Slow Sea-level Rise Research Articles

Factors Controlling the Formation and Evolution of a Beach Zone in Front of a Coastal Cliff: The Case of the East Coast of Evia Island in the Aegean Sea, Eastern Mediterranean

The present study examines the recent evolution of a cliff coast along the Aegean Sea, considering its geotectonic context, oceanographic factors, sediment dynamics, and human impact. Initially, the formation of this coastal stretch was influenced by neotectonic faults, oriented both semi-parallel and diagonally relative to the present coastline orientation (NE–SW). Subsequently, the delivery of terrestrial sediment from ephemeral rivers and cliff erosion, along with nearshore wave-induced hydrodynamics have played a secondary role in shaping its current configuration, which includes a beach zone along the base of the cliff. This secondary phase of coastal evolution occurred over the past 4–5 thousand years, coinciding with a period of slow sea level rise (approximately 1 mm/year). Evidence such as uplifted notches and beachrock formations extending to around 5 m water depth suggests intervals of relative sea level stability, interrupted by episodic tectonic events. Anthropogenic interventions, related to both changes in coastal sediment budget and coastal engineering projects, have caused beach erosion, particularly in its central and northern sectors.

Depositional mechanism of Duwi Formation organic-rich rocks in anoxic Campanian-early Maastrichtian condensed sections in the Qusseir–Safaga region in Eastern Desert of Egypt and their economic importance

The organic-rich rocks of the Duwi Formation have gained much attention in recent years because of the growing demand for their utilization as energy and metal sources. A depositional model for these important rocks is delineated in the present study based on multiple analytical approaches. Samples from these organic-rich rocks were collected from eight mines in the Qusseir-Safaga region along the Red Sea coast in the Eastern Desert of Egypt. These mines are located at El Nakheil, Younis, El Beida, Atshan, Hamadat, Tundub Bahri, Tundub Qubli, and Zog EL Bahr. The depositional model is based firstly on organic geochemical and petrographical analyses of the organic matter to identify its enrichment, composition, hydrocarbon potential, types and origin, and their relationship to rock minerals. Secondly, the inorganic geochemical analysis, including mineralogy and trace elements, is integrated to explore the lithological characteristics and to confirm the results obtained from other analyses. Only the El Nakheil, Atshan, Tundub Bahri, and Tundub Qubli mines are found to have total organic carbon content above 10 wt%. These mines contain hydrogen-rich organic matter that reached a maximum in the El Nakheil Mine as reflected in the Rock-Eval parameters of S2 (137.95 mg HC/g rock) and hydrogen index (HI of 707 mg HC/g TOC). The organic matter is composed mainly of large sheet-like alginite particles and prasinophytes that are finely laminated with minerals, planktonic debris of fish bones, and foraminifera without any sign of the presence of benthic organisms or bioturbation. This lamination is attributed to the occurrence of condensed sections in the studied mines. In addition, the high organic enrichment in terms of quantity and quality is accompanied by enriched metal composition including trace elements that signify anoxic conditions and low sedimentation rates. This composition points to the occurrence of prominent anoxic conditions that are stabilized by a slow sea level rise, which inhibits water circulation and water column stagnation in a restricted basin. The depositional model emphasizes the optimal balance between anoxia, sedimentation rate, and paleoproductivity that resulted in enhanced organic matter preservation in a condensed section. The deposition of the organic-rich rocks is situated in the deep parts of the basin or depocenters that reached their present-day distribution by topographic inversion. The organic and metalliferous reserves in these organic-rich sediments are calculated in the studied mines. The estimation of these reserves is found to be economic for many trace metals in an ore reserve that reached 151742 tons in one bed alone within the Duwi Formation.

Authigenic greigite in late MIS 3 sediments: Implications for the Yellow Sea Cold Water Mass and Yellow Sea Warm Current evolution

Yellow Sea current conditions during the late Marine Isotope Stage 3 (late MIS3, 40–30 ka B.P.) highstand remain unknown. Here, environmental magnetism, geochemistry, particle size, and scanning electron microscope methods are employed to analyze core YS01A with a basal age of 40 kyr from the South Yellow Sea mud deposits. Greigite formed in marine sedimentary layers with thickness >7 m during early diagenesis. Greigite formation is related to the redox state and total organic content (TOC) availability, which are controlled, respectively, by the Yellow Sea Cold Water Mass (YSCWM) and the Yellow Sea Warm Current (YSWC). In MIS1 (7–0 ka B.P.), a strong YSWC brought greater TOC, and a strong YSCWM (thickness of 48 m) resulted in a strongly reducing low-oxygen environment. This led to massive magnetite dissolution and pyrite preservation. In late MIS3 (37–31 ka B.P.), the weak Kuroshio Current and East Asian Winter Monsoon (EAWM) resulted in a low-intensity YSWC that provided less TOC. A weak YSCWM (thickness of 35 m), caused by shallow water depths and a weak EAWM, contributed to a less reducing sedimentary environment. Thus, pyritization was interrupted and greigite was preserved. Greigite content can, thus, be used to trace the development of Yellow Sea currents. During a period of slow sea level rise at 41–37 ka B.P., minor greigite formed with most magnetite being preserved, which indicates that the environment started to become reducing. This can be interpreted as due to initial formation of a thin and weak YSCWM. During the 37–31 ka B.P. highstand, the greigite content increased, which suggests more reducing conditions related to establishment of a thicker and intensified YSCWM. In addition, the greigite content decreased progressively, which may have resulted from YSWC weakening. Our results suggest that greigite can be used as a simple tool to reflect current evolution in the Yellow Sea, which can give a better understanding of continental shelf environment change.

The structure of the nonmarine fossil record: predictions from a coupled stratigraphic–paleoecological model of a coastal basin

AbstractPresented here is a coupled model of the nonmarine fossil record, based on a geometric model of deposition, a random-branching model of evolution, and an ecological model based on an elevation gradient. This model provides testable predictions about the stratigraphy and fossil occurrences in coastal nonmarine settings under three scenarios of sea-level change. A slow relative rise in sea level causes a declining ratio of channel to floodplain deposits, plus changes in community composition that reflect an upward increase in elevation relative to sea level. A rapid relative rise in sea level drives increasing aggradation rates, decreases the ratio of channel to floodplain deposits, and triggers a shift from higher-elevation (more inland) to lower-elevation (more coastal) communities. A fall in sea level produces an unconformity, manifested by valleys separated by interfluves. The resumption of deposition following the sea-level fall causes an abrupt shift in community composition across the unconformity, reflecting the duration of the hiatus and the increased elevation relative to sea level. This produces a cluster of first and last occurrences at the unconformity, and it is the only sequence-stratigraphic source of such clusters in a nonmarine system, in contrast to the multiple mechanisms for generating these clusters in marine systems. A central prediction of these models is that the nonmarine fossil record preserves systematic changes in community composition that reflect elevation (or equivalently, distance from shore). Diagnosing these gradients in ancient systems is a promising avenue of future research.

Implications of Coastal Conditions and Sea-Level Rise on Mangrove Vulnerability: A Bio-Morphodynamic Modeling Study.

Mangrove forests are valuable coastal ecosystems that have been shown to persist on muddy intertidal flats through bio‐morphodynamic feedbacks. However, the role of coastal conditions on mangrove behavior remains uncertain. This study conducts numerical experiments to systematically explore the effects of tidal range, small wind waves, sediment supply and coastal slope on mangrove development under sea‐level rise (SLR). Our results show that mangroves in micro‐tidal conditions are more vulnerable because of the gentler coastal equilibrium slope and the limited ability to capture sediment, which leads to substantial mangrove landward displacement even under slow SLR. Macro‐tidal conditions with large sediment supply promote accretion along the profile and platform formation, reducing mangrove vulnerability for slow and medium SLR, but still cause rapid mangrove retreat under fast SLR. Small wind waves promote sediment accretion, and exert an extra bed shear stress that confines the mangrove forest to higher elevations with more favorable inundation regimes, offsetting SLR impacts. These processes also have important implications for the development of new landward habitats under SLR. In particular, our experiments show that landward habitat can be created even with limited sediment supply and thus without complete infilling of the available accommodation space. Nevertheless, new accommodation space may be filled over time with sediment originating from erosion of the lower coastal profile. Consistent with field data, model simulations indicate that sediment accretion within the forest can accelerate under SLR, but the timing and magnitude of accretion depend non‐linearly on coastal conditions and distance from the mangrove seaward edge.

Seismic Attributes Aided Characterization of Margin Backstepping and Advance along Isolated Carbonate Sequences, Sirt Basin, Libya

Isolated carbonate platforms are common and contain significant hydrocarbon accumulations, particularly in the tectonically complex Sirt Basin in Libya. This study investigates the margin cyclicity of two carbonate stratigraphic sequences developed on an isolated carbonate platform in the NW Sirt Basin using 3-D post-stack seismic volume and wireline log data. The two sequences (sequences 4 and 5) are bounded by unconformity surfaces from the base and top. Seismic attributes show that each sequence displays a cycle of margin backstepping followed by margin advance for several hundred meters. This study concludes that the margin backstepping and advance are mainly influenced by sea-level changes. A rapid sea-level rise caused the backstepping, whereas slow sea-level rise caused the margin advance.

Sea-level rise, localized subsidence, and increased storminess promote saltmarsh transgression across low-gradient upland areas

Saltmarsh area is decreasing globally from natural and anthropogenic stressors. Accelerating relative sea-level rise (SLR) is projected to exacerbate losses if not offset by upland saltmarsh migration (transgression). In the absence of coastal upland development, saltmarsh transgression rates increase with accelerating SLR and lower upland surface gradients. Storm wind and surge stress coastal upland forests causing defoliation, uprooting, and soil salinization, which makes upland areas more habitable for saltmarsh species and can promote transgression. This study aims to elucidate the contribution of storms to saltmarsh transgression by reconstructing transgression rates over the past 600 years during stormy and non-stormy conditions and fast and slow SLR rates. Our reconstructions are based on the stratigraphic record and historical aerial photography at three sites in North Carolina, U.S.A. where low-gradient pocosin upland grades into expansive saltmarsh. When sea level was rising <0.9 mm yr−1, saltmarsh transgression rates at the two sites where saltmarsh is > 100 years were an average of 2 and 10 times faster during a paleo-stormy period (1400–1675 CE) than a subsequent non-stormy period. After 1865 CE when SLR accelerated to 2.4 mm yr−1, transgression rates were an average of 7 times faster than the preceding slow SLR non-stormy period. The two sites where the historical record was not confounded by dredging show transgression was 7 times faster and saltmarsh areas increased an average of 28% during stormy decades than non-stormy decades; however, the rate of transgression only increased at the site with greatest surge during the stormy period characterized by strong northeast winds. Modeled transgression rates, using the paleo-upland slope and a sea level curve, do not match observed transgression rates for the paleo-stormy and rapid SLR periods. Furthermore, the thickness of saltmarsh peat younger than 1957 CE is greater than what would be predicted from independent records of SLR. Changes in the elevation of the upland surface, which is composed of peat, contributes to the disparity between predicted and observed transgression rates. The upland surface elevation can keep pace with some rates of SLR through vertical accretion; however, salinization and decomposition of upland vegetation from storm surge plus SLR decreases the elevation of the paleo-upland surface and increases accommodation and transgression rates. Along low-gradient coastlines with pocosin upland areas, SLR, subsidence, and storminess are coupled in modulating transgression rates and those processes need to be included in forecasts of saltmarsh response to climate change.

“Continuous” Backstepping of Holocene Coastal Barrier Systems into Incised Valleys: Insights from the Ofanto and Carapelle-Cervaro Valleys

Two recently recognised incised valleys in the Manfredonia Gulf are described. The first (CCV) is correlated with the current Carapelle and Cervaro streams. The second (OSFV) is correlated mostly with the current Ofanto River. Six seismic facies and seven unconformity-bounded seismic units have been identified, which infilled CCV and OSFV. In CCV, during the sea-level ranges from −29 to −18 and from −18 to −4.7 m b.s.l., two barrier/spit-backbarrier systems formed in the most landward sector of the valley. The lower system was attributed to a time interval between 9.2 ka BP and ca. 8.3 ka BP, chronologically constrained by the ZS2 borehole. In OSFV, during the sea level ranges from −39 to −29, and from −29 and to −18 m b.s.l., two beach/spit-backbarrier systems, arranged in a “continuous” landward backstepping pattern, formed. The phase that contributed most to the beach/spit-backbarrier systems formation is that which is coeval with the formation of the sapropel S1 in the Mediterranean. The conservation of barrier/spit-backbarrier systems arranged in a “continuous” landward backstepping pattern, is due to a strong and continued sediment supply that occurred during the sapropel S1 formation, coupled with low-gradient settings and a regime of slow sea-level rise.

Geochemistry of estuarine sediments from Marakkanam area, Tamil Nadu, India: source area weathering and provenance implications

In the present study, 135 cm and 125 cm sediment cores were collected from Yedayanthittu estuary at a water depth of 1 m to infer the provenance and paleoweathering conditions of the source rocks. The core samples were carbon-dated and analyzed for calcium carbonate, organic matter, and major oxides to decipher the sea level changes, source area weathering, and provenance. The calcium carbonate is chiefly derived from terrestrial and coastal input into the mangrove ecosystem, and the rapid increase of calcium carbonate percentage at certain levels of the cores is due to enrichment of shell fragment. The organic matter content of the sediments is mostly derived from terrestrial input and mangrove debris. Geochronological studies indicate that the sediments deposited during early Holocene period with an average sedimentation rate of 0.015 cm/y−1. The 14C dates and Holocene sea level curve suggest the gradual and slow sea level rise along the study area. The chemical index of alteration (CIA), plagioclage index of alteration (PIA), and A-CN-K diagram reveal that the source rocks were subjected from low to moderate intensity of chemical weathering. The index of chemical variability (ICV) values indicates that the sediments are immature to moderately mature in nature. Major oxide concentrations of core sediments indicate that they were derived mainly from recycled felsic source rocks.

Microfacies Analysis and Stratigraphic Development of the Mishrif Formation in the Eastern of the Mesopotamian Zone, Southeastern Iraq

Mishrif Formation is the most important succession in the southern part of Iraq and has extensive distribution in the Arabian Plate. The present study focuses upon the sequence stratigraphy and development of Mishrif Formation basin in four oil fields within the eastern part of the Mesopotamian Zone are:- Halfaya (Hf-1), Noor (No-1) and Abu Ghirab (AG-3) and Fauqi oil fields (Fq-1). There are several types of microfacies were distinguished in the succession of the Mishrif Formation. Their characteristic of the grain types and carbonate texture enabled to interpret of five facies associations (depositional environments) were observed in this formation, they are: deep marine, shallow open marine, Shoal, rudist biostorm, and shallow restricted associations facies. The stratigraphic development of Mishrif succession in the studied oil fields was summarized by three depositional stages during the Cenomanian-Early Turonian cycle:- First stage:- the basin of Rumaila Formation during this stage was continued to deposition the lower part of Mishrif Formation within the deep marine environment. The end of deposition in this basin (Rumaila basin) was represented by shallow open marine associated facies in the studied area. The High stand sequence distinguished by deposition the deep marine facies and the shallow open marine as two cycle in the southwest, while to the northeast one cycle. The end of the first stage was finished by the shoal facies in all studied area to mark a sequence boundary type II (prograde stage A). Second stage:- the basin was developed from shoal to biostorm facies association with slow sea level rise. The deposition of the open marine associated facies within the biostorm-shoal sequence marked the mfs surface. The final step of this stage was shown the shallowing up-ward by overlaying the shallow open marine association facies upon the biostorm and shoal. At the end of this period, the lagoon/restricted facies were spread in the studied area to mark the prograde stage B as sequence boundary type II. Third stage:- the sea level raised in the southwest direction as open sea association facies, while to the northeast the restricted facies was dominated. This sequence appeared the shoal facies underly the open sea facies marked the mfs surface to start the final high stand deposition overly the restricted facies. This stage is representing the prograde stage C for the Mishrif Formation, where ended the deposition to mark the unconformable surface (SBI) with Khasib Formation.

Sea-level oscillations in the East China Sea and their implications for global seawater redistribution during 14.0–10.0 kyr BP

The sea-level curve during the last deglaciation is characterized by two episodes of rapid sea-level rise, termed Meltwater Pulses (MWPs) 1A (14.6–14.3 kyr BP) and 1B (11.45–11.1 kyr BP), as well as an episode of relatively slow sea-level rise during the Younger Dryas stadial (YD; 12.85–11.65 kyr BP). However, the relative sea-level changes during the YD and MWP-1B periods are still not well defined. Here, we use precisely dated intertidal sediments derived from 6 sediment cores on the tectonically stable continental shelf of the East China Sea (ECS) to reconstruct a high-resolution sea-level curve between 14.0 kyr BP and 10.0 kyr BP. Although linear regression analysis suggests that the sea level rose continuously, with an average rate of 10.6 ± 0.6 mm/yr (r = −0.87, p(a) < 0.01, n = 95), the mode of sea-level rise differs before, during, and after the YD stadial. A rapid sea-level rise of 30.5 ± 4.9 mm/yr (r = −0.79, p(a) < 0.05, n = 25) occurred during 14.0–12.85 kyr BP. Subsequently, the rate of sea-level rise decreased significantly in response to the YD stadial, and it increased smoothly to 12.0 ± 1.4 mm/yr (r = −0.86, p(a) < 0.01, n = 29) from 11.65–10.0 kyr BP, indicating that MWP-1B was absent on the ECS shelf. Furthermore, based on comparisons of these data with other high-resolution curves of sea level or elevation at different latitudes, we suggest that the poleward seawater migration from intertropical broad oceans occurred because glacial isostatic adjustment could have generated a relatively consistent global sea-level height during the last deglaciation, especially during the YD, when the rate of sea-level rise was slowed.

Geoengineer polar glaciers to slow sea-level rise.

Stalling the fastest flows of ice into the oceans would buy us a few centuries to deal with climate change and protect coasts, argue John C. Moore and colleagues. Stalling the fastest flows of ice into the oceans would buy us a few centuries to deal with climate change and protect coasts, argue John C. Moore and colleagues.

Social vulnerability projections improve sea-level rise risk assessments

Rising seas will impact millions of coastal residents in coming decades. The vulnerability of coastal populations exposed to inundation will be greater for some sub-populations due to differences in their socio-demographic characteristics. Many climate risk and vulnerability assessments, however, model current populations against future environments. We advance sea-level rise risk assessments by dynamically modeling environmental change and socio-demographic change. We project three scenarios of inundation exposure due to future sea-level rise in coastal Georgia from 2010 to 2050. We align the sea-level rise projections with five population projection scenarios of socially vulnerable sub-populations via the Hamilton-Perry method and the theory of demographic metabolism. Our combined fast sea-level rise and middle population scenarios project a near doubling of the population exposed, and a more than five-fold increase for those at risk (i.e., residing in a census tract with high social vulnerability) and most at risk (i.e., high social vulnerability and high exposure) compared to the same estimate based on 2010 population data. Of vulnerable sub-populations, women had the largest absolute increase in exposure for all scenario combinations. The Hispanic/Latinx population's exposure increased the largest proportionally under the fast and medium sea-level rise projections and elderly people's (65+) under the slow sea-level rise scenario. Our findings suggest that for coastal areas experiencing rapid growth (or declines) in more socially vulnerable sub-populations, estimates based on current population data are likely to underestimate (or overestimate) the proportion of such groups' risk to inundation from future sea-level rise.

Depositional and sea-level history from MIS 6 (Termination II) to MIS 3 on the southern continental shelf of South Africa

Pleistocene shoreline deposits comprised of calcified shallow marine (palaeobeach) and aeolian (palaeodune) facies found along mid-latitude coastlines can be useful indicators of past sea levels. Here, we describe a succession of such deposits that are presently exposed both above (subaerial) and below (submerged) mean sea level along the southern Cape coast of South Africa, 18 km east of the town of Mossel Bay. The submerged units provide a window on Late Pleistocene coastal processes, as palaeoshoreline deposits in this study extend to water depths of up to 55 m on the mid-shelf. Five sedimentary facies were identified in the strata and were compared to modern depositional environments of the local littoral zone, which include aeolian dune, upper shoreface, foreshore, intertidal swash and back-barrier settings. Twenty-two geological units were observed and mapped. Some of these units were directly dated with optically stimulated luminescence (OSL) dating. OSL ages were obtained for ten samples from the subaerial and twelve samples from the submerged deposits. Those geological units not directly dated were interpreted based on sedimentology and field/stratigraphic relationships to dated units. The stratigraphy and chronology of the succession indicates a record of initial deposition during Termination II (T-II) meltwater events, preceding and leading to marine isotope stage (MIS) 5e. Indicators for multiple sea-level fluctuations between MIS 5d and MIS 4, and sediment deposition at the end of MIS 4 and start of MIS 3 are also found. Both regressive and transgressive depositional cycles are well-preserved in the succession. We propose that palaeodune and palaeobeach deposits along the South Coast of South Africa have no clear preference for deposition during sea-level transgressions or regressions. Sediment deposition more closely mirrors the rate of sea level change, with deposition and preservation either during times of rapid sea-level movement, or oscillation around still-stand events. Periods of relatively slow average rise or fall of sea level are represented by erosional planation surfaces in this record.

Coastal dune development and morphological changes along the littorals of Garigliano, Italy, and Elis, Greece, during the Holocene

Geomorphological and sedimentological studies were carried out along the Garigliano and Elis littorals with the aim to highlight if similar geoenvironmental features are controlled by same coastal processes. Actually, both sites are in Mediterranean climate regions very far each other, modeled by western winds and storms, characterized by wide sandy coastal dunes parallel to the present shoreline, with abundant pumices, and locally anthropized. The Garigliano littoral is characterized by Holocene dune and Pleistocene aeolian deposits. The beach is bounded landwards by a dune system emplaced during the Holocene. Geoarchaeological surveys highlighted the presence of a Roman road which cut the dune, with age older than Graeco-Roman Period. Since the end of the 1950’s, strong littoral retreat affected the beach-dune system, partly due to human activity. The coastland of Elis is characterized by Quaternary marine deposits. Three significant morphogenetic phases occurred during the Holocene. During the last phase, from Graeco-Roman Period to current, shoreline retreat and deposition of aeolian sands occurred. Geoarchaeological evidences suggest that this phase is related to a sea-level lowstand followed by a slow sea-level rise up to the present position, and by humid-temperate climate. Geomorphological surveys of the dunes of Garigliano and Elis, each other compared, suggest that the main phases of their development are related to the effects of climatic conditions, sea-level changes, and secondly to the recent anthropization. The coarse pumices found on both beaches of Campania and Peloponnese regions show the same mineralogical and petrographic features, so we assumed that they likely originated from the Aeolian Arc, southern Italy, which have same composition. These pumices reached the studied coasts by flotation, under the influence of winds and marine surface currents from the southwest-southeast and northwest-west respectively, participating to local coastal processes and representing a good geoindicator of long-distance drift. Precisely for these morphologically converging aspects, such distant sites have been selected and compared.

Effect of irregular, complex underlying topography in Holocene sedimentation revealed from late Quaternary sequences in the mid-western coast of Korea

Through a detailed analysis of seismic profile and vibra-/drilling-core sediments (up to 25.5 m long) with AMS 14C ages from a tidal flat in the mid-western coast of Korea, we reconstruct development of coastal sedimentary sequences in response to sea-level changes for more than about 150 ka, and reveal effect of irregular, complex underlying topography in the Holocene coastal sedimentation. Unit I overlying rock basement and the lower part of Unit II consist of fluvial sediments deposited during sea-level lowstands prior to interglacial period of Eemian Stage (MIS 5e). During the sea-level highstand of MIS 5e, muddy tidal sediments between 7.40 and 10.76 m deep below the present tidal-flat surface were deposited in the upper to middle part of Unit II. The study area had been subaerially exposed for a long duration from MIS 5e to ca. 10 ka. During this period, the muddy tidal sediments in Unit II had been underwent oxidization and significant erosion by fluvial process, forming irregular and complex morphology of the upper boundary of Unit II with a large topographic relief (up to ca. 7 m) even over a short (ca. 560 m) distance. On the upper boundary of Unit II, topographic highs could act as barriers for weakening wave effects from ca. 8–9 ka to 3–4 ka (period of relatively rapid sea-level rise), depositing muddy tidal sediments (Unit III-B). As the muddy tidal sediments (Unit III-B) filled the irregular, complex underlying morphology, surface topography was nearly flat without barriers around about 3–4 ka. Since then, the nearly flat surface morphology without barriers, together with relatively slow sea-level rise and direct exposure of strong onshore winter waves/storms, could promote to deposit wave-/storm-driven sandy sediments (Unit III-A). This study suggests that change in surface morphology could affect stratigraphic evolution of the Holocene coastal sequence by variation in depositional regime.

Acceleration of the global coastal sea level rise during the 20th century re-evaluated

Abstract In contrast to some of the recent investigations, this study shows that far less number of tide gauge stations experienced statistically significant accelerations in sea level rise during the 20th century. Twenty-seven tide gauge stations with century long data were analyzed for the presence of an acceleration in global sea level rise using a kinematic model inclusive of a secular trend, acceleration, and compounded periodicities with autocorrelated random effects. Eight out of twenty-seven stations revealed statistically significant but slow sea level rise acceleration (p&lt;0.01) within the 0.01-0.02 mm/yr2 range compared to the sixteen stations with accelerations estimated using the models by the previous investigations,which did not account for the compounded periodicities and autocorrelations in sea level changes.

Coastal barrier stratigraphy for Holocene high-resolution sea-level reconstruction.

The uncertainties surrounding present and future sea-level rise have revived the debate around sea-level changes through the deglaciation and mid- to late Holocene, from which arises a need for high-quality reconstructions of regional sea level. Here, we explore the stratigraphy of a sandy barrier to identify the best sea-level indicators and provide a new sea-level reconstruction for the central Portuguese coast over the past 6.5 ka. The selected indicators represent morphological features extracted from coastal barrier stratigraphy, beach berm and dune-beach contact. These features were mapped from high-resolution ground penetrating radar images of the subsurface and transformed into sea-level indicators through comparison with modern analogs and a chronology based on optically stimulated luminescence ages. Our reconstructions document a continuous but slow sea-level rise after 6.5 ka with an accumulated change in elevation of about 2 m. In the context of SW Europe, our results show good agreement with previous studies, including the Tagus isostatic model, with minor discrepancies that demand further improvement of regional models. This work reinforces the potential of barrier indicators to accurately reconstruct high-resolution mid- to late Holocene sea-level changes through simple approaches.

The Messinian sea-level fall in the western Black Sea: small or large? Insights from offshore Romania

The Messinian sea-level fall in the western Black Sea is poorly understood and often debated. We provide evidence for the sea-level fall, offshore Romania. There, the Messinian sedimentation is closely related to the gravitational collapse of the basin margin above the Maykop shales. This thin-skinned system controlled the Messinian lowstand depocentres. We estimated about 500–600 m of sea-level drop based on the erosional valleys cut into the formed lower Pontian slope and the Messinian erosional surface (MES). The Messinian lowstand sediments are delimited by the basal erosional surface (BES) formed at the onset of the sea-level fall and by the MES related to transgressive wave erosion during the initial slow rise in sea level. Subsequent rapid sea-level rise drowned the remaining erosional topography on the lower Pontian palaeo-shelf. Similar features have been described in the Mediterranean Basin.

Submerged shoreline preservation and ravinement during rapid postglacial sea-level rise and subsequent “slowstand”

Submerged shorelines hold much potential for examining the interplay between the rate of sea-level rise and geomorphic setting, and informing the development of models of contemporary shoreline behavior. This paper describes the sedimentary architecture of a submerged barrier shoreline complex off Durban, South Africa. The complex consists of several barriers that have survived the postglacial transgression and associated erosive ravinement processes. The main shoreline sequence (–60 m) dates to 11,690 ± 90 calibrated (cal) yr B.P. and rests on a Pleistocene lagoonal deposit (35,395 ± 592 cal yr B.P.). The entire barrier shoreline complex is truncated by a strongly diachronous wave ravinement surface. The ravinement surface seaward of the main –60 m shoreline is steep, but the gradient declines across and landward of the subordinate landward shoreline complexes. The steep ravinement surface is attributed to fast sea-level rise (possibly associated with meltwater pulse 1B), while the gentle ravinement surface is associated with a subsequent slowing of the rate of sea-level rise (to 0.15 mm yr –1 ). Preservation of the main barrier and back-barrier deposits through overstepping is associated namely with rapid transgression and increased back-barrier accommodation. The smaller barriers landward of the main barrier were preserved through overstepping related to gentle antecedent gradients, despite more intense ravinement during a very slow rise in sea level (slowstand). This process was assisted by a sediment deficit. The resulting post-transgressive drape is also influenced by antecedent topography created by the barriers themselves; damming along the landward sides of overstepped barriers thickens the drape and creates a temporal disconnect between the migration of the shoreface and more landward elements of the littoral system. In examining the rates of shoreline migration associated with the overstepped barrier system, these are far greater than those calculated for the predicted rates of shoreline change on similarly steep coastal profiles. Future rates of shoreline migration appear to be insufficient to cause overstepping, and rollover or erosional responses are more likely.