The kettle-hole mire as archives of postglacial changes in biogenic sedimentation (Tuchola Forest, north-Central Poland)

Kettle holes are a circular-shape product of ice decay, and thus are strongly linked with young glacial landscapes. Once glaciation terminates, these holes transform either into wetland and lakes or occasionally into kettle-hole mires. Since an entire sediment sequence preserve in the kettle-holes, these provide an excellent settings to exploit any sensitive paleoenvironmental changes. Here, the kettle-hole mire located onto the Brda River outwash plain (Tuchola Forest) is explored towards a better understanding of local and global environmental trends in the Late Glacial – present day time frame. To fulfill this, multi-proxy study as geochemical, palynological and macrofossils analyses along with the radiocarbon dating are used. Therefore, this study allows to distinguish five phases of steep environmental gradients in the investigated mire, as follows: (1) paludification after glaciation, when dead-ice melted and long-term permafrost was degraded, (2) lake started to disappear in the Late Glacial, followed by a rich vegetation in the first part of the Holocene, (3) vegetation encroachment onto the lake in the first part of the Holocene, which consequently turned into an peat bog, (4) the late Holocene peat bog with a limited human influence, and finally (5) the peat bog with a major human impact along with acidification as related to sandy underlying sediments, leaching of calcium carbonate, recharge from precipitation and pine monoculture. As additionally apparent from this small ecosystem, both local (character of substrate sediments, morphology of the area, rate of permafrost melting, climate conditions and human activity) and regional (climate changes and human activity) are detectable. Nevertheless, the record of these changes is sometimes unclear.