A first annual-layer-counted chronology for the EastGRIP ice core and the search for a precise dating for the Thera eruption

• Main Authors: Sinnl, Giulia, Rasmussen, S. O., Cook, Eliza, Svensson, Anders, Skov Jensen, Mathias, Erhardt, Tobias, Marie Jensen, Camilla, Mojtabavi, Seyedhamidreza, Wilhelms, Frank, Winstrup, Mai
• Format: Conference Object
• Language: unknown
• Published: 2019
• Subjects: Greenland; Rasmussen; East Greenland; Greenland ice cores; ice core; North Greenland
• Online Access: https://epic.awi.de/id/eprint/50833/; https://app.oxfordabstracts.com/events/574/program-app/submission/93536; https://hdl.handle.net/10013/epic.96142db8-0b0a-4786-99cd-9cde26ccc088

The development of paleoclimatic timescales is of vital importance for the understanding of climate. Ice cores are optimal tools for the construction of a timescale because they record the signal of multiple annually resolved proxies with well preserved stratigraphy. In 2018, the East GReenland Ice Coring Project (EastGRIP) reached a depth of 1760 m, corresponding to an age of approximately 21000 years BP. The newly drilled core has been matched to other Greenland ice cores to adapt the GICC05 ice-core timescale. This provides a chronological basis for the study of the core that is consistent with other Greenland cores. The techniques adopted for matching of the ice cores rely on the assumed synchronicity of deposits from volcanic eruptions, biomass burning events, and solar events [1]. These time markers are essential for the synchronization of different time records as well as for the determination of regional leads and lags occurring at the onset of climatic transitions. The measurements used for volcanic matching are electrical conductivity measurements (ECM) and dielectric profiling (DEP), which were performed directly in the field and then processed to a high precision in depth assignment. Independent matching of DEP and ECM matching was performed to assess the precision of the synchronization before the two records were merged. The strength of the volcanic matching between Greenland ice cores is increased by locating the same Northern Hemisphere volcanic ash deposits (tephra), which possess unique geochemical `fingerprints'. This challenging search is conducted along the length of each core and is particularly useful in the Last Glacial Maximum, where the presence of acidic spikes is scarce both in ECM and DEP data. The transferred timescale is complemented by automated counting of annual layers between the observed tie-points, using annually resolved proxy data measured by chemical Continuous Flow Analysis (CFA). Ultimately, these new results will feed into the revision of the GICC05 time scale and hopefully reconcile the differences between GICC05 and the timescale proposed by Sigl et al [2]. In this framework, we are trying to narrow down the dating of the Thera eruption on Santorini (around 3500 BP). The timing of this event is still debated, because of an apparent discrepancy of about 100 years between carbon-14 dating and historical dating [3]. [1] S. O. Rasmussen et al. “A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core". In: Climate of the Past 9.6 (2013), pp. 2713{2730. [2] M. Sigl et al. “Timing and climate forcing of volcanic eruptions for the past 2,500 years". In: Nature 523 (2015), pp. 543{549. [3] C. L. Pearson et al. “Annual radiocarbon record indicates 16th century BCE date for the Thera eruption". In: Science Advances 4.8 (2018).