Tag: marine reservoir effect

Repton Revisited

There is no doubt that Repton was an important place to the Mercians and was also the site where the Viking Great Army overwintered in 873-874.  Repton is frequently mentioned as a place where Mercian kings granted charters and the churchyard at Repton contains several graves that are distinctively Scandinavian.

The site around the Church was excavated by the Biddles between 1974 and 1980.  Their conclusion was that the church was part of a defensive D shaped enclosure that had housed the Great Army.  A nearby mausoleum was excavated and found to contain the bones of at least 264 individuals and the Biddles postulated that these individuals were part of the Great Army.  However, the initial radiocarbon dates did not support this with some individuals appearing to have died in the 8th century.  Cat Jarman looked at the bones again and concluded that many of the individuals had consumed a mostly marine diet and this had distorted the radiocarbon dates (the marine reservoir effect).  When she corrected the radiocarbon dates for this effect all the individuals now had a date of death that was compatible with death around 873/874.

The D shaped enclosure

In their recent book ‘The Viking Great Army and the Making of England’, Julian Richards and Dawn Hadley (2021) question some of the conclusions about the D-shaped enclosure.  The archaeology is complicated by the presence of ditches belonging to the bailey of the 12th century castle and Richards and Hadley believe it is possible that the archaeology may have been misinterpreted. To clarify this the excavation archive would need to be studied.  It is possible that there never was a D shaped enclosure.

Did those buried in the mausoleum really have a marine diet?

The Great Army had been in England since 865.  Their known overwintering sites were not near the sea and there is no evidence that they brought in vast quantities of fish for the 5000 or so members of the Great Army to eat.  They appear to have lived off the tribute brought to them or foraged for in the local area.  However, according to Cat Jarman, the isotopic evidence is that many of those buried in the mausoleum did have a diet with a significant marine food content.  This is based upon C13 content of bone collagen which turns over about every 10-15 years.  After 8 years in England there wouldn’t be much evidence left of a marine diet and this is the result obtained from samples sent to the University of Utrecht. The results from five samples indicated a marine food content of around 10%.  A larger number of samples were analysed by the Oxford Radiocarbon Accelerator Unit but the same five samples indicated a marine food content of between 15 and 28%.  The authors felt that the Utrecht figures were less reliable than those from Oxford, and only used the Oxford C13 results to calculate percentage marine diet content and revised radiocarbon dates that took into account the marine reservoir effect. A number of assumptions were made in the calculation and these had a significant impact on the precision of the results.

The revised radiocarbon dates were impacted in two ways.  The dates became less old and the dates became less precise.  Take sample G529 for example.  The original radiocarbon date was 670-770.  Taking into account marine reservoir effect the dates become 690 to 939.  The range of possible dates has changed from 100 years to 249 years so almost any measurements will now include the 873/874 dates.  Simply by including the marine reservoir effect in the calculation, the hypothesis that all the bones relate to the overwintering of the Great Army is now possible.  This is very poor use of science.

So, in summary, the evidence for a D shaped enclosure is not convincing and the evidence that all the people buried in the mausoleum belonged to the Great Army is also a bit shaky.