The Aller⊘d-Younger Dryas pollen zone boundary in an 800-year varve chronology from southeastern Sweden

Abstract

This is the first pollen stratigraphical investigation of late Weichselian deposits in the area which was situated close to the late Weichselian Fennoscandian ice sheet margin and the Baltic Ice Lake shore during the Aller⊘d-Younger Dryas climatic transition. Pollen analyses were carried out on varved clay sequences, covering a time span of 350 years of an AMS radiocarbon-dated 800-year varve chronology, and on two lacustrine sequences. The Aller⊘d-Younger Dryas pollen zone boundary has been defined at the local varve year 2000. The pollen zone boundary coincides with an apparent drop of AMS radiocarbon ages from c. 11,000 to 10,800-10,600 ¹⁴C years BP. The Aller⊘d, Younger Dryas, and Preboreal climatic events are distinguished in the pollen records of the lacustrine sites. Pollen and macrofossil evidence and AMS radiocarbon dates at these sites indicate that the area was deglaciated during the Aller⊘d. Soon after the deglaciation Betula pendula/pubescens immigrated. At the Aller⊘d/Younger Dryas transition the vegetation changed to a herb tundra indicating cooler and/or drier conditions. The Younger Dryas/Preboreal boundary is characterised by a vegetation change from a herb tundra to a park tundra with tree birch. Later in the Preboreal the vegetation became more dense and was dominated again by Betula pendula/pubescens.

Keywords:

• Late Weichselian
• southeastern Sweden
• Baltic Ice Lake
• Fennoscandian ice sheet
• clay varve chronology
• GRIP
• isotope stratigraphy
• pollen analysis
• radiocarbon dates