TY - ABST

T1 - Salt marsh stability modelled in relation to sea level rise

AU - Bartholdy, Jesper

AU - Bartholdy, Anders

AU - Kroon, Aart

N1 - EGU General Assembly 2010

PY - 2010

Y1 - 2010

N2 - Accretion on a natural backbarrier salt marsh was modeled as a function of high tide level, initial salt marsh leveland distance to the source. Calibration of the model was based on up to ca 80 year old marker horizons, supplementedby 210Pb/137Cs datings and subsequent measurements of clay thickness. Autocompaction was incorporatedin the model, and shown to play a major role for the translation of accretion rates measured as length per unit timeto accumulation rates measured as mass per area per unit time. This is important, even for shallow salt marshdeposits for which it is demonstrated that mass depth down core can be directly related to the bulk dry densityof the surface layer by means of a logarithmic function. The results allow for an evaluation of the use of markerhorizons in the topmost layers and show that it is important to know the level of the marker in relation to the saltmarsh base. In general, deeper located markers will indicate successively smaller accretion rates with the samesediment input. Thus, stability analysis made on the basis of newly established marker horizons will be biased andindicate salt marsh stabilities far above the correct level. Running the model with a constant sea level revealed thatbalance between the inner and the outer salt marsh deposition can not be achieved within a reasonable time scale.Likewise it is shown that only one specific sea level rise provides equilibrium for a given location on the salt marsh.With a higher sea level rise, the marsh at the specific location will eventually drown, whereas - with a sea levelrise below this level – it will grow towards the top of the rising tidal frame. The short term variation of salt marshaccretion was found to correlate well with variations in the North Atlantic Oscillation - the NAO winter index.Comparisons between the geomorphological development of wind tide affected salt marshes, like those presenton the Danish North Sea coasts, and primary astronomically controlled tidal marshes like those in the GeorgianBight, USA showed that the former - when first established - relatively quickly grow above the level of the highestastronomical tide, whereas this - in practice - will never happen for the latter.

AB - Accretion on a natural backbarrier salt marsh was modeled as a function of high tide level, initial salt marsh leveland distance to the source. Calibration of the model was based on up to ca 80 year old marker horizons, supplementedby 210Pb/137Cs datings and subsequent measurements of clay thickness. Autocompaction was incorporatedin the model, and shown to play a major role for the translation of accretion rates measured as length per unit timeto accumulation rates measured as mass per area per unit time. This is important, even for shallow salt marshdeposits for which it is demonstrated that mass depth down core can be directly related to the bulk dry densityof the surface layer by means of a logarithmic function. The results allow for an evaluation of the use of markerhorizons in the topmost layers and show that it is important to know the level of the marker in relation to the saltmarsh base. In general, deeper located markers will indicate successively smaller accretion rates with the samesediment input. Thus, stability analysis made on the basis of newly established marker horizons will be biased andindicate salt marsh stabilities far above the correct level. Running the model with a constant sea level revealed thatbalance between the inner and the outer salt marsh deposition can not be achieved within a reasonable time scale.Likewise it is shown that only one specific sea level rise provides equilibrium for a given location on the salt marsh.With a higher sea level rise, the marsh at the specific location will eventually drown, whereas - with a sea levelrise below this level – it will grow towards the top of the rising tidal frame. The short term variation of salt marshaccretion was found to correlate well with variations in the North Atlantic Oscillation - the NAO winter index.Comparisons between the geomorphological development of wind tide affected salt marshes, like those presenton the Danish North Sea coasts, and primary astronomically controlled tidal marshes like those in the GeorgianBight, USA showed that the former - when first established - relatively quickly grow above the level of the highestastronomical tide, whereas this - in practice - will never happen for the latter.

M3 - Conference abstract in journal

VL - 12

SP - EGU2010-15265

JO - Geophysical Research Abstracts

JF - Geophysical Research Abstracts

SN - 1607-7962

T2 - Salt marsh stability modelled in relation to sea level rise

Y2 - 29 November 2010

ER -