Tephras in the Greenland Ice-cores and the Synchronisation of Palaeoclimatic Records

In recent years, increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the Greenland ice-cores. The Greenland ice-cores are key records for understanding climatic changes that have occurred over the past 123,000 years due to their unparallelled resolution of high-magnitude, abrupt climatic changes that punctuated the last glacial period - the so-called Dansgaard-Oeschger (DO) events - and the transition from glacial to interglacial conditions during Termination 1. The correlation and synchronisation of these records to other palaeoclimatic archives is key to understanding the mechanisms driving these dramatic changes. The tracing of volcanic ash horizons between records can provide climatically-independent isochronous tie-lines, facilitate the direct correlation of key marine and terrestrial climatic archives to the Greenland ice-cores, permit the testing of phase relationships in proxy records and underpin chronological frameworks through the transferral of high-precision ice-core ages for the horizons. Here we review the results of over 25 years of research into tephra horizons in the GRIP, GISP2 and NGRIP cores. We provide high-precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the Greenland Ice Sheet and identified in the cores. The principal source of horizons has been identified as Icelandic volcanic eruptions, however, horizons from more distal sources such as North America, Alaska, and potentially Mediterranean, Asian and low latitude volcanic regions, have been identified. Examples are provided of previous successful correlations between the Greenland ice-cores, North Atlantic marine records and European terrestrial sequences to demonstrate the power of tephrochronology for the synchronisation of disparate palaeoclimatic records.