1. Hans Burchard … … and many others from inside and outside IOW Leibniz Institute for Baltic Sea Research Warnemünde hans.burchard@io-warnemuende.de The overturning circulation of the Baltic Sea and its ecological consequences

2. The Baltic Sea

3. Baltic Sea under stress Climate changeEutrophication Constructions Fishery IPCC BACC

5. www.getm.eu

6. The philosophy behind GETM GETM is a coastal and shelf sea (and lake?) hydrodynamic model. GETM is a Public Domain Community Model. GETM is released under the Gnu Public Licence. GETM is Open Source. GETM has a modular structure (open for extentions). GETM has an international developer and user community. GETM started in 1997 and has been steadily developed since then.

7. Nested modelling hierarchy Gräwe et al. (in prep.)

8. Domain decomposition

9. Example for simulated summer sea surface temperature Gräwe et al. (in prep.)

10. Example for simulated bottom salinity Gräwe et al. (in prep.)

11. T and S at Darss Sill in 2003 Baltic Sea salinity Baltic Sea major inflow event October 2002 (before inflow) June 2003 (after inflow)

12. October 2002 (before inflow) June 2003 (after inflow) Baltic Sea oxygen concentration hydrogen sulfur

13. Oxygen observations in the central Baltic Sea Reissmann et al. (2009)

14. Baltic Sea suboxic and anoxic areas before major inflow

15. Baltic Sea suboxic and anoxic areas after major inflow

16. Matthäus (2006) History of Major Baltic Inflows (MBIs)

17. Data from Markus Meier, SMHI (in Burchard et al., 2008)

18. Kabel et al. 2012 (Nature Climate Change) Tex-86 derived SST Proxies: surface water conditions, central Baltic MODIS Rapid Response System 232 m water depth

19. MODIS Rapid Response System Tex-86 derived SST Proxies: surface water conditions, central Baltic Kabel et al. 2012 175 m water depth

20. Baltic Sea overturning circulation

21. How is the Baltic Sea overturning circulation closed? Reissmann et al., 2009 Exchange flow Inflows Boundary and internal mixing

22. Knudsen formula s=0 Volume conservation: Salt conservation: 0

23. Computersimulation Western Baltic Sea

25. Model validation: Data Darsser Schwelle Burchard et al. (2009)

26. + + + Drogden Sill Darss Sill Kriegers Flak N Before inflowDuring inflow Rennau & Burchard, 2009

27. FS Professor Albrecht Penck Kriegers Flak Schweden 16.11.2005 Detailed inflow study in 2005 Umlauf et al. (2007)

28. Observed Transverse Structure (Nov 2005) wegde-shaped interface interface jet lateral buoyancy gradient in interior three-layer transverse circulation Umlauf et al., GRL, (2007) Dissipation rate Down-channel velocity Cross-channel velocity I.BBL mixing II.Interfacial mixing III.Quiescent core IV.Slope mixing Umlauf et al. (2007), Reissmann et al. (2009), Umlauf & Arneborg (2009a,b)

29. Which is the most simple model that can reproduce this? 2-D shallow-water equations (GETM) homogenous in down-channel direction ‘infinitely’ deep 2nd-moment turbulence closure model (GOTM) adaptive coordinates Umlauf et al. (2010)

30. Feistel, 2005 Surface salinity lags more than 10 years behind bottom salinity

31. Mixing processes in the Baltic Sea Reissmann et al. 2009 Courtesy Peter Holtermann

32. Investigation of deep water mixing during a stagnation period Reissmann et al. 2009 Courtesy Peter Holtermann

33. Reissmann et al. 2009 Boundary Mixing Internal Mixing Courtesy Peter Holtermann Investigation of deep water mixing during a stagnation period

34. The Baltic Sea Tracer Release Experiment Tracer Spreading Courtesy Peter Holtermann

37. Interior Diffusivity Normalised tracer profile Oct. 2007 44 DAI m 2 /s Holtermann et al. (2012)

38. One diffusivity fits T, S, tracer ! Basin wide eddy diffusivity Leg 3 Feb. 2008 Leg 4 July 2008 Basin-wide mixing is one order of magnitude larger than local diffusivity ! Holtermann et al. (2012)

39. Tracer experiment

40. Sediment Deep water Surface water Air Climate InputSensitive Nonlinear ResponseEcosystem output O2O2 H2SH2S P N2N2 O 2 -Depletion       Cyanobacteria  mixing settling   P Chemical switch Random ventilation O2O2 The Baltic Sea as a complex ecosystem random ventilation

41. Near-bottom oxygen & phosphate observations in the central Baltic Sea Reissmann et al. (2009)

42. Phosphate concentrations in winter surface layer in the Eastern Gotland Basin Reissmann et al. (2009)