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University of Helsinki Faculty of XXX

Environmental Change Research Unit - ECRU


Tracking carbon dynamic patterns and climate forcing through post-glacial mire development history by combining modern flux measurements and palaeoecological information
Impacts of climate change on Arctic environment, ecosystem services and society (CLICHE)
Biomarkers a new potential method to study highly humified peat components
Past water table fluctuations and related changes in carbon accumulation rates in mires a quantitative multi proxy-based reconstruction from different climate regimes
Impacts of multiple environmental stressors on subarctic lake food web dynamics (MESS)
Climate variability in NW Europe during the past 4000 years and its ecological consequences (CLIM-ECO)
Science workshop on past, present and fututure climate change
Long-term changes in lake ice conditions in northern Finland
Responses of Boreal ecosystem carbon exchange to changing environment in different spatio-temporal scales
Former Projects

Contact information:

Environmental Change Research Unit (ECRU)
Department of Environmental Sciences
P.O. Box 65 (Viikinkaari 1)
FIN-00014 University of Helsinki

Phone: +358-9-1911
(main switch board)
or see People


Jan Weckström



Lake Kilpisjärvi viewed from the top of fjäll Saana. Photo: Ari Weckström


Academy of Finland

Duration 2008-2011

The research consortium has three main research themes:

  1. Using biological lake sediment data to hindcast climate change and ecosystem response
  2. Using clastic-biogenic varve sediments to derive high-resolution information on abrupt environmental shifts in the recent geological past
  3. Develop and improve mathematical theories and predictive models for temporal dynamics

Climatic effects on ecosystems can only be detected when long-term data, such as proxy data or adequate long-term monitoring data are available. Long-term time series define the range of natural variability of climate and ecological systems and provide a baseline from which to assess whether a system has changed significantly. It is important to realise that whatever anthropogenic climate changes occur in the future, they will be superimposed on a background of natural variability. Therefore, to anticipate future changes, we must understand how and why climates and ecosystems varied in the past (Bradley 2000).
Even on a global scale Fennoscandia is probably unrivalled in its collection of annually laminated (i.e. varved) lake sediment archives that span the Holocene. Such archives can be considered as ideal palaeoenvironmental archives due to their seasonal resolution. CLIM-ECO aims to combine  seasonally-resolved varve records of geophysical, geochemical and biological indicators of local and regional response to climate forcing.

Overall objectives

CLIM-ECO will:

  • obtain more precise palaeoclimatic reconstructions of the late-Holocene (the last ≈4000 years) from lake environments by using carefully calibrated proxy archives, ultra-high-resolution data and novel statistical tools
  • deepen our understanding of the basic principles of ecological resilience and dynamics; identify key taxa, structures or processes that clearly indicate impending or realised global change through their loss, occurrence or behaviour
  • investigate ecological reorganisations and regime shifts by climate change that are recorded in palaeo-archives during the Late Holocene climatic oscillations
  • provide a means to distinguish between anthropogenically and non-anthropogenically induced changes in climate and biological systems
  • communicate this information and understanding to users, stakeholders and the wider public

Project I: Using biological lake sediment data to hindcast climate change and ecosystem response (PI prof. Atte Korhola)

This project will expand the existing organism-based transfer functions to cover the entire Finland, use the improved transfer functions to hindcast climatic changes from annually resolved proxy archives, validate the palaeolimnological records using modern process studies, and assess the responses of aquatic ecosystems to climate change using carefully selected, independent biological indicators. Three mutually linked sub-projects will be established.

Sub-project 1: Expansion and improvement of modern climate calibration data sets

Key hypotheses:

  • The expansion and amalgamation of the already existing datasets in Fennoscandia will significantly improve analogues between fossil and modern biological proxy data and decrease the estimation errors of the created transfer functions
  • The combination of new methods (project III) based on biological proxy data with physical variables and new biological proxies analysed from the annually laminated sediments will produce unprecedentedly accurate reconstructions of climatic shifts during the last 4000 yrs

Key deliverables:

  • Expanded and improved modern diatom and chironomid calibration data sets in order to improve the accuracy, analogues and hence application potential of the transfer functions
  • Reliable quantitative reconstructions of climate variables (e.g. mean, max, min T, degree days, ice cover duration) from fossil assemblages in both varved and non-varved lakes
  • New proxies to derive climate information from lake sediments

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Sub-project 2: Increased understanding of aquatic climate proxies

Key hypotheses:

  • Integration of palaeoecological and standard limnological approaches will significantly improve our understanding of lake ecosystem processes related to climate change
  • New proxies can be developed for climate change assessment after careful consideration of lake processes and taphonomic biases
  • Climate change may fundamentally alter the structure and functioning of lakes

Key deliverables:

  • Analysis of climate change impacts on key ecological and limnological processes in boreal lakes
  • Analysis of how climate signal is incorporated in sediment archives
  • Improved understanding of sensitivity of biological proxies to climate change
  • New proxies for palaeoclimate assessment

Sub-project 3: Aquatic ecosystem responses to climate forcing

Key hypotheses:

  • The different periods of warming in the palaeoclimatic record show similar species changes; the species revert to the communities present before warming when the climate cools
  • There occurs hysteresis in organismal response to rapid events;
  • Ecological reorganisations are observed during periods of both marked cooling and warming

Key deliverables:

  • Long-term records of species assemblage changes across a broad range of trophic groups
    Detailed information on regime shifts in boreal aquatic ecosystems during the last 4000 years
  • Analysis of changes in diversity and ecological reorganisations during periods of climate change

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Project II. Using clastic-biogenic varve sediments to derive high-resolution information on abrupt environmental shifts in the recent geological past (PI Dr. Antti E.K. Ojala)

This project will use the primary material of thicknesses of varves and seasonal laminae that has been collected so far from the key sites in the central southern Finland (Ojala 2001; Tiljander 2003; Ojala & Alenius 2005). Studies now will focus according to two sub-projects on (i) inferring past winter precipitation and severity through variability of spring discharge and erosion, and transportation of mineral material into lakes, and (ii) investigating palaeoenvironmental evolution of varved lakes based on carbon and oxygen isotope analysis of sediment cellulose. In addition, it will carry out a pilot-type study of high-resolution variability of heavy stable isotopes through different time scales.

Sub-project 1: Seasonal-scale mineral grain-size variability

Key hypotheses:

  • Mineral matter grain-size variability responds to character (intensity, duration, occurrence) of the spring melt-water discharge and autumn runoff after heavy storms. Thereby, it offers us seasonal-scale information of environmental and climate variability
  • Ultra-high resolution study of varve structure is a key to understand and separate different sedimentation forcing mechanisms and differentiate local disturbance effects from larger-scale climate variability

Key deliverables:

  • Reconstruction of runoff intensity and winter snowfall in southern Finland for the last 4000 years using mineral matter grain-size variability data sets from two varved lakes
  • Overall climate characteristics and different modes of catchment erosion; i.e. periods with diminished spring runoff (mild winters with little snow), pronounced flooding and catchment erosion (severe winters with high net accumulation of snow), and periods with higher/lower than average organic matter accumulation (strength and length of lake primary productivity)
  • Reconstruction of occurrence of autumn peak stream discharges caused by rain storm events
  • A better understanding of the forcing mechanisms behind sedimentation and varve formation

Sub-project 2: Stable isotopes

Key hypotheses:

  • There exists a relationship between isotopic composition of sediments and environmental forcing on sedimentation processes in lakes with clastic-biogenic varves
  • Analysis of isotopic composition provides a means for producing precise and statistically-evaluated semi-quantitative reconstructions of the changes in effective humidity
  • Heavy isotopes have potential to become a new proxy of environmental change

Key deliverables:

  • A long-term record of regional variations in the isotopic composition of precipitation;
  • A sub-centennial-scale record of palaeohumidity (effective moisture) for the study area
  • The addition of an independent palaeohydrological proxy of regional significance that can be used as a basis for modelling experiments and for validation of locally responding lithological and biological proxies
  • Reconstruction of food-web relationships using stable isotope analyses
  • Experimental modelling of the heavy isotope distribution in clastic-biogenic varved sequences and enhanced information on their transportation pathways in lake systems
  • Reconstruction of past pollution history in central southern Finland based on varved sediment cores (absolute accumulation g m-2 yr-1)

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Project III. Mathematical theory and predictive models for temporal dynamics (PI Lasse Holmström)

In this project, the accuracy and intepretability of climate reconstructions will be improved through the development and adoption of novel modelling tools and data analysis approaches (e.g. Vasko et al. 2000; Toivonen et al. 2001; Korhola et al. 2000; Holmström et al. 2000, Erästö & Holmström 2005, Erästö & Holmström 2006a, Erästö & Holmström 2006b). One key research direction is to develop further the idea of SiZer (Significant Zero Crossings of Derivatives, Chaudhuri & Marron 1999), where the trends in the time series of a reconstructed variable are inspected using various different levels of smoothing. Analysis based on multiscale smoothing is known as the scale-space approach and it is uniquely well suited for palaeoecological reconstructions because of the natural correspondence between a time resolution of interest and the particular smoothing scale employed. In our novel Bayesian approach to multiscale smoothing (BSiZer) we use a roughness penalty approach to uncover salient features in time series that manifest themselves in a whole range of different time resolutions (Erästö & Holmström 2005). Bayesian methods will also be important in the further development of environmental reconstruction models. The data analyses will typically be based on algorithmic estimation methods such as Markov Chain Monte Carlo (MCMC).

Sub-project 1: New and improved Bayesian single- and multi-proxy reconstructions

Key Hypotheses:

  • The Bayesian reconstruction model can be developed to minimise the effect of biasing prior information, to account for correlations, and to make it applicable to various proxies and environmental variables
  • A new multi-proxy reconstruction model with integrated feature analysis will allow integration of multiple palaeocological data sources at an unprecedented level of sophistication
  • Spatio-temporal scale-space analyses will provide new insights to environmental change

Key deliverables:

  • Further development the Bayesian reconstruction model to minimize the possibly biasing effect of overly strict prior assumptions
  • Accounting for correlations in the Bayesian reconstruction model
  • Extending the model to various proxies and variables
  • Design of a new multi-proxy reconstruction technique that allows for intra- and inter-proxy correlations and includes an integrated scale-space feature analyzer
  • Investigation of environmental change in a range of spatial scales

Sub-project 2: Detection of periodicities in environmental reconstructions

Key Hypotheses:

  • Scale-space smoothing is a valuable tool for spectral analysis of time-series
  • Analysis of reconstruction time series can be used to test previously proposed decadal- to century-scale periodicities, including those at ≈200, 125, and 88 yr which are associated with solar variability

Key deliverables:

  • Scale-space methodology for the detection of significant periodicities in time series
  • Investigation of the merits of the new methods as compared with established methods
  • Application of the new techniques to the reconstructions made in the consortium

Expected results

  • to reduce uncertainties concerning the spatial distribution of climate changes and their ecological impacts; these will enhance the capacity of risk management, improved societal planning and enable informed policies focused on climate adaptation and mitigation policies
  • to establish likely rates of change to ensure precaution
  • to assess the natural range of hydrological changes in order to improve the accuracy of estimations of future changes in water resources
  • to increase public awareness of the problem of global warming in order for the public to be involved in the issue and to endorse climate policies


Atte Korhola - coordinator
Jan Weckström
Sanna Korkonen
Heikki Seppä
Antti Ojala – subcoordinator
Emilia Kosonen
Lasse Holmström - subcoordinator
Juha-Matti Tirilä
Liisa Ilvonen
Panu Erästö

International and national cooperation will be central in the overall project. Through our activite participation in large EU and Nordic projects and international research and science policy programmes (PAGES, HOLIVAR, AMAP, SCANTRAN, ACIA), CLIM-ECO has a large international network to draw from.

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