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Week 5/2010: Rude belching from northern peatlands

The methane concentration in the atmosphere clearly increased about 5,000 years ago. The gas peak has usually been attributed to East Asia's rice cultivators, but an explanation may also be found in the expansion of northern peatlands.

In peatland studies, a typical approach is to drill one sample set from the oldest, and usually thickest, section of the peatland," says Minna Väliranta, Docent. Based on the peat profile, the area's climate history has then been investigated by means of pollen analysis, for example.

In a recent study, the aim was also to include the peatland's own dynamics after its emergence. Consequently, the viewpoint of the expansive growth of peatlands was linked to studies where the interaction between peatlands and the atmosphere are analysed.

From previous studies conducted on the northern boreal forest belt, the researchers compiled information on the ages of approximately 3,000 bottom peat samples as their study material. To the database, the team accepted peatlands with samples of at least three eras. Meri Ruppel looked for samples full-time for three months, and wrote her master's thesis on the subject.

"The three samples depict the peatland's expansive growth. Previous studies, addressing the impact of peatlands on the methane concentration in the atmosphere, have kind of assumed that a peatland emerges in its entirety at the same time," say Väliranta and Ruppel.

The expansive growth and methane emissions are strongly interlinked, as new peatland area is usually always sedge peat that produces a lot of methane.

Through analysis (statistically based on the location data of the samples ), the researchers found that the expansive growth of peatlands accelerated at the same time as the methane concentration in the atmosphere increased. Before this, the methane peak taking place in the late Holocene era has mainly been explained by the rice cultivation in East Asia.

The study, conducted under the supervision of Professor Atte Korhola, was recently published in the Quaternary Science Reviews  series. The contributors are from the University of Helsinki's Environmental Change Research Unit (ECRU) and the departments of Geosciences and Geography.

Text: Anna-Kaisa Kontinaho
Translation: AAC Global
Photo: Torronsuo National Park in Tammela, Finland/GNU Free Documentation License.

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