Late Holocene palsa formation in northern Fennoscandia: Fossil pollen indication and climatic trigger

Abstract

Palsa is a peat mound with a permanently frozen core, occurring in the (sub)polar zone. So far, the history of European palsa mires has been investigated mainly by means of analysis of plant macroremains. To better understand how the formation of palsa is reflected in pollen records, we investigated fossil pollen of two sites in northern Fennoscandia: a conical palsa close to Abisko National Park (NW Sweden) and low palsa mire close to Nikel, Kola Peninsula (NW Russia).

At both sites, the formation of palsa is demonstrated by the same pattern in pollen record: decrease of Cyperaceae pollen and Pteridophyta and Lycopodiophyta spores, and the associated increase of ericoid dwarf shrubs and Rubus chamaemorus pollen. This pattern represents the change from a wet fen to a dry bog plant community after the uplift of the palsa mound above the surrounding terrain.

The age of both palsas formation around 2370 cal BP (Abisko) and 2270 cal BP (Nikel) falls in the two main periods of palsa initiation in Europe and thus represents further evidence of significant cooling in the period 2600–2100 cal BP. At both investigated sites, this cooling is also reflected by the decline of pine and the expansion of birch tundra.

Besides new original data, we provide an overview of so-far dated palsa formation in northern Fennoscandia and an interpretative key for identifying palsa in the palaeoecological record, based on plant species typical of the different stages of palsa development.