Sea-level rise: A review of recent past and near-future trends

Global mean sea level is a potentially sensitive indicator of climate change. Global warming will contribute to worldwide sea-level rise (SLR) from thermal expansion of ocean water, melting of mountain glaciers and polar ice sheets. A number of studies, mostly using tide-gauge data from the Permanent Service for Mean Sea Level, Bidston Observatory, England, have obtained rates of global SLR within the last 100 years that range between 0·3 and 3 mm yr^?1, with most values concentrated between 1 and 2 mm yr^?1. However, the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability. Sources of uncertainty in the sea-level data include variations in winds, ocean currents, river runoff, vertical earth movements, and geographically uneven distribution of long-term records. Crustal motions introduce a major source of error. To a large extent, these can be filtered by employing palaeo-sea-level proxies, and geophysical modelling to remove glacio-isostatic changes. Ultimately, satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges. Future sea level is expected to rise by ～ 1 m, with a ‘best-guess’ value of 48 cm by the year 2100. Such rates represent an acceleration of four to seven times over present rates. Local land subsidence could substantially increase the apparent SLR. For example, Louisiana is currently experiencing SLR trends nearly 10 times the global mean rate. These recently reduced SLR estimates are based on climate models that predict a zero to negative contribution to SLR from Antarctica. Most global climate models (GCMs) indicate an ice accumulation over Antarctica, because in a warmer world, precipitation will exceed ablation/snow-melt. However, the impacts of attritional processes, such as thinning of the ice shelves, have been downplayed according to some experts. Furthermore, not all climate models are in agreement. Opposite conclusions may be drawn from the results of other GCMs. In addition, the West Antarctic Ice Sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict. Because of the great uncertainty in SLR projections, careful monitoring of future sea-level trends by upgraded tide-gauge networks and satellite geodesy will become essential. Finally, because of the high spatial variability in crustal subsidence rates, wave climates and tidal regimes, it will be the set of local conditions (especially the relative sea-level rise), rather than a single global mean sea-level trend, that will determine each locality's vulnerability to future SLR.     

Long-term sea-level variations in the central Great Barrier Reef

Low frequency sea-level variations and associated geostrophic currents in the central Great Barrier Reef (GBR) region near Townsville are studied using optimally-lagged multivariate regression. The analyses show that pressure-adjusted coastal sea levels and mid-shelf geostrophic currents are influenced predominantly by local along-shelf wind stress at the weather time-scale, and by climatic variables, such as atmospheric pressure and temperature, at seasonal and inter-annual time-scales. These forcing variables can specify sea levels over annual and inter-annual time-scales with a forecasting skill of 0.53 and 0.22, respectively (where 1.0 is perfect skill). Associated along-shelf geostrophic currents can be forecast with a skill of 0.57 over an annual time scale. If, instead, absolute coastal sea levels or offshore sea-level differences are used to specify the along-shelf geostrophic current, the forecasting skill is 0.75. A characteristic El Niño/Southern Oscillation (ENSO) response is detected for time periods up to 25 years in monthly sea-level both at Townsville and at western Pacific island sea-level stations. This spatially coherent response varies in intensity and phase within the Coral Sea. Sea-level differences show a pattern which characterizes known features of the large-scale circulation of the Coral Sea. These very low frequency sea-level variations in the Coral Sea must be taken into account to obtain accurate predictions of along-shelf geostrophic current variations on seasonal and inter-annual time scales. Regression analysis and a diagnostic river plume model show that the influence of the major rivers can produce sea-level changes due to buoyancy of order 5 cm. The corresponding errors in geostrophic velocities estimated using pressure-adjusted Townsville sea-level data alone are of order 5 cm s⁻¹ rms.     

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth’s climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modes and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this paper, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.     

Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model

Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring on the adjacent inner continental shelf, especially during storm and coastal upwelling events.     

On the sensitivity of the sedimentary system in the East Frisian Wadden Sea to sea-level rise and wave-induced bed shear stress

The paper addresses the individual and collective contribution of different forcing factors (tides, wind waves, and sea-level rise) to the dynamics of sediment in coastal areas. The results are obtained from simulations with the General Estuarine Transport Model coupled with a sediment transport model. The wave-induced bed shear stress is formulated using a simple model based on the concept that the turbulent kinetic energy (TKE) associated with wind waves is a function of orbital velocity, the latter depending on the wave height and water depth. A theory is presented explaining the controls of sediment dynamics by the TKE produced by tides and wind waves. Several scenarios were developed aiming at revealing possible trends resulting from realistic (observed or expected) changes in sea level and wave magnitude. The simulations demonstrate that these changes not only influence the concentration of sediment, which is very sensitive to the magnitude of the external forcing, but also the temporal variability patterns. The joint effect of tides and wave-induced bed shear stress revealed by the comparison between theoretical results and simulations is well pronounced. The intercomparison between different scenarios demonstrates that the spatial patterns of erosion and deposition are very sensitive to the magnitude of wind waves and sea-level rise. Under a changing climate, forcing the horizontal distribution of sediments adjusts mainly through a change in the balance of export and import of sediment from the intertidal basins. The strongest signal associated with this adjustment is simulated North of the barrier islands where the evolution of sedimentation gives an integrated picture of the processes in tidal basins.     

Satellite-derived variability of the Aegean Sea ecohydrodynamics

Eight years of AVHRR-derived sea surface temperature (SST) and SeaWiFS-derived surface chlorophyll (Chl) data (1998–2005) are used to investigate key processes affecting the spatial and temporal variability of the two parameters in the Aegean Sea. Seasonal mean SST and Chl maps are constructed using daily data to study seasonal dynamics whereas empirical orthogonal function (EOF) and correlational analysis is applied to the 8-day composite SST and Chl anomaly time-series in order to study the variability and co-variability of the two parameters from subseasonal to interannual time-scales. The seasonal mean fields show that Black Sea cold and chlorophyll-rich waters enter through the Dardanelles Strait and they are accumulated in the north-eastern part of the Aegean Sea, steered by the Samothraki anticyclone. Large chlorophyll concentrations are encountered in the hydrological front off the Dardanelles Strait as well as in coastal areas affected by large riverine/anthropogenic nutrient loads. The SST seasonal mean patterns reveal strong cooling that is associated with upwelling along the eastern boundary of the basin during summer due to strong northerly winds, a process which is not present in the surface chlorophyll climatology. The Chl dataset presents much stronger sub-seasonal variability than SST, with large variations in the phase and strength of the phytoplankton seasonal cycles. EOF analysis of the anomaly time-series shows that SST non-seasonal variability is controlled by synoptic weather variations and anomalies in the north–south wind-stress component regulating the summer coastal upwelling regime. Mean SST and Chl patterns, and their associated variations, are not closely linked implying that Black Sea and riverine inputs mainly control the intra-annual and interannual variability of the surface chlorophyll in the Aegean Sea rather than mixing and/or upwelling processes.     

Understanding coastal wetland hydrology with a new regional‐scale,process‐based hydrological model

Coastal wetlands represent an ecotone between ocean and terrestrial ecosystems, providing important services, including flood mitigation, fresh water supply, erosion control, carbon sequestration, and wildlife habitat. The environmental setting of a wetland and the hydrological connectivity between a wetland and adjacent terrestrial and aquatic systems together determine wetland hydrology. Yet little is known about regional‐scale hydrological interactions among uplands, coastal wetlands, and coastal processes, such as tides, sea level rise, and saltwater intrusion, which together control the dynamics of wetland hydrology. This study presents a new regional‐scale, physically based, distributed wetland hydrological model, PIHM‐Wetland, which integrates the surface and subsurface hydrology with coastal processes and accounts for the influence of wetland inundation on energy budgets and evapotranspiration (ET). The model was validated using in situ hydro‐meteorological measurements and Moderate Resolution Imaging Spectroradiometer (MODIS) ET data for a forested and herbaceous wetland in North Carolina, USA, which confirmed that the model accurately represents the major wetland hydrological behaviours. Modelling results indicate that topographic gradient is a primary control of groundwater flow direction in adjacent uplands. However, seasonal climate patterns become the dominant control of groundwater flow at lower coastal plain and land–ocean interface. We found that coastal processes largely influence groundwater table (GWT) dynamics in the coastal zone, 300 to 800 m from the coastline in our study area. Among all the coastal processes, tides are the dominant control on GWT variation. Because of inundation, forested and herbaceous wetlands absorb an additional 6% and 10%, respectively, of shortwave radiation annually, resulting in a significant increase in ET. Inundation alters ET partitioning through canopy evaporation, transpiration, and soil evaporation, the effect of which is stronger in cool seasons than in warm seasons. The PIHM‐Wetland model provides a new tool that improves the understanding of wetland hydrological processes on a regional scale. Insights from this modelling study provide benchmarks for future research on the effects of sea level rise and climate change on coastal wetland functions and services.     

Tidal and wind-induced circulation within the Southeastern limit of the Bay of Biscay: Pasaia Bay,Basque Coast

The Basque coastal area, in the southeastern Bay of Biscay, can be characterised as being more influenced by land climate and inputs, than other typically ‘open sea’ areas. The influence of coastal processes, together with the presence of irregular and steep topography, complicate greatly the water circulation patterns. Water movement along the Basque coastal area is not well understood; observations are scarce and long-term current records are lacking. The knowledge available is confined to the surface currents: the surface water circulation is controlled mainly by wind forcing, with tidal and density currents being weak. However, there is a lack of knowledge available on currents within the lower levels of the water column; likewise, on the main time-scales involved in the water circulation. This study quantifies the contribution of the tidal and wind-induced currents, to the overall water circulation; it identifies the main time-scales involved within the tidal and wind-induced flows, investigating difference in such currents, throughout the water column, within Pasaia Bay (Basque coast). Within this context, extensive oceanographic and meteorological data have been obtained, in order to describe the circulation. The present investigation reveals that the circulation, within the surface and the sub-surface waters, is controlled mainly by wind forcing fluctuations, over a wide range of meteorological frequencies: third-diurnal, semidiurnal and diurnal land–sea breezes; synoptic variability; frequencies, near fortnightly periods; and seasonal. At the lower levels of the water column, the main contribution to the water circulation arises from residual currents, followed by wind-induced currents on synoptic time-scales. In contrast, tidal currents contribute minimally to the overall circulation throughout the water column.     

Arctic Sea Level During the Satellite Altimetry Era

Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite altimetry era. We investigate the closure of the sea-level budget since 2002 using two altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.     

The long-term salinity field in San Francisco Bay

Data are presented on long-term salinity behaviour in San Francisco Bay, California. A two-level, width averaged model of the tidally averaged salinity and circulation has been written in order to interpret the long-term (days to decades) salinity variability. The model has been used to simulate daily averaged salinity in the upper and lower levels of a 51 segment discretization of the Bay over the 22-yr period 1967–1988. Monthly averaged surface salinity from observations and monthly-averaged simulated salinity are in reasonable agreement. Good agreement is obtained from comparison with daily averaged salinity measured in the upper reaches of North Bay.The salinity variability is driven primarily by freshwater inflow with relatively minor oceanic influence. All stations exhibit a marked seasonal cycle in accordance with the Mediterranean climate, as well as a rich spectrum of variability due to extreme inflow events and extended periods of drought. Monthly averaged salinity intrusion positions have a pronounced seasonal variability and show an approximately linear response to the logarithm of monthly averaged Delta inflow. Although few observed data are available for studies of long-term salinity stratification, modelled stratification is found to be strongly dependent on freshwater inflow; the nature of that dependence varies throughout the Bay. Near the Golden Gate, stratification tends to increase up to very high inflows. In the central reaches of North Bay, modelled stratification maximizes as a function of inflow and further inflow reduces stratification. Near the head of North Bay, lowest summer inflows are associated with the greatest modelled stratification. Observations from the central reaches of North Bay show marked spring-neap variations in stratification and gravitational circulation, both being stronger at neap tides. This spring-neap variation is simulated by the model. A feature of the modelled stratification is a hysteresis in which, for a given spring-neap tidal range and fairly steady inflows, the stratification is higher progressing from neaps to springs than from springs to neaps.The simulated responses of the Bay to perturbations in coastal sea salinity and Delta inflow have been used to further delineate the time-scales of salinity variability. Simulations have been performed about low inflow, steady-state conditions for both salinity and Delta inflow perturbations. For salinity perturbations a small, sinusoidal salinity signal with a period of 1 yr has been applied at the coastal boundary as well as a pulse of salinity with a duration of one day. For Delta inflow perturbations a small, sinusoidally varying inflow signal with a period of 1 yr has been superimposed on an otherwise constant Delta inflow, as well as a pulse of inflow with a duration of one day. Perturbations in coastal salinity dissipate as they move through the Bay. Seasonal perturbations require about 40–45 days to propagate from the coastal ocean to the Delta and to the head of South Bay. The response times of the model to perturbations in freshwater inflow are faster than this in North Bay and comparable in South Bay. In North Bay, time-scales are consistent with advection due to lower level, up-estuary transport of coastal salinity perturbations; for inflow perturbations, faster response times arise from both upper level, down-estuary advection and much faster, down-estuary migration of isohalines in response to inflow volume continuity. In South Bay, the dominant time-scales are governed by tidal dispersion.     

Sea level: A review of present-day and recent-past changes and variability

In this review article, we summarize observations of sea level variations, globally and regionally, during the 20th century and the last 2 decades. Over these periods, the global mean sea level rose at rates of 1.7 mm/yr and 3.2 mm/yr respectively, as a result of both increase of ocean thermal expansion and land ice loss. The regional sea level variations, however, have been dominated by the thermal expansion factor over the last decades even though other factors like ocean salinity or the solid Earth's response to the last deglaciation can have played a role. We also present examples of total local sea level variations that include the global mean rise, the regional variability and vertical crustal motions, focusing on the tropical Pacific islands. Finally we address the future evolution of the global mean sea level under on-going warming climate and the associated regional variability. Expected impacts of future sea level rise are briefly presented.     

Identification of extreme storm surges with high-impact potential along the German North Sea coastline

Planning and design of coastal protection rely on information about the probabilities of very severe storm tides and the possible changes that may occur in the course of climate change. So far, this information is mostly provided in the form of high percentiles obtained from frequency distributions or return values. More detailed information and assessments of events that may cause extreme damages or have extreme consequences at the coast are so far still unavailable. We describe and compare two different approaches that may be used to identify highly unlikely but still physically possible and plausible events from model simulations. Firstly, in the case when consistent wind and tide-surge data are available, different metrics such as the height of the storm surge can be derived directly from the simulated water levels. Secondly, in cases where only atmospheric data are available, the so called effective wind may be used. The latter is the projection of the horizontal wind vector on that direction which is most effective in producing surges at the coast. Comparison of events identified by both methods show that they can identify extreme events but that knowledge of the effective wind alone does not provide sufficient information to identify the highest storm surges. Tracks of the low-pressure systems over the North Sea need to be investigated to find those cases, where the duration of the high wind is too short to induce extreme storm tides. On the other hand, factors such as external surges or variability in mean sea level may enhance surge heights and are not accounted for in estimates based on effective winds only. Results from the analysis of an extended data set suggest that unprecedented storm surges at the German North Sea coast are possible even without taking effects from rising mean sea level into account. The work presented is part of the ongoing project “Extreme North Sea Storm Surges and Their Consequences” (EXTREMENESS) and represents the first step towards an impact assessment for very severe storm surges which will serve as a basis for development of adaptation options and evaluation criteria.     

Recent Changes in Land Water Storage and its Contribution to Sea Level Variations

Sea level rise is generally attributed to increased ocean heat content and increased rates glacier and ice melt. However, human transformations of Earth’s surface have impacted water exchange between land, atmosphere, and ocean, ultimately affecting global sea level variations. Impoundment of water in reservoirs and artificial lakes has reduced the outflow of water to the sea, while river runoff has increased due to groundwater mining, wetland and endorheic lake storage losses, and deforestation. In addition, climate-driven changes in land water stores can have a large impact on global sea level variations over decadal timescales. Here, we review each component of negative and positive land water contribution separately in order to highlight and understand recent changes in land water contribution to sea level variations.     

Surge modelling in the eastern Irish Sea: present and future storm impact

It is believed that, in the future, the intensity and frequency of extreme coastal flooding events may increase as a result of climate change. The Natural Environment Research Council (NERC) Flood Risk from Extreme Events (FREE) project, Coastal Flooding by Extreme Events and EU FP7 Morphological Impacts and Coastal Risks Induced by Extreme Storm Events project are investigating the flood risks in the eastern Irish Sea, an area that includes most of England’s coastal types. Using a previously modelled and validated historical extreme surge event, in November 1977, we now investigate the changes in peak surge as a result of possible future climate conditions. In order to simulate the surge, we have set up a one-way nested approach, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System 3D baroclinic model, from a domain covering the whole NW European continental shelf, through to a 1.85 km Irish Sea model; both areas are forced by tides, atmospheric pressure and winds. We use this modelling system to investigate the impact of enhanced wind velocities and increased sea levels on the peak surge elevation and residual current pattern. The results show that sea level rise has greater potential to increase surge levels than increased wind speeds.     

Mechanisms controlling the intra-annual mesoscale variability of SST and SPM in the southern North Sea

Thermal and optical remote sensing data were used to investigate the spatial and temporal distribution of sea surface temperature (SST) and of suspended particulate matter (SPM) in the southern North Sea. Monthly SST composites showed pronounced seasonal warming of the southern North Sea and delineated the English coastal and continental coastal waters. The East-Anglia Plume is the dominant feature of the English coastal waters in the winter and autumn SPM composites, and the Rhine region of freshwater influence (ROFI), including the Flemish Banks, is the dominant feature of the continental waters. These mesoscale spatial structures are also influenced by the evolution of fronts, such as the seasonal front separating well-mixed water in the southern Bight, from the seasonally stratified central North Sea waters. A harmonic analysis of the SST and SPM images showed pronounced seasonal variability, as well as spring-neap variations in the level of tidal mixing in the East Anglia Plume, the Rhine ROFI and central North Sea. The harmonic analysis indicates the important role played by the local meteorology and tides in governing the SST and near-surface SPM concentrations in the southern North Sea. In the summer, thermal stratification affects the visibility of SPM to satellite sensors in the waters to the north of the Flamborough and Frisian Fronts. Haline stratification plays an important role in the visibility of SPM in the Rhine ROFI throughout the year. When stratified, both regions typically exhibit low surface SPM values. A numerical model study, together with the harmonic analysis, highlights the importance of tides and waves in controlling the stratification in the southern North Sea and hence the visibility of SPM.     

Sea level variability in the Gulf of Mexico since 1900 and its link to the Yucatan Channel and the Florida Strait flows

The long-term variability of sea level and surface flows in the Gulf of Mexico (GOM) is studied using global monthly sea level reconstruction (RecSL) for 1900–2015. The study explored the long-term relation between the dynamics of the GOM and inflows/outflows through the Yucatan Channel (YC) and the Florida Straits (FS). The results show a century-long trend of increased mean velocity and variability in the Loop Current (LC); however, no significant upward trend was found in the YC and FS flows, only increased variability. Empirical orthogonal function (EOF) analysis of sea surface height found spatial patterns dominated by variations in the LC and temporal variations on time scales ranging from a few months to multidecadal. The time evolution of each EOF mode of sea level is correlated with the velocity of either the LC, the YC, or the FS or some combination of the different flows. The mean sea level difference between the GOM and the northwestern Caribbean Sea was found to be influenced by the North Atlantic Oscillation (NAO), with unusually high differences during the 1970s when the NAO index was low and the Atlantic Ocean circulation was weak. Extreme peaks in SL difference coincide with the extension of the LC and the seasonal eddy shedding pattern. The observed seasonal cycle in the extension area of the LC as obtained from 20 years of altimeter data is significantly correlated (R = 0.63; confidence level = 98%) with the seasonal YC flow obtained from 116 years of the RecSL data. However, the same LC extension record had lower correlation (R = 0.45; confidence level = 90%) with the observed YC transport obtained from direct moored measurements over ~ 5 years, indicating the need for much longer measurements, since the LC extension and the YC flow are strongly affected by interannual and decadal variations. The study demonstrates the usefulness of even a coarse-resolution reconstruction for studies of regional ocean variability and climate change over longer time scales than current direct observations allow.

     

Long-term variations in river and sea factors responsible for the hydrological regime and morphological structure of the Thames River mouth area

General geographic features of the Thames River, its basin, and mouth area, consisting of the tidal mouth reach of the river, a large estuary, and an open nearshore zone of the river mouth (the North Sea coastal zone) are discussed. The peculiarities of river and sea hydrological factors responsible for the regime of the Thames River mouth area are described in detail. Characteristics of the river water runoff were specified and supplemented by the data on the river inundations in the area of London. Particular emphasis was placed on variations in the mean sea level in the area of the Thames River mouth as well as on specific features of tides and storm surges in the area of the sea inlet into the estuary. Main regularities in the estuary evolution during Holocene and present-day morphological processes in the Thames River mouth area were revealed.     

Seasonal drivers and patterns of sediment temperatures in a New England salt marsh

Salt marshes are globally important ecosystems and thus their resilience to climate change holds societal importance. To date, studies addressing salt marsh responses to climate change have focused on sea-level rise and biogeochemical feedbacks with increasing inundation. Less is known about how salt marsh sediment temperatures, which impact physical, biological, and chemical ecosystem processes, will respond to climate change. In this study, we present multi-depth sediment temperature and porewater level data from low-, mid-, and high-marsh sites at a New England salt marsh for a 1-year period and investigate how salt marsh sediment temperatures respond to atmospheric and oceanic forcing. We use spectral analyses to identify the frequencies at which sediment temperatures vary and link the temperature variations to specific forcing mechanisms. We find that all sites across the marsh responded to air temperature with roughly equal amplitude whereas the responses to radiative heating and ocean tides varied spatially. The high-marsh site is more sensitive to radiative heating than the mid- and low-marsh sites. The low-marsh is affected by tidal processes and inundation whereas the high- and mid-marsh sites are not. In addition, we find that the bulk thermal diffusivity of the saturated sediments decreases with distance from the tidal channel. These factors contribute to considerable temporal and spatial variability in sediment temperatures with elevation, distance from the tidal channel, and time of year (season) being most important.     

Interactions between wind and tidally induced currents in coastal and shelf basins

This paper addresses the impact of atmospheric variability on ocean circulation in tidal and non-tidal basins. The data are generated by an unstructured-grid numerical model resolving the dynamics in the coastal area, as well as in the straits connecting the North Sea and Baltic Sea. The model response to atmospheric forcing in different frequency intervals is quantified. The results demonstrate that the effects of the two mechanical drivers, tides and wind, are not additive, yet non-linear interactions play an important role. There is a tendency for tidally and wind-driven circulations to be coupled, in particular in the coastal areas and straits. High-frequency atmospheric variability tends to amplify the mean circulation and modify the exchange between the North and the Baltic Sea. The ocean response to different frequency ranges in the wind forcing is area-selective depending on specific local dynamics. The work done by wind on the oceanic circulation depends strongly upon whether the regional circulation is tidally or predominantly wind-driven. It has been demonstrated that the atmospheric variability affects the spring-neap variability very strongly.     

Interpreting the sea surface temperature warming trend in the Yellow Sea and East China Sea

Previous studies have demonstrated that the low-frequency sea surface temperature (SST) variability in the Yellow Sea and East China Sea (YECS) is linked to large-scale climate variability, but explanations on the mechanisms vary. This study examines the low-frequency variability and trends of some atmospheric and oceanic variables to discuss their different effects on the YECS warming. The increasing temperature trend is also observed at a hydrographic section transecting the Kuroshio. The increasing rate of ocean temperature decreases with depth, which might result in an increase in vertical stratification and a decrease in vertical mixing, and thus plays a positive role on the YECS warming. The surface net heat flux (downward positive) displays a decreasing trend, which is possibly a result of the YECS warming, and, in turn, inhibits it. Wind speeds show different trends in different datasets, such that its role in the YECS warming is uncertain. The trends in wind stress divergence and curl have large uncertainties, so their effects on SST warming are still unclear. The Kuroshio heat transport calculated in this study, displays no significantly increasing trend, so is an unlikely explanation for the SST warming. Limited by sparse ocean observations, sophisticated assimilative climate models are still needed to unravel the mechanisms behind the YECS warming.