Recent Sea-level Rise Research Articles

Vulnerability of endemic insular mole skinks to sea‐level rise

AbstractAlthough coastal islands are home to many endemic species, they are also at risk of inundation from storm surge and sea level rise. Three subspecies of mole skink (Plestiodon egregius egregius, P. e. insularis, and the Egmont Key Mole Skink known from a single occurrence) occur on a small number of islands off the Gulf Coast of Florida, USA. We used the most recent sea level rise projections and the latest storm surge simulation data to predict impacts to habitat for insular mole skinks in Florida from 2030 to 2150. Our models predicted that in <100 years (by 2100; intermediate sea level rise scenario; ~1.08–1.15 m sea level rise), >78% of preferred habitat for the Florida Keys Mole Skink, >65% of preferred habitat for the Cedar Key Mole Skink, and >36% of preferred habitat for the Egmont Key Mole Skink will be inundated from sea level rise. Storm surge from tropical cyclones presents a more immediate risk to insular mole skink habitat: our models predicted that between 58% and 75% of Florida Keys Mole Skink habitat is at risk of being submerged under an average maximum of between 0.60 (SD = 0.86) and 0.98 (SD = 0.36) m of storm surge water for a category 1 storm, and the amount of habitat predicted to be impacted increases for higher intensity storms. Our models predicted similar trends for Cedar Key and Egmont Key Mole Skink habitat. Given current sea level rise projections, our models predicted that all three subspecies could be extinct by 2140 due to habitat inundation. There remains uncertainty about how species and ecosystems will respond to sea level rise, thus research to fill these gaps could help mitigate the effects of sea level rise in areas most vulnerable to the effects of climate change.

Unveiling 4500 years of environmental dynamics and human activity at Songo Mnara, Tanzania

Coastal East Africa has undergone massive transformations through the Late Holocene, with a combination of changes in sea level, increasing human settlement, and ensuing use of coastal resources. A comprehensive multi-proxy analysis, including pollen, phytolith, charcoal, stratigraphy, particle size, and geochemical data from sedimentary cores extracted from mangrove ecosystems combined with soils from archaeological contexts, provided valuable insights into vegetation dynamics, environmental changes, and human interactions within the mangrove ecosystem of Songo Mnara Island, Tanzania over the last 2590 BCE (4540 cal yr BP). The bottommost layers indicate a lack of vegetation, as deduced from the presence of coral rags and high calcium and carbonate content, possibly due to high mid-Holocene sea-level. Evidence of mangrove taxa suggests a decrease in sea level, enabling the establishment of mangroves from around 2590 BCE. A brief period of sea-level rise occurred between 90 BCE and 320 CE before sea-level fell until 1570 CE. Significant evidence of human activity is recorded from around 1400 CE indicated by increased charcoal, crop phytoliths, and evidence of marine resource utilisation. The timing of this human-environment interaction is also linked to the time of lower sea level. However, there was evidence suggesting human abandonment of the island from around 1500 CE. This coincided with a subsequent rise in sea levels and potentially prolonged drought conditions spanning from 1570 to 1700 CE. These factors likely contributed to a shortage of food resources in the area, impacting both agricultural practices due to the scarcity of natural freshwater and the accessibility of marine food resources. From 1700 CE to the present, fluctuations in sea level have been observed, with a signal of recent sea-level rise in tandem with shifts in mangrove, terrestrial herbaceous taxa and fire activity.The low sedimentation rates within mangrove areas suggest that the mangroves on Songo Mnara Island may not keep pace with the current rate of sea-level rise.

The contribution of coastal land subsidence to potential sea-level rise impact in data-sparse settings: The case of Ghana’s Volta delta

Deltas are highly valuable environmental systems, ensuring various livelihoods through their ecosystem services. However, human impact and climate change stressors are impacting deltas immensely. Consequently, many deltas, including Ghana's Volta Delta, are facing increasing risks, especially as hazards are increasing in magnitude and impacting coastal livelihoods. To provide a better understanding of coastal hazards in the Volta Delta, this study assessed the Delta's subsidence regime and its consequences for the potential impact of sea-level rise (SLR). Using the Interferometric Synthetic Aperture Radar (InSAR) technique and Global Navigation Satellite System (GNSS) surveys, vertical land motion (VLM) was documented. Interferograms of Sentinel-1 data from 2016 to 2020 indicated subsiding rates of up to −9.2 mm/yr. By combining local VLM information with recent SLR projections and elevation data, this study updates those projections and provides local assessments of potential Relative SLR (rSLR) impact. According to these locally improved scenarios, up to ∼45 % of the Delta will fall below local sea level by 2100, of which close to 10 % is explained by the integration of local VLM data alone. Depending on the climate change scenarios used, land subsidence will increase the deltaic area at risk by 4.31 % (96.27 km2) to 10.18 % (227.64 km2) and consequently exacerbate its exposure to coastal inundation. To avert the projections, the study recommends robust monitoring regimes; alternative freshwater sources to groundwater; reduced sediment trapping and river obstruction; and the need to stall ongoing oil and gas prospecting and subsequent extraction in the Voltain Basin.

Assessing Models of Sea Level Rise and Mean Sea Surface with Sentinel-3B and Jason-3 Altimeter Data near Taiwan: Impacts of Data Quality and Length

Studying the local sea level rise (SLR) is vital for coastal sustainability and resilience amid climate change. Using the latest altimeter data from the Sentinel-3B (S3B) and Jason-3 (J3) missions, we investigated the regional variability and accuracy of SLR rates around Taiwan and evaluated the accuracies of three mean sea surface (MSS) models: NCTUMSS, CLS15, and DTU18. NCTUMSS is a regional model for defining the new depth datum of Taiwan. The least-squares method with outlier removal was used to compute the along-track SLRs and MSS heights from S3B and J3. Our results show that the SLR rates around Taiwan in the recent 3–6 years from S3B and J3 were 2.0–3.0 mm/year higher than the global rate of 3.3 mm/year. Positive SLR rates were observed in most waters around Taiwan, but negative rates occurred in some parts of the Taiwan Strait. Short-term SLR rates from S3B and J3 were significantly different from the long-term rates determined using altimeter data from the TOPEX/POSEIDON (TP), Jason-1, Jason-2, and J3 missions from 1992.96 to 2021.92. The comparison between the along-track MSS heights from S3B and J3 and the modeled MSS heights showed that CLS15 had the highest accuracy. The DTU18 model exhibited lower sea surface heights near Penghu in the Taiwan Strait compared with CLS15 and NCTUMSS. The NCTUMSS model incorporates tide gauge measurements and Taiwan’s hybrid geoid for a smooth transition from ocean to land. It was concluded that the SLR rates around Taiwan were not uniform, and the rates provided by the three global models, as well as the along-track S3B and J3 altimeter data, suffered from problems like limited spatial resolutions and accuracies, which originated from limited altimeter data qualities and record lengths. One must be cautious about the accuracy of an MSS model for constructing a depth datum and the accuracy of an SLR model for mitigating SLR-induced hazards. We recommend updating the MSS model around Taiwan every 7 years to ensure a 2 cm accuracy requirement, considering the average SLR rate of 3.3 mm/year around Taiwan. Short-term data reflects recent sea level rise but lacks accuracy, while the long-term sea level record may be more precise but may not capture recent rates, necessitating a comprehensive approach that considers both factors for producing accurate assessments and the planning of sea level rise impacts.

Evidence of recent sea-level rise and the formation of a classic Maya canal system inferred from Boca Paila cave sediments, Sian Ka'an biosphere, Mexico

Cave sediments along the eastern coast of the Yucatán Peninsula contain important records of paleoenvironmental change that have not been fully explored. Reconstructing environmental changes in Boca Paila lagoon reveals details about sea level, flooding of the Sian Ka'an Biosphere, and the timeline of occupation at Muyil, an important Classic Maya maritime trading site. Three sediment cores (BP1, BP2, and BP3) were collected from a cave system beneath Boca Paila lagoon in the Sian Ka'an Biosphere. Radiocarbon dating, geochemical (X-Ray Fluorescence Core Scanning, δ13C, C/N), and microfossil (foraminifera, diatoms, pollen) analyses were performed. The combined results show three distinct phases of coastal evolution. Phase 1 (1157 BCE or earlier), an upland area with mangrove associate Conocarpus erectus, grasses, and ferns, is characterized by: organic-rich detrital peat; a relative absence of foraminifera and diatoms; organic geochemistry results within terrestrial ranges (δ13C values of −28‰ to −26‰); and low Sr/Ca, Si/Ti, and Ti/K ratios. These indicate dry conditions at the karst surface. Phase 2 (1157 BCE – 312 CE), a shallow wetland, is represented by: an increase in weathering products (Ti/K) and diatom productivity (Si/Ti); more positive δ13C values (−27‰ to −22‰) and decreasing C/N ratios; and increased marine foraminifera (e.g., Ammodiscus sp.). These indicate more open water conditions. Phase 3 (>312 CE), a wetland/lagoon environment, is characterized by: carbonate-rich marl; a greater diversity of foraminifera (Ammonia spp., Elphidium spp., Rosalina spp., and Bolivina spp.), diatoms (Cyclotella meneghiniana, Craticula spp., Amphora spp., Hyalosynedra laevigata, and Grammatophora spp.) and pollen (from mangroves, ferns, grasses, palms, and pine); increased Si/Ti and Sr/Ca values; and mixed marine and terrestrial organic geochemistry values (δ13C values of −22‰ to −20‰). These indicate increased input of marine organic sediment during sea-level rise. Sea-level and climate records support the interpretation of a dry upper karst environment prior to ∼1157 BCE, with sea-level rise forming shallow (<50 cm) wetlands by ∼312 CE. Previous archaeological analysis estimates that the first settlers arrived at Muyil ∼350 BCE, but that population expansion and construction of most structures occurred during the Postclassic (925–1550 CE). Sea-level rise would have been an important factor in the expansion of coastal settlements and trade routes; continued sea-level rise after ∼312 CE allowed for the formation of deeper lagoons and channels connecting the coast to Muyil and other inland sites which would likely not have been navigable prior to the Early Classic period (250–600 CE) as they would be too shallow. This study highlights the impacts of environment on society, as well as the importance of karst cave systems for obtaining paleoenvironmental records.

Determination of Current and Future Extreme Sea Levels at the Local Scale in Port-Bouët Bay (Côte d’Ivoire)

The Port-Bouët Bay shoreline is threatened by extreme sea level (ESL) events, which result from the combination of storm tide, wave run-up, and sea level rise (SLR). This study provides comprehensive scenarios of current and future ESLs at the local scale along the bay to understand the evolution of the phenomenon and promote local adaptation. The methodological steps involve first reconstructing historical storm tide and wave run-up data using a hydrodynamic model (D-flow FM) and the empirical model of Stockdon et al. Second, the Generalized Pareto Distribution (GPD) model fitted to the Peaks-Over-Thresholds (POT) method is applied to the data to calculate extreme return levels. Third, we combine the extreme storm tide and wave run-up using the joint probability method to obtain the current ESLs. Finally, the current ESLs are integrated with recent SLR projections to provide future ESL estimates. The results show that the current ESLs are relatively high, with 100-year return levels of 4.37 m ± 0.51, 4.97 m ± 0.57, and 4.48 m ± 0.5 at Vridi, Petit-Bassam, and Sogefiha respectively. By end-century, under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios, the future SLR is expected to increase the current ESLs by 0.49 m, 0.62 m, and 0.84 m, respectively. This could lead to a more frequent occurrence of the current 100-year return period, happening once every 2 years by 2100, especially under SSP5-8.5. The developed SLR scenarios can be used to assess the potential coastal flood risk in the study area for sustainable and effective coastal management and planning.

High-Resolution Multiproxy Record of Environmental Changes and Anthropogenic Activities at Unguja Ukuu, Zanzibar, Tanzania during the Last 5000 Years

A high-resolution multiproxy sedimentary record comprising pollen, charcoal, trace element, stratigraphy and particle size data is used to reveal environmental changes from the mangrove ecosystem at Unguja Ukuu, Zanzibar, Tanzania, over the last 5000 years. Historical human–environment interactions over the last millennia are explored by a comparison of the stratigraphic and archaeological data. The area was characterised by a mixture of mangrove forest and beaches, indicating a low level of tidal inundation to at least 3300 BCE. From 2750 BCE, mangrove forest expanded as the area experienced sea-level rise. Further sea-level rise is recorded between 600 and 1100 CE, indicated by the pollen record, particle size analysis and the presence of shell fragments. After 1100 CE, mangrove forest decreased with back mangrove species increasing, indicating a falling sea level. Cocos nucifera decreased after 1900 CE, which reflects a recent sea-level rise and possibly a phase of exploitation. Cereal pollen shows a high presence at around 1500 CE, which coincided with the arrival of the Portuguese on Zanzibar and the transition to Omani colonisation. The sedimentation rate in the core top indicates that mangroves in Unguja Ukuu cannot keep pace with the current rate of sea-level rise.

Resolving Uncertainties in Foraminifera-Based Relative Sea-Level Reconstruction: a Case Study from Southern New Zealand

Abstract Since the pioneering work of David Scott and others in the 1970s and 1980s, foraminifera have been used to develop precise sea-level reconstructions from salt marshes around the world. In New Zealand, reconstructions feature rapid rates of sea-level rise during the early to mid-20th century. Here, we test whether infaunality, taphonomy, and sediment compaction influence these reconstructions. We find that surface (0–1 cm) and subsurface (3–4 cm) foraminiferal assemblages show a high degree of similarity. A landward shift in assemblage zones is consistent with recent sea-level rise and transgression. Changes associated with infaunality and taphonomy do not affect transfer function-based sea-level reconstructions. Applying a geotechnical modelling approach to the core from which sea-level changes were reconstructed, we demonstrate compaction is also negligible, resulting in maximum post-depositional lowering of 2.5 mm. We conclude that salt-marsh foraminifera are indeed highly accurate and precise indicators of past sea levels.

The Royal Naval Dockyard in Bermuda: Use of a novel biological indicator and historical photographs for measuring local sea-level rise

The authors explore a novel interdisciplinary approach to researching, collecting and communicating local site-specific data on recent sea-level rise using persistent black-zone biotic levels evident on historical coastal stone structures by a stable community of cyanobacteria (blue-green algae) at the Royal Naval Dockyard in Bermuda. Photographs taken at the Dockyard in 1870, 2007 and 2017 show an upward shift in this living cyanobacterial community. A spatio-temporal digital twin computed from historical and contemporary photo assets was created to test the viability of these black-zone lines as a proxy for sea-level-rise measurements in Bermuda. Black-zone cyanobacteria are highly sensitive to sea-level rise and, over long timescales, comparative imagery of black zones could present a proper indicator of average sea-level rise.

Plant traits affect vertical accretion of salt marshes

The current climate crisis is associated with rising sea levels, which raises the concerning prospect of losing coastal ecosystems, such as salt marshes. Where inland migration is impossible, salt marshes will only persist if their vertical accretion exceeds the rate of sea-level rise. Positive vertical accretion is mainly driven by sedimentation, whereas negative vertical accretion is driven by erosion and soil compaction, among others. These processes can be influenced by abiotic and biotic factors. The biotic factors, best described by plant functional traits of the salt-marsh vegetation, are, however, not well understood. We assembled a large dataset of 336 plots with vertical accretion time series and plant abundances and coupled it with trait data from salt marsh species of the German Wadden Sea, covering natural unmanaged, anthropogenic unmanaged, and grazed marshes. By using multiple logistic regression analyses, we studied the effects of plant functional traits and distance to the marsh edge on vertical accretion. Mean vertical accretion was in the range of recent sea level rise, except for plots on elevated grazed marshes. There were, however, pronounced local differences in vertical accretion. Positive accretion increased with distance to marsh edge and increasing leaf and stem roughness, described by specific stem length, canopy height, stem mass, leaf mass and leaf area. Except on grazed marshes, leaf traits contributed more strongly to the explanation of positive accretion than stem traits. Negative accretion by e.g., erosion was facilitated by low specific root length and low root and rhizome mass, i.e., lower anchoring capacity. To better assess coastal resilience to sea level rise, our findings suggest (i) to include these effect traits in models and experimental analyses of salt marsh vertical accretion and (ii) to consider effects of vegetation roughness on accretion in salt marsh management schemes.

Millennial-Scale Carbon Storage in Natural Pine Forests of the North Carolina Lower Coastal Plain: Effects of Artificial Drainage in a Time of Rapid Sea Level Rise

Coastal forested wetlands provide important ecosystem services along the southeastern region of the United States, but are threatened by anthropogenic and natural disturbances. Here, we examined the species composition, mortality, aboveground biomass, and carbon content of vegetation and soils in natural pine forests of the lower coastal plain in eastern North Carolina, USA. We compared a forest clearly in decline (termed “ghost forest”) adjacent to a roadside canal that had been installed as drainage for a road next to an adjacent forest subject to “natural” hydrology, unaltered by human modification (termed “healthy forest”). We also assessed how soil organic carbon (SOC) accumulation changed over time using 14C radiocarbon dating of wood sampled at different depths within the peat profile. Our results showed that the ghost forest had a higher tree density at 687 trees ha−1, and was dominated by swamp bays (Persea palustric), compared to the healthy forest, which had 265 trees ha−1 dominated by pond pine (Pinus serotina Michx). Overstory tree mortality of the ghost forest was nearly ten times greater than the healthy forest (p &lt; 0.05), which actually contributed to higher total aboveground biomass (55.9 ± 12.6 Mg C ha−1 vs. 27.9 ± 8.7 Mg ha−1 in healthy forest), as the dead standing tree biomass (snags) added to that of an encroaching woody shrub layer during ecosystem transition. Therefore, the total aboveground C content of the ghost forest, 33.98 ± 14.8 Mg C ha−1, was higher than the healthy forest, 24.7 ± 5.2 Mg C ha−1 (p &lt; 0.05). The total SOC stock down to a 2.3 m depth in the ghost forest was 824.1 ± 46.2 Mg C ha−1, while that of the healthy forest was 749.0 ± 170.5 Mg C ha−1 (p &gt; 0.05). Carbon dating of organic sediments indicated that, as the sample age approaches modern times (surface layer year 2015), the organic soil accumulation rate (1.11 to 1.13 mm year−1) is unable to keep pace with the estimated rate of recent sea level rise (2.1 to 2.4 mm year−1), suggesting a causative relationship with the ecosystem transition occurring at the site. Increasing hydrologic stress over recent decades appears to have been a major driver of ecosystem transition, that is, ghost forest formation and woody shrub encroachment, as indicated by the far higher overstory tree mortality adjacent to the drainage ditch, which allows the inland propagation of hydrologic/salinity forcing due to SLR and extreme storms. Our study documents C accumulation in a coastal wetland over the past two millennia, which is now threatened due to the recent increase in the rate of SLR exceeding the natural peat accumulation rate, causing an ecosystem transition with unknown consequences for the stored C; however, much of it will eventually be returned to the atmosphere. More studies are needed to determine the causes and consequences of coastal ecosystem transition to inform the modeling of future coastal wetland responses to environmental change and the estimation of regional terrestrial C stocks and flux.

Assessment of stability of an exposed microtidal beach, Western Tasmania

Beach erosion is an increasing threat to the natural resources of many countries, and is expected to increase with rising sea-level. West Tasmania has extensive fetch from the circum-polar Antarctic Ocean, also located in the “Roaring Forties” latitudes. Beaches of this coastline previously studied have shown major erosion, attributed to recent relative sea-level rise as they are largely secluded from human impacts. This study assessed Four Mile Beach, located in the central section of the west coast using methods of spatial analysis 1952–2011, beach profile survey and sediment analysis. Results showed only minor erosion of the vegetation line to the north, and stability and progradation in the central and southern extents of the beach. Blowouts showed more major changes, with three large blowouts towards the south becoming parabolic dunes, and one in the north re-vegetating. Dune sediment was mostly rounded fine sand indicative of active aeolian processes, while seaward edge sediment was sub-angular with a 15–20% of carbonate content on most transects, indicative of a sediment supply from offshore. Ongoing coastal stability of this pristine coastline would be facilitated by continued monitoring, management of any potential human impacts, and control of any potential invasive species that may affect sediment budgets.

Using logistic regression to model the risk of sewer overflows triggered by compound flooding with application to sea level rise

Coastal wastewater and storm water systems can be overwhelmed during high precipitation events, particularly when compounded by high storm surge that blocks spillways and drainage ways. Sea level rise (SLR) brings increased risk of such compound flooding events, triggering sanitary sewer overflows (SSO) which release waste water into the local environment. A logistic regression model was developed to better predict this risk in southern Pinellas County, FL. Model variables were selected from 2000 to 2017 cumulative precipitation and coastal water levels using both objective and subjective criteria. The 2 day (P2) and 90 day (P90) cumulative precipitation, and 2 day water level maximum (W2) were identified as significant predictors from the p-value of their model coefficients, but required an interaction term P2*W2 for model fidelity. The model correctly hindcasted all 6 identified SSOs from 2000 to 2017. SLR was represented by a range of values up to 0.5 m added to W2. For a SLR of 0.5 m the number of SSO days increased by a factor of 42–52 and the number of individual events increased by a factor of ~15. Subtracting recent SLR from W2 reduced the probability of some recent events, suggesting that SLR already is increasing the rate of SSOs.

The sea-level budget: an assessmentof observations at the Norwegian coast

Sea level is a major indicator of climate change and thus a key essential climate variable. The source of recent sea-level rise can be understood by measuring the ocean’s temperature, salinity, mass, and sea-surface height. Based on those observations, sea-level change is determined in terms of total sea level and its two major contributions, ocean-mass and steric (density-related) sea level. The sea-level budget is closed when the sum of the independent contributions agrees with the measurements of total sea level, indicating that the observations can be used to understand recent and predict future sea-level change.

Non-linear interaction modulates global extreme sea levels, coastal flood exposure, and impacts

We introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual in order to quantify its contribution to extreme sea levels and hence its role in modulating coastal protection levels, globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components, as is often done in impact case studies). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. Furthermore, we further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting the increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by ~16%, and population affected by ~8%.

Origin, development and prospects of sand islands off the north coast of Viti Levu Island, Fiji, Southwest Pacific

This study sought to understand why/when sand islands formed off the north coast of Viti Levu Island (Fiji), how they subsequently developed, and what is likely to happen to them in future. During fieldwork in 2010 and 2016, six groups of sand islands were mapped and their sub-surface stratigraphy analysed; radiocarbon ages were obtained for 16 samples. All islands rise from emerged bevelled reefal platforms 0.55 m below msl on average. Radiocarbon ages from sediments overlying these platforms suggest they emerged above low-tide level around AD 1300. Once emerged, mangroves and/or seagrass beds developed on platform surfaces, allowing sediment to accumulate. Interior sand islands developed and grew to occupy most of the emerged platforms, pushing mangroves and seagrasses to their margins. Recent sea-level rise has seen island shorelines recede; Severe Tropical Cyclone Winston (February 2016) caused profound changes to the form of some and led to deposition of rubble banks along their fringes. This study contributes evidence for the origin, development and likely prospects of such sand islands under a changing climate. It has implications for the future sustainability of coastal ecosystems in such regions and for the livelihoods of the peoples who depend upon them.

Sea-level rise in Denmark: Bridging local reconstructions and global projections

Between 1850 and 2006 global mean sea level rose by 24 ± 18 cm. It is projected to rise a further 52 ± 21 cm under the Representative Concentration Pathway (RCP) 4.5 scenario, which approximates the carbon emissions reductions of the ‘Paris Agreement’ climate pathway. It is projected to rise 74 ± 28 cm under the RCP8.5 scenario, which represents a ‘business-as-usual’ climate pathway (Box &amp; Colgan 2017). These rates of recent and future sea-level rise are faster than those reconstructed for previous warm intervals, such as the Medieval Climatic Optimum (c. 1000 to 1400 CE) and the Holocene Thermal Maximum (c. 7000 to 3000 BCE) (Gehrels &amp; Shennan 2015). Moreover, palaeo reconstructions indicate a global sea-level sensitivity of two metres per degree of warming (Levermann et al. 2013).&#x0D; The forces driving global sea-level change are complex. The global sea-level budget includes the transfer of land ice into the ocean, thermal expansion of seawater, changes in land water storage, and changes in ocean basin volume (Church et al. 2013). At the local scale, the evolving planetary gravity due to shifting water and ice masses, shifting oceanic and atmospheric currents and persistent tectonic and glacial isostatic adjustment processes can also be important. Sea-level changes around the globe are therefore far from uniform (Jevrejeva et al. 2016).&#x0D; Here, we highlight the value of combining palaeo reconstructions of sea level, the measured tide gauge record, and projections of future sea level. This allows us to understand local sea-level changes from the recent past in the context of global projections for the near future (0 to 2100 CE). We explore the strong differences in local sea-level histories and future projections at three Danish cities: Skagen and Esbjerg, as they have contrasting glacio-isostatic adjustment histories, and Copenhagen, where we also compare local and global drivers of present-day sea-level rise based on previously published research.

INTEGRATED MODELLING TO PREDICT LANDSCAPE EVOLUTION, FLOODING, AND WATER QUALITY IN JAMAICA BAY, NY

It is well-known that rising sea levels will increase pressure along shorelines, yet how society and natural systems will respond is uncertain. Natural systems such as wetlands can respond dynamically to changing conditions, and recent sea level rise has been matched in many places with a rising marsh substrate. The societal response to increasing flooding by necessity is adaptation, particularly in areas with a higher population. However, the subsequent influences on flooding, habitat, and water quality have rarely been evaluated. Jamaica Bay, NY is a coastal embayment bounded on the south by the Rockaway Peninsula and the Atlantic Ocean, on the north by Brooklyn, Queens, and Nassau counties, on the east by the John F. Kennedy Airport, and to the lower bay of New York Harbor on the west through the Rockaway Inlet (Sanderson et al. 2016). The Bay perimeter is home to a large human population, as well as a variety of wildlife that live within the Bay’s salt marsh and adjacent upland ecosystems. The Bay has been identified as an area where ecosystem restoration will potentially have a major impact for protection of the Bay’s population, as well as enhancing the recreational, commercial, and ecological services the Bay provides.

Lateral Marsh Edge Erosion as a Source of Sediments for Vertical Marsh Accretion

AbstractWith sea level rise accelerating and sediment inputs to the coast declining worldwide, there is concern that tidal wetlands will drown. To better understand this concern, sources of sediment contributing to marsh elevation gain were computed for Plum Island Sound estuary, MA, USA. We quantified input of sediment from rivers and erosion of marsh edges. Maintaining elevation relative to the recent sea level rise rate of 2.8 mm yr−1 requires input of 32,299 MT yr−1 of sediment. The input from watersheds is only 3,210 MT yr−1. Marsh edge erosion, based on a comparison of 2005 and 2011 LiDAR data, provides 10,032 MT yr−1. This level of erosion is met by &lt;0.1% of total marsh area eroded annually. Mass balance suggests that 19,070 MT yr−1 should be of tidal flat or oceanic origin. The estuarine distribution of 14C and 13C isotopes of suspended particulate organic carbon confirms the resuspension of ancient marsh peat from marsh edge erosion, and the vertical distribution of 14C‐humin material in marsh sediment is indicative of the deposition of ancient organic carbon on the marsh platform. High resuspension rates in the estuarine water column are sufficient to meet marsh accretionary needs. Marsh edge erosion provides an important fraction of the material needed for marsh accretion. Because of limited sediment supply and sea level rise, the marsh platform maintains elevation at the expense of total marsh area.

Climate, tectonics and beach erosion: the case of Espinho (NW Portuguese coast)

Sea level is a very changeable surface. Furthermore, the land may also be moving, in a slower rate,generating relative sea level changes. The causes of relative sea level changes are variable, but the onesthat cause more intense variations are related to climate.During Little Ice Age (LIA) Northern Hemisphere's summer temperatures fell significantly below theAD 1961–1990 range. This climate situation was responsible for a greater discharge of rivers, whichcould lead to a greater transportation of sediments to the coastline. During these cold periods, sea levelwas lower than in present time. All this could imply a coastline progradation, with the successiveabandon of older beach ridges, reinforcing the sandy supply for dune building. The coastal situationshould be, in some sense, the opposite of the situations that we face today.In present warm period, rivers carry less sediment than during LIA. Moreover, the recent sea level risecontributes to a coastal migration inlands and the erosion of previous beaches and dunes.Our investigation on ancient marine levels and Holocene cemented dunes suggests that the area nearEsmoriz (20 km south of Porto, NW Portuguese coast) is probably subsiding. This possible subsidence,together with recent sea level rise, induced by the end of LIA, could explain the severe coastal erosionthat is taking place at Espinho area (15 km south of Porto) since the middle of the XIX century.This example shows clearly the complexity of relative sea-level changes. Because of this complexity,sea level curves are not similar worldwide, as they depend on the interference of multiple time-scalesphenomena.