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We compared DNA, pollen and macrofossil data obtained from Weichselian interstadial (age more than 40 kyr) and Holocene (maximum age 8400 cal yr BP) peat sediments from northern Europe and used them to reconstruct contemporary floristic compositions at two sites. The majority of the samples provided plant DNA sequences of good quality with success amplification rates depending on age. DNA and sequencing analysis provided five plant taxa from the older site and nine taxa from the younger site, corresponding to 7% and 15% of the total number of taxa identified by the three proxies together. At both sites, pollen analysis detected the largest (54) and DNA the lowest (10) number of taxa, but five of the DNA taxa were not detected by pollen and macrofossils. The finding of a larger overlap between DNA and pollen than between DNA and macrofossils proxies seems to go against our previous suggestion based on lacustrine sediments that DNA originates principally from plant tissues and less from pollen. At both sites, we also detected Quercus spp. DNA, but few pollen grains were found in the record, and these are normally interpreted as long-distance dispersal. We confirm that in palaeoecological investigations, sedimentary DNA analysis is less comprehensive than classical morphological analysis, but is a complementary and important tool to obtain a more complete picture of past flora.

Old sedimentological and geochronological records can be preserved underneath the central parts of the continental ice sheets under non-erosive, cold-based subglacial conditions. Organic deposits that predate the last deglaciation are of particular value for the information held on glacial-time climate and environmental conditions. In this study, we present multiproxy data derived from a well-preserved MIS 3 interstadial (55–25 ka ago) organic layer from inside the Arctic Circle in the Finnish Lapland. Biological proxy evidence, namely coming from aquatic plant species, indicates July temperatures as high as 14.4 °C, i.e. higher than those of today for the study site. Macrofossil evidence demonstrates for the first time the presence of pines accompanied by tree birch during the MIS 3 interstadial in northern Fennoscandia. These results concur with contemporary insolation model outcomes but contradict with the previous proxy-based view of open tundra conditions during the MIS 3. The data suggest that there are highly dynamic interstadial continental ice-sheet dynamics following changes in orbital forcing. Warm climate enabled the establishment of forests on exposed landscape. Moreover, we suggest that in the light of these new data, previous MIS 3 pollen data could be re-interpreted.

In the northern boreal zone, revegetation and landscaping of closed mine tailings are challenging due to the high concentrations of potentially toxic elements; the use of nutrient-poor, glacigenic cover material (till); cool temperatures; and short growing period. Recycled waste materials such as biochar (BC) and composted sewage sludge (CSS) have been suggested to improve soil forming process and revegetation success as well as decrease metal bioavailability in closed mine tailing areas. We conducted two field experiments in old iron mine tailings at Rautuvaara, northern Finland, where the native mine soil or transported cover till soil had not supported plant growth since the mining ended in 1989. The impacts of CSS and spruce ( Picea abies )–derived BC application to till soil on the survival and growth of selected plant species ( Pinus sylvestris , Salix myrsinifolia , and grass mixture containing Festuca rubra , Lolium perenne , and Trifolium repens ) were investigated during two growing seasons. In addition, the potential of BC to reduce bioaccumulation of metals in plants was studied. We found that (1) organic amendment like CSS markedly enhanced the plant growth and is therefore needed for vegetation establishment in tailing sites that contained only transported till cover, and (2) BC application to till soil-CSS mixture further facilitated the success of grass mixtures resulting in 71–250% higher plant biomass. On the other hand, (3) no effects on P. sylvestris or S. myrsinifolia were recorded during the first growing seasons, and (4) accumulation of metals in cover plants was negligible and BC application to till further decreased the accumulation of Al, Cr, and Fe in the plant tissues. Graphical abstract

In the formerly glaciated terrains in the northern hemisphere and countries such as Finland, till is the most common sediment covering the bedrock. Specifically, indicator or heavy mineral studies utilising till as a vector for mineral deposits undercover have been successful. The pyrite trace-element composition from in situ mineral analyses has been shown to be an effective discriminator between different mineral deposit types, and this has led to research using heavy mineral pyrite in till to identify potential mineral deposits in a given area. However, pyrite is easily oxidised in till beds, and thus, alternative methods should be considered. Goethite pseudomorphs are more commonly found in the till sediments as remnants after pyrite oxidation. This study evaluates trace element compositions of goethitised pyrite recovered in the till beds from central Lapland in northern Finland. Intra-grain trace-elemental variations gathered using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) between the intact pyrite core and oxidised rim demonstrated complex dynamics and variations between different trace-element values. For example, Cu, V and Mn exhibited elevated trace-element values in the goethite rim compared to the pyrite core. However, elemental ratios such as Ni/As and Co/Ni remain stable between the pyrite core and oxidised rim. Therefore, these ratios have the potential to be used as a discriminating tool between the pyrite core and oxidised rim. In addition, nanoscale variabilities using focused ion beam (FIB) and transmission electron microscopy (TEM) were utilised to inspect possible nano inclusions within the studied heavy mineral grain. The FIB and TEM studies revealed a nanocrystalline pyrite nodule observation within the goethite rim.

We compared DNA, pollen and macrofossil data obtained from Weichselian interstadial (age more than 40 kyr) and Holocene (maximum age 8400 cal yr BP) peat sediments from northern Europe and used them to reconstruct contemporary floristic compositions at two sites. The majority of the samples provided plant DNA sequences of good quality with success amplification rates depending on age. DNA and sequencing analysis provided five plant taxa from the older site and nine taxa from the younger site, corresponding to 7% and 15% of the total number of taxa identified by the three proxies together. At both sites, pollen analysis detected the largest (54) and DNA the lowest (10) number of taxa, but five of the DNA taxa were not detected by pollen and macrofossils. The finding of a larger overlap between DNA and pollen than between DNA and macrofossils proxies seems to go against our previous suggestion based on lacustrine sediments that DNA originates principally from plant tissues and less from pollen. At both sites, we also detected Quercus spp. DNA, but few pollen grains were found in the record, and these are normally interpreted as long-distance dispersal. We confirm that in palaeoecological investigations, sedimentary DNA analysis is less comprehensive than classical morphological analysis, but is a complementary and important tool to obtain a more complete picture of past flora.

The new international network PalaeoArc (Processes and Palaeo Environmental Changes in the Arctic: From Past to Present) held its first meeting in Poznan, 20-24 May 2019. The meeting was hosted by the Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznan, and organized by a local committee chaired by Witold Szczuciński.

The stratigraphy and sedimentology of a diamicton-stratified sand deposit have been studied in the Veskoniemi area, near Lake Inarijarvi in central Finnish Lapland. Test pit excavations were used for stratigraphical investigations. Till-covered laminar and cross-bedded sands were dated using optically stimulated luminescence (OSL). Ages range between 21.0 ± 1.5 and 22.4 ± 1.6 ka for laminated sands at upper levels and 39 ± 3 and 46 ± 3 ka for sands at deeper levels. These dating results strengthen the evidence for a Middle Weichselian interstadial in northern Finland during oxygen isotope stage 3, and can be compared with other results in eastern and southern Lapland. This is the first time that sediments from the Middle and Late Weichselian contact have been identified in Finland. These new dating results indicate that an ice-free period could have lasted from halfway through the Middle Weichselian to the beginning of the Late Weichselian about 22-25 ka ago in northern Finland.

The stratigraphy and sedimentology of a diamicton-stratified sand deposit have been studied in the Veskoniemi area, near Lake Inarijärvi in central Finnish Lapland. Test pit excavations were used for stratigraphical investigations. Till-covered laminar and cross-bedded sands were dated using optically stimulated luminescence (OSL). Ages range between 21.0 ± 1.5 and 22.4 ± 1.6 ka for laminated sands at upper levels and 39 ± 3 and 46 ± 3 ka for sands at deeper levels. These dating results strengthen the evidence for a Middle Weichselian interstadial in northern Finland during oxygen isotope stage 3, and can be compared with other results in eastern and southern Lapland. This is the first time that sediments from the Middle and Late Weichselian contact have been identified in Finland. These new dating results indicate that an ice-free period could have lasted from halfway through the Middle Weichselian to the beginning of the Late Weichselian about 22–25 ka ago in northern Finland.