Tide Gauge Data Research Articles

Saltmarsh sustainability throughout the Holocene in Boston Harbor: A new sea-level curve for the lower Gulf of Maine and implications of recent anthropogenic alteration

Saltmarsh evolution is closely linked to sea-level rise (SLR) and sediment supply. In a regime of accelerating SLR, saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation, and laterally via transgression over adjacent uplands. In formerly glaciated settings, the formation and maintenance of a saltmarsh are complicated by steep uplands, low sediment availability, isostatic rebound, changes to tidal amplitudes, and anthropogenic alteration. While much work has examined the development of large saltmarshes in New England since the mid-Holocene and Anthropocene, little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline. We use radiocarbon dates from newly uncovered index points (basal peat) within Boston Harbor to date one of the oldest saltmarshes in the region (∼4.2 ka), and calculate the polynomial relative sea-level curve (RSLR) for the lower Gulf of Maine taking into account tidal amplification throughout the Holocene. This study informs the historical persistence of isolated saltmarshes under varying rates of sea-level rise (magnitude as much as 2 mm yr−1). Additionally, we refine the timing and rates of the mid-Holocene sea-level deceleration in this region: between 2.8 and 3.3 ka, slowing from 2.1 mm yr−1 to 0.5 mm yr−1. RSLR determined from the past century of tide gauge data is 2.86 mm yr−1, five times greater than historic rates over the past 2000 years. Recent vertical accretion rates (determined from marker horizons and 210Pb data) indicate that portions of Boston Harbor’s saltmarshes are able to keep pace with current RSLR. However, historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms, largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces. These results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results. More importantly, anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines, whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface, facilitating vertical accretion that offsets RSLR. Under modern accelerated sea-level rise and decreased sediment supply, this cannibalization process may now be the only pathway for saltmarsh survival.

UK meteotsunamis: a revision and update on events and their frequency

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Observation of continental shelf wave propagating along the eastern Taiwan Strait during Typhoon Meranti 2016

This study is the first to depict typhoon-induced continental shelf wave (CSW) propagation in the eastern Taiwan Strait (TWS) during the passage of Typhoon Meranti in 2016 using tidal gauge data and along-track satellite altimeter data. The strong amplitude response of sea level oscillations (within the range of 0.30–0.54 m) as a free, barotropic CSW after Meranti, which impacted the TWS, was clearly detected in time and frequency (in bands of 64–81 h) using wavelet and cross-wavelet analyses. The measured group and phase speeds were consistent with the dispersion curves for CSW with the first-mode derived from the cross-shelf sections of the eastern TWS, with the mean speeds reaching 3 and 5.6±0.7 m/s, respectively. Coincidentally, the typhoon-induced sea level anomaly (SLA) was also captured by the satellite altimeter before this CSW entered into the TWS. Using the theoretical cross-shore CSW modes to fit the SLA data, the results indicated that the first three wave modes can interpret this CSW event appeared in the southern TWS very well, with the first mode being the dominant one.

Field surveys and numerical modelling of the 2004 December 26 Indian Ocean tsunami in the area of Mumbai, west coast of India

ABSTRACTIn the aftermath of the 2004 Indian Ocean (Sumatra-Andaman) tsunami, numerous survey teams investigated its effects on various locations across the Indian Ocean. However, these efforts were focused only on sites that experienced major destruction and a high death toll. As a consequence, some Indian Ocean coastal megacities were not examined. Among the cities not surveyed was Mumbai, the principal west coast port and economical capital of India with a population of more than 12 million. Mumbai is at risk of tsunamis from two major subduction zones in the Indian Ocean: the Sumatra–Andaman subduction zone (SASZ) and the Makran subduction zone (MSZ). As a part of the present study, we conducted a field survey of the 2004 Indian Ocean tsunami effects in Mumbai, analysed the available tide gauge records and performed tsunami simulations. Our field survey in 2018 January found run-up heights of 1.6−3.3 m in the Mumbai area. According to our analysis of tide gauge data, tsunami trough-to-crest heights in Okha (550 km to the north of Mumbai) and in Mormugao (410 km to the south of Mumbai) were 46 cm and 108 cm, respectively. Simulations of a hypothetical MSZ Mw 9.0 earthquake and tsunami, together with the Mw 9.1 Sumatra–Andaman earthquake and tsunami, show that the tsunami heights generated in Mumbai by an MSZ tsunami would be significantly larger than those generated by the 2004 Sumatra–Andaman tsunami. This result indicates that future tsunami hazard mitigation for Mumbai needs to be based on a potential large MSZ earthquake rather than an SASZ earthquake.

Validation of Sentinel-3A SRAL Coastal Sea Level Data at High Posting Rate: 80 Hz

Altimetry data of two and a half years (June 2016–November 2018) of Sentinel-3A SRAL (S3A-SRAL) were validated at the sampling frequency of 80 Hz. The data were obtained from the European Space Agency (ESA) Grid Processing On Demand (GPOD) service over three coastal sites in Spain: Huelva (HU) (Gulf of Cadiz), Barcelona (BA) (Western Mediterranean Sea), and Bilbao (BI) (Bay of Biscay). Two tracks were selected in each site: one ascending and one descending. Data were validated using in situ tide gauge (TG) data provided by the Spanish Puertos del Estado. The altimetry sea level anomaly time series were obtained using the corrections available in GPOD with the exception of the sea state bias (SSB) correction, not available at 80 Hz. Hence, the SSB was approximated to 5% of the significant wave height (SWH). The validation was performed using two statistical parameters, the Pearson correlation coefficient (r) and the root mean square error (rmse). In the 5–20-km segment with respect to the coastline, the results were 6–8 cm (rmse) and 0.7–0.8 (r) for all the tracks. The 0–5-km segment was also analyzed in detail to study the land effect on the altimetry data quality. The results showed that the track orientation, the angle of intersection with the coast, and the land topography concur to determine the nearest distance to the coast at which the data retain a similar level of accuracy than in the 5–20-km segment. This “distance of good quality” to shore reaches a minimum of 3 km for the tracks at HU and the descending track at BA.

The Seasonal Cycle of Mean Sea Level in the North East Atlantic Ocean

Payo-Payo, M. and Bertin, X., 2020. The seasonal cycle of mean sea level in the North East Atlantic Ocean. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1515-1519. Coconut Creek (Florida), ISSN 0749-0208.The analysis of long-term tide gauge data collected in the Northeast Atlantic Ocean reveals that the seasonal cycle of mean sea level (hereafter MSL) exhibits amplitudes of up to 0.4 m. The position of MSL is of fundamental importance for many issues such as storm-induced flooding or the morphodynamics of shallow inlets, yet the underlying mechanisms are not fully understood. We characterize the seasonal cycle based on field observations complemented with a numerical hindcast. We analyzed long-term series (2000-2010) of in-situ tide gauge data along the coasts of Portugal, Spain and France. The combined analysis of field observation and model results revealed that atmospheric pressure, wind and steric effect are the main contributors to the seasonal cycle of MSL along North East Atlantic Ocean coastlines. We find a coherent signal over the region: the cycle peaks around November and has its minimum in February. Monthly mean sea level rises slowly and falls quickly. The different features between north and south mirror the different forcing mechanisms acting in each area. To the north, the seasonal cycle of MSL is more irregular and controlled by atmospheric forcing because this region is on the track of low-pressure storms, especially during winter. To the south, the steric effect plays an important role mostly due to the persistence of high pressure and a narrow continental shelf. Our results suggest that for a given storm, the water level and subsequent flooding damage will be higher if it occurs at the end of the autumn than at the end of the winter, which suggest that the seasonal cycle of MSL should be represented in flooding modeling systems.

Evaluation of Real-Time PPP-Based Tide Measurement Using IGS Real-Time Service.

Tide data plays a key role in many marine scientific research fields such as seafloor topography measurement and navigation safety. To obtain reliable tide data, various methods have been proposed, e.g., tide station measurement, satellite altimeter measurement, and differential global positioning system (GPS) buoy measurement. However, these methods suffer from the limitation that continuous observations at different areas might not be always available. In order to provide high-precision as well as continuous real-time tide data, we propose a method based on real-time precise point positioning (RT-PPP) by using International GNSS Service (IGS) real-time service (RTS) products. Firstly, compared with the IGS final products, the accuracy of the RTS satellite orbit and clock is evaluated. Secondly, the positioning performance of RT-PPP is compared with the IGS ultra-fast products. Finally, a robust Vondrak filter is proposed to eliminate the influence of high-frequency noise and errors and to obtain tide results. Experimental results show that three-dimensional (3D) accuracy of the RTS orbit is better than 0.05 m, and also has 0.22 ns less clock bias. An improvement of 60% is achieved for positioning accuracy using RTS products compared to IGS ultra-fast products. Compared with the post-processing PPP method, the double difference (DD) method and tide gauge data, the root mean square (RMS) values of RT-PPP tide are 0.090, 0.194 and 0.167 m, respectively.

SEA LEVEL ANOMALY ASSESSMENT OF SARAL/ALTIKA MISSION USING HIGH AND LOW RESOLUTION DATA

Peninsular Malaysia is located at the focal point of Sunda Shelf, encompassed by the South China Sea to the East and by Andaman Sea at Indian Ocean in the west that causes various phenomena relevant to sea level along Malaysian coast. When the monsoons strike, the effect of wind and other factors will change the variability of Sea Level Anomaly (SLA) along coastal Malaysia. Traditionally, sea level change is observed using tide gauge installed along Malaysian coastal area. However, the data obtained is limited to the tide gauge station area, the sea level data for the deep sea cannot be obtained and there is no long-term record of observation. Therefore, satellite altimeter is used as a new alternative which enables sea level data to be obtained from space observation and to monitor SLA via SARAL/AltiKa which available since 2013, thus complementing the tide gauge. The aim of this study is to derive SLA parameter from high and low resolution of satellite altimetry data. This study involved the acquisition of SLA data by using RADS and PEACHI (AVISO) database system from satellite mission SARAL/AltiKa. Sequentially, SLA data has been analysed and evaluated based on tide gauge data provided by using UHSLC system. Comparison between the high resolution (PEACHI) and low resolution (RADS) data has been made to evaluate the density of altimetry data in term of distance to coast. As a result, high resolution (PEACHI) data are more accurate for coastal application with root mean square error (RMSE) of ±0.14 metre level. The analysis shows that the footprint of high resolution altimetry data is denser than the low resolution altimetry data. Data from distance to coast for PEACHI achieved a satisfactory standard deviation of residual, which is ranged between 0cm to 1.04cm as compared to altimetry RADS which is ranged 0.34cm to 12.57cm. The results can be used by various agencies in planning and developing Malaysian coastal areas as well as in assisting the development of community economies such as fishery and tourism activities.

Optimal Lowest Astronomical Tide Estimation Using Maximum Likelihood Estimator with Multiple Ocean Models Hybridization

Developing an accurate Lowest Astronomical Tide (LAT) in a continuous form is essential for many maritime applications as it can be employed to develop an accurate continuous vertical control datum for hydrographic surveys applications and to produce accurate dynamic electronic navigation charts for safe maritime navigation by mariners. The LAT can be developed in a continuous (surface) using an estimated LAT surface model from the hydrodynamic ocean model along with coastal discrete LAT point values derived from tide gauges data sets to provide the corrected LAT surface model. In this paper, an accurate LAT surface model was developed for the Red Sea case study using a Maximum Likelihood Estimator (MLE) with multiple hydrodynamic ocean models hybridization, namely, WebTide, FES2014, DTU10, and EOT11a models. It was found that the developed optimal hybrid LAT model using MLE with multiple hydrodynamic ocean models hybridization ranges from 0.1 m to 1.63 m, associated with about 2.4 cm of uncertainty at a 95% confidence level in the Red Sea case study area. To validate the accuracy of the developed model, the comparison was made between the optimal hybrid LAT model developed from multiple hydrodynamic ocean models hybridization using the MLE method with the individual LAT models estimated from individual WebTide, FES2014, DTU10, or EOT11a ocean models based on the associated uncertainties estimated at a 95% confidence level. It was found that the optimal hybrid LAT model accuracy is superior to the individual LAT models estimated from individual ocean models with an improvement of about 50% in average, based on the estimated uncertainties. The importance of developing optimal LAT surface model using the MLE method with multiple hydrodynamic ocean models hybridization in this paper with few centimeters level of uncertainty can lead to accurate continuous vertical datum estimation that is essential for many maritime applications.

Complex Extreme Sea Levels Prediction Analysis: Karachi Coast Case Study.

In this study, the analysis of the extreme sea level was carried out by using 10 years (2007–2016) of hourly tide gauge data of Karachi port station along the Pakistan coast. Observations revealed that the magnitudes of the tides usually exceeded the storm surges at this station. The main observation for this duration and the subsequent analysis showed that in June 2007 a tropical Cyclone “Yemyin” hit the Pakistan coast. The joint probability method (JPM) and the annual maximum method (AMM) were used for statistical analysis to find out the return periods of different extreme sea levels. According to the achieved results, the AMM and JPM methods erre compatible with each other for the Karachi coast and remained well within the range of 95% confidence. For the JPM method, the highest astronomical tide (HAT) of the Karachi coast was considered as the threshold and the sea levels above it were considered extreme sea levels. The 10 annual observed sea level maxima, in the recent past, showed an increasing trend for extreme sea levels. In the study period, the increment rates of 3.6 mm/year and 2.1 mm/year were observed for mean sea level and extreme sea level, respectively, along the Karachi coast. Tidal analysis, for the Karachi tide gauge data, showed less dependency of the extreme sea levels on the non-tidal residuals. By applying the Merrifield criteria of mean annual maximum water level ratio, it was found that the Karachi coast was tidally dominated and the non-tidal residual contribution was just 10%. The examination of the highest water level event (13 June 2014) during the study period, further favored the tidal dominance as compared to the non-tidal component along the Karachi coast.

Sea-level inundation and risk assessment along the south and southwest coasts of Sri Lanka

Global sea-level changes have been a major topic among scientists. Sea-level changes are not globally uniform. Reconstruction of paleo sea-level changes and monitoring of variations in regional sea-level are important to (i) evaluate future sea-level changes, and (ii) predict risk assessment. In this study, we examined sea-level inundation during the middle Holocene highstands based on paleo sea-level indicators along the south and southwest coasts of Sri Lanka. Besides, future sea-level inundation was predicted considering the calculated sea-level trends based on tidal gauge data and high-resolution surface elevation data. Light Detection and Ranging (LiDAR) is one of the most accurate optical remote sensing methods currently available to obtain high-resolution land surface elevation data. Therefore, in this study, Digital Elevation Models (DEMs) were prepared using LiDAR data for estimating the risk assessment in coastal lowlands. Tide gauge data of Colombo in Sri Lanka (from 2006 to 2017), Gan in the Maldives (from 1995 to 2017), and Hulhule in the Maldives (from 1995 to 2017) showed that sea-level has increased with a rate of 0.288 ± 0.118, 0.234 ± 0.025, and 0.368 ± 0.027 mm/month, respectively. DEMs based on LiDAR data suggested that south and southwest coasts are a risk of future sea-level inundation (height = 0.1–0.2 m during next 50 years and about 0.7 m in height during next 200 years, and distance = about 3.5–15.0 m from the present sea-level towards the inland). Consequently, it is important to consider future sea-level changes in disaster management and mitigation activities along the south and southwest coasts of Sri Lanka.

Forcing ocean model with atmospheric model outputs to simulate storm surge in the Bangladesh coast

Tropical cyclones are devastating hazards and have been a major problem for the coastal population of Bangladesh. Among the advancements in atmospheric and oceanic prediction, accurate forecasting of storm surges is of specific interest due to their great potential to inflict loss of life and property. For decades, the numerical model based storm surge prediction systems have been an important tool to reduce the loss of human lives and property damage. In order to improve the accuracy in predicting storm surge and coastal inundation, recent model development efforts tended to include more modeling components, such as meteorology model and surface wave model in storm surge modeling. In this study, we used the outputs of an atmospheric model to force the ocean model for simulating storm surges in the Bay of Bengal with particular focus on the Bangladesh coast. The ability of the modeling system was investigated simulating water levels in the Bangladesh coast of two tropical cyclones Sidr (2007) and Aila (2009). The effectiveness of the model was verified through comparing the obtained computational outputs against tide gauge data. The cyclone tracks and intensities reproduced by the atmospheric model were reasonable, though the model had a tendency to overestimate the cyclone intensity during peaks and also close to coast. The water levels are reproduced fairly well by the ocean model, although errors still exist. The root mean square errors in water level at different gauges range from 0.277 to 0.419 m with coefficient of correlation (R2) between 0.64 and 0.97 in case of Sidr and 0.209–0.581 m with R2 0.62 to 0.98 for Aila. The overall coupled modeling system is found to be useful with reasonable accuracy and precision, though there are spaces for improvement. Higher-resolution modeling approaches are recommended to gain more skills.

Global positioning system interferometric reflectometry for accurate tide gauge measurement: Insights from South Beach, Oregon, United States

Global positioning system (GPS) stations located along coastal areas have the ability to measure tide gauge records by reflected signal reception from the sea water surface. In this study we used the GPS signal-to-noise ratio data from the GPS station (44.6257 ⁰N, 124.0455 ⁰W) located at South Beach, Oregon, United States, to estimate the tide gauge records using seasonal measurements. First, we derived the tide gauge record from the station and used traditional tide gauge data from the National Water Level Observation Network (NWLON) sentinel station (Station ID: 9435380) located in Oregon for validation purposes because it was closest to the GPS station. Our results show that the GPS tide gauge and NWLON tide gauge correlate well with the correlation coefficient of 0.942 and the root mean square of their residuals was about 12.90 cm. The corresponding tide gauge prediction by auto-regressive moving average and singular spectrum analysis models are evaluated for their effectiveness over the station. The comparative analysis demonstrates that the GPS tide gauge has improved correlation with auto-regressive moving average predicted tide gauge (correlation coefficient of ~0.981 and root mean square of ~4.80 cm), and singular spectrum analysis predicted tide gauge (correlation coefficient of ~0.998 and root mean square of ~0.88 cm) compared to the NWLON tide gauge (correlation coefficient of ~0.942 and root mean square of ~12.90 cm) values. We believe the outcomes from this study contribute to a better understanding of the numerical modeling of tide gauge records as well as other measurements based on reflectometry techniques.

Low-frequency sea level variability and impact of recent sea ice decline on the sea level trend in the Arctic Ocean from a high-resolution simulation

The Arctic Ocean is undergoing significant changes, with rapid sea ice decline, unprecedented freshwater accumulation, and pronounced regional sea level rise. In this paper, we analyzed the sea level variation in the Arctic Ocean based on a global simulation with 4.5-km resolution in the Arctic Ocean using the multi-resolution Finite Element Sea Ice-Ocean Model (FESOM). The simulation reasonably reproduces both the main spatial features of the sea surface height (SSH) and its temporal evolution in the Arctic Ocean in comparison with tide gauge and satellite data. Using the model results, we investigated the low-frequency variability of the Arctic SSH. Both the first two dominant modes of the annual-mean SSH evolution in the Arctic Ocean present decadal variability and can be mainly attributed to the variability of the halosteric height, thus the freshwater content. The first mode can be explained by the Arctic Oscillation (AO). The AO-related atmospheric circulation drives the accumulation and release of freshwater in the Arctic deep basin and the consequent ocean mass change over the continental shelf, leading to the antiphase changes in SSH between the shelf seas and the deep basin. The second mode shows an antiphase oscillation between the two Arctic deep basins, the Amerasian and Eurasian Basins, which is driven by the Arctic dipole anomaly (DA). The DA-related wind anomaly causes a spatial redistribution of freshwater between the two basins, leading to the antiphase SSH changes. By using a dedicated sensitivity simulation in which the recent sea ice decline is eliminated, we find that the sea ice decline contributed considerably to the observed sea level rise in the Amerasian Basin in the recent decades. Although the sea ice decline did not change the mean SSH averaged over the Arctic Ocean, it significantly changed the spatial pattern of the SSH trend. Our finding indicates that both the wind regime and ongoing sea ice decline should be considered to better understand and predict the changes in regional sea level in the Arctic Ocean.

Influence of atmospheric rivers on the Leeuwin Current system

Previous work has demonstrated the strong ocean response to atmospheric rivers (ARs) in the northeast Pacific including coastal currents along the west coast of North America, because of strong surface winds associated with ARs. A recent study on the global distribution of ARs also suggests that the southeast Indian Ocean is one of the areas of relatively strong AR activity. This study investigates the influence of ARs on the Leeuwin Current system, which is one of the major boundary currents in the Indian Ocean. It is demonstrated that winds associated with typical ARs in the southeast Indian Ocean can generate strong poleward coastal currents and sea level rise along the west coast of Australia using a high-resolution ocean reanalysis (0.08° HYCOM). The composite of upper ocean currents and sea surface height (SSH) associated with landfalling ARs along the west coast of Australia is constructed using the HYCOM reanalysis, long-term AR data set, and tide gauge data. The enhancement of the poleward currents generated by ARs is found in the composite, and the magnitude of the enhancement is comparable to the strength of the Leeuwin Current itself. The results also indicate that the fluctuation of SSH and coastal currents along the west coast propagates along the southern coast all the way to the southeast coast (Pacific side) of Australia. The SSH propagation along the coasts is also detected in the tide gauge data in the west and southern coasts of Australia.

Simple numerical tests for ocean tidal models

There is a growing interest in tidal effects on the global wind-driven oceanic circulation. Tidal models used in such investigations have been verified by comparison with satellite and tide gauge data, but synthetic tests have not been published. In this paper we present three numerical tests in spherical geometry, which are suitable for testing the tidal component of global ocean models. The first test is a tsunami-like propagation of an initial Gaussian depression with no external forcing. The other two tests examine the tidal response of an ocean with an undulating bottom with four Gaussian ridges and an ocean with a flat bottom with a realistic land mask. We provide the results from six model configurations, which differ in the time-stepping scheme and computational grid used. Most of them are implemented in present-day global ocean models. Although the proposed numerical tests are simple compared to realistic simulations, their analytic solutions are not available. We thus check the conservation of time invariants to ensure that the solutions are physically meaningful. We also compare the time evolution of certain physical quantities and the differences in sea surface heights at particular time instants with respect to a reference solution. All tested time stepping schemes are suitable for tidal studies except for the Euler implicit time stepping scheme. Model configurations based on the Arakawa grids B/E use smoothing to suppress the grid-scale noise which results in an energy leakage of around 5%. The B/E-grid energy leakage is probably acceptable if we consider that tuned diffusive terms are used in real-world configurations. The C-grid and B/E-grid solutions differ in the vicinity of solid boundaries as a consequence of different boundary conditions. The B-grid and E-grid solutions are similar, unless the shape of the solid boundaries is complex due to the different shapes of the respective grid cells.

Tide‐Induced Periodic Sea Surface Temperature Drops in the Coral Reef Area of Nanwan Bay, Southern Taiwan

AbstractTidal current‐induced cyclonic eddies cause cold‐water upwelling and periodic sea surface temperature (SST) drops around the coral reef area in Nanwan Bay, which is located at the southern tip of Taiwan. This study used Himawari‐8 satellite data and tide gauge and coastal ocean dynamics application radar (CODAR) data to analyze the characteristics of the SST drops and cyclonic eddy propagation and used an oceanic general circulation model (OGCM) to simulate the tidal current flowing process. According to the CODAR data analysis, the mixed primary semidiurnal tide had an average current velocity of 0.3–0.4 m s−1 throughout the bay, and the average life cycle of a cyclonic eddy is 6.6 hr, with a propagation speed of 0.35 m s−1. The SST drop during the spring tide period was greater than that during the neap tide period, and the SST dropped in both summer and winter. The average daily SST drop in the summer reached 2 °C with a maximum observed value of 4.7 °C, and the SST drop rate was 0.3–0.5 °C hr−1. The annual mean chlorophyll‐a concentration was 0.25 mg m−3. This study explored the special properties of the Nanwan Bay coral reef area from the perspective of ocean physics to allow ecologists to facilitate the implementation of long‐term conservation and monitoring programs.

Recent Sea Level Change in the Black Sea from Satellite Altimetry and Tide Gauge Observations

Global mean sea level has been rising at an increasing rate, especially since the early 19th century in response to ocean thermal expansion and ice sheet melting. The possible consequences of sea level rise pose a significant threat to coastal cities, inhabitants, infrastructure, wetlands, ecosystems, and beaches. Sea level changes are not geographically uniform. This study focuses on present-day sea level changes in the Black Sea using satellite altimetry and tide gauge data. The multi-mission gridded satellite altimetry data from January 1993 to May 2017 indicated a mean rate of sea level rise of 2.5 ± 0.5 mm/year over the entire Black Sea. However, when considering the dominant cycles of the Black Sea level time series, an apparent (significant) variation was seen until 2014, and the rise in the mean sea level has been estimated at about 3.2 ± 0.6 mm/year. Coastal sea level, which was assessed using the available data from 12 tide gauge stations, has generally risen (except for the Bourgas Station). For instance, from the western coast to the southern coast of the Black Sea, in Constantza, Sevastopol, Tuapse, Batumi, Trabzon, Amasra, Sile, and Igneada, the relative rise was 3.02, 1.56, 2.92, 3.52, 2.33, 3.43, 5.03, and 6.94 mm/year, respectively, for varying periods over 1922–2014. The highest and lowest rises in the mean level of the Black Sea were in Poti (7.01 mm/year) and in Varna (1.53 mm/year), respectively. Measurements from six Global Navigation Satellite System (GNSS) stations, which are very close to the tide gauges, also suggest that there were significant vertical land movements at some tide gauge locations. This study confirmed that according to the obtained average annual phase value of sea level observations, seasonal sea level variations in the Black Sea reach their maximum annual amplitude in May–June.

Tide prediction machines at the Liverpool Tidal Institute

Abstract. The 100th anniversary of the Liverpool Tidal Institute (LTI) was celebrated during 2019. One aspect of tidal science for which the LTI acquired a worldwide reputation was the development and use of tide prediction machines (TPMs). The TPM was invented in the late 19th century, but most of them were made in the first half of the 20th century, up until the time that the advent of digital computers consigned them to museums. This paper describes the basic principles of a TPM, reviews how many were constructed around the world and discusses the method devised by Arthur Doodson at the LTI for the determination of harmonic tidal constants from tide gauge data. These constants were required in order to set up the TPMs for predicting the heights and times of the tides. Although only 3 of the 30-odd TPMs constructed were employed in operational tidal prediction at the LTI, Doodson was responsible for the design and oversight of the manufacture of several others. The paper demonstrates how the UK, and the LTI and Doodson in particular, played a central role in this area of tidal science.

Estimating sea level rise around Australia using a new approach to account for low frequency climate signals

Regional sea level studies help to identify the vulnerable areas to the sea level rise. This study investigates the impact of climate modes on sea level variations and trends around Australia using altimetry data, climate indices, and sea level records from tide gauge stations. Here, we show that the sea level variations are negatively correlated with climate indices to the north and west of Australia. The spectral analyses of the climate indices and tide gauge data suggest that a low frequency signal with a period of 11 years emerges during the mid 1980s. Since the 25-year length of the satellite altimetry record is yet too short to detect low frequency signals, their effect on the estimation of regional sea level trend is unknown. Therefore, we estimate the sea level trend with consideration of this signal and using a two-step method. All signals with periods shorter than 7.5 years are first removed from sea level time series and then the trend is estimated using the parametric model that includes the 11-year signal. The skill of the parametric model in explaining the variations in sea level anomaly validates the presence of the 11-year signal detected in the spectrograms of the tide gauge data and climate indices. The average sea level trend for the study area is estimated as 3.85 ± 0.15 mm/year.