Palaeolimnological Development of Lake Njargajavri, Northern Finnish Lapland, in a Changing Holocene Climate and Environment |
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| Authors: | Kaarina Sarmaja-Korjonen Marjut Nyman Seija Kultti Minna Väliranta |
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| Institution: | (1) Department of Geology, University of Helsinki, P.O. Box 64, FIN-00014, Finland;(2) Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, FIN-00014, Finland |
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| Abstract: | This study used palaeolimnological approaches to determine how Holocene climatic and environmental changes affected aquatic
assemblages in a subarctic lake. Sediments of the small Lake Njargajavri, in northern Finnish Lapland above the present treeline,
were studied using multi-proxy methods. The palaeolimnological development of the lake was assessed by analyses of chironomids,
Cladocera and diatoms. The lake was formed in the early Holocene and was characterized by prominent erosion and leaching from
poorly developed soils before the establishment of birch forests, resulting in a high pH and trophic state. The lake level
started to lower as early as ca. 10,200 cal. BP. In the resulting shallow basin, rich in aquatic mosses, pH decreased and
a diverse cladoceran and chironomid assemblage developed. It is likely that there was a slight rise in the water level ca.
8000 cal. BP. Later, during the mid-Holocene characterized by low effective moisture detected elsewhere in Fennoscandia, the
lake probably completely dried out; this is manifest as a hiatus in the stratigraphy. The sediment record continues from ca.
5000 cal. BP onwards as the lake formed again due to increased effective moisture. The new lake was characterized by very
low pH. The possible spread of pine to the catchment and the development of heath community may have contributed to the unusually
steep (for northern Fennoscandia) decline in pH via change in soils, together with the natural decrease in leaching of base cations. Furthermore, the change in pH may have been
driven by cooling climate, affecting the balance of dissolved inorganic carbon in the lake. |
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| Keywords: | Chironomid-inferred July air temperature Cladocera Diatoms Holocene lake-level changes Multi-proxy research Northern Fennoscandia |
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