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The volume transport of the Tsugaru warm current (TWC), defined as the branch current of the western boundary current of the North Pacific subtropical gyre flowing through the Tsugaru Strait, is a critical factor affecting the acidification in the strait as well as the surrounding coastal regions by promoting the enhancement of the vertical mixing of the deep water rich in dissolved inorganic carbon. The in-phase sea-level variation along the coast of mainland Japan with a gap at the Tsugaru Strait permits the discharge of the sea surface water from the Sea of Japan to the Pacific Ocean, which is significantly correlated to the variation in the sea-level difference across the Tsugaru Strait, being possibly related to that in the TWC volume transport. Furthermore, by averaging the wind-driven Sverdrup streamfunction along the eastern coast of mainland Japan—from the southern end of Kyushu (30 ∘ N) to the separation latitude of the Kuroshio (36 ∘ N)—and scaling by a factor of the ratio between the depths of the Tsushima Strait and the East China Sea, we obtained the volume transport varying similarly with the sea-level difference across the Tsugaru Strait. As obtained, the interannual wind stress variation in this latitude band to the east of mainland Japan on the North Pacific is suggested to altered the strength of the TWC.

The East China Sea (ECS) is a shallow marginal sea that is sensitive to glacio-eustatic sea-level changes and is influenced by warm oligotrophic water of the Kuroshio Current (KC), the nutrient-rich Taiwan Warm Current, and freshwater discharges from rivers in southern China during the East Asian summer monsoon season. In this area, local paleoceanographic changes for times prior to 40 ka remain poorly studied because of high sediment accumulation rates on the seafloor. During Integrated Ocean Drilling Program Expedition 346, long sediment cores representing the last 400 kyr were retrieved from the northern part of the ECS (Site U1429). In these cores, radiolarians are abundant and well-preserved, thus using the ecological properties of radiolarians, we analyzed how glacio-eustatic sea-level variations have influenced the paleoceanography of the ECS over the last 400 kyr, with a focus on changes in water properties at intermediate depths. Additionally, the summer sea surface temperature (SST) and intermediate water temperature at about 500 m were quantified by means of data on selected radiolarian species. The KC influenced the shallow water at Site U1429 during each interglacial period over the last 400 kyr (marine isotope stages [MISs] 1, 5, 7, 9, and 11), causing a high summer SST (about 27 °C), although inflow of the KC into the ECS was probably delayed until after the sea-level maximum of interglacial MIS 1 and MIS 5. During this lag time, ECS shelf water was the dominant influence on the system. During glacial periods (MISs 2–4, 6, and 10), our data suggest that coastal conditions prevailed, probably because of a sea-level drop of more than 90 m. At these times, the summer SST was colder, ca. 20 °C. Changes in the relative abundance of Cycladophora davisiana indicate that the most significant changes in the bottom water occurred during MIS 6, when the bottom water likely became poorer in oxygen. An increase in the shallow-water primary productivity during MIS 7 and MIS 6 was probably the key factor causing the oxygen-poor conditions.

The article presents the results of dynamic-stochastic modeling of long-term variations of Caspian Sea level during the Early khvalyn (Buinak stage) and the Late khvalyn (Makhachkala stage) transgressions. A linearized model of Caspian level variations with a negative feedback due to the dependence of sea water area on water level is shown to be applicable to the paleo-Caspian. The calculations were based on the results of simulation and analytical modeling. The regimes of long-term level variations in the paleo-Caspian Sea for the considered transgressions are shown to differ. For example, the variance of the Caspian Sea level for the Early and Late khvalyn transgressions is equal to 4.2 and 2.5 m 2 , respectively, and the average duration of the level rise above its equilibrium value during a single event is ~50 and ~40 years, respectively. Estimates of the duration of sea level rises can be used to assess the possibility of formation of various coastal–shelf geomorphological forms during long-term level rises. The obtained characteristics of the processes of long-term sea level variations, including the variance, autocorrelation, probability distribution density, the mean duration of level rises above (or level drops below) specified level marks during one such event, the dependence of the parameter of inertia of level variations significantly expand our knowledge about the character of Caspian Sea level variations in the paleotime.

Variations in the Earth's water cycle are commonly quantified by their effect on global mean sea‐level. However, the interaction between passive adjustment of the ocean to changes in gravitational attraction due to mass redistribution, the related deformation of the solid Earth and disturbances in the Earth's rotation vector will yield a distribution that is more complicated than a uniform rise or fall of the ocean's surface. In this study, we present the first estimates of seasonal changes in passive sea‐level (which we define as the height difference between the sea surface at rest and ocean floor, excluding steric and dynamical effects) based on direct observations of surface mass redistribution, made by the Gravity Recovery and Climate Experiment (GRACE) between 2003 and 2010. We show that this “selfgravitation‐effect” causes seasonal variations of the sea‐level of up to 1 cm – comparable to the amplitude of the long‐period tides – and that inclusion in numerical ocean models results in a better agreement between observed and modelled ocean bottom pressure variations, particularly in coastal zones.

Coastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems 1 , 2 , primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates 3 . Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-first century 4 , but these carbon–climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion 4 , 5 . Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1 at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillar collapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space 6 created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate–carbon modelling. Wetlands exposed to rapid sea-level rise over the late Holocene contain more soil carbon than those that experienced a long period of sea-level stability.

The city of Venice and the surrounding lagoonal ecosystem are highly vulnerable to variations in relative sea level. In the past ∼150 years, this was characterized by an average rate of relative sea-level rise of about 2.5 mm/year resulting from the combined contributions of vertical land movement and sea-level rise. This literature review reassesses and synthesizes the progress achieved in quantification, understanding and prediction of the individual contributions to local relative sea level, with a focus on the most recent studies. Subsidence contributed to about half of the historical relative sea-level rise in Venice. The current best estimate of the average rate of sea-level rise during the observational period from 1872 to 2019 based on tide-gauge data after removal of subsidence effects is 1.23 ± 0.13 mm/year. A higher – but more uncertain – rate of sea-level rise is observed for more recent years. Between 1993 and 2019, an average change of about +2.76 ± 1.75 mm/year is estimated from tide-gauge data after removal of subsidence. Unfortunately, satellite altimetry does not provide reliable sea-level data within the Venice Lagoon. Local sea-level changes in Venice closely depend on sea-level variations in the Adriatic Sea, which in turn are linked to sea-level variations in the Mediterranean Sea. Water mass exchange through the Strait of Gibraltar and its drivers currently constitute a source of substantial uncertainty for estimating future deviations of the Mediterranean mean sea-level trend from the global-mean value. Regional atmospheric and oceanic processes will likely contribute significant interannual and interdecadal future variability in Venetian sea level with a magnitude comparable to that observed in the past. On the basis of regional projections of sea-level rise and an understanding of the local and regional processes affecting relative sea-level trends in Venice, the likely range of atmospherically corrected relative sea-level rise in Venice by 2100 ranges between 32 and 62 cm for the RCP2.6 scenario and between 58 and 110 cm for the RCP8.5 scenario, respectively. A plausible but unlikely high-end scenario linked to strong ice-sheet melting yields about 180 cm of relative sea-level rise in Venice by 2100. Projections of human-induced vertical land motions are currently not available, but historical evidence demonstrates that they have the potential to produce a significant contribution to the relative sea-level rise in Venice, exacerbating the hazard posed by climatically induced sea-level changes.

Vertical land movements can cause regional relative sea-level changes to differ substantially from climate-driven absolute sea-level changes. Whereas absolute sea level has been accurately monitored by satellite altimetry since 1992, there are limited observations of vertical land motion. Vertical land motion is generally modelled as a linear process, despite some evidence of nonlinear motion associated with tectonic activity, changes in surface loading or groundwater extraction. As a result, the temporal evolution of vertical land motion, and its contribution to projected sea-level rise and its uncertainty, remains unresolved. Here we generate a probabilistic vertical land motion reconstruction from 1995 to 2020 to determine the impact of regional-scale and nonlinear vertical land motion on relative sea-level projections up to 2150. We show that regional variations in projected coastal sea-level changes are equally influenced by vertical land motion and climate-driven processes, with vertical land motion driving relative sea-level changes of up to 50 cm by 2150. Accounting for nonlinear vertical land motion increases the uncertainty in projections by up to 1 m on a regional scale. Our results highlight the uncertainty in future coastal impacts and demonstrate the importance of including nonlinear vertical land motions in sea-level change projections. A probabilistic reconstruction of vertical land motion reveals regional variations in relative sea-level changes and large uncertainties in sea-level projections due to nonlinear effects.

Predictions for sea-level rise this century due to melt from Antarctica range from zero to more than one metre. The highest predictions are driven by the controversial marine ice-cliff instability (MICI) hypothesis, which assumes that coastal ice cliffs can rapidly collapse after ice shelves disintegrate, as a result of surface and sub-shelf melting caused by global warming. But MICI has not been observed in the modern era and it remains unclear whether it is required to reproduce sea-level variations in the geological past. Here we quantify ice-sheet modelling uncertainties for the original MICI study and show that the probability distributions are skewed towards lower values (under very high greenhouse gas concentrations, the most likely value is 45 centimetres). However, MICI is not required to reproduce sea-level changes due to Antarctic ice loss in the mid-Pliocene epoch, the last interglacial period or 1992–2017; without it we find that the projections agree with previous studies (all 95th percentiles are less than 43 centimetres). We conclude that previous interpretations of these MICI projections over-estimate sea-level rise this century; because the MICI hypothesis is not well constrained, confidence in projections with MICI would require a greater range of observationally constrained models of ice-shelf vulnerability and ice-cliff collapse. By better quantifying uncertainties for marine ice-cliff instability, future Antarctic ice loss is predicted to be much lower than previously estimated.

Coastal areas epitomize the notion of ‘at-risk’ territory in the context of climate change and sea level rise (SLR). Knowledge of the water level changes at the coast resulting from the mean sea level variability, tide, atmospheric surge and wave setup is critical for coastal flooding assessment. This study investigates how coastal water level can be altered by interactions between SLR, tides, storm surges, waves and flooding. The main mechanisms of interaction are identified, mainly by analyzing the shallow water equations. Based on a literature review, the orders of magnitude of these interactions are estimated in different environments. The investigated interactions exhibit a strong spatiotemporal variability. Depending on the type of environments (e.g., morphology, hydrometeorological context), they can reach several tens of centimeters (positive or negative). As a consequence, probabilistic projections of future coastal water levels and flooding should identify whether interaction processes are of leading order, and, where appropriate, projections should account for these interactions through modeling or statistical methods.

We show that steric sea‐level varies with a period of 18.6 years along the western European coast. We hypothesize that this variation originates from the modulation of semidiurnal tides by the lunar nodal cycle and associated changes in ocean mixing. Accounting for the steric sea level changes in the upper 400 m of the ocean solves the discrepancy between the nodal cycle in mean sea level observed by tide gauges and the theoretical equilibrium nodal tide. Namely, by combining the equilibrium tide with the nodal modulation of steric sea level, we close the gap with the observations. This result supports earlier findings that the observed phase and amplitude of the 18.6‐year cycle do not always correspond to the equilibrium nodal tide. Plain Language Summary The orbital position of the moon and the gravity pull it exerts on the earth varies with a period of 18.6 years. This cycle is called the lunar nodal cycle and it results in small variations of yearly averaged sea level (∼1–2 cm). Understanding this variability is important because it allows, for example, to quickly detect an acceleration in local sea‐level rise due to global warming. Here we show that the lunar nodal cycle also has an influence on the temperature and salinity in the surface 400m of the ocean. As a result, the ocean density changes and amplifies sea level variations along the western European coast. We make the hypothesis that since the lunar nodal cycle also influences the amplitude of the semidiurnal tides, and since those tides are known to be responsible for a large part of ocean mixing, a change in ocean mixing could be the cause of the ocean density variability that we observe. Key Points Steric sea level changes are influenced by the 18.6‐year lunar nodal cycle along the western European coast This influence could result from the modulation of semidiurnal tides by the lunar nodal cycle and the associated change in ocean mixing This finding is a step toward resolving the long‐standing discrepancy between the theoretical long‐period nodal tide and observed signal