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.

Abstract The tree growth response in polar region (Kola Peninsula and Finnish Lapland) to the most powerful (VEI>4) volcanic eruptions is assessed over a period of 1445-2005. The analysis was based on the Loparskaya (1445-2005) and Finnish supra-long (~ 7500 years) tree-ring chronologies. These chronologies were developed from Pinus sylvestris L. samples collected near the northern tree line at Loparskaya station (68.63º N, 33.25º E) and Finnish Lapland (68-70º N; 20-30º E), respectively. A superposed epoch analysis indicated a significant decrease in polar tree-ring growth over 7 years after the eruptions with subsequent recovery to its normal level. The level of tree growth in polar region is affected by most powerful low-latitude volcanic eruptions. By contrast, high-latitude Icelandic volcanoes have no significant impact on the climate of Kola Peninsula and Finnish Lapland. The application of wavelet analysis for the Loparskaya tree ring chronology allowed to identify the existence of the main cycles of solar activity (11, 20-25, and ~ 100 years). Moreover, the wavelet analysis revealed a strong coherence in the 8-13 and 20-30 year bands, indicating a possible link between solar activity and climate change on a regional scale.

Resumen En este trabajo, se evalúa la respuesta del crecimiento de los árboles en la región polar (Península de Kola y la Laponia de Finlandia) a las erupciones volcánicas más potentes (VEI > 4) durante un periodo de 1445-2005. El análisis se basó en dos cronologías de anillos de árboles de elevada resolución: Loparskaya (1445-2005) y Finnish (~ 7500 años). Estas cronologías se desarrollaron a partir de muestras de Pinus sylvestris L. recogidas cerca de la línea de árboles del norte en la estación de Loparskaya (68.63º N, 33.25º E) y la Laponia finlandesa (68-70º N; 20-30º E), respectivamente. El análisis de sobreposición de época indicó una disminución significativa en el crecimiento de los anillos de los árboles polares durante 7 años después de las erupciones. Asimismo, el estudio de los anillos muestra que el nivel de crecimiento de los árboles en la región polar se ve afectado por las más poderosas erupciones volcánicas producidas en latitudes bajas. En cambio, los volcanes islandeses no tienen un impacto significativo en el clima de la Península de Kola y la Laponia finlandesa. La aplicación del análisis wavelet para la cronología del anillo de árboles de Loparskaya permitió identificar la existencia de los ciclos principales de actividad solar (11, 20-25 y ~ 100 años). Además el análisis wavelet reveló una fuerte coherencia en las bandas 8-13 y 20-30 años indicando un posible vínculo entre la actividad solar y el cambio climático a escala regional.