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Climatic influence on the inter-annual variability of late-Holocene minerogenic sediment supply in a boreal forest catchment
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 Mathematics and Mathematical Statistics. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
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2010 (English)In: Earth Surface Processes and Landforms, ISSN 0197-9337, E-ISSN 1096-9837, Vol. 35, no 4, 390-398 p.Article in journal (Refereed) Published
Abstract [en]

Processes controlling sediment yield vary over a range of timescales, although most process-based observations are extremely short. Lake sediments, however, can be used to extend the observational timescale and are particularly useful when annually laminated (varved) sediment is present. The sediment record at Kassjön (N. Sweden) consists of ∼6400 varves, each 0·5–1 mm thick. Image analysis was used to determine grey-scale variation and varve thickness from which annual minerogenic accumulation rate (MinAR) (mg cm−2 year−1) was inferred for the period 4486 BC – AD 1900. MinAR varies on annual to centennial scales and mainly reflects channel bank erosion by the inflow streams. The mineral input reflects the intensity of the spring run-off, which is dependent on the amount of snow accumulated during the winter, and hence MinAR is a long-term record of variability in past winter climate; other factors will be a variable response to catchment uplift, vegetation succession and pedogenesis. A major shift from low to high MinAR occurred ∼250 BC, and peaks occurred around AD 250, 600, 1000, 1350 and 1650. Wavelet power spectrum analysis (confirmed by Fourier analyses) indicated significantly different periodicities throughout the period 4000 BC – AD 1700, including 275 years for the period 4000 BC – 2900 BC, 567 years for the period 2901 BC – 1201 BC, and 350 and 725 years for the period 1200 BC – AD 1700. The long-term, centennial scale variability (∼350 years) may reflect solar forcing (cf the 385-year peak in tree-ring calibrated 14C activity) but interestingly, there is no obvious link to high frequency forcing, such as the North Atlantic Oscillation. The high resolution component of the record highlights the relevance of varved lake sediment records for understanding erosion dynamics in undisturbed forested catchments and their link to long-term climate dynamics and future climate change. 

Place, publisher, year, edition, pages
John Wiley & Sons, 2010. Vol. 35, no 4, 390-398 p.
Keyword [en]
varves, image analysis, climate change, snow melt, temperature, minerogenic matter accumulation rate, sediment supply, stream erosion
National Category
Environmental Sciences
Identifiers
URN: urn:nbn:se:umu:diva-31007DOI: 10.1002/esp.1933ISI: 000276677100002OAI: oai:DiVA.org:umu-31007DiVA: diva2:290387
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Functional clustering methods and marital fertility modelling
Open this publication in new window or tab >>Functional clustering methods and marital fertility modelling
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis consists of two parts.The first part considers further development of a model used for marital fertility, the Coale-Trussell's fertility model, which is based on age-specific fertility rates. A new model is suggested using individual fertility data and a waiting time after pregnancies. The model is named the waiting model and can be understood as an alternating renewal process with age-specific intensities. Due to the complicated form of the waiting model and the way data is presented, as given in the United Nation Demographic Year Book 1965, a normal approximation is suggested together with a normal approximation of the mean and variance of the number of births per summarized interval. A further refinement of the model was then introduced to allow for left truncated and censored individual data, summarized as table data. The waiting model suggested gives better understanding of marital fertility and by a simulation study it is shown that the waiting model outperforms the Coale-Trussell model when it comes to estimating the fertility intensity and to predict the mean and variance of the number of births for a population.

The second part of the thesis focus on developing functional clustering methods.The methods are motivated by and applied to varved (annually laminated) sediment data from lake Kassj\"on in northern Sweden. The rich but complex information (with respect to climate) in the varves, including the shapes of the seasonal patterns, the varying varve thickness, and the non-linear sediment accumulation rates makes it non-trivial to cluster the varves. Functional representations, smoothing and alignment are functional data tools used to make the seasonal patterns comparable.Functional clustering is used to group the seasonal patterns into different types, which can be associated with different weather conditions.

A new non-parametric functional clustering method is suggested, the Bagging Voronoi K-mediod Alignment algorithm, (BVKMA), which simultaneously clusters and aligns spatially dependent curves. BVKMA is used on the varved lake sediment, to infer on climate, defined as frequencies of different weather types, over longer time periods.

Furthermore, a functional model-based clustering method is proposed that clusters subjects for which both functional data and covariates are observed, allowing different covariance structures in the different clusters. The model extends a model-based functional clustering method proposed by James and Suger (2003). An EM algorithm is derived to estimate the parameters of the model.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2017. 24 p.
Keyword
censoring, Coale-Trussell model, EM-algorithm, functional data analysis, functional clustering, marital fertility, normal approximation, Poisson process, varved lake sediments, warping
National Category
Probability Theory and Statistics
Research subject
Mathematical Statistics
Identifiers
urn:nbn:se:umu:diva-130734 (URN)978-91-7601-669-5 (ISBN)
Public defence
2017-02-24, Hörsal 1, Lindellhallen, Umeå Universitet, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2017-02-03 Created: 2017-02-01 Last updated: 2017-02-09Bibliographically approved

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Petterson, GunillaRenberg, IngemarSjöstedt-de Luna, SaraArnqvist, Per
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