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Palaeoenvironmental changes in the northern boreal zone of Finland: local versus regional drivers
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. , p. 41
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 40
Keywords [en]
Palaeolimnology, Palaeoecology, Biological assemblages, Sediment geochemistry, Regional drivers, Local drivers, Quantitative temperature reconstructions, Transfer-functions, Holocene, MIS 5d-c, Northern boreal zone, NE Finland
National Category
Earth and Related Environmental Sciences
Research subject
Quaternary Geology
Identifiers
URN: urn:nbn:se:su:diva-97588ISBN: 978-91-7447-838-9 (print)OAI: oai:DiVA.org:su-97588DiVA, id: diva2:679423
Public defence
2014-01-31, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

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.

Available from: 2014-01-09 Created: 2013-12-15 Last updated: 2017-09-20Bibliographically approved
List of papers
1. Palaeoenvironmental record of glacial lake evolution during the early Holocene at Sokli, NE Finland
Open this publication in new window or tab >>Palaeoenvironmental record of glacial lake evolution during the early Holocene at Sokli, NE Finland
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2014 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 43, no 2, p. 362-376Article in journal (Refereed) Published
Abstract [en]

The development of a glacial lake impounded along the retreating, northeastern ice margin of the Fennoscandian Ice Sheet during the last deglaciation and environmental conditions directly following the early Holocene deglaciation have been studied in NE Finland. This so-called Sokli Ice Lake has been reconstructed previously using topographic and geomorphologic evidence. In this paper a multiproxy approach is employed to study a 3-m-thick sediment succession consisting of laminated silts grading into gyttja cored in Lake Loitsana, a remnant of the Sokli Ice Lake. Variations in the sediment and siliceous microfossil records indicate distinct changes in water depth and lake size in the Loitsana basin as the Sokli Ice Lake was drained through various spillways opening up along the retreating ice front. Geochemical data (XRF core-scanning) show changes in the influence of regional catchment geochemistry (Precambrian crystalline rocks) in the glacial lake drainage area versus local catchment geochemistry (Sokli Carbonatite Massif) within the Lake Loitsana drainage area during the lake evolution. Principal component analysis on the geochemical data further suggests that grain-size is an additional factor responsible for the variability of the sediment geochemistry record. The trophic state of the lake changed drastically as a result of morphometric eutrophication once the glacial lake developed into Lake Loitsana. The AMS radiocarbon dating on tree birch seeds found in the glaciolacustrine sediment indicates that Lake Loitsana was deglaciated sometime prior to 10 700 cal. a BP showing that tree Betula was present on the deglaciated land surrounding the glacial lake. Although glacial lakes covered large areas of northern Finland during the last deglaciation, only few glaciolacustrine sediment successions have been studied in any detail. Our study shows the potential of these sediments for multiproxy analysis and contributes to the reconstruction of environmental conditions in NE Finland directly following deglaciation in the early Holocene.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-97569 (URN)10.1111/bor.12043 (DOI)000333455400006 ()
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2017-12-06Bibliographically approved
2. Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana, NE Finland
Open this publication in new window or tab >>Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana, NE Finland
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2014 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 52, no 4, p. 311-329Article in journal (Refereed) Published
Abstract [en]

This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry C-14 dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.

Keywords
Aquatic macrophytes, Chironomidae, Diatoms, Pollen, Sediment geochemistry, Local lake development, Holocene, Northern boreal zone, NE Finland
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-147281 (URN)10.1007/s10933-014-9795-1 (DOI)000345095100003 ()
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2017-09-20Bibliographically approved
3. Assessment of quantitative Holocene temperature reconstructions using multiple proxies from the Lake Loitsana sediment record
Open this publication in new window or tab >>Assessment of quantitative Holocene temperature reconstructions using multiple proxies from the Lake Loitsana sediment record
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(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-97586 (URN)
Available from: 2013-12-15 Created: 2013-12-15 Last updated: 2013-12-17Bibliographically approved
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