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Reconstructing past atmosperic circulation changes using oxygen isotopes in lake sediments from Sweden
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
NERC Isotope Geosciences Laboratory, BGS, UK.
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.

Place, publisher, year, edition, pages
2010. Vol. 6, no 1, 49-62 p.
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-36854DOI: 10.5194/cp-6-49-2010ISI: 000274994500004OAI: oai:DiVA.org:su-36854DiVA: diva2:290637
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
In thesis
1. Holocene climate and atmospheric circulation changes in northern Fennoscandia: Interpretations from lacustrine oxygen isotope records
Open this publication in new window or tab >>Holocene climate and atmospheric circulation changes in northern Fennoscandia: Interpretations from lacustrine oxygen isotope records
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2009. 30 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 18
Keyword
oxygen isotope, diatom silica, lake sediment, atmospheric circulation, North Atlantic Oscillation, northern Fennoscandia, The Holocene, Little Ice Age
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-29343 (URN)978-91-7155-904-3 (ISBN)
Public defence
2009-10-02, 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: In press. Paper 2: Submitted. Paper 5: In progress.Available from: 2009-09-10 Created: 2009-08-24 Last updated: 2010-04-22Bibliographically approved
2. Late Holocene humidity variability in central Sweden
Open this publication in new window or tab >>Late Holocene humidity variability in central Sweden
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
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:nbn:se:su:diva-36884 (URN)978-91-7155-929-6 (ISBN)
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

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