Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Long-Term Trends in the Surface Salinity and Temperature in the Baltic
Sea
Anniina Kiiltomäki, Tapani Stipa, Mika Raateoja, Petri Maunula
Finnish Institute of Marine Research, 00931 Helsinki, Finland, anniina.kiiltomaki@fimr.fi
1. Introduction
In the Baltic Sea large fluctuations occurs in the ecosystem
and salinity fields. Salinity is strongly influenced by the
water exchange between the North Sea and the Baltic Sea,
advection and mixing of fresh water originating from the
large rivers. In this examination the horizontal distribution
and temporal variation of salinity and temperature are
investigated in the Baltic Sea by using the data derived from
Alg@line program. The long-term variations are studied
using the gradients of salinity and temperature.
2. Alg@line – unattended algal monitoring in the
Baltic Sea line
Alg@line is a research program of the Finish Institute of
Marine Research that monitors extensively the fluctuations
in the Baltic Sea ecosystem both in place and time. The
main emphasis of Alg@line is adequate monitoring of
phytoplankton, especially the harmful blooms. Except
biological parameters also the hydrographical parameters,
surface water salinity and temperature, are measured with
high frequency to give additional information of the water
masses (Rantajärvi, E. 2003). Alg@line research program
gives the real-time information about the state of algal
blooms, water nutrification and the movements of water
masses in competent spatial scope. (The information is
shown on the Baltic Sea Portal web site at
www2.fimr.fi/itamerikanta.html.) Furthermore, one of the
aims has been to record a long time-series to observe the
long-term variations and changes.
3. Measurements and Results
The data used in this study was automatically collected
during M/S Finnpartners continuous voyages between
Travemünde/Lübeck and Helsinki through out the study
years 1993-2003. The measurements were carried out with a
flow-through system (which pumps the water from beneath
the ships’ hull to the measurement equipment and out again
continuously while the ship is moving). The fixed sampling
depth is about 5 meters and the water sample represent the
surface water mass (about 0-7m).
Two different kinds of measurements were carried out on
the ship. The temperature and salinity of the water was
recorded frequently (in every 20 seconds) by in vivo
measurements. Furthermore, 24 water samples were
collected on each voyage for other biological and chemical
purposes. The water samples were always collected at the
same locations on the sea-lane. Temporal frequency of in
vivo measurements was about 1-3 days and of water samples
about one week –depending on the schedule of the ferry.
We used only the data recorded on the water sampling
locations, even though the data obtained from the frequent in
vivo measurements is more extensive. The gradients are used
because of the uncertainty of absolute values of
measurements. The gradient variations provide an excellent
view of the Salinity and Temperature trends in the long run.
Absolute values of the data are feasible from the last years
and a comparison between those and gradients are also
carried out. Horizontal and temporal distribution of
salinity and temperature for the year 2002 is shown in
figure 1.
Figure 1. The annual variation of Salinity and
Temperature [ºC] as a function of position and time along
the ship route (between Travemünde-Helsinki), for year
2002. The water sampling locations are indicated with red
points, and with triangles when the ship was traveling on
the west side of Gotland. Cumulative day number is used
as a temporal scale.
References
Rantajärvi, Eija, Alg@line IN 2003: 10 years of innovative
plankton monitoring and research and operational
information service in the Baltic Sea, Meri, No. 48,
pp. 3-17, 2003