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Diatom assemblages from an Eemian palaeolake in northern Europe with morphological observations of rare Aulacoseira sp. resting spores
Stockholm University, Faculty of Science, Department of Physical Geography.ORCID iD: 0000-0001-6523-0796
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

An overview of the diatom flora of the last interglacial (Eemian) lacustrine gyttja deposit at Sokli, northeastern Finland is presented together with detailed descriptions including photomicrographs of resting spores similar to the Aulacoseira islandica-skvortzowii group, not found in recent material from Europe. Comparisons are made with literature data on similar taxa. The morphology of the resting spores (e.g. the number of striae and areolae in 10 µm) attributes them to the A. islandica-skvortzowii group but the lack of vegetative cells in the Sokli record makes declaration of true synonymy difficult. The presence of spores similar/related to the A. islandica-skvortzowii group in the Sokli Eemian palaeolake may reflect a more widespread  distribution of this group in the past.

Keywords [en]
Aulacoseira, Aulacoseira islandica, Aulacoseira skvortzowii, resting spore, morphology, Pleistocene, Finland
National Category
Earth and Related Environmental Sciences
Research subject
Quaternary Geology
Identifiers
URN: urn:nbn:se:su:diva-155499OAI: oai:DiVA.org:su-155499DiVA, id: diva2:1199955
Available from: 2018-04-23 Created: 2018-04-23 Last updated: 2018-05-08Bibliographically approved
In thesis
1. The Eemian Interglacial at Sokli, northern Finland: A multi-proxy environmental and climatic reconstruction based on a 9 m long lacustrine sediment sequence
Open this publication in new window or tab >>The Eemian Interglacial at Sokli, northern Finland: A multi-proxy environmental and climatic reconstruction based on a 9 m long lacustrine sediment sequence
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding the fundamentals of the Earth’s climate system during the Quaternary Period (the past ca 2.6 million years) is of imminent interest in light of the reported recent climatic changes. The Eemian Interglacial (ca 129,000-116,000 years ago) is the last period before the present interglacial (the Holocene, the last ca 11,700 years) when temperatures were as warm as or warmer than today and may serve as an analogue to future climatic warming. The Eemian is a relatively well-studied period, but many aspects of the interglacial climatic dynamics still remain unresolved. One reason for this is the chronological uncertainties of many records from this time period; another is the relatively uneven distribution of palaeoarchives. Especially from high latitude areas, terrestrial records from the Eemian are few due to the impact of glacial erosion during the Weichselian Glacial (ca 116,000-11,700 years ago).

This thesis is based on data from Sokli, N Finland, where cold-based conditions of the Weichselian ice sheets and non-typical bedrock conditions have allowed preservation of an unusually thick Eemian lacustrine deposit in stratigraphic sequence with overlying Weichselian and Holocene deposits. The main purpose of this thesis is to contribute to the knowledge of climate variability in Fennoscandia and the North Atlantic region during the Eemian, and it involves a qualitative multi-proxy reconstruction of the Eemian lake and its development as well as a quantitative reconstruction of the regional Eemian July temperature evolution using subfossil chironomids. Attention is paid also to the identification and characterization of short-term climatic events in the Sokli record.

The main contribution of this study is to increase the spatial coverage of Eemian palaeoclimatological data. Specific results include the description of the lake development, identifying phases where non-climatic variables likely affect the quantitative chironomid-based temperature reconstruction, as well as qualitative and quantitative reconstructions of climatic features such as changes in seasonality and temperature. Five major lake phases are distinguished. A glaciolacustrine phase is followed by an early Eemian lake phase characterized by short mixing periods and rising nutrient levels. The following early mid-Eemian lake phase is characterized by a prolonged open water season and high productivity and possibly corresponds to the Eemian climatic optimum. The late mid-Eemian lake phase is characterized by infilling and eutrophic conditions while the late Eemian lake phase reflects shallow, dynamic and cooling conditions.

The qualitative study suggests a shift from a higher seasonality in the early Eemian towards more oceanic conditions during the mid-Eemian, while chironomid-inferred July temperatures indicate that near present-day temperatures prevailed at Sokli already from the beginning of the interglacial and that optimum temperatures were only moderately (ca + 1°C) higher  than at present. These results suggest that the climatic development at Sokli followed that of central Europe during the Eemian. Two events characterized by colder and more arid conditions are identified, and can be tentatively correlated to meltwater events registered in marine records from the Nordic seas and subpolar north Atlantic, possibly reflecting the effect that meltwater pulses and related disruptions in the thermohaline circulation had on adjacent continental areas.

 

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2018. p. 47
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 74
Keywords
Last Interglacial (MIS5e), northern Europe, palaeolimnology, palaeoecology, temperature reconstruction, multiple proxies, climate dynamics, climatic events
National Category
Earth and Related Environmental Sciences
Research subject
Quaternary Geology
Identifiers
urn:nbn:se:su:diva-155573 (URN)978-91-7797-159-7 (ISBN)978-91-7797-160-3 (ISBN)
Public defence
2018-06-15, Högbomsalen, Geovetenskapens hus, Svante Arrhenius väg 12, 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 4: Submitted. Paper 5: Manuscript.

Available from: 2018-05-23 Created: 2018-04-25 Last updated: 2018-05-15Bibliographically approved

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