Estran | EPFL Graph Search

L'estran, zone de balancement des marées, zone de marnage, zone intertidale ou replat de marée également appelé foreshore (de l'anglais) en sédimentologie, est la partie du littoral située entre les limites extrêmes des plus hautes et des plus basses marées. Il constitue un biotope spécifique, qui peut abriter de nombreux sous-habitats naturels. Il est découpé en trois étages, de haut en bas : l’étage supralittoral, l’étage médiolittoral et l’étage infralittoral. Terminologie thumb|250px|Battures du fleuve Saint-Laurent. vignette|250px|Carte de 1751 signalant des zones de battures sur les côtes de l'île Royale (Nouvelle-Écosse). L'estran est aussi appelé batture en Amérique du Nord francophone. On utilise aussi pour le désigner le terme « zone de marnage » ou l'anglicisme « zone intertidale » (de l'anglais tidal signifiant « relatif à la marée ») ; en termes administratifs et juridiques, on emploie aussi l'expression « zone de balancement des marées ». Provenant du née

Effects of temperature on tidally influenced coastal unconfined aquifers

David Andrew Barry, Li Pu, Chenming Zhang

Aquifer-ocean temperature contrasts are common worldwide. Their effects on flow and salinity distributions in unconfined coastal aquifers are, however, poorly understood. Based on laboratory experiments and numerical simulations, we examined the responses of flow processes in tidally influenced aquifers to aquifer-ocean temperature differences. The extent of seawater intrusion and seawater circulation were found to vary with the aquifer-ocean temperature contrast. Compared with the isothermal case, an increase of up to 40% of the tide-induced seawater circulation rate in the intertidal zone was observed when seawater is warmer than groundwater. In contrast, saltwater circulation in the lower saltwater wedge declines notably no matter whether the seawater is warmer or colder than groundwater. As the seawater temperature rises, the contribution of tide-induced circulation to the overall increase of submarine groundwater discharge becomes more important compared with that of density-driven seawater circulation. Both the upper saline plume and the freshwater discharge zone expand significantly with warmer seawater whereas the lower saltwater wedge contracts.

2020

Estuarine tidal response to sea level rise: The significance of entrance restriction

Giovanni De Cesare, Steve Hottinger

Estuarine environments, as dynamic low-lying transition zones between rivers and the open sea, are vulnerable to sea level rise (SLR). To evaluate the potential impacts of SLR on estuarine responses, it is necessary to examine the altered tidal dynamics, including changes in tidal amplification, dampening, reflection (resonance), and deformation. Moving beyond commonly used static approaches, this study uses a large ensemble of idealised estuarine hydrodynamic models to analyse changes in tidal range, tidal prism, phase lag, tidal current velocity, and tidal asymmetry of restricted estuaries of varying size, entrance configuration and tidal forcing as well as three SLR scenarios. For the first time in estuarine SLR studies, data analysis and clustering approaches were employed to determine the key variables governing estuarine hydrodynamics under SLR. The results indicate that the hydrodynamics of restricted estuaries examined in this study are primarily governed by tidal forcing at the entrance and the estuarine length. In addition, SLR increases the average water depth and alters the nodal point location in a seaward direction, thereby significantly affecting tidal wave propagation patterns and reducing the degree of flood domination. In estuaries with restricted entrances, tidal range diminishes drastically in the restricted zone by 20–60%, and the maximum tidal current velocity is higher in the restricted part but lower in the upstream part compared to unrestricted estuaries. For estuary types examined, inundation extent under SLR will likely be greater than the extent expected through simply adjusting existing water levels upwards. The findings also underline that an engineered entrance restriction could regulate tidal wave propagation within an estuary to offset SLR induced tidal range amplification. However, this may pose additional management challenges.

2020

A benthic foraminifera species respond to anoxia with a strong metabolic shift suggesting a state of dormancy

Emmanuelle Geslin, Charlotte Madeleine Nicole Lekieffre, Anders Meibom

Low-oxygenation events are more and more frequent and strong on continental shelves and in coastal areas where renewal of bottom waters is slow. Among the meiofauna living in such environments, foraminifera are among the most tolerant to the lack of oxygen. Some benthic foraminiferal species are able to survive hypoxia, and even anoxia, for weeks to months. Different species must have developed different mechanisms for survival - hypotheses include reduction of the metabolism, symbiosis with bacteria, or denitrification. Ammonia tepida, one of the most abundant species in intertidal environments, is able to survive up to 60 days in anoxia. Here we combined a 4 week feeding experiment using 13C-enriched microalgae (diatoms), with correlated transmission electron microscopy (TEM) and NanoSIMS (Secondary Ion Mass Spectrometry) imaging, and concentrations (GC/MS, GC/FFID), as well as bulk and compound specific carbon isotope ratios (13C/12C obtained by EA/IRMS and GC/C/IRMS) of individual fatty acids (FAs) to study the metabolic differences in intertidal Ammonia tepida exposed to oxic and anoxia conditions, respectively. Strongly contrasting cellular-level dynamics of integration and transfer of the ingested biofilm components were observed under the two conditions. Under oxic conditions, within a few days, intact diatoms (i.e. including the frustule) were ingested, assimilated and consumed, in part for biosynthesis of different cellular components: 13C-labeled lipid droplets formed over a timescale of a few days and were then partly lost through respiration. In contrast, in anoxia, fewer diatoms were initially ingested and these were not assimilated or metabolized further, but remained visible within the foraminiferal cytoplasm even after 4 weeks. The compound specific 13C/12C ratios indicated substantial de novo synthesis by the foraminifera of polyunsaturated FAs (PUFAs), such as 20:4(n-6), in oxic conditions; very limited PUFA synthesis was observed under anoxia. Together, our results indicate that anoxia induced a greatly reduced rate of heterotrophic metabolism in Ammonia tepida on a time scale of about 24 hours, which seems consistent with a state of dormancy.

2016

A benthic foraminifera species respond to anoxia with a strong metabolic shift suggesting a state of dormancy

Emmanuelle Geslin, Charlotte Madeleine Nicole Lekieffre, Anders Meibom

2016

Estuarine tidal response to sea level rise: The significance of entrance restriction

Giovanni De Cesare, Steve Hottinger

2020