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Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde , Germany

Thermohaline circulation in the Wadden Sea . Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde , Germany Cooperation: Thomas Badewien 1 , Johannes Becherer 2 , Kaveh Purkiani 2 Götz Flöser 3 , Ulf Gräwe 2 , Robert Hetland 5 , Volker Mohrholz 2 ,

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Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde , Germany

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  1. Thermohaline circulationin the Wadden Sea Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde, Germany Cooperation: Thomas Badewien1, Johannes Becherer2, Kaveh Purkiani2 Götz Flöser3, Ulf Gräwe2, Robert Hetland5, Volker Mohrholz2, Rolf Riethmüller3, Henk Schuttelaars4, Joanna Staneva3, Lars Umlauf2 1. University Oldenburg, Germany 2. Leibniz Institute for Baltic Sea Research Warnemünde, Germany 3. Helmholtz CenterGeesthacht, Institute for Coastal Research, Germany 4. TU Delft, The Netherlands 5. Texas A&M, College Station, TX, USA

  2. WaddenSea … and … thermo-halinecirculation? www.rapid.ac.uk

  3. The WaddenSeacirculation in a nutshell WarmingPrecipitation Land Ocean Downwardsurfacebuoyancyflux Seabed Weaktidalmixing: verticallystratified River? Thermohalineestuarinecirculation Strong tidalmixing: horizontallystratified

  4. Global ocean: Spatiallyinhomogeneoussurfacebuoyancyfluxesplus internalmixingleadsto global overturningcirculation. WaddenSea: Spatiallyhomogenoussurfacebuoyancyfluxesoverslopingbathymetry plus tidalmixingshouldleadto residual overturningcirculation. But doesitreally happen?

  5. Conceptual model Burchard et al. (in prep.)

  6. Width-averagedWaddenSea model Burchard et al. (in prep.)

  7. Width-averagedWaddenSea model: Net precipitation Burchard et al. (in prep.)

  8. Width-averagedWaddenSea model: nobuoyancyflux Burchard et al. (in prep.)

  9. Width-averagedWaddenSea model: Net evaporation Burchard et al. (in prep.)

  10. Howcanweapproachthis withobservations ? Locations of five automatic monitoring poles in the Wadden Sea of the German Bight, recording temperature and salinity, (and thus density). Burchard et al. (JPO 2008)

  11. Climatology: Salinitydifference HW-NW Burchard et al. (JPO 2008)

  12. Climatology: Temperaturedifference HW-LW Burchard et al. (JPO 2008)

  13. Climatology: Densitydifference HW-LW Burchard et al. (JPO 2008)

  14. Longitudinal densitygradientsleadto: 1. Gravitationalcirculation MacCreadyand Geyer (2010)

  15. Longitudinal densitygradients & tidaloscillationsleadto: 2. Tidalstraining 75% level 75% level MacCready & Geyer (2010) after Jay & Musiak (1994)

  16. Tidally-averagedcurrentsfor typicalWaddenSeaconditions Estuarinecirc. Withfull-scale1D model (GOTM): Gravitationalcirculation andtidalstrainingprofiles Straining Gravitational Result: Tidal straining makes about 2/3 of estuarine circulation. Burchard andHetland (JPO 2010)

  17. Enhancement of estuarine circulation in channelised tidal flow (2D slice modelling with GETM) www.getm.eu Burchard et al. (JPO 2011)

  18. Circulation in transverse estuary

  19. Transverse structure ofestuarinecirculation Gravitationalcirculation Tidalstrainingcirculation Advectivecirculation Barotropiccirculation Burchard et al. (JPO 2011)

  20. Does this all happen in nature? Ok, let’s go out to the Wadden Sea and measure:

  21. Campaign in Lister Deep (April 2008) shoals Becherer et al. (GRL 2011)

  22. Becherer et al. (GRL 2011)

  23. Puzzling however: Water column stability Tidal phase Near lateral shoals, stratification kicks in already during flood ... See following model study. Becherer et al. (GRL 2011)

  24. Tides in theWaddenSea (asseen in 200 m resolution model)

  25. Results of fully baroclinic 3D model (100 m resolution) Tidally averaged water column stability Purkiani et al. (in prep.)

  26. Results of fully baroclinic 3D model (100 m resolution) (S1) (S2) Purkiani et al. (in prep.)

  27. Results of fully baroclinic 3D model (100 m resolution) Flood Ebb Purkiani et al. (in prep.)

  28. Residual sedimentfluxes in estuaries (analyticalsolutions) Burchard et al. (JPO, submitted)

  29. Decompositionofsedimentflux transportflux fluctuationflux totalflux

  30. Residual sedimentfluxes in estuaries (transient numericalsolutions) Fullyerodablebed Semi-erodablebed Non-erodablebed Burchard et al. (JPO, submitted)

  31. Implicationsfor sedimenttransport Suspended matter concentrations are substantially increased in the Wadden Sea of the German Bight, without having significant sources at the coast. Why ? Total suspended matter from MERIS/ENVISAT on August, 12, 2003.

  32. 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)

  33. Surface salinity at high and low water Burchard et al. (JPO 2008)

  34. Withdensitydifferences Total waterand SPM volume V / km3 Burchard et al. (JPO 2008)

  35. Withoutdensitydifferences Total waterand SPM volume V / km3 Burchard et al. (JPO 2008)

  36. WaddenSea model Model systembased on GETM: NA: 5.4 km X 5.4 km (2D) NSBS: 1.8 km X 1.8 km (3D) SNS, WBS: 600 m X 600 m (3D) WaddenSea: 200 m X 200 m (3D) PACE project (NWO-BMBF): „The futureoftheWaddenSea sedimentfluxes: Still keepingpace withsealevelrise?“ (2011-2014) Gräwe et al., in prep.

  37. Tides in theWaddenSea (asseen in 200 m resolution model)

  38. Overarchingresearchquestions Whatarethehydrodynamicprocessesdrivingsedimenttransport in thecoastalzone? How do thesedimentfluxesaffectthecoastalecosystem? How do thesedimentfluxesdeterminethe morphologicalevolution in thecoastalzone? Howisthesusceptibilityoftheseprocessesandthe subsequent sedimentfluxes on human interventionandnaturalchange?

  39. Derivedspecificquestions Uptowhichdegreeofsealevelrise will theintertidalflatsofthe WaddenSeabepreventedfromdrowning? Will furtherdeepeningofnavigationalchannels in tidalestuaries turn themintogiganticsediment traps? Is nutrientsupplythroughparticulate matter transportproviding increasedcarryingcapacity in thecoastalzonetogiveroomfor invasive species? Note thatforansweringanyofthesequestons, thecurrent processunderstandingis not sufficient!

  40. Conclusions Other than in real estuaries, the residual circulation in the Wadden Sea is truly thermohaline with sometimes salinity being the major driver and sometimes temperature ... ... and it has a significant impact on sediment transport ... ... by supporting landward sediment fluxes. The big questions are: How much does thermohaline circulation support sediment accumulation? Can it help the Wadden Sea to survive sea level rise ? Fundedby:

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