Holocene environmental history in northwest Finnish Lapland reflected in the multi-proxy record of a small subarctic lake |
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| Authors: | Krystyna Szeroczyńska Andrzej Tatur Jan Weckström Michał Gąsiorowski Agnieszka M Noryśkiewicz Elwira Sienkiewicz |
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| Institution: | 1.Institute of Geological Sciences,Polish Academy of Sciences,Warsaw,Poland;2.Centre for Ecological Research, PAS,?omianki,Poland;3.Department of Antarctic Biology,PAS,Warsaw,Poland;4.Environmental Change Research Unit (ECRU), Department of Biological and Environmental Sciences,University of Helsinki,Helsinki,Finland;5.Institute of Archaeology,Nicolaus Copernicus University,Toru?,Poland |
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| Abstract: | A 2.5-m-long sediment core was retrieved from Lake Somaslampi, a small lake located in a kame field on the north slope of
the Scandes Mountains in Finnish Lapland. Holocene environmental changes were inferred from the lithological, geochemical,
pollen, diatom and Cladocera records stored in the lake sediment. The chronology was based on six radiocarbon AMS dates supported
by a palynological control chronology. The sediment profile consists of a glacial sedimentary sequence truncated by a lacustrine
one. A hiatus, tentatively correlated with climate cooling and advances of glaciers during the 8.2 ka yrs BP “Finse cooling
Event”, occurs between these sequences. The glacial sequence was composed of fluvioglacial clastics, smoothly changing into
glacio-lacustrine diatomaceous ooze deposited in a meromictic proglacial lake that covered the kame field. The meromixis was
probably caused by the greater depth of the lake, the extended ice-cover, and the microbial mats covering large areas of the
lake bottom. A distinct change in the biota of the glacio-lacustrine sediments indicates higher trophic conditions than during
deposition of the fluvioglacial clastics. The late-Pleistocene vegetation was characterised by subarctic birch tundra vegetation
(Betula–Salix–Ericaceae) with low biodiversity gradually changing to Betula–Pinus dominance in the early Holocene. The lake was deep and had a diatom inferred pH ~ 7 indicated also by the dominance of planktonic
Cladocera.
The base of the lacustrine sediment sequence (6,650–6,300 cal. BP) consisted of loess-rich sediment indicating an increase
in eolian activity. This is also supported by the pollen record, which is dominated by more long-distant taxa such as Alnus and Pinus, and by the increased C/N ratio of the sediment. After the initial meromictic phase of the lake, an abrupt lowering of the
water level occurred. Lake Somaslampi was isolated from the larger Pre-Lake Somas basin and became holomictic, shallow, much
warmer and more productive, until the deterioration of climate around 3,000 yr BP and the increased input of clastics from
the tundra soils. The vegetation followed the general climatic trend by gradually changing from the dominance of Betula and Pinus to the dominance of more tundra-related vegetation like Poaceae and Cyperaceae. However, the higher frequencies of planktonic
Cladocera and centric diatoms in the most recent sediments indicates higher trophic conditions, increased turbulence and a
prolonged ice-free period, which can possibly be linked to the recent climate warming especially in areas of higher altitude
and latitude. |
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| Keywords: | Subarctic Finnish Lapland Holocene Paleolimnology Pollen Diatoms Cladocera Geochemistry Meromixis |
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