Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE

VIKINGS is a multi-disciplinary project that aims to understand the role of volcanic eruptions and climate change in shaping the early history of Scandinavia. The period 500-1250 Common Era (CE) is characterized by societal unrest, Viking expansion, emerging kingship - and large volcanic eruptions evidenced by geochemical markers in natural archives. The climate variations in Europe, especially in Scandinavia during this period, are however poorly resolved even on a timescale of centuries. Moreover, available dating of archeological findings from that time have never been interpreted within a framework of climatic and environmental change. The VIKINGS project seeks to reveal the climate of this intriguing historic period and to address the role of volcanic eruptions in triggering environmental changes. 1) We have carried out a new multi-proxy investigation of lake Ljøgodttjern sediments, including geochemical, palynological, and DNA analyses, to reconstruct past changes in temperature and agricultural practices of pre-Viking and Viking societies in Southeastern Norway during the period 200 CE to 1300 CE. The periods 200-300 and 800-1300 CE were warmer than 300-800 CE, which is known as the “Dark Ages Cold Period”. This cold period was punctuated by century-scale more temperate intervals, which were dominated by cultivation of cereals and hemp. In between, cold intervals were dominated by livestock farming. Our results demonstrate that the pre-Viking societies changed their agricultural strategy in response to climate variability during the Late Antiquity (ter Schure et al 2021; Bajard et al 2022). In addition, we are analyzing the varved Lake Sagtjernet (120 km north of Oslo) with an annual resolution age model spanning the Holocene period. A large suite of analytical techniques such as core scanning XRF, varve counting, pollen studies, and cryptotephra identification have been carried out to analyse environmental, climatic, and societal changes. During Jan-April 2022, Eirik Ballo was a RCN visiting fellow at Lamont-Doherty Earth Observatory (Columbia University, USA) analysing sedimentary hydrogen isotopes to reconstruct past hydroclimate. A paper on the Lake Sagtjernet age model is currently under review (Ballo et al 2022). 2) We have run aerosol chemistry climate model simulations for key volcanic eruptions during 500-1250 CE. We simulate 17 Tg SO2 eruptions with and without co-injecting volcanic halogens for different latitudes, seasons and injections heights. We are focusing on Icelandic eruptions for the Katla system at 64 N and compare them with tropical eruptions from the Central American Volcanic Arc at 15 N using the same eruption parameters for both. The model analyses are completed and two publications are currently prepared for submission. 3) During the last 8000 years extremely cold periods have occurred, which according to our climate model simulations can only be explained by a series of large explosive volcanic eruptions. Volcanic-induced multi-centennial cold periods occurred every once or twice per millennia throughout this Holocene period. The fourth coldest of these long-lasting cold periods took place during the mid-6th century. Our climate model simulations combined with a growing-degree-day model and local pollen records reveal that this cooling had a severe impact on societies in Southern Norway up to 20 years (van Dijk et al 2022). The mountainous inland study area as well as the west coast in Norway experienced a reduction in agricultural activity and farm abandonment, whereas in the Oslo fjord area the agriculture and society were hardly affected (van Dijk et al 2022 in press). The PhD thesis of Evelien van Dijk has been submitted to UiO (van Dijk 2022) and the defense is on the 16. December 2022. 4) It has been suggested that half of the population of Scandinavia perished following the volcanic double event. To explore the population dynamics of the Scandinavian Iron Age societies we have assembled a database of pre-Christian burials (c. 11,000 dated) within the modern borders of Norway. Analyses of lake sediments from lake Ljøgodttjern have provided novel information on the climate of the Iron Age and changes in agricultural strategies over time, as mentioned above. On the south bank of Ljøgodttjern we find the largest constructed mound in northern Europe. We have undertaken a new wiggle match analysis of logs from the mound, suggesting that it was built in the summer of 552 CE. Shortly after the volcanic eruptions of 536 and 540 CE. The data and analyses are currently prepared for publication. The pronounced surface climate cooling over Scandinavia during the mid-6th century may have led to the Norse myths of the Fimbulwinter as discussed by Ingar Mørkestøl Gundersen (2021). His PhD thesis on the societal impact on Scandinavian Iron Age communities from the 536/540 CE volcanic double event, coupled with GDD modelling, has been successfully defended at MCH in January 2022.

This novel multi-disciplinary project aims to understand the role of volcanic eruptions and climate change in shaping the early history of Europe. The period 500-1250 CE is characterized by natural disasters, societal unrest, Viking expansion, emerging kingship - and large volcanic eruptions evidenced by geochemical markers in natural archives. At present, we know little about the climate variations in Europe and especially in Scandinavia during this period. The VIKINGS project seeks to reveal the climate of the early historic period, and resolve how volcanic eruptions and their environmental impacts facilitated societal changes during the Viking era. "The sun became dark and its darkness lasted for one and a half years" (Michael the Syrian), "Each day it shone for about four hours and still this light was only a feeble shadow" (John of Ephesus) (Stothers and Rampino 1983). These reports of a mysterious cloud which dimmed the light of the sun for at least a year were written at the dawn of the Middle Ages which marked the beginning of an unusual cold period in the mid of the 6th century lasting several years to decades due to the 536/540 CE volcanic eruptions (Toohey et al 2016a). New evidence from multiple tree ring records from the Altai Mountains in Russia led Büntgen et al (2016) to term it "The Late Antiquity Little Ice Age", lasting from about 536 to 660 CE. However, the spatial extent and duration of such a prolonged cold period is vigorously debated (Helama et al 2017a/b). Did the cold period really last more than a century? Were volcanic eruptions the major drivers for climate as proposed for the Little Ice Age (c. 1450-1850 CE)? What role did volcanic eruptions and climate change play in shaping Scandinavian society and the emergence and decline of the Vikings (c. 800-1050 CE)? We seek to address these questions and others within the VIKINGS proposal on "Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE".