Hans Burchard

Leibniz Institute for Baltic Sea Research Warnemünde

hans.burchard@io-warnemuende.de

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