Drivers of Holocene palsa distribution in North America

Palsas and peat plateaus are climatically sensitive landforms in permafrost peatlands. Climate envelope models have previously related palsa/peat plateau distributions in Europe to modern climate, but similar bioclimatic modelling has not been attempted for North America. Recent climate change has rendered many palsas/peat plateaus in this region, and their valuable carbon stores, vulnerable. We fitted a binary logistic regression model to predict palsa/peat plateau presence for North America by relating the distribution of 352 extant landforms to gridded modern climate data. Our model accurately classified 85.3% of grid cells that contain observed palsas/peat plateaus and 77.1% of grid cells without observed palsas/peat plateaus. The model indicates that modern North American palsas/peat plateaus are supported by cold, dry climates with large seasonal temperature ranges and mild growing seasons. We used palaeoclimate simulations from a general circulation model to simulate Holocene distributions of palsas/peat plateaus at 500-year intervals. We constrained these outputs with timings of peat initiation, deglaciation, and postglacial drainage across the continent. Our palaeoclimate simulations indicate that this climate envelope remained stationary in western North America throughout the Holocene, but further east it migrated northwards during 11.5–6.0 ka BP. However, palsa extents in eastern North America were restricted from following this moving climate envelope by late deglaciation, drainage and peat initiation. We validated our Holocene simulations against available palaeoecological records and whilst they agree that permafrost peatlands aggraded earliest in western North America, our simulations contest previous suggestions that late permafrost aggradation in central Canada was climatically-driven

Non-Pollen Palynomorphs Characteristic for the Dystrophic Stage of Humic Lakes in the Wigry National Park, Ne Poland

The numerous dystrophic (humic) lakes are a very important feature of Wigry National Park, NE Poland. As the most recent palaeoecological data indicate, at the beginning of its development (in the Late Glacial and Early and Middle Holocene) these water bodies functioned as harmonious lakes, and their transformation into dystrophic lakes and the stabilization of the trophic state took place at the beginning of the Subboreal. Palynological analysis of sediments from two such lakes (Lake Ślepe and Lake Suchar II), with special emphasis on non-pollen palynomorphs (NPPs), was aimed at a detailed biological characterization of dystrophic lakes during their long-lasting existence. The obtained results allowed for the designation of organisms characteristic for dystrophic lakes, of which representatives appeared with the decreasing pH of the water and the formation of Sphagnum peat around lakes. These organisms were divided into four groups: algae, fungi, testate amoebas, and animals. Their representatives appear invarious developmental stages of dystrophic lakes