Transgressive wave- and tide-dominated barrier-lagoon system and sea-level rise since 8.2 ka recorded in sediments in northern Bohai Bay, China

This article aimed to provide an overview of relative and absolute sea level rise in the Baltic Sea based on different studies, where researchers have used data from tide gauges, satellite altimetry, sea level rise, and land uplift models. These results provide an opportunity to get an overview of the sea level rise in the Baltic Sea. However, to better understand the impact of sea level rise on the coastal area of the Baltic Sea, and especially in Estonia, two post-glacial land uplift models, the latest land uplift model NKG2016LU of the Nordic Commission of Geodesy (NKG) and Estonian land uplift model EST2020VEL, were used. These models enabled to eliminate post-glacial land uplift from absolute sea level rise. To determine the relative sea level rise in the coastal area of the Baltic Sea, the rates from land uplift models were compared to ESA’s BalticSEAL absolute sea level rise model. It was found that the relative sea level rise between 1995–2019 was −5 to 4.5 mm/yr (based on NKG2016LU) in the Baltic Sea. In addition, the southern area is more affected by relative sea level rise than the northern part. During the research, it was also found that the IPCC AR5 sea level projections predict a maximum relative sea level rise in the Baltic Sea by the year 2100 of between 0.3 to 0.7 m. As coastal areas in the southern part of the Baltic Sea are predominantly flat, the sea level may reach the real estate properties by the end of the 21st century. In the coastal area of Estonia, the relative sea level rise in the period 1995–2019 was −1.1 to 3.1 mm/yr (based on NKG2016LU) and −0.3 to 3.4 mm/yr (based on EST2020VEL), the difference between the land uplift models is −0.9 to 0.1 mm/y. In Estonia, the west and southwest area are most threatened by sea level rise, where the coast is quite flat. One of the largest cities in Estonia, Pärnu, is also located there. Using the ESA’s sea level and EST2020VEL land uplift models, it was found that the relative sea level rise will be 0.28 m by the year 2100. Based on the large spatial resolution IPCC AR5 sea level projections, the relative sea level rise will be on the same scale: 0.2–0.4 m.

The nature and impact of relative sea level rise on the coastal areas of Bangladesh: trend analysis and vulnerability assessment

Global mean sea level (GMSL) has risen by about 7-8 inches (about 16-21 cm) since 1900, with about 3 of those inches (about 7 cm) occurring since 1993. Human-caused climate change has made a substantial contribution to GMSL rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years. Relative to the year 2000, GMSL is very likely to rise by 0.3-0.6 feet (9-18 cm) by 2030, 0.5-1.2 feet (15-38 cm) by 2050, and 1.0-4.3 feet (30-130 cm) by 2100. Future pathways have little effect on projected GMSL rise in the first half of the century, but significantly affect projections for the second half of the century. Emerging science regarding Antarctic ice sheet stability suggests that, for high emission scenarios, a GMSL rise exceeding 8 feet (2.4 m) by 2100 is physically possible, although the probability of such an extreme outcome cannot currently be assessed. Regardless of pathway, it is extremely likely that GMSL rise will continue beyond 2100. Relative sea level (RSL) rise in this century will vary along U.S. coastlines due, in part, to changes in Earth's gravitational field and rotation from melting of land ice, changes in ocean circulation, and vertical land motion (very high confidence). For almost all future GMSL rise scenarios, RSL rise is likely to be greater than the global average in the U.S. Northeast and the western Gulf of Mexico. In intermediate and low GMSL rise scenarios, RSL rise is likely to be less than the global average in much of the Pacific Northwest and Alaska. For high GMSL rise scenarios, RSL rise is likely to be higher than the global average along all U.S. coastlines outside Alaska. Almost all U.S. coastlines experience more than global mean sea level rise in response to Antarctic ice loss, and thus would be particularly affected under extreme GMSL rise scenarios involving substantial Antarctic mass loss. As sea levels have risen, the number of tidal floods each year that cause minor impacts (also called nuisance floods) have increased 5- to 10-fold since the 1960s in several U.S. coastal cities. Rates of increase are accelerating in over 25 Atlantic and Gulf Coast cities. Tidal flooding will continue increasing in depth, frequency, and extent this century. Assuming storm characteristics do not change, sea level rise will increase the frequency and extent of extreme flooding associated with coastal storms, such as hurricanes and nor'easters. A projected increase in the intensity of hurricanes in the North Atlantic could increase the probability of extreme flooding along most of the U.S. Atlantic and Gulf Coast states beyond what would be projected based solely on RSL rise. However, there is low confidence in the projected increase in frequency of intense Atlantic hurricanes, and the associated flood risk amplification and flood effects could be offset or amplified by such factors as changes in overall storm frequency or tracks.

Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial adjustments, mean sea level time series were used to calculate different empirical projections for sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent with an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Applying the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies, and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of vertical land velocity and residual synoptic regional dynamic effects. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland. A mean sea level rise of 1.14 m was obtained for the epoch of 2100, with a likely range of 95% of probability between 0.39 m and 1.89 m.

Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in coastal impacts. These changes represent a changing exposure or risk to our society. Here, we present 21st century sea-level projections for Norway largely based on the Fifth Assessment Report from the Intergovernmental Panel for Climate Change (IPCC AR5). An important component of past and present sea-level change in Norway is glacial isostatic adjustment. We therefore pay special attention to vertical land motion, which is constrained using new geodetic observations with improved spatial coverage and accuracies, and modelling work. Projected ensemble mean 21st century relative sea-level changes for Norway are, depending on location, from −0.10 to 0.30 m for emission scenario RCP2.6; 0.00 to 0.35 m for RCP 4.5; and 0.15 to 0.55 m for RCP8.5. For all RCPs, the projected ensemble mean indicates that the vast majority of the Norwegian coast will experience a rise in sea level. Norway’s official return heights for extreme sea levels are estimated using the average conditional exceedance rate (ACER) method. We adapt an approach for calculating sea level allowances for use with the ACER method. All the allowances calculated give values above the projected ensemble mean Relative Sea Level (RSL) rise, i.e., to preserve the likelihood of flooding from extreme sea levels, a height increase above the most likely RSL rise should be used in planning. We also show that the likelihood of exceeding present-day return heights will dramatically increase with sea-level rise.

Sea-level rise enhances carbon accumulation in United States tidal wetlands

Mid- to late Holocene vegetation response to relative sea-level fluctuations recorded by multi-proxy evidence in the Subei Plain, eastern China

Future sea level (SL) change in the Mediterranean Sea is one of the major climate hazards for populations living in coastal areas. In this study, we analyze projections of relative sea level (RSL) rise in the Mediterranean Sea until the end of the 21st century. For the first time, we provide a detailed characterization of regional patterns of future SL change using an ensemble of three multi-decadal SSP5-8.5 scenario simulations with high-resolution fully coupled regional climate system models (RCSMs) of the Med-CORDEX initiative and their driving global climate models (GCMs). At the basin-scale, RCSMs do not significantly modify the GCM-projected RSL changes by 2100, with a mean RSL change of 69 cm (60-93 cm, 17th-83rd percentiles) relative to 1995-2014. Among the RSL components, the sterodynamic (primarily driven by the global thermal expansion) and the surface mass balance drive the basin-scale RSL rise, with the latter being the largest source of uncertainty. We find that the RSL rise in the Mediterranean is expected to be 4-12% lower than the global mean due to differences in the surface mass contribution, and 6-15% lower than in the nearby Atlantic as a result of dynamic adjustments within the semi-enclosed basin. While dynamic SL drives the mean regional patterns, vertical land motion introduces the greatest local spatial variability along coasts, resulting in a projected local RSL rise by 2100 of -26 cm to +178 cm in GCMs and -39 cm to +170 cm in RCSMs. Furthermore, compared to GCMs, RCSMs incorporate local details that result in greater spatial variability, which is important to consider in risk assessments and adaptation planning.

Onset of runaway fragmentation of salt marshes

Depositional environments and sequence stratigraphy of paralic glacial, paraglacial and postglacial Upper Ordovician siliciclastic deposits in the Murzuq Basin, SW Libya

Tidal gauge data from stations along the Texas Gulf Coast document high long-term rates of relative sea-level rise. Shoreline retreat and loss of coastal land in Texas have also been documented, and attributed to a combination of erosion and submergence. Submergence is caused by relative sea-level (RSL) rise: a combination of eustatic sea-level (ESL) rise and subsidence caused both by man9s withdrawal of pore fluids and natural consolidation. The Texas coastline is regressing at present and will continue into the future. We anticipate future accelerated loss of land in response to accelerated sea-level rise. Three scenarios (baseline, low-rise, and high-rise) for shoreline retreat and resulting loss of land to the year 2050 are developed for the Upper Texas Gulf Coast, north of Galveston Bay. The scenarios integrate projections of future RSL rise with empirical relations between RSL rise and shoreline retreat over a historical baseline period. The projections of future RSL rise combine estimates of eustatic sea-level rise derived from a delphic analysis with an assumed constant rate of land-surface subsidence. RSL rises of 0.49 m, 0.63 m, and 1.87 m are computed for the year 2050 in the baseline, low-rise, and high-rise scenarios, respectively. These rises correspond to losses of land of 17.1 km 2 (4,224 acres), 22.4 km 2 (5,533 acres), and 68.5 km 2 (16,920 acres) within the study area. Although the loss of land varies considerably throughout the study area, shoreline retreats of up to 1.85 km by 2050 are predicted in the worst-case (high-rise) scenario. Our assessment indicates that the Upper Texas Coast will experience significant loss of land in the future. Although this analysis contains much uncertainty, we believe it provides useful projections that should influence the future development and use of coastal resources. Such projections should be considered in geotechnical analysis, site investigations, and land-use planning.

Petrographic study of a well-exposed submarine canyon fill sequence indicates that petrologic variation corresponds to changes in relative sea level. These changes are recorded as textural variation in the canyon fill: a basal coarse-grained unit capped by a middle fine-grained unit records a rise in sea level, and an upper coarse-grained unit records a temporary fall in sea level. These sea level fluctuations do not correlate with published eustatic sea level curves, although the temporary fall may be recorded on a regional (San Diego to San Carlos, 400 km) scale. Sandstone samples from the lower and upper coarse-grained units contain higher concentrations of volcanic rock fragments and plagioclase than the middle fine-grained unit, whereas the middle fine-grained unit contains higher concentrations of quartz and K-feldspar. Fluctuations in relative sea level may have been controlled by tectonic or magmatic events: (1) a tectonically controlled rise in relative sea level could have resulted in longer residence tie of the sediment in a nearshore environment, causing increased mechanical and chemical weathering of the least-resistant grains (i.e., plagioclase and volcanic fragments) relative to quartz and K-feldspar; or (2) a temporary lull in volcanism could have resulted in increased dissection of the arc and decreasedmore » sediment input due to lowered base level within the arc, resulting in a marine transgression and an increase in the concentration of quartz and K-feldspar in the sediment. The lack of significant alteration of the feldspar grains in the fine-grained unit relative to the coarse-grained units may favor the second hypothesis.« less

Reconstructions of relative sea-level (RSL) change from far-field regions (i.e., located far from extinct ice sheets) since the Last Glacial Maximum (LGM) provide fundamental constraints to global ice volumes. Most published sea-level records are temporally restricted to the Holocene (last ~11.7 ka BP) with very few extending to the LGM. Here, we present two new databases that quantify the magnitudes and rates of sea-level changes along the Atlantic coast of Africa and Southeast Asia from the LGM to present. (1) Along the Atlantic coast of Africa, we compiled a database of 341 sea-level index points. During the LGM, RSL progressively dropped from -99.4 ± 2 m at 26.7 ± 0.5 ka BP to -103.0 ± 0.8 m at 19.9 ± 0.8 ka BP with average rates by -1 mm/yr. From ~15 to ~7.5 ka, RSL show phases of major accelerations with rates up to ~25 mm/yr, the timing of which is non-coincident with the Meltwater Pulse 1B and a major deceleration triggered by the ~8.2 ka cooling event. In the mid to late Holocene, data indicate the emergence of a sea-level highstand, which varied in magnitude (0.8 ± 0.8 to 4.0 ± 2.4 m above present mean sea level) and timing (5.0 ± 1.0 to 1.7 ± 1.0 ka BP). In Southeast Asia we compiled a database of 113 sea-level index points from the Sunda Shelf and Singapore. RSL rose from a lowstand of −121.1 m at 20.7 ka BP to −112.3 m at ~19 ka BP at rates of RSL rise up to ~7 mm/yr. Between ~16 ka and ~13 ka BP, RSL rose to −70 m with a cluster of SLIPs associated with the Meltwater Pulse 1A. The average rate of RSL rise reached ~15 mm/yr. In the Holocene RSL rose from −20.6 m at 9.4 ka BP to −0.25 m at ~7 ka BP at a maximum rate of 15 mm/yr. The rate of RSL rise subsequently slowed as RSL continued to rise and reached a mid-Holocene highstand of ~4.6 m at 5.2 ka BP. SLIPs constraining the mid- to late-Holocene transition suggest RSL fell below present level to −2.2 m between ~2.5 and ~0.25 ka BP at a rate of −1 mm/yr.

ABSTRACTDecreasing rates of eustatic sea-level rise during the Holocene accompanied the deposition of transgressive coastal deposits worldwide. However, unraveling how transgressive deposition varies in response to different rates of relative sea-level (RSL) rise is limited by the scarcity of long (10+ m) well-dated cores spanning the entire middle to late Holocene record along macrotidal coasts. To investigate the sedimentary response of this macrotidal coast to decreasing rates of RSL rise, we acquired four cores up to 32 m in length and Chirp seismic profiles along the west coast of Korea. Core sediments were analyzed in terms of sedimentary texture, structure, and facies. Nineteen optically stimulated luminescence (OSL) and fourteen 14C accelerated mass spectrometry (AMS) ages constrain the timing of deposition of the sandy sediments. This relatively dense distribution of ages is used to determine how deposition rates changed through time. We also use a compilation of previously published RSL indices for the southwestern Korean coast in order to better constrain RSL changes through time. Results show that the evolution of the Gochang coastline switched from a tide-dominated environment to a wave-dominated environment during the latter stage of transgression as the rate of the sea-level rise decreased. Rugged antecedent topography likely led to the development of tidal currents and the formation of a tide-dominated tidal flat during rapid RSL rise from 10 to 6 ka. As the tidal channels filled with fine-grained sediments from 6 to 1 ka, tidal amplification likely waned leading to a greater role of wave energy in shaping the formation of the sandy open-coast tidal flat. Since 1 ka, wave-dominated environments formed sand-rich tidal beaches and flats. Decreasing changes in rates of the RSL rise resulted in changes in depositional environments from a tide-dominated intertidal flat to an open-coast tidal flat and finally a wave-dominated tidal beach. This study highlights the important role that rates of RSL rise play on not only sedimentation rates in a shelf setting but also playing a role in the switch from a tide-dominated to a wave-dominated setting.

A new analysis of ‘global’ sea level has been made that largely avoids space/time bias of previous works. A coherent pattern of increasing relative sea level (RSL) was found to exist on average at all stations analyzed between 1903–1969. Subject to considerable assumption, the rate of RSL increase associated with this pattern was 15 cm/century. A similar analysis of the period 1930–1975 again showed RSL increasing on average everywhere but in the western half of the North Pacific Ocean. Decrease of RSL in this area was substantiated by hydrographic data. Thus in recent years the concept of a ‘global’ sea level rise is not supported. The temporal behavior of thenear global signals from both time periods was well approximated by a simple linear trend. There was no evidence of a more rapid rise in RSL in recent years. Potential causes of the above RSL change were investigated. Changes in the position of the earth's axis of rotation support the idea that the RSL change was due to approximately equal melting of Greenland/Antarctica. Changes in the length of day only marginally support this idea. However, other attractive geophysical explanations for variations in both these astronomical parameters exist. Observed change in sea surface temperature (SST), if representative of reasonable changes in vertical thermal structure, could give the observed RSL change. However, the SST data are likely biased instrumentally toward increasing trend. Also, thermal expansion of the oceans would not significantly affect the rotational parameters although changes in these parameters could be due to non-RSL related processes. Changes in ocean circulation and/or subsidence along all the coastal margins simultaneously seem unlikely causes of the observed change in RSL. In summary, it is not possible at this time to explain reliably the apparent increase in RSL.