C04_P05

Single-year ¹⁴C dating of the lake-fortress at Āraiši, Latvia

Meadows J^1,2, Zunde M³, Lēģere L⁴, Dee M⁵, Hamann C²

¹ZBSA (Centre for Baltic and Scandinavian Archaeology), Schleswig, Germany, ²Leibniz-Laboratory for AMS Dating and Stable Isotope Research, Christian-Albrechts-University Ki, Kiel, Germany, ³Institute of Latvian History, University of Latvia, Riga, Latvia, ⁴Āraiši lake-fortress archaeological park, Cēsis, Latvia, ⁵Centre for Isotope Research, University of Groningen, Groningen, Netherlands

A timber lake-fortress on a flooded island in Lake Āraiši, central Latvia, was excavated in 1965-69 and 1975-79 by the pioneering underwater archaeologist Jānis Apals, who recognised five construction phases. Dendrochronological analysis originally produced a mixed-species conifer site chronology, which was tentatively cross-matched to a reference chronology from Novgorod, Russia, indicating a felling date of c.AD 930 for timbers from the earliest phase. A more rigorous analysis produced a 95-year floating chronology for the best-preserved Norway spruce (Picea abies (L.) Karst.) timbers from the earliest phase, which was dated by ¹⁴C wiggle-matching with the IntCal13 calibration curve, suggesting a felling date of cal AD 775–784 (Meadows and Zunde 2014, Geochronometria 41(3):223-33). If this range was accurate, it should have been possible to locate the AD 775 Miyake event (Miyake et al. 2012, Nature 486(7402):240-2) in single-year cellulose samples from the final decade of the Āraiši spruce chronology. However, repeated attempts, with replication of the final decade between the Kiel and Groningen laboratories, were unsuccessful. Additional sampling in 2020-21 unambiguously located the AD 775 event 60 years before the spruce felling date, dating the first phase of construction to AD 835. The new results raise questions both about the treatment of ¹⁴C outliers in the original (2014) wiggle-match, and about the IntCal20 data set; like Philippsen et al. (2021, Nature 601(7893):392-6), we suspect that IntCal20 is too low in the 830s AD.