Phytoplankton are vital for energy transfer within the marine ecosystem, they depend on light for energy capture. The light environment in the Baltic is generally browner in the north than in the south. This shift in the visible light spectrum towards red wavelengths is caused by chromophoric dissolved organic matter (CDOM) which absorbs light in the blue part of the visible spectrum. Terrestrial CDOM levels in seawater are predicted to increase as climate change induces greater rainfall. The Baltic Sea system presents an opportunity to better determine the effect of this aspect of climate change on phytoplankton.