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A chronology of environmental changes in the Lake Vättern basin from deglaciation to its final isolation
Stockholm University, Faculty of Science, Department of Geological Sciences.ORCID iD: 0000-0002-2023-8361
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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2018 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 2, p. 609-624Article in journal (Refereed) Published
Abstract [en]

During and after deglaciation, Lake Vättern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70‐m composite sediment core recovered in southern Lake Vättern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice‐sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11 480±290 cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c. 300 years and was followed by a c. 1600 year freshwater period before the Vättern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing δ13C values and the appearance of diatoms in the upper 15 m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530±50 cal. a BP. Consequently, the isolation of Lake Vättern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.

Place, publisher, year, edition, pages
2018. Vol. 47, no 2, p. 609-624
National Category
Geology
Research subject
Marine Geology
Identifiers
URN: urn:nbn:se:su:diva-153900DOI: 10.1111/bor.12288ISI: 000428369500016OAI: oai:DiVA.org:su-153900DiVA, id: diva2:1188389
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-05-02Bibliographically approved
In thesis
1. In the wake of deglaciation - sedimentary signatures of ice-sheet decay and sea-level change: Studies from south-central Sweden and the western Arctic Ocean
Open this publication in new window or tab >>In the wake of deglaciation - sedimentary signatures of ice-sheet decay and sea-level change: Studies from south-central Sweden and the western Arctic Ocean
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lacustrine and marine sedimentary archives help unravel details concerning the withdrawal of large ice sheets and resulting sea-level changes during the last deglaciation (22 -11 kyr). In a series of four manuscripts, this PhD thesis investigates the sedimentological signatures from deglacial processes at three key locations in the northern hemisphere: (i) Lake Vättern (LV) in south-central Sweden, (ii) Herald Canyon (HC) in the western Chukchi Sea, and (iii) Mackenzie Trough (MT) on the westernmost edge of the Canadian Beaufort Shelf. One lacustrine (LV) and two marine (HC and MT) sediment cores were analyzed using a broad range of methods to describe the physical, chemical, mineralogical and biological characteristics, and used to construct paleoenvironmental interpretations.

Constituting the westernmost part of the Baltic Sea during parts of the last deglaciation, LV has long been envisaged as a key region for deglacial studies in southern Scandinavia. Sediments in LV highlight four major lake development stages following the withdrawal of the Fennoscandian Ice Sheet. These include the Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the ultimate isolated lake stage. New radiocarbon dates indicate that the lake became isolated at 9530±50 cal. yr BP. A sharp transition from a varved clay unit to a partly sulfide laminated clay unit marks the final drainage of the Baltic Ice Lake, dated to 11 650±280 cal. yr BP. However, an earlier peak in pore water chlorinity identified in the sediment provides the most compelling evidence to date for an initial drainage of the Baltic Ice Lake (~12.8 cal. kyr BP) near the onset of the Younger Dryas cold event.

Located downstream from where Pacific water flows into the Arctic, HC is a key location for understanding the details of the early Holocene (~11 cal. yr BP) flooding of the Bering Strait, and investigating sedimentological proxies for Pacific water in Arctic Ocean sediment cores. The deglacial transgression of the shelf and opening of the Bering Strait is reflected in the grain size and biogenic silica content from the HC sediment core. However, a clear Pacific water signature is not seen in the clay mineralogy which exhibits increased variability after the opening of the Bering Strait. This is interpreted as a combination of Pacific and East Siberian sources for bottom waters in HC. The absence of a clear Pacific water signature in the clay mineralogy highlights potential limitations to using this proxy in other records from the western Arctic.

Far field studies from the Arctic Ocean have argued that Mackenzie River sediments in Younger Dryas age sediments can be recognized by a unique mineral and isotopic composition, but no detailed proximal study of Mackenzie River sediments exists to support this assertion. The mineral and isotopic (Sr and Nd) studies presented in this thesis from the third of the key regions, the MT, fills this gap. The results show that the mineral assemblage and ɛNd of fine fraction material remained relatively stable during the decay of the Laurentide Ice Sheet. An exception to this exists in a transitional sedimentary unit, deposited immediately after transgression at the site, and might be related to meltwater pulses associated with the drainage of the Lake Agassiz. The results suggest that the modern mineral and isotopic signature of Mackenzie River sediments may not be a suitable proxy for deglacial meltwater events in far field sedimentary records.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2018. p. 40
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper ; 369
Keywords
paleoenvironmental changes, last deglaciation, sedimentology, Lake Vättern, western Arctic Ocean, Mackenzie Trough, Herald Canyon
National Category
Earth and Related Environmental Sciences Geology Geosciences, Multidisciplinary
Research subject
Marine Geology
Identifiers
urn:nbn:se:su:diva-153906 (URN)978-91-7797-163-4 (ISBN)978-91-7797-164-1 (ISBN)
Public defence
2018-04-27, William-Olssonsalen, 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 3: Manuscript. Paper 4: Manuscript.

Available from: 2018-04-04 Created: 2018-03-07 Last updated: 2018-04-16Bibliographically approved

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Swärd, HenrikO'Regan, MattBjörck, SvanteGreenwood, Sarah L.Kylander, Malin E.Mörth, Carl-MagnusPearce, ChristofJakobsson, Martin
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