Future Sea Level Research Articles

Evaluation of Potential Seawater Intrusion in the Coastal Aquifers System of Benin and Effect of Countermeasures Considering Future Sea Level Rise

In the present study, a three-dimensional SEAWAT model was developed to generally simulate the impact of climate change and anthropogenic activities on seawater intrusion (SWI) in the coastal region of Benin by the end of 2050. The model was calibrated and validated from 2015 to 2020, considering groundwater head and salt concentration measured in 30 wells. After calibration, a sensitivity analysis was performed with the model parameters (hydraulic conductivity, recharge, storage coefficient and boundary conditions). For the calibration, model computed and observed values displayed good correlation, approximatively 0.82 with a root mean square error (RMSE) of 0.97 m and 13.38 mg/L for groundwater head and salt concentration, respectively. The simulation results indicate that freshwater head had declined by 1.65 m from 2015 to 2020 (taking reference from the average groundwater head in 2015: 27.08 m), while the seawater intrusion area increased in the same period by an average of 1.92 km2 (taking reference from the seawater intrusion area in 2015: 20.03 km2). The model is therefore used to predict groundwater level decline and seawater intrusion area increase by the end of 2050, considering the predicted sea level rise (SLR) and estimated groundwater pumping rate. Furthermore, the interface fresh groundwater–saltwater change was studied using the SHARP interface developed by USGS in 1990. The interface variation was found to be influenced by the distance from shoreline, sea level, groundwater level and geological formation hydraulic conductivity. Finally, the 3D model was used to simulate the effect of a managed aquifer recharge system on reducing SWI rate in the study region.

Spatially heterogeneous nonlinear signal in Antarctic ice-sheet mass loss revealed by GRACE and GPS

SUMMARYNonlinear trends (i.e. quadratic trends, usually defined as accelerations) in Antarctic ice mass loss due primarily to the complex climate warming forcing regimes have induced large uncertainty to future sea level projection. Here, we quantify the nonlinear and spatially varying mass losses in the Antarctic ice sheet during the last two decades using the satellite gravimetry data collected by Gravity Recovery And Climate Experiment (GRACE) and its successor GRACE Follow-On. We use a regional inversion methodology to generate the mass change time-series over Antarctica. Our findings reveal that seven regions have evidenced significant nonlinear mass change. These regions are all concentrated along the coast of Antarctica and show spatially heterogeneous mass balance nonlinear trend patterns. Among them, the Amundsen Sea Embayment (ASE) and the Dronning Maud Land (DML) are found to be particularly sensitive to short-term climate variability. The GRACE-inferred nonlinear mass balance signal can be confirmed by independent Global Positioning System (GPS) observations, and the difference between the nonlinear vertical deformation trends estimated by GRACE and GPS, especially in ASE, is likely due to the imperfect correction of the glacial isostatic adjustment (GIA) effect. For Antarctic ice sheet as a whole, GRACE satellite gravimetry indicates an ice mass loss of −101.3 ± 18.0 Gt yr−1, with an accelerated loss of −6.4 ± 1.3 Gt yr−2 during 2002–2021.

Sea Level and Socioeconomic Uncertainty Drives High-End Coastal Adaptation Costs.

Sea-level rise and associated flood hazards pose severe risks to the millions of people globally living in coastal zones. Models representing coastal adaptation and impacts are important tools to inform the design of strategies to manage these risks. Representing the often deep uncertainties influencing these risks poses nontrivial challenges. A common uncertainty characterization approach is to use a few benchmark cases to represent the range and relative probabilities of the set of possible outcomes. This has been done in coastal adaptation studies, for example, by using low, moderate, and high percentiles of an input of interest, like sea-level changes. A key consideration is how this simplified characterization of uncertainty influences the distributions of estimated coastal impacts. Here, we show that using only a few benchmark percentiles to represent uncertainty in future sea-level change can lead to overconfident projections and underestimate high-end risks as compared to using full ensembles for sea-level change and socioeconomic parametric uncertainties. When uncertainty in future sea level is characterized by low, moderate, and high percentiles of global mean sea-level rise, estimates of high-end (95th percentile) damages are underestimated by between 18% (SSP1-2.6) and 46% (SSP5-8.5). Additionally, using the 5th and 95th percentiles of sea-level scenarios underestimates the 5%-95% width of the distribution of adaptation costs by a factor ranging from about two to four, depending on SSP-RCP pathway. The resulting underestimation of the uncertainty range in adaptation costs can bias adaptation and mitigation decision-making.

Damage detection on antarctic ice shelves using the normalised radon transform

Areas of structural damage mechanically weaken Antarctic ice shelves. This potentially preconditions ice shelves for disintegration and enhanced grounding line retreat. The development of damage and its feedback on marine ice sheet dynamics has been identified as key to future ice shelf stability and sea level contributions from Antarctica. However, it is one of the least understood processes that impact ice shelf instability since quantifying damage efficiently and accurately is a challenging task. Challenges relate to the complex surface of Antarctica, variations in viewing-illumination geometry, snow or cloud cover and variable signal-to-noise levels in satellite imagery. Therefore, automated damage assessment approaches require careful pre- and post-processing, lacking the option to be applied to wider spatiotemporal domains. Simultaneously, studies that use manual mapping are usually limited due to the effort required for extensive mapping, which either results in a limited spatial domain or the use of low resolution data.This study proposes the NormalisEd Radon transform Damage detection (NeRD) method to detect damage features and their orientations from multi-source satellite imagery. NeRD performs robust, high resolution, large-scale damage assessments. NeRD is applied to the ice shelves in the Amundsen Sea Embayment (ASE) and validated with both manually labelled and existing fracture maps. Validation shows that NeRD detects damage with high recall and provides an accurate physical representation of multi-scale damage features and their orientation. Sensitivity analyses indicate NeRD is robust to different resolution parameter settings. NeRD consistently detects damage for different data sources ranging from optical Landsat 7/8 and Sentinel-2 optical to Synthetic Aperture Radar Sentinel-1 data. Therefore, NeRD paves the way for synergistic multi-source damage detection that overcomes remaining limitations from individual sources. Results show varying damage patterns on the ice shelves in the ASE area in austral summer 2020–2021, with most damage located on the Pine Island, Crosson and Thwaites ice shelves. We show a damage increase on the Pine Island ice shelf between 2013–2019, and display advection and rotation of crevasses. The detected damage orientation can provide insight in the type of crevasse opening mode and the development of damage over time. The damage maps produced with NeRD can help evaluate ice sheet models or machine learning approaches, improving our understanding of damage evolution.

Evidence of the variation in the rate of change of temperature and precipitation

One of the most pressing challenges currently is climate change, and to face it, it is desirable to have the most detailed information possible on the distribution of climate metrics and the covariates that alter their fluctuations. This study investigated the spatial variations of the temperature and precipitation variables more sensitive to the unit change in elevation above sea level, considering the relative effects of latitude and solar radiation as covariates. For this, the analysis of covariance was applied to analyze data from 32,111 sampling units, systematically distributed in mainland Mexico, hypothesizing a constant and uniform rate of change of climate variables as the values of elevation above sea level increase and a non-significant effect of the covariates on the elevation-climate relationships. The results show that the rate of change of the studied variables varies at different latitudinal and altitudinal gradients. For example, without considering any covariate, for each meter that the elevation increases, the mean annual temperature decreases on average by 0.00473 °C, the mean temperature of the driest quarter decreases by 0.00488 °C, and the mean temperature of the warmest quarter decreases by 0.00449 °C. This means that for every kilometer of elevation, these variables decrease by 4.73, 4.88, and 4.49 °C, respectively. Yet, when the data were stratified by covariates, these values, as well as the rates of change in precipitation, varied significantly. There were also signs of a stronger correlation between altitude and precipitation for the driest month and driest quarter of over 30°N than in latitudes nearer to the equator.

Climate Change and Cultural Heritage: From Small- to Large-Scale Effects—The Case Study of Nora (Sardinia, Italy)

Rising sea levels are mainly due to increases in environmental temperatures that are causing ice to melt. The weathering of geomaterials is mainly due to the increase in the concentration of greenhouse gases in the atmosphere. This research addresses current and future sea level rises and their weathering effects on the building stones in the Phoenician–Punic archaeological area of Nora (Sardinia, Italy). Some forecasting models, selected according to real-world scenarios (shared socioeconomic pathways—SSPs), give a definitive overview of both the rising sea levels and stone weathering conditions in Nora. The year 2100 A.D. was selected as the base of our investigations because the SSPs are scenarios of projected socioeconomic global changes up to 2100 A.D. The data on the expected alteration of geomaterials were reconstructed by considering the temperatures, the rainfall amount, and the atmospheric CO2 of every scenario. This was made possible by knowing the current degree of alteration of the geomaterials and their weathering resistance. The rising sea level models were obtained through the SSPs scenarios data and built using geographic information systems software. The projections show a slowing down of the weathering degrees of the stone materials in Nora. This is due to the increase in the average annual temperature and the decrease in the average annual rainfall. However, it is shown that some other factors, such as the marine spray in the area, could accelerate the decay. Projections of the rising sea levels show how the settlement will be partially submerged, losing between 3.54% and 8.49% of the emerged land. The models provided a maximum ingression of the coastline, ranging from 23.7 m to 29.5 m, based on the severity of the scenarios. Coastline-shifting maps indicate the flooding of some buildings located on the western coast of Nora, the most sensitive part of the territory.

Loss of reef roughness increases residence time on an idealized coral reef

Through idealized, numerical models this paper investigates flows on a reef geometry which has received significant attention in the literature; a shallow, fringing reef with deeper, shore-ward pools or lagoons. Given identical model geometries and varying only reef flat drag coefficients between model runs (C_D = [0.001,0.005,0.01,0.05,0.1]), two distinct circulation patterns emerge. One is related to low reef water levels and high roughness, and efficiently flushes the entire reef system resulting in low residence times (an ‘open reef’). The other is related to high reef water levels and low roughness, and in spite of the development of an offshore undertow, this dynamic is inefficient at flushing the reef-pool system and facilitating exchange flow with offshore waters (a ‘closed reef’). This paper shows that even given indistinguishable geometry and offshore conditions, this information is insufficient to predict reef dynamics, and suggests that reef roughness (and thus reef health) plays a comparable role in determining circulation patterns and residence times. Furthermore, a transition from open to closed or vice versa caused by e.g., a loss of reef roughness or increase in mean sea level could have implications for transport and mixing of nutrients and water masses, as well as larval dispersal.

Geographical features of Tulipa suaveolens Roth (Liliaceae, Magnoliophyta) distribution by flower color across its European range

The range of the polychromous Tulipa suaveolens Roth comprises almost the whole Ponto-Caspian Steppe, from the south-east of Ukraine to western Kazakhstan. High variation in flower color is a unique feature of this species, but features of its geographical distribution remain unclear. We studied T. suaveolens tepal color variation in 56 natural populations across the European range. Tepal colors were detected from digital images using the Lab color model with two chromatic components, a (red color intensity) and b (yellow color intensity). A conclusion was made that, throughout the European range, an obvious T. suaveolens flower color gradient is expressed in the direction from the south-west to the north-east, along which the red chromatic component intensity decreases. A similar gradient is observed when the height above mean sea level increases. The chromatic component a was shown to have a spatial autocorrelation and to depend on the long-term bioclimatic environmental parameters, temperature and precipitation. Thus, the identified geographical trends in the T. suaveolens flower color distribution across the studied part of its range are a consequence of natural selection caused by these two abiotic factors.

Study on the new technologies that will boost hydrogen as a global energy vector

The emission of greenhouse gases (GHG) into the atmosphere represents a real problem and a great challenge for the following decades; the effects of climate change are already palpable: warmer temperatures, ocean and sea level rise as well increased frequency of high precipitations events. Further warming will inevitably occur in the decades to come-the question is whether it can be limited to two degree rise-and will place higher pressure on ecosystems and human populations, particularly those living in tropical areas. Middle and upper classes of emerging countries increased their CO2e emission more than any other group within the past 15 years. The new geography of global emitters calls for climate action in all countries.1 Based on our new global energy paradigm; the present work aims to carry out a study in the field for renewable energies, on the great potential that would take advantage of the use of hydrological resources available in the potential zones of the developing economies, on the production and use of Hydrogen as a clean energy vector like a promising source and sustainable economy in the coming years. Overpopulation, uncontrolled massive migratory flows and the current Codiv-19 pandemic, all this coincides and is presented in a timely manner; given the current energy situation, which is practically becoming unsustainable, due to the intense and irrational use of fossil fuel. Which as a consequence of this the entire planet is suffering the effects of global warming; which failure to reverse the situation will cause major environmental catastrophes in the short term. Hydrogen, the most abundant element of the universe since it is not free in nature, is necessary to produce it from hydrogenated substances, mainly water and hydrocarbons. The easy availability and abundance of the material from which hydrogen can be obtained, as well as the diversity of means to obtain it; provide a great potential as an energy alternative. This, coupled with the fact that the use of hydrogen only leaves water as the only residue; makes it very favorable to the environment, looking for ways to produce it only with renewable energy sources, such as solar, wind, hydraulic, among others. These characteristics will boost energy economy based abundant hydrogen.2 In order to have a clear and general idea of the research project to be carried out, it will begin with a study in different segments, given the extensive information required, it will begin as follows: Firstable an analysis of greenhouse gas emission globally; what countries lead the most greenhouse emission to the atmosphere. Second the new trends and research that involved the hydrogen in advanced economies. What recent technologies will drive the massive consumption of hydrogen globally? To respond this question, It will be investigated what countries that currently lead the use of hydrogen and which technologies currently are already demanding a significant consumption of hydrogen, then will be analyzed data collected from studies about this new energetic paradigm, and if there is a correlation between population growth, percentage of energy demand, geographical area and the technological services sector. Variables obtained will be graphed and analyzed; and finally some preliminary results will be reported in the present work

Coastal Vulnerability Assessment for Future Sea Level Rise and a Comparative Study of Two Pocket Beaches in Seasonal Scale, Ios Island, Cyclades, Greece

The coastal zone may be considered as the location where the marine and land environments interact dynamically and coexist with human societies. Globally, natural and human systems are being severely threatened by the sea level rise related to climate change. The outcome between the dynamic relationship of coastal environments and marine processes, and the future sea level rise as predicted by scientific reports, is the vulnerability of coastal areas such as sandy beaches, pocket beaches and low-lying coastal areas. The current research aims to assess the coastal vulnerability of Ios Island, Cyclades, Greece for the next 100 years and to identify areas that are comparatively more vulnerable to future sea level changes. Moreover, the seasonal changes concerning sedimentological and morphological characteristics of two pocket beaches of Ios Island, Mylopotas and Magganari, are also examined. From the application of the Coastal Vulnerability Index, 92.37% of the total length of the coastline of Ios Island is characterized by a very low vulnerability as it consists of rocky shores and cliffs, while sandy and pocket beaches are characterized by a very high vulnerability. From the fieldworks and data processing, the seasonal changes mainly concern the seabed’s topography, the sediments’ texture of the collected sand samples, the foreshore and backshore topography, as well as seasonal shoreline displacement, using the Digital Shoreline Analysis System tool (DSAS).

Predicting coastal inundation triggered by the oceanic forcing across Jakarta Bay

Coastal inundation becomes a severe hazard to many world’s cities near shorelines. A recent publication by the Intergovernmental Panel on Climate Change (IPCC) in 2021 projected the increase in mean sea level and the probability of extreme waves in the future that would add more pressure to the cities like Jakarta, Indonesia. Hence, the estimations of the region’s vulnerability due to the hazard are critical steps for designing the adaptation measures. The study is aimed to spatially estimate the future coastal flooding in Jakarta Bay caused by oceanic forcing under the IPCC 2021 scenarios, including the High Highest Water Level (HHWL), the predicted sea level rise by 50 years, the extreme wave setup, and the infragravity (IG) waves. The spatial inundation is generated by projecting the estimated total water level to the Jakarta region’s Digital Surface Model (DSM) and further overlaid on the rectified Google Earth image. The result shows that the increase in water level due to climate change may reach ~1.8 m, increasing the spatial inundation area around the Jakarta shoreline by 37 %. Considering the severe impacts of the projected inundation, the decision-makers need to focus on adaptation efforts soon.

Implications of sea level variability on the formation and evolution of subtropical Rainbow Beach patterned fen complexes, Queensland, Australia

The Great Sandy National Park [K’gari (Fraser Island) and Cooloola] contains the largest subtropical patterned fen complexes in the world. These globally significant, groundwater-dependent ecosystems have been previously studied in relatively undisturbed areas on K’gari and were suggested to be resilient to changes in hydrology, sea level and wildfires. The Rainbow Beach patterned fens are under-studied systems thought to be formed in local perched aquifers. The palaeoenvironmental conditions required for the formation and continuation of these peatlands, and how they react to changes in hydroclimate, sea level and human activities are uncertain. We attempt to resolve this ambiguity using proxies for vegetation and environmental changes over the last ~12,770 cal yr BP from a sediment core located in the Rainbow Beach patterned fen complex. We infer the formation of an aquitard layer and Empodisma minus mire development at ~12,770 cal yr BP, with conditions conducive for patterning ~12,000–10,000 cal yr BP. Paludification occurred in the early Holocene, coincident with increased sea levels, which expanded the mire inland. Increased salt marsh taxa during this period coincides with decreased E. minus values, while further peatland development occurred ~4200 cal yr BP, suggesting that marine influences greatly effect these coastal peatlands. Evidence of vegetation thickening associated with post-European fire suppression was observed. Compared to those on K’gari, the Rainbow Beach complex appears to have initiated through different processes and show greater sensitivity to changes in sea levels. Therefore, subtropical patterned fens should be assessed independently to identify individual trajectories and sensitivities.

Monitoring Megathrust-Earthquake-Cycle-Induced Relative Sea-Level Changes near Phuket, South Thailand, Using (Space) Geodetic Techniques

Temporal changes in vertical land motion (VLM) in and around Phuket Island in southern Thailand following the great 2004 Sumatra–Andaman megathrust earthquake have impacted the relative sea-level change estimates based on tide-gauge (TG) records. To better monitor the VLM, two new continuous global navigation satellite system (GNSS) stations have been installed in the past 5 years, situated on bedrock both near and at the Koh Taphao Noi Island TG in Phuket, which together with older global positioning system (GPS) data provides a clear insight in the VLM of Phuket Island from 1994 onward. In addition, satellite altimetry (SALT) data has been analyzed since 1992. The VLM (GPS) position and relative (TG) and absolute (SALT) sea-level change time series were successfully combined in pairs to validate each independent result (e.g., SALT − GNSS = TG): prior to the 2004 earthquake, the relative sea-level rise in Phuket was 1.0 ± 0.7 mm/yr, lower by 2.4 ± 0.2 mm/yr than the absolute sea-level rise caused by VLM. After the earthquake, nonlinear post-seismic subsidence has caused the VLM to drop by 10 cm in the past 17 years, resulting, by the end of 2020, in a relative sea-level rise by up to 16 cm. During the same period, other TG stations in south Thailand recorded similar sea-level increases. Combination with SALT further suggests that, prior to 2005, uplift (5.3 ± 1.4 mm/yr) of the coastal region of Ranong (north of Phuket) resulted in a relative sea-level fall, but since then, post-seismic-induced negative VLM may have significantly increased coastal erosion along the entire Andaman Sea coastline.

Source assessment of tropical-marshland sediment for evaluating seawater intrusion in Chandipur, India: An integrated granulometric and stable isotope approach

Recent increases in sea level have emerged as a major threat to coastal wetland ecosystems and their biodiversity. Due to the continued increase in sea level, the changed salinity condition of marshland will have an adverse effect on the vegetation community and organic carbon content. Tropical salt marshes store a significant quantity of organic carbon and their potential for carbon storage may be impacted by the changes in the carbon source due to ongoing sea level rise. Towards this, we have collected samples along two transects (BK and CS) in the tropical saltmarsh of Chandipur, India. For this study, we collected and analyzed three organic matter sources such as C3, C4 plants, and particulate organic matter (POM). A total of 33 samples were analyzed from the two surface transects, and both exhibit comparable granulometric and geochemical distributions. Mean grain size suggests a fining trend from the lower to upper marsh of the transect (BK), ranging from 4.29 to 7.27 ø. The stable carbon isotope (δ13C) values show a lowering trend from −21.5‰ to −23.3‰ and carbon to nitrogen ratios (C/N) increase 6.8 to 10 from the low to upland portion of the wetland. The source mixing model was used with the Bayesian SIMMR (i.e., Stable isotope mixing model implemented in R) method to compute the organic source contribution to these salt marsh sediments using δ13C and C/N as system tracers. The results of this model showed a sustained drop in vegetation contribution and an increase in tidal/marine water derived POM contribution as the salinity increases from 25.1 to 30.6. The cluster analysis of granulometric and geochemical data suggest three distinct assemblages governed by the salinity regime. The average total organic carbon (Corg) content drops by around 55% from the lower to higher saline region. Salinity is the main decisive factor for the development of marshland vegetation, as well as their contribution to the organic carbon. Lower concentrations of organic carbon was found in the high-salinity lower marsh near the tidal flat, where the amount of marine/tidal-derived POM increased by 21 ± 8% compared to the relatively low-salinity upper marsh. As part of measures to mitigate climate change, total Corg stocks of marshland must be conserved in order to prevent significant CO2 emissions resulting from changes in salinity brought on by continued sea level rise.

Negative Storm Surges in the Elbe Estuary—Large-Scale Meteorological Conditions and Future Climate Change

Negative storm surges in the Elbe estuary can affect shipping as well as shoreline infrastructure. The significant reduction of water level caused by strong offshore winds can lead to extreme low water events, which endanger waterfront structures. The current study analyses the large-scale meteorological conditions inducing such situations and possible future changes due to climate change. The analysis is based on tide gauge data from Cuxhaven, atmospheric reanalysis data and an objective weather classification approach. It is found that south-easterly wind directions in combination with strong gales favour extreme low water events at Cuxhaven. Furthermore, the analysis of a single model large ensemble of climate projections shows a significant decrease in the frequency of such conditions for the far future (2071–2100). Regarding future global mean sea level rise the simulation results of a sensitivity study indicate that water levels during such extreme events approximately follow the development of the mean sea level rise. Therefore, our study suggests that both meteorological conditions and mean sea levels in a warmer future climate will be less favourable for the occurrence of extreme low water events in the Elbe estuary.

Observation-based trajectory of future sea level for the coastal United States tracks near high-end model projections

With its increasing record length and subsequent reduction in influence of shorter-term variability on measured trends, satellite altimeter measurements of sea level provide an opportunity to assess near-term sea level rise. Here, we use gridded measurements of sea level created from the network of satellite altimeters in tandem with tide gauge observations to produce observation-based trajectories of sea level rise along the coastlines of the United States from now until 2050. These trajectories are produced by extrapolating the altimeter-measured rate and acceleration from 1993 to 2020, with two separate approaches used to account for the potential impact of internal variability on the future estimates and associated ranges. The trajectories are used to generate estimates of sea level rise in 2050 and subsequent comparisons are made to model-based projections. It is found that observation-based trajectories of sea level from satellite altimetry are near or above the higher-end model projections contained in recent assessment reports, although ranges are still wide.

Sea-level rise in Denmark: paleo context, recent projections and policy implications

We present the most recent Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6) sea-level projections for four Danish cities (Aarhus, Copenhagen, Esbjerg and Hirtshals) under the Shared Socioeconomic Pathway (SSP) family of climate scenarios. These sea-level changes projected over the next century are up to an order of magnitude larger than those observed over the previous century. At these cities, year 2150 sea-level changes of between 29 and 55 cm are projected under the very low emissions scenario (SSP1-1.9), while changes of between 99 and 123 cm are projected under the very high emissions scenario (SSP5-8.5). These differences highlight the potentially significant impact of remaining opportunities for climate change mitigation. Due to this increase in mean sea level, the mean recurrence time between historically extreme events is expected to decrease. Under the very high emissions scenario, the historical 100-year storm flood event will become a 1- to 5-year event at most Danish harbours by 2100. There is considerable uncertainty associated with these sea-level projections, primarily driven by uncertainty in the future evolution of the Antarctic ice sheet and future sterodynamic changes in ocean volume. The AR6 characterises collapse of the West Antarctic ice sheet as a low-probability but high-impact event that could cause several metres of sea-level rise around Denmark by 2150. In climate adaptation policy, the scientific landscape is shifting fast. There has been a tremendous proliferation of diverse sea-level projections in recent years, with the most relevant planning target for Denmark increasing c. 50 cm in the past two decades. Translating sea-level rise projections into planning targets requires value judgments about acceptable sea-level risk that depend on local geography, planning timeline and climate pathway. This highlights the need for an overarching national sea-level adaptation plan to ensure municipal plans conform to risk and action standards.

Circulation and Transport Processes during an Extreme Freshwater Discharge Event at the Tagus Estuary

During the winter of 2013, the Tagus estuary was under the influence of intense winds and extreme freshwater discharge that changed its hydrodynamics and, consequently, the salt and heat transport. Moreover, the dynamics of the estuary may change due to climate change which will increase the frequency of heat waves and increase the mean sea level. Therefore, it is of utmost importance to study the impact of the future increase in air temperature and mean sea level under extreme events, such as that in the winter of 2013, to ascertain the foreseen changes in water properties transport within the estuary and near coastal zone. Several scenarios were developed and explored, using the Delft3D model suite, considering the results of the CMIP6 report as forcing conditions. Before the event, the mixing region of the estuary presented well-mixed conditions and its marine area a slight stratification. During the event, the estuary was filled with freshwater and the mixing region migrated toward the coast, leading to lower water temperature values inside the estuary. SLR has a higher impact on the salinity and stratification patterns than the air temperature increase. The response of water temperature is directly related to the increase in air temperature. The estuary mouth and the shallow regions will be more prone to changes than the upstream region of the estuary. The projected changes are directly linked to the future CO2 emissions scenarios, being intensive with the highest emission scenario.

Regimes and Transitions in the Basal Melting of Antarctic Ice Shelves

Abstract The Antarctic Ice Sheet is losing mass as a result of increased ocean-driven melting of its fringing ice shelves. Efforts to represent the effects of basal melting in sea level projections are undermined by poor understanding of the turbulent ice shelf–ocean boundary layer (ISOBL), a meters-thick layer of ocean that regulates heat and salt transfer between the ocean and ice. To address this shortcoming, we perform large-eddy simulations of the ISOBL formed by a steady, geostrophic flow beneath horizontal ice. We investigate melting and ISOBL structure and properties over a range of free-stream velocities and ocean temperatures. We find that the melting response to changes in thermal and current forcing is highly nonlinear due to the effects of meltwater on ISOBL turbulence. Three distinct ISOBL regimes emerge depending on the relative strength of current shear and buoyancy forcing: “well-mixed,” “stratified,” or “diffusive-convective.” We present expressions for mixing-layer depth for each regime and show that the transitions between regimes can be predicted with simple nondimensional parameters. We use these results to develop a novel regime diagram for the ISOBL which provides insight into the varied melting responses expected around Antarctica and highlights the need to include stratified and diffusive-convective dynamics in future basal melting parameterizations. We emphasize that melting in the diffusive-convective regime is time dependent and is therefore inherently difficult to parameterize. Significance Statement The purpose of this study is to investigate the processes that control ocean-driven melting of Antarctic ice shelves (100–1000-m-thick floating extensions of the Antarctic ice sheet). Currently, these processes are poorly understood due to the difficulty of accessing the ocean beneath ice shelves. Using an ocean model, we determine the melting response to different ocean conditions, including feedbacks whereby cold, fresh meltwater can enhance or suppress turbulent eddies beneath the ice, depending on the ocean state. Our results point the way to improvements in the representation of ocean-driven melting in ocean/climate models, which will allow more accurate predictions of future climate and sea level.

Ice Sheet and Climate Processes Driving the Uncertainty in Projections of Future Sea Level Rise: Findings From a Structured Expert Judgement Approach.

The ice sheets covering Antarctica and Greenland present the greatest uncertainty in, and largest potential contribution to, future sea level rise. The uncertainty arises from a paucity of suitable observations covering the full range of ice sheet behaviors, incomplete understanding of the influences of diverse processes, and limitations in defining key boundary conditions for the numerical models. To investigate the impact of these uncertainties on ice sheet projections we undertook a structured expert judgement study. Here, we interrogate the findings of that study to identify the dominant drivers of uncertainty in projections and their relative importance as a function of ice sheet and time. We find that for the 21st century, Greenland surface melting, in particular the role of surface albedo effects, and West Antarctic ice dynamics, specifically the role of ice shelf buttressing, dominate the uncertainty. The importance of these effects holds under both a high-end 5°C global warming scenario and another that limits global warming to 2°C. During the 22nd century the dominant drivers of uncertainty shift. Under the 5°C scenario, East Antarctic ice dynamics dominate the uncertainty in projections, driven by the possible role of ice flow instabilities. These dynamic effects only become dominant, however, for a temperature scenario above the Paris Agreement 2°C target and beyond 2100. Our findings identify key processes and factors that need to be addressed in future modeling and observational studies in order to reduce uncertainties in ice sheet projections.