14,700 years of climate and environmental change recorded in 17.8 meters of lake and peat deposits in the Nieuwe Veen pingo remnant, NE Netherlands

Pingo remnants are the deep lakes that formed by melting of ice lenses during permafrost degradation at the end of the Last Glacial, and they are particularly abundant in the northern Netherlands. Most of these isolated circular depressions have a diameter of 100-200 meters and are filled with a 5-10 meters thick sequence of lake and peat deposits, making them valuable archives of climate and environmental change. These natural sediment- and pollen-traps record not only the rapid changes during the Last Glacial-Interglacial Transition but also reveal the Holocene forest development as well as traces of human impact in the surrounding landscape.

In this study, we report on the study of a continuous organic fill of nearly 18 meters in Nieuwe Veen, which may be the deepest pingo remnant in NW Europe. The pingo remnant fill is composed of a sequence of partly sand laminated lake and peat deposits containing fine and coarse detrital gyttjas, calcium- and iron-carbonate gyttjas and wood, sedge and moss peats with abundant macrofossils. A series of radiocarbon dates on selected terrestrial macrofossils provides a solid age model for the complete sequence starting 14,700 calendar years ago, coinciding with the first warming of the Late-Glacial Interstadial, corresponding to the onset of Greenland Interstadial 1 (GI-1). The results from 5-10 cm resolution palynological analyses reveal a complete picture of vegetation development while loss on ignition measurements at cm-resolution show the openness of the vegetation cover associated to colder periods as well as phases of human forest clearance.

A phase of particular interest is the cold Younger Dryas stadial corresponding to Greenland Stadial 1 (GS-1), which is represented by a more than 10 meters thick layer of sandy gyttjas. This allows for a reconstruction of environmental change in unprecedented detail with a resolution of potentially 1 cm/yr. The onset of the Younger Dryas stadial is abrupt and clearly visible in the core, as well as in the botanical and lithological proxies. There appear to be at least three distinct phases during the Younger Dryas stadial interval, especially reflected in the aquatic flora and lithological proxies, indicating shifting conditions in (hydro-)climate.

At the onset of the Holocene, also clearly visible, sand influx in the basin decreased rapidly due to an increasing vegetation cover in the surrounding landscape indicated by the botanical proxies. The lake system eventually changes into a fen and bog. In the Early Holocene, carbonate rich lake deposits indicate the influence of groundwater seepage. During the infilling, the source of the water changes towards atmospheric water, as evidenced by more oligotrophic species in the palynological record. Phases of forest opening related to human impact appear remarkably late in the record at about 5500 calendar years ago, with clear indications of agriculture only after 3000 calendar years ago. Final cultivation of the peatbog in the beginning of the 20^th century caused the record younger than Medieval times to be destroyed.