Hans Burchard

Baltic Sea Research Institute Warnemnde, Germany

hans.burchard@io-warnemuende.de

Collaboration: Lars Arneborg, Thomas Badewien, Karsten Bolding, Jorn Bruggeman, Volker Fiekas, Gtz Flser, Hans Ulrich Lass, Volker Mohrholz, Rolf Riethmller, Piet Ruardij, Joanna Staneva, Lars Umlauf

Applications of the General Estuarine Transport Model (GETM) for coastal ocean process studies

Program today

Tools:

General Ocean Turbulence Model, www.GOTM.netGeneral Estuarine Transport Model, www.GETM.eu

Applications:

Western Baltic Sea dense bottom currentsWadden Sea suspended matter accumulation

GOTM is a water column model with modules for state-of-the-art turbulence closure models biogeochemical models of various complexities

GETM is a 3D numerical model for estuarine,coastal and shelf sea hydrodynamics with applications to the

Tidal Elbe Wadden Sea Limfjord Lake of Geneva, Western Baltic Sea, North Sea Baltic Sea system

Present GETM characteristics ... physics ...

Solves three-dimensional primitive equations withhydrostatic and Boussinesq approximations.

Based on general vertical coordinates.

Options for Cartesian, spherical and curvilinear coordinates.

Fully baroclinic with tracer equations for salinity, temperature,suspended matter and ecosystem (from GOTM bio module).

Two-equation turbulence closure models with algebraicsecond-moment closures (from GOTM turbulence module).

Wetting and drying of intertidal flats is supported also inbaroclinic mode.

Present GETM characteristics ... numerics ...

Consistent explicit mode splitting into barotropic and baroclinic mode.

High-order positive-definite TVD advection schemes withdirectional split.

Choice of different schemes for internal pressure gradientcalculation.

Consistent treatment of zero-velocity bottom boundary condition for momentum.

Positive-definite conservative schemes for ecosystem processes (in GOTM-Bio module).

GETM-GOTM-Bio coupling example: ERSEM simulation for North Sea(Simulation and animation by Piet Ruardij, NIOZ, The Netherlands)

Western Baltic Sea Study

Motivation: wind farms in the Western Baltic Sea

Western Baltic Sea monitoring stationsDarss Sill: 19 m+Drogden Sill: 8 m+MARNET (IOW/BSH)Farvandsvsenet

baroclinicbarotropicInflows over Drogden SillsurfacebottomSource: Farvandsvsenet

Where does the Sound plume go ??

5 days15 days31 daysSound lock-exchange experiment with GETMMain plume goes via northof Kriegers Flak: Is this real ?Bottom salinity: 8 25 psu

Plume passing Kriegers Flak (Feb 2004)

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

Model validation: Darss Sill

Model derived annual mean mixing in Western Baltic Sea

Nov 2005: Velocity structure of dense bottom currentEastcomp.Northcomp.Can we explain the flow structure ?

GETM 2DV Slice Model: Transverse gravity current structure

Western Baltic Sea conclusions:

Density currents in Western Baltic Sea are highly variable,show a complex transverse structure and induce substantial natural transports and mixing.

For evaluating additional anthropogenic mixing due tooffshore structures on these currents, proper parameterisations need to be foundand inserted into 3D model (QuantAS-Off).

Multiple bridges and wind farms may result incumulative mixing effects.

Suspended matter concentrationsare substantially increased in theWadden Sea of the German Bight.Total suspended matter from MERIS/ENVISAT on August, 12, 2003. Wadden Sea study

The areal view showslocations of five automatic monitoring poles in theWadden Sea of theGerman Bight, operated byGKSS and the University of Oldenburg. They record several parameters in thewater column, such as temperature and salinity.

Salinity difference HW-LW

Temperature difference HW-LW

Density difference HW-LW

Hypothesis: This must have a dynamic impact on tidal flow and SPM transport, see the theory of Jay and Musiak (1994) below.

Testing with GOTM supports hypothesis:Residualonshorenear-bedcurrentAlong-tidesalinity gradientprescribedBottom-surface salinity

3D simulations with GETM for the Sylt-Rm bight Approach:

Simulating a closed Wadden Sea basin (Sylt-Rm bight) with small freshwater-runoff and net precipitation. Spin up model with variable and with constant density until periodic steady state. Then initialise both scenarios with const. SPM concentration. Quantify SPM content of fixed budget boxes.

The Sylt-Rm bight

Bottom salinity at high and low water during periodically steady state.

Vertically averaged current velocity during full flood and full ebb.

Cross-sectionaldynamics

Total water volume and SPM unit mass in budget boxesCase with density differences, tidal periods # 46-55

Total excess SPM mass in budget boxesCase with density differences, tidal periods # 46-55

Total water volume and SPM unit mass in budget boxesCase with no density differences, tidal periods # 46-55

Total excess SPM mass in budget boxesCase with no density differences, tidal periods # 46-55

Wadden Sea conclusions:

The hypothesis is strongly supported.

Other mechanisms than density differences which are also reproduced by the model system (such as settling lag and barotropic tidal asymmetries)do not play a major role in this scenario.

Now, targeted field studied are needed for further confirming the hypothesis.

RV Gauss leaving Warnemnde for its last research cruiseGeneral conclusion:

Sufficient knowledge about coastal processes is a prerequisite for assessing regional consequences of climate and anthropogenically induced change.