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Oinonen M.,University of Helsinki | Oinonen M.,University of Turku | Hilasvuori E.,University of Helsinki | Hilasvuori E.,Finnish Environmental Institute | And 4 more authors.
Radiocarbon | Year: 2013

The era of early urbanization in Finland coincides with large variations in the atmospheric radiocarbon concentration around the 13th-14th centuries AD. Therefore, the uncertainties of an individual 14C date are too large to support studies of this time period effectively. In this work, we have employ tree-ring wiggle-matching methodology and used Bayesian modeling of dates to account for stratigraphical a priori information within Aboa Vetus Museum, Turku, Finland. The wiggle-match method helps significantly to overcome the calibration-curve-induced challenges within 14C dating. The results of the dating model agree with the typological dates of the archaeological finds and illustrate a gradual evolution of urbanization in one of the oldest cities in Finland. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona. Source


Kuusisto E.,Finnish Environmental Institute
Lecture Notes in Earth Sciences | Year: 2012

The hydrological cycle is by far the largest material cycle of the Earth. The intensity of this cycle varies considerably as a function of time and space. Its annual volume has been fairly constant, but climate change is going to enhance the cycle, at the same time redistributing the temporal and spatial variability. This may have tremendous consequences both for nature and mankind. The majority of global climate models suggest, unfortunately, that many areas with scarce water resources will get drier in the future. On the other hand, in high latitudes where there already is plenty of water, more abundant water resources may be anticipated. © 2012 Springer-Verlag Berlin Heidelberg. Source


Jurvelius J.,Finnish Game And Fisheries Research Institute | Marjomaki T.J.,University of Jyvaskyla | Peltonen H.,Finnish Environmental Institute | Degtev A.,Petrozavodsk State University | And 3 more authors.
Hydrobiologia | Year: 2016

To evaluate the consistency of mobile and vertical echosounding results from the 1980s to the 2000s, fish density (fish ha−1) and target strength (TS, dB) estimates of single (70 and 200 kHz) and split (38 and 120 kHz) beam echo sounders were compared under varying light conditions. Acoustic estimates were compared with trawling results. During daytime hauls, the catch per swept area (CSA) of vendace and smelt were high at 10–15 m depth and low at 15–30 m depth. Around sunset, vendace and to some degree also smelt were concentrated at some meters above the thermocline. Around midnight, the CSA showed that smelt occupied higher water layers than vendace. Under different light conditions, both single and split beam echo sounders were in good agreement regarding the general level of fish density. In dusk and darkness, density estimates from echosounding and trawling as well as the TS-distribution between the single and split beam sounders were more consistent than those in daylight. We conclude that in boreal lakes single and split beam echosoundings outline, in comparable light conditions, consistent time series from the 1980s up to the year 2010. Darkness gives the best condition for estimating fish density and acoustic fish size. © 2016 Springer International Publishing Switzerland Source


Vahatalo A.V.,University of Helsinki | Vahatalo A.V.,Novia University of Applied Sciences | Aarnos H.,University of Helsinki | Hoikkala L.,University of Helsinki | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

We assessed the responses of a nitrogen (N)-limited < 10 μm plankton community from the Baltic Sea to the 12 d photochemical transformation of dissolved organic matter (DOM). The photochemical transformation of DOM increased the biomass and the production of heterotrophic bacteria, flagellates, and ciliates in the following 10 d bioassay. The succession of heterotrophic plankton indicated a 3-level trophic transfer of photoproduced bioavailable DOM through bacteria and flagellates to ciliates. The photochemical transformation of DOM also stimulated the biomass and the production of phytoplankton through the photoproduction of bioavailable N initially incorporated into bacterial biomass. The grazing of bacterioplankton supplied N to phytoplankton directly, presumably due to mixotrophy, and indirectly by releasing dissolved N. The carbon stable isotope signature of plankton biomass was similar to that of allochthonous carbon, indicating that the photochemical transformations concerned primarily terrestrial DOM and therefore represented a microbial link between terrestrial DOM and planktonic production. The bacterial production stimulated by the photochemically produced labile DOM was related to the number of photons absorbed during the photochemical transformation of DOM for the determination of apparent quantum yield. According to the apparent quantum yield, the calculated summertime photoproduction of labile substrates contributes 2 to 5% to total bacterial production in the northern Baltic Sea. According to this study, the photochemical transformation of terrestrial DOM influences not only the initial production of bacterioplankton but can also stimulate higher trophic levels and autotrophic plankton in coastal waters. © Inter-Research 2011. Source


Majaneva M.,University of Helsinki | Majaneva M.,Finnish Environmental Institute | Rintala J.-M.,University of Helsinki | Rintala J.-M.,Finnish Environmental Institute | And 3 more authors.
Polar Biology | Year: 2012

The Baltic Sea is one of the world's largest brackish water basins and is traditionally considered to be species poor. Here, we assessed the diversity of the nano-sized eukaryotic microbial wintertime community, using molecular ecological methods based on sequencing of small-subunit ribosomal RNA gene clone libraries. The results demonstrate that a rich community of small eukaryotes inhabits the Baltic Sea ice and water during winter. The community was dominated by alveolates and stramenopiles. Ciliates and cercozoans were the richest groups present, while in contrast to previous studies, diatoms showed a lower richness than expected. Furthermore, fungi and parasitic Syndiniales were present both in the water and in the sea ice. Some of the organisms in the sea-ice community were active, based on the RNA data, but a number of organisms were inactive or remnants from the freezing process. The results demonstrate that the sea-ice communities in the Baltic Sea are highly diverse and that water and ice of different ages include different protistan assemblages. Our study emphasizes the potential loss in biodiversity through diminishing ice cover as a result of climate change. © 2011 Springer-Verlag. Source

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