A palaeoenvironmental record of MIS 3 climate change in NE Poland—Sedimentary and geochemical evidence

Abstract In Eastern Europe Marine Isotope Stage (MIS) 3 represents a period characterised by severe climate change of very rapid onset, which is recorded in the regional sedimentary record. Hitherto this work, the geomorphic impact of these abrupt changes to NE Poland's 1st-order-stream valleys has been under-represented in studies. Here the combined results of lithological, geochemical, and palynological analyses—coupled with sediment OSL dating—demonstrate that MIS 3's earlier events (60–45 ka) mark an interval when contemporary dry valleys functioned as active stream corridors, places where deep fluvial incision had occurred. Prior to this MIS 3 fluvial activity there is an observed depositional hiatus encompassing sediments from MIS 5d to the oldest part of MIS 3. Valley-bottom sediment accumulation began ~44–40 ka, commencing at a time when shallow water reservoirs began to function. The resultant mineral infill is devoid of calcium carbonate and organic matter (OM). This sedimentation occurred under dry and cold climate conditions—i.e. under the influence of permafrost aggradation. The geochemical composition of the MIS 3 deposits indicates that environmental conditions are deteriorating. In effect, calcium carbonate was completely removed from the deposits, which resulted in the reduction of mobile elements (such as Na), removal of selected soil horizons, and an increased content of immobile elements—e.g. sedimentary Al, Rb, Ti. These processes are confirmed in the study sediments by magnetic susceptibility analysis. Here, in MIS 3 lake deposits, the presence of fissure structures filled with grey clay or fine sand is a common feature. Climatic changes during MIS 3's younger part were reflected in the slight increase of OM, which in turn increased the contribution of mobile, immobile, and trace elements. Most likely these change intervals represent more humid conditions during MIS 3. Sediment-trapping lakes within dry valley bottoms completely disappeared by ~30 ka.