Lake Ecosystem Responses to Holocene Climate Change at the Subarctic Tree-Line in Northern Sweden |
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Authors: | Nina S Reuss Dan Hammarlund Mats Rundgren Ulf Segerström Lars Eriksson Peter Rosén |
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Institution: | 1. GeoBiosphere Science Centre, Quaternary Sciences, Lund University, S?lvegatan 12, 223 62, Lund, Sweden 5. Freshwater Biological Laboratory, Department of Biology, University of Copenhagen, Helsing?rsgade 51, 3400, Hiller?d, Denmark 2. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Ume?, Sweden 3. Department of Environmental Assessment, Swedish University of Agricultural Sciences, Box 7050, 750 07, Uppsala, Sweden 4. Climate Impacts Research Centre (CIRC), Ume? University, 98107, Abisko, Sweden
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Abstract: | A Holocene sediment sequence from Lake Seukokjaure, a subarctic lake at tree-line in northern Sweden, was analyzed to assess
major changes in the structure and functioning of the aquatic ecosystem in response to climate change and tree-line dynamics.
The compiled multi-proxy data, including sedimentary pigments, diatoms, chironomids, pollen, biogenic silica (BSi), carbon
(C), nitrogen (N) elemental and stable-isotope records, and total lake-water organic carbon (TOC) concentration inferred from
near-infrared spectroscopy (NIRS), suggest that the Holocene development of Lake Seukokjaure was closely coupled to changes
in terrestrial vegetation with associated soil development of the catchment, input of allochthonous organic carbon, and changes
in the light regime of the lake. A relatively productive state just after deglaciation around 9700 to 7800 cal years BP was
followed by a slight long-term decrease in primary production. The onset of the local tree-line retreat around 3200 cal years
BP was accompanied by more diverse and altered chironomid and diatom assemblages and indications of destabilized soils in
the catchment by an increase in variability and absolute values of δ13C. An abrupt drop in the C/N ratio around 1750 cal years BP was coupled to changes in the internal lake structure, in combination
with changes in light and nutrient conditions, resulting in a shift in the phototrophic community from diatom dominance to
increased influence of chlorophytes, likely dominated by an aquatic moss community. Thus, this study emphasizes the importance
of indirect effects of climate change on tree-line lake ecosystems and complex interactions of in-lake processes during the
Holocene. |
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