Sea-level Fluctuations Research Articles

Ichnoguild analysis of the Bajocian-Bathonian Yellow Flagstone Member (Goradongar Formation) from the Kachchh Basin, Western India

The Yellow Flagstone is the oldest member of the Goradongar Formation exposed in the Pachchham Island, Kachchh Basin. The members exposed in four sections are mapped for trace fossils, and 17 ichnofossils have been documented. The concept of ichnoguild (IG) is applied to reveal the infaunal tiering structure and the strategies organisms adapt to exploit the resources. Ten IG of similar characteristics and ecological functions have been identified. Five are shallow-tier IGs ( Asterosoma IG, Gyrochorte IG, Nereites IG, Planolites IG and Bolonia IG), three middle-tier IGs ( Rhizocorallium IG, Arenicolites-Diplocraterion IG and Zoophycos-Teichichnus IG) and two deep-tier IGs ( Skolithos Arenicolites IG and Thalassinoides-Ophiomorpha IG). The analysis of three ichnological tiers and their IGs, namely shallow, middle and deep-tiers across the stratigraphy of Yellow Flagstone Member suggests a transition from a lower shoreface environment to offshore transition environments. The transition is supported by an increase in deep-tier IG and the marginal increase in the ichnodiversity and density. Changes in the composition and abundance of IGs over time can indicate shifts in sedimentation patterns, sea level fluctuations and paleoenvironmental conditions within the basin. Thus, the findings suggest an environmental shift from shoreface to offshore transition indicative of a transgression during the deposition of upper Bajocian to lower Bathonian Yellow Flagstone Member in the Kachchh Basin. The study also examines the temporal and spatial changes in the IGs, contributing to a better understanding of ecological changes within the basin. The findings contribute to the broader knowledge of paleoecology and provide valuable data for sedimentological and stratigraphic interpretations in sedimentary basins.

Paleoenvironmental reconstruction of coal deposition during the Cretaceous-Paleogene transition in the Eastern Cordillera Basin, Colombian Andes

Stratal stacking patterns and factors influencing peat accumulation in coastal and continental settings represent a significant problem in studying coal-bearing sequences. To address this issue, this work focused on the Cretaceous-Paleogene Guaduas Formation on the Checua-Lenguazaque Syncline (CLS) coalfield in the Eastern Cordillera Basin (Colombian Andes). This study relies on geological survey, facies analysis, sequence stratigraphy, organic geochemistry, and coal petrography. Through these methods, depositional systems and sequences were characterized, and their relationship with coal composition was established. Sedimentary facies were categorized into four Facies Associations (FAs): lagoon, tidal flat, delta plain, and mixed fluvial system. Five T-R sequences (S1 to S5, in ascending order) were identified. S1 consists of lagoon and tidal sandstone, mudstone, and coal. S2-S4 comprise tidal, deltaic, and fluvial deposits. S5 is composed mainly of deltaic and fluvial facies. Thick coal seams (> 0.7 m) were concentrated in the regressive system tracts of S1 and S3, while the transgressive coals were deposited in S2-S3 and are associated with tidal environments. The organic petrography showed enrichment in vitrinite (30.00–85.20 %), while liptinite (0.00–16.60 %) and inertinite (4.60–34.40 %) varied according to depth and paleoenvironments. CLS coalfield displays an environmental evolution from shallow marine and lagoon deposits to deltaic and fluvial environments. Minor sea-level fluctuations, changes in accommodation, siliciclastic influx, and plant community distinguish this sedimentary succession. The deposition of the Guaduas Formation is characterized by a prograding pattern with dominant shallowing-upward cycles in a high accommodation setting. The organic matter accumulated under limno-telmatic to telmatic conditions in mesotrophic to ombrotrophic environments with nutrients derived mainly from rainfall. The paleoclimate for the Guaduas Formation indicates wet and hot conditions for flora expansion. This investigation determined paleoenvironments of the Maastrichtian-Paleocene coastal to fluvial successions within the tropical latitudes, indicating a strong relationship between depositional systems, sequence stratigraphy, paleoclimate, and coal composition.

Palaeodrainages of the Sunda Shelf detailed in new maps

The Sunda Shelf is a prime biodiversity hotspot where some of the planet's most endemic species can be found. Much of the diversity in this important bioregion has been shaped by sea-level fluctuations that took place during the Pleistocene. Using depth contours obtained from the General Bathymetric Chart of the Oceans Grid 2023, we provide high-resolution reconstruction of land areas and palaeo-drainages on the Sunda Shelf at the 50, 75, 100, and 120 m isobaths, as well as palaeo-catchments at the 120 m isobath, in order to elucidate the history of this region. The maps presented here aim to reconstruct the connection between palaeo-rivers in the Sunda Shelf and contemporary rivers and identify possible dispersal routes and barriers for the floras and faunas/biotas associated with riverine systems found here.

SPECIFIC FEATURES OF TIDAL EXCHANGE IN THE KURIL STRAITS ACCORDING TO MODELING DATA

Specific features of tidal fluctuations of sea level and tidal currents in the straits of the Kuril Islands are studied using numerical modeling. Two-time intervals, i. e. 02.06.1977-03.06.1977 and 11.10.1977-12.10.1977, were taken to compare the parameters of tropical and equatorial tides. The simulation results were verified with the field data. It was found that the straits of the northeastern part of the Kuril Ridge have a mixed type of tides with a predominance of the diurnal course, and in the southwestern part a semi-diurnal course prevails. The highest tides (up to 2,5-3 m) in the study period were observed on 02.06.1977 near the Kamchatka Peninsula and the Hokkaido Island, as well as large islands of the Kuril Ridge. Four main oscillation periods of 12, 12,4, 24 and 25,8 hours were identified, which corresponds to the S2, M2, K1 and O1 harmonics. Analysis of the data obtained showed that the maximum velocities of the depthaveraged currents reach 4,5 m/s. The highest speeds were recorded in the Kruzenshtern, Frieze and Sredny Straits. Estimates of the tidal flow have shown that semi-daily fluctuations are more pronounced in the straits with lower average depths during a tropical tide. In deeper straits, semi-daily fluctuations at tropical tides are very weak or absent at all, an example is the Boussol Strait. It is calculated that when using a two-dimensional model, the maximum values of the tidal flow are observed in the Boussol Strait, reaching ~40 Sverdrups (Sv).

Historical biogeography of North American killifishes (Cyprinodontiformes) recapitulates geographical history in the Gulf of México watershed

Abstract We analysed phylogenetic relationships within a major clade of Cyprinodontiformes (Teleostei) that includes five families of North American killifishes. We used DNA sequences from five genes for 130 species, with four fossil calibrations and three secondary calibrations, to generate a time-calibrated phylogeny. We estimated diversification rates, ancestral areas, and ancestral habitats for each node. Findings were interpreted within a detailed biogeographical synthesis. The results indicate that the clade arose in the Eocene along the Gulf of México coast. The speciation rate was uniform through time, except for acceleration in Cyprinodontidae after ~10.9 Mya. In other families, neither viviparity nor marine-to-freshwater transition was associated with accelerated speciation. Sea-level fluctuations might have created a speciation pump by stimulating cycles of dispersal and vicariance along the coast. Diversification also included many cases of inland immigration from coastal ancestors. For upland lineages, ancient river drainages accord with lineage distributions, including enigmatic disjunctions in Goodeidae and Fundulus. Diversification in uplands occurred via barrier displacement within alluvial or tectonically active landscapes. Killifishes also display high environmental tolerance and persist within harsh, peripheral environments unsuitable for most other fishes. Hence, a combination of clade antiquity, adaptability, dynamic geography, and persistence can explain the living diversity of New World killifishes.

Sediment source-to-sink patterns along the Southeast China coast during the late quaternary: New insights from sediment geochemistry and OSL ages in the Ningde Bay

The geomorphology and environmental conditions of the southeast China coast are significantly influenced by sediment discharge from the Yangtze River, a major river located to the north. Nonetheless, the extent to which the Yangtze River affects sediment transport processes from source to sink along the southeast coast remains unclear. Our recent findings in coastal/marine deposits from the late Quaternary period (MIS5e, MIS3, and MIS1) in Ningde Bay offer new perspectives on this issue. Provenance discrimination of the late Quaternary boreholes was carried out using sediment geochemical analysis and OSL dating of fine- and medium-grained quartz. The results indicate varying provenances during sea-level fluctuation, with distal Yangtze River origins during MIS5e, MIS3, and MIS1, and a local source during MIS4. The findings also suggest that the southward transport of Yangtze sediments along the southeast China coast has occurred since MIS5e. However, OSL ages of the fine-grained quartz in the MIS3 deposit range from approximately 90 to 140 kyr, notably older than those of medium-grained quartz (40–80 kyr). This remarkable age discrepancy indicates that Yangtze-derived sediments previously deposited on the shelf of the East China Sea during MIS5 were reworked and transported southward in MIS3. This phenomenon can be elucidated by the insufficient supply of Yangtze sediments during MIS3, which could be linked to the weakened East Asian monsoon. This new source-to-sink pattern for the southeast China coast is characterized by a compensating mechanism of inner shelf old sediment in response to the inadequate supply of Yangtze sediments. This study contributes to a better understanding of the significant impacts of reduced Yangtze sediment input on its distal sedimentary systems over time.

Molecular to macrofossils indicating last millennium sea level in Lavsa saltpans, Croatia

Intertidal salt production sites existed continuously around the Mediterranean since classical antiquity, and their remains are present in large numbers along the Dalmatian (east Adriatic) coast. Most of them are preserved and dated to medieval times. This study aims to develop complementary proxies identifying the salt production layer in submerged ancient saltpans of Lavsa, a remote island on the central Dalmatian coast, to date the saltwork units by optically stimulated luminescence (OSL) and use them to infer changes in sea level. The significance of the study is in the application of molecular fossil analyses identifying the hypersaline layer in the sediments from a core drilled in the saltpan's site. The molecular fossil analyses correlate with the results of micro and macrofossil analyses and geochemical findings, all representing the saltwork unit. The depth of the hypersaline layers and the OSL dates provide relative sea level (RSL) lower limiting points of −145 ± 5 cm at 1309 ± 33 CE, probably the time when salt production started in Lavsa, and −115 ± 5 cm at 1364 ± 52 CE when saltwork activities ended. These limiting points extend the known RSL index point in Lavsa Island of −92 ± 8 cm, with an updated average age of 1337 ± 62 CE, correlating with the historical records. Medieval lower sea levels were also observed in the northern and southern parts of the east Adriatic coast as well as in other parts of the Mediterranean, probably driven by climate-related events, generating centennial-scale fluctuations in past sea levels that cannot be predicted by glacial isostatic adjustment (GIA) models.

40Ar/39Ar geochronologic and paleoenvironmental constraints to glacial termination III and MIS 7e, 7c, and 7a sea level fluctuations on the Tyrrhenian Sea coast of Italy

We provide detailed sedimentological, paleontological, and tephrochronological data on a complex sedimentary succession cropping out in the Tyrrhenian coastal area of central Italy, which was deposited in response to sea-level rise during MIS 7, coeval with the Latera phase of activity in the Vulsini Volcanic District. Diffuse intercalations of primary volcanic layers erupted during this phase and their geochronologic and chemostratigraphical characterization based on 40Ar/39Ar dating and EMP analyses, allowed for the identification of three stacked aggradational successions separated by erosive phases and their correlation with the Oxygen isotope record and phases in the relative sea-level curve. The ages of the tephra layers strictly frame the sedimentation in the interval of 253–206 ka, providing independent dating to glacial Termination III and to the three sea-level oscillations during MIS 7e, 7c, and 7a.Moreover, micro- and macrofaunal-based analyses provide information on the paleoenvironments and bathymetry during the highstands, which complement the geomorphological analysis reconstructing the inner edges of the corresponding marine terraces, allowing us to assess precise maximum sea level reached during MIS 7e and MIS 7a.The results of this multidisciplinary study enable us to establish in great detail the chronology, dynamics, relative amplitude, and effects of the sea-level fluctuations in the Tyrrhenian Sea during the whole MIS 7, providing independent, precise geochronological constraints for this period.

Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy

The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.

Reconstructing CO2 uptake capacity and pH dynamics in the Middle Ordovician Taebaeksan Basin, Korea

This study presents the first continuous carbonate boron isotope (δ11Bcarb) record from Middle Ordovician carbonate rocks, focusing on the Taebaek section in Korea. The δ11Bcarb values analyzed from the Makgol, Jigunsan, and Duwibong formations range between 7.5 ‰ and 17.8 ‰, falling within the published Paleozoic range. Samples exhibit minimal diagenetic alteration, as evidenced by weak correlations between isotopic factors and elemental ratios (δ11Bcarb, δ13Ccarb, δ15Nbulk, B/Ca, Mn/Sr, and Na/Ca) as well as mineralogical observations used to select unaltered micrite portions. Using the δ11Bcarb data, we reconstruct pH levels (8.4 to 9.1) which suggest that this shallow shelf environment acted as a CO2 sink during the Middle Darriwilian, despite periods of acidification coinciding with sea level rise and expansion of anoxic zones. Weakening of the basin's CO2 uptake capacity via reduced CaCO3 precipitation and photosynthesis accompanied these oceanographic changes. Our findings provide new insights into the dynamics of CO2 accumulation and pH in Middle Ordovician shallow marine settings in relation to sea level fluctuations. This work lays the foundation for further research into ocean chemistry and carbon cycle perturbations during this important period in Earth's history.

Ecological connectivity of the Qiongzhou Strait: a case form Orangefin Ponyfish (Photopectoralis bindus) haplotype diversity and genetic structure

Grasping the genetic structure of marine fish populations is vital for comprehending species connectivity patterns and determining the appropriate spatiotemporal scales for conservation management strategies. Here, we analyzed the population genetics of the Orangefin Ponyfish (Photopectoralis bindus Valenciennes, 1835) by examining a portion of the gene coding for the mitochondrial cytochrome c oxidase subunit I. The aim was to evaluate the haplotype pattern, genetic structure, demographic history, as well as the influence of ecological connectivity through the Qiongzhou Strait on the distribution patterns of this species in the northern South China Sea and the Beibu Gulf. In total, 257 specimens yielded only 13 haplotypes, with the predominant haplotype present at all sampling locations. The analysis revealed a “star-like” haplotype pattern, indicating low levels of both haplotype and nucleotide diversity. Additionally, a small but significant genetic structure was observed between the coastal regions flanking the Leizhou Peninsula. These patterns in the haplotype network and genetic structure may be significantly influenced by contemporary currents, particularly through the connectivity of the Qiongzhou Strait. Tajima’s D and Fu’s Fs demonstrated pronouncedly negative values, along with a unimodal mismatch distribution, suggested a recent demographic expansion of Photopectoralis bindus during the late Pleistocene, likely influenced by fluctuations in sea levels.

The IoT-Based Early Warning System for Detecting High Tide Floods (ROB-EWS) in Tambak Lorok, Semarang Indonesia

Background and Objectives: The Tambaklorok fishing village area, located on the northern coast of Semarang City, Indonesia, is susceptible to sea level fluctuations, which often lead to tidal flooding and seawater encroaching into residential areas. Consequently, a seawater flood detector (rob) is needed for effective disaster mitigation for affected communities. This study aims to implement a disaster mitigation system by installing an IoT-based Seawater Flood (Rob) Early Warning System to reduce disaster risks and their impacts on the community. Methods: The IoT-based Early Warning System is designed to detect floods by monitoring sea level height parameters. Results: IoT-based devices measure sea level using ultrasonic sensors, with the readings processed by a microprocessor. The data is then periodically analyzed and transmitted to an application in real-time. This technology allows for real-time information dissemination through web applications and alerts in the form of sirens. These warnings enable residents to evacuate and move to safer areas. The siren alerts are categorized into two levels: Alert 1 indicates that seawater is approaching the land boundary, while Alert 2 signals that water has begun to enter residential areas. Additionally, designated evacuation zones will guide affected communities to safer areas. Conclusion: The installation of an IoT-based Early Warning System delivers real-time information to help mitigate the impact of rising sea levels (rob) in the Tambak Lorok fishing village community.

Mitochondrial markers revealed genetic panmixia in the data-deficient yellowfin snapper, Lutjanus xanthopinnis (Actinopterygii: Eupercaria: Lutjanidae), from a hotspot of the southern region of the South China Sea

Understanding the genetic structure and diversity of marine fish is crucial for a sustainable management program. We examined the genetic diversity and historical demographics of the yellowfin snapper, Lutjanus xanthopinnis Iwatsuki, Tanaka et Allen, 2015, in the coastal waters of east Peninsular Malaysia which is bordered by the southern part of the South China Sea using the mitochondrial genes (mtDNA) D-loop and Cytochrome b (Cyt-b). A total of 99 (D-loop) and 78 (Cyt-b) specimens of L. xanthopinnis were successfully sequenced from six locations within the range of species distribution along the Malaysian South China Sea. In the presently reported study, the lack of genetic differentiation among populations can be attributed to historical demographic events, eggs and planktonic larvae’ ability to disperse, spawning patterns, and the absence of physical barriers in the geographical landscape. Maximum likelihood gene trees demonstrated that the populations under study had limited structuring and formed a panmictic population that lacks support for internal clades. The AMOVA (Analysis of Molecular Variance) and population pairwise ФST values indicated high genetic exchange between the study areas. A high level of haplotype diversity (D-loop: 0.948–1.000; Cyt-b: 0.542–0.928), low nucleotide diversity (D-loop: 0.0095–0.0159; Cyt-b: 0.0022–0.0049) and starlike haplotype network indicates a recent expansion of L. xanthopinnis populations in Malaysian South China Sea. However, neutrality and goodness of fit tests revealed non-significant values. Furthermore, the BSP (Bayesian skyline plot) analysis estimated population expansion events during the late Pleistocene. During this epoch, the fluctuation in sea level may have led to an increase in the abundance of resources and favorable habitats for the yellowfin snapper. The presently reported findings could initiate efficient management strategies for L. xanthopinnis along the coastal areas of the Malaysian South China Sea and other nearby nations that share the same waterways.

Pollen evidence of enhanced Yellow River provenance into the South Yellow Sea after the Middle Pleistocene Transition

Quaternary sediment of the South Yellow Sea (SYS) is usually assumed to record climatic changes, tectonic activities and major river evolutions. However, as an important terrigenous indicator, a long sequence of pollen proxy in the SYS lacks for studies of river provenance and climate changes. In this study, we focused on a 150-m pollen record in the SYS that covered most of the Quaternary period over the past 1.8 Ma. The most significant changes of pollen assemblage were caused by river provenance, that high pollen percentages of broadleaved trees such as Castanea/Castanopsis reflect a dominant provenance of the Yangtze River since ca. 1.8 Ma, with a decline trend during the Mid-Pleistocene transition (MPT) mainly between 1.1 and 0.8 Ma. The sharp increase in coniferous pollen, particularly Picea, originated from the Yellow River drainage areas, suggesting a major alteration in terrigenous pollen source from the Yangtze River to the Yellow River at ∼0.8 Ma, which agrees well with the timing of the final integration of the modern Yellow River. The high pollen quantities of Artemisia and Ephedra also shows the enhanced Yellow River provenance where most landscape was covered by semi-arid open vegetation (e.g. steppe). The alternate appearances of marine foraminifera and dinoflagellate cysts, and freshwater wetland plants (Cyperaceae, Poaceae) through the interglacial intervals from MIS 19/21 demonstrate different estuary sedimentary environments and diverse salinity, associated with the sea-level fluctuations. The pollen concentration suggests an increase in terrigenous materials towards the interglacial MIS 11 and the preliminary delta formation of the Yellow River. We propose that the terrigenous input from the Yellow River accelerated after the MPT, and combined effects of tectonic movement drove the evolution of the river delta plains in eastern China. Our data also reveal some secondary periodic changes in evergreen broadleaved forest during the past 1.8 Ma and cold-tolerant coniferous forest since particularly the MPT, which are generally linked with the 400-ka long eccentricity cycle and the variability of monsoon climate.

Depositional Environment and Ecological Response of Bioconstructions: A Case Study of Southern China (Guizhou Province) in Moscovian-Gzhelian.

From the late Carboniferous to the early Permian, multiple pulses of glaciation and deglaciation have been caused by the LPIA. The Pennsylvanian period experienced phases of recovery, proliferation, and decline, ultimately forming a reef system distinctly different from that of the Mississippian period. During the late Bashkirian to Moscovian, the metazoan reef experienced a limited resurgence, with reef predominantly formed by chaetetid developing in the United States, northern China, and Japan. During the Kasimovian to Gzhelian, the phylloid algal reef dominated the global reef systems. In the late Pennsylvanian, bioconstruction cases and paleoenvironmental proxies in southern Guizhou Province were studied to investigate the composition, recovery, and evolutionary processes of the bioconstructions as well as their response to environmental variations during this period. Several bioconstructions have been reported in the Lumazhai section of Houchang Town, Guizhou Province, southern China, from the Moscovian to the Gzhelian. The upper Carboniferous strata are well-preserved and continuously exposed. The continuous strata, abundant fossils, and diverse bioconstructions provide excellent research materials for exploring the mutual constraints between organisms and their environment. This study identified ten microfacies, whose vertical evolution indicated significant changes in the depositional environment related to relative sea-level fluctuations. Skeletal grains are widely present in these facies. Among them, foraminifera, algae, bryozoans, crinoids, and Tubiphytes are the most common and exhibit distinct distribution characteristics in various environments. Quantitative statistics, CCA and theoretical ecospace have been utilized to examine and interpret environmental impact factors. Quantitative analysis of their relative abundance and distribution patterns provides insights into the complex interactions between organisms and environmental factors. The relative abundances of different organisms and factors controlling their bioconstructions are influenced by relative sea-level changes. CCA analysis reveal that hydrodynamic conditions are the primary influencing factor. Variation trends in average tiering and motility reveal the characteristics of biological communities during environmental changes in phylloid algae and microbial bioconstructions. These bioconstructions are not directly correlated with changes in environmental factors, and the biological communities in phylloid algae mounds and biostromes exhibit similar organism compositions and ecological niches across different environments.

Extreme sea levels and floods: the case study of Klaipėda City, Lithuania

Klaipėda City is located in the Southeast Baltic Sea region, where sea level rise has been observed for decades. The Klaipėda Strait, which separates the Baltic Sea and the Curonian Lagoon, where the port is located, is also more prone to sudden extreme changes in water levels, usually caused by windstorms. Extreme sea level changes pose a threat to port operations, technical structures, city residents, buildings, and infrastructure. Fluctuations in sea levels also affect the water level of the Danė River, which enters the Klaipėda Strait and divides the city into two parts. Therefore, this study aims to determine the past extreme sea level events and their influence on floods in the Danė River within Klaipėda City from 1961 to 2022. For this, the impact of meteorological parameters caused dangerous sea level rises in the Klaipėda Strait, and the following rise of the Danė River was studied. The results show that the annual mean, annual mean maximum, and annual mean minimum water levels in the Klaipėda Strait increased from 1961 to 2022. Also, the number of events where the water level in the Klaipėda Strait was ≥ 100 cm in the Baltic Elevation System was increasing. The increasing frequency of extreme water level events in the Klaipėda Strait puts urban areas at greater risk from Danė River compound floods.

Late-Holocene sea-level markers preserved in a beach ridge system on Phra Thong Island, Thailand

Instrumental sea-level records are insufficient to understand the response of sea-level changes to global temperature on centennial timescales. Sea-level histories spanning at least the Common Era have not been widely studied in Southeast Asia. This period is crucial for providing a pre-industrial context to understand sea-level change with climate. Linking sea-level change to climate change is proxy dependant, with most proxies only providing decadal to centennial scale resolution of both sea level and climate. This study examines the efficiency of beach ridge stratigraphy as a proxy for reconstructing regional sea-level histories in the tropics. We present topographically corrected Ground Penetrating Radar (GPR) profiles from a prograded coast in Phra Thong Island, Thailand, where we identify downlap point marking the boundary between the foreshore and shoreface subzones and use this as a past low-tide marker. The low-tide markers were corrected (considering the tidal range) and then connected to approximate the past sea level. Optically Stimulated Luminescence (OSL) samples collected at locations slightly offset from the shore-normal GPR profile line were incorporated to create a relative sea-level record. Overall, the shore-normal GPR record shows a ∼ 1.06 m fall in sea level between ∼2660 and ∼ 370 years ago. The study also highlighted stepwise fluctuations in sea level that were not identified in previous studies. Between ∼2600 and ∼ 2200 years ago, the record indicates a steep fall in sea level, followed by a phase of relatively stable to slightly falling sea level between ∼2200 and ∼ 550 years ago. Finally, for the seaward side, between ∼550 and ∼ 350 years ago, the record indicates an accelerating sea-level fall. This study confirms that the investigation of tropical beach ridge systems using GPR and OSL techniques can be a highly efficient and effective means for reconstructing regional sea-level trends throughout the Common Era and beyond.

Mean sea level, tidal components and surges in Guanabara Bay (Rio de Janeiro) from 1990 to 2021

AbstractGuanabara Bay, located in the Metropolitan Region of Rio de Janeiro, one of the largest urban coastal areas in the Southern Hemisphere, is subject to intense maritime traffic due to the presence of several ports. These facilities are affected by sea level fluctuations, influenced by atmospheric and astronomical forces, which motivates synoptic and climatological analysis, including meteorological and astronomical tidal phenomena. This study aimed to assess the evolution of tidal components and the relative mean sea level (MSL) between 1990 and 2021, as well as the atmospheric influence on extreme meteorological tide events, in which the MSL exceeded ±2 and ±3 (±29.98 and ±44.97 cm) standard deviations. The results have shown that, albeit small, the main tidal components (, , , , , , and ) indicated positive trends in the increase of amplitude and phase, despite the small quantities. For the relative MSL, an increase of 0.30 cm·year−1 was observed in agreement with estimates from global series from satellite altimeters and climate model predictions. Pressure and wind field analyses led to the identification of seasonal variability and the pattern of evolution of atmospheric systems associated with extreme events. In the case of positive surges, very intense winds from the SW, extending along the S/SE Brazilian coast, are caused by the presence of a high‐pressure centre over the continent and low‐pressure centres over the ocean, leading to water piling up. In turn, negative surges are caused by the presence of an anticyclone over the ocean, generating NE winds parallel to the coast of Rio de Janeiro, inducing Ekman transport and lowering the sea level. Therefore, the extreme sea level events in the Guanabara Bay are not triggered by local forces, but rather depend on the temporal persistence and direction of winds along the S/SE Brazilian coast.

Identification of the mode of evolution in incomplete carbonate successions

BackgroundThe fossil record provides the unique opportunity to observe evolution over millions of years, but is known to be incomplete. While incompleteness varies spatially and is hard to estimate for empirical sections, computer simulations of geological processes can be used to examine the effects of the incompleteness in silico.We combine simulations of different modes of evolution (stasis, (un)biased random walks) with deposition of carbonate platforms strata to examine how well the mode of evolution can be recovered from fossil time series, and how test results vary between different positions in the carbonate platform and multiple stratigraphic architectures generated by different sea level curves.ResultsStratigraphic architecture and position along an onshore-offshore gradient has only a small influence on the mode of evolution recovered by statistical tests. For simulations of random walks, support for the correct mode decreases with time series length.Visual examination of trait evolution in lineages shows that rather than stratigraphic incompleteness, maximum hiatus duration determines how much fossil time series differ from the original evolutionary process. Gradual directional evolution is more susceptible to stratigraphic effects, turning it into punctuated evolution. In contrast, stasis remains unaffected.Conclusions• Fossil time series favor the recognition of both stasis and complex, punctuated modes of evolution.• Not stratigraphic incompleteness, but the presence of rare, prolonged gaps has the largest effect on trait evolution. This suggests that incomplete sections with regular hiatus frequency and durations can potentially preserve evolutionary history without major biases. Understanding external controls on stratigraphic architectures such as sea level fluctuations is crucial for distinguishing between stratigraphic effects and genuine evolutionary process.

Geochemistry of Quaternary sediments in the northwestern South China Sea: Sediment provenance and mid-Pleistocene transition

The Quaternary sediments in the northwestern South China Sea (NW-SCS) provide valuable information about provenance, climate and sea level changes. However, the correlation between the geochemical records in marine sediments and these influencing factors remains less understood in the NW-SCS. Two wells penetrated Quaternary sediments on the shelf and shelf margin of the NW-SCS and provide an excellent dataset. In this study, the major, trace, and rare earth elements in the sediments were analyzed to reveal the Quaternary provenance changes that correlate with the climatic Middle Pleistocene transition (MPT). These results indicate that the core sediments were mainly derived from felsic source rocks and the degree of chemical weathering in the source areas is relatively low (CIA averaged at 58). The Quaternary provenance of the NW-SCS did not undergo significant changes, recording mixed sedimentation from the Red River, Hainan Island, and central Vietnamese sources. The felsic source rocks and negative Eu anomaly indicated the shelf area received sediments primarily from the Red River and Hainan Island. However, a positive Eu anomaly on the shelf margin suggests additional contributions from mafic rocks sourced from central Vietnam. During the MPT (1.3–1.4 to 0.8–0.9 Ma), the dominant periodicity of climate cycles changed from a 40 kyr obliquity cycle to a 100 kyr eccentricity cycle; the cooling climate led to a slight weaking in chemical weathering and a minor decrease in sediment supply from terrestrial sources. After the MPT, the mixed sourced sediments in the shelf and shelf margin areas of the NW-SCS likely suffered from multiple hydrodynamic forces under the influence of the Pleistocene high-frequency and high-amplitude sea level fluctuations. These climate induced changes led to significant fluctuations in element content that provide new insights into Quaternary sources and climatic events in the NW-SCS.