Minute Sea-Level Analysis (MISELA): a high-frequency sea-level analysis global dataset

Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research on sea-level extremes is restricted to hourly datasets, which prevent the quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter-period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low tidal basins. Therefore, a new global 1 min sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T<2 h) obtained from 331 tide-gauge sites (https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites, and lengths of time series. The dataset is appropriate for global, regional or local research of atmospherically induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments.

The role of geological mouth islands on the morphodynamics of back-barrier tidal basins

The morphodyamics of back-barrier tidal basins have been extensively investigated by numerical modelling, but the influence of mouth islands (which may be submerged under future sea level rise) has been rarely explored. Using the Dongshan Bay in southern China as a reference site, we explore numerically the effects of geological constraints (i.e., islands) on the long-term morphodynamics of back-barrier basins. Model results indicate that the spatial configuration of mouth islands can considerably affect the morphological development of tidal basins. The presence of mouth islands can increase both the current velocity and the residual current by narrowing the inlet cross-sectional area, resulting in more sediment suspension and transport. Meanwhile, erosion tends to occur in the tidal basin and sedimentation occurs in the ebb-delta area, and the erosion (or sedimentation) volume is larger with the presence of more mouth islands. Further, the spatial distribution of mouth islands can also considerably affect tidal basin evolution: the basin-side mouth islands tend to cause more basin erosion with higher tidal currents and more sediment transport, while the delta-side ones may play a hindering role resulting in sediment deposition in the basin. Finally, larger tidal prisms are observed in basins with more mouth islands and those with basin-side mouth islands, suggesting that the number and location of mouth islands can also affect the empirical relation between tidal prism and inlet cross-sectional area. This modelling study furthers the understanding of barrier basin morphodynamics affected by mouth islands and informs management strategies under a changing environment.

MISELA: 1-minute sea-level analysis global dataset

Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research of sea-level extremes is restricted to hourly datasets, which prevent quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low-tidal basins. Therefore, a new global 1-minute sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T < 2 h) obtained from 331 tide-gauge sites (https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality-control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites and lengths of time-series. The dataset is appropriate for global, regional or local research of atmospherically-induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments.

Reef-building oysters record seasonal variations in water mass-properties of tidal basins from the Central Wadden Sea (North Sea)

&lt;p&gt;Before proxy records can be reliably employed in palaeoclimate research, calibration studies have to be conducted to assess the confidence intervals of the respective proxies. Here, we use shells of the fast growing Pacific oyster &lt;em&gt;Magallana gigas&lt;/em&gt; from the Central Wadden Sea, North Sea, a temperate barrier island-backbarrier tidal flat-salt marsh system with large seasonal changes of water mass-properties, for the calibration of geochemical proxies. &lt;em&gt;M. gigas&lt;/em&gt; represents a non-native invasive species that rapidly develops oyster reefs. Calcite shells of two specimens from the intertidal and subtidal zones were sampled in high resolution yielding sub-monthly data sets. The time period represented in the shell, based on &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O age modelling, was estimated at 8-10 years and the growth of the shells was restricted from (late) spring to (early) autumn of each year. Mg/Ca, Mn/Ca and Sr/Ca ratios of the intertidal and subtidal specimens show similar seasonal patterns. Mg/Ca and Sr/Ca ratios are investigated as high-resolution sea surface temperature (SST) proxies. Important ontogenetic effects (i.e., increasing time-averaging with increasing age) as well as intra-species variability are discussed as limiting factors for the proxy development. Intertidal Mg/Ca ratios show only a significant correlation to the high-resolution SST record of the Central Wadden Sea when the early ontogenetic stage is considered. Sr/Ca ratios were comparable in terms of absolute values and amplitudes to those of &lt;em&gt;M. gigas&lt;/em&gt; in the Northern Wadden Sea, but amplitudes were decreasing with increasing ontogeny. These findings seriously hamper the application of Mg/Ca and Sr/Ca for reliable palaeotemperature reconstructions regardless of ontogenetic stage. The Mn/Ca ratios were investigated as proxy for Mn cycling in tidal basins, where it is interrelated with seasonal changes in primary production. In addition to the generally observed seasonal variability of the Mn/Ca records, the subtidal Mn/Ca is significantly elevated compared to intertidal Mn/Ca. The subtidal Mn/Ca offset likely reflects differences in Mn cycling in tidal settings and could, therefore, serve in the palaeorecord as indicator to differentiate inter- and subtidal habitats in the same embedding sedimentary facies. This habitat effect has to be considered as an important factor besides environmental change when interpreting the high-resolution proxy record of fossil oysters.&lt;/p&gt;

Intertidal floodplain controls on centennial-scale morphological channel development

&lt;p&gt;Intertidal areas disappear in deltas worldwide because of land reclamations. This greatly impacts delta morphology because the presence and physiological characteristics of intertidal areas determine the tidal regime and, as a result, residual sediment transport patterns in tidal basins. Understanding how the interaction between intertidal areas and channels in tidal basins in&amp;#64258;uence morphodynamics is therefore important to predict morphological development and to assess the resilience of delta&amp;#8217;s to changing boundary conditions.&lt;/p&gt;&lt;p&gt;In the Ems estuary (The Netherlands), the gradual embankment of a large intertidal embayment altered the planform and cross-sectional geometry of the estuary, leading to changes in the tidal regime and associated residual sediment transport patterns. As early as 1952, it was already suggested that these changes eventually caused a shift towards an alternative historical development of the geometric con&amp;#64257;guration of the channels; from a multiple to a single channel system.&lt;/p&gt;&lt;p&gt;This study shows through centennial-scale morphological modelling that the observed system shift can be hind-casted, while conserving model validity by comparison to the observed gross morphodynamics trends. The results indicate that the system shift is indeed driven by land reclamations. This provides a unique case to study the processes leading to the observed developments and evaluate the value of tidal-asymmetry based stability relationships to predict regime shifts in estuarine development.&lt;/p&gt;