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Inter-annual variation of seasonal diatom dynamics reveals importance of process timing for sediment signal formation
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Paleolimnology)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Disentangling the process information contained in a diatom sediment signature is crucial for reliable future predictions based on paleolimnological records. The aim of this study was to identify the hierarchical importance of seasonal processes for the formation of an annual diatom sediment record. We combined annual vertical water column chemistry, lake thermal structure, sequential sediment trap samples and annually resolved varved sediment diatom records from a boreal lake in northern Sweden. Whole-year water column monitoring indicates that the entire annual diatom sediment signal in different years can be driven by winter air temperature-induced timing of ice and snow melt and persistent under-ice stratification, which promote an early diatom bloom under the ice before spring lake over-turn. In a year of late ice thinning and development of a chlorophyll maximum after spring lake over-turn, an annually integrated diatom sediment signal was built by a continuous diatom flux, with important implications for diatom-based model predictions.

Keyword [en]
Diatoms, limnological process timing, sediment trap, varve lake sediment, seasonal air temperature
National Category
Climate Research
Identifiers
URN: urn:nbn:se:umu:diva-135326OAI: oai:DiVA.org:umu-135326DiVA: diva2:1098098
Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-23
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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Maier, Dominique Béatrice
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