Climate warming and vegetation response after Heinrich event 1 (16 70016 000 cal yr BP) in Europe south of the Alps

Abstract

Chironomids preserved in a sediment core from Lago di Origlio (416 masl.), a lake in the foreland of the Southern Swiss Alps, allowed quantitative reconstruction of Late Glacial and Early Holocene summer temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. We reconstruct July air temperatures of ca. 10 A°C between 17 300 and 16 000 cal yr BP, a rather abrupt warming to ca. 12.0 A°C at ca. 16 500-16 000 cal yr BP, and a strong temperature increase at the transition to the BAlling/AllerAd interstadial with average temperatures of about 14 A°C. During the Younger Dryas and earliest Holocene similar temperatures are reconstructed as for the interstadial. The rather abrupt warming at 16 500-16 000 cal yr BP is consistent with sea-surface temperature as well as speleothem records, which indicate a warming after the end of Heinrich event 1 (sensu stricto) and before the BAlling/AllerAd interstadial in southern Europe and the Mediterranean Sea. Pollen records from Origlio and other sites in southern Switzerland and northern Italy indicate an early reforestation of the lowlands 2000-1500 yr prior to the large-scale afforestation of Central Europe at the onset of the BAlling/AllerAd period at ca. 14 700-14 600 cal yr BP. Our results suggest that these early afforestation processes in the formerly glaciated areas of northern Italy and southern Switzerland have been promoted by increasing temperatures. © Author(s) 2012.