Multi-proxy palaeoecological data (pollen, diatom, Cladocera) about the environment during the middle-Holocene from Suchar II and Suchar Wielki, dystrophic lakes, in NE Poland are presented. Fluctuations in the pollen concentration, indicative of changes in pollen productivity and shifts in woodland composition, document the considerable instability of the climate in NE Poland between 9200 and 5750 cal. yr BP. The recognised colder events were dated to ca. 9050–8950, 8700–7800, 7600–7250, 7100–6600 and 6050–5900 cal. yr BP. All these coolings are expressed as decreases in the pollen concentration of thermophilous taxa such as Corylus avellana, Ulmus, Quercus, Tilia cordata t. and Fraxinus exelsior. The most pronounced was the second of these cold climatic anomalies, which lasted about nine centuries and can be equated with the 8.2-ka event. Significant cooling at that time is confirmed by the appearance of cold-water species of cladocerans and diatoms.

Fourier Transform Infrared (FT-IR) spectroscopy and imaging combined with hierarchical cluster analysis (HCA) was applied to analyse biochemical properties of Early Middle Ages hemp (Cannabis sativa L.) bast fibres collected from lake bottom sediment of lake Słone. The examined plant macrofossil material constitutes residues of the hemp retting process that took place in the 7th–8th century. By comparison of three samples: untreated isolated bast fibres, and fibres incubated overnight at 4 and 37 °C, we were able to mimic the retting conditions. Using FT-IR qualitative and semi-quantitative assessment of the primary polysaccharides content, total protein content, and their spatial distribution was performed within the hemp fibres. The concentration of cellulose remained vastly unchanged, while the concentration of lignin and pectin was the highest in the untreated sample. The spatial distributions of compounds were heterogeneous in the untreated and 4 °C-incubated samples, and homogenous in the specimen processed at 37 °C. Interestingly, a higher amide content was detected in the latter sample indicating the highest degree of enzymatic degradation. In this study, we show that the spectroscopic methods allow for a non-destructive evaluation of biochemical composition of plant fibres without preparation, which can be an appropriate approach for studying ancient plant remains.