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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
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The Baltic Sea
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Baltic Sea under stress Climate changeEutrophication Constructions Fishery IPCC BACC
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www.getm.eu
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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.
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Nested modelling hierarchy Gräwe et al. (in prep.)
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Domain decomposition
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Example for simulated summer sea surface temperature Gräwe et al. (in prep.)
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Example for simulated bottom salinity Gräwe et al. (in prep.)
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T and S at Darss Sill in 2003 Baltic Sea salinity Baltic Sea major inflow event October 2002 (before inflow) June 2003 (after inflow)
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October 2002 (before inflow) June 2003 (after inflow) Baltic Sea oxygen concentration hydrogen sulfur
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Oxygen observations in the central Baltic Sea Reissmann et al. (2009)
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Baltic Sea suboxic and anoxic areas before major inflow
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Baltic Sea suboxic and anoxic areas after major inflow
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Matthäus (2006) History of Major Baltic Inflows (MBIs)
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Data from Markus Meier, SMHI (in Burchard et al., 2008)
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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
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MODIS Rapid Response System Tex-86 derived SST Proxies: surface water conditions, central Baltic Kabel et al. 2012 175 m water depth
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Baltic Sea overturning circulation
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How is the Baltic Sea overturning circulation closed? Reissmann et al., 2009 Exchange flow Inflows Boundary and internal mixing
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Knudsen formula s=0 Volume conservation: Salt conservation: 0
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Computersimulation Western Baltic Sea
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Model validation: Data Darsser Schwelle Burchard et al. (2009)
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+ + + Drogden Sill Darss Sill Kriegers Flak N Before inflowDuring inflow Rennau & Burchard, 2009
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FS Professor Albrecht Penck Kriegers Flak Schweden 16.11.2005 Detailed inflow study in 2005 Umlauf et al. (2007)
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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)
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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)
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Feistel, 2005 Surface salinity lags more than 10 years behind bottom salinity
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Mixing processes in the Baltic Sea Reissmann et al. 2009 Courtesy Peter Holtermann
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Investigation of deep water mixing during a stagnation period Reissmann et al. 2009 Courtesy Peter Holtermann
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Reissmann et al. 2009 Boundary Mixing Internal Mixing Courtesy Peter Holtermann Investigation of deep water mixing during a stagnation period
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The Baltic Sea Tracer Release Experiment Tracer Spreading Courtesy Peter Holtermann
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Interior Diffusivity Normalised tracer profile Oct. 2007 44 DAI m 2 /s Holtermann et al. (2012)
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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)
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Tracer experiment
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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
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Near-bottom oxygen & phosphate observations in the central Baltic Sea Reissmann et al. (2009)
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Phosphate concentrations in winter surface layer in the Eastern Gotland Basin Reissmann et al. (2009)
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