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Abstract: Long term observations of clay thicknesses from 1949 to 2007 and measurements of the bulk dry density of salt marsh on the backbarrier of Skallingen (west Denmark) formed the basis of constructing a space distributed model of salt marsh deposition. The deposition potential (an empirical constant, β) was measured at 32 locations across the studied salt marsh platform. It was found to correlate with two independent variables: (1) distance to marsh edge and (2) distance to creeks of 2nd or higher order. They explained in combination 71% of the variation. The derived algorithms for estimating the salt marsh deposition made it possible to tune in a model in a 4 by 4m grid covering the studied salt marsh area of app 3km2. This was used to describe the general pattern of deposition on the salt marsh platform. Running the model with a constant sea level revealed that balance between the inner and the outer salt marsh deposition cannot be achieved within a time scale of 1000s of years. Modeling salt marsh sedimentation under rising sea level scenarios revealed that only one specific sea level rise provides equilibrium for a given location. With a higher sea level rise, the marsh at the specific location will eventually drown, whereas it – with a sea level rise below this level – will grow towards the top of the rising tidal frame. Short term scenarios (100years) showed that the Skallingen salt marsh will survive a sea level rise of 4mmyr−1 and become unstable in the inner part with a sea level rise of 6mmyr−1. [ABSTRACT FROM AUTHOR]

Abstract: Empirically derived algorithms are suggested by means of which it is possible to evaluate relations between physical properties in silty salt marsh clay. A relation between loss on ignition, sand content and bulk dry density in the topmost 5cm was found to explain 84% of the variation of the latter. The bulk dry density in the topmost ≈0.5m was found to vary as a logarithmic function of depth below the surface controlled by two constants directly dependent on the bulk dry density in the topmost 5cm. Integration of this function illustrates that mass depth (MSD z ) down core can be directly related to the bulk dry density of the surface layer. For sediments with a surface bulk dry density between 400kgm−3 and 800kgm−3 the porosity was found to vary (+/−10%) with MSD z as another logarithmic function. The results allow for an evaluation of the use of marker horizons in the topmost layers. Right after such a layer has been spread on the surface, sedimentation measured in length per time (accretion), will be significantly larger than for subsequent periods. Using marker horizons, it is therefore not trivial to know the level of the marker, as deeper located markers will indicate successively smaller accretion rates with the same sediment input. [Copyright &y& Elsevier]