and exposure to the northerly winds and waves, whereas parts of the coastal lowland, where the remains of the ancient city lie, are inundated, forming extended wetlands. The future impacts of rsl rise on the seafront of ancient Delos are illustrated on very-high-resolution digital surface models, evaluating both the flooding risk under different climatic projections, as provided by the IPCC AR6 report, and the ongoing land subsidence, as recorded by GNSS data. An rsl rise ranging from 87 cm (SSP1-2.6 scenario) to 148 cm (SSP5-8.5 scenario) is anticipated by 2150, requiring both resilience strategies and adaptation solutions as well as mitigation policies to cope with the effects of climate change.