Rate Of Sea-level Change Research Articles

Vertical land movement over China coasts determined by tide gauge and satellite altimetric data

Sea level change (SLC) extracted from tide gauge data references to the benchmark fixed coastal land. Sea level change determined from satellite altimetric data references to ellipsoid with respect to the Earth’s mass center in a terrestrial reference frame. In order to study the vertical land movement over China coasts, we simultaneously process altimetric data of TOPEX/Poseidon (T/P), Jason-1 and Jason-2, and tide gauge data of 21 stations from 1993 to 2012. We use altimetric data in the tandem stages to correct biases point by point between T/P and Jason-1, Jason-1 and Jason-2 to get precise sea level changes over China seas. Monthly and yearly averaged sea level changes near the corresponding tide gauge stations are estimated from tide gauge data from University of Hawaii Sea Level Center (UHSLC) and Permanent Service for Mean Sea Level (PSMSL). Correlation coefficients between two time series of SLCs determined by 21 tide gauge stations and altimetry data near each station with the same time span are calculated. The result shows that there are 8 stations correlation coefficient between 0.6 and 0.9, 10 stations correlation coefficient between 0.3 and 0.6, and 3 stations correlation coefficient below 0.3 which indicate that SLCs from these two techniques have the identical trends. Differences of SLC rates determined from altimetry data and tide gauge data can stand for the vertical land movement over China coasts. Fifteen tide gauge stations were selected over China coast whose data integrities are high, time spans are long, and correlation coefficients with altimetry SLCs are greater than 0.4. Lands over China mainland coast sink except Laohutan and Shanwei in this study. The land coast sink ranges of China mainland is mostly from −0.05 to −0.58 cm/year but the most settlement takes place in Haikou which sink up to −1.71 cm/year. Laohutan and Shanwei stations rise at 0.3 and 0.72 cm/year, respectively. Lands over Taiwan Island and Hong Kong basically rise in these 20 years and the rise range is from 0.11 to 0.47 cm/year.

Rates of Sea Level Changes—A Clarifying Note

The values of present to future rates in sea level changes vary in an almost chaotic way. In view of the urgent need to handle this question in a constructive way, we must anchor the issue in observational facts, physical laws and long-term scientific experience. Doing so, we can put a solid ultimate frame of any possible rise in sea level in the next centuries: viz. 10.0 mm/yr or 1.0 m per century. If this is the ultimate possible rate, the expected rate in the 21st century must be far less. The author’s proposition is +5 cm ± 15 cm by year 2100.

Assessment of Coastal Vulnerability Due to Sea Level Change at Bhola Island, Bangladesh: Using Geospatial Techniques

With continued climate change, coastal areas are subjected to undesirable situations in the form of sea-level rise and its adverse outcomes like storm surge, flooding and erosion. Being a unique geographic location, low topography, relatively higher population density as well as overwhelming dependence on natural resources, Bangladesh is one of the vulnerable countries exposed to the impacts of global warming and climate change. Bhola in southern Bangladesh represents the world’s most dynamic estuary is potentially vulnerable to accelerated sea level rise and associated calamities. The present study aims to develop a coastal vulnerability index (CVI) using eight parameters namely (a) geomorphology, (b) slope, (c) relative sea level change rate, (d) mean tide range (e) shoreline erosion and accretion, (f) population (g) bathymetry and (h) coastal flooding which were addressed as the relative risk variable for the study area using geospatial techniques i.e., Remote Sensing and GIS. The aforementioned parameters were ranked on the basis of their potential contribution to physical changes on the coast, as sea-level rises, and the final calculation was done over 263.87 km shoreline by the square root of the mean values of the ranked variables. According to the vulnerability index, about 22 % corresponding to 57.23 km of the entire coast is under very high-risk and another 29 % representing 75.26 km is under high-risk. Again, 25 % encompassing 67.69 km shoreline is at moderate risk and 24 %, that is 63.69 km shoreline is found to be at low risk. The most vulnerable coastal regions are found mainly along the western coast of Char Fasson and northern and southwestern coast of Bhola Sadar of Bhola Island.

Modeling sea-level change using errors-in-variables integrated Gaussian processes

We perform Bayesian inference on historical and late Holocene (last 2000 years) rates of sea-level change. The input data to our model are tide-gauge measurements and proxy reconstructions from cores of coastal sediment. These data are complicated by multiple sources of uncertainty, some of which arise as part of the data collection exercise. Notably, the proxy reconstructions include temporal uncertainty from dating of the sediment core using techniques such as radiocarbon. The model we propose places a Gaussian process prior on the rate of sea-level change, which is then integrated and set in an errors-in-variables framework to take account of age uncertainty. The resulting model captures the continuous and dynamic evolution of sea-level change with full consideration of all sources of uncertainty. We demonstrate the performance of our model using two real (and previously published) example data sets. The global tide-gauge data set indicates that sea-level rise increased from a rate with a posterior mean of 1.13 mm$/$yr in 1880 AD (0.89 to 1.28 mm$/$yr 95% credible interval for the posterior mean) to a posterior mean rate of 1.92 mm$/$yr in 2009 AD (1.84 to 2.03 mm$/$yr 95% credible interval for the posterior mean). The proxy reconstruction from North Carolina (USA) after correction for land-level change shows the 2000 AD rate of rise to have a posterior mean of 2.44 mm$/$yr (1.91 to 3.01 mm$/$yr 95% credible interval). This is unprecedented in at least the last 2000 years.

A unique asymmetry in the pattern of recent sea level change

AbstractThe spatial pattern of 20 year sea surface height trends from satellite altimetry is placed into the context of historical modes of wind‐driven ocean volume redistribution identified in basin‐scale, regional averages of tide gauge data. The difference between recent rates of sea level change in northern and southern regions is found to be twice as large and statistically greater than any other 20 year period during the twentieth century. This unique asymmetry in the pattern of sea level change coincides with a departure from a historical mode of volume redistribution between southern regions related to a measure of asymmetry in the Southern Annular Mode. The asymmetry also coincides with a maximum in the rate of global mean sea level rise during recent decades, but the asymmetry is not apparent during an early twentieth century maximum in the global rate of similar magnitude.

Sea-level rise in the Mediterranean Sea by 2050: Roles of terrestrial ice melt, steric effects and glacial isostatic adjustment

To assess the regional pattern of future low-frequency sea-level variations in the Mediterranean Sea, we combine the terrestrial ice melt, the glacio-isostatic and the steric sea-level components. The first is obtained from global scenarios for the future mass balance of the Greenland and Antarctica ice sheets, glaciers and ice caps. The second is based on modeling, using different assumptions about the Earth's rheology and the chronology of deglaciation since the Last Glacial Maximum. The third is obtained from published simulations based on regional atmosphere–ocean coupled models. From a minimum and a maximum scenario by 2040–2050, we find that the total, basin averaged sea-level rise will be 9.8 and 25.6cm. The terrestrial ice melt component will exceed the steric contribution, which however will show the strongest regional imprint. Glacial isostatic adjustment will have comparatively minor effects. According to our estimates, at the Mediterranean Sea tide gauges, the rate of sea-level change will increase, by 2050, by a factor of ~1–6 relative to the observed long-term rates.

Sea-level variability over five glacial cycles.

Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2 m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2 kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records.

Wind-Driven Coastal Sea Level Variability in the Northeast Pacific

Abstract The rate of coastal sea level change in the northeast Pacific (NEP) has decreased in recent decades. The relative contributions to the decreased rate from remote equatorial wind stress, local longshore wind stress, and local windstress curl are examined. Regressions of sea level onto wind stress time series and comparisons between NEP and Fremantle sea levels suggest that the decreased rate in the NEP is primarily due to oceanic adjustment to strengthened trade winds along the equatorial and coastal waveguides. When taking care to account for correlations between the various wind stress time series, the roles of longshore wind stress and local windstress curl are found to be of minor importance in comparison to equatorial forcing. The predictability of decadal sea level change rates along the NEP coastline is therefore largely determined by tropical variability. In addition, the importance of accounting for regional, wind-driven sea level variations when attempting to calculate accelerations in the long-term rate of sea level rise is demonstrated.

Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea

Sixteen piston core samples collected from the Heuksan Mud Belt on the southeastern inner shelf of Korea were analyzed to characterize sediment property and distribution in relation to interpreted seismic units. The results from seven of 16 cores are presented in this study using core locations along a seismic track line. Variations in physical properties with depth gradually increased and/or decreased, depending on the characteristics of the specific property. Property patterns are primarily the result of dewatering caused by compaction and/or consolidation. Significant variations in depth are due to differences in sediment texture. In particular, core P03 is largely composed of sandy sediments below 170 cm. All core data come from three specific seismic Units: I, IIa and IIb, in descending order. The seismic patterns that define these units are interpreted as related to the rate of sea-level change during transgressions and depositional processes during the Holocene. Regionally, the variation of physical properties along the seismic profile is likely to reflect the relative characteristics of the seismic units. Unit I is characterized by low shear strength/wet bulk density and high porosity. Unit IIa appears to have higher shear strength than Units I and IIb. Unit IIb shows high wet bulk density and velocity. These observations suggest that the physical properties are mainly controlled by depositional processes related to sea-level change. Clay fabric analysis that uses a scanning electron microscope for two core samples shows the change of particle arrangement due to compaction caused by overburden loading with burial depth. In the upper part of the core, edge-to-edge and edge-to-face contacts dominate. In contrast, face-to-face contact characterized by the well-oriented arrangement of clay particles frequently occurs in the lower parts of the cores, indicating sediment compaction or initial consolidation caused by overburden pressure.

Evidence for a differential sea level rise between hemispheres over the twentieth century

AbstractTide gauge records are the primary source of sea level information over multidecadal to century timescales. A critical issue in using this type of data to determine global climate‐related contributions to sea level change concerns the vertical motion of the land upon which the gauges are grounded. Here we use observations from the Global Positioning System for the correction of this vertical land motion. As a result, the spatial coherence in the rates of sea level change during the twentieth century is highlighted at the local and the regional scales, ultimately revealing a clearly distinct behavior between the Northern and the Southern Hemispheres with values of 2.0 mm/yr and 1.1 mm/yr, respectively. Our findings challenge the widely accepted value of global sea level rise for the twentieth century.

A New Look at Barrier-Inlet Morphodynamics

Davis, R.A., 2013. A New Look at Barrier-Inlet Morphodynamics.Coastal morphodynamics is dependent on the interaction of multiple variables. An earlier publication demonstrated that the comparative influence of waves and tides was the fundamental relationship in coastal morphology. The discussion in this paper adds the important variables of tidal prism, sediment abundance, and sea-level change to the equation. Tidal prism is critical in that it can be the primary factor in morphodynamics if both wave and tidal climate are held constant. Abundant or scarce sediment availability can produce coastal morphology that would not develop otherwise. Because of the extremely slow rate of sea-level change, its impact is less prominent than the other variables and we see less evidence of its influence than the others, except in certain coastal reaches.

Characterising the distribution and morphology of creeks and pans on salt marshes in England and Wales using Google Earth

By using Google Earth images and simple morphometric analyses, pan and creek characteristics of salt marshes across England and Wales have been mapped and related to key environmental variables, including tidal range, sea level change, coastal configuration, sediment type and erosion state. Pan density was found to be higher on the west coast or where there is a moderate tidal range and low sea level change. Pan density is also higher on back barrier and drowned valley marshes and when creek density is low. Maximum pan size is partly controlled by pan density. Creek density and sinuosity showed great variability between areas with marshes in the south having a higher creek density. Creek density is related to tidal prism and marshes undergoing high rates of sea level change usually have higher creek densities. Marshes with an upstream configuration (embayment, drowned valley and back barrier) have lower creek densities due to a lower tidal prism. Sediment type also plays a role with lower creek densities found on coarser sediment types. Creek sinuosity seems to be largely controlled by tidal range with higher sinuosities on meso- or macro-tidal marshes. This large-scale, Google Earth-based, analysis of the distribution and likely environmental controls on salt marsh morphometry illustrates the utility of Digital Globes as sources of freely-available, high resolution imagery for geomorphological research.

Characterizing and minimizing the effects of noise in tide gauge time series: relative and geocentric sea level rise around Australia

We quantify the rate of sea level rise around the Australian continent from an analysis of tide gauge and Global Positioning System (GPS) data sets. To estimate the underlying linear rates of sea level change in the presence of significant interannual and decadal variability (treated here as noise), we adopt and extend a novel network adjustment approach. We simultaneously estimate time-correlated noise as well as linear model parameters and realistic uncertainties from sea level time series at individual gauges, as well as from time-series differences computed between pairs of gauges. The noise content at individual gauges is consistent with a combination of white and time-correlated noise. We find that the noise in time series from the western coast of Australia is best described by a first-order Gauss–Markov model, whereas east coast stations generally exhibit lower levels of time-correlated noise that is better described by a power-law process. These findings suggest several decades of monthly tide gauge data are needed to reduce rate uncertainties to −1 for undifferenced single site time series with typical noise characteristics. Our subsequent adjustment strategy exploits the more precise differential rates estimated from differenced time series from pairs of tide gauges to estimate rates among the network of 43 tide gauges that passed a stability analysis. We estimate relative sea level rates over three temporal windows (1900–2011, 1966–2011 and 1993–2011), accounting for covariance between time series. The resultant adjustment reduces the rate uncertainty across individual gauges, and partially mitigates the need for century-scale time series at all sites in the network. Our adjustment reveals a spatially coherent pattern of sea level rise around the coastline, with the highest rates in northern Australia. Over the time periods beginning in 1900, 1966 and 1993, we find weighted average rates of sea level rise of 1.4 ± 0.6, 1.7 ± 0.6 and 4.6 ± 0.8mmyr −1 , respectively. While the temporal pattern of the rate estimates is consistent with acceleration in sea level rise, it may not be significant, as the uncertainties for the shorter analysis periods may not capture the full range of temporal variation. Analysis of the available continuous GPS records that have been collected within 80 km of Australian tide gauges suggests that rates of vertical crustal motion are generally low, with the majority of sites showing motion statistically insignificant from zero. A notable exception is the significant component of vertical land motion that contributes to the rapid rate of relative sea level change (>4mmyr −1 ) at the Hillarys site in the Perth area. This corresponds to crustal subsidence that we estimate in our GPS analysis at a rate of −3.1 ± 0.7mmyr −1 , and appears linked to groundwater withdrawal. Uncertainties on the rates of vertical displacement at GPS sites collected over a decade are similar to what we measure in several decades of tide gauge data. Our results motivate continued observations of relative sea level using tide gauges, maintained with high-accuracy terrestrial and continuous co-located satellite-based surveying.

Analysing the 100 year sea level record of Leixões, Portugal

► The long-term historic sea level data from Leixões (Portugal) has been recovered. ► Estimated mean sea level trend is not in line with global MSL rise predictions. ► Observed sea levels are influenced by prevailing weather systems and local atmospheric pressure. ► Caution is needed using a single tide gauge as representative of regional sea level. A new data set from the tide gauge at Leixões (North–West Portugal) has recently been transferred from its paper format into a digital time series of hourly sea level values. By measuring sea level variations since 1890, this tide gauge station is one of the few in the world with over 100 yr of digitised hourly records and the longest for the South West of Europe and Iberian Peninsula. This paper presents the procedures adopted to recover the Leixões sea level data from paper chart records as well as the data quality control and data editing methodologies. The mean rate of sea level change between 1906 and 2008 is −0.70 ± 0.27 mm yr −1 , which does not agree with the global mean sea level rise of 1–2 mm yr −1 . No evidence for vertical land movement was found and Global Isostatic Adjustment influence on sea level, at this location, can be neglected. It is likely that prevailing weather systems in the North Atlantic, especially in the winter, and local atmospheric pressure, influence sea levels at Leixões. A further contribution is found from tides and surges. The evolution of the port cannot be ignored when trying to understand sea level change.

Identification of Physical Transportation Infrastructure Vulnerable to Sea Level Rise

The objective of this research was developing a methodology for assessing the potential impacts of sea level rise (SLR) on Florida’s state transportation infrastructure to assist the state with transportation planning. The proposed approach integrates the Florida Department of Transportation (FDOT) information system, satellite imagery, local roadway and hydrologic data with existing topographical and geographical data to generate SLR projections to facilitate i) the evaluation of current and projected SLR impacts on transportation infrastructure located along Florida’s coastline and low-lying terrain areas, and ii) the identification of the physical transportation infrastructure components that are vulnerable given the United States Army Corps of Engineers’ scenario-based methodology to project the timing of future low, intermediate and high rates of sea level change. A detailed case study in Dania Beach, Florida and a comparative example in Punta Gorda, Florida were used to evaluate the soundness of the methodology. Further research was performed to develop a preliminary evaluation of the impact of groundwater levels as an exacerbating factor with respect to sea level rise. Storm surge with SLR is a future, more difficult area of investigation.

Holocene relative sea levels and paleogeographies of the Delaware River estuary: implications for current rates of sea-level change

Isolation basins, raised tidal marshes, coastal wetlands and dune systems around Arisaig in northwest Scotland produce a ∼16 000-year record of relative sea-level (RSL) change from the time of local deglaciation following the Last Glacial Maximum (LGM) to the present. New sea-level index points from Mointeach Mhor North define the culmination of the mid-Holocene RSL highstand to ∼7600–7400 cal yr BP and 6.74±0.2 m above present. Numerous sea-level index points indicate that the RSL highstand persisted more than 1000 years before the onset of any significant RSL fall. This points to a gradual cessation of melting of the Laurentide and Antarctic ice sheets, rather than an abrupt termination. Isolation basin evidence, from a marine limit ∼34 to 38 m above present down to sites close to current sea level, constrain the acceleration of eustatic sea-level rise during meltwater pulse 1a to ∼30 mm yr−1 or ∼11 km3 yr−1 meltwater discharge. Comparison of RSL observations with glacial isostatic adjustment (GIA) model predictions show differences in the pattern of residuals dependent upon the GIA model used. Changes to the far-field ice model components can partly explain the patterns of residuals.

Selective extinction of Triassic marine reptiles during long-term sea-level changes illuminated by seawater strontium isotopes

The relationship between cycles of sea-level change and marine diversity has long been the subject of debate. Large predators may be particularly sensitive to changes in habitat availability and marine productivity driven by changes in sea-level, especially those dependent on nearshore benthic food resources. To test this relationship, we compared the proportional diversity of differing marine reptile ecotypes through the Triassic with the isotopic composition of seawater strontium (87Sr/86Sr), a geochemical index linked to tectonically controlled sea-level change. The proportional abundance of marine reptiles adapted toward a diet of shelled prey rose during times of rapid sea-level rise and fell during times of rapid sea-level fall, while open water forms were more resistant to these changes. Our results indicate that the rate of sea-level change, rather than the absolute magnitude of sea-level or flooded shelf area, played a role in shaping patterns of ecological diversification and ecologically selective extinction during the Triassic. The link between the isotopic composition of seawater strontium and the evolution of marine reptiles demonstrates that sea-level change played an important role in the structuring of marine ecosystems over geologic time.

Mitigating the effects of vertical land motion in tide gauge records using a state-of-the-art GPS velocity field

This study aims to correct for long-term vertical land motions at tide gauges (TG) by estimating high-accurate GPS vertical velocities at co-located stations (GPS@TG), useful for long-term sea-level change studies and satellite altimeter drift monitoring. Global Positioning System (GPS) data reanalyses are mandatory when aiming at the highest consistency of the estimated products for the whole data period. The University of La Rochelle Consortium (ULR) has carried out several GPS data reanalysis campaigns with an increasing tracking network, an improving processing strategy and the best methodology. The geodetic results from the latest GPS velocity field estimated at ULR (named ULR5) are presented here. The velocity field includes 326 globally distributed GPS stations, from which 200 are GPS@TG (30% more than previous studies). The new GPS data processing strategy, the terrestrial frame definition and the velocity estimation procedures are described. The quality of the estimated vertical velocities is empirically assessed through internal and external velocity comparisons, including the analysis of the time-correlated noise content of the position time series, to be better than 0.6mm/yr (2 sigma). The application of this velocity field is illustrated to appraise to what extent vertical land motions contaminate the estimates of satellite altimetry drifts. The impact on the altimeter-derived sea level trends was evaluated to be up to 0.6mm/yr. Worldwide TGs were grouped into regions in order to explore long-term spatial sea level variability in the rates of sea level change. By taking into account the vertical land motion of the tide gauges, the dispersion of the observed sea level rates within each region was reduced by 60%. Long-term regional mean sea level variations up to 70% from the global mean were found.

Modern beachrock formation in Durban, KwaZulu-Natal

We explored the recent cementation of modern beachrock on the seaward margin of the Durban Bluff, central KwaZulu-Natal. The low latitude and subtropical climatic setting is a unique context compared to the more commonly documented contemporary beachrock formation in the tropics. Geological field mapping was carried out and here we present results based on sedimentary facies of a clastic shoreline and carbonate diagenesis of interstitial cements using transmitted light microscopy. The beachrock was cemented by micrite and aragonite, and iron oxide infilled voids. The presence of human artefacts within the deposit showed evidence for cementation within the last century. The elevation (at Mean Low Water) and correlation to rates of sea level change for the east coast of South Africa showed that the beachrock is less than 72 years in age. In contrast to older local Pleistocene deposits, beachrocks have cemented along this stretch of coast during successive sea level highstands with similar climatic regimes – the last Interglacial, the Holocene High and the present. Here we report the most southerly documentation of modern beachrock in KwaZulu-Natal, which, to our knowledge, represents the youngest deposit reported in southern Africa.

Sea-level rise and coastal change: the past as a guide to the future

There is a broader awareness than ever that we live in a changing environment. The spectre of climate change is of wide concern, and the observed trends and anticipated consequences of an acceleration of sea-level rise pose a series of threats for the future of people who live in coastal communities. Coastal geoscientists are able to reconstruct the position of former sea levels; they can also explain much of the geographical variation in relative sea-level history. Successive collaborative projects (many under the auspices of international programmes sponsored by IGCP and INQUA) derived local sea-level histories and compiled atlases of relative sea-level curves, and some addressed past coastal behaviour in response to these changes. The most recent International Geological Correlation programme project 588, ‘Preparing for coastal change’, continues this impressive lineage of projects that have laid the foundations for our understanding of sea-level behaviour over the late Quaternary. Today, these issues are a major focus in the debate about climate change, its impacts, and the need for adaptation on the most vulnerable shorelines. There is clearly a role for the palaeoenvironmental skillset honed through successive geoscientific projects. Investigations of past coastal environments have provided the tools for delineating past levels of the sea, but the stratigraphical and geochronological studies which were necessary to reconstruct the sea-level position also provide insights into where the shoreline lay and how the coast behaved as sea level changed. If the present is the key to the past, then the past, seen from the context of the present, can be a guide to the future. Collaborative projects and international co-operation between scientists from different disciplines can play important roles in future debates about how our world will change. First, the lessons learnt about the patterns of variation of relative sea level need to be more widely recognised by climate scientists. Efforts aimed at establishing the rate of future global sea-level rise need to be complemented by protocols to determine regional deviations from that mean rate of sea-level change. Second, modes of coastal change need to be identified to replace simplistic heuristics of coastal response, such as the Bruun rule. Simulation modelling offers a suite of tools that appear to give coastal managers guidance, but geoscientists should strive to produce evidence that can be used to develop and validate model behaviour. Coastal scientists presently have a relatively good understanding of coastal behaviour at millennial timescales, and process operation at contemporary timescales. However, there is less certainty about how coasts change on decadal to century timescales. It is these latter timescales which are particularly important for managers and policy-makers. These, and related challenges, provide a focus for research that will have a relevance for society that the coastal geoscience research community has rarely experienced.