Hans Burchard
Leibniz Institute for Baltic Sea Research Warnemünde
Coastal Ocean Dynamics
Forth course: Wadden Sea Dynamics
The Wadden Sea
http://en.wikipedia.org/wiki/Wadden_Sea
www.rapid.ac.uk
Wadden Sea … and … thermo-haline circulation?
Warming Precipitation
Weak tidal mixing: vertically stratified
Strong tidal mixing: horizontally stratified
Land Ocean
Downward surface buoyancy flux
Estuarine circulation
Sea bed
River
Global ocean:Spatially inhomogeneous surface buoyancy fluxes plus internal mixing leads to global overturning circulation.
Wadden Sea:Spatially homogenous surface buoyancy fluxes over sloping bathymetry plus tidal mixing should lead to redidual overturning circulation.
But does it really happen?
Locations of five automatic monitoring poles in theWadden Sea of theGerman Bight, recordingtemperature and salinity,(and thus density).
How can we approach this with observations ?
Burchard et al. (JPO 2008)
Climatology: Salinity difference HW-NW
Burchard et al. (JPO 2008)
Climatology: Temperature difference HW-LW
Burchard et al. (JPO 2008)
Climatology: Density difference HW-LW
Burchard et al. (JPO 2008)
Suspended matter concentrationsare substantially increased in theWadden Sea of the German Bight, withouthaving significantsources at the coast.
Why ?
Total suspended matter from MERIS/ENVISAT on August, 12, 2003.
Sediment transportin the Wadden Sea
Conceptual model
Burchard et al. (in prep.)
Width-averaged Wadden Sea model
Burchard et al. (in prep.)
Width-averaged Wadden Sea model: Net precipitation
Burchard et al. (in prep.)
Width-averaged Wadden Sea model: no buoyancy flux
Burchard et al. (in prep.)
Width-averaged Wadden Sea model: Net evaporation
Burchard et al. (in prep.)
Does this all happen in nature?Ok, let’s go out to the Wadden Sea and measure:
Campaign in Lister Deep (April 2008)
Becherer et al. (GRL 2011)
shoals
Becherer et al. (GRL 2011), Purkiani et al. (in prep)
Data and model results at S1
Data and model results at S2
Purkiani et al. (in prep)
Potential energy anomaly
(amount if energy needed to homogenise water column)
Wat
er c
olum
n st
abili
ty
Tidal phase
Near lateral shoals, stratification kicks in already during flood.
Becherer et al. (GRL 2011)
Results of fully baroclinic 3D model (100 m resolution)
Purkiani et al. (in prep.)
(S1)
(S2)
Results of fully baroclinic 3D model (100 m resolution)
Purkiani et al. (in prep.)
Flood Ebb
Model approach:
1. Simulating a closed Wadden Sea basin (Sylt-Rømø bight) with small freshwater-runoff and net precipitation. 2. Spin up model with variable and with constant density until periodic steady state.3. Then initialise both scenarios with const. SPM concentration.4. Quantify SPM content for control volume.
Burchard et al. (JPO 2008)
Surface salinity at high and low water
Burchard et al. (JPO 2008)
Total water and SPM volume
With density differences
V /
km3
Burchard et al. (JPO 2008)
Total water and SPM volume
Without density differences
V /
km3
Burchard et al. (JPO 2008)
Sea level rise & tidal flat growth (Danish Wadden Sea)
Data and graphics from Morten Pejrup, Copenhagen University