Total Sea Level Research Articles

Numerical Modeling of Extreme Sea Levels on the Laptev Sea Coast

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.

INUNDATION PREDICTION AS THE EFFECT OF RISING MEAN SEA LEVEL AND HIGH ASTRONOMICAL TIDE IN NORTH JAKARTA BASED ON 2013-2021 TIDAL DATA

Future sea level rise in North Jakarta is one of the potential hazards that threaten the safety of coastal communities and infrastructure. Prediction of sea level rise is needed to reduce the vulnerability of the people living on the coast. This study was conducted to estimate the height of sea level rise in 2045 using linear regression analysis of hourly tidal data for 2013-2021 coupled with the highest astronomical tide value from the results of tidal harmonic analysis in 2021 using the t_tide application in matlab. The water elevation was then projected on the Digital Elevation Model to obtain the inundation area in 2045. The result of this study is an inundation area of 56 km2 in North Jakarta in 2045 due to an increase in total sea level of 117 cm at high tide.

Wave contributions to sea levels along the coast of northern South China Sea over 2002–2022

To better understand the wave contribution to coastal sea level variation in the northern South China Sea (SCS), the total sea level time series, which is estimated as the sum of waves, tides, atmospheric surges and altimetric sea levels, over the period of 2002–2022 are used in this study. It is found that tides and waves are two dominate contributors to coastal sea level changes at seasonal (45.7 % and 40.8 %) and interannual (58.6 % and 28.4 %) time scales. The sea level trend is dominated by the altimetric sea levels, but waves can also influence the trends in the Taiwan Strait and Beibu Gulf. The amount of sea level rise that doubles the frequency of the former 50-year return level is analyzed by using the Generalized Extreme Value Distribution (GEVD) model. The results show that the amount of sea level rise is closely related to the amplitude and variance of extreme sea levels. Because waves can significantly increase probability of occurrence of exceedingly large extreme sea levels, the amount of sea level rise (∼1 m) that doubles the coastal flooding frequency is much greater than that (∼10 cm) without the wave contribution. This result demonstrates the important role of waves in changing the coastal flooding frequency.

Impact of Mass Redistribution on Regional Sea Level Changes Over the South China Sea Shelves

AbstractThis study investigates long‐term sea level changes in the South China Sea (SCS) using a validated high‐resolution regional ocean model simulation for the Maritime Continent. The contributions of ocean mass redistribution and steric sea level are examined to understand the sea level variations. The ocean bottom pressure (OBP) serves as an indicator of sea level variations linked to alterations in ocean mass flux. The OBP accounts for over 80% of the total sea level change over the shelves, while the steric sea level emerges as the dominant factor, contributing over 50% to the sea level change in the deep SCS. Luzon Strait transport shows a weakening trend in the last six decades, resulting in higher heat accumulation and larger steric expansion in the deep SCS. The ocean mass redistribution acts as a mechanism to balance the contrasting steric induced sea level changes over the deep SCS and shallow continental shelves.

Global Sea Level Change Rate, Acceleration and Its Components from 1993 to 2016

Investigating the global sea level budget is essential to quantify the total sea level change (altimetry) and its components, including the steric sea level change and the ocean mass change (gravity), where the latter is mainly attributed to four mass-driven components (Greenland, Antarctica, glaciers and land water storage). In this study, a 24-year global ocean mass change is derived by the joint use of Tongji-LEO2021 and Tongji-Grace2018 monthly gravity field models over 1993–2016, with which the sea level budgets in terms of rate and acceleration are investigated over global oceans within the latitudes 66oN to 66oS together with the IGG-SLR-HYBRID gravity field models, altimetry, steric and four mass-driven components. The statistical results show that the global mean ocean mass change rate accounts for ∼54% of 2.85 ± 0.30 mm/year of global mean total sea level change. The accelerations of global mean total sea level change and its components are 0.145 ± 0.025 mm/year2 (altimetry), 0.003 ± 0.021 mm/year2 (steric), 0.139 ± 0.047 mm/year2 (ocean mass from Tongji), and 0.137 ± 0.010 mm/year2 (the sum of mass-driven components) respectively, indicating that the global sea level budget in terms of acceleration can be closed and nearly no acceleration exists in the global mean steric sea level change for the period 1993–2016.

Projection of Sea Level Change in the South China Sea Based on Dynamical Downscaling

The projection of future sea level change is usually based on the global climate models (GCMs); however, due to the low spatial resolution of the GCMs, the ability to reproduce the spatial heterogeneity of sea level is limited. In order to improve the sea level simulation capability in the South China Sea (SCS), a high-resolution ocean model has been established by using the dynamic downscaling technology. By evaluating and testing 20 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), average results of seven models were selected as the forcing condition of the high-resolution ocean model. The ocean model conducted the historical (1980~2014) and future (2015~2100) simulation under three scenarios of Shared Socio-economic Pathways (SSP1–2.6, SSP2–4.5 and SSP5–8.5). The selected average results of seven models in CMIP6 are better than any of them individually. The downscaled dynamic ocean model provides fruitful spatial characteristics of the sea level change, with a decrease in the dynamic sea level (DSL) in the central and southeastern parts of the SCS, and with a significant increase in the coastal DSL. The local steric sea level (SSL) is dominated by the local thermosteric sea level (TSSL), and the changes of local TSSL more than half of the sea level rise in SCS, indicate the magnitude of total sea level rise is dominated by local TSSL. But the spatial variation in total sea level is dominated by the spatial variation in DSL. Compared with CMIP5, the rise magnitude of the DSL and the local TSSL have been increased under the CMIP6 scenarios. The dynamic downscaling of sea level reveals more spatial details, provides more reliable projection of future sea level under the background of global warming, and can provide a new reference for coastal areas in the SCS to cope with the increasing risk of extreme water level disasters in the future.

Flood vulnerability under sea level rise for a coastal community located in a backbarrier environment, Portugal

Sea level rise will be a major threat to coastal communities within the next century due to the intensity and severity of the floods it can cause. A new methodology considering water infiltration, slope, and hydraulic connectivity was developed to assess the potential inundation extension associated with different total water level and sea level rise scenarios on sandy coasts. This methodology was applied for the current conditions as well as 2050 and 2100 scenarios of storm surge and high tide levels with return periods of 1 year and 100 years. The study area is Culatra village, located on the lagoon side of a barrier island in southern Portugal. The effects of shoreline evolution after the construction of a harbor and associated beach nourishment were also evaluated within the inundation scenarios. The results show that, within the study area, total water level variations caused by sea level rise have a greater influence on the inundation extension than shoreline retreat. The village appears to be safe for the current and 2050 total water level scenarios with a 1-year return period but would be highly affected by 100-year return periods, especially from 2050 onwards. This novel approach represents an improvement on more common flood mapping methods such as the bathtub approach and can be easily applied to other backbarrier environments under sea level rise or facing coastal erosion.

Extreme Sea Levels and Their Attribution for the Canadian Pacific Coast From a Baroclinic Regional Ocean Model and Tide‐Gauge Data

AbstractThe existing operational storm surge model for the Canadian Pacific coast is barotropic without coupling with tides. Here a baroclinic ocean model, which includes tides, storm surges, intra‐seasonal, seasonal, and interannual variations, is developed to reproduce coastal sea levels in the northeast Pacific from 1993 to 2020. The model results are validated against observations at tide‐gauge sites, demonstrating overall good skills for tides and non‐tidal sea levels. The Gumbel distribution is applied to derive extreme sea levels from hourly sea level anomalies. The model‐based extreme sea levels agree approximately with the observation‐based ones. For the 100‐year return period, modeled total extreme sea levels range from 2.14 m at Victoria Harbour to 4.43 m at Queen Charlotte City, and modeled non‐tidal extreme sea levels from 1.02 m at Bella Bella to 1.78 m at Queen Charlotte City. On average, the model‐based values underestimate the 100‐year return level by 0.18 m for total extreme sea levels and by 0.23 m for non‐tidal extreme sea levels. Both the model‐ and observation‐based results reveal that the storm surge at periods less than 10 d accounts for 60% of the 100‐year non‐tidal extreme sea level, and the intra‐seasonal, seasonal, and interannual variations account for 40% of it. The present study improves coastal sea level modeling and model‐based extreme level estimates. Moreover, this study also demonstrates for the first time that the intra‐seasonal to interannual changes contribute substantially to extreme sea levels and that El Niño can enhance this contribution on the Canadian Pacific coast.

Modelling the barotropic sea level in the Mediterranean Sea using data assimilation

Abstract. This paper analyses the variability of the sea level barotropic components in the Mediterranean Sea and their reproduction using a hydrodynamic model with and without data assimilation. The impact of data assimilation is considered both in reanalysis and short-forecast simulations. We used a two-dimensional finite element model paired with an ensemble Kalman filter, which assimilated hourly sea level data from 50 stations in the Mediterranean basin. The results brought about a significant improvement given by data assimilation in the reanalysis of the astronomical tide, the surge, and the barotropic total sea level, even in coastal areas and far from the assimilated stations (e.g. the southeastern Mediterranean Sea). As with the reanalysis simulations, the forecast simulations, which start from analysis states, improve, especially on the first day (37 % average error reduction) and when seiche oscillations are triggered. Since seiches are free barotropic oscillations that depend only on the initial state, their reproduction improves very effectively with data assimilation. Finally, we estimate the periods and the energy of these oscillations by means of spectral analysis, both in the Adriatic Sea, where they have been extensively studied, and in the Mediterranean Sea, where the present documentation is scarce. While the periods are well reproduced by the model even without data assimilation, their energy shows a good improvement when using it.

Reconstruction of Mediterranean coastal sea level at different timescales based on tide gauge records

Abstract. A coastal sea level reconstruction based on tide gauge observations is developed and applied to the western basin of the Mediterranean sea. The reconstructions are carried out in four frequency bands and are based on an optimal interpolation method in which the correlation between tide gauge data and all coastal points has been determined from the outputs of a numerical model. The reconstructions for frequencies lower than 1 month use monthly observations from the Permanent Service for Mean Sea Level (PSMSL) database and cover the period from 1884 to 2019. For the reconstruction of higher frequencies, hourly observations from the Global Extreme Sea Level Analysis (GESLA-2) dataset are used and cover from 1980 to 2015. Total sea level is retrieved with high accuracy from the merging of the different frequency bands. Results of a cross-validation test show that independent tide gauge series are highly correlated with the reconstructions. Moreover, they correlate significantly better with the reconstructions than with altimetry data in all frequency bands, and therefore the reconstruction represents a valuable contribution to the attempts of recovering coastal sea level. The obtained reconstructions allow us to characterize the coastal sea level variability, estimate coastal sea level trends along the entire coastline, and examine the correlation between western Mediterranean coastal sea level and the main North Atlantic climate indices. The limitations and applicability of the method to other regions are also discussed.

The collapse of the Cordilleran–Laurentide ice saddle and early opening of the Mackenzie Valley, Northwest Territories, Canada, constrained by 10Be exposure dating

Abstract. Deglaciation of the northwestern Laurentide Ice Sheet in the central Mackenzie Valley opened the northern portion of the deglacial Ice-Free Corridor between the Laurentide and Cordilleran ice sheets and a drainage route to the Arctic Ocean. In addition, ice sheet saddle collapse in this section of the Laurentide Ice Sheet has been implicated as a mechanism for delivering substantial freshwater influx into the Arctic Ocean on centennial timescales. However, there is little empirical data to constrain the deglaciation chronology in the central Mackenzie Valley where the northern slopes of the ice saddle were located. Here, we present 30 new 10Be cosmogenic nuclide exposure dates across six sites, including two elevation transects, which constrain the timing and rate of thinning and retreat of the Laurentide Ice Sheet in the area. Our new 10Be dates indicate that the initial deglaciation of the eastern summits of the central Mackenzie Mountains began at ∼15.8 ka (17.1–14.6 ka), ∼1000 years earlier than in previous reconstructions. The main phase of ice saddle collapse occurred between ∼14.9 and 13.6 ka, consistent with numerical modelling simulations, placing this event within the Bølling–Allerød interval (14.6–12.9 ka). Our new dates require a revision of ice margin retreat dynamics, with ice retreating more easterly rather than southward along the Mackenzie Valley. In addition, we quantify a total sea level rise contribution from the Cordilleran–Laurentide ice saddle region of ∼11.2 m between 16 and 13 ka.

Increase in the Erosion Rate Due to the Impact of Climate Change on Sea Level Rise: Victoria Beach, a Case Study

This article provides a general methodology for calculating the retreat of the coastline and the volume of sand necessary to renourish a beach due to sea level rise (SLR) in the medium-long term. An example is presented, Victoria Beach, and a projection is made for the years 2030, 2040, 2050, and 2100. The results obtained take into account global sea level rise (GSLR), which is worldwide, and local sea level rise (LSLR), which considers climate variability and vertical land movements. Regarding GSLR, data were provided by the projections from IPCC (Intergovernmental Panel on Climate Change) scenarios and empirical models, such as Rahmstorf and Pfeffer. The LSLR data came from the tide gauge station located in Cadiz. Finally, the results obtained showed that global warming impacts erosive effects and the subsequent volume of sand required to renourish beaches. The total sea level rise (TSLR) projections indicated for Victoria Beach are relatively higher than the GSLR projections. Even in the best IPCC scenario (RCP 2.6), Victoria Beach presents a significant erosion of 52 m, requiring a volume of sand of 1.0 Mm3 to supply renourishment.

Relative Contributions of Open‐Ocean Forcing and Local Wind to Sea Level Variability Along the West Coasts of Ocean Basins

AbstractThis study aims to reconstruct sea level at the coast by quantifying relative contributions of local wind forcing and the penetrated open‐ocean signals, and thus to build a dynamical connection that seamlessly links the ocean basin to the coast. A linear, modified arrested topographic wave (ATW) model is used to examine the transmission of interior sea level across the continental shelf and the role of alongshore wind in determining the coastal sea level. The local wind stress substantially influences the coastal sea level but does not affect the transmission of open‐ocean signals in the linear framework. Increased bottom friction or gentler slope of shelf favors the penetration of open‐ocean signals. This modified ATW model is then applied to the shelf seas of North Pacific and North Atlantic, with model parameters being set according to the realistic features of regional oceanography. The offshore boundary condition is determined by the integrated barotropic and baroclinic ocean responses in the ocean basin and the transmission processes across western boundary currents. Based on the proposed “basin‐to‐coast” dynamical linkage framework, one can estimate the relative contributions of open‐ocean forcing and local wind to the total coastal sea level. According to these partitions, the reconstructed coastal sea levels along the west coasts of North Pacific and North Atlantic on seasonal time scale are in close agreement with tide‐gauge observations. The idea and specific calculations of coastal sea level reconstruction could be readily applied to other coasts of the global ocean.

Analysis of Global Sea Level Change Based on Multi-Source Data

Global sea level rise is both a major indicator and consequence of global warming. At present, global warming is causing sea level rise in two main ways: one is the thermal expansion of sea water, and the other is the injection of large amounts of fresh water into the ocean after glaciers and ice sheets melt. In this paper, satellite altimeter data are used to study the total changes of global sea level from 2002 to 2020. Different from most previous studies, this study proposes a calculation method of sea level anomaly using only the along track altimetry data, which is similar to considering the satellite points as tide gauges, in order to avoid the error caused by interpolation in the map data. In addition, GRACE satellite data are used to calculate the changes of global sea level caused by water increase; temperature and salinity data are used to calculate the changes from ocean thermal expansion. Next, using satellite altimetry data, the calculation results show that the global sea level rise rate in the period of 2002–2020 is 3.3 mm/a. During this period, the sea level change caused by the increase of sea water calculated with GRACE satellite data is 2.07 mm/a, and that caused by the thermal expansion of seawater is 0.62 mm/a. The sea level rise caused by the increase of water volume accounts for 62.7% of the total sea level rise.

Barystatic and steric sea level variations in the Baltic Sea and implications of water exchange with the North Sea in the satellite era

Satellite altimetry, satellite gravimetry, and in-situ subsurface salinity and temperature profiles are used to investigate the total, barystatic, and steric sea level variations in the Baltic Sea, respectively. To estimate the steric sea level, the density variations are weighted in deeper layers to prevent overestimation of their contribution. We show that the sum of barystatic and steric components exhibits excellent cross correlation (0.9) with satellite altimetry sea level variations and also explains up to 84% of total signal variability from 2002 to 2019. Considering the dominance of barystatic sea level variations in the basin and the limitation of satellite gravimetry in resolving the mass change in water-land transition zones (known as the leakage problem), the mismatch is likely attributed to the inadequate accuracy of the barystatic datasets. The total sea level and its contributors are further decomposed into seasonal, interannual, and decadal temporal components. It is shown that despite its insignificant contributions to seasonal and interannual changes, the steric sea level plays an important role in decadal variations. Additionally, we show that the interannual variations of the barystatic sea level are governed by the North Atlantic Oscillation in the basin. The sea level variation in the North Sea is also examined to deduce the water exchange patterns on different time scales. A drop in the North Sea level can be seen from 2005 to 2011 which is followed by the Baltic Sea level with a ~3-year lag, implying the outflow from the Baltic Sea to the North Sea.

Uncertainty in GRACE/GRACE-follow on global ocean mass change estimates due to mis-modeled glacial isostatic adjustment and geocenter motion

Global mean sea level has increased about 3 mm/yr over several decades due to increases in ocean mass and changes in sea water density. Ocean mass, accounting for about two-thirds of the increase, can be directly measured by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) satellites. An independent measure is obtained by combining satellite altimetry (measuring total sea level change) and Argo float data (measuring steric changes associated with sea water density). Many previous studies have reported that the two estimates of global mean ocean mass (GMOM) change are in good agreement within stated confidence intervals. Recently, particularly since 2016, estimates by the two methods have diverged. A partial explanation appears to be a spurious variation in steric sea level data. An additional contributor may be deficiencies in Glacial Isostatic Adjustment (GIA) corrections and degree-1 spherical harmonic (SH) coefficients. We found that erroneous corrections for GIA contaminate GRACE/GFO estimates as time goes forward. Errors in GIA corrections affect degree-1 SH coefficients, and degree-1 errors may also be associated with ocean dynamics. Poor estimates of degree-1 SH coefficients are likely an important source of discrepancies in the two methods of estimating GMOM change.

Sea Levels Dynamical Downscaling and Climate Change Projections at the Uruguayan Coast

This work implements a dynamical downscaling approach, based on a set of nested two-dimensional hydrodynamic models, to quantify the expected changes in the total sea level climate and its components for the Uruguayan coast, using surface wind and sea level pressure projections from global climate models generated during the Phase 5 of the Coupled Models Inter-Comparison Project, considering three time horizons: historical period (1986-2005), short term (2027-2045) and long term (2082-2100), and the future scenarios RCP 4.5 and RCP 8.5. It is concluded that the main contribution to the projected changes in the area is the regional mean sea level rise, followed in importance by the effect that the increase in the water depth has on the amplitude of the tidal components. Moreover, it is concluded that changes in the meteorological residuals (or surges), associated with potential changes in the atmospheric circulation patterns, are negligible in the study area. The obtained results reinforce the need to resort to dynamic downscaling for projecting total sea level changes in areas characterized by wide and shallow continental shelfs and estuaries, as this approach allows to resolve the interactions that may arise between tides, surges and the mean sea level rise, something that cannot addressed with an approach based solely on statistical downscaling.

Sea level changes mechanisms in the MPI-ESM under FAFMIP forcing conditions

Mechanistic causes for sea level (SL) change patterns are analyzed as they emerge from the Coupled Model Intercomparison Project Phase 6 (CMIP6) endorsed Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) coupled climate experiments imposing individual forcing anomalies in wind stress, heatflux and freshwater flux to the Max-Planck-Institute Earth System Model (MPI-ESM). It appears that the heat flux perturbations have the largest effect on the sea level. In contrast, the direct impact of momentum and freshwater flux anomalies on SL anomalies appear to be limited to some region e.g. the Southern Ocean, Arctic Ocean and to some extent the North Pacific and North Atlantic Ocean. We find that thermosteric changes dominate the total SL change over large parts of the global ocean, except north of 60 °N where halosteric changes prevail. An analysis of added and redistributed components of heat and freshwater further suggests that the added component dominates the thermosteric SL and the redistributed component dominates the halosteric SL. Due to feedback processes a superposition of all forcing components together leads to the simulated sea level changes in each individual experiment. As a result, large surface heat flux anomalies over the Atlantic lead to wind stress change outside of the Atlantic through teleconnections, which in turn appear to be the primary driving agent for changes of sea level outside of the Atlantic in all three experiments. The associated wind driven Sverdrup stream function implicates that outside of the Atlantic most of the feedback can be explained by changes in the Sverdrup circulation.

Steric and atmospheric contributions to interannual sea level variability in the eastern mediterranean sea over 1993–2019

Sea level trends and their forcing over the eastern Mediterranean basin are investigated by using 27 years (1993–2019) of gridded sea level anomalies (SLA) derived from satellite altimetry and 9 tide gauge stations, along with sea surface temperature (SST) and temperature and salinity profiles. The contributions of atmospheric (wind and pressure) and steric components to the interannual variability of total SLA were evaluated. The thermosteric component represents the major contributor to the linear trend and was positive over most of the eastern Mediterranean, with a spatially averaged trend of 2.13±0.41 mm/year, accounting for 69% of the total sea level trend (3.1±0.61 mm/year). In contrast, the halosteric effect has a negative contribution to the steric SLA, with a mean trend of -0.75±0.19 mm/year. The atmospheric component trend was much lower at 0.32±0.24 mm/year. The interannual variability of SLA accounts for about 36% of overall sea level variability. Steric and atmospheric contributions to the interannual variability of sea level in the eastern Mediterranean account for about 52% and 18%, respectively. The strongest interannual variability and trends in SLA were observed over the basin's main recurrent gyres, with the maximum positive trend obtained over the Mersa–Matruh and Cyprus gyres, as well as the North Shikmona eddy, and maximum negative trend over the Ierapetra gyre. Over the study period, all tide gauges showed a positive and statistically significant trend, ranging from 1.47±0.77 to 5.79±1.32 mm/year after applying glacial isostatic adjustment and atmospheric correction, and were in good agreement with reconstructed steric sea level data.

Impact of Ocean Domain Definition on Sea Level Budget

Total sea level changes from space radar altimetry are mainly decomposed into two contributions of mass addition and volume expansion of oceans, measured by GRACE space gravimeter and Argo float array, respectively. However, the averages of altimetry, mass, and steric sea level changes have been usually examined over the respective data domains, which are different to one another. Errors arise from this area inconsistency is rarely discussed in the previous studies. Here in this study, an alternative definition of ocean domain is applied for examining sea level budgets, and the results are compared with estimates from different ocean areas. It shows that the impact of area inconsistency is estimated by about 0.3 mm/yr of global trend difference, and averages based on a consistent ocean area yield a closer agreement between altimetry and mass + steric in trend. This contribution would explain some discordances of past sea level budget studies.