Relative Sea-level Changes Research Articles

Relationship between depositional environments and preservabilities of Holocene tsunami deposits on the Hidaka coast, Hokkaido, Japan

Rising sea levels and associated coastal topography changes are expected to increase coastal vulnerability to tsunamis. Reliable records of the periodicity of the most damaging tsunamis, with recurrence intervals of several centuries, are often incomplete. To understand the likelihood of coastal disasters that would be worsened by sea-level rise, as well as their possible occurrence leading to the actual extent of inland inundation, it is useful to examine the geological record of the mid-Holocene highstand periods to supplement the written archives. However, the formation and preservation potential of event layers depends heavily on the depositional environment resulting from coastal evolutions. This study attempted to reconstruct the depositional environment changes using diatom and chemical analyses on the Hidaka coast of Hokkaido, Japan, to examine the preservation of event layer archives.Following field investigations, we found three sand layers formed by extreme waves from field investigations. The relationship between the depositional environment and the timing of the event layer formation over the past 7000 years along the central Hidaka coast indicates that supratidal to freshwater marsh environments are the most suitable for preserving tsunami deposits in this region. Since sand layers in the distant areas from wave sources were not well preserved in upland (as at elevations above marsh environment) and saltmarsh environments, the time windows of preservation were very limited depending on the depositional environments with relative sea-level changes. On the other hand, in areas closer to the Kuril Trench, sand layers were preserved not very sensitive to the depositional environment, suggesting that the event archive length is related to the magnitude of tsunamis.

Exploring Geomorphic Features in Lower Sabarmati River Basin as Signatures of Palaeoenvironmental Change, Gujarat: A Remote Sensing Approach

Abstract The aim of this work is to unravel the role of geomorphic indicators and/or signatures to be used as evidence for palaeo-environmental changes and other forcing mechanisms from the lower reaches of the Sabarmati river basin, Gujarat, India region. In the present study, geomorphic features have been used as archives to debate the past land-sea interactions using satellite imagery. In the lower reaches of the Sabarmati river, a number of meanders, sinuosity changes, palaeochannels, and scroll plains have been identified. As a result of the rise and fall of the sea during the Holocene period, the changes in hydrodynamic and steady-state conditions of the river can be visualized in terms of changes in landforms. Thus, the intriguing geomorphic landforms in the lower portions of the Sabarmati basin delineate the likely archives and signs of previous environmental change, in particularly ~ the relative sea level change. This approach provides first-hand documentation of the fluvial evolution under the direct impact of the varying forcing mechanisms. This attempt shows the effectiveness of satellite images in unravelling the clues to past changes from the landscape in a fast and insightful manner.

Estimating the magnitude of early Permian relative sea-level changes in southern North China

Estimating the magnitude of early Permian relative sea-level changes in southern North China

Post-glacial RSL changes and the demise of a local remnant Laurentide Ice-Sheet ice cap: A view from Anticosti island beach-ridges (Gulf of St Lawrence, Canada)

Widely spread worldwide, beach-ridge systems are established along prograding coastlines, either fostered by a falling Relative Sea-Level (RSL), by substantial sediment stocks being provided to the coastline, or by the combination of both agents. As such, they can form valuable archives of either large scale RSL and isostatic dynamics and/or of more local coastal processes, e.g. related to variations in riverine sediment supply. In this study, we analyze three raised beach-ridge complexes located on the island of Anticosti (Gulf of St.-Lawrence, Québec, Canada). Using both field and LiDAR DEM data, we produce new RSL histories for the north-eastern and north-western sectors of Anticosti Island region over the ca. 14.400 to 8.300 yrs cal. B.P. period. These new sea-level data allow to considerably refine the postglacial RSL history of the region, hence carrying large implications for the comprehension of the isostatic dynamics of the St-Lawrence region. Considerable misfits between our observations and outputs of the GIA models notably allow to propose refinements on the LIS architecture and melting history as well as on the rheological characteristics of the St-Lawrence valley. Locally, chronologies of progradation of the beach-ridges were mostly forced by RSL changes, yet also apparently recorded the demise of the local Anticosti remnant ice-cap throughout the changes in sediment supply the melting of the latter produced locally. Finally, some results of paleo-oceanographic significance could also be derived from the study of the beach-ridges, pertaining for instance to changes in sea-ice cover.

Spatial and Temporal Distributions of Live Salt-Marsh Foraminifera in Southern New Jersey: Implications for Sea-Level Studies

ABSTRACT Geological reconstructions of relative sea-level change have been greatly enhanced by continuous high-resolution records with the use of salt-marsh foraminifera due to their relationship with tidal level in modern environments and subsequent preservation of tests in sediments. A detailed understanding of how live foraminifera assemblages compare to dead or total (live + dead) assemblages and the influence of environmental variables on foraminiferal distributions is essential for their use as a proxy to reconstruct sea level. Here, we evaluated small-scale spatial and temporal (seasonal and interannual) variability of live foraminifera assemblages from four high marsh monitoring stations along a salinity gradient in southern New Jersey over three years. In addition, we measured porewater and sedimentary variables and stable carbon isotopes during each sampling period every three months. In the 184 samples, we identified 11 live agglutinated foraminifera species and four distinct clusters of live foraminifera that correspond to the stations from which they were sampled and to the dead and total assemblages. We found no clear correlation over time between variability in live assemblages and measured environmental variables; however, elevation was the primary controlling factor influencing foraminiferal distributions, with secondary influences from salinity and substrate. The consistency of foraminiferal assemblages on spatial and temporal scales and among live, dead, and total assemblages further reinforces the value of salt-marsh foraminifera as reliable sea-level indicators.

The high-frequency sea-level change in the aftermath of the Marinoan snowball Earth: Evidence from the Doushantuo formation in the northern margin of the Yangtze Craton, South China

The rapid rise of glacioeustatic change is the most extreme paleoenvironment alteration in the aftermath of Snowball Earth. Although geologists conducted a lot of multi-subdiscipline research on this issue previously, there still exists the potential room for further discussions of the process in detail. For decades, the practice proved that the Fischer plot is a simple and robust tool to illustrate the fluctuations of accommodation patterns v.s. cycle sets or strata depth which could be interpreted as relative sea-level changes. This research simulates the Fischer plot to unravel the sea-level change in the aftermath of Marinoan glaciation by measuring the lower Ediacaran Doushantuo Formation in Shennongjia, South China. The result shows that 131 fifth-order cycles and nine third-order cycles help us propose a completed second-order cycle variation of ice melting-forced sea-level change, i.e., (1) early high-frequency and slow to rapid stepwise rising, and (2) followed by a stable decrease in the latter. In addition, the vertical sedimentary facies of the lower Doushantuo Formation display, in ascending order, (1) intertidal carbonate rock, (2) subtidal clastics with turbidite, and (3) intertidal lagoon fine clastics, indicating the process of the relative waxing and waning of sea-level. Such interpretation of the Fischer plot and the sedimentary facies’ vertical evolution is beneficial for studying the high-frequency sea-level change and paleogeographic reconstruction of post-Marinoan deglaciation.

River effects on sea-level rise in the Río de la Plata estuary during the past century

Abstract. Identifying the causes for historical sea-level changes in coastal tide-gauge records is important for constraining oceanographic, geologic, and climatic processes. The Río de la Plata estuary in South America features the longest tide-gauge records in the South Atlantic. Despite the relevance of these data for large-scale circulation and climate studies, the mechanisms underlying relative sea-level changes in this region during the past century have not been firmly established. I study annual data from tide gauges in the Río de la Plata and stream gauges along the Río Paraná and Río Uruguay to establish relationships between river streamflow and sea level over 1931–2014. Regression analysis suggests that streamflow explains 59 %±17 % of the total sea-level variance at Buenos Aires, Argentina, and 28 %±21 % at Montevideo, Uruguay (95 % confidence intervals). A long-term streamflow increase effected sea-level trends of 0.71±0.35 mm yr−1 at Buenos Aires and 0.48±0.38 mm yr−1 at Montevideo. More generally, sea level at Buenos Aires and Montevideo respectively rises by (7.3±1.8)×10-6 m and (4.7±2.6)×10-6 m per 1 m3 s−1 streamflow increase. These observational results are consistent with simple theories for the coastal sea-level response to streamflow forcing, suggesting a causal relationship between streamflow and sea level mediated by ocean dynamics. Findings advance understanding of local, regional, and global sea-level changes; clarify sea-level physics; inform future projections of coastal sea level and the interpretation of satellite data and proxy reconstructions; and highlight future research directions. Specifically, local and regional river effects should be accounted for in basin-scale and global mean sea-level budgets as well as reconstructions based on sparse tide-gauge records.

Sea level changes and sequence stratigraphy of the Lower-Middle Jurassic Quse and Sewa formations in the Qiangtang Basin, central Tibet: Geochemical and palynological perspectives

ABSTRACT Sequence stratigraphy is a commonly used approach to understand basin-fill history and the occurrence of conventional reservoir and/or probable source rocks. Reconstructing a sequence stratigraphic framework in carbonates, marls, and organic-rich mudstones is challenging due to environmental, petrophysical, and sedimentological variations that can be subtle, whereas seismic data may be lacking or of limited use. For this reason, incorporation between palynological analysis and chemostratigraphic profiles is becoming increasingly common to facilitate sequence stratigraphic reconstruction. This study investigates the Quse (lower Toarcian) and Sewa formations (upper Bajocian-Bathonian) in the Bilong Co section from the Qiangtang Basin of central Tibet. Eighty-three rock samples were analysed for their whole-rock inorganic geochemical composition, of which 25 rock samples were tested for palynological and palynofacies analyses. The palynological composition defined two associations for the study section. The lower part of the Bilong Co section consisted is dominated by a moderate to high abundance of opaque phytoclasts versus low to moderate amorphous organic matter (AOM) content with a high concentration of sphaeromorphs pollen grains, revealing deposition of this interval at times of low relative sea level in fluvio-deltaic settings. The middle to upper parts of the section comprised of significantly high AOM content versus low phytoclasts and high content of sphaeromorphs pollen grains, but with increasing the relative abundance of dinoflagellate cysts, indicating a phase of high sea level. Chemostratigraphic variations relevant to changes in relative sea level delineated the subdivision of the Quse and Sewa formations into two and three third-order transgressive-regressive sequences, respectively. The collision between the Lhasa and Qiangtang blocks during the Early-Middle Jurassic is suggested to control consequent subduction and sea level highstand, especially during deposition of the Sewa Formation. Geochemical proxies that relate to shelf carbonate production are calcium, strontium, whereas proxies that relate to siliciclastics include titanium, zirconium, manganese, aluminium, and silicon, other redox-sensitive proxy like uranium is also implemented. This indicates that chemostratigraphic proxies are a promising tool for the interpretation of sea level cyclicity in terms of systems tracts and bounding surfaces.

Time-frequency analysis framework for understanding non-stationary and multi-scale characteristics of sea-level dynamics

Rising sea level caused by global climate change may increase extreme sea level events, flood low-lying coastal areas, change the ecological and hydrological environment of coastal areas, and bring severe challenges to the survival and development of coastal cities. Hong Kong is a typical economically and socially developed coastal area. However, in such an important coastal city, the mechanisms of local sea-level dynamics and their relationship with climate teleconnections are not well explained. In this paper, Hong Kong tide gauge data spanning 68 years was documented to study the historical sea-level dynamics. Through the analysis framework based on Wavelet Transform and Hilbert Huang Transform, non-stationary and multi-scale features in sea-level dynamics in Hong Kong are revealed. The results show that the relative sea level (RSL) in Hong Kong has experienced roughly 2.5 cycles of high-to-low sea-level transition in the past half-century. The periodic amplitude variation of tides is related to Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO). RSL rise and fall in eastern Hong Kong often occur in La Niña and El Niño years, respectively. The response of RSL to the PDO and ENSO displays a time lag and spatial heterogeneity in Hong Kong. Hong Kong's eastern coastal waters are more strongly affected by the Pacific climate and current systems than the west. This study dissects the non-stationary and multi-scale characteristics of relative sea-level change and helps to better understand the response of RSL to the global climate system.

Forecasting Impacts on Vulnerable Shorelines: Vulnerability Assessment along the Coastal Zone of Messolonghi Area—Western Greece

The coastal areas of the Mediterranean have been extensively affected by the transgressive event that followed the Last Glacial Maximum, with many studies conducted regarding the stratigraphic configuration of coastal sediments around the Mediterranean. The coastal zone of the Messolonghi area, western Greece, consists of low-relief beaches, containing low cliffs and eroded dunes, a fact that, in combination with the rising sea levels and tectonic subsidence of the area, has led to substantial coastal erosion. Coastal vulnerability assessment is a useful means of identifying areas of coastline that are vulnerable to impacts of climate change and coastal processes, highlighting potential problem areas. Commonly, coastal vulnerability assessment takes the form of an “index” that quantifies the relative vulnerability along a coastline. Here, the Coastal Vulnerability Index (CVI) methodology by Thieler and Hammar-Klose was employed, by considering geological features, coastal slope, relative sea-level change, shoreline erosion/accretion rates, and mean significant wave height as well as mean tide range, to assess the present-day vulnerability of the coastal zone of the Messolonghi area. In light of this, an impact assessment is performed under three different sea-level-rise scenarios. This study contributes toward coastal zone management practices in low-lying coastal areas that have little data information, assisting decision-makers in adopting best adaptation options to overcome the impact of sea-level rise on vulnerable areas, similar to the coastal zone of Messolonghi.

Coastal Evolution and Relative Sea Level Changes at Psatha (Alkyonides Bay, Greece)

Geomorphological and sedimentological indicators are often used to reconstruct not only coastal evolution, but also relative sea level changes. In this work, we studied the coastal sediments of Psatha bay (Alkyonides Gulf, Greece) and beachrock outcrops in order to reconstruct the coastal evolution of the area. The drillings analysis included stratigraphy, sediment texture and radiocarbon dating. Detailed mapping of the beachrocks was accomplished using DGPS-GNSS, as well as mineralogical analysis and OSL dating of beachrock samples. The new beachrock index points indicate a sea level that fell by 0.64 ± 0.13 m since 2200 ± 210 years BP and by 0.95 ± 0.13 m since 4160 ± 320 years BP, as a direct result of its location near the uplifting footwall of Psatha fault, suggesting further a rate of tectonic uplift of ~0.26 mm/yr for the late Holocene.

Sedimentary facies, lithofacies paleogeography, and an evaluation of the Ordovician sequences in the Sichuan Basin, southwest China

Ordovician strata in the Sichuan Basin occur in formations of varying thicknesses. Deposited in intracratonic and craton margin depressions of the Yangtze Block, these strata are rarely exposed in the basin with poorly described facies types and multiple controversies in sequence stratigraphy, which can lead to inaccurate interpretations of depositional settings and paleogeography. We studied outcrops, samples, and thin sections, and conducted interpretations of the environment of deposition and sequence stratigraphy as well as the lithofacies paleogeographic characteristics of different depositional stages of Ordovician units. Macroscopic facies (08) and their associated microfacies (14) were identified from outcrops and thin sections. The depositional environments of the carbonate rocks were interpreted using the standard microfacies types (SMF) of Flügel (2010) as a reference. The Ordovician units in the Sichuan Basin were divided into three 2nd-order sequences, including two complete cycles (SSQ1 and SSQ2) and one semi-cycle (SSQ3), and further subdivided into ten 3rd-order sequences (SQ1-SQ10). Ordovician units were partitioned into seven formations: the Tongzi, Honghuayuan, Meitan, Shizipu, Baota-Linxiang, and Wufeng formations. Based on the variation characteristics of the carbon-13 isotope (δ13C) curve, two large cycles of sea-level rise and fall were detected in the study area. An extensional rifting event occurred in the basin during the first cycle (Lower Tongzi Formation to Early/Middle Meitan Formation). The basin was in a compressive stage during the second cycle (Late Meitan Formation to Late Wufeng Formation). The Early Ordovician Tongzi and Honghuayuan formations were deposited in shallow water. During the deposition of these units, shoal facies occurred in the platform margin. Afterward, rimmed carbonate platforms occurred in the platform margin with a fauna mainly composed of brachiopods, echinoderms, trilobites, bryozoans, and algae. The Middle Ordovician Meitan Formation is characterized by increased clastic components deposited in continental shelf environments with graptolite and trilobite fossils. The Late Ordovician Baota Formation is marked by the development of slope facies deposited in carbonate ramp environments with cephalopod and trilobite fragments. The Late Ordovician Wufeng Formation was deposited in deep water shelf settings characterized by graptolite fossils. Tectonic activities and relative sea-level change mainly controlled the paleogeographic pattern and the evolution of the Sichuan Basin. The results presented in this study provide valuable insights and fill a significant gap in facies analysis, sequence stratigraphic division, and paleogeography of Ordovician units in the Sichuan Basin.

Coastal switching of dominant depositional processes driven by decreasing rates of Holocene sea-level rise along the macrotidal coast of Gochang, SW Korea

ABSTRACTDecreasing rates of eustatic sea-level rise during the Holocene accompanied the deposition of transgressive coastal deposits worldwide. However, unraveling how transgressive deposition varies in response to different rates of relative sea-level (RSL) rise is limited by the scarcity of long (10+ m) well-dated cores spanning the entire middle to late Holocene record along macrotidal coasts. To investigate the sedimentary response of this macrotidal coast to decreasing rates of RSL rise, we acquired four cores up to 32 m in length and Chirp seismic profiles along the west coast of Korea. Core sediments were analyzed in terms of sedimentary texture, structure, and facies. Nineteen optically stimulated luminescence (OSL) and fourteen 14C accelerated mass spectrometry (AMS) ages constrain the timing of deposition of the sandy sediments. This relatively dense distribution of ages is used to determine how deposition rates changed through time. We also use a compilation of previously published RSL indices for the southwestern Korean coast in order to better constrain RSL changes through time. Results show that the evolution of the Gochang coastline switched from a tide-dominated environment to a wave-dominated environment during the latter stage of transgression as the rate of the sea-level rise decreased. Rugged antecedent topography likely led to the development of tidal currents and the formation of a tide-dominated tidal flat during rapid RSL rise from 10 to 6 ka. As the tidal channels filled with fine-grained sediments from 6 to 1 ka, tidal amplification likely waned leading to a greater role of wave energy in shaping the formation of the sandy open-coast tidal flat. Since 1 ka, wave-dominated environments formed sand-rich tidal beaches and flats. Decreasing changes in rates of the RSL rise resulted in changes in depositional environments from a tide-dominated intertidal flat to an open-coast tidal flat and finally a wave-dominated tidal beach. This study highlights the important role that rates of RSL rise play on not only sedimentation rates in a shelf setting but also playing a role in the switch from a tide-dominated to a wave-dominated setting.

Effects of climate change and sea-level rise on coastal habitat: Vulnerability assessment, adaptation strategies and policy recommendations

On a first-order basis, the global “sea level rise” induced by climate change magnifies coastal land subsidence. Various research related to this discipline is associated with estimated sea level vulnerability in various spatial scales. But the potential impact of climate change on sea level rise and its amalgamated vulnerability to the species remain undiscovered with appropriate procedures. So, in this perspective, our main objective of this research is to estimate the potential impact of climate change on sea level rise and it is associated with vulnerability to coastal habitat. From this research, it is established that the increasing tendency of sea level from the base period to the projected period. The major port city of India has been considered in this research. The qualitative “coastal vulnerability index (CVI)” is based on quantitative estimates to characterize the physical setting, including “geomorphology (G), sea level change (SLC), coastal slope (CS), relative sea-level change (RSLC), mean wave height (MWH), mean tide range (MTR), shoreline change rate (SCR), land use and human activities (LU), and population (P)”. The projected sea level rise (SLR) is increasing at the highest rate under the higher RCP (Representative Concentrations Pathways) scenario. This information is very helpful to the decision maker for considering the most appropriate development strategies to maintain the sustainable development of coastal ecology in India.

Earth, wind and fire: Interactions between Quaternary environmental dynamics and human occupation on the southern coast of Brazil

The southern coast of Brazil has been settled in different episodes between ca. 7.5 and 0.5 ka before the present by hunter-fisher-gatherers, shell mound builders of the pre-colonial Sambaqui cultural tradition. The factors that influenced human migrations in these episodes are diverse. They include cultural changes due to the coming of other groups, chronic food shortages, sea level changes, and lagoon silting. This paper combines geological, geomorphological, meteorological, and archaeological data to show how interactions between environmental dynamics and human settlement played a central role in modeling coastal sedimentary and rocky landscapes on the southern coast of Brazil during the middle Pleistocene to late Holocene. On Costão do Ilhote, a north-south oriented granitic promontory in Laguna County, Santa Catarina State, erosional features such as facets, keels, grooves, flutes, pits, and polished surfaces that developed on granitic boulders and pavements were recognized as ventifacts. In the same context, hundreds of fixed sharpeners/polishers from the production of polished objects by the sambaqui culture have been found crosscutting the ventifacts. Based on crosscut relationships between pre-colonial aged fixed sharpeners/polishers and ventifacts, relative sea-level changes during the Holocene, the age of distinct generation of sand dunes, and the age of shellmounds (sambaquis), four potential intervals of ventifaction are proposed: last 650 ka, last 350 ka, between ca. 115 and 5 ka BP, and between ca. 2.0 and ∼0.5 ka BP, with separated estimated abrasion rates of approximately 3.5 × 10−5 mm/yr, 7.0 × 10−5 mm/yr, 1.7 × 10−4 mm/yr, and 1.3 × 10−2 mm/yr, respectively. The ca. ∼1.5 ka of the last ventifaction interval was synchronous with a period of sambaqui culture retreat in the southern coastal plain of Santa Catarina, and also coincided with a period of abundant sand availability. This period is characterized by a drastic decline in sambaquis construction along the sand barrier and paleolagoon and a migration towards lagoonal and coastal rocky promontories, including Costão do llhote. Based on these pieces of evidence, we propose to add new components to the close interactions between environmental evolution and prehistoric human occupation on the southern coast of Santa Catarina during the Holocene: the strong winds combined with sand availability.

Development of Pag-asa Reefs, West Philippine Sea: Role of Relative Sea Level Change and Wave Exposure

Atoll reefs are associated with subsiding regions. In the West Philippine Sea, the Kalayaan Island Group is an emergent feature of the region’s atoll reefs. In this study, we established the long-term rate of subsidence in the Pag-asa Atoll Reefs by indicators of sea level positions on the seafloor and in Pag-asa Island. For submerged indicators of paleo-sea levels, a multibeam bathymetry with a 5-m resolution was used as the primary data source. Four pairs of submerged terraces and scarps, interpreted as former coral reef flats and reef fronts, respectively, were mapped. The terraces, PARa-d, from shallowest to deepest, occur at depth ranges of 7–10, 36–45, 82–90, and 115–120 m. The step-like morphology of the slopes off Pag-asa is likely due to the backstepping of reefs during the overall rise of sea level from the Last Glacial Maximum (LGM). Terraces PARa-d are interpreted as records of reef re-establishments during the stillstand periods following meltwater pulse event (MWP)-1C, MWP-1B, MWP-1A, and MWP-2B/2A. There is no clear morphological indicator of coral terraces that can be attributed to the LGM period. Variation in the widths and depths of the terraces between the leeward and windward sides of the island is also observed. Greater wave exposure appears favorable for coral reef terrace growth in Pag-asa, except for deeper terraces. The possible absence of the deepest terrace on the north side and an LGM terrace is attributed to possible thinner coral reef accretion due to the combination of cooler waters and possible swifter winds prior to 14 kyr. Correlation of the terrace depths and beach rock elevations as Pag-asa with the paleo-sea level of correlative stillstand events indicate long-term subsidence of 1.2 mm/yr between 15–12 kyr that declined to 0.3 mm/yr between 12 kyr to present. With sea level rise due to global warming and continuing subsidence, Pag-asa Island is threatened by coastal erosion, more frequent inundation, and groundwater salinization that needs to be addressed through proper adaptation practices.

Evolution from Carbonate Platform to Siliciclastic Shelf Driven by Relative Sea–Level Changes: Lower Cretaceous of the Zagros Area, Southwest, Iran

Evolution from Carbonate Platform to Siliciclastic Shelf Driven by Relative Sea–Level Changes: Lower Cretaceous of the Zagros Area, Southwest, Iran

20th to 21st Century Relative Sea and Land Level Changes in Northern California: Tectonic Land Level Changes and their Contribution to Sea-Level Rise, Humboldt Bay Region, Northern California

20th to 21st Century Relative Sea and Land Level Changes in Northern California: Tectonic Land Level Changes and their Contribution to Sea-Level Rise, Humboldt Bay Region, Northern California

Novel insights into the sea level evolution along the coast of Bozburun Peninsula (Turkey): A study on submerged Bronze Age harbor in Çamçalık

AbstractA recent discovery of a Bronze Age harbor site in Çamçalık provides new data for the relative sea level history along the coast of the Bozburun Peninsula over the last 3600 years. In this study, we compared the new and previously published data from nearby sites to determine the long‐term relative sea level changes. Further comparison of the observed sea level data and newly produced glacial isostatic adjustment (GIA) models clarified the tectonic contribution to the relative sea level changes. Our results suggest a nonlinear tectonic subsidence trend in the coastal zone since 3600 B.P. The increase in the relative sea level accelerated over the last 1400 years, mostly due to the seismic events controlled by the tectonic regime of the southeastern Aegean Sea. We can conclude that, as in the past, this active tectonic process will have a major impact on the future sea level evolution of the coastal sector of the Bozburun Peninsula. Notably, our study can be used to understand the historical trend of sea level rise while providing a foundation for future trend prediction.

Within-region replication of late Holocene relative sea-level change: An example from southern New England, United States

Tide-gauge measurements in the western North Atlantic Ocean show coherent, multi-decadal relative sea-level (RSL) trends across multiple spatial scales. Proxy reconstructions developed from salt-marsh sediment can extend this instrumental record. However, the degree of coherence in proxy reconstructions is underexamined through within-region replication. To explore within-region replication, we developed a new RSL reconstruction from Fox Hill Marsh, Rhode Island to complement similar records at nearby sites. We established the elevation of former sea level from assemblages of foraminifera and bulk-sediment δ13C values using a Bayesian transfer function. We employed radiocarbon dating and recognition of pollution horizons to construct a core chronology. Since ∼1200 BCE, RSL rose by ∼3.7 m at Fox Hill Marsh. After correction for glacial isostatic adjustment, application of a statistical model intended to quantify (multi-) century-scale trends showed that the fastest rate of rise in at least the past 3000 years was 1.71 ± 0.84 mm/yr (95% credible interval) in 2020 CE. This result replicates regional tide-gauge measurements and other proxy reconstructions. Using an alternative statistical model constructed to identify sub-centennial sea-level changes, we examined if there was a hotspot of 18th century rise in the northeastern United States and found no spatially-coherent trend (i.e., occurring at all or most sites). This lack of replication indicates that accelerated rise during the 18th century is likely local (site-specific) in scale, or an artifact of individual reconstructions. Continued efforts to replicate RSL reconstructions will increase confidence in the accuracy of records and their subsequent interpretation.