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Compaction of recent varved lake sediments
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2013 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 135, no 3-4, 231-236 p.Article in journal (Refereed) Published
Abstract [en]

To assess the rates of compaction in recent, varved (annually laminated) lake sediments, we used a collection of 13 freeze cores sampled from 1979 to 2012 in Nylandssjon (northern Sweden). This unique series of stored freeze cores allowed us to measure how the thickness of individual varves changed when they were overlain by new varves. The compaction rate was greatest during the first few years after deposition; varve thickness decreased by 60% after 5 years (sediment depth 5cm). Thereafter, the compaction rate declined, but after 33 years (the study period) there was still a weak trend of continued compaction (sediment depth 12cm). The rate of compaction is clearly linked to loss of water along with an increase in dry-bulk density of the sediment. Despite compaction causing considerable varve thickness changes over time, the year-to-year variation in varve thickness is preserved while sediment ages. Understanding compaction processes is of fundamental importance to paleolimnology, for example in studies involving calibration of varve thicknesses of recent varves against environmental parameters.

Place, publisher, year, edition, pages
Taylor & Francis, 2013. Vol. 135, no 3-4, 231-236 p.
Keyword [en]
varved lake sediment, compaction, varve thickness, bulk density, diagenesis, post-depositional changes, paleolimnology
National Category
Geology
Identifiers
URN: urn:nbn:se:umu:diva-85095DOI: 10.1080/11035897.2013.788551ISI: 000327571800002OAI: oai:DiVA.org:umu-85095DiVA: diva2:691764
Note

Special Issue: Varve Genesis, Chronology and Paleoclimate

Available from: 2014-01-28 Created: 2014-01-28 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
Open this publication in new window or tab >>Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Paleoclimatic archives, such as lake sediments, extend our understanding of terrestrial and aquatic ecosystem dynamics in relation to climate variability beyond the period covered by instrumental data. In this context, annually laminated (i.e. varved) lake sediments are particularly valuable, as they offer high temporal resolution and undisturbed sediment. However, in order to extract reliable climate information from lake sediments, a careful calibration with the processes controlling the sediment formation is essential. This thesis combines limnological and paleolimnological data from a varved, boreal lake in northern Sweden (Nylandssjön, Nordingrå) collected over different time scales. The main aim of the thesis is to gain a more refined insight into which processes are reflected in the sedimentary diatom assemblage. More specifically, sequential sediment trap records were coupled with physical, chemical and biological lake monitoring and environmental data for comparison and validation with the varved sediment record. The main result of the thesis is that timing, succession and inter-annual variability of key limnological and environmental processes (e.g. ice-cover duration, lake over-turn or catchment run-off) are of major importance for the sedimentary diatom assemblage formation. Continuous monitoring of physico-chemical parameters over three consecutive years identified varying winter air temperature as a major factor influencing in-lake processes and hence the diatom record. Timing of lake over-turn and catchment run-off seemed to be the driver for monospecific diatom blooms, which are reflected in the annual sediment signal. The integrated annual diatom signal in the sediment was dominated by spring or autumn blooms, resulting either from a Cyclotella glomerata dominated spring bloom after relatively warm winter conditions, or a Asterionella formosa dominated autumn bloom after relatively cold winter conditions. The analysis of the diatom stratigraphy in the varved sediment over several decades corroborated the importance of climatic variables (late winter air temperature and NAO), even though the variables with the most predictive power for variance in the diatom data were associated with sediment composition (C, N and sedimentation rate) and pollution (Pb and Cu). Overall, the analysis of the drivers of inter-annual and decadal diatom assemblage fluctuations emphasizes the importance of winter air temperature, indicating that weather extremes may be disproportionately represented in annual sediment records in contrast to nutrient concentrations or sedimentation rate.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2017. 29 p.
Keyword
varved lake sediments, diatom sediment signal formation, sequential sediment trap, seasonal process timing, ice thinning, varve compaction, climate impact, catchment properties
National Category
Earth and Related Environmental Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
urn:nbn:se:umu:diva-135231 (URN)978-91-7601-603-9 (ISBN)
Public defence
2017-06-15, KB3A9, KBC, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-05-24 Created: 2017-05-22 Last updated: 2017-05-24Bibliographically approved

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