Asynchronous dynamics of the last Scandinavian Ice Sheet along the Pomeranian Phase ice-marginal belt: a new scenario inferred from surface exposure 10Be dating

We present a new set of 25 10Be surface exposure ages of boulders located on the Pomeranian moraines and of erratic boulders located directly upstream of the Pomeranian moraines in northern Poland. Together with recalculated 10Be surface exposure ages along the Pomeranian Phase ice-marginal belt from Denmark to the west to Lithuania and Belarus to the east, the full data set (n = 86) enabled us to constrain the timing of the ice front standstill and its subsequent retreat. The investigated area consists of geomorphological record along ~2000 km of the ice margin associated with the ice sheet limit correlated so far with the Late Weichselian P...  more

We present a new set of 25 10Be surface exposure ages of boulders located on the Pomeranian moraines and of erratic boulders located directly upstream of the Pomeranian moraines in northern Poland. Together with recalculated 10Be surface exposure ages along the Pomeranian Phase ice-marginal belt from Denmark to the west to Lithuania and Belarus to the east, the full data set (n = 86) enabled us to constrain the timing of the ice front standstill and its subsequent retreat. The investigated area consists of geomorphological record along ~2000 km of the ice margin associated with the ice sheet limit correlated so far with the Late Weichselian Pomeranian Phase (Bælthav in Denmark, Baltija in Lithuania and Braslav in Belarus).

We constrained the age of the ice margin position in the area occupied by the Baltic Ice Stream to ~20–19 ka, in the area occupied by the Odra Ice Stream to ~19–18 ka, in the interstream area between the Odra and the Vistula Ice Streams to ~20–19 ka, in the area occupied by the Vistula Ice Stream to ~19–18 ka, in the area occupied by the Mazury Ice Stream to ~18–17 ka, in the area occupied by the Riga Ice Stream to ~17–16 ka, and in the area occupied by the Novgorod Ice Stream to ~16–15 ka. Our best age estimates are based on: (1) a minimum age of the ice margin retreat inferred from new and recalculated 10Be ages of boulders as well as interpretation of available radiocarbon ages from organic deposits and OSL ages from sediments overlying tills, and (2) a maximum age of the ice margin stillstand and retreat inferred from interpretation of available OSL ages from sandur sediments deposited in front of the ice sheet. The asynchrony of the ice margin positions along the Pomeranian Phase ice-marginal belt shows about 3–5 ka difference between the Bælthav ice margin in Denmark and the Braslav ice margin in Belarus. We propose a new scenario of the Pomeranian Phase ice sheet evolution and a time-slice reconstruction of the last Scandinavian Ice Sheet’s southern fringe for the period ~20–15 ka.