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Late Holocene humidity variability in central Sweden
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. Stable isotopes (δ18O and δ13C) on Chara spp encrustations and Pisidium spp mollusc shells and carbon content were analysed in the lake record, whereas peat stratigraphy, humification, testate amoebae assemblages, C/N ratio and stable isotopes (δ13C and δ15N) were analysed in the mire record. Stable isotopes (δ2H and δ18O) on lake water showed that Lake Blektjärnen responded to changes in the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate during which evaporation and atmospheric equilibration likely enrich lake water in 18O and 13C, respectively, and vice versa for a low E/I ratio. The relatively high Chara δ18O and δ13C values between ca 4400 and 4000 cal yr BP thus suggest relatively dry and likely warm conditions, whereas depleted values suggest wetter and probably cooler conditions between ca 4000 and 3000 cal yr BP. Again, drier and probably warmer conditions were inferred from the relatively enriched δ18O values between ca 2500 and 1000 cal yr BP, and depleted δ18O values were recorded between ca 1000 and 50 cal yr BP indicating wetter and likely cooler conditions. The results from the mire mainly indicated vegetation succession, however, the changes inferred at ca 2600 and 1000 cal yr BP could have been triggered by climate change. This study shows that the proxies responded sensitively to humidity changes in the investigated archives allowing for reconstruction of climate change in central Sweden during late Holocene.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2010. , 60 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 20
Keyword [en]
humidity change, stable isotopes, Chara spp, Pisidium spp, testate amoebae assemblages, humification, C/N ratio, late Holocene, central Sweden
National Category
Geology
Research subject
Quarternary Geology
Identifiers
URN: urn:nbn:se:su:diva-36884ISBN: 978-91-7155-929-6 (print)OAI: oai:DiVA.org:su-36884DiVA: diva2:290897
Public defence
2010-03-05, 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: Submitted. Paper 3: Accepted. Paper 5: In progress.Available from: 2010-02-11 Created: 2010-01-28 Last updated: 2010-10-07Bibliographically approved
List of papers
1. Late Holocene climate change in central Sweden inferred from lacustrine stable isotope data
Open this publication in new window or tab >>Late Holocene climate change in central Sweden inferred from lacustrine stable isotope data
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(English)In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417Article in journal (Other academic) Submitted
Abstract [en]

Stable isotopes (18O and 13C) of lacustrine carbonates (Chara spp algae and Pisidium spp molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (18O and 2H) show that Lake Blektjärnen water isotope composition is responsive to the water balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara 18O values we infer that conditions were dry and warm between 4400-4000 cal yr BP whereas more negative values indicate that conditions were wetter and probably cooler between 4000-3000 cal yr BP. A drier climate is inferred from more positive values between 2500-1000 cal yr BP. However, a successive depletion after ca 1750 cal yr BP, also detected in several other 18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased zonal flow.

Keyword
stable isotopes, Chara spp, Pisidium spp, lake hydrology, humidity, central Sweden, late Holocene
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-36877 (URN)
Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2017-12-12Bibliographically approved
2. Reconstructing past atmosperic circulation changes using oxygen isotopes in lake sediments from Sweden
Open this publication in new window or tab >>Reconstructing past atmosperic circulation changes using oxygen isotopes in lake sediments from Sweden
2010 (English)In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, no 1, 49-62 p.Article in journal (Refereed) Published
Abstract [en]

Here we use lake sediment studies from Sweden to illustrate how Holocene-aged oxygen isotope records from lakes located in different hydrological settings, can provide information about climate change. In particular changes in precipitation, atmospheric circulation and water balance. We highlight the importance of understanding the present lake hydrology, and the relationship between climate variables and the oxygen isotopic composition of precipitation (d18Op)and lake waters (d18Olakewater) for interpretation of the oxygen isotopic record from the sediments (d18O). Both precipitation reconstructions from northern Sweden and water balance reconstructions from south and central Sweden show that the atmospheric circulation changed from zonal to a more meridional airflow over the Holocene. Superimposed on this Holocene trend are δ18Op minima resembling intervals of the negative phase of the North Atlantic Oscillation (NAO), thus suggesting that the climate of Northern Europe is strongly influenced by atmospheric and oceanic circulation changes over the North Atlantic.

National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-36854 (URN)10.5194/cp-6-49-2010 (DOI)000274994500004 ()
Note
First published in Climate of the Past (CP) Discussions, special issue, 5, 1609–1644.Available from: 2010-01-27 Created: 2010-01-27 Last updated: 2017-12-12Bibliographically approved
3. Surface wetness and mire development during the late Holocene in central Sweden
Open this publication in new window or tab >>Surface wetness and mire development during the late Holocene in central Sweden
(English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885Article in journal (Refereed) Accepted
Abstract [en]

Late Holocene mire development and surface wetness changes have been studied in a small mixed mire located in central Sweden. Today the mire is characterised by a mainly ombrotrophic centre dominated by Sphagnum mosses whereas Carex content increase towards the more minerotrophic mire margins. Two peat sequences extracted from the central ombrotrophic part were investigated for stratigraphy, humification, testate amoebae analysis, C/N ratio and 13C and 15N stable isotopes. Three main stages of mire development are identified with a first stage between ca 4200-2600 cal yr BP, characterised by water-logged conditions suggesting a minerotrophic fen stage. The second stage between ca 2600-1000 cal yr BP is characterised by more ombrotrophic conditions and Sphagnum dominated vegetation. The onset of the prominent change at ca 2600 cal yr BP could have been initiated by by climate change coincident with a change in solar activity. The last stage, between ca 1000-50 cal yr BP, is dominated by more ombrotrophic conditions suggesting increased precipitation. This study shows that the response of hydrological proxies in a mixed mire during its development towards more ombrotrophic conditions might result in conflicting results, which has to be considered in palaeoenvironmental reconstructions from mires that changes between ombrotrophic and minerotrophic settings.

Keyword
mire development, testate amoebae, surface wetness, C/N ratio, humification, late Holocene, central Sweden
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-36881 (URN)
Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2017-12-12Bibliographically approved
4. A new mid-Holocene tephra in central Sweden
Open this publication in new window or tab >>A new mid-Holocene tephra in central Sweden
2009 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 131, no 4, 293-297 p.Article in journal (Refereed) Published
Abstract [en]

A mid Holocene tephra, LBA-2 has been found in a peat bog in central Sweden. Geochemical analyses suggest an origin in an evolved volcanic centre, most likely the Snæfellsnes volcanic centre in western Iceland. The geochemistry of the LBA-2 tephra is similar to the youngest of three silicic tephra layers from Snæfellsjökull, Sn-1 dated to 1780 cal yr BP. However, wiggle-match dating indicates an age of 3550-3650 cal yr BP, close in age to the Hekla-S/Kebister tephra (3720 cal yr BP), previously found in several sites in Scandinavia. Detailed geochemical analyses and dating is lacking for the mid Holocene Sn-2 tephra in Iceland but it is likely that the geochemical composition is similar as the Sn-1 tephra. The LBA-2 tephra is tentatively correlated with the Sn-2 tephra and we also suggest that the ‘x’ tephra layer (ca 3500 BP) found in the Dyngjufjöll area, central Iceland (Sigvaldason et al. 1992) can be correlated with the Sn-2 tephra.

Place, publisher, year, edition, pages
London: Taylor & Francis, 2009
National Category
Geology
Identifiers
urn:nbn:se:su:diva-32910 (URN)10.1080/11035890903452662 (DOI)000272850400003 ()
Available from: 2009-12-17 Created: 2009-12-17 Last updated: 2017-12-12Bibliographically approved
5. Synthesis of proxy response to climate change in central Sweden during the late Holocene
Open this publication in new window or tab >>Synthesis of proxy response to climate change in central Sweden during the late Holocene
(English)Article in journal (Other academic) In Progess
Abstract [en]

Biological and geochemical proxies from two lakes and two peat sites in central Sweden are used to test if the inferred climate change can be connected to previously reported temperature anomalies, inferred from stacked pollen mean annual and mean July temperatures mainly in Fennoscandia, during the late Holocene. We show that the reported temperature deviations (lower temperatures between 3800-3000, higher temperatures between 3000-500, and lower temperatures again between 500-50 cal yr BP), can be related to recorded changes in the investigated proxies. These periods correspond to changes inferred from two of the sites; in one of the lakes the reconstructed evaporation and input ratio (E/I) show a high ratio from a dry and likely warmer climate, with decreased importance of precipitation input, and vice versa for a low ratio, and, from one of the peat humification records. Beyween 600-300 cal yr BP magnetic susceptibility increased in a lacustrine sediment record and water table rose according to peat records. The proxies from central Sweden seem to support a late Holocene temperature maximum around ca 2000 cal yr BP, although this is speculative since it is represented by a few samples only.

National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-36882 (URN)
Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2010-01-29Bibliographically approved

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