hans burchard … … and many others from inside and outside iow leibniz institute for baltic sea...

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

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 mixing

II. Interfacial mixing

III. Quiescent core

IV. 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 Diffusivity

Normalised tracer profile Oct. 2007 44 DAI

2

2

z

cκ=

dt

dc

m2/sm2/s

Holtermann et al. (2012)

One diffusivity fits T, S, tracer !

Basin wide eddy diffusivity

Leg 3Feb. 2008

Leg 4July 2008

)z

c(Aκz

=dt

dcA

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

mixin

g settling

P

Chemicalswitch

Randomventilation

O2

The Baltic Sea as a complex ecosystem

random ventilation

Near-bottom oxygen & phosphate observations in the central Baltic Sea

Reissmann 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

ph

os

ph

ate

(µ

mo

l/l)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

inflo

w

inflo

w

inflo

w

inflo

w

Phosphate concentrations in winter surface layer in the Eastern Gotland Basin

Reissmann et al. (2009)