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TURBERAS: Reconstruction of Holocene hydro-climatic fluctuations based on multi-proxy peatland records

Applicant Stoffel Markus
Number 182032
Funding scheme Project funding
Research institution Institut des Sciences de l'Environnement Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Other disciplines of Environmental Sciences
Start/End 01.06.2019 - 31.05.2023
Approved amount 892'910.00
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All Disciplines (2)

Discipline
Other disciplines of Environmental Sciences
Environmental Research

Keywords (5)

paleoclimate; tree ring; dendroecology; peatland; Holocene

Lay Summary (French)

Lead
Les tourbières sont des zones humides caractérisées par l'accumulation progressive de la tourbe, un sol caractérisé par sa très forte teneur en matière organique, peu ou pas décomposée, d'origine végétale. Dans ces sols tourbeux, l’installation, la survie et la croissance des arbres ne sont possibles que dans les secteurs les moins humides. L’expansion des peuplements forestiers peut être favorisée par un assèchement d’origine climatique et/ou anthropique. En revanche, des phases plus humides peuvent entrainer la disparition des arbres. Les troncs piégés dans le milieu tourbeux anaérobie peuvent alors se conserver pendant plusieurs milliers d’années et constituent des archives paléo-environnementales particulièrement précieuses.
Lay summary

Contenu et objectifs du travail de recherche

Pourtant à ce jour, ces archives paléoenvironnementales ont été peu utilisées pour la reconstruction de la variabilité hydroclimatqiue au cours de l’Holocène. Notre principal objectif est donc (i) d’affiner les connaissances sur les interactions existant entre la croissance des arbres, les fluctuations du niveau de la nappe d’eau dans les tourbières et les variations du climat. Pour cela, un réseau de placettes de suivi micro-météorologique, hydrologique et dendrométrique (suivi en continu de la croissance des arbres vivants) sera mis en place au sein de tourbières situées en Scandinavie et dans l’aire Baltique. En outre, nous souhaitons également (ii) reconstituer, l’évolution du climat des 12000 dernières années avec une résolution annuelle.  Nous utiliserons pour cela une approche dendrochronologique, basée sur l’analyse des cernes de croissance des arbres subfossiles piégés dans la tourbe.

Contexte scientifique et social du projet de recherche

Notre travail générera des informations inédites et essentielles quant aux conditions et changements hydroclimatiques au cours de l'Holocène et permettra de mieux cerner les interactions entre variabilité du climat et la croissance radiale des arbres dans les tourbières. Cette information sera essentielle pour mieux comprendre le fonctionnement de ces écosystèmes particuliers et fragiles, cruciaux dans le contexte actuel de changements climatiques, puisqu'ils constituent un des principaux puits de carbone de la planète.

Direct link to Lay Summary Last update: 14.12.2018

Responsible applicant and co-applicants

Employees

Project partner

Associated projects

Number Title Start Funding scheme
191614 ClimatiZENs - Climats du passé pour citoyens de demain 01.01.2021 Agora

Abstract

The anticipated impact of ongoing and projected future climate changes on ecosystems and societies is a crucial concern that requires detailed understanding of the climate system in general, but also natural climate variability and its forcing mechanisms in particular. A suite of paleoclimate reconstructions has advanced our understanding of climate dynamics over much of the Holocene, mostly in terms of temperature variations. By contrast, it is quite striking to see how little we still know about past hydro-climatic changes, mostly because of a persistent scarcity of annually resolved proxies that has so far prevented an extension or densification of annually resolved, hydro-climatic reconstructions across major parts of the Holocene. Subfossil trees from peatlands of Northern Europe and Scandinavia have been shown to be sensitive to changes in hydro-climatic variability. Paradoxically, however, the resulting tree-ring series could not be used so far to quantify the amplitude of moisture changes at the annual scale. This was due to the fact that peatland trees, in contrast to trees growing on mineral soils, show more complex, often weaker, and clearly site-dependent responses to monthly temperature and precipitation changes, with the latter presumably reflecting a multi-annual synthesis of moisture variability and water-table changes related to a hydrological lag in peatlands. Here we hypothesize that our current understanding of past hydro-climatic variability would benefit quite substantially from a systematic coupling of different, peat-based proxies - such as testate amoebae, diatoms, pollen, non-pollinic microfossils, tree rings - with different temporal resolutions. Based on the above considerations, the TURBERAS project has four key objectives that will be addressed in two case study regions in Estonia and Sweden: (i) augment the pool of existing, moisture-sensitive peatland tree-ring width series in the case-study region; (ii) understand and quantify hydrological lag effects recorded in tree growth following changes in precipitation and water-table fluctuations using automated dendrometers, cell-wall thickness and isotope measurements; (iii) develop transfer functions between the tree-growth parameters identified under point (ii) and climate variables by taking account of hydrological lags; (iv) based on point (iii), reconstruct climate using a multi-proxy approach in which other, existing peatland proxies (i.e. testate amoebae, diatoms, pollen, non-pollinic microfossils,) are used to add the middle and low frequency signals to the annually-resolved tree-ring records. The key innovation of the project in terms of long-term hydro-climatic reconstructions lies in the diversification of tree proxies (tree-ring width, cell wall thickness, isotopes) and their systematic coupling with water-table-sensitive proxies such as plant macrofossil assemblages, testate amoebae and diatoms existing at the two case-study regions, but for the latter mostly with lower temporal resolutions. The proposed procedure uses three analytical steps: (a) a spectral algorithm with a Fast Fourier Transformation to decompose both the different proxy records and climatic matrixes into their low and high frequency components. After decomposition, (b) using the proxy matrix for each frequency component to reconstruct the corresponding band of climatic data over the Holocene. Finally, (c) assembling the two bands in one single band and back-transformation of results into original meteorological data using an inverse modeling procedure.The TURBERAS project is designed in a way that should allow key insights into how woody vegetation in fragile wetland ecosystems evolves over time and into how tree growth is controlled by hydro-climatic fluctuations. In return, we also expect to provide reconstructions of past hydro-climatic changes for key periods of the Holocene.
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