hans burchard baltic sea research institute warnemünde, germany hans.burchard@io-warnemuende.de

Hans Burchard

Baltic Sea Research Institute Warnemünde, Germany

hans.burchard@io-warnemuende.de

The invisible extremes:The dynamics of Baltic Sea inflow events

Let us first have a lookinto the observed long-termsurface salinity in the Central Baltic Sea

Sea surface salinity in the Central Baltic Sea

Feistel et al., 2006

How to attribute this to a certain process ?

Bottom salinity in the Central Baltic Sea

Feistel et al., 2006

A century of salinity in the Central Baltic Sea

Graphics: Courtesy to Markus Meier

All inflows have to pass the Western Baltic Sea

Western Baltic Sea monitoring stations

Darss Sill: 19 m

+

Drogden Sill: 8 m

+MARNET (IOW/BSH)

Farvandsvæsenet

Arkona Sea: 48 m

+

Three types of Baltic Sea inflow events:

Major Baltic inflows – barotropic (wind driven)

Strong Baltic inflows – baroclinic (density driven)

Medium Baltic inflows – mixed (typically through Sound)

Baltic Inflows over Darss Sill: the year 2003

Major barotropic inflow

Strong baroclinic inflow

Source: IOW

baroclinic barotropic

Inflows over Drogden Sill (through Sound)

surface

bottom

Graphics: Frank Janssen (BSH)

Where does the Sound plume go ?

?

GETM is a 3D numerical model for estuarine,coastal and shelf sea hydrodynamics with applications to the

• Tidal Elbe • Wadden Sea• Limfjord• Lake of Geneva, • Western Baltic Sea,• North Sea – Baltic Sea system• …

5 days

15 days

31 days

Sound lock-exchange experiment with GETM

Main plume goes via northof Kriegers Flak: Is this real ?

Bottom salinity: 8 – 25 psu

Burchard et al., OD, 2005.

Plume passing Kriegers Flak (Feb 2004)

Burchard et al., OD, 2005.

Current east [cm /s] / Salin ity [psu]

-35

-30

-25

-20

-15

-10

-5

0

Dep

th [m

]

-30-20-12-8-404812203040506070

12/05 01/06 02 /06 03/06 04/06 05 /06 06/06Current north [cm /s]

-35

-30

-25

-20

-15

-10

-5

0

Dep

th [m

]

-30-20-12-8-404812203040506070

12/05 01/06 02 /06 03/06 04/06 05 /06 06/06

Inflows north of Kriegers Flak

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

Model validation: Darss Sill

Model derived monthly mean vertically integrated physically and numerically induced salinity variance decay

Physical mixing Numerical mixing

Burchard et al., 2007 (submitted), Burchard and Rennau, 2007 (submitted)

Nov 2005: Velocity structure of dense bottom current

Ship A:TL-ADCP

Ship B: Microstructure

View

1 km

Flow

Eastcomp.

Northcomp.

Can we explain the flow structure ?

Umlauf et al., GRL, 2007

GETM 2DV Slice Model: Transverse gravity current structure

Conclusion:

Even after decades of intensive Baltic Sea research, there are still many miracles to be understood.

The major physical process question is:

How does the Baltic Sea overturn work ?

This includes the understanding of the entire pathway (in time and space) of water and its contentsfrom entering to exiting the Baltic Sea.