Sea-level Estimates Research Articles

Relative sea-level change during the Last Interglacial as recorded in Bahamian fossil reefs

Despite an abundance of UTh age data for Last Interglacial fossil corals in the Bahamas, the accuracy and precision of corresponding elevation data are poor, casting uncertainty on existing estimates of peak relative sea level and rates of sea-level change inferred from these deposits. We revisited two key sites at Great Inagua (GI) and San Salvador (SS) Island to test existing hypotheses about (1) the rate of sea level changes during the Last Interglacial period and (2) a possible gradient in peak sea level between these sites. Here, we provide precise elevation survey results for discrete stratigraphic horizons preserved at both locations, where two stages of reef growth are separated by a discontinuity that truncates corals in the lower reef. The discontinuity at Great Inagua manifests as a sharp wave-cut bench, with a maximum elevation of +1.14 m above mean sea level (MSL), that is sub-horizontal on the promontories and gradually slopes seaward in the embayments. At San Salvador, we observed a discontinuity that undulates between +0.85 and + 1.52 m. The uppermost surface of corals in growth position was measured at +1.94 m (GI) and +2.76 m (SS), although in situ collapse and truncation of large Acropora palmata colonies at the latter site implies that primary coral elevations were somewhat higher. Ultimately, assumptions regarding the amount of material truncated and paleowater depth of the observed reef facies at both sites dominate the uncertainty in calculating past sea level position and hence rates of sea-level change. Full consideration of errors associated with age and elevation data implies an ephemeral sea level drop of at least 1 m over a time frame of approximately one thousand years between two peaks in sea level.

Sea level implications from Late Quaternary/Holocene paleosols from the Oujiang Delta, China

ABSTRACTWe describe two coastal paleosols recovered in sediment cores from the Oujiang Delta, Southeast China. These provide useful benchmarks for past sea level change on the East China Sea coast. Radiocarbon (14C) dates on charcoal and plant matter show that one formed during Marine Isotope Stage 3 (MIS 3) and was exposed for perhaps 20 ka, during the Last Glacial Maximum. The other formed in the Early Holocene and was briefly exposed, during a period of fluctuating sea level. Similar paleosols have been described from the Changjiang (Yangtze) Delta, and at many other sites from the East China Sea. The MIS 3 paleosol records a regional relative sea level of about –27 m at the end of MIS 3. While this value is consistent with other paleo sea level estimates for the East China Sea region, it is much higher than predicted by eustatic sea level estimates.

Global sea-level budget 1993–present

Abstract. Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g., acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled Regional Sea Level and Coastal Impacts, an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017–2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3 mm yr−1 and acceleration of 0.1 mm yr−2 over 1993–present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42 %, 21 %, 15 % and 8 % to the global mean sea level over the 1993–present period. We also study the sea-level budget over 2005–present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr−1 (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.

GNSS Reflectometry of the Black Sea Level in the Experiments at the Stationary Oceanographic Platform

The results of sea level estimation by GNSS reflectometry (GNSS-R) in the Black Sea in the experiments at the stationary oceanographic platform are presented. The influence of the layout of the antennas and the characteristics of the wind waves on the GNSS-R sea level estimates is studied with the use of multi-antenna GPS/GLONASS receiver and wire resistance wave gauge. For the selected geometry of the experiment, the threshold amplitudes and frequencies of the wind waves at which estimation of the sea level by GNSS reflectometry becomes impossible are determined.

Seamless transition of altimetric retracked sea levels using neural network technique: case study using simulated data

Waveform retracking has become a standard data processing protocol to optimize the estimation of sea level, particularly over coastal oceans. In the proximity of land, combining different retracking algorithms are essential for dealing with high diversity of altimetric waveform patterns. However, retrackers cannot be simply switched to another due to the existence of offset among retrackers. The existence of offset value creates ‘a jump’ in the sea level profiles, thus reducing the precision of the estimated sea level parameter. In this paper, neural network technique is explored to reduce the offset values, and to produce a seamless transition of sea level when switching retrackers. The analysis is conducted over 100,000 simulated data based on Monte Carlo simulation. The experiment includes six sets of varying parameters (i.e. number of hidden layer, algorithms in hidden and output layers, and training algorithm). The results indicate that the neural network (set 2) with six hidden layers, algorithms of Logsig and Tansig for hidden and output layers, respectively, and Levenberg-Marquardt for training algorithm is the best parameters for offset reduction. It has the highest correlation, and the lowest root mean square error and standard deviation of difference, giving it the best rank when compared to the other five sets.

Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years.

The East Antarctic Ice Sheet (EAIS) is the largest potential contributor to sea-level rise. However, efforts to predict the future evolution of the EAIS are hindered by uncertainty in how it responded to past warm periods, for example, during the Pliocene epoch (5.3 to 2.6 million years ago), when atmospheric carbon dioxide concentrations were last higher than 400 parts per million. Geological evidence indicates that some marine-based portions of the EAIS and the West Antarctic Ice Sheet retreated during parts of the Pliocene1,2, but it remains unclear whether ice grounded above sea level also experienced retreat. This uncertainty persists because global sea-level estimates for the Pliocene have large uncertainties and cannot be used to rule out substantial terrestrial ice loss 3 , and also because direct geological evidence bearing on past ice retreat on land is lacking. Here we show that land-based sectors of the EAIS that drain into the Ross Sea have been stable throughout the past eight million years. We base this conclusion on the extremely low concentrations of cosmogenic 10Be and 26Al isotopes found in quartz sand extracted from a land-proximal marine sediment core. This sediment had been eroded from the continent, and its low levels of cosmogenic nuclides indicate that it experienced only minimal exposure to cosmic radiation, suggesting that the sediment source regions were covered in ice. These findings indicate that atmospheric warming during the past eight million years was insufficient to cause widespread or long-lasting meltback of the EAIS margin onto land. We suggest that variations in Antarctic ice volume in response to the range of global temperatures experienced over this period-up to 2-3 degrees Celsius above preindustrial temperatures 4 , corresponding to future scenarios involving carbon dioxide concentrations of between 400 and 500 parts per million-were instead driven mostly by the retreat of marine ice margins, in agreement with the latest models5,6.

Towards the incorporation of tipping elements in global climate risk management: probability and potential impacts of passing a threshold

Evidence suggests that several elements (i.e., subsystems) of the Earth’s climate system could tip into a qualitatively different state due to on-going and future anthropogenically induced climate change. Risks associated with tipping could form a component of critical climate risks, and their consideration should be indispensable in decision-making. However, there is lack of scientific knowledge about the risks associated with tipping elements, inhibiting their incorporation into comprehensive risk assessments of climate change (i.e., assessments of impact, adaptation, and mitigation with uncertainty). Using two major tipping elements (Arctic summer sea-ice loss and Greenland ice-sheet melting) as examples, this study attempted to address this lack of knowledge by conducting several calculations under various policy choices based on target temperature, including (i) the probability of passing a threshold temperature in this century and (ii) the potential impact of passing a threshold temperature on a millennial timescale beyond this century. The first theme of this study [Item (i) above] suggested that probability of exceeding the threshold within this century is 24.8% for the Greenland ice sheet and 2.7% for Arctic summer sea ice under a 1.5 °C temperature goal. However, it should be noted that the estimated probabilities of exceeding the threshold are largely dependent on the specification of the probability density function and key assumptions. With regard to the second theme of this study [Item (ii) above], estimation of the potential global coastal exposure using the estimated sea level exhibited a significant gap between scenarios not exceeding the threshold (1.5 °C target) and those exceeding the threshold.

Time Series Observation on Phytoplankton Dynamics in the Coastal Waters of the World Heritage Site of Indian Sundarban Mangrove Forest, NE Coast of Bay of Bengal

Sea levels on the Indian sub-continent are increasing at the rate of about 2.5 mm/year; the rate of increment is greater in the eastern coast, with an estimated sea level rise of about 3.14 mm/year. This suggests that mean annual sea levels in the Indian sub-continent will be some 15 cm higher in 2060 than what it was during 2000. The Indian Sundarbans in northeast coast of the country, at the apex of the Bay of Bengal is an extremely dynamic deltaic lobe sustaining a wide spectrum of mangrove flora and fauna. It is estimated that sea level in this deltaic lobe has increased by about 15 cm since the 1950s and this has been correlated with changes in the pattern and rates of erosion and accretion in the islands of the Indian Sundarbans. Such geo-physical phenomena may not only pose serious impact on the adjacent aquatic system by way of increasing turbidity, nutrient budget, salinity, pH etc., but the phenomenon has every possibility to shift the biodiversity spectrum of the adjacent land masses (supporting mangrove and mangrove associate species) and aquatic system due to salinization of land, alteration of soil pH, increased erosional activities leading to reduction of water transparency, increased salinity of the water bodies and invasion of the areas with more number of stenohaline species (preferably phytoplankton). The present paper is an attempt to scan the time series observation on phytoplankton dynamics in the coastal waters of Indian Sundarban mangrove forest, NE coast of Bay of Bengal. Twenty four stations have been selected in the present programme at different salinity gradients to evaluate the temporal variations of selective hydrological parameters like surface water temperature, salinity, pH, dissolved oxygen, transparency and nutrient load. Simultaneous data on phytoplankton diversity was also assessed to critically analyze the impact of temporal oscillation of hydrological parameters on the tiny, free floating, drifting, primary producer community. Duncan test applied on the data set of 25 years (1990 to 2015) revealed significant temporal variations of surface water temperature, salinity, pH, transparency, nitrate concentration, phosphate concentration and phytoplankton composition. Since 1990, nine stenohaline phytoplankton species have been recorded in the upstream regions of the deltaic lobe indicating a gradual shifting of aquatic phase towards high salinity. Few environmental variables like dissolved oxygen and silicate did not show variations at significant level. Although the time span is too short to predict potential impact of aquatic climate change on phytoplankton community of the mangrove dominated Indian Sundarbans, but significant temporal variation in the phytoplankton community since 1990 speaks in favour of using these tiny, free floating, drifting, primary producer community as potential bioindicators of aquatic climate change in short term scale.

Daily sea level prediction at Chiayi coast, Taiwan using extreme learning machine and relevance vector machine

Abstract The analysis and the prediction of sea level fluctuations are core requirements of marine meteorology and operational oceanography. Estimates of sea level with hours-to-days warning times are especially important for low-lying regions and coastal zone management. The primary purpose of this study is to examine the applicability and capability of extreme learning machine (ELM) and relevance vector machine (RVM) models for predicting sea level variations and compare their performances with powerful machine learning methods, namely, support vector machine (SVM) and radial basis function (RBF) models. The input dataset from the period of January 2004 to May 2011 used in the study was obtained from the Dongshi tide gauge station in Chiayi, Taiwan. Results showed that the ELM and RVM models outperformed the other methods. The performance of the RVM approach was superior in predicting the daily sea level time series given the minimum root mean square error of 34.73 mm and the maximum determination coefficient of 0.93 (R2) during the testing periods. Furthermore, the obtained results were in close agreement with the original tide-gauge data, which indicates that RVM approach is a promising alternative method for time series prediction and could be successfully used for daily sea level forecasts.

Risk and resilience in the late glacial: A case study from the western Mediterranean

The period spanning the Last Glacial Maximum through early Holocene encompasses dramatic and rapid environmental changes that offered both increased risk and new opportunities to human populations of the Mediterranean zone. The regional effects of global climate change varied spatially with latitude, topography, and distance from a shifting coastline; and human adaptations to these changes played out at these regional scales. To better understand the spatial and temporal dynamics of climate change and human social-ecological-technological systems (or SETS) during the transition from full glacial to interglacial, we carried out a meta-analysis of archaeological and paleoenvironmental datasets across the western Mediterranean region. We compiled information on prehistoric technology, land-use, and hunting strategies from 291 archaeological assemblages, recovered from 122 sites extending from southern Spain, through Mediterranean France, to northern and peninsular Italy, as well as 2,386 radiocarbon dates from across this region. We combine these data on human ecological dynamics with paleoenvironmental information derived from global climate models, proxy data, and estimates of coastlines modeled from sea level estimates and digital terrain. The LGM represents an ecologically predictable period for over much of the western Mediterranean, while the remainder of the Pleistocene was increasingly unpredictable, making it a period of increased ecological risk for hunter-gatherers. In response to increasing spatial and temporal uncertainty, hunter-gatherers reorganized different constituents of their SETS, allowing regional populations to adapt to these conditions up to a point. Beyond this threshold, rapid environmental change resulted in significant demographic change in Mediterranean hunter-gatherer populations.

Impact of ITRS 2014 realizations on altimeter satellite precise orbit determination

This paper evaluates orbit accuracy and systematic error for altimeter satellite precise orbit determination on TOPEX, Jason-1, Jason-2 and Jason-3 by comparing the use of four SLR/DORIS station complements from the International Terrestrial Reference System (ITRS) 2014 realizations with those based on ITRF2008. The new Terrestrial Reference Frame 2014 (TRF2014) station complements include ITRS realizations from the Institut National de l’Information Géographique et Forestière (IGN) ITRF2014, the Jet Propulsion Laboratory (JPL) JTRF2014, the Deutsche Geodätisches Forschungsinstitut (DGFI) DTRF2014, and the DORIS extension to ITRF2014 for Precise Orbit Determination, DPOD2014. The largest source of error stems from ITRF2008 station position extrapolation past the 2009 solution end time. The TRF2014 SLR/DORIS complement impact on the ITRF2008 orbit is only 1–2mm RMS radial difference between 1992–2009, and increases after 2009, up to 5mm RMS radial difference in 2016. Residual analysis shows that station position extrapolation error past the solution span becomes evident even after two years, and will contribute to about 3–4mm radial orbit error after seven years. Crossover data show the DTRF2014 orbits are the most accurate for the TOPEX and Jason-2 test periods, and the JTRF2014 orbits for the Jason-1 period. However for the 2016 Jason-3 test period only the DPOD2014-based orbits show a strong and statistically significant margin of improvement. The positive results with DTRF2014 suggest the new approach to correct station positions or normal equations for non-tidal loading before combination is beneficial. We did not find any compelling POD advantage in using non-linear over linear station velocity models in our SLR & DORIS orbit tests on the Jason satellites. The JTRF2014 proof-of-concept ITRS realization demonstrates the need for improved SLR+DORIS orbit centering when compared to the Ries (2013) CM annual model. Orbit centering error is seen asan annual radial signal of 0.4mm amplitude with the CM model. The unmodeled CM signals show roughly a 1.8mm peak-to-peak annual variation in the orbit radial component. We find the TRF network stability pertinent to POD can be defined only by examination of the orbit-specific tracking network time series. Drift stability between the ITRF2008 and the other TRF2014-based orbits is very high, the relative mean radial drift error over water is no larger than 0.04mm/year over 1993–2015. Analyses also show TRF induced orbit error meets current altimeter rate accuracy goals for global and regional sea level estimation.

Sensitivity of Last Interglacial sea-level high stands to ice sheet configuration during Marine Isotope Stage 6

Estimates of peak global mean sea level (GMSL) during the Last Interglacial (LIG, ∼129-116 ka) based on geological sea level high-stand markers require a correction for the contaminating influence of glacial isostatic adjustment (GIA). This correction is obtained by calculating the viscoelastic response of the Earth to changes in the ice and ocean load prior to and following the LIG. While ice retreat over the last deglaciation is relatively well constrained, changes in ice cover prior to the LIG are more uncertain. We investigate the sensitivity of numerical predictions of GIA during the LIG to variations in the geometry of pre-LIG ice cover and the timing of the deglaciation into the LIG, with a particular focus on Marine Isotope Stage (MIS) 6 (∼190-130 ka). We demonstrate that reconstructing the pre-LIG ice history by replicating the last glacial cycle back in time, rather than using ice volume approximations based on oxygen isotope records, can introduce errors in LIG high-stand predictions of ∼5 m at sites on the peripheral bulge of major ice complexes, and up to ∼2 m at far-field sites. We also demonstrate that predictions of LIG sea level are more sensitive to the geographic distribution of ice cover during MIS 6 than previously recognized. Adopting simulations which vary the relative size of Late Pleistocene ice cover over North America and Eurasia can yield a change in predicted high-stand elevations of ∼5 m in both the near and far field of northern hemisphere ice sheets. This far-field sensitivity arises, in part, from the reorientation of Earth's rotation axis during MIS 6, which in turn drives sea-level changes with a distinct geographic signature. In future work we will apply the insights gained here to re-evaluate the observed geographic variability in geological high-stand markers of LIG age and estimates of GMSL based upon them.

Applicability of transfer functions for relative sea-level reconstructions in the southern North Sea coastal region based on salt-marsh foraminifera

Abstract We studied the foraminiferal distribution in two naturally grown salt marshes from the southern North Sea with respect to the tidal frame, salinity, grain size and pH. The salt marshes are situated on the landward sides of the islands of Sylt (Rantum, Germany) and Fano (Sonderho, Denmark). In both study areas, foraminifera have a vertical distribution with respect to water level, but also show inter-site variability, which can be related to environmental differences (e.g., in salinity and pH) and different flooding dynamics of the coastal salt marsh (Rantum) and the tidal-creek salt marsh (Sonderho). We developed different transfer functions, based on the widely applied standardized water level index (SWLI) approach and on three flooding parameters (duration of submergence (DoS), mean submergence time (MST), and flooding frequency (FF)), in order to assess their predictive ability for relative sea-level estimates for the southern North Sea coastal region. The water-level data used for these approaches are determined based on local water-level conditions, corrected for tidal distortions using water-level measurements for the Sonderho salt marsh and the Rantum tide gauge. The SWLI approach shows a precision (root mean squared error of prediction (RMSEP) of 0.23 m), which is around 15% of the tidal range. All three flooding approaches show comparable results at around mean tide level to mean high water, while at higher elevations, foraminiferal distribution becomes non-linearly correlated to flooding parameters resulting in lower precision of > 1.0 m. Our results suggest that the SWLI approach performs well and that the flooding approaches offer a suitable addition for assessing relative sea-level estimates in the North Sea region. We enhanced the knowledge on changing precision for tide level reconstructions along the elevational gradient in a storm dominated tidal area where elevation and flooding parameters are non-linear correlated.

Assessing tectonic subsidence from estimates of Holocene relative sea-level change: An example from the NW Mediterranean (Magra Plain, Italy)

New sedimentological sea-level indicators are presented from the River Magra coastal plain, in NW Italy. Chronologically well-constrained paralic peats and organic sediments which had been deposited in a defined relationship with sea level were recovered in four of the seven boreholes considered in this work. Their evolution scatters in the time span of the past 6000 years. Since the cores are located within a single sedimentary basin, it was possible to correct the elevation of marker horizons for the effect of sediment compaction by means of both a field and a geotechnical method. Thus, seven reliable index points for the mid- to late-Holocene sea-level rise were obtained. The age–depth model derived from them was compared with that of sea-level predictions from two different Glacial Isostatic Adjustment (GIA) models available for the area. In both cases, the modelled sea-level estimates overlie the index points, suggesting lower relative sea-level elevation than the one predicted considering the combined eustatic and hydro-isostatic components. Based on the general tectonic setting of the area, this finding was interpreted as the effect of a tectonic subsidence of the basin, the rate of which can be quantified on average as 0.5 mm/yr since the middle Holocene, with a sharp increase after 2500 yr BP. By providing a reliable estimate of the rate of tectonic subsidence in a coastal area of NW Italy, this research contributes to refining the geodynamic model of this part of the Mediterranean basin.

Impact of Geophysical and Datum Corrections on Absolute Sea-Level Trends from Tide Gauges around Taiwan, 1993–2015

The Taiwanese government has established a complete tide gauge network along the coastline for accurate sea-level monitoring. In this study, we analyze several factors impacting the determination of absolute or geocentric sea-level trends—including ocean tides, inverted barometer effect, datum shift, and vertical land motion—using tide gauge records near Taiwan, from 1993–2015. The results show that datum shifts and vertical land motion have a significant impact on sea-level trends with a respective average contribution of 7.3 and 8.0 mm/yr, whereas ocean tides and inverted barometer effects have a relatively minor impact, representing 9% and 14% of the observed trend, respectively. These results indicate that datum shifts and vertical land motion effects have to be removed in the tide gauge records for accurate sea-level estimates. Meanwhile, the estimated land motions show that the southwestern plain has larger subsidence rates, for example, the Boziliao, Dongshi, and Wengang tide gauge stations exhibit a rate of 24–31 mm/yr as a result of groundwater pumping. We find that the absolute sea-level trends around Taiwan derived from tide gauges or satellite altimetry agree well with each other, and are estimated to be 2.2 mm/yr for 1993–2015, which is significantly slower than the global average sea-level rise trend of 3.2 mm/yr from satellite altimeters. Finally, a recent hiatus in sea-level rise in this region exhibits good agreement with the interannual and decadal variabilities associated with the El Niño-Southern Oscillation and Pacific Decadal Oscillation.

Mid-Holocene relative sea-level changes along Atlantic Patagonia: New data from Camarones, Chubut, Argentina

This paper concerns the relative sea-level changes associated with the Atlantic Patagonian coast derived from sea-level index points whose elevation was determined by a differential global position system (DGPS). Bioencrustations from outcrops located near Camarones, Chubut, Argentina, consist of autochthonous deposits characterized by Austromegabalanus psittacus (Molina, 1782), encrusting acervulinid foraminifera, coralline red algae and bryozoans. The association of the different organisms is interpreted as being associated with an intertidal environment, and they have been used as index points to establish the relative sea-level position. The main conclusion is that the relative sea-level between c. 7000 and 5300 cal. yr BP was in the range of c. 2–4 m a.s.l., with a mean value of c. 3.5 m a.s.l. Our data seem to support the existence of different rates of relative sea-level fall in different sectors of Atlantic Patagonia during the Holocene and highlight the importance of a more precise and accurate relative sea-level estimation by producing new data and revisiting the indicative meaning of most of the indicators so far used in the area.

Mean dynamic topography over Peninsular Malaysian seas using multimission satellite altimetry

The development of satellite altimeters (SALTs) has brought huge benefits, among which is the ability to more adequately sense ocean-surface topography. The radar altimeter database system was used to capture and process ENVISAT, CRYOSAT-2, SARAL, JASON-1, and JASON-2 SALT data of 5 years between 2011 and 2015. The time series of monthly multimission SALT data showed an estimated sea level trend of 1.0, 2.4, 2.4, 3.6, and 12.0 mm/year at Gelang, Port Kelang, Kukup, Cendering, and Keling. The correlation analysis for the selected tide gauge stations produced satisfying results of R-squared with 0.86, 0.89, 0.91, and 0.97 for Cendering, Sedili, Gelang, and Geting, respectively. The ITG-Grace2010s geoid model was used to compute the mean dynamic topography (MDT) and plot to a grid of 0.25 deg for the Malacca Strait and South China Sea of Peninsular Malaysia, with Keling, Port Kelang, Geting, Sedili, and Johor Bahru tide gauge stations having values determined by interpolation to be 1.14, 1.19, 1.26, 1.88, and 2.91 m, respectively. MDT is computed from the SALT with respect to Port Kelang, the north–south sea slope ranges between −0.64 and 0.29 m/50 km and −0.01 and 0.52 m/50 km along the east and west coasts of Peninsular Malaysia, respectively.

Predicted bounds on peak global mean sea level during marine isotope stages 5a and 5c

Estimates of marine isotope stage (MIS) 5c and 5a global mean sea level (GMSL) based on marine terraces and coastal indicators range from 15–37 m and 9–30 m below present, respectively. Tectonic displacement and glacial isostatic adjustment (GIA) complicate efforts to refine this range. We revisit this issue using numerical predictions of post-glacial sea-level change and updated estimates of site-specific tectonic signals based upon these predictions. Laurentide and Cordilleran peripheral bulge dynamics and variations in the gravitational effect of these ice masses dominate the GIA signal along the east and west coasts of North America. Published compilations suggest that MIS 5 sea-level indicators extending from Virginia to the Caribbean lie on the outer flank of the peripheral bulge, while those along a transect from Oregon to Baja California sit on the inner flank of the bulge. Our GIA modeling reconciles these data by adopting a significantly weaker (i.e., lower viscosity) upper mantle in analyzing data on the Pacific coast relative to the Atlantic, an inference supported by seismic tomography. We present a sensitivity analysis that compares the observed elevation of globally distributed high stand markers to a suite of GIA simulations that vary the Earth model and GMSL from the Last Interglaciation (MIS 5e, ∼130-115 ka) to 70 ka. We conclude that GMSL peaked at −8.5 ± 4.6 m (1σ) during MIS 5a and −9.4 ± 5.3 m during MIS 5c. A more restrictive analysis yields slightly wider bounds corresponding to −10.5 ± 5.5 m and −11.1 ± 6.6 m, respectively.

On the Robustness of Bayesian Fingerprinting Estimates of Global Sea Level Change

Global mean sea level (GMSL) over the twentieth century has been estimated using techniques that include regional averaging of sparse tide gauge observations, combining satellite altimetry observations with tide gauge records in empirical orthogonal function (EOF) analyses, and most recently the Bayesian approaches of Kalman smoothing (KS) and Gaussian process regression (GPR). Estimated trends in GMSL over 1901–90 obtained using the Bayesian techniques are 1.1–1.2 mm yr−1, approximately 20% lower than previous estimates. It has been suggested that the adoption of a less restrictive subset of records biased the Bayesian-derived estimates. In this study, different subsets of records are used to demonstrate that GMSL estimates based on the Bayesian methodologies are robust to tide gauge selection. A method for determining the resolvability of individual sea level components estimated in a Bayesian framework is also presented and applied. It is found that the incomplete tide gauge observations result in posterior correlations between individual sea level contributions, making robust separation of the individual components impossible. However, various weighted sums of these components, as well as the total sum (i.e., GMSL), are resolvable. Finally, the KS and GPR methodologies allow for the simultaneous estimation of sea level at sites with and without observations. The first KS and GPR global maps of sea level change over the twentieth century are presented. These maps provide new estimates of twentieth-century sea level in data-sparse regions.

A comparison of sea level projections based on the observed and reconstructed sea level data around the Korean Peninsula

In an attempt to estimate accurate local sea level change, “sea level trend” modes are identified and separated from natural variability via cyclostationary empirical orthogonal function (CSEOF) analysis applied to both the tide gauge data (1965–2013) and the reconstruction data (1950–2010) around the Korean Peninsula. For the tide gauge data, ensemble empirical mode decomposition (EEMD) method is also used to estimate sea level trend to understand an uncertainty from different analysis tools. The three trend models—linear, quadratic, and exponential—are fitted to the amplitude time series of the trend mode so that future projection of sea level can be made. Based on a quadratic model, the rate of local sea level rise (SLR) is expected to be 4.63 ± 1.1 mm year−1 during 2010–2060. The estimates of “local” sea level trend vary up to ∼30%. It should be noted that, although the three trend models estimate similar sea level trends during the observational period, the projected sea level trend and subsequent SLR differ significantly from one model to another and between the tide gauge data and the reconstruction data; this results in a substantial uncertainty in the future SLR around the Korean Peninsula.