A photo voltaic storm dates Viking Age commerce

Chronology, the measurement of time, is important for our understanding of the previous. It places occasions on a timeline, tells us which occasions have been synchronous or through which order they occurred. It’s thus step one on our method to disentangle causes and results. Historians use e.g. written sources, or artefacts with date stamps reminiscent of cash, for constructing a chronology. Nonetheless, this solely works for latest instances and for areas the place writing and calendars have been established.

Imported beads from the excavations in Ribe, in stratigraphical order.
Imported beads from the excavation in Ribe, in stratigraphical order. Radiocarbon courting places absolute dates (i.e., calendar dates) on the relative chronology (i.e., the temporal order of artefacts).

For prehistory, in distinction, scientific courting strategies are used to construct chronologies. Considered one of these is radiocarbon courting, which is a well-established courting methodology for the previous 50,000 years. Till now, nonetheless, I’ve solely utilized radiocarbon courting to questions on prehistory, particularly the Stone Age. For more moderen intervals, such because the Early Medieval/Viking Age, nonetheless, the precision of radiocarbon courting had been too restricted. This was notably true for city contexts, that’s, early cities. Within the thoughts of a radiocarbon courting specialist, city websites are websites the place so much is going on quick on the identical spot for a protracted time frame. Which means that city deposits are very complicated and require detailed chronologies – a degree of element that radiocarbon courting hitherto has not been capable of ship. Different courting strategies reminiscent of dendrochronology (tree-ring courting) or artefact typologies (e.g., which sorts of pottery have been widespread through which intervals) had been used as a substitute.

A photograph of the Viking Age layers at Ribe, exposed in a profil.
This profile on the nook of the excavation trench exhibits the good variety of archaeological layers that had been deposited on prime of one another. Co-author Søren M. Sindbæk has joined the photograph to supply a scale.

This modified after I acquired the chance to work on the Centre for City Community Evolutions (UrbNet), Aarhus College, at a time when extra detailed radiocarbon calibration curves have been developed in a world effort. Calibration is the method of changing the measured radiocarbon age into an age on our calendar scale. The 2 aren’t the identical due to small fluctuations within the atmospheric radiocarbon focus. Tree rings type the premise of calibration curves, as a result of every tree ring data the radiocarbon focus of the yr through which it grew. Till not too long ago, calibration curves had been based mostly on decadal samples, thus averaging over ten years of progress.

Nonetheless, in 2021, Fusa Miyake and her colleagues found a speedy enhance in radiocarbon focus in tree rings from the yr 774-775 CE. This spurred intense exercise at radiocarbon courting centres world wide, and shortly extra occasions of this sort have been discovered. The will increase in atmospheric radiocarbon concentrations are brought on by photo voltaic particle occasions and illustrate that some element is misplaced when calibration curves are constituted of decadal samples.

Subsequently, I and plenty of colleagues world wide minimize up slices of timber into particular person yr rings and measured their radiocarbon concentrations. This led to the primary model of a calibration curve permitting for annual calibration, IntCal20. Work on annual calibration curves is ongoing, and you may be fairly certain that within the second you might be studying this, a radiocarbon specialist someplace on this planet is slicing, extracting or measuring on tree rings.

Photograph of tree rings, seen through a microscope
A slab of oak tree, seen by way of a microscope, with the tip of the scalpel we use for slicing the tree-rings. The bands of pores are the early wooden, produced in spring and partially incorporating carbon from the earlier progress season. The opposite, extra stable, bands are the late wooden, which characterize the summer season progress of just one yr, and which we use for our calibration curve.

Throughout my work at UrbNet, my process was to develop chronologies for city websites. Considered one of these websites is the city of Ribe in present-day Denmark, referred to as the oldest city in Scandinavia and an necessary Viking Age commerce centre.

In Ribe, a big grant from the Carlsberg basis gave us the possibility to do a analysis excavation on a small plot within the centre of the city. We excavated an space of c. 87 m2 masking most of a constructing plot, along with elements of a road and adjoining plots. Layer upon layer of clay flooring revealed the place the homes as soon as stood. We adopted a scientific stratigraphic protocol and high-definition documentation strategies, together with 3D laser scanning of all uncovered surfaces, moist sieving of all excavated soil, and systematic geoarchaeological sampling of excavation models. It was superb to witness the large numbers of tiny artefacts that have been recovered as all of the soil from the excavation was sieved.

A photograph of different artefacts from the Northern Emporium excavation in Ribe.
Totally different artefacts from the excavation in Ribe. The tiny object within the center is a miniature axe made from amber. Though it broke into three items already within the Viking Age, it may very well be reassembled after we discovered the fragments in three completely different wheelbarrows of soil throughout wet-sieving.

A few of these artefacts had been imported from distant – we discovered antler and slate from Norway, pottery from the Rhine space, and glass beads from the Center East. By radiocarbon courting the precise layers the place these artefacts have been discovered, we may put time stamps on the completely different commerce routes. As we used the brand new IntCal20 calibration curve, with some extra tree-ring information measured for this examine, we have been capable of date these layers with a precision of some a long time. Moreover, we recognized the layer through which the 775 CE Miyake occasion, an enormous Photo voltaic Particle Occasion, had taken place. This was like an anchor for our complete sequence of about 140 radiocarbon dates. Now we are able to conclude that oversea commerce routes with Norway have been established lengthy earlier than impulses from the Islamic world initiated proto-globalised commerce in Afro-Eurasia, and lengthy earlier than Viking raids have been recorded in European historic sources. The Viking Age, outlined by artefact types and imports reminiscent of Center Jap beads, started in 790±10 CE in a society which had been used to maritime commerce for a number of a long time.

Photo of the excavation
On the excavation in Ribe. I ponder which treasures are hidden in these buckets stuffed with filth.


Miyake F, Nagaya Ok, Masuda Ok, Nakamura T. A signature of cosmic-ray enhance in AD 774–775 from tree rings in Japan. Nature. 2012;486(7402):240-2

Philippsen B, Feveile C, Olsen J, Sindbæk SM. Single-year radiocarbon courting anchors Viking Age commerce cycles in time. Nature. 2021. https://doi.org/10.1038/s41586-021-04240-5

Reimer PJ, Austin WEN, Bard E, Bayliss A, Blackwell PG, Ramsey CB, et al. The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0-55 kcal BP). Radiocarbon. 2020;62(4):725-57.



This examine was funded by the Carlsberg Basis (Semper Ardens Grant CF16-0008 Northern Emporium) and the Danish Nationwide Analysis Basis grant DNRF119 – Centre of Excellence for City Community Evolutions (UrbNet). Brødrene Hartmanns Fond (grant software A34514) and Grosserer P.L. Jørgensens Mindefond supported the tree-rings measurements with 50.000 DKK and 25.000 DKK, respectively.

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