Project description

The Baltic Sea is optically dominated by coloured dissolved organic matter (CDOM).
CDOM occurs naturally in the Baltic Sea as a results from breakdown of organic material
and due to the high freshwater input and a relatively low water exchange with the North
Sea. CDOM absorbs light mostly in the blue and the blue-green part of the visible
spectrum, and therefore makes the water appear yellow-brown. Cyanobacteria are the
only type of phytoplankton that have been shown to be able to adapt to changes in the
underwater light field. This is due to their ability to generate phycoerythrin or
phycocyanin – dependent on the spectral composition of the underwater light regime.

Fig. 1 Jerlov (1976) classified natural waters by their spectral light transmission into oceanic water types I-III and coastal water types 1-9. The Baltic Sea belongs to coastal waters type 9 with maximum transmission in the green to red part of the visible spectrum due to its high CDOM content.
Fig. 1 Jerlov (1976) classified natural waters by their spectral light transmission into oceanic water types I-III and coastal water types 1-9. The Baltic Sea belongs to coastal waters type 9 with maximum transmission in the green to red part of the visible spectrum due to its high CDOM content.

We hypothesis that cyanobacteria will also change their pigment composition if grown under
different light conditions in the laboratory (e.g. yellow vs. blue light filters). Initial laboratory tests
will be performed to measure the light adaptation of laboratory cultures. The ultimate aim
of the Masters project is to relate the changes in underwater light field along a natural
light gradient the Öre estuary in the Gulf of Bothnia and to evaluate the effect on the
absorption spectrum of cyanobacteria.

Optical measurements and an optical model will be used to characterize the underwater
light field (spectral diffuse attenuation of light). In parallel, water samples will be taken
to measure the in vivo spectrum of phytoplankton (filter pad method). The changes in the
light field will then be related to the changes in the spectral signature of the
phytoplankton.

The successful candidate will work closely with another Master’s student who will focus
on quantifying the gene expression for the picocyanobacteria pigments grown in varying
light conditions / and varying concentrations of CDOM.

Strong communication and interpersonal skills are required. In addition, field expeditions
in the Baltic Sea / including the Gulf of Bothnia are planned, hence the successful
candidate should be willing and able to participate in these. Previous experience with lab
work is of advantage. A driver’s license is of advantage for planning and performing the
field work.

Information

For further information about the position, please contact Associate
Professor Susanne Kratzer by email: Susanne.Kratzer@su.se