Fourth Study Conference on BALTEX Scala Cinema Gudhjem

Baltic Sea Inflow Events
Jan Piechura
- 59 -
Institute of Oceanology, PAS, Powstańców Warszawy 55, Sopot, Poland, e-mail: piechura@iopan.gda.pl
Abstract
After nearly a decade (since 1993) without any major
inflow, during August 2002 – July 2003 we observed at
least two small and one medium size inflows. All of them
were quite unusual: Small inflows occurred during
summer of 2002 (R. Feistel et al 2003) and again summer
2003 and brought unusually warm water (T>11-12 o C) to
the Baltic Sea while the medium size inflow took place in
January 2003 and brought unusually cold water ( ≈1 o C)
into the Baltic Sea (J. Piechura and A. Beszczyńska-
Möller, 2003).
Warm inflows
Because of their lower density, summer inflow events
were moving to the east along the deep channels and
basins of the Baltic Proper in the intermediate layers (in
the Bornholm Deep) first and only in Słupsk Channel and
Gdansk Deep they occupied the bottom layer as well
(fig.1).
The warm water occupied the layer of 40-70 m in the
Bornholm Deep and 65 m to the bottom in the Slupsk
Channel, and these layers’ temperatures were 10-11 o C
and 8-9 o C, respectively. Some amount of warm water is
found in the near bottom layer on the slope towards the
Gdansk Deep; its temperature is lower with about 6 o C.
On top of this layer remains cold, so called winter water,
which is much stronger and colder (4-6 o C) in the Slupsk
Channel and Gdansk Deep than in the Bornholm deep (6-
7 o C).
In January, the warm layer moved to the east, now it was
observed in central and eastern parts of the Bornholm
Deep (layer of 50-75 m) in the Slupsk Channel (60 m -
bottom) and on the slope towards Gdansk Deep (80 mbottom).
It’s temperature was lower (8-10 o C in the
Bornholm Deep, 6-9 o C in Slupsk Furrow) except near to
the Gdansk Deep where temperature rose to 6-8 o C. The
eastward movement of the warm layer the decrease of it’s
temperature continued in February.
Cold Inflow
Cold waters brought by the winter inflow occupied the
bottom layer everywhere. Relatively unchanged they
were found in Arkona Basin, Bornholm Gate and
Bornholm Deep only. Very intensive mixing occurred in
the Bornholm Deep in particular, causing strongly mixed
waters to move father to the east.
Inflowing cold and salty water pushed ambient waters
upwards and to the east. The halocline in the Bornholm
Deep was shifted up by 20-30 m. Moving into Slupsk
Furrow inflow/mixed waters have to pass over Slupsk
Sill. This overflow has a splash – like character similar to
that observed in May 1995.
The full cycle of the overflow event lasted for about 30
hours. Pulsating manner of the flow is also confirmed by
observations made in December 2003 in the Slupsk
Channel (fig.2).
At depth of about 70 m currents direction changes
rapidly and its speed increased from less than 10 cm . s -1
to nearly 45 cm . s -1 . At the same time temperature and
salinity increased by nearly 5 o C and 5 psu, respectively,
and fell down again. It took about 50 hours for this body
of warm, salty water to pass over moored instruments
anchored in this area.
Mesoscale eddies were observed all the time, particularly
numerous in the Bornholm Basin. Most provably those
eddies were responsible for intensive mixing of inflowing
and ambient waters.
References
Rainer Feistel, Günther Nausch, Volker Mohrholz,
Elżbieta Łysiak-Pastuszak, Torsten Seifert,
Wolfgang Matthäus, Siegfried Krüger, Ian Sehestad
Hansen, Warm waters of summer 2002 in the deep
Baltic Proper, Oceanologia, 45(4), 571-592, 2003
Jan Piechura, Agnieszka Beszczyńska-Möller, Inflow
waters in the deep regions of the souther Baltic Sea
– transport and transformations, Oceanologia,45(4),
593-621, 2003