Relative Mean Sea Level Research Articles

Co-seismic change in ocean bottom topography: Implication to absolute global mean sea level change

Earthquakes perturb both the ocean bottom topography due to displacements of sea floor and the geoid due to mass redistribution, which induces the relative sea level (RSL) change. However, the relative global mean sea level (GMSL) change is zero in that sea water mass is conserved. But the absolute GMSL change is not zero because earthquakes displace total ocean mass with respect to the Earth's center of mass (CM) which remains unchanged after an earthquake. This displacement, i.e. the absolute GMSL change, may be detectable by altimetry since the satellites are orbiting around CM. In this paper, we proposed a method to estimate co-seismic absolute GMSL change caused by earthquakes based on the point dislocation theory for a spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth. This change can be directly connected to the perturbation of ocean bottom topography. We first computed co-seismic displacements as well as the change in geo-potential and solved the sea level equation to validate the insignificance of the oceans' feedback, i.e. the loading effect due to RSL change, to co-seismic displacements. The results imply that the loading effect due to RSL change is negligible on displacements while is considerable on geoid. We then computed the absolute GMSL change caused by co-seismic vertical and horizontal displacements by making use of the integrated Green's function method. The numerical results show that a large earthquake may raise the absolute GMSL by magnitude of sub-millimeter and the recent three large events cause GMSL to rise about one millimeter, in which the contribution from horizontal displacement is non-negligible.

Quantifying the impacts of human interventions on relative mean sea level change in the Pearl River Delta, China

Due to the impact of both natural and human-induced changes, the hydrological regimes of many river deltas worldwide have been experienced either gradual or abrupt shifts. However, little work has explored the relative impacts of natural and human-induced changes on the natural balance of these delta systems. This study explores the overall influences of intensive human interventions (e.g., dam constructions, sand excavations, and land reclamations) on the relative mean sea level (RMSL) changes in the Pearl River Delta (PRD) in China. The analysis uses long-term measurements based on monthly averaged RMSL in 26 stations and reproduces the RMSL that would have occurred in the absence of large-scale human interventions by means of a simple bivariate linear regression model. Generally, we observe that the RMSL dynamics can be categorized into three distinct types, descending, ascending and fluctuant, according to the Mann-Kendall trend test. The analysis shows that the RMSL in the upper and central parts of the PRD displays a significant descending tendency owing to the deepening of the channels, which is primarily attributed to large-scale sand excavation. In contrast, for stations near the outlets, we observed an ascending tendency in RMSL that can be attributed to the combined effects of both the rise in global sea level and channel extension due to large-scale land reclamations. The regression model confirms that the human interventions have greater impacts in the upper and central parts of the PRD that feature river-dominated dynamics, compared with the lower parts of the PRD that are characterized by tide-dominated dynamics. In addition, the simulated results display a marked seasonal alteration in the RMSL: the alteration induced by human interventions is apparently greater during the flood season than it is during the dry season. The proposed method used here to quantify the impacts of both natural and human-induced interventions on the RMSL is particularly useful for setting scientific guidelines for water managements (e.g., flood control and salt intrusion prevention) and regulation projects (e.g., dam constructions and land reclamations) in river deltas.

Investigating the Aerosol Optical Depth and Angstrom Exponent and Their Relationships with Meteorological Parameters Over Lahore in Pakistan

In the present work, AERONET (AErosol RObotic NETwork) data of 2006–2014 have been used to analyze the variations in aerosol optical depth (AOD) at 500 nm and Angstrom exponent (440/870) (AE). In order to have an in-depth knowledge of aerosol variability, we have analyzed the association of aerosol properties with the meteorological parameters such as temperature, mean sea level pressure, rainfall, dew point, and dust storm frequency. Long-term observations of MODIS-AOD are also validated with AERONET-AOD over Lahore. The peak monthly mean value of AOD is found in July (1.00 ± 0.34) with the corresponding AE value of 0.85 ± 0.29 pointing toward the fact that desert/soil dust aerosols dominated the atmosphere of Lahore. The lowest value of AOD is found in February (0.47 ± 0.26) with the corresponding AE value of 1.22 ± 0.29 representing the presence of urban/industrial aerosols in the atmosphere over Lahore. The monthly mean AE value is found to be maximum in January (1.36 ± 0.15), whereas lowest value of AE is found in June (0.55 ± 0.25). AOD shows positive correlations with temperature, dew point, relative humidity, visibility, rain and dust storm frequency, and negative with mean sea level pressure and wind speed. AE exhibits positive correlations with relative humidity and mean sea level pressure, while with temperature, dew point, visibility, rain and dust storm frequency, it shows negative correlations.

Mean relative sea level rise along the coasts of the China Seas from mid-20th to 21st centuries

Mean relative sea level (MRSL) rise has caused more frequent flooding in many parts of the world. The MRSL rise varies substantially from place to place. Here we use tide-gauge data and satellite measurements to examine past MRSL trends for the coasts of the China Seas. We then combine climate model output and satellite observations to provide MRSL projections in the 21st century. The MRSL trend based on tide-gauge data shows substantial regional variations, from 1 to 5mm/yr. The vertical land motion (VLM) based on altimetry and tide-gauge (ATG) data indicates large land subsidence at some tide-gauge locations, consistent with the Global Positioning Systems (GPS)-based VLM but different significantly from small uplift estimated by a Glacial Isostatic Adjustment (GIA) model, which suggests other important factors causing the VLM instead of the GIA process. When GPS- or ATG-based VLM estimates are used, the projected MRSL rise between 1986–2005 and 2081–2100 at tide-gauge sites varies from 60 to 130cm under the Representative Concentration Pathway 8.5 (RCP8.5) scenario of the Intergovernmental Panel on Climate Change (IPCC). Our projections are significantly larger than those of IPCC and other literature, as a result of accounting for the land subsidence derived from observations. Steric and dynamic ocean effects and land-ice melt effects are comparable (about 30cm each) and do not vary much over the tide-gauge locations. The VLM effect varies from −10 to 60cm. The projections between 1986–2005 and 2081–2100 under RCP4.5 show a similar spatial distribution to that under RCP8.5, with a smaller amount of rise by 18cm on average for this region.

Projected 21st Century Sea-Level Changes, Observed Sea Level Extremes, and Sea Level Allowances for Norway

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

Spatiotemporal changes of geomorphic environment in the Muriganga–Saptamukhi estuarine interfluve of Indian Sundarban in the context of climate change: a case study

The surface of the earth has been continuously sculptured by the exogenetic processes primarily by the climatic hydrological attributes. Over the sequential phases of evolution of earth, the climatic attributes have altered. The alternative processes such as glaciation and declaciation, fluctuations of sea level and variability in rainfall pattern have changed the surface configuration through maneuvering the operations of the geographical processes. The issue of climate change has become a matter of scientific concern all over the world as the human communities are facing severe problems manifested in the form of flood, drought and submergence of low-lying coastal regions, estuaries and deltas. The present study is an attempt to understand the nature and extent of climate change (1890–2012) and related sea level rise (1970s–2010) in the deltaic Sundarban region of India since the last century and how far they are impacting the erosion–depositional processes (1925, 1926–2014). The changing trend of mean annual temperature, rainfall pattern and frequencies of tropical cyclones has been studied in detail, and spatiotemporal changes of geomorphic environment in different reaches of the study area have also been monitored with available multi-temporal geospatial data. The observation reveals that the flat sandy coastal belt and low-lying island in the extreme southern part have been severely affected by wave dash and seasonal storm surges which are mostly responsible for vigorous erosion. On the other hand, high tidal velocity is observed along the exposed concave bank in the upper–middle reaches of the Muriganga estuary and exposed outer bank in lower–middle reaches of Saptamukhi estuary. The thalweg line, which is very close to the river bank in those reaches of estuary, intensifies the hydraulic pressure along marginal parts of river bank which leads to erosion. Depositional activities are mostly observed along the sheltered inner reaches and convex river banks of the estuaries due to less effective tidal rushes, shallow channel depth, marginal flow velocity and gentle channel slope. Therefore, erosional and depositional processes cannot be explain by the relative mean sea level rise, because increasing mean sea level will affect the erosional processes uniformly in the entire estuary. In this present study area, both the erosional and depositional processes are simultaneously active depending on geographical exposure, sinuous channel pattern, channel depth and lithological compositions.

Reconstruction of Holocene relative sea-level change and residual uplift in the Lake Inba area, Japan

We collected and analyzed fossil diatoms and volcanic ash and determined 14C ages in core samples from the lowlands around Lake Inba in the eastern Kanto Plain, central Japan, an area where late Quaternary sea-level change, fluvial erosion, and tectonic uplift have affected a region of archeological interest. We inferred Holocene paleoenvironmental changes and relative sea levels on the basis of indicators, such as high tide levels, derived from fossil diatom assemblages as well as the stratigraphic positions of 14C-dated samples and the K–Ah tephra. Our results lead to estimates of the upper half tidal range during 6800–7000cal yr BP of 1.7m. The Holocene highstand took place at approximately 6400–6500cal yr BP, and mean sea level reached an elevation of 1.9m. However, the timing of this sea-level rise is earlier in the Lake Inba area than documented in previous studies, and it is suggested that the timing of the Holocene highstand may appear at least 1000years earlier as a result of Holocene residual uplift. After this, sea-level fell abruptly around 4000cal yr BP. We also recognized a sea-level fall corresponding to the Yayoi regression at about 2600cal yr BP, during which the mean relative sea level may have been as low as −2.5m after compensating for uplift, subsidence or geomorphologic effects in this area.

Nonlinear Change in Sea Level Observed at North American Tide Stations

ABSTRACT Boon, J.D. and Mitchell, M., 2015. Nonlinear change in sea level observed at North American tide stations. The rate at which coastal sea level is expected to rise or fall is of considerable interest to coastal residents and managers who view changes on the time scale of a 30-year mortgage. Analysis of historical records at North American tide stations provides evidence of recent nonlinear sea-level change at this scale using relative mean sea-level (RMSL) observations. RMSL tracks local inundation risk directly without the need to correct an accepted worldwide geocentric measure—e.g., global mean sea-level rise—with locally estimated vertical rate adjustments. Published RMSL linear trends provide essential information but are routinely compared between tide stations with widely varying record lengths, thereby obfuscating nonlinear change (acceleration or deceleration) over a specific period of time. Here monthly averaged RMSL data from 45 U.S. tide stations and one Canadian tide station are analy...

Changes in Mean Relative Sea Level around Canada in the Twentieth and Twenty-First Centuries

Trends in regional mean sea levels can be substantially different from the global mean trend. Here, we first use tide-gauge data and satellite altimetry measurements to examine trends in mean relative sea level (MRSL) for the coasts of Canada over approximately the past 50–100 years. We then combine model output and satellite observations to provide sea level projections for the twenty-first century. The MRSL trend based on historical tide-gauge data shows large regional variations, from 3 mm y−1 (higher than the global mean MRSL rise rate of 1.7 mm y−1 for 1900–2009) along the southeast Atlantic coast, close to or below the global mean along the Pacific and Arctic coasts, to –9 mm y−1 in Hudson Bay, as indicated by the vertical land motion. The combination of altimeter-measured sea level change with Global Positioning System (GPS) data approximately accounts for tide-gauge measurements at most stations for the 1993–2011 period. The projected MRSL change between 1980 and 1999 and between 2090 and 2099 under a medium-high climate change emission scenario (A2) ranges from −50 cm in northeastern Canada to 75 cm in southeastern Canada. Along the coast of the Beaufort Sea, the MRSL rise is as high as 70 cm. The MRSL change along the Pacific coast varies from −15 to 50 cm. The ocean steric and dynamical effects contribute to the rise in MRSL along Canadian coasts and are dominant on the southeast coast. Land-ice (glaciers and ice sheets) melt contributes 10–20 cm to the rise in MRSL, except in northeastern Canada. The effect of the vertical land uplift is large and centred near Hudson Bay, significantly reducing the rise in MRSL. The land-ice melt also causes a decrease in MRSL in northeastern Canada. The projected MRSL change under a high emission scenario (Representative Concentration Pathway 8.5) has a spatial pattern similar to that under A2, with a slightly greater rise in MRSL of 7 cm, on average, and some notable differences at specific sites.

Measuring sediment deposition and accretion on anthropogenic marshland – Part II: The adaptation capacity of the North Frisian Halligen to sea level rise

Low coastlands, marshlands and islands all over the world are challenged by rising water levels due to climatic changes. The adaptation capacity of such lowlands is based on frequent inundations and according sedimentation processes. Exemplarily, a system of small islands west of Northern Germany was investigated over three years. At three out of ten so-called Halligen located in the Wadden Sea, the adaptation capacity of the anthropogenic marshland was determined. The Halligen Hooge, Langeness and Nordstrandischmoor have surface elevations only a few decimetres above mean high water and have to cope with an inundation frequency of nowadays up to 22 times per year. By use of methods introduced in Schindler et al. (2014, this volume) in combination with a 137Cs and 210Pb dating campaign on 12 sediment cores, vertical accretion rates were measured and detailed sediment accretion patterns presented. A good agreement was found between the used methods to calculate long term and short term marshland accretion rates. Sediment deposition and vertical marshland accretion is mainly controlled by the high tide events (single storm surges). Coastal protection structures, established in the early 20th century, decrease the inundation frequency and hinder the efficiency of the sediment transport by the tidal channel system on the Halligen. Vertical marshland accretion based on 210Pb dating for the time span 1915–2011 (1.0 ± 0.3 mm/a, Hooge, 1.2 ± 0.3 mm/a, Langeness and 2.6 ± 0.9 mm/a, Nordstrandischmoor) is in disequilibrium with the fast increasing mean high water level (MHW, 5.0 ± 0.3 mm/a). Projections until 2100 revealed that the extreme values (highest high waters, HHW) tend to rise much faster than the MHW or relative mean sea level (RMSL). Therefore an increasing hazard potential for the Halligen has to be expected if vertical marshland accretion does not accelerate in the future.

English

Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time at a given location. It is carried out by collecting quantitative data about the current state of the atmosphere and past and/or present experiences. In this study Adaptive Neuro-Fuzzy Inference System (ANFIS) and Multiple linear regression model were used to analyze metrological data sets obtained from the metrological station. The Multiple linear regression model is simple due to the fact that it uses simple mathematical equation using Multiple Linear Regression (MLR) equations that can be easily understood by a medium educated farmer. Adaptive Neuro- Fuzzy Inference Systems (ANFIS) combines the capabilities of Artificial Neural Networks (ANN) and Fuzzy Inference Systems (FIS) to solve different kinds of problems.The data covers a five year period (2008-2012) were for the monthly means of minimum and maximum temperature, wind speed, and relative humidity and mean sea level pressure (MSLP). The results showed that both models could be applied to weather prediction problems. The performance evaluation of the two models that was carried out on the basis of root mean square error (RMSE) showed that the ANFIS model yielded better results than the multiple linear regression (MLR) model with a lower prediction error.

Mean sea level changes near Weizhou island from 1969 to 2010

Tidal data from Weizhou, Zhapo, and Shanwei stations between 1969 and 2010 and from five gauging stations in the western Pacific Ocean provided by PSMSL, and the global mean sea level data recorded between December 1992 and December 2010 by TOPEX and Jason satellites were compiled and analyzed. The results show that the perennial mean sea level near Weizhou Island is 211.7 cm (relative to the water gauge zero), and the relative mean sea level rising rate is 2.2 mm yr−1 from 1969 to 2010, which is consistent with the relative mean sea level rising rate recorded at other gauging stations in the western Pacific regions and with the global mean sea level rising rate. The absolute mean sea level rising rate at Weizhou Island is 3.0 mm yr−1 from 1993 to 2010, also conforming with the global mean sea level rising rate (3.1±0.4 mm yr−1) during the same time period. The highest annual tide level at Weizhou Island has a rising rate of 4.6 mm yr−1 and shows a 20-year quasi-periodic variation from 1966 to 2010. The primary cause of the mean sea level rising is global warming.

Anomalous MIS 7 sea level recorded on Bermuda

Three new U-series ages from coral fragments found in the Belmont Formation of Bermuda fall in a range of ∼198 ka to ∼196 ka. These late MIS 7 ages are consistent with those of ∼201 ka and ∼199 ka measured in a previous study. The disputed interpretation of the Belmont Formation as a unit that is allostratigraphically distinct from subsequent MIS 5e deposits, of the Rocky Bay Formation, is vindicated by a minimum age of 196 ± 3 ka for the total of 6 coral fragments it has yielded. Emergent marine deposits of the Belmont Formation include sedimentary lithofacies that are considered to be reliable relative sea level indicators. Prominent among these is a facies representing the “beach step”: a feature that develops sub-tidally, directly at the base of the swash zone. From this facies, and others preserved along 6 km of Belmont Formation coastal exposure, it is concluded that MIS 7 relative mean sea level reached +4.5 m, and likely peaked at or above +6.0 m, relative to present sea level at Bermuda. Lower MIS 7 sea level positions that are evidenced and that have been quoted, in the past, are considered transitory positions, not maxima. The MIS 7 sea-level elevations on Bermuda, reconstructed in this study, are above the majority of those reported from elsewhere in the world. This challenges the long-standing notion of Bermuda as a vertically stable “tide-gauge”, but is consistent with glacio-hydroisostatic models which predict land-mass subsidence at intermediate field sites, such as Bermuda, at the end of long interglacials. However, because of evidence of instability at Bermuda in the form of seismic activity and faulting, which require further investigation, judgement is reserved on the global implications of this palaeo-sea-level anomaly.

Secular Trends in Tidal Parameters along the Coast of Japan

The secular trends for local tidal datums, tide ranges, and tidal harmonic constituents at 13 tidal gauge stations located along the coast of Japan were analyzed in this study. The general trends for mean higher high water (MHHW), mean high water (MHW), diurnal tide range (DTR), mean tide range (MTR), and relative mean sea level (RMSL) were positive, and for mean lower low water (MLLW) and mean low water (MLW) the trends were negative. The variation patterns were largest at Kushiro and Ofunato stations, both located in the open waters of the North Pacific Ocean. The tidal datums and tide ranges remained fairly stable at the Hakodate station, and an opposite trend was observed at the Maisaka station. The analysis of tidal harmonic constituents revealed a less pronounced pattern. The most distinct trend was observed for the M2 amplitude, which appears to be negative at a majority of the stations. The largest decrease in the M2 amplitude was observed at Kushimoto and Mera stations, also located in the open waters of the North Pacific Ocean. The negative trend is attributed to decreasing water depths at these stations, owing to small-scale local processes.

Regional differences of relative sea level changes in the Northwest Atlantic: Historical trends and future projections

Mean sea level is one of the most important indicators for climate variability and change. Here, we use tide‐gauge data and satellite measurements to examine recent trends in the mean relative sea level (RSL) in the Northwest Atlantic. We then combine model output and satellite observations to provide sea level projections in the 21st century. The mean RSL trend based on historical tide‐gauge data shows large regional variations, from 2 to 4 mm/yr (above the global mean RSL rise rate) in the southeast to −2 mm/yr in the northwest along East Canada. This spatial difference can to a large degree be attributed to that in the vertical land motion measured by the Global Positioning System (GPS). The combination of altimeter‐measured sea level change with the GPS data can approximately account for tide‐gauge measurements at most stations over 1993–2011. When the GPS data are used, the projected mean RSL rise between 1980–1999 and 2090–2099 ranges from 38 to 63 cm along the Scotia‐Fundy and Newfoundland coasts and smaller along Labrador, the northern Gulf of St. Lawrence, and the St. Lawrence Estuary. In spite of considerable uncertainties the ocean steric and dynamical effect is the dominant contributor (35–70 cm) to the RSL rise along the Canadian east coast. The land‐ice (glaciers and ice sheets) melt contributes to the RSL rise by 10–15 cm except at Nain where it is negligible. The effect of the vertical land uplift is large (40–50 cm) at Nain, Sept‐iles and Rimouski, significantly reducing the magnitude of the RSL rise.

Rapid rise in effective sea-level in southwest Bangladesh: Its causes and contemporary rates

Evidence is presented from three estuarine tide gauges located in the Sundarban area of southwest Bangladesh of relative sea level rise substantially in excess of the generally accepted rates from altimetry, as well as previous tide-gauge analyses. It is proposed that the difference arises from the use of Relative Mean Sea Level (RMSL) to characterise the present and future coastal flood hazard, since RMSL can be misleading in estuaries in which tidal range is changing. Three tide gauges, one located in the uninhabited mangrove forested area (Sundarban) of southwest Bangladesh, the others in the densely populated polder zone north of the present Sundarban, show rates of increase in RMSL ranging from 2.8mma−1 to 8.8mma−1. However, these trends in RMSL disguise the fact that high water levels in the polder zone have been increasing at an average rate of 15.9mma−1 and a maximum of 17.2mma−1. In an area experiencing tidal range amplification, RMSL will always underestimate the rise in high water levels; consequently, as an alternative to RMSL, the use of trends in high water maxima or ‘Effective Sea Level Rise’ (ESLR) is adopted as a more strategic parameter to characterise the flooding hazard potential. The rate of increase in ESLR is shown to be due to a combination of deltaic subsidence, including sediment compaction, and eustatic sea level rise, but principally as a result of increased tidal range in estuary channels recently constricted by embankments. These increases in ESLR have been partially offset by decreases in fresh water discharge in those estuaries connected to the Ganges. The recognition of increases of the effective sea level in the Bangladesh Sundarban, which are substantially greater than increases in mean sea level, is of the utmost importance to flood management in this low-lying and densely populated area.

Reconstruction of a two-century long sea level record for the Pertuis d’Antioche (France)

This paper describes the work of sea level data rescue, digitization, reduction to a common vertical reference and quality control leading to the reconstruction of a time series for the Atlantic NW coast of France (Pertuis d’Antioche). A total of 14 sea level data sets were merged to build a consistent composite time series of monthly and annual mean sea levels spanning 188 years (1824–2011).The estimation of a linear trend for this time series yields a relative mean sea level rise for the region of 1.3±0.1mmyr−1 for the whole study period, and 1.9±0.2mmyr−1 for the 20th century, consistent with previous studies in the region. This work evidences the importance of data archaeology in the pursuing of historical information useful for sea level studies, which can be relevant for climate research and coastal management amongst other applications.

Influence of various land surface parameterization schemes on the simulation of Western Disturbances

Five western disturbances (WDs) are simulated using the National Center for Atmospheric Research (NCAR) Weather Research and Forecasting (WRF) model with different land surface parameterization (LSP) schemes. The LSP schemes used in this study are thermal diffusion, Noah and rapid update cycle (RUC). The spatial distribution and area averaged values of 24 h accumulated rainfall simulated by the model using above LSP schemes are compared with corresponding Tropical Rainfall Measuring Mission (TRMM) observed values. The model simulated rainfall is also compared with those obtained from India Meteorological Department (IMD) station observations. Area averaged root mean square error (RMSE) in rainfall obtained from the three LSP schemes for the five cases are also compared against those in TRMM. Results show that the rainfall obtained using the RUC LSP scheme is closer to the observed values in comparison to those obtained in the thermal diffusion and Noah LSP schemes. It is clear from the results that circulation features and precipitation amounts obtained by the model are sensitive to LSP schemes. Compared to the verification analysis, the wind patterns at 850, 500 and 200 hPa are simulated by the model with reasonable accuracy. The relative humidity and mean sea level pressure are also well simulated by the model when RUC LSP is used. Copyright © 2013 Royal Meteorological Society

Signatures of sea level changes on tidal geomorphology: Experiments on network incision and retreat

How do tidal networks respond to changes in relative mean sea level (RMSL)? The question on whether the morphological features of a tidal landscape retain signatures of past environmental forcings, or are in equilibrium with current ones, is critical to our prediction of the fate of residual tidal landforms. In the case of tidal networks, the issue is quite relevant owing to their fundamental role on landscape eco‐morphodynamic evolution. Here we explore the response of tidal networks to cyclic variations in RMSL triggering tidal prism changes on the basis of laboratory experiments carried out in a synthetic lagoonal environment. A decrease in the tidal prism leads to network retreat and contraction of channel cross sections. Conversely, an increase in the tidal prism promotes network re‐incision and re‐expansion of channel cross sections: Network retreat and expansion tend to occur within the same planar blueprint. Our results show that the drainage density of tidal channels is linearly related to the landscape‐forming prism, although this relation is speculated to hold with reasonable approximation as a statistical tendency rather than as a pointwise, instantaneous adaptation. Changes in tidal prism rapidly influence network efficiency in draining the intertidal platform and the related transport of water, sediments, nutrients and pollutants. This bears important consequences for quantitative predictions of the long‐term ecomorphological adaptation of the tidal landscape to RMSL changes.

The long sea level record at Cadiz (southern Spain) from 1880 to 2009

[1] Mean sea level observations from an historical tide gauge located in Cadiz (Southern Spain) spanning the period 1880–1924 were recovered from national archives. Daily sea level averages stored in handwritten log books were digitized, quality controlled, and referred to the same benchmark. A careful analysis of all the high precision leveling surveys available in the area of the tide gauge enabled the establishment of a common datum with a modern record starting in 1961 from another tide gauge located only 2.5 km apart, with accuracy better than 5 mm. As a result, a consistent daily mean sea level record from 1880 to 2009 was constructed. The 20th century relative mean sea level rise in Cadiz is 0.7 ± 0.1 mm yr−1, which becomes 1.0 ± 0.2 mm yr−1 once corrected for vertical land movement with high precision GPS data, in agreement with nearby records. The analysis of the seasonal sea level cycle indicated that the amplitude of the annual cycle has increased during the 20th century. This work evidences the significance of sea level data rescue for present-day climate research.