The Younger Dryas cooling in northeast Germany: summer temperature and environmental changes in the Friedländer Groβe Wiese region

Abstract

A lake sediment record from the Friedla¨nder Grobe Wiese in northeast Germany was studied to reconstruct summer temperature changes associated with changes in vegetation development during the Weichselian Lateglacial. The record was analysed for pollen, chironomids, and oxygen and carbon isotopes of lake marl. The combination of radiocarbon dates, the presence of the Laacher See Tephra and correlation of lithological and palynological changes with other records from the region indicated that the record encompassed the Allerød to the early Holocene. Pollen assemblages reflect development of birch and later pine-dominated forests during the Allerød, comparable to other sites in the region. Chironomid-inferred mean July air temperatures (C-IT) for this period range between 14.0 and 14.88C. A temporary decrease in C-IT of 18C, a negative shift in the isotope records, and a minor decline of birch may correspond to Greenland Interstadial 1b. Even though the transition to the Younger Dryas appears to be affected by reworking and redeposition processes, a drop in C-IT to 11.18C is reconstructed for the later part of the Younger Dryas, while it appears that pine locally persisted in the region. Comparison with a nearby pollen record further indicates a local expansion of wetland grasses during this period. At the transition to the Holocene, C-IT increased to 15.78C, while birch and pine forests re-expanded.