Reconciling multiple ice-core volcanic histories: The potential of tree-ring and documentary evidence, 670–730 CE

Chronologically-secure volcanic event histories are important for improving our understanding of volcano-climate responses, and securing ice core chronologies. We present an exploratory case-study that attempts to reconcile the chemical fingerprints of major volcanism in Greenland ice-cores for the years 670–730 CE. This period experienced considerable volcanic perturbation with multiple volcanic signals registered in all 8 Greenland ice-core datasets studied, including some comparable in magnitude to the great 1815 Tambora eruption, but reconciling signals with divergent dating between datasets presents a number of challenges. To further our understanding of the volcanic history of this period, frost-rings, tree-ring growth width and density minima from Europe, Siberia and China are considered together with Western European, Near Eastern and Chinese documentary evidence. These reveal a striking sequence of co-occurring inter-regional climatic extremes and social crises. We further examine a recently proposed 7-year adjustment to the GICC05 chronology used by many Greenland ice cores, and find that this results in a more coherent volcanic history for these years, and an improved agreement with tree-ring and written records. Three major volcanic events can now be identified, dated to 681, 684–686 and 706–707, with several moderate events further contributing to a sustained climate perturbation reflected in prolonged temperature reductions in high-resolution reconstructions.