Response of sediment grain size to sea-level rise during the middle Holocene on the west coast of the Gulf of Thailand

<p>Coastal flooding worldwide causes the vast majority of natural disasters; for the UK costing &#163;2.2 billion/year. Fluvial and surge-tide extremes can occur synchronously resulting in combination flooding hazards in estuaries, intensifying the flood risk beyond fluvial-only or surge-only events. Worse, this flood risk has the potential to increase further in the future as the frequency and/or intensity of these drivers change, combined with projected sea-level rise. Yet, the sensitivity of contrasting estuaries to combination and compound flooding hazards at sub-daily scales &#8211; now and in the future &#8211; is unclear. Here, we investigate the dependence between fluvial and surge interactions at sub-daily scales for contrasting catchment and estuary types (Humber vs. Dyfi, UK), using 50+ years of data: 15-min fluvial flows and hourly sea levels. Additionally, we simulate intra-estuary (<50&#160;m resolution) sensitivities to combination flooding hazards based on: (1) realistic extreme events (worst-on-record); (2) realistic events with shifted timings of the drivers to maximise flooding; and (3) modified drivers representing projected climate change.</p><p>For well-documented flooding events, we show significant correlation between skew surge and peak fluvial flow, for the Dyfi (small catchment and estuary with a fast fluvial response on the west coast of Britain), with a higher dependence during autumn/winter months. In contrast, we show no dependence for the Humber (large catchment and estuary with a slow fluvial response on the east coast of Britain). Cross-correlation results, however, did show correlation with a time lag (~10 hours). For the Dyfi, flood extent was sensitive to the relative timing of the fluvial and surge-tide drivers. In contrast, the relative timing of these drivers did not affect flooding in the Humber. However, extreme fluvial flows in the Humber actually reduced water levels in the outer estuary, compared with a surge-only event. Projected future changes in these drivers by 2100 are likely to increase combination flooding hazards: sea-level rise scenarios predicted substantial and widespread flooding in both estuaries. However, similar increases in storm surge resulted in a greater seawater influx, altering the character of the flooding. Projected changes in fluvial volumes were the weakest driver of estuarine flooding. On the west coast of Britain containing many small/steep catchments, combination flooding hazards from fluvial and surges extremes occurring together is likely. Moreover, high-resolution data and hydrodynamic modelling are necessary to resolve the impact and inform flood mitigation methodology.</p>

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Magnetic Properties of a Holocene Sediment Core from the Yeongsan Estuary, Southwest Korea: Implications for Diagenetic Effects and Availability as Paleoenvironmental Proxies

Frontiers in Earth Science ◽

10.3389/feart.2021.593332 ◽

2021 ◽

Vol 9 ◽

Author(s):

Hyeon–Seon Ahn ◽

Jaesoo Lim ◽

Sung Won Kim

Keyword(s):

Grain Size ◽

Magnetic Properties ◽

Magnetic Susceptibility ◽

South Korea ◽

Size Distribution ◽

Sea Level ◽

West Coast ◽

Magnetic Minerals ◽

The West ◽

Saturation Moment

The sensitivity of magnetic properties, which characterize the mineralogy, concentration, and grain size distribution of magnetic minerals, to environmental processes may provide useful information on paleoenvironmental changes in estuarine environments. Magnetic property studies of estuaries are less common than other environments and, due to the west coast of South Korea having an abundance of estuaries, it provides a good place to study these processes. In this study, we analyzed a variety of magnetic properties based on magnetic susceptibility, hysteresis parameters, progressive acquisition of isothermal remanent magnetization and first-order reversal curve data from a Holocene muddy sediment core recovered from the Yeongsan Estuary on the west coast of South Korea. We examined diagenetic effects on magnetic properties and tested their availability as proxies of paleoenvironmental change. The presence of generally low magnetic susceptibility, ubiquitous greigite-like authigenic magnetic component, and very fine magnetic particle occurrence suggested that the analyzed sediments had undergone considerable early diagenetic alteration. Electron microscopic observations of magnetic minerals support this suggestion. Our results confirm that the use of initial bulk susceptibility as a stand-alone environmental change proxy is not recommended unless it is supported by additional magnetic analyses. We recognized the existence of ferromagnetic-based variabilities related to something besides the adverse diagenetic effects, and have examined possible relationships with sea-level and major climate changes during the Holocene. The most remarkable finding of this study is the two distinct intervals with high values in magnetic coercivity (Bc), coercivity of remanence (Bcr), and ratio of remanent saturation moment to saturation moment (Mrs/Ms) that were well coincident with the respective abrupt decelerations in the rate of sea-level rise occurred at around 8.2 and 7 thousand years ago. It is then inferred that such condition with abrupt drop in sea-level rise rate would be favorable for the abrupt modification of grain size distribution toward more single-domain-like content. We modestly propose consideration of the Bc, Bcr, and Mrs/Ms variability as a potential indicator for the initiation/occurrence of sea-level stillstand/slowstand or highstand during the Holocence, at least at estuarine environments in and around the studied area.

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Assessment of Sea Level Rise at West Coast of Portugal Mainland and Its Projection for the 21st Century

10.20944/preprints201902.0113.v1 ◽

2019 ◽

Author(s):

Carlos Antunes

Keyword(s):

Time Series ◽

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

West Coast ◽

Satellite Altimetry ◽

Tide Gauge ◽

The West ◽

Relative Sea Level ◽

Global Sea Level

Data collected at the Cascais tide gauge, located on the west coast of Portugal Mainland, have been analyzed and sea level rise rates have been updated. Based on a bootstrapping linear regression model and on polynomial adjustments, time series are used to calculate different empirical projections for the 21st century sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent to an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Appling the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of composed vertical land velocity from tectonic and post-glacial isostatic adjustment, and residual synoptic regional dynamic effects rather than a trend. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland.

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Response of tidal flow regime and sediment transport in North Male' Atoll, Maldives to coastal modification and sea level rise

10.5194/os-2020-80 ◽

2020 ◽

Author(s):

Shuaib Rasheed ◽

Simon C. Warder ◽

Yves Plancherel ◽

Matthew D. Piggott

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Sea Level Rise ◽

Sea Level ◽

Land Reclamation ◽

Tidal Flow ◽

Sediment Grain Size ◽

Sediment Distribution ◽

Time Periods ◽

The Impact

Abstract. Changes to coastlines and bathymetry alter tidal dynamics and associated sediment transport process, impacting upon a number of threats facing coastal regions, including flood risk and erosion. Especially vulnerable are coral atolls such as those that make up the Maldives archipelago which has undergone significant land reclamation in recent years and decades, and is also particularly exposed to sea level rise. Here we develop a tidal model of Male' Atoll, Maldives, and use it to assess potential changes to sediment grain size distributions under sea level rise and coastline alteration scenarios. The results indicate that the impact of coastline modification over the last two decades at the island scale is not limited to the immediate vicinity of the modified island, but can also significantly impact the sediment grain size distribution across the wider atoll basin. Additionally, the degree of change in sediment distribution which can be associated with sea level rise that is projected to occur over relatively long time periods is predicted to occur over far shorter time periods with coastline changes, highlighting the need to better understand, predict and mitigate the impact of land reclamation and other coastal modifications before conducting such activities.

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Coldspot of Decelerated Sea-Level Rise on the Pacific Coast of North America

Quaestiones Geographicae ◽

10.1515/quageo-2016-0024 ◽

2016 ◽

Vol 35 (3) ◽

pp. 31-37 ◽

Cited By ~ 7

Author(s):

Albert Parker

Keyword(s):

United States ◽

Sea Level Rise ◽

Sea Level ◽

San Francisco ◽

West Coast ◽

Average Rate ◽

The United States ◽

The West ◽

Sea Levels

Abstract We show here the presence of significant “coldspot” of sea level rise along the West Coast of the United States and Canada (including Alaska). The 30-years sea level for the area are mostly falling also at subsiding locations as San Francisco and Seattle where subsidence is responsible for a long term positive rate of rise. The 20 long term tide gauges of the area of length exceeding the 60-years length have a naïve average rate of rise −0.729 mm/year in the update 30-Apr-2015, down from −0.624 mm/year in the update 14-Feb-2014. Therefore, along the West Coast of the United States and Canada the sea levels are on average falling, and becoming more and more negative.

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Holocene Sea-Level Rise Recorded by a Radiocarbon-Dated Mussel in a Submerged Speleothem beneath the Mediterranean Sea

Quaternary Research ◽

10.1006/qres.1996.0024 ◽

1996 ◽

Vol 45 (2) ◽

pp. 241-244 ◽

Cited By ~ 24

Author(s):

Fabrizio Antonioli ◽

Marco Oliverio

Keyword(s):

Sea Level Rise ◽

Mediterranean Sea ◽

Sea Level ◽

West Coast ◽

Mussel Shell ◽

The West ◽

Relative Sea Level ◽

Temperate Area ◽

Report Data ◽

Lithophaga Lithophaga

AbstractFossil shells of the boring mussel Lithophaga lithophaga provide a means for dating changes in relative sea level. These bivalves, being among the first colonizers of bare calcareous substrates, can mark the earliest stages of marine submergence of caves. Here we report data concerning the deepest submerged speleothem presently sampled in a temperate area, at 48 m below present sea level off the west coast of Italy (Mediterranean Sea). A fossil mussel shell beneath encrusting layers from later marine colonists gave an AMS age of 9580 ± 35 14C yr B.P. (10,253 ± 72 cal yr B.P.).

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Response of tidal flow regime and sediment transport in North Malé Atoll, Maldives, to coastal modification and sea level rise

Ocean Science ◽

10.5194/os-17-319-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 319-334

Author(s):

Shuaib Rasheed ◽

Simon C. Warder ◽

Yves Plancherel ◽

Matthew D. Piggott

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Sea Level Rise ◽

Sea Level ◽

Land Reclamation ◽

Transport Processes ◽

Sediment Grain Size ◽

Sediment Distribution ◽

Time Periods ◽

The Impact

Abstract. Changes to coastlines and bathymetry alter tidal dynamics and associated sediment transport processes, impacting upon a number of threats facing coastal regions, including flood risk and erosion. Especially vulnerable are coral atolls such as those that make up the Maldives archipelago, which has undergone significant land reclamation in recent years and decades and is also particularly exposed to sea level rise. Here we develop a tidal model of Malé Atoll, Maldives, the first atoll-scale and multi-atoll-scale high-resolution numerical model of the atolls of the Maldives and use it to assess potential changes to sediment grain size distributions in the deeper atoll basin, under sea level rise and coastline alteration scenarios. The results indicate that the impact of coastline modification over the last two decades at the island scale is not limited to the immediate vicinity of the modified island but can also significantly impact the sediment grain size distribution across the wider atoll basin. Additionally, the degree of change in sediment distribution which can be associated with sea level rise that is projected to occur over relatively long time periods is predicted to occur over far shorter time periods with coastline changes, highlighting the need to better understand, predict and mitigate the impact of land reclamation and other coastal modifications before conducting such activities.

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