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The overturning circulation of the Baltic Sea and its ecological consequences. Hans Burchard … … and many others from inside and outside IOW Leibniz Institute for Baltic Sea Research Warnemünde [email protected]. The Baltic Sea. Baltic Sea under stress. - PowerPoint PPT Presentation
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Hans Burchard …… and many others from inside and outside IOW
Leibniz Institute for Baltic Sea Research Warnemünde
The overturning circulation of the Baltic Sea and its ecological consequences
The Baltic Sea
Baltic Sea under stress
Figure SPM.5
Climate change Eutrophication
Constructions Fishery
IPCC BACC
www.getm.eu
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.
Nested modelling hierarchy
Gräwe et al. (in prep.)
Gräwe et al. (in prep.)
Domain decomposition
Example for simulated summer sea surface temperature
Gräwe et al. (in prep.)
Example for simulated bottom salinity
Gräwe et al. (in prep.)
T and S at Darss Sill in 2003
Baltic Sea salinity
Baltic Sea major inflow event
October 2002(before inflow)
June 2003(after inflow)
October 2002(before inflow)
June 2003(after inflow)
Baltic Sea oxygen concentration hydrogen
sulfur
Oxygen observations in the central Baltic Sea
Reissmann et al. (2009)
Baltic Sea suboxic andanoxic areasbefore major inflow
Baltic Sea suboxic andanoxic areasafter major inflow
Matthäus (2006)
History of Major Baltic Inflows (MBIs)
Data from Markus Meier, SMHI (in Burchard et al., 2008)
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
MODIS Rapid Response System
Tex-86 derived SST
Proxies: surface water conditions, central Baltic
Kabel et al. 2012
175 m water depth
Baltic Sea overturning circulation
How is the Baltic Sea overturning circulation closed?
Reissmann et al., 2009
Exchange flow
Inflows
Boundary and internal mixing
Knudsen formula
s=0Volume conservation:
Salt conservation: 0
Computersimulation Western Baltic Sea
Computersimulation Western Baltic Sea
Model validation: Data Darsser Schwelle
Burchard et al. (2009)
+
+
+
Drogden Sill
Darss Sill
Kriegers Flak N
Before inflow
During inflow
Rennau & Burchard, 2009
FS Professor Albrecht Penck
Kriegers Flak
Schweden
16.11.2005
Detailed inflow study in 2005
Umlauf et al. (2007)
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 mixingII. Interfacial mixingIII. Quiescent coreIV. Slope mixing
Umlauf et al. (2007), Reissmann et al. (2009), Umlauf & Arneborg (2009a,b)
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)
Feistel, 2005
Surface salinity lags more than 10 years behind bottom salinity
Mixing processes in the Baltic Sea
Reissmann et al. 2009
Courtesy Peter Holtermann
Investigation of deep water mixing during a stagnation period
Reissmann et al. 2009
Courtesy Peter Holtermann
Reissmann et al. 2009
Boundary Mixing
Internal Mixing
Courtesy Peter Holtermann
Investigation of deep water mixing during a stagnation period
The Baltic Sea Tracer Release Experiment
Tracer Spreading
Courtesy Peter Holtermann
Interior DiffusivityNormalised tracer profile Oct. 2007 44 DAI
2
2
zcκ=
dtdc
m2/sm2/s
Holtermann et al. (2012)
One diffusivity fits T, S, tracer !
Basin wide eddy diffusivity
Leg 3Feb. 2008
Leg 4July 2008
)zc(Aκ
z=
dtdcA
Basin-wide mixing is one order of magnitude larger than local diffusivity !
Holtermann et al. (2012)
Tracer experiment
Sediment
Deep water
Surface water
Air
Climate Input Sensitive Nonlinear Response Ecosystem output
O2 H2S
P
N2
O2-Depletion
Cyanobacteria
mixing settling
P
Chemicalswitch
Randomventilation
O2
The Baltic Sea as a complex ecosystem
random ventilation
Near-bottom oxygen & phosphate observations in the central Baltic SeaReissmann et al.
(2009)
19581960 1965 1970 1975 1980 1985 1990 1995 2000 20050
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
phos
phat
e (µ
mol
/l)
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8inf lo
w
inf lo
w
inf lo
w
inf lo
w
Phosphate concentrations in winter surface layer in the Eastern Gotland Basin
Reissmann et al. (2009)
