One of the issues that we had with the dating of the 934 Eldgja, was that it appeared initially to be correct. As we discuss in the paper, frost rings in bristlecone pine, can be indicative of a large explosive volcanic eruption, and of course, as nature would have it, there is a frost ring at AD 934. So we naturally thought that this eruption may have been correctly dated by the GICC05 timescale, and GISP2 was incorrect. However, this 934 date is now becoming contentious, since Sun et al 2014 highlight that two tephra horizons in GICC05 and GISP2 timescales have been identified (Eldgja and the Millennium eruption), which are around 6-7 years apart, but which appear to fit well with either a 933/940 (GICCO5) or 939/946 (GISP2) dating. When we consider eastern historical records the Millennium eruption occurred around 946.

If our hypothesis is correct, then it could aid in firming up some uncertainties in the historical records.

There is of course a further interesting physical issue. The frost ring at AD 934 could just be a natural localised cooling, but with reports of weak suns etc, and cold weather, it sound like a dust veil event, but we have no evidence from ice cores of a volcanic event occurring around 5 years before the Eldgja volcanic horizon.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup