Future Sea Level Rise Research Articles

Importance of coarse sedimentation events in the resilience of microtidal back-barrier saltmarshes to sea-level rise

An improved understanding of the resilience capacity of salt-marsh environments, which are recognized as one of the most vulnerable yet valuable coastal morpho-sedimentary systems is important for enhancing adaptation to ongoing and future sea-level rise. The aim of this study is to provide a long-term (multi-centennial) context to the capacity of response of saltmarsh environments to relative sea-level rise and extreme wave events by reconstructing the accretion histories of two microtidal back-barrier (one aggradational and one transgressive) saltmarshes in the Bay of Gaspé (Québec, Eastern Canada) over the last centuries. Particular emphasis is put on coarse minerogenic sedimentation and the role it played in the response of the two marshes to relative sea-level changes. To do so, lithostratigraphic, geochronological, and geochemical analyses are carried out on sedimentary cores taken in the back-barrier marsh areas. The accretion histories and the chronology of coarse deposition upon the marshes are reconstructed and yield the following two main results: (1) Coherent yet contrasting records of coarse sedimentation histories are obtained for the two sites, which relate to the distinct configurations and functioning of the fronting barrier systems. The coarse sedimentation time-series of both marshes carry pluri-decadal periodicities typical of atmospheric and intra-oceanic modes of variability, as well as periodicities of 18.0 to 18.5 years, which are interpreted as the expressions of the influence of the 18.6-year nodal tidal cycle. (2) We observe intra- and inter-site variations in the accretionary behavior of the two systems as well as in their respective histories of coarse minerogenic deposition. We show that coarse sedimentation at the surface of the two marshes has been crucial for maintaining accretion rates both in minerogenic and organogenic environments, and thus for allowing saltmarshes to build a resilience capacity in a regime of relative sea-level rise.

Sources, Mechanisms, and Timescales of Sediment Delivery to a New England Salt Marsh

AbstractThe availability and delivery of an external clastic sediment source is a key factor in determining salt marsh resilience to future sea level rise. However, information on sources, mechanisms, and timescales of sediment delivery are lacking, particularly for wave‐protected mesotidal estuaries. Here we show that marine sediment mobilized and delivered during coastal storms is a primary source to the North and South Rivers, a mesotidal bar‐built estuary in a small river system impacted by frequent, moderate‐intensity storms that is typical to New England (United States). On the marsh platform, deposition rates, clastic content, and dilution of fluvially‐sourced contaminated sediment by marine material all increase down‐estuary toward the inlet, consistent with a predominantly marine‐derived sediment source. Marsh clastic deposition rates are also highest in the storm season. We observe that periods of elevated turbidity in channels and over the marsh are concurrent with storm surge and high wave activity offshore, rather than with high river discharge. Flood tide turbidity also exceeds ebb tide turbidity during storm events. Timescales of storm‐driven marine sediment delivery range from 2.5 days to 2 weeks, depending on location within the estuary; therefore the phasing of storm surge and waves with the spring‐neap cycle determines how effectively post‐event suspended sediment is delivered to the marsh platform. This study reveals that sediment supply and the associated resilience of New England mesotidal salt marshes involves the interplay of coastal and estuarine processes, underscoring the importance of looking both up‐ and downstream to identify key drivers of environmental change.

Sensitivity of the West Antarctic Ice Sheet to +2 °C (SWAIS 2C)

Abstract. The West Antarctic Ice Sheet (WAIS) presently holds enough ice to raise global sea level by 4.3 m if completely melted. The unknown response of the WAIS to future warming remains a significant challenge for numerical models in quantifying predictions of future sea level rise. Sea level rise is one of the clearest planet-wide signals of human-induced climate change. The Sensitivity of the West Antarctic Ice Sheet to a Warming of 2 ∘C (SWAIS 2C) Project aims to understand past and current drivers and thresholds of WAIS dynamics to improve projections of the rate and size of ice sheet changes under a range of elevated greenhouse gas levels in the atmosphere as well as the associated average global temperature scenarios to and beyond the +2 ∘C target of the Paris Climate Agreement. Despite efforts through previous land and ship-based drilling on and along the Antarctic margin, unequivocal evidence of major WAIS retreat or collapse and its causes has remained elusive. To evaluate and plan for the interdisciplinary scientific opportunities and engineering challenges that an International Continental Drilling Program (ICDP) project along the Siple coast near the grounding zone of the WAIS could offer (Fig. 1), researchers, engineers, and logistics providers representing 10 countries held a virtual workshop in October 2020. This international partnership comprised of geologists, glaciologists, oceanographers, geophysicists, microbiologists, climate and ice sheet modelers, and engineers outlined specific research objectives and logistical challenges associated with the recovery of Neogene and Quaternary geological records from the West Antarctic interior adjacent to the Kamb Ice Stream and at Crary Ice Rise. New geophysical surveys at these locations have identified drilling targets in which new drilling technologies will allow for the recovery of up to 200 m of sediments beneath the ice sheet. Sub-ice-shelf records have so far proven difficult to obtain but are critical to better constrain marine ice sheet sensitivity to past and future increases in global mean surface temperature up to 2 ∘C above pre-industrial levels. Thus, the scientific and technological advances developed through this program will enable us to test whether WAIS collapsed during past intervals of warmth and determine its sensitivity to a +2 ∘C global warming threshold (UNFCCC, 2015).

Housing market impairment from future sea-level rise inundation

Housing market impairment from future sea-level rise inundation

Age and source of coastal loess in Shandong Peninsula, Bohai Sea, China: Implications for dust aggradation in respond to sea-level change

Coastal loess is a unique and intriguing eolian sediment on Earth, but understanding its formation time, provenance, composition and the geomorphic processes that resulted in its accumulation is very limited compared to its inland counterpart. In this paper, we focused on a loess section at Xiazhupan (XZP) Village, Penglai City in Shandong Peninsula, the only known coastal loess bluffs preserved in China. The coastal loess here not only has characteristics that are common to loess terrains such as being composed of predominantly silt-sized particles and the tendency to stand in vertical exposures, but it also reportedly preserves planktonic foraminifera, sizable pebbles and volcanic glass. In addition to its peculiar near-shore locality, these features make it more unusual compared to other loess deposits. Systematic optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL and pIRIR) and radiocarbon dating reveal it was deposited mostly during 60–20 ka, Marine Isotope Stage (MIS) 4-2, which correlates to the deposition of the Malan loess (L1) in the Chinese Loess Plateau. High-resolution grain size data indicate that the coastal loess is relatively coarse-grained, suggesting a source terrain that is at least partially proximal. Given its proximal source and the geochronological evidence, this coastal loess was sourced from the exposed continental shelf during the sea-level lowstand of the last glacial period, and this hypothesis is further supported by a core collected from the Bohai Sea in which silt was present and would have been subaerially exposed during MIS 4-2. In addition, this source area of exposed continental shelf is comparable to coastal loess in Europe. The coastal loess in Shandong can be regarded as a special type of desert or dryland loess, rather than glacial loess. Finally, future sea level rise will likely increase the erosion potential of these vulnerable coastal loess bluffs, making it urgent to study this special landform.

Potential Sea Level Rise Inundation in the Mediterranean: From Susceptibility Assessment to Risk Scenarios for Policy Action

Coastal ecosystems and anthropic activities are prone to be affected by the negative impact of marine-related processes induced by climate change, such as erosion, flooding and permanent inundation. Studies aiming at defining potential risk scenarios represent a valuable tool for the identification of the most suitable coastal adaptation measures. After outlining sea level rise implications at the Mediterranean scale, this paper deals with inundation risk scenarios for the years 2050 and 2100 for the north-eastern sector of the Island of Gozo (Malta), central Mediterranean Sea. The analysis, carried out by applying an index-based procedure, firstly required the evaluation of the susceptibility to inundation of the investigated coastal stretch under different sea level projections. Then, the spatial combination of inundation susceptibility with the exposure and vulnerability of the area allowed identification of the most critical sectors in terms of coastal risk. The results of the analysis showed that, under the worst-case climate scenarios, 5.5% and 8.1% of the investigated coastal sector are prone to very high inundation risk (Class R4) in 2050 and 2100, respectively. In particular, the bays of Ramla and Marsalforn, which are characterized by significant economic and touristic activities, were found to be the sites where the expected impacts of future sea level rise will be higher if no management strategy and adaptation action are taken in the near future.

Slope Break and Avulsion Locations Scale Consistently in Global Deltas

AbstractUnderstanding how deltas respond to changing sea level is crucial as deltas provide important ecosystems, are inhabited by ∼500 million people, and are nexuses of food, energy and economic activity. The response of delta distributary channels to sea‐level rise depends on the geomorphic controls on delta morphology and their scaling relationships. Our data from 105 deltas globally show strong scaling between the upstream distances to slope breaks and to avulsion nodes, and confirm the previously known scaling between backwater and avulsion lengths. The break in slope is proposed to be the principal control on delta development, along with other proposed secondary controls. We identify and discuss the implications of this slope break‐avulsion length scaling, leading to a conceptual model of delta morphology and sedimentology. This model suggests how deltas may respond to future sea level rise and guides interpretation of deltaic deposits in the rock record.

On the influence of vertical ground movements on Late-Quaternary sea-level records. A comprehensive assessment along the mid-Tyrrhenian coast of Italy (Mediterranean Sea)

The mid-Tyrrhenian coast is the most complex volcano-tectonic sector in the Mediterranean basin. Here the vertical ground movements (VGMs) due to the interaction between extensive tectonic processes and volcano-tectonic activities have a significant impact on both past and future sea-level evolution. This area represents the youngest basin of the western Mediterranean and it hosts one of the most active volcanic districts, formed by the Campi Flegrei and Vesuvius volcanoes, which are worldwide known for the vertical ground movements accompanying their volcanic activity since the Late Pleistocene. The short-lived alternation of subsidence and uplift has induced great changes in inland areas and abrupt coastal landscape transformations since that time. This study aimed to spatially constrain the magnitude of the vertical displacements which significantly affected this coastal sector during the last millennia. We then reconstructed the multiple relative sea-level oscillations that occurred during the Late-Quaternary by developing a comprehensive WebGIS of sea-level index and limiting points (https://dist.altervista.org/seaproxy/). This includes newly produced sea-level data from recent marine surveys, which were coupled to previously available data standardized according to the recent international guidelines for RSL studies. This allowed producing a multiproxy dataset composed of depositional, erosional, biological, and archaeological sea-level markers, in this very complex Mediterranean area. The collected sea-level data were further compared with a number of geophysical predictions in order to disentangle the different components which influenced the sea-level evolution. Moreover, the tectonic rates derived from the available MIS 5e sea-level data were used to shift the LIG elevations vertically and backwards in time in order to constrain the Last Interglacial RSLs to certain levels depending on the areas. Finally, we used GIS techniques to spatially constrain the coastal sectors more vulnerable to the coupled effects of future sea-level rise and VGMs in the next decades.

Sea-Level Rise: From Global Perspectives to Local Services

Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea-level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers as well as the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of the two ice sheets, which combined represent a sea-level rise potential of ∼65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks.

Sedimentation strategies provide effective but limited mitigation of relative sea-level rise in the Mekong delta

The Mekong delta is experiencing rapid environmental change due to anthropogenic activities causing accelerated subsidence, sea-level rise and sediment starvation. Consequentially, the delta is rapidly losing elevation relative to sea level. Designating specific areas for sedimentation is a suggested strategy to encourage elevation-building with nature in deltas. We combined projections of extraction-induced subsidence, natural compaction and global sea-level rise with new projections of fluvial sediment delivery to evaluate the potential effectiveness of sedimentation strategies in the Mekong delta to 2050. Our results reveal that with current rates of subsidence and sediment starvation, fluvial sediments alone can only preserve elevation locally, even under optimistic assumptions, and organic sedimentation could potentially assume a larger role. While sedimentation strategies alone have limited effectiveness in the present context, combined with enhanced organic matter retention and interventions reducing anthropogenic-accelerated subsidence, they can considerably delay future relative sea-level rise, buying the delta crucial time to adapt.

The Uncertain Future of Antarctica’s Melting Ice

A new multidisciplinary, international research program aims to tackle one of the grand challenges in climate science: resolving the Antarctic Ice Sheet’s contribution to future sea level rise.

Insurance Retreat in Residential Properties from Future Sea Level Rise in Aotearoa New Zealand

Insurance Retreat in Residential Properties from Future Sea Level Rise in Aotearoa New Zealand

Building and Raising Land: Mud and Vegetation Effects in Infilling Estuaries.

Many Holocene estuaries were infilled to form convergent, single‐channel systems, while others remained partially or wholly unfilled. This difference in the degree of infilling depends partly on the balance between fluvial and coastal sediment input and the hydrodynamics that can export sediment. However, it remains unclear to what degree this balance is tipped by mud supply and eco‐engineering vegetation, and by what planform patterns the infilling proceeds. This study aims to explore experimentally how mud and vegetation change the degree and process of infilling, elevate and merge bars above intertidal levels and affect the planform of estuaries. To this end, three experiments were conducted in the Metronome, a flume that tilts periodically to create tidal currents, wherein forced tidal asymmetry resulted in net importing estuaries. In the second and third experiments, mud was supplied and in the third experiment seedlings were released of three vegetation species with eco‐engineering traits at a laboratory scale. With only sand, the estuary fills sufficiently to form a multi‐channel pattern with intertidal bars. Both mud and vegetation settle on intertidal bars and on the fluvial bay‐head delta, thereby contributing to bar stabilization and further estuary infilling, pointing at effective strategies to keep up with future sea‐level rise. This reduces channel mobility and effectively narrows the summed subtidal channel width toward an ideally converging funnel shape. This seems especially effective where vegetation stabilizes the mud. The experiments suggest that a range of steady states exists between the end‐members of an unfilled and a completely infilled, ideal estuary.

Reviewing the elements of marine ice cliff instability

Antarctica’s ice sheets are the largest potential sea-level rise contributors, but projections of future sea-level rise yield wide ranges of estimates under different emission scenarios. An important factor in the variability of estimates is marine ice cliff instability (MICI). Inclusion of MICI yields the highest potential sea-level rise cases but also the largest uncertainty due to poor understanding of the factors that control it and the mechanisms of how it happens. Although evidence for MICI has been implied by paleo-ice sheet studies and observations of keel plough mark on sea-floor, recent statistical and modelling studies have suggested a lower magnitude of MICI effect on sea-level rise due to thinning of ice sheets and buttressing forces exerted on potentially failing cliffs. This paper reviews the factors that control MICI with the goal of identifying priorities for modern ice sheet studies to better bound the estimates.

A preliminary assessment of coastal vulnerability for Ngazidja Island, Comoros Archipelago, Western Indian Ocean

In previous studies, an emphasis on the particular vulnerability of small island states to future sea-level rise and the intensity of increasing storm surges have been discussed. This preliminary assessment develops a Coastal Vulnerability Index (CVI) along the 202 km-long coastline of Ngazidja Island (formerly Grande Comore, Comoros Archipelago), using fieldwork, remote sensing, and geographic information system tools (GIS). The CVI considers nine variables: geology (a), geomorphology (b), topography (c), shoreline change (d), shoreline exposure (e), relative sea-level rise (f), significant wave height (g), mean tide range (h), and land-use (i). The land-use variable was added in this analysis to highlight the human asset exposure in the surrounding areas. Each variable was ranked based on local physical and hydrodynamic conditions and their vulnerability contribution to sea-level rise. The CVI was computed in 270 sections. According to the vulnerability index, approximately 57.5% of the coastline is under low and moderate vulnerability. High and very high vulnerabilities refer specifically to beaches and shores with old volcanic lava flows located mainly in the northern, northeastern, and southeastern parts of the island, approximately 42.5% of the coastline. The lowest value of CVI is 9.2 on high, rocky cliffs and the highest value is 160 on beaches. This vulnerability partition along the coastline is consistent with in situ indicators of coastal erosion and flooding. In a sea-level rise context, it is of prime importance to integrate coastal vulnerability maps with planning and sustainable management of the coastal zone.

Assessment of Prevention Performance Target Rainfall in Coastal Cities with Sea Level Rise

The rise in average sea level due to climate change aggravates the vulnerability of coastal areas, increasing the likelihood of flooding due to erosion of outfall to the coast and rivers. Therefore, the design standards of defense facilities should be strengthened to address such increased risk of flooding. Accordingly, in this study, a plan to adjust the disaster prevention performance target rainfall for two research areas was selected in consideration of the regional characteristics of the coastal area and the average sea level rise predicted for 2050, and the disaster prevention performance target rainfall increased from at least 89% to up to 169%. Based on these results, it is believed that this study can serve as a basis for improving data on rainfall targets for disaster prevention performance with consideration of future sea level rise in coastal cities.

Path Analysis of Sea-Level Rise and Its Impact

Global sea-level rise has been drawing increasingly greater attention in recent years, as it directly impacts the livelihood and sustainable development of humankind. Our research focuses on identifying causal factors and pathways on sea level changes (both global and regional) and subsequently predicting the magnitude of such changes. To this end, we have designed a novel analysis pipeline including three sequential steps: (1) a dynamic structural equation model (dSEM) to identify pathways between the global mean sea level (GMSL) and various predictors, (2) a vector autoregression model (VAR) to quantify the GMSL changes due to the significant relations identified in the first step, and (3) a generalized additive model (GAM) to model the relationship between regional sea level and GMSL. Historical records of GMSL and other variables from 1992 to 2020 were used to calibrate the analysis pipeline. Our results indicate that greenhouse gases, water, and air temperatures, change in Antarctic and Greenland Ice Sheet mass, sea ice, and historical sea level all play a significant role in future sea-level rise. The resulting 95% upper bound of the sea-level projections was combined with a threshold for extreme flooding to map out the extent of sea-level rise in coastal communities using a digital coastal tracker.

Acceleration of Dynamic Ice Loss in Antarctica From Satellite Gravimetry

The dynamic stability of the Antarctic Ice Sheet is one of the largest uncertainties in projections of future global sea-level rise. Essential for improving projections of the ice sheet evolution is the understanding of the ongoing trends and accelerations of mass loss in the context of ice dynamics. Here, we examine accelerations of mass change of the Antarctic Ice Sheet from 2002 to 2020 using data from the GRACE (Gravity Recovery and Climate Experiment; 2002–2017) and its follow-on GRACE-FO (2018-present) satellite missions. By subtracting estimates of net snow accumulation provided by re-analysis data and regional climate models from GRACE/GRACE-FO mass changes, we isolate variations in ice-dynamic discharge and compare them to direct measurements based on the remote sensing of the surface-ice velocity (2002–2017). We show that variations in the GRACE/GRACE-FO time series are modulated by variations in regional snow accumulation caused by large-scale atmospheric circulation. We show for the first time that, after removal of these surface effects, accelerations of ice-dynamic discharge from GRACE/GRACE-FO agree well with those independently derived from surface-ice velocities. For 2002–2020, we recover a discharge acceleration of -5.3 ± 2.2 Gt yr−2 for the entire ice sheet; these increasing losses originate mainly in the Amundsen and Bellingshausen Sea Embayment regions (68%), with additional significant contributions from Dronning Maud Land (18%) and the Filchner-Ronne Ice Shelf region (13%). Under the assumption that the recovered rates and accelerations of mass loss persisted independent of any external forcing, Antarctica would contribute 7.6 ± 2.9 cm to global mean sea-level rise by the year 2100, more than two times the amount of 2.9 ± 0.6 cm obtained by linear extrapolation of current GRACE/GRACE-FO mass loss trends.

Mapping Habitat Quality and Threats for Eastern Black Rails (Laterallus jamaicensis jamaicensis)

Documenting the spatial distribution of high-quality habitat patches, the distributions of threats and protected areas, and the vulnerability of habitat patches to changes in environmental conditions is vital for conservation of rare species. Range-wide species distribution models were developed for Black Rails (Laterallus jamaicensis) to predict the distribution of high-quality habitat patches for breeding Eastern Black Rails (L. j. jamaicensis). Overlay analyses were conducted to quantify the distribution of habitat relative to human development and existing protected areas, as well as the vulnerability of the best habitat to future sea level rise. The amount of high-quality habitat varied among states (0.4-7.6% of area) and was relatively rare throughout the subspecies' range (3.3% of area). Human development was common but the amount varied spatially among states (2.2-15.3% of area). Higher-quality breeding habitat was more common on federal lands (9.4% of area) and protected areas (6.4% of area), yet 33-42% of the highest-quality habitat patches were vulnerable to sea level rise of 0.61-1.83 m. Our results imply that even though many of the highest-quality habitat patches may be less likely sites for development they are often vulnerable to rising seas, and thus maintenance of existing high-quality habitat patches may be difficult without management that takes into account the likelihood of future inundation.

Dynamic response of East Antarctic ice sheet to Late Pleistocene glacial–interglacial climatic forcing

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.