Recent shift in diatom record from Lake Rabbvatnet: response to global warming or solar variability?

ABSTRACT

Within the last decades, phytoplankton biomass has significantly risen in many lakes worldwide. Global warming was proposed as the most probable cause of the discovered effect. In this work, attention was paid to other drivers than just global warming, in particular, variability in solar radiation to explain this unexpected diatom shift. Here, we use a combination of paleolimnological, dendrochronological and meteorological datasets, as well as local pollution information, to analyze the recent growth of diatom total abundance in Lake Rabbvatnet (69.7º N, 30.5º E, Northern Norway). The results show that the diatoms of the genus Aulacoseira were most abundant in the top layers of the sediment core. On the contrary, the biomass of small-sized Cyclotella species, which, as a rule, should grow simultaneously with warming, has decreased over the past decades. We suggest basing on the experimental data analysis (comparison of diatom abundance with solar irradiance and heavy metals, testing of air temperature trends) that the recent growth of the total diatom abundance observed in the subarctic Rabbvatnet Lake could be mainly due to an increase in photosynthetically active spectral solar irradiance fluxes in the visible and infrared ranges.

Keywords: Diatom response; palaeolimnological data; climate warming; solar radiation; Arctic lake