Palaeoenvironmental changes in the northern boreal zone of Finland: local versus regional drivers
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Multiple proxies derived from the Lake Loitsana sediment sequence (NE Finland) are employed to determine the timing of deglaciation, characterise an early Holocene proglacial lake stage and reconstruct Holocene lake development. Local-scale processes causing shifts in biological assemblages are identified and the most likely Holocene mean July air temperature (Tjul) development is assessed. The study area was deglaciated shortly prior to 10 700 cal. a BP. The sediment record reflects four local events; the presence of a glacial lake, glacial lake drainage and formation of Lake Loitsana, changes in fluvial input due to progressive wetland expansion, and gradual lake infilling. The results suggest that local events have driven changes in biological assemblages through various processes, and that biotic proxies reflect changes in environmental parameters in a highly individual manner. Furthermore, biological assemblages can themselves act as important drivers, influencing the composition of other assemblages. It is suggested that future studies should consider macrophyte abundance and food-web interactions as equally important factors when assessing changes in biological assemblages. Quantitative Tjul reconstructions based on biotic proxies display contrasting trends. While Tjul reconstructions based on pollen found in the Loitsana sequence display relatively low early Holocene values, plant macrofossil and chironomid data reflect warm summer conditions also during the early Holocene, i.e. at the peak of summer insolation. The early Holocene Tjul recorded by terrestrial pollen are affected by local factors possibly combined with a delayed response of the terrestrial ecosystem compared to the aquatic one. This study emphasises the importance of using multiple proxies in palaeoenvironmental studies and shows that local factors have a potential to drive changes in biological assemblages that can affect transfer-function based temperature reconstructions.
Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2014. , 41 p.
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 40
Palaeolimnology, Palaeoecology, Biological assemblages, Sediment geochemistry, Regional drivers, Local drivers, Quantitative temperature reconstructions, Transfer-functions, Holocene, MIS 5d-c, Northern boreal zone, NE Finland
Earth and Related Environmental Sciences
Research subject Quaternary Geology
IdentifiersURN: urn:nbn:se:su:diva-97588ISBN: 978-91-7447-838-9OAI: oai:DiVA.org:su-97588DiVA: diva2:679423
2014-01-31, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Bigler, Christian, Docent
Helmens, Karin H., Docent
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Epub ahead of print. Paper 2: Accepted. Paper 3: Manuscript.2014-01-092013-12-152014-01-10Bibliographically approved
List of papers