Biotic responses to rapid warming about 14,685 yr BP: Introduction to a case study at Gerzensee (Switzerland)

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Ammann, Brigitta, von Grafenstein, Ulrich, van Raden, Ulrike J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2013
• Subjects: 580 Plants (Botany); Greenland; Zero Point; Dansgaard-Oeschger events; Greenland ice core; ice core; NGRIP
• Online Access: https://boris.unibe.ch/106882/1/2013_PalaeogeogrPalaeocl_391_3.pdf; https://boris.unibe.ch/106882/

The late-glacial climatic warming indicated in the Greenland ice-core record about 14,685 years before 1950 AD belongs to a type of very rapid high-amplitude warming similar the onsets of Dansgaard-Oeschger events during marine isotope stage 3 (MIS 3). In order to estimate the nature and rates of change of biotic responses to such a major climatic shift we need a reliable time scale as well as climatic indicators independent of the biota. Both are provided by a high-resolution oxygen-isotope record from precipitated carbonates of lake marl in Gerzensee, Switzerland (van Raden et al., 2013-this issue). On the basis of the assumption of synchronous climatic changes between Greenland and Gerzensee, the close correlation of the oxygen-isotope changes at the two sites allows the use of the NGRIP GICC05-timescale at Gerzensee (with the zero point at 1950 AD to maintain comparability with the numerous radiocarbon dates in Europe). The delta O-18-record measured in precipitated carbonates is checked and refined by the delta O-18 measured in mono-specific ostracod samples (Von Grafenstein et al., 2013-in this issue). The shift of 3.6 parts per thousand delta O-18 PDB in only about 112 years at the end of the GS-2 represents a very rapid temperature increase of at least 6.2 degrees C. This increase is confirmed by reconstructions based on transfer functions for pollen and chironomids by Lotter et al. (2012) (possibly 4-7 degrees C in the annual mean and 2-5 degrees C in summer temperatures). After this major shift the Greenland late-glacial interstadial GI-1 (corresponding to the regional biozones Bolling and Allerod) delta O-18-records of both Greenland and Gerzensee exhibit four minor fluctuations (about 1.0-1.2 parts per thousand delta O-18), of which the second and the fourth are especially clearly correlated with several of terrestrial records in the northern hemisphere. The oxygen-isotope record is used as a template for all these sediment- and bio-stratigraphies. The biotic responses may include at least five types ...