Rate Of Sea-level Rise Research Articles

Causal Mechanisms of Sea-level and Freshwater Content Change in the Beaufort Sea

AbstractIn the Arctic’s Beaufort Sea, the rate of sea-level rise over the last two decades has been an order of magnitude greater than that of its global mean. This rapid regional sea-level rise is mainly a halosteric change, reflecting an increase in Beaufort Sea’s freshwater content comparable to that associated with the Great Salinity Anomaly of the 1970s in the North Atlantic Ocean. Here we provide a new perspective of these Beaufort Sea variations by quantifying their causal mechanisms from 1992 to 2017 using a global, data-constrained ocean and sea-ice estimate of the Estimating the Circulation and Climate of the Ocean (ECCO) consortium. Our analysis reveals wind and sea-ice jointly driving the variations. Seasonal variation mainly reflects near-surface change due to annual melting and freezing of sea-ice, while interannual change extends deeper and mostly relates to wind-driven Ekman transport. Increasing wind stress and sea-ice melt are, however, equally important for decadal change that dominates the overall variation. Strengthening anticyclonic wind stress surrounding the Beaufort Sea intensifies the ocean’s lateral Ekman convergence of relatively fresh near-surface waters. The strengthening stress also enhances convergence of sea-ice and ocean heat that increase the amount of Beaufort Sea’s net sea-ice melt. The enhanced significance at longer time-scales of sea-ice melt relative to direct wind forcing can be attributed to ocean’s advection and mixing of melt-water being slower than its dynamic adjustment to mechanical perturbations. The adjustments’ difference implies that the sea-ice-melt-driven diabatic change will persist longer than the direct wind-driven kinematic anomaly.

Observing tidal and storm generated wave height impact on groundwater levels in a tropical delta (the Sundarbans)

Groundwater level (GWL) of coastal aquifers are strongly influenced by the ocean tide at sub-daily to seasonal scale. Similarly, GWL are influenced by storm induced ocean wave surge lasting few hours to a day. There has not been a detailed study on the conjunctive impact of such tidal and storm waves on coastal groundwater and its vulnerability. Through our coastal and field-laboratory observations at one of the world’s most extreme climate affected regions, the Ganges river mega-delta, we delineate the influence of ocean wave surge impacts on the shallow (<24 m below ground level [m bgl]) and deep (115 m bgl) aquifers GWL. Our study on the multi-layered delta-front aquifers, adjoining the tropical BoB shows that the high-temporal resolution GWL fluctuation due to wave surges are instantaneous, rapid and synchronous at all depths of the aquifers. The potential rise of ocean waves caused by tropical cyclone Bulbul (November 2019) significantly increases the GWL, both in shallow and deeper aquifer. Using multivariate statistics and machine learning techniques, we have attempted to quantify the rise of GWL during each of the ocean wave surge event. The model shows good predictability for deeper groundwater, however it is unable to quantify the shallower GWL of each of the ocean wave surge during storm events. Such phenomenon indicates aquifer vulnerability, thereby posing an emerging threat to drinking water availability to millions of groundwater-dependent inhabitants in coastal areas, globally, which may rapidly intensify with increasing rates of tropical cyclones and sea level rise in recent times and impending future.

The evolution of saltmarsh mosquito control water management practices relative to coastal resiliency in the Mid-Atlantic and northeastern United States

Salt marshes are dynamic ecosystems that change in response to local geographic and geologic factors as well as sea level changes. Most east coast salt marshes are the result of rising sea levels since the end of the last ice age, about 20,000 ybp. To compound this natural process, anthropogenic manipulations for farming, development and other purposes have occurred for centuries. Alterations to salt marshes for the purpose of controlling larval mosquitoes at their source, at least along the east coast of the United States, have occurred since the early twentieth century. These alterations have included large-scale manipulations such as extensive parallel grid-ditching and impounding. Within the last 50 years, more selective source reduction methods such as Open Marsh Water Management (OMWM) have been employed with fewer deleterious impacts to marsh resources. Even more recently, the more holistic approach of Integrated Marsh Management (IMM) has been used with considerable success particularly in the northeastern and Mid-Atlantic states. IMM not only uses OMWM techniques but incorporates the judicious use of mosquito control pesticides, tidal flow restoration, impoundment management, wildlife habitat enhancement, invasive plant control, and selective shallow ditching (“runneling”) depending on local conditions and management plans. As many marshes are becoming wetter and either drowning or migrating inland (where possible) due to the effects of increasing rates of sea level rise, the compounding long-term impacts of parallel grid-ditching and past manipulations on marsh surface elevation and hydrology are being more intently studied. These changes in saltmarsh dynamics have had and will continue to have impacts on where saltmarsh mosquitoes are produced, which could have corollary effects on public health and quality of life near coastal communities. As salt marshes continue to change, mosquito control agencies can play a significant role in providing input for salt marsh restoration and management in addition to their primary objective of vector control and enhancing quality of life.

An Integrated Approach to Coastal Zone Management to Control Development and Ensure Sustainability in a Rapidly Increasing Coastal Urban Environment: The Sultanate of Oman

Reckless construction and overextraction of resources have placed tremendous stress on the Sultanate of Oman's coastal ecosystems at Al-Batinah. The rate of sea level rise (SLR) intensifies under t...

Long-Term Community Dynamics Reveal Different Trajectories for Two Mid-Atlantic Maritime Forests

Maritime forests are threatened by sea-level rise, storm surge and encroachment of salt-tolerant species. On barrier islands, these forested communities must withstand the full force of tropical storms, hurricanes and nor’easters while the impact is reduced for mainland forests protected by barrier islands. Geographic position may account for differences in maritime forest resilience to disturbance. In this study, we quantify two geographically distinct maritime forests protected by dunes on Virginia’s Eastern Shore (i.e., mainland and barrier island) at two time points (15 and 21 years apart, respectively) to determine whether the trajectory is successional or presenting evidence of disassembly with sea-level rise and storm exposure. We hypothesize that due to position on the landscape, forest disassembly will be higher on the barrier island than mainland as evidenced by reduction in tree basal area and decreased species richness. Rate of relative sea-level rise in the region was 5.9 ± 0.7 mm yr−1 based on monthly mean sea-level data from 1975 to 2017. Savage Neck Dunes Natural Area Preserve maritime forest was surveyed using the point quarter method in 2003 and 2018. Parramore Island maritime forest was surveyed in 1997 using 32 m diameter circular plots. As the island has been eroding over the past two decades, 2016 Landsat imagery was used to identify remaining forested plots prior to resurveying. In 2018, only plots that remained forested were resurveyed. Lidar was used to quantify elevation of each point/plot surveyed in 2018. Plot elevation at Savage Neck was 1.93 ± 0.02 m above sea level, whereas at Parramore Island, elevation was lower at 1.04 ± 0.08 m. Mainland dominant species, Acer rubrum, Pinus taeda, and Liquidambar styraciflua, remained dominant over the study period, with a 14% reduction in the total number of individuals recorded. Basal area increased by 11%. Conversely, on Parramore Island, 33% of the former forested plots converted to grassland and 33% were lost to erosion and occur as ghost forest on the shore or were lost to the ocean. Of the remaining forested plots surveyed in 2018, dominance switched from Persea palustris and Juniperus virginiana to the shrub Morella cerifera. Only 46% of trees/shrubs remained and basal area was reduced by 84%. Shrub basal area accounted for 66% of the total recorded in 2018. There are alternative paths to maritime forest trajectory which differ for barrier island and mainland. Geographic position relative to disturbance and elevation likely explain the changes in forest community composition over the timeframes studied. Protected mainland forest at Savage Neck occurs at higher mean elevation and indicates natural succession to larger and fewer individuals, with little change in mixed hardwood-pine dominance. The fronting barrier island maritime forest on Parramore Island has undergone rapid change in 21 years, with complete loss of forested communities to ocean or conversion to mesic grassland. Of the forests remaining, dominant evergreen trees are now being replaced with the expanding evergreen shrub, Morella cerifera. Loss of biomass and basal area has been documented in other low elevation coastal forests. Our results indicate that an intermediate shrub state may precede complete loss of woody communities in some coastal communities, providing an alternative mechanism of resilience.

Linking the Surface and Subsurface in River Deltas—Part 2: Relating Subsurface Geometry to Groundwater Flow Behavior

AbstractUnderstanding subsurface structure and groundwater flow in deltaic aquifers is essential for evaluating the vulnerability of groundwater resources in delta systems. Deltaic aquifers contain coarse‐grained paleochannels that preserve a record of former surface river channels as well as fine‐grained floodplain deposits. The distribution of these deposits and how they are interconnected control groundwater flow and contaminant transport. In this work, we link depositional environments of deltaic aquifers to stratigraphic (static) and flow and transport (dynamic) connectivity metrics. Numerical models of deltaic stratigraphy were generated using a reduced‐complexity numerical model (DeltaRCM) with different input sand fractions (ISF) and rates of sea‐level rise (SLR). The groundwater flow and advective transport behavior of these deltas were simulated using MODFLOW and MODPATH. By comparing the static and dynamic metrics calculated from these numerical models, we show that groundwater behavior can be predicted by particular aspects of the subsurface architecture, and that horizontal and vertical connectivity display different characteristics. We also evaluate relationships between connectivity metrics and two environmental controls on delta evolution: ISF and SLR rate. The results show that geologic setting strongly influences both static and dynamic connectivity in different directions. These results provide insights into quantitatively differentiated subsurface hydraulic behavior between deltas formed under different external forcing (ISF and SLR rate) and they are a potential link in using information from delta surface networks and depositional history to predict vulnerability to aquifer contamination.

Environmental Controls on the Distribution of Modern Benthic Foraminifera in the Florida Everglades and Their Use as Paleoenvironmental Indicators

ABSTRACT This study examined the environmental factors that control the distribution of modern foraminiferal assemblages in the Everglades in order to provide baseline data for a paleoenvironmental study. Total assemblages from the surface 2 cm of 30 sites across the marsh and mangrove environments of southwest Florida were investigated. Eight environmental variables, including average salinity, salinity range, pH, total phosphorus, temperature, and dissolved oxygen, and total organic carbon and total inorganic carbon measured on bulk sediments, as well as the elevation and distance from the coastline were determined for each of the 30 sampling locations. In total, 82 species were identified, the majority of which were calcareous. Diversity decreases, dominance increases, and agglutinated taxa increase from the coastline inland. Rotaliina are equally abundant across the intertidal environment, whereas Miliolina are common near the coast and in lagoons or inland lakes. The most important factor controlling foraminiferal distribution is total organic carbon, followed by total inorganic carbon, distance from coastline, total phosphorus, and salinity. Jadammina macrescens and Miliammina fusca indicate lower salinities (&amp;lt;15 psu). Good indicators for higher salinities are Haplophragmoides wilberti (10–20 psu) and Arenoparrella mexicana (10–20 psu and 28–30 psu). Ammonia spp. prefer salinities &amp;gt;15 psu and Elphidium spp. &amp;gt;20 psu. Ammonia tepida, Helenina anderseni, Trochammina inflata, and A. mexicana prefer organic-rich sediments. Thus, the benthic foraminifera from Everglades sediments are excellent salinity proxies and can be used to determine the history of habitat change in this area as well as to assess past trends in the rate of sea level rise.

Submergence of the Western Greco-Roman Archaeological Site at the Eastern Harbor of Alexandria: Emerged from High Resolution Geophysical Mapping

Marine geophysical surveys were carried out at the underwater site in the south-western sector of the Eastern Harbor of Alexandria, opposite to the Egyptian Sea Scout Club. Survey works aimed to detect and study the surface and subsurface geomorphological changes caused by historic sea-level rise and natural hazards, by integrating the results of high-resolution geophysical mapping for the seafloor textures and the subsurface layers with previously published core data and sea-level records, the survey works employed echo-sounder, side scan sonar, and sub-bottom profiler. Acoustic data were ground-truthed using an ROV camera and sediment grab sampler. Results of bathymetric mapping and sonar imaging outlined two breakwaters and quay corresponding to a submerged ancient port; also, sediment types were classified according to variation in the magnitude of the backscattered intensities. Interpretation of sub-bottom profiles illustrated the depositional sequence of the topmost sedimentary layers where the sediment thicknesses were thickened by rates that perfectly matched with the recorded sea-level rise rate during the last two millennia, as indicated by isopach maps. Anthropogenic activities were noticed in particular outcropping areas on the sub-bottom profiles. The results explained the role of natural hazards and sea-level rise in changing the geomorphology of the coastline and seabed features.

Morphodynamic adaptation of a tidal basin to centennial sea-level rise: The importance of lateral expansion

Global climate changes have accelerated sea-level rise (SLR), which exacerbates the risks of coastal flooding and erosion. It is of practical interest to understand the long-term hydro-morphodynamic adaptation of coastal systems to SLR at a century time scale. In this work we use a numerical model to explore morphodynamic evolution of a schematized tidal basin in response to SLR of 0.25–2.0 m over 100 years with special emphasis on the impact of lateral basin expansion. Starting from a sloped initial bed, morphodynamic development of the system leads to the formation of alternating bars and meandering channels inside the tidal basin and an ebb-tidal delta extending seaward from the basin. Imposing rising sea level causes progressive inundation of the low-lying floodplains, found along the basin margins, inducing an increase in basin plain area and tidal prism, as well as intertidal area and storage volume. Although the overall channel-shoal structure persists under SLR, lateral shoreline expansion alters the basin hypsometry, leading to enhanced sediment export. The newly-submerged floodplains partly erode, supplying sediment to the system for spatial redistribution, hence buffering the impact of SLR. The vertical accretion rate of the tidal flats inside the tidal basin lags behind the rate of SLR. However, lateral shoreline migration under SLR creates new intertidal flats, compensating intertidal flat loss in the original basin. In contrast, a constrained tidal basin without low-lying floodplains is subject to profound drowning and tidal flat losses under SLR. Overall, the model results suggest that an unconstrained tidal system allowing lateral shoreline migration has buffering capacity for alleviating the drowning impact of SLR by evolving new intertidal areas, sediment redistribution and morphodynamic adjustment. These findings suggest that preserving tidal flats located along the margins of tidal basins (instead of reclaiming them) sustains the system's resilience to SLR.

Seasonal and long-term sea-level variations and their forcing factors in the northern Bay of Bengal: A statistical analysis of temperature, salinity, wind stress curl, and regional climate index data

In the northern Bay of Bengal, mechanisms of seasonal sea-level variation have not previously been examined, and the understanding of longer-term inter-annual sea-level variation is also not concrete. These parameters are addressed in this study utilizing available tide gauge and satellite altimetry data. The contribution of steric sea level to seasonal and longer-term inter-annual sea-level variations is quantified, and statistical analysis is performed to determine the correlations of various atmospheric and oceanic factors with sea level. This study suggests that the trend of sea-level rise in this bay (4 ± 1.33 mm/year) is higher than the global average (3.32 ± 0.46 mm/year) for the studied period 1993 to 2018. The rate of sea-level rise is higher along the coast than in the offshore area and the highest in the central part of the coast. Sea level shows a strong seasonal variation: sea level is the lowest in the winter but the highest in autumn. The contribution from the thermosteric sea level is higher to the observed sea level from winter to early summer, whereas contributions from the halosteric sea level and wind stress curl are higher during autumn. Long-term variations in sea level show strong positive correlations with thermosteric sea level, indicating that temperature is a major local controlling factor for sea-level change. In addition to local factors, long-term sea level also varies by remote forcing (equatorial zonal wind stress), which explains approximately 36 % of the sea-level variation in this bay. Sea level is low during the combined events of positive Indian Ocean dipole (IOD) and El Niño, whereas the sea level is high during the combined events of negative IOD and La Niña. This study provides an improved understanding of seasonal and longer-term inter-annual variations of sea level and the necessary groundworks for a dedicated model study to further quantify all the components of the sea-level budget in the study areas.

High-resolution sea level change around China seas revealed through multi-satellite altimeter data

Sea level change is not uniform across the oceans and high-resolution sea level trend (SLT) models reveal that the rate of sea level change differs between different waters. In this study, we developed a new method for obtaining a high-resolution, 1′×1′-grid SLT model, using the time-varying mean sea surface (MSS) of several MSSs calculated from averaged multi-satellite-derived sea surface heights (TOPEX/Poseidon, Jason-1/2/3, ERS-1/2, Envisat, GFO, Cryosat-2, SARAL/AltiKa, Sentinel-3A, HY-2A) over different periods. We applied this model to estimate the mean sea level change in the China seas and their adjacent ocean (0°–41°N, 100°–140°E). This new model revealed the patterning of sea level change within the study region in detail, and detected a sea level change dipole south of Japan. A zonal SLT pattern was identified in three regions: the region of the North Pacific Subtropical Counter Current (an eastward current located in the band of 19.5°–22.5°N, populated with eddies), and the areas east of Taiwan and east of Luzon Island. Moreover, the rate of sea level rise in the offshore zone was found to be ~ 0.67 mm/yr (20%) higher than that in the open ocean. This finding has important implications for coastal protection.

Twentieth century global glacier mass change: an ensemble-based model reconstruction

Abstract. Negative glacier mass balances in most of Earth's glacierized regions contribute roughly one-quarter to currently observed rates of sea-level rise and have likely contributed an even larger fraction during the 20th century. The distant past and future of glaciers' mass balances, and hence their contribution to sea-level rise, can only be estimated using numerical models. Since, independent of complexity, models always rely on some form of parameterizations and a choice of boundary conditions, a need for optimization arises. In this work, a model for computing monthly mass balances of glaciers on the global scale was forced with nine different data sets of near-surface air temperature and precipitation anomalies, as well as with their mean and median, leading to a total of 11 different forcing data sets. The goal is to better constrain the glaciers' 20th century sea-level budget contribution and its uncertainty. Therefore, five global parameters of the model's mass balance equations were varied systematically, within physically plausible ranges, for each forcing data set. We then identified optimal parameter combinations by cross-validating the model results against in situ annual specific mass balance observations, using three criteria: model bias, temporal correlation, and the ratio between the observed and modeled temporal standard deviation of specific mass balances. These criteria were chosen in order not to trade lower error estimates by means of the root mean squared error (RMSE) for an unrealistic interannual variability. We find that the disagreement between the different optimized model setups (i.e., ensemble members) is often larger than the uncertainties obtained via the leave-one-glacier-out cross-validation, particularly in times and places where few or no validation data are available, such as the first half of the 20th century. We show that the reason for this is that in regions where mass balance observations are abundant, the meteorological data are also better constrained, such that the cross-validation procedure only partly captures the uncertainty of the glacier model. For this reason, ensemble spread is introduced as an additional estimate of reconstruction uncertainty, increasing the total uncertainty compared to the model uncertainty merely obtained by the cross-validation. Our ensemble mean estimate indicates a sea-level contribution by global glaciers (outside of the ice sheets; including the Greenland periphery but excluding the Antarctic periphery) for 1901–2018 of 69.2 ± 24.3 mm sea-level equivalent (SLE), or 0.59 ± 0.21 mm SLE yr−1. While our estimates lie within the uncertainty range of most of the previously published global estimates, they agree less with those derived from GRACE data, which only cover the years 2002–2018.

Sea-level rise, localized subsidence, and increased storminess promote saltmarsh transgression across low-gradient upland areas

Saltmarsh area is decreasing globally from natural and anthropogenic stressors. Accelerating relative sea-level rise (SLR) is projected to exacerbate losses if not offset by upland saltmarsh migration (transgression). In the absence of coastal upland development, saltmarsh transgression rates increase with accelerating SLR and lower upland surface gradients. Storm wind and surge stress coastal upland forests causing defoliation, uprooting, and soil salinization, which makes upland areas more habitable for saltmarsh species and can promote transgression. This study aims to elucidate the contribution of storms to saltmarsh transgression by reconstructing transgression rates over the past 600 years during stormy and non-stormy conditions and fast and slow SLR rates. Our reconstructions are based on the stratigraphic record and historical aerial photography at three sites in North Carolina, U.S.A. where low-gradient pocosin upland grades into expansive saltmarsh. When sea level was rising <0.9 mm yr−1, saltmarsh transgression rates at the two sites where saltmarsh is > 100 years were an average of 2 and 10 times faster during a paleo-stormy period (1400–1675 CE) than a subsequent non-stormy period. After 1865 CE when SLR accelerated to 2.4 mm yr−1, transgression rates were an average of 7 times faster than the preceding slow SLR non-stormy period. The two sites where the historical record was not confounded by dredging show transgression was 7 times faster and saltmarsh areas increased an average of 28% during stormy decades than non-stormy decades; however, the rate of transgression only increased at the site with greatest surge during the stormy period characterized by strong northeast winds. Modeled transgression rates, using the paleo-upland slope and a sea level curve, do not match observed transgression rates for the paleo-stormy and rapid SLR periods. Furthermore, the thickness of saltmarsh peat younger than 1957 CE is greater than what would be predicted from independent records of SLR. Changes in the elevation of the upland surface, which is composed of peat, contributes to the disparity between predicted and observed transgression rates. The upland surface elevation can keep pace with some rates of SLR through vertical accretion; however, salinization and decomposition of upland vegetation from storm surge plus SLR decreases the elevation of the paleo-upland surface and increases accommodation and transgression rates. Along low-gradient coastlines with pocosin upland areas, SLR, subsidence, and storminess are coupled in modulating transgression rates and those processes need to be included in forecasts of saltmarsh response to climate change.

Climate pacing of millennial sea-level change variability in the central and western Mediterranean

Future warming in the Mediterranean is expected to significantly exceed global values with unpredictable implications on the sea-level rise rates in the coming decades. Here, we apply an empirical-Bayesian spatio-temporal statistical model to a dataset of 401 sea-level index points from the central and western Mediterranean and reconstruct rates of sea-level change for the past 10,000 years. We demonstrate that the mean rates of Mediterranean industrial-era sea-level rise have been significantly faster than any other period since ~4000 years ago. We further highlight a previously unrecognized variability in Mediterranean sea-level change rates. In the Common Era, this variability correlates with the occurrence of major regional-scale cooling/warming episodes. Our data show a sea-level stabilization during the Late Antique Little Ice Age cold event, which interrupted a general rising trend of ~0.45 mm a−1 that characterized the warming episodes of the Common Era. By contrast, the Little Ice Age cold event had only minor regional effects on Mediterranean sea-level change rates.

Effects of Vegetation, Sediment Supply and Sea Level Rise on the Morphodynamic Evolution of Tidal Channels

AbstractTidal channels play a leading role in the morphodynamic evolution of tidal environments by driving the exchange of water, sediments, and nutrients within these systems. Despite their fundamental function on landscape construction, current knowledge on their plano‐altimetric evolution in response to environmental forcing is still limited. We developed a mathematical model to address the interplay of biogeomorphic processes on the plano‐altimetric equilibrium of a straight tidal channel flanked by adjacent intertidal platforms. The model couples a one‐dimensional hydrodynamic model with a bed evolution model. The former describes the flow field within the channel and the storage contribution of lateral shoals. The latter accounts for the main physical processes responsible for shaping the tidal landscape, namely erosion, deposition, and sea level rise, mediated by halophytic vegetation growth. Model results reproduce a variety of channel morphologies, ranging from those typical of tidal‐flat channels, with large width‐to‐depth ratios, to those characterizing salt‐marsh creeks, which have much narrower cross sections and small width‐to‐depth ratios. Our results show that vegetation encroachment on the marsh surface produces two competing effects. First, vegetation increases flow concentration within the channel, owing to the increased flow resistance on the vegetated platform thus favoring channel incision. Second, vegetation promotes a reduction in the tidal prism, owing to higher accretion rates of the salt‐marsh surface thus leading to channel infilling. Which effect prevails over the other depends on the elevation of the intertidal platform in the tidal frame. The latter is in turn dictated by sediment availability, the rate of relative sea level rise, and vegetation biogeomorphic effects.

Sediment Accumulation, Elevation Change, and the Vulnerability of Tidal Marshes in the Delaware Estuary and Barnegat Bay to Accelerated Sea Level Rise

Tidal marshes are highly valued habitats, yet are vulnerable to loss from both anthropogenic and natural disturbances including sea-level rise (SLR). Many tidal marshes have kept pace with SLR over the last century; on average, however, recent escalations in SLR increase the vulnerability of marshes to submergence. Relative sea-level rise near our study sites in the Mid-Atlantic U.S. averaged 4.34 mm year−1 over the last 50 years, yet over the last 19 years, relative sea-level rise averaged 6.25 mm year−1 and the rise in high tide water levels averaged 8.13 mm year−1. We compared these rates of water rise to rates of marsh surface elevation change using surface elevation tables in ten tidal marshes—three tidal freshwater and four saline marshes in the Delaware Estuary and three salt marshes in Barnegat Bay, NJ, USA. We also examined the effects of marsh type and geomorphic setting on rates of elevation change, surface accretion, and subsurface change as well as the influence of marsh elevation, distance from a channel, and tidal range (n = 3 sites per marsh). Surface elevation change measured over the last 4 to 9 years averaged less than 6 mm year−1 in nine out of ten of the study stations, less than rates of relative SLR. Tidal freshwater marshes in the Delaware Estuary had greater rates of surface accretion and elevation change than salt marshes in Barnegat Bay. Marshes sitting lower in the tidal frame and experiencing higher tidal ranges tended to have higher surface accretion rates, but shallow subsidence had a stronger influence on these elevation change rates. We estimated time to submergence (i.e., lifespan) for using rates of marsh elevation change, a SLR rate of 10 mm year−1, and thresholds for conversion to open water using geospatial datasets. The calculated time to submergence for the majority of marshes was 60 to 80 years with some predicted to submerge in as few as 5 years. These data suggest that in order to keep pace with accelerating SLR, surface accretion in many of these marshes will have to increase at a rate that surpasses shallow subsidence (1–7 mm year−1).

Root-zone carbon and nitrogen pools across two chronosequences of coastal marshes formed using different restoration techniques: Dredge sediment versus river sediment diversion

Coastal marshes have among the highest rates of soil carbon accumulation of any ecosystem on Earth, yet they are increasingly being lost due to high rates of relative sea-level rise, changes to their hydrology, and other natural and anthropogenic factors. To mitigate some of this wetland loss, restoration strategies in Louisiana have been focused on creating marshes using dredge spoil and diverting river flow into deteriorating wetland basins. Here, we aimed to compare these two different restoration approaches in terms of the development of soil carbon and nitrogen within the root zone (top 30 cm) by examining two chronosequences of newly formed marshes that span 32- and 25-year timeframes—one of which was a series of brackish, created marshes in the Chenier Plain (Sabine; marsh creation), and the other, a series of deltaic, tidal, freshwater marshes in the currently prograding Wax Lake Delta (WLD; sediment diversion). We also assessed the vegetation coverage and the relative chemical stability of the soil organic carbon and nitrogen (refractory versus labile) that has accumulated across these restoration sites. We observed that vegetation coverage initially increased more rapidly in the Sabine marshes, but it was similar to that in the WLD marshes by ~30 years post-establishment. Whereas the soil carbon pool reached similar quantities between the two chronosequences, it increased nearly twice as fast on average in WLD versus Sabine. The density of soil nitrogen closely tracked soil carbon in WLD, but it remained uniform across the Sabine marshes. Refractory soil carbon accounted for 59 ± 12% of the total soil carbon, and the refractory carbon pool increased at a rate that was similar between both chronosequences, despite the characteristic differences in salinity, nutrient input, plant species composition, and mineral sedimentation rates. Overall, our results suggest that marshes formed from sediment diversions in Louisiana have the potential to rival or outpace marshes created using dredge sediment in terms of vegetation and soil organic matter development.

The contribution of sand and mud to infilling of tidal basins in response to a closure dam

Human interventions and climate change can heavily influence the large-scale morphological development of tidal basins. This has implications on sediment management strategies, as well as ecological and recreational purposes. Examples of heavily impacted tidal basins are those in the Western Dutch Wadden Sea. The closure of a large sub-basin in 1932 triggered a shift in the sediment budgets of the remaining basins, leading to sediment infilling that is still ongoing. This paper presents a quantitative analysis of the post-closure sediment volumes, differentiating between sand and mud. Analysis of historical sediment composition data combined with bathymetry data revealed that the intervention caused a redistribution of sand and mud sedimentation. The responses of both sediment types differ spatially and temporally. The total infilling of the basins over the last century was substantially caused by mud (~32%, which is much larger than the average mud content in the bed). Initially, large mud volumes accreted in abandoned channels. At present, mud sedimentation along the mainland coast is still ongoing with nearly constant sedimentation rates over the past century, while the net import of sand significantly decreased over time and has been fluctuating around 0 over the last two decades. This research shows the importance of distinguishing between the response of sandy and muddy sediments when analysing the morphodynamic impact of an intervention, since they operate on different time and spatial scales. Sea level rise is currently a major threat for the existence of the Wadden Sea; its future fate will depend on whether the tidal flats are able to keep pace. Our results show that the supply of mud is sufficient to keep pace with the current sea level rise rates.

Multi-decadal planform changes on coral reef islands from atolls and mid-ocean reef platforms of the equatorial Pacific Ocean: Gilbert Islands, Republic of Kiribati

Constructed of poorly lithified carbonate sediments with elevations of <3–5 m above MSL, coral reef islands are considered extremely vulnerable to the effects of anthropogenic climate change, particularly sea-level rise. While some studies have shown islands are dynamic landforms with the ability to physically adjust their shape and position on the reef platform, large geographical gaps still exist in reef island change records. This study presents a multi-decadal analysis of shoreline changes and planform geomorphic adjustments across coral reef islands in the equatorial Pacific from the Gilbert archipelago, Republic of Kiribati. Shoreline positions of 71 islands from 3 atolls and 4 mid-ocean reef platforms were analysed by comparing historical aerial photographs (from 1940s and 1960s) and recent satellite imagery covering a period of local sea-level rise rate of ~2.2 mm/year. Results show ~47% of the shorelines were characterised by statistically significant accretion leading to a net increase of 274.07 ha (2.45%) of planform land area. A comparative examination of changes on platform-islands and atoll-islands revealed platform-islands were relatively more stable (mean rate of 0.01 m/year) with significantly less variability in shoreline change rates, while atoll-islands were characterised by a higher mean rate of accretion (0.09 m/year). Further analysis of change rates across various shoreline exposure categories, demonstrate high dynamism across atoll-island shorelines is a function of distinctive local-scale processes occurring within atoll settings; lagoon-facing shorelines were characterised by the highest rate of accretion (0.14 m/year), spits were found to be highly dynamic and embayment infilling accounted for ~9% of the net increase in land area across the study islands. Results are instructive in defining styles of morphological change across various geomorphic settings to inform projections of future island adjustments, assessments of attribution of island change and formulation of adaptation responses across atoll nations.

Global Data Gaps in Our Knowledge of the Terrestrial Cryosphere

The IPCC Special Report on Oceans and Cryosphere in a Changing Climate identified major gaps in our knowledge of snow and glacier ice in the terrestrial cryosphere. These gaps are limiting our ability to predict the future of the energy and water balance of the Earth's surface, which in turn affect regional climate, biodiversity and biomass, the freezing and thawing of permafrost, the seasonal supply of water for one sixth of the global population, the rate of global sea level rise and the risk of riverine and coastal flooding. Snow and ice are highly susceptible to climate change but although their spatial extents are routinely monitored, the fundamental property of their water content is remarkably poorly observed. Specifically, there is a profound lack of basic but problematic observations of the amount of water supplied by snowfall and of the volume of water stored in glaciers. As a result, the climatological precipitation of the mountain cryosphere is, for example, biassed low by 50–100%, and biases in the volume of glacier ice are unknown but are likely to be large. More and better basic observations of snow and ice water content are urgently needed to constrain climate models of the cryosphere, and this requires a transformation in the capabilities of snow-monitoring and glacier-surveying instruments. I describe new solutions to this long-standing problem that if deployed widely could achieve this transformation.