Sea Level Regime Research Articles

LAGOA SALGADA: AN OVERVIEW OF A BRAZILIAN HYPERSALINE LAGOON ENVIRONMENTAL STUDIES OVER THE LAST 5000 YEARS USING RADIOCARBON DATE CORRECTIONS

ABSTRACTThe Lagoa Salgada is located in the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, and is one of the few lagoons in the world that have well-developed recent stromatolites. Lagoa Salgada is a hypersaline lagoon formed in a very complex environmental system subjected to terrestrial and oceanic influences under different sea level regimes and climate variations. In addition, sediment and stromatolites are characterized by unusually positive inorganic δ13C VPDB values. For this reason, it has been the target of several geological and paleoenvironmental studies, which, in their great majority, require a geochronological technique in order to determine the changes in the environment over time. When radiocarbon (14C) dating is used, it is necessary to consider some details as the source of 14C in the environment and perform 14C ages calibration accordingly. In the present paper, a bibliographic survey was carried out in order to review the data treatment and improve the environmental evolution discussion based on accurate calibration. Using the Marine20 curve and an undetermined ΔR, we generated growth and depositional models to establish an overview of the formation of this lagoon.

Physical Modelling in Development of the Regulatory Framework for Transport Construction

Application of the physical modelling method to justify regulatory requirements for design of structures for engineering protection of transport facilities from wave action is considered using the example of three completed research and development works. The described experimental studies of interaction of waves with structures were carried out in wave basins and tanks.The objective of the research is to scientifically substantiate the requirements of regulatory documents for design of shore protection to ensure safe operation of the roadbed of railways and roads, bridge supports, and other transport structures operated under conditions of wave action on the shores of seas and lakes. In this case, the normalised parameters, depending on the hydrological (wind-wave and sea-level regimes of the water area and current), geological-morphological and lithodynamic (coastal zone dynamics) conditions are the types of protective structures used, planned and design solutions for protective hydraulic structures (location, elevations, dimensions), as well as the materials and products used for construction (including quality requirements).The experimental design part of the described studies was carried out by the method of physical (hydraulic) modelling in wave basins and tanks. Physical modelling was carried out in accordance with the theory of similarity. At the same time, a «flat problem» is solved in wave tanks, and a «spatial problem» is solved in wave basins.

Stages of palaeoenvironmental evolution, climate and sea level change of the Niger Delta, east Equatorial Atlantic: Novelty from elemental tracers, sedimentary facies and pollen records

This study used the comparative analysis of 3 gravity cores (GCs) obtained from the shallow offshore at ~40 m water depth to reconstruct the morphological evolution of the delta (East Equatorial Atlantic). The focus of this study is on the interpretation of elemental tracers and their justification between these tracers and microfossil data to understand the impact of climate-sea level controls on the evolution of the Niger Delta during the Late Quaternary. Key elemental tracers comprising Ti, Zr, Fe and S were explored to strengthen this concept. High Ti/Zr ratio values down-hole indicate fluvial transport of terrestrial components to the marine setting (20–11.7 ka), whereas high values of Fe/S ratio up-hole provide an extent of inherent marine shale of the Niger Delta (11.7–6.5 ka). In addition, the integrated multiple proxy (mangrove and hinterland pollen, planktonic foraminifera and sedimentary facies) with elemental tracer ratios provided robust and coherent information for delineating the late glacial (MIS2) prograding and interglacial (MIS1) retrograding deltaic transition, respectively. The overall trends of the two elemental tracer ratios (Lower and Mid-upper depths of the GCs) provide a new distinction on the depositional patterns (prograding and retrograding delta) to determine the proximal/upper (clay, silt and very fine sand) and distal offshore/lower shorefaces (coarse-medium sand), and gross palaeoenvironments based on planktonic foraminifera records. These sequential records provide a new clue as evidence of the morphological evolutionary stages (delta plain, delta front and prodelta) of the Niger Delta landscape, gross palaeoenvironments, and vegetation dynamics (pollen data) during two distinct time-bound intervals (20–6.5 ka), which potentially delineate the climate and sea level regime of the coastal offshore.

Late Ordovician climate and sea-level record in a mixed carbonate-siliciclastic-evaporite lithofacies, Williston Basin, USA

The Late Ordovician late Katian was a period of generally warm, transitional greenhouse to icehouse climate with sea-level oscillations dominated by moderate-amplitude eustasy. This study aims to improve the understanding of the climatic and sea-level fluctuations prior to the end-Ordovician glaciation, using a comprehensive core, wireline log, and thin-section dataset spanning the topmost Red River-Stony Mountain Formation within the subsurface of North Dakota, Williston Basin, North America. Eleven facies are identified, interpreted, and grouped into four facies associations, including salina to peritidal evaporative, restricted-marine subtidal, open-marine subtidal, and open-marine deeper water. Stratigraphic trends, basin-wide facies variations, and correlation of individual surfaces for ~380 km across the study area, suggest that the facies were deposited under different climatic and sea-level regimes as part of the long-term Stony Mountain sequence. The sequence (37–52 m) is bounded by anhydrites (basin center) and their correlative thin exposure-related breccias (updip proximal basin), and contains a set of high-frequency sequences (HFS; 2–26 m) that can be traced across the study area. The lowstand systems tract (LST) anhydrites formed in a shallow and well‑oxygenated setting under an arid climate during relatively short periods of the basin restriction. The sea-level rise during the early transgressive system tract (TST) resulted in a higher evapotranspiration rate and an increasingly humid climate that peaked during the late TST with the input of siliciclastics off the Transcontinental Arch. The increased precipitation and runoff resulted in quasiestuarine circulation. Return to semi-arid conditions characterizes the highstand systems tract (HST), with increasingly more restricted, shallow-marine and oxygenated setting with antiestuarine circulation. The work provides insight into the interaction of siliciclastic input, climate, and sea-level changes on depositional dynamics and sequence architecture of a mixed carbonate-siliciclastic-evaporite succession that formed in a tropical epicontinental basin setting prior to the end-Ordovician glaciation.

Mid–late Holocene event registered in organo-siliciclastic sediments of Lagoa Salgada carbonate system, southeast Brazil

Abstract. The formation of the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, gave rise to diverse lagoons formed under different sea level regimes and climate variations. Sedimentary core lithology, organic matter geochemistry, and isotopic composition (δ13C and δ15N) were analyzed to interpret the sedimentation of the paleoenvironment of the Lagoa Salgada carbonate system. Different lithofacies reflect variations in the depositional environment. The abundance of silt and clay between 5.8 and 3.7 kyr enhances the interpretation of a transgressive system, which promoted the stagnation of coarse sediment deposition due to coast drowning. Geochemistry data from this period (5.8–3.7 kyr) suggest the dominance of a wet climate with an increase of C3 plants and a marked dry event between 4.2 and 3.8 kyr. This dryer event also matches with previously published records from around the world, indicating a global event at 4.2 ka. Between 3.8 and 1.5 kyr, Lagoa Salgada was isolated; sand and silt arrived at the system by erosion with the retreat of the ocean and less fluvial drainage. Geochemistry from this moment marks the changes to favorable conditions for microorganisms active in the precipitation of carbonates, forming microbial mats and stromatolites in the drier phase.

SEA-LEVEL EFFECT ON ANNUAL CYCLIC BEACH MORPHOLOGY IN SWASH ZONE AT HASAKI COAST

depend on the accurate knowledge of the beach response to sea level regime on multi-time scale. For the long-term beach response, Bruun (1962) suggested that the equilibrium beach profile would move to new equilibrium profile in response to a rising sea level. In this concept called as Bruun rule, the upper part of the beach profile is eroded due to the sea level rise, resulting in the shoreline retreat. It is widely used for the future shoreline prediction. However, the Bruun rule predicts just only the final beach state with a constant wave impinging for an infinite period after sea level rise. On the other hand, simultaneous function of wave and sea level is more important on interannual to decadal-scale beach response. El niño in 2015 and 2016 increased wave energy and sea level, corresponding to large beach erosion across the US west coast (Barnard et al., 2017). Sea level influences the response sensitivity to the wave forcing as a subordinate factor on the morphological change. High water level anomalies made the beach more eroded even if the wave condition was equal. Beach morphology in the swash zone often changes on a 1-year cycle due to seasonal wave conditions. The effect of sea level on the annual cyclic beach morphology in swash zone is still unclear because long-term beach observation data required for the analysis are difficult to obtain. In this study, we investigated the simultaneous effects of the wave and sea level on annual cyclic beach morphology in the swash zone with spectrum analysis for 25-year Hasaki beach observation data.

A high-resolution hindcast of sea level and 3D currents for marine renewable energy applications: A case study in the Bay of Biscay

In this work, we develop a high-resolution oceanographic database, suitable for marine renewable energy (MRE) applications. We apply downscaling techniques, using ROMS numerical model, to generate a 29-year (1985–2013), high-resolution (325 m), hourly sea level and currents (10 vertical levels) hindcast that reproduces storm surge and astronomical tide dynamics at a MRE test site (BiMEP) in the Bay of Biscay.The results are fully validated using instrumental data. We also analyze the result sensitivity to the open boundary conditions. We find that using boundary conditions from a baroclinic reanalysis, reproducing a wide range of physical processes, does not give more accurate results than a barotropic reanalysis, reproducing storm surge and astronomical tides, the main forcings at the study area. This analysis also leads us to address the importance of the temporal extent in the databases used for MRE applications.Finally, the generated hindcast is used to analyze normal and extreme currents and sea level regimes in BiMEP, following the internationally accepted standards for the design of MRE converters. The generated database offers MRE converter developers an alternative to the often-proposed empirical formulae for the definition of the design cases to consider in the loads and safety analysis of their devices.

Methodology for determining the mean and extreme sea level regimes (astronomical and meteorological tides) considering scarce records in microtidal zones: colombian Caribbean case

Se calibraron y modelaron series sintéticas del nivel del mar (NM) con una extensión temporal de 20 años (1991-2010) en la Bahía de Cartagena y el Golfo de Urabá. Las series simuladas fueron ajustadas a diferentes funciones de probabilidad obteniendo los mejores ajustes con las funciones de distribución Normal y de Gumbel para los regímenes medios y extremos respectivamente. Dentro y fuera de la bahía de Cartagena no existen variaciones representativas en el régimen medio, mientras que en el Golfo de Urabá la magnitud aumenta al doble en la parte sur. Además, el régimen extremo presenta magnitudes superiores en la parte sur del Golfo en relación a las demás zonas estudiadas. Esta metodología podría implementarse en áreas donde los registros del nivel del mar son escasos o poco confiables. Por lo tanto, puede ser valiosa para planificar y construir infraestructuras portuarias y costeras, o implementar medidas de reducción de riesgos.

Effect of the North Atlantic on the hydrological regime of the Caspian Sea basin

The cause of Caspian level variations is still to be found, and their forecasting is still among the problems to be solved. This study proposes a new approach based on the results of analysis of the effect the North Atlantic has on climate formation in the Caspian Sea basin. The article presents the results of analysis of moisture transport into the Caspian Sea basin, as well as a relationship between precipitation and temperature in this basin and the indices of atmospheric and oceanic circulation for the periods of Caspian level drop and rise. A pioneer study of moisture transport from the North Atlantic showed this transport to govern the formation of Caspian Sea level regime.

Late Pleistocene–Holocene seismic stratigraphy of Nha Trang shelf, central Vietnam

The late Pleistocene–Holocene stratigraphic architecture on the steep and narrow shelf off Nha Trang, central Vietnam has been explored by high resolution seismic profiles integrated with sediment core data. Sequence stratigraphic results reveal five major seismic units and three bounding surfaces which are composed of two distinctive sequences. Those sequences are bounded by two regional unconformities (SB1, SB2) which have been formed in respond to different sea-level regimes. The revealed relict beach–ridge deposits at water depth of about ∼130 m below the present water depth indicate that the Last Glacial Lowstand (LGM) sea-level in this area was lower than in neighboring areas and it probably resulted from subsidence due to high sedimentation rate and/or neotectonic movements of the East Vietnam Fault System. The late Pleistocene high amplitude of sea-level change during a long fourth-order and superimposed by shorter fifth-order cycle is the principal factor in reorganizing the formation of the Nha Trang continental shelf sequence. Other local controlling factors as fluctuations in sediment supply, morphological variations of the LGM surface, subsidence rate and hydrodynamic conditions provided the distinctive features of the Nha Trang shelf sequence stratigraphic model in comparison with neighboring other areas.

Late Holocene morphodynamics in the littoral zone of the Iwik Peninsula area (Banc d'Arguin — Mauritania)

In the littoral zone of the Banc d'Arguin both littoral sedimentary units and man-made deposits (shell-middens) abound. They were formed during the Late Holocene after the final onset of the post-glacial transgression. Here, a geo-archaeological approach is used to study them. The geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the Iwik–Aouatil zone between an ancient shoreline which formed on the Tafaritian substratum ca 6.7–5.7 cal. ka BP and the present one: (i) very extensive sand flats and (ii) linear relief features, both covered by a thin veneer of anthropogenic Anadara senilis shell-middens. They developed under a stable sea-level regime. The sand flats expanded at variable rates throughout the period. The linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell-middens, supplemented by 14C dating. Two series of linear sedimentary units are identified. First, a complex north–south system of dunes and hook-ended sand barriers developed from 4.8 to 4.1 cal. ka BP and, secondly, two regular and linear beach barriers developed between 3.7 and 3.3 cal. ka BP. Their morphological characteristics suggest that they were generated through littoral drift processes. Directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former Iwik Island and the land. A comparison with the nearby Jerf el Oustani coastal area in the Late Holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units. Processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change.

A full sea-level cycle in 65years: barrier dynamics along Caspian shores

The Caspian Sea, being a closed basin, shows much higher rates of sea-level change (up to 340 mm/yr) than the oceans. It experienced a full sea-level cycle with an amplitude of 3 m between 1929 and 1995. Its coasts therefore present an attractive physical model to test predicted changes along oceanic coasts as a result of expected eustatic sea-level rise, and to validate sequence-stratigraphical interpretations of ancient sediments. Along the wave-dominated coasts with intermediate shore-face slopes in Dagestan, low onshore bars were formed during the 1929–1977 sea-level fall. They represent minor short lived (1–2 years) transgressive oscillations within the major regressional trend. After the 1977 lowstand a prominent barrier–lagoon system was formed, which during the first phase of sea-level rise (1977–1988) encroached landwards about 18 m each year by washover during storms (continuous retreat). Between 1988 and 1995, however, barrier size diminished, lagoons widened and deepened, apparently due to lack of coarse-grained sediment supply (discontinuous retreat). The 1995 highstand prevented the barriers from being overstepped altogether. Sea-level fall after 1995 again produced low bars without lagoons. The Caspian Sea barrier coast demonstrates that for the formation of barrier–lagoon complexes the combination of transgression and storms is essential. Barriers may show either continuous or discontinuous development at constant rate of sea-level rise and constant offshore slope, depending essentially on the availability of coarse-grained sediments. The rate of sea-level rise as a factor in barrier behaviour cannot be viewed independently from barrier dimensions, which in turn depend on wave base depth and maximum storm wave height. Relations between (para)sequence thickness, and frequency and amplitude of sea-level change in closed basins with an independent sea-level regime may differ markedly from those in basins influenced by eustasy.

Interaction of tectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin

This study provides an integrated view of the growth patterns and factors that controlled the evolution of the Gulf of Cadiz continental margin based on studies of the tectonic, sedimentologic and oceanographic history of the area. Seven sedimentary regimes are identified, but there are more extensive descriptions of the late Cenozoic regimes because of the larger data base. The regimes of the Mesozoic passive margin include carbonate platforms, which become mixed calcareous–terrigenous deposits during the Late Cretaceous–early Tertiary. The Oligocene and Early Miocene terrigenous regimes developed, in contrast, over the active and transcurrent margins near the African–Iberian plate boundary. The top of the Gulf of Cadiz olistostrome, emplaced in the Late Miocene, is used as a key horizon to define the `post-orogenic' depositional regimes. The Late Miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the Miocene Atlantic–Mediterranean gateways. The terrigenous drift depositional regime of the Early Pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the Mediterranean outflow currents that developed after the opening of the Strait of Gibraltar. The Late Pliocene and Quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels. Deposition of shelf-margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence. During the highstand regimes of the Holocene, inner shelf prograding deltas and deep-water sediment drifts were developed under the influence of the Atlantic inflow and Mediterranean outflow currents, respectively. A modern human cultural regime began 2000 years ago with the Roman occupation of Iberia; human cultural effects on sedimentary regimes may have equalled natural factors such as climate change. Interplay of tectonic and oceanographic controls dominated the evolution of the Cadiz margin during the Cenozoic. Depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional Atlantic inflow currents on the shelf and Mediterranean outflow currents on the slope. The entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the Betic and Rif gateways, which become closed during the Late Miocene, and after the Messinian by the opening of the Strait of Gibraltar. Strong current development during eustatic sea level highstands of the Pliocene and Quaternary has controlled deposition because of maximum sill depths at Gibraltar for water circulation. Lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf. More recently, the human industrial revolution has caused heavy metal contamination of sediment and water over the Cadiz margin. Human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed. Future research efforts will need to focus on: (1) the effect of increased Mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages; (2) assessments of geologic hazards for planning man-made shoreline structures, developing offshore petroleum resources and maintaining undersea communications cables; and (3) confirmation of the general geologic history of the Cadiz margin.

Factors controlling late Cenozoic continental margin growth from the Ebro Delta to the western Mediterranean deep sea

The Ebro continental margin sedimentation system originated with a Messinian fluvial system. This system eroded both a major subaerial canyon cutting the margin southeastward from the present Ebro Delta and an axial valley that drained northeastward down Valencia Trough. Post-Messinian submergence of this topography and the Pliocene regime of high sea levels resulted in a marine hemipelagic drape over the margin. Late Pliocene to Pleistocene glacial climatic cycles, drainagebasin deforestation, and sea-level lowstands combined to increase sediment supply, cause the margin to prograde, and create a regime of lowstand sediment-gravity flows in the deeper margin. The depositional patterns of regressive, transgressive and highstand sea-level regimes suggest that location of the sediment source near the present Ebro Delta throughout the late Cenozoic, southward current advection of sediment, and greater subsidence in the southern margin combined to cause generally asymmetric progradation of the margin to the southeast. Thicker, less stable deposits filling the Messinian subaerial canyon underwent multiple retrograde failures, eroded wide gullied canyons and formed unchanneled base-of-slope sediment aprons in the central margin area; other margin areas to the north and south developed a series of channel-levee complexes. On the basin floor, the formation of Valencia Valley over the Messinian subaerial valley and earlier faults led to draining of about 20% of the Ebro Pleistocene sediment from channel-levee complexes through the valley to prograde Valencia Fan as much as 500 km northeast of the margin. Thus, the Ebro margin has two growth directions, mainly southeastward during higher sea levels, and eastward to northeastward during lower sea levels. The northeastward draining of turbidity currents has produced unusually thin and widely dispersed turbidite systems compared to those on ponded basin floors. During the past few centuries, man's impact has exceeded natural controls on Ebro margin growth. Deforestation of the drainage basin more than doubled the normal Holocene sediment supply, and construction of dams then reduced the supply by 95%. This reduction of the past 50 years has caused erosion of the delta and contamination of bottom sediment because normal Holocene sediment discharge is not available to prograde the delta or help dilute pollutants.

Barrier and lagoon coast evolution under differing relative sea-level regimes: examples from Ireland and Nova Scotia

Although the coasts of southern Ireland and eastern Nova Scotia possess many basic similarities, especially in terms of geology, glacial history, sediment character, resistance to erosion and wave and tide regimes, there is a fundamental contrast in Holocene sea-level history. In Ireland, recent (the past 4000 years) sea-level rise has been limited to less than 1 mm/year. By contrast, the Atlantic coast of Nova Scotia has been experiencing sea-level rises up to three to five times greater over the same period. Under these markedly differing relative sea-level rise regimes, barrier and lagoon evolution has varied considerably. In Ireland, barrier-lagoon form is controlled by local basement expression, particularly through the emergence of headlands (creating largely closed sediment systems) and the requirement to maintain cross-shore drainage. It is this latter factor that leads to a simple four-fold categorization of the Irish barriers and lagoons, from freshwater seepage to open tidal environments. The Nova Scotian examples are associated with rapidly moving erosional fronts, with local basement control relegated to a subordinate role at the expense of rapid changes in sediment supply. Barriers can both grow and decay under these conditions (subject to certain critical, but as yet ill-defined, thresholds), simultaneously forcing development and destruction of adjoining lagoons. These major differences also find expression in sedimentary sequences.