Peatland response to climate warming after the Little Ice Age

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Title: Peatland response to climate warming after the Little Ice Age
Author: Alanko, Joonas
Contributor: University of Helsinki, Faculty of Science, Department of Geosciences and Geography
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
Thesis level: master's thesis
Discipline: Geography
Abstract: Northern peatlands are a valuable, volatile carbon stock and hold 30 % global terrestrial organic carbon. Climate is the most important control on peatland ecology. Positive and negative feedback loops between peatlands and climate make this complex relationship. Climate change affects high northern latitudes in particular, making the northern peatlands prone to experience massive changes in ecology. It is unclear exactly how long-term climate change will affect such an integral part of the carbon cycle. My intent was to produce a reliable study of what kind of response did bogs develop after the Little Ice Age (LIA) and how climate warming has affected these important carbon stocks. This study uses high frequency, multi-proxy, post-LIA peatland response data to map the ecological response of a boreal ombrotrophic peatland ecosystems. Study sites are located in Southern-Finland and Estonia. I concentrate on three distinct micro-habitats. I use low-frequency data from previous studies to compare with my novel data and to give the study more spatial scope. My analysis is structured around a chronology consisting of 210 Pb-dates. Plant macrofossil data, present vegetation data, Sphagnum mosses as the most important group, and modern water-table data are used to model past plant composition and hydrology. Age-depth models and water-table reconstructions have been created on this basis. Bulk density and C/N ratio were also analysed. Large and fast paced shifts in accumulation rates and changes in vegetation composition were revealed. After LIA, peatland surfaces have dried and dry-habitat vegetation has increased. I identified a two-step pattern in response to post-LIA climate shifts. A wet period ended LIA, followed by a two-step warming identified from different proxies and models. The pattern of change coincides with the known changes in climate. This suggests that after the LIA, changes in climate have been the driving force behind changes in peatland ecology and carbon sequestration in it. The results show that the way northern bogs respond to changes in climate can on the short term have huge effects for the vegetation, and on long term threaten the whole peatland and its carbon stocks. These changes are manifested through changes in the relation of primary production to decomposition and local hydrology. Different microhabitats are more vulnerable to climate shifts than others. In future climate warming will continue to influence northern peatlands. Depending on the scale of change, peatlands can act as a sink of atmospheric carbon, or if a watershed is reached, release large amounts of carbon to the atmosphere. Most likely this would not only destroy peatlands in large quantities, but also further enhance the positive feedback between carbon release and peatland drying.

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