The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Shu Gao - One of the best experts on this subject based on the ideXlab platform.

  • Modeling the effect of progressive grain-size sorting on the scale dependence of back-barrier tidal basin morphology
    Continental Shelf Research, 2014
    Co-Authors: Yunwei Wang, Shu Gao, Burg Flemming
    Abstract:

    Two categories of empirical relationships between morphological parameters and spatial scale factors have been studied by field observations of tidal basins along the Dutch and German North Sea coast, one being about channel-flat system parameters, i.e., the relative channel area and the ratio of channel volume to tidal prism, the other on tidal flat morphology, i.e., the mean tidal flat elevation and the convexity of tidal flat Hypsometry. In the present study, the morphodynamic evolution of tidal basins has been coupled with grain size such that there was a constant feedback of the progressive gain-size sorting process on the morphological evolution itself. In order to investigate sorting effects on morphological scaling relationships, a series of numerical modeling exercises were carried out with multiple grain-size fractions in schematized rectangular back-barrier tidal basins similar to those found in the German Wadden Sea. To identify the effect of progressive grain-size sorting on the morphological evolution, the results of the multiple size-fraction model was compared with those of single fraction models. The comparison suggests that, although the same scaling relationships apply for the channel-flat system as a whole, the scaling of tidal flats proceeds at reduced rates, i.e., the tidal flat Hypsometry curves modeled with multiple fractions are almost identical to those with a single fraction for small basins but more convex-up for large basins. The former can be explained by the balance of erosion processes between mobile fine sediments and stable coarse grains, the latter by the increasing difference in grain size between upper and lower tidal flats.

  • Modelling the equilibrium Hypsometry of back-barrier tidal flats in the German Wadden Sea (southern North Sea)
    Continental Shelf Research, 2012
    Co-Authors: Yunwei Wang, Burg Flemming, Shu Gao
    Abstract:

    Abstract Hypsometry is the distribution of volume or horizontal surface area with respect to elevation. Some observations show contradictory scale-dependent characteristics of tidal flat hypsometries in back-barrier tidal basin environments, and traditional theory explains the flattening Hypsometry by relating concave-up hypsometries in low tidal range basins to the dominating influence of wind waves rather than tidal currents. In order to investigate these two problems, two series of numerical modelling exercises were carried out using schematized rectangular back-barrier tidal basins roughly corresponding to the tidal basins found in the German Wadden Sea. The results show that, in the equilibrium states of tidal basins, hypsometries of back-barrier tidal flats are dependent on the basin scale and tidal range. Thus, large basin areas and low tidal ranges favour strong concave-up hypsometries, whereas small basin areas and high tidal ranges favour less concave-up hypsometries. Because wind waves were excluded in the model, these relationships are purely associated with tidal-current action. In addition to the traditional theory, which emphasises the relative importance of wind waves, the flattening of hypsometric profile shapes can, therefore, also be interpreted as a response to the relative area of intertidal areas or channels in the tidal basins. Thus, if tidal channels have relatively large areas, the development of tidal flats between channels is markedly restrained, the tidal flats being prevented from growing upward to higher elevations. As a result, strong concave-up hypsometries are formed that are associated with relatively large areas of low tidal flats and small areas of high tidal flats. As basins with large areas and low tidal ranges have large relative channel areas, this results in pronounced concave-up hypsometries, and vice versa.

Frank Kösters - One of the best experts on this subject based on the ideXlab platform.

  • Tidal response to sea level rise and bathymetric changes in the German Wadden Sea
    Ocean Dynamics, 2020
    Co-Authors: Benno Wachler, Rita Seiffert, Caroline Rasquin, Frank Kösters
    Abstract:

    Tidally dominated coasts are directly affected not only by projected rise in mean sea level, but also by changes in tidal dynamics due to sea level rise and bathymetric changes. By use of a hydrodynamic model, which covers the entire German Bight (South-Eastern North Sea), we analyse the effects of sea level rise and potential bathymetric changes in the Wadden Sea on tidal current velocities. The model results indicate that tidal current velocities in the tidal inlets and channels of the Wadden Sea are increased in response to sea level rise. This is explained by the increased ratio of tidal prism to tidal inlet cross-sectional area, which is due to the characteristic Hypsometry of tidal basins in the Wadden Sea including wide and shallow tidal flats and relatively narrow tidal channels. The results further indicate that sea level rise decreases ebb dominance and increases flood dominance in tidal channels. This is, amongst others, related to a decreased intertidal area again demonstrating the strong interaction between tidal wave and tidal basin Hypsometry in the Wadden Sea. The bathymetry scenario defined in this study includes elevated tidal flats and deepened tidal channels, which is considered a potential future situation under accelerated sea level rise. Application of these bathymetric changes to the model mostly compensates the effects of sea level rise. Furthermore, changes in current velocity due to the altered bathymetry are in the same order of magnitude as changes due to mean sea level rise. This highlights the significance of considering potential bathymetric changes in the Wadden Sea for regional projections of the tidal response to sea level rise.

Burg Flemming - One of the best experts on this subject based on the ideXlab platform.

  • Modeling the effect of progressive grain-size sorting on the scale dependence of back-barrier tidal basin morphology
    Continental Shelf Research, 2014
    Co-Authors: Yunwei Wang, Shu Gao, Burg Flemming
    Abstract:

    Two categories of empirical relationships between morphological parameters and spatial scale factors have been studied by field observations of tidal basins along the Dutch and German North Sea coast, one being about channel-flat system parameters, i.e., the relative channel area and the ratio of channel volume to tidal prism, the other on tidal flat morphology, i.e., the mean tidal flat elevation and the convexity of tidal flat Hypsometry. In the present study, the morphodynamic evolution of tidal basins has been coupled with grain size such that there was a constant feedback of the progressive gain-size sorting process on the morphological evolution itself. In order to investigate sorting effects on morphological scaling relationships, a series of numerical modeling exercises were carried out with multiple grain-size fractions in schematized rectangular back-barrier tidal basins similar to those found in the German Wadden Sea. To identify the effect of progressive grain-size sorting on the morphological evolution, the results of the multiple size-fraction model was compared with those of single fraction models. The comparison suggests that, although the same scaling relationships apply for the channel-flat system as a whole, the scaling of tidal flats proceeds at reduced rates, i.e., the tidal flat Hypsometry curves modeled with multiple fractions are almost identical to those with a single fraction for small basins but more convex-up for large basins. The former can be explained by the balance of erosion processes between mobile fine sediments and stable coarse grains, the latter by the increasing difference in grain size between upper and lower tidal flats.

  • Modelling the equilibrium Hypsometry of back-barrier tidal flats in the German Wadden Sea (southern North Sea)
    Continental Shelf Research, 2012
    Co-Authors: Yunwei Wang, Burg Flemming, Shu Gao
    Abstract:

    Abstract Hypsometry is the distribution of volume or horizontal surface area with respect to elevation. Some observations show contradictory scale-dependent characteristics of tidal flat hypsometries in back-barrier tidal basin environments, and traditional theory explains the flattening Hypsometry by relating concave-up hypsometries in low tidal range basins to the dominating influence of wind waves rather than tidal currents. In order to investigate these two problems, two series of numerical modelling exercises were carried out using schematized rectangular back-barrier tidal basins roughly corresponding to the tidal basins found in the German Wadden Sea. The results show that, in the equilibrium states of tidal basins, hypsometries of back-barrier tidal flats are dependent on the basin scale and tidal range. Thus, large basin areas and low tidal ranges favour strong concave-up hypsometries, whereas small basin areas and high tidal ranges favour less concave-up hypsometries. Because wind waves were excluded in the model, these relationships are purely associated with tidal-current action. In addition to the traditional theory, which emphasises the relative importance of wind waves, the flattening of hypsometric profile shapes can, therefore, also be interpreted as a response to the relative area of intertidal areas or channels in the tidal basins. Thus, if tidal channels have relatively large areas, the development of tidal flats between channels is markedly restrained, the tidal flats being prevented from growing upward to higher elevations. As a result, strong concave-up hypsometries are formed that are associated with relatively large areas of low tidal flats and small areas of high tidal flats. As basins with large areas and low tidal ranges have large relative channel areas, this results in pronounced concave-up hypsometries, and vice versa.

Yunwei Wang - One of the best experts on this subject based on the ideXlab platform.

  • Modeling the effect of progressive grain-size sorting on the scale dependence of back-barrier tidal basin morphology
    Continental Shelf Research, 2014
    Co-Authors: Yunwei Wang, Shu Gao, Burg Flemming
    Abstract:

    Two categories of empirical relationships between morphological parameters and spatial scale factors have been studied by field observations of tidal basins along the Dutch and German North Sea coast, one being about channel-flat system parameters, i.e., the relative channel area and the ratio of channel volume to tidal prism, the other on tidal flat morphology, i.e., the mean tidal flat elevation and the convexity of tidal flat Hypsometry. In the present study, the morphodynamic evolution of tidal basins has been coupled with grain size such that there was a constant feedback of the progressive gain-size sorting process on the morphological evolution itself. In order to investigate sorting effects on morphological scaling relationships, a series of numerical modeling exercises were carried out with multiple grain-size fractions in schematized rectangular back-barrier tidal basins similar to those found in the German Wadden Sea. To identify the effect of progressive grain-size sorting on the morphological evolution, the results of the multiple size-fraction model was compared with those of single fraction models. The comparison suggests that, although the same scaling relationships apply for the channel-flat system as a whole, the scaling of tidal flats proceeds at reduced rates, i.e., the tidal flat Hypsometry curves modeled with multiple fractions are almost identical to those with a single fraction for small basins but more convex-up for large basins. The former can be explained by the balance of erosion processes between mobile fine sediments and stable coarse grains, the latter by the increasing difference in grain size between upper and lower tidal flats.

  • Modelling the equilibrium Hypsometry of back-barrier tidal flats in the German Wadden Sea (southern North Sea)
    Continental Shelf Research, 2012
    Co-Authors: Yunwei Wang, Burg Flemming, Shu Gao
    Abstract:

    Abstract Hypsometry is the distribution of volume or horizontal surface area with respect to elevation. Some observations show contradictory scale-dependent characteristics of tidal flat hypsometries in back-barrier tidal basin environments, and traditional theory explains the flattening Hypsometry by relating concave-up hypsometries in low tidal range basins to the dominating influence of wind waves rather than tidal currents. In order to investigate these two problems, two series of numerical modelling exercises were carried out using schematized rectangular back-barrier tidal basins roughly corresponding to the tidal basins found in the German Wadden Sea. The results show that, in the equilibrium states of tidal basins, hypsometries of back-barrier tidal flats are dependent on the basin scale and tidal range. Thus, large basin areas and low tidal ranges favour strong concave-up hypsometries, whereas small basin areas and high tidal ranges favour less concave-up hypsometries. Because wind waves were excluded in the model, these relationships are purely associated with tidal-current action. In addition to the traditional theory, which emphasises the relative importance of wind waves, the flattening of hypsometric profile shapes can, therefore, also be interpreted as a response to the relative area of intertidal areas or channels in the tidal basins. Thus, if tidal channels have relatively large areas, the development of tidal flats between channels is markedly restrained, the tidal flats being prevented from growing upward to higher elevations. As a result, strong concave-up hypsometries are formed that are associated with relatively large areas of low tidal flats and small areas of high tidal flats. As basins with large areas and low tidal ranges have large relative channel areas, this results in pronounced concave-up hypsometries, and vice versa.

Willem Jan Van De Berg - One of the best experts on this subject based on the ideXlab platform.

  • Low elevation of Svalbard glaciers drives high mass loss variability.
    Nature communications, 2020
    Co-Authors: Brice Noël, Stef Lhermitte, Bert Wouters, Carleen Reijmer, Constantijn L. Jakobs, W. J. J. Van Pelt, Jack Kohler, Jon Ove Hagen, Bartłomiej Luks, Willem Jan Van De Berg
    Abstract:

    Compared to other Arctic ice masses, Svalbard glaciers are low-elevated with flat interior accumulation areas, resulting in a marked peak in their current Hypsometry (area-elevation distribution) at  ~450 m above sea level. Since summer melt consistently exceeds winter snowfall, these low-lying glaciers can only survive by refreezing a considerable fraction of surface melt and rain in the porous firn layer covering their accumulation zones. We use a high-resolution climate model to show that modest atmospheric warming in the mid-1980s forced the firn zone to retreat upward by  ~100 m to coincide with the Hypsometry peak. This led to a rapid areal reduction of firn cover available for refreezing, and strongly increased runoff from dark, bare ice areas, amplifying mass loss from all elevations. As the firn line fluctuates around the Hypsometry peak in the current climate, Svalbard glaciers will continue to lose mass and show high sensitivity to temperature perturbations.

  • Low-elevation of Svalbard glaciers drives high mass loss variability
    2020
    Co-Authors: Brice Noël, Constantijn Jakobs, Ward Van Pelt, Stef Lhermitte, Bert Wouters, Carleen Reijmer, Willem Jan Van De Berg, Michiel Van Den Broeke
    Abstract:

    <p>With a maximum in glaciated area below 450 m elevation (peak in the Hypsometry), most Svalbard glaciers currently experience summer melt that consistently exceeds winter snowfall. Consequently, these glaciers can only exist through efficient meltwater refreezing in their porous firn layers. Before the mid-1980s, refreezing retained 54% of the meltwater in firn above 350 m. In 1985-2018, atmospheric warming migrated the firn line upward by 100 m, close to the Hypsometry peak, which triggered a rapid ablation zone expansion (+62%). The resulting melt increase in the accumulation zones reduced the firn refreezing capacity by 25%, enhancing runoff at all elevations. In this dry climate, the loss of refreezing capacity is quasipermanent: a temporary return to pre-1985 climate conditions between 2005 and 2012 could not recover the meltwater buffer mechanism, causing strongly amplified mass loss in subsequent warm years (e.g. 2013), when ablation zones extend beyond the Hypsometry peak.</p>