LAUSR

The high northern latitudes currently experience amuch stronger warming than other parts of the globe (ACIA 2005; IPCC 2013). This amplifiedwarming is believed to be due to complex feedback mechanisms in the atmosphere, in theoceanandon land,which, however, arepoorly understood. Improving the understanding of both the modern warming and future climate change in high northern latitudes requires amore detailed investigation of the natural variability on a range of geological time scalesunderdifferentclimaticboundaryconditions(Miller et al. 2010). Major progress in the reconstruction of the climatic and environmental history of the Eurasian North was recentlyachievedwithinthescopeoftheRussian-German project PLOT (Paleolimnological Transect) and theNorwegian-Russian project CHASE (Climate History along the Arctic Seaboard of Eurasia). Both projects focus on lake sediment records as natural palaeoenvironmental archives for the Holocene and beyond. The PLOT and CHASEprojects conducted jointworkshops inCologne, Germany, inMay2017and inRosendal,Norway, inMay 2018, when new information concerning the glaciation and climate history of northern Eurasia was compiled. This special issue ofBoreas synthesizes themajor findings presented at the workshops, complemented by selected results from other projects working in the same scientific field, in order to provide the palaeoenvironmental stateof-the-art and to evaluate themethods available aswell as the need for further research. The 17 papers of this special issue present palaeoenvironmental results from different locations, with different age ranges andbased on differentmethods. The areal distribution comprises northeastern Greenland, northern Scandinavia and various regions in Russia, from Lake Ladoga in thewest to Lake El’gygytgyn in the east. The study sites thereby formawest–east transect of about 8500 km length (Fig. 1A). The age ranges of the archives comprise aperiodbetween2and90kawithin thepast246 ka (i.e. since lateMarine Isotope Stage (MIS) 8; Fig. 1B). The different methods include various field techniques, such as hydro-acoustic site surveys, geomorphological studiesanddifferentcoringtechniques.Theyalsocomprise different analytical methods, addressing the sediment composition as well as physical (e.g. grain size, water content and magnetic susceptibility), chemical (loss on ignition, organic and inorganic elemental composition, stable isotopes, DNA and biomarker) and biological (pollen, dinoflagellates, chironomids, ostracods, diatoms and macrofossils including bones) proxies and proxyrelated transfer functions (for biomes, temperature and precipitation).Moreover, thedatingmethodsemployedare highly variable, selectively comprising radiocarbon dating, luminescence dating, exposure dating, varve chronology and tephrochronology. Kusch et al. (2019) conducted a biomarker and macrofossil study on a Holocene record from Trifna Sø in northernGreenland (Fig. 1). The results confirm earlier information concerning the Holocene thermal maximum in the area, and provide new insights into the limitationsofbrGDGT-basedpalaeothermometry inhighlatitude regions. Biomarker analyses were also conducted byThienemann et al. (2019)ona6-m-longsedimentcore fromLake Tornetr€ask in northern Sweden (Fig. 1) from a coring site selected based on hydro-acoustic data. The biomarker data suggest temperature changes due to changes in the regional atmospheric circulation, which may explain a time-lag in the onset of theHolocene thermal maximum by several hundred years compared to northern Greenland. In northeastern Norway, a 2.4-mlong sediment succession of the small lake Uhca Rohci (Fig. 1) was investigated for ancient DNA and pollen by Clarke et al. (2019) and Lammers et al. (2019). The results provide new information concerning the Holocene floristic and faunistic diversity and environmental changeandnew insights into thevalueofDNAstudies in palaeoenvironmental research. LakeLadoga, locatedclose to the cityofSt.Petersburg in western Russia (Fig. 1), is the largest lake in Europe. Basedonsediment echosounder andseismicdata, a 22.7m-long sediment recordwas recovered in the northwestern lake areaand studiedbydifferentmethods.Chronostratigraphical and sedimentological data fromthe record document theScandinavian IceSheet (SIS) retreat across the lake basin between c. 15.9 and 11.4 cal. ka BP aswell