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Low-frequency and high-frequency changes in temperature and effective humidity during the Holocene in south-central Sweden: implications for atmospheric and oceanic forcings of climate
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2005 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 25, no 2-3, 285-297 p.Article in journal (Refereed) Published
Abstract [en]

An integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes. Here we report a 10,000 year quantitative record of annual mean temperature ( T ann), based on pollen-climate transfer functions and pollen-stratigraphical data from Lake Flarken, south-central Sweden. The pollen-based temperature reconstruction is compared with a reconstruction of effective humidity, as reflected by a d18O record obtained on stratigraphy of lacustrine carbonates from Lake Igelsj�n, c. 10 km from Lake Flarken, which gives evidence of pronounced changes in effective humidity. The relatively low T ann, and high effective humidity as reflected by a low evaporation/inflow ratio suggest a maritime early Holocene climate (10,000�8,300 cal year BP), seemingly incompatible with the highly seasonal solar insolation configuration. We argue that the maritime climate was due to the stronger-than-present zonal flow, enhanced by the high early Holocene sea-surface temperatures in the North Atlantic. The maritime climate mode was disrupted by the abrupt cold event at 8,200 cal year BP, followed at 8,000 cal year BP by a stable Holocene Thermal Maximum. The latter was characterized by T ann values about 2.5�C higher than at present and markedly dry conditions, indicative of stable summer-time anti-cyclonic circulation, possibly corresponding with modern blocking anticyclonic conditions. The last 4,300 year period is characterized by an increasingly cold, moist, and unstable climate. The results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability, generality, and interpretability of the palaeoclimatic results. Further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial-scale climate dynamics.

Place, publisher, year, edition, pages
2005. Vol. 25, no 2-3, 285-297 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94347DOI: 10.1007/s00382-005-0024-5OAI: oai:DiVA.org:uu-94347DiVA: diva2:168169
Available from: 2006-04-13 Created: 2006-04-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Holocene Climate in Central and Southern Sweden: Quantitative Reconstructions from Fossil Data
Open this publication in new window or tab >>Holocene Climate in Central and Southern Sweden: Quantitative Reconstructions from Fossil Data
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In quantitative palaeoecology modern species-environmental relationships can be statistically modelled, and recent development has made the calibration models more statistically robust. These models are used to transform fossil assemblages to quantitative estimates of past environmental conditions. The aim of this thesis is to infer Holocene temperatures from fossil pollen data sampled from lakes in central and southern Sweden. This reconstruction is done by using a north-European pollen-climate calibration model, which was extended with 37 modern pollen samples from the southern deciduous vegetation zone in Sweden within this project. A statistical method is used for deriving the pollen-climate calibration model, weighted averaging partial least square (WA-PLS) method. The long term trends in pollen inferred temperatures from this study reflect low, but rapidly rising temperatures in the early-Holocene, a trend that was temporarily interrupted by a cool period about 8500 cal yr BP, but continued after 8000 cal yr BP. A Holocene thermal maximum (HTM) with temperatures roughly 2°C higher than at present was recorded about 7000 cal yr BP and by 4000 cal yr BP pollen inferred temperatures starts to decline. In order to create a more comprehensive picture of past climate patterns in the investigated area inferred temperatures from this study are compared with independent palaeorecords, a stable oxygen isotope record for moisture variability (paper I) and chironomids for summer temperature (paper II). Taken all together, these records reflect a coherent Holocene climate pattern which also is supported by several studies from Scandinavia and the north Atlantic region. Pollen inferred temperatures and the moisture record are indicating markedly dry, continental climate conditions in southern Sweden during the HTM possibly as a result of reorganisations in regional atmosphere circulations. The local observations in this study of regional climate events, such as the cold period at about 8200 cal yr BP and the dry period at about 7000 to 4000 cal yr BP are of particular interest because they suggest that vegetation in the study region has responded sensitively both to long-term climatic trends and more transient climate events.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 37 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 168
Keyword
Quaternary geology, pollen analysis, climate reconstructions, transfer functions, vegetation dynamics, Sweden, Kvartärgeologi
Identifiers
urn:nbn:se:uu:diva-6805 (URN)91-554-6539-0 (ISBN)
Public defence
2006-05-08, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2006-04-13 Created: 2006-04-13 Last updated: 2013-05-23Bibliographically approved

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