Maximum Sea Level Research Articles

This review presents an investigation of the evolution of the Baltic Sea basin and its connections through the Eemian Stage interglacial, based upon sequences of marine and associated deposits from the White Sea to the southwest Baltic, via the Karelian channel. Pollen analyses and foraminiferal and ostracod analyses are combined to provide the evolution of relative sea‐level change, supported by dinoflagellate cyst and diatom records. An independent chronology is established by correlation of the pollen record with that from the Bispingen laminated lake deposits in north Germany. Additional published sites from the area are included in a wider reconstruction of events. The evidence from five selected areas is assessed, with detailed evaluation of two critical time slices, respectively, in the Corylus pollen zone (E4) and that during the Carpinus ‐ Picea zones (E5–E6). Ostracod analyses indicate that freshwater lakes initially existed in the basin prior to the marine inundation. This was followed by an early marine transgression. The timing of the first marine conditions varies across the basin. For example, in the southeast Baltic they were established in pollen zones E2–E3, and in the southwest Baltic they occurred at the base of E3, with fully marine conditions established in zone E4, continuing into E5. In the White Sea area marine conditions occurred in zone E2. In most areas, regression of the sea in the Baltic basin began late in zone E5–E6 and was occasionally followed by freshwater deposition in zone E7. Compared to the Holocene, the salinity of the basin was markedly higher during the period of maximum sea level (zones E4–E5) as shown by the foraminifera and other marine fossils. The Eemian transgression occurred through the Kiel Canal area in addition to the Danish straits‐Kattegat seaway, indicating that a connection to the North Sea was present in the area during the interglacial sea‐level maximum highstand. Moreover, the nature, duration and regional impact of the link to the White Sea via Karelia are discussed.

Sea level rise (SLR) and increased urbanisation of coastal areas have exacerbated coastal flood threats, making them even more severe in important cultural sites. In this context, the role of hard coastal defences such as promenades and embankments needs to be carefully assessed. Here, a thorough investigation is conducted in Grado, one of the most significant coastal and historical towns in the Friuli Venezia Giulia region of Italy. Grado is located on a barrier island of the homonymous lagoon, the northernmost of the Adriatic Sea, and is prone to flooding from both the sea and the back lagoon. The mean and maximum sea levels from the historical dataset of Venice (1950–2023) were analysed using the Gumbel-type distribution, allowing for the identification of annual extremes based on their respective return periods (RPs). Grado and Trieste sea level datasets (1991–2023) were used to calibrate the statistics of the extremes and to calculate the local component (subsidence) of relative SLR. The research examined the occurrence of annual exceedance of the minimum threshold water level of 110 cm, indicating Grado’s initial notable marine ingression. The study includes a detailed analysis of flood impacts on the urban fabric, categorised into sectors based on the promenade elevation on the lagoon side, the most vulnerable to flooding. Inundated areas were obtained using a high-resolution digital terrain model through a GIS-based technique, assessing both the magnitude and exposure of the urban environment to flood risk due to storm surges, also considering relative SLR projections for 2050 and 2100. Currently, approximately 42% of Grado’s inhabited area is inundated with a sea level threshold value of 151 cm, which occurs during surge episodes with a 30-year RP. By 2100, with an optimistic forecast (SSP1-2.6) of local SLR of around +53 cm, the same threshold will be met with a surge of ca. 100 cm, which occurs once a year. Thus, extreme levels linked with more catastrophic events with current secular RPs will be achieved with a multi-year frequency, inundating more than 60% of the urbanized area. Grado, like Venice, exemplifies trends that may impact other coastal regions and historically significant towns of national importance. As a result, the generated simulations, as well as detailed analyses of urban sectors where coastal flooding may occur, are critical for medium- to long-term urban planning aimed at adopting proper adaptation measures.

Mass loss from polar ice sheets is poorly constrained in estimates of future global sea-level rise. Today, the marine-based West Antarctic Ice Sheet is losing mass at an accelerating rate, most notably in the Thwaites and Pine Island glacier drainage basins. Early Pliocene surface temperatures were about 4 °C warmer than preindustrial and maximum sea level stood ~20 m above present. Using data from a sediment archive on the Amundsen Sea continental rise, we investigate the impact of prolonged Pliocene ocean warmth on the ice-sheet−ocean system. We show that, in contrast to today, during peak ocean warming ~4.6 − 4.5 Ma, terrigenous muds accumulated rapidly under a weak bottom current regime after spill-over of dense shelf water with high suspended load down to the rise. From sediment provenance data we infer major retreat of the Thwaites Glacier system at ~4.4 Ma several hundreds of km inland from its present grounding line position, highlighting the potential for major Earth System changes under prolonged future warming.

Long-term variations in sea ice extent can influence trends in maximum sea level in the northeastern Baltic Sea

Abstract The monthly mean sea level along the U.S. Mid‐Atlantic Coast varies seasonally, reaching a minimum in January and a maximum in September during the 1960–2020 period. However, this seasonal cycle has changed significantly on multi‐decadal timescales. In the last two decades, the annual minimum has shifted from January to February. The amplitude of seasonal changes increased by 65% from 14.16 cm in 1980–1999 to 23.16 cm in 2000–2020. Even more concerning, the maximum sea level in September rose by 82%, from 6.81 to 12.38 cm, potentially exacerbating coastal flooding over the past 20 years. A two‐layer ocean model effectively replicates both the phase and magnitude of the observed changes and attributes these shifts to changes in wind stress near the coast, with relatively minor influence from deep ocean forcing. Both alongshore and cross‐shore wind stress changes are found to contribute to changes in the sea level's seasonal cycle.

The Hong Kong Observatory has been using a parametric storm surge model to forecast the rise of sea level due to the passage of tropical cyclones. This model includes an offset parameter to account for the rise in sea level due to other meteorological factors. By adding the sea level rise forecast to the astronomical tide prediction using the harmonic analysis method, coastal sea level prediction can be produced for the sites with tidal observations, which supports the high water level forecast operation and alert service for risk assessment of sea flooding in Hong Kong. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modelling System, which comprises the Weather Research and Forecasting (WRF) Model and Regional Ocean Modelling System (ROMS), which in itself is coupled with wave model WaveWatch III and nearshore wave model SWAN, was tested with tropical cyclone cases where there was significant water level rise in Hong Kong. This case study includes two super typhoons, namely Hato in 2017 and Mangkhut in 2018, three cases of the combined effect of tropical cyclone and northeast monsoon, including Typhoon Kompasu in 2021, Typhoon Nesat and Severe Tropical Storm Nalgae in 2022, as well as two cases of monsoon-induced sea level anomalies in February 2022 and February 2023. This study aims to evaluate the ability of the WRF-ROMS-SWAN model to downscale the meteorological fields and the performance of the coupled models in capturing the maximum sea levels under the influence of significant weather events. The results suggested that both configurations could reproduce the sea level variations with a high coefficient of determination (R2) of around 0.9. However, the WRF-ROMS-SWAN model gave better results with a reduced RMSE in the surface wind and sea level anomaly predictions. Except for some cases where the atmospheric model has introduced errors during the downscaling of the ERA5 dataset, bias in the peak sea levels could be reduced by the WRF-ROMS-SWAN coupled model. The study result serves as one of the bases for the implementation of the three-way coupled atmosphere–ocean–wave modelling system for producing an integrated forecast of storm surge or sea level anomalies due to meteorological factors, as well as meteorological and oceanographic parameters as an upgrade to the two-way coupled Operational Marine Forecasting System in the Hong Kong Observatory.

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

The present study is devoted to the analysis of extreme sea level oscillations of the Laptev Sea using the ADCIRC model. The numerical modeling is performed on a high-resolution grid and verified for sea level observations from three tide gauges. We have revealed regional characteristics of extreme sea level oscillations for different parts of the Laptev Sea coast. The maximum total sea level range was 544 cm in Ebelyakh Bay, while the minimum was 267 cm in Khatanga Bay, where maximum tidal ranges were obtained. Some areas in Khatanga Bay and Anabar Bay had maximum tidal ranges exceeding 200 cm. The study provided an estimation of the possible magnitude of coastal flooding by calculating the extreme total and residual sea levels for different return periods: 1, 2, 5, 10, 20, 50, and 100 years. The amplitude of extreme surges calculated for the 100-year return period can exceed 300 cm for several sections of the Laptev Sea coast, with the maximum sea level range being about 680 cm for Anabar and Ebelyakh Bays.

Abstract This research introduces a novel index for the South Atlantic High Pressure (SAHP) system to enhance understanding of regional climate variability and change. Subtropical highs significantly influence regional climates, yet comprehensive indices to measure their behaviours are lacking. Utilizing ERA5 reanalysis data from 1940 to 2023, the proposed index estimates a weighted centroid of the area surrounding the maximum sea level pressure within a 3 hPa range. This method ensures robustness and flexibility in contiguous area estimation specific to subtropical high events. Results showed the index effectively reflects the position and intensity of the SAHP. The study reveals that latitudinal variability of the SAHP has a strong unimodal structure, whereas longitudinal variability exhibits a bimodal structure. Seasonal patterns of the index show noticeable changes, with winter (JJA) and spring (SON) months having relatively high index values compared to summer (DJF) and autumn (MAM) months, underscoring the intra‐annual variability of the SAHP index. During ENSO events, the mean centroid position of the SAHP shifts significantly, moving westwards and polewards during El Niño and showing greater stability during La Niña. The index, with minimal computation requirements and flexibility, can be applied across diverse datasets, aiding in the assessment of future subtropical high changes.

Coastal locations around the world face the multifaceted challenge of rising sea levels, posing threats to coastal communities, particularly during storm surges and high wave conditions. We have examined the dynamics of sea-level fluctuations along Denmark’s coastline, with focus on wave-induced phenomena, such as wave setup. We analysed wave data from DMI’s operational model spanning from 2006 to 2022, as well as climate projections that extend until the middle of the 21st century. We conducted an analysis of the 2% exceedance of the significant wave height maxima during specific time frames (denoted “storm days”) and “storm surge conditions” (the maximum sea level within a 30-year period). We found that the impact of climate change on extreme wave events was insignificant when focusing solely on the wave component, but heightened wave setup during “storm surge conditions” along the north-western coasts of Jutland. In this area, there is a notable increase in wave setup due to longer swells, ranging from 5 to 10 cm, by the mid-century, which is double the current wave setup in the region. Interestingly, other parts of the country did not show significant changes in wave setup. This regional variation highlights the nuanced impact of wave-induced processes on sea level dynamics and underscores the need for tailored adaptation strategies targeting specific vulnerable zones.

Based on the data of the Baltic Sea Physics Analysis and Forecast (BSPAF) regional reanalysis of hydrophysical fields and instrumental measurements of sea level and salinity, the peculiarities of the variability of oceanographic processes in the Baltic Sea during the spread of the Major Baltic Inflow (MBI) of saline North Sea waters, which occurred in December 2014, are investigated. The maximum sea level difference between the Kattegat and the southwestern Baltic during the Major Baltic Inflow in December 2014 is investigated. It is shown that the 2014 MBI cannot be identified as barotropic, since slopes caused by the heterogeneity of the seawater density field make a significant contribution to the observed sea-level slopes in the Danish Straits during the MBI. Vertical profiles of water density and currents during the MBI demonstrate the preservation of stratification in the Danish Straits and the presence of a unidirectional flow directed from the Kattegat to the Baltic, with velocities at the surface of 1.0-1.2 m/s and at the bottom of 0.10-0.30 m/s. Significant vertical gradients of the flow velocity are due to the influence of the baroclinic component, the velocities of which reach 0.2 – 0.6 m/s. that 243.7 km3 of Kattegat waters passed into the southwestern Baltic during the entire period of the BBZ, which is consistent with earlier calculations made using other methods. Analysis of changes in the time of near-bottom salinity at three sections in the Baltic Sea shows that the transformed waters of the MBI reached the Gotland Basin in early April 2015 and then continued to spread to the north of the open Baltic, where they turned south and reached the western Gotland basin in December 2015.

Abstract. Extreme sea level events, such as storm surges, pose a threat to coastlines around the globe. Many tide gauges have been measuring the sea level and recording these extreme events for decades, some for over a century. The data from these gauges often serve as the basis for evaluating the extreme sea level statistics, which are used to extrapolate sea levels that serve as design values for coastal protection. Hydrodynamic models often have difficulty in correctly reproducing extreme sea levels and, consequently, extreme sea level statistics and trends. In this study, we generate a 13-member hindcast ensemble for the non-tidal Baltic Sea from 1979 to 2018 using the coastal ocean model GETM (General Estuarine Transport Model). In order to cope with mean biases in maximum water levels in the simulations, we include both simulations with and those without wind-speed adjustments in the ensemble. We evaluate the uncertainties in the extreme value statistics and recent trends of annual maximum sea levels. Although the ensemble mean shows good agreement with observations regarding return levels and trends, we still find large variability and uncertainty within the ensemble (95 % confidence levels up to 60 cm for the 30-year return level). We argue that biases and uncertainties in the atmospheric reanalyses, e.g. variability in the representation of storms, translate directly into uncertainty within the ensemble. The translation of the variability of the 99th percentile wind speeds into the sea level elevation is in the order of the variability of the ensemble spread of the modelled maximum sea levels. Our results emphasise that 13 members are insufficient and that regionally large ensembles should be created to minimise uncertainties. This should improve the ability of the models to correctly reproduce the underlying extreme value statistics and thus provide robust estimates of climate change-induced changes in the future.

Under certain environmental and oceanographic conditions, macroalgae can overgrow and accumulate in massive quantities on beaches, causing serious ecological and economic impacts. To address this problem, a citizen science monitoring platform was created to determine the spatial and temporal distribution of macroalgae accumulations along the beaches of Algarve in southern Portugal, with the aim to assess the extent of beach-cast events and their relationship with abiotic factors. A Redundancy Analysis (RDA) and a permutational analysis of variance (PERMANOVA) were carried out to explore the relationship between macroalgae accumulation level and the abiotic variables: sea surface temperature, wind speed, wind direction, currents, maximum sea level, significant wave height, salinity, nitrate, ammonium, phosphate, precipitation and radiation. The citizen science campaign showed great participation, resulting in 404 submissions between July 2021 and September 2023. The campaign revealed that three species of macroalgae accumulated on the beaches of Algarve, Ulva sp. (with the presence of Ectocarpales and Dyctiotales) along the sandy eastern coast, and the invasive species Asparagopsis armata and Rugulopteryx okamurae in the rocky central and western beaches, respectively. The accumulations of R. okamurae increased from 2021 to 2023, were registered throughout the year and were more abundant than those of Ulva sp. and A. armata, which were only observed in spring and summer. The highest levels of R. okamurae beach-cast depositions were related to strong wave conditions, and high sea surface temperature and salinity. The accumulation of Ulva sp. was related to high sea surface temperature and salinity whereas A. armata was also correlated with winds parallel to the shore (NW-W). PERMANOVA analysis revealed that sea surface temperature and wave conditions had a significant effect on the overall abundance of macroalgae beach-cast accumulations. Overall, our citizen science campaign effectively involved the public, leading to the collection of important data on monitoring macroalgae accumulations. Through these findings, we were able to pinpoint the environmental, atmospheric, and hydrodynamic factors that contribute to their development, movement, and buildup along the Algarve coastlines.

Analysis of compound floods from storm surge and extreme precipitation in China

Effects of rising seas and geomorphological changes in the islands of northern Bay of Bengal

Abstract We integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea‐level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus‐bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice‐sheet volumes and derived global sea levels that are based on benthic oxygen isotope records.

Abstract. Occurrence probabilities of extreme sea levels required in coastal planning, e.g. for calculating design floods, have been traditionally estimated individually at each tide-gauge location. However, these estimates include uncertainties, as sea-level observations typically have only a small number of extreme cases such as annual maxima. Moreover, exact information on sea-level extremes between the tide-gauge locations and incorporation of dependencies between the adjacent stations is often lacking in the analysis. In this study, we use Bayesian hierarchical modelling to estimate return levels of annual maxima of short-term sea-level variations related to storm surges in the Finnish coastal region. We use the generalised extreme value (GEV) distribution as the basis and compare three hierarchical model structures of different complexity against tide-gauge-specific fits. The hierarchical model structures allow us to share information on annual maximum sea levels between the neighbouring stations and also provide a natural way to estimate uncertainties in the theoretical estimates. The results show that compared to the tide-gauge-specific fits, the hierarchical models, which pool information across the tide gauges, provide narrower uncertainty ranges for both the posterior parameter estimates and the corresponding return levels in most locations. The estimated shape parameter of the GEV model is systematically negative for the hierarchical models, which indicates a Weibull type of behaviour for the extremes along the Finnish coast. The negative shape parameter also allows us to calculate the theoretical upper limit for the annual maximum sea levels on the Finnish coast. Depending on the tide gauge and hierarchical model considered, the median value of the theoretical upper limit was 47–73 cm higher than the highest observed sea level.

ABSTRACT The actions of wind and atmospheric pressure associated with tropical cyclones (e.g. typhoons) are considered the primary factors behind the generation of storm surges, though the fields used in meteorological models can sometimes deviate from observations. To improve these, the direct modification method (DMM) has been previously proposed, though this only modifies the wind field of a typhoon, and further development is necessary for applying it to storm surge hindcasts. The present work describes the development of a semi-empirical gradient wind balance-based method (GWB-M) for modifying both the wind and pressure fields in meteorological models, based on the dynamic relationship between the wind and pressure in typhoons (i.e. gradient wind balance). The applicability of GWB-M was assessed through a storm surge hindcast based on Typhoon Faxai in 2019, which generated powerful waves and a storm surge at Tokyo Bay. GWB-M improved the time series of 10 m wind speed and sea level pressure, with their spatial distributions being more realistic than those in DMM and blending parametric typhoon models (BM), which cannot take into account the influence of the complex topography around Tokyo Bay. Further, the maximum sea level anomalies after the typhoon made landfall were also captured by GWB-M with a higher accuracy than DMM.

Forecasting of absolute dynamic topography using deep learning algorithm with application to the Baltic Sea

The Cotinguiba Formation, of Cretaceous age, located in the Sergipe-Alagoas Basin, Brazilian Northeastern coast, comprises carbonate breccias and carbonate shales interlayered with fine to coarse clastic sediments (mudstones, marls), deposited in the maximum sea level episode during the Cenomanian-Coniacian transgressive event. Core sections were selected from the formation materials, from which 20 plugs were obtained, representing the main carbonate horizons present in Cotinguiba Formation. The selected samples were analyzed with petrophysical and physical methods (air porosimetry, mercury injection, and acoustic wave velocity) and mineralogical methods (optical microscopic analysis, x-ray diffraction (XRD) and scanning electron microscopy (SEM)). Results showed that the clay minerals’ content in the carbonates varies from 2% to 20%, with illites/micas and interstratified illite/smectite as the most abundant clay minerals, containing also traces of chlorite and kaolinite, and presence of palygorskite varying from trace to 8%. According to the percentages of calcite, dolomite, and siliciclastic + clay minerals obtained in the XRD analysis, the carbonates were lithologically identified as limestone, impure limestone, dolomitic limestone, impure dolomitic limestone, impure calcitic dolostone, and impure dolostone. The rocks have a good porosity, varying from 6% to 20% in the carbonates, predominantly related to microporosity. Clay minerals’ content influenced the grain density and acoustic properties, albeit not having the same role with porosity and permeability. SEM images, though, show that they have an important role in microporosity. Grain density variation related to phyllosilicate content was observed more significantly in impure limestones with a clay content higher than 8%, and a more pronounced decrease was observed in samples with palygorskite. Microporosity is the main factor for reducing Vp and Vs velocities in those carbonates, with values not exceeding 5341 m/s for Vp and 3026 m/s for Vs but, when clay content is higher than 4%, the Vp and Vs wave velocities do not exceed 4100 m/s and 2480 m/s, respectively. Therefore, the research allowed evaluating the influence of mineralogical and textural properties in the petrophysical properties of Cotinguiba Formation.