Prof Christopher Ramsey

Abstract:

We test a recent prediction that stable carbon isotope ratios from UK oaks will display age-trends of more than 4‰ per century by measuring >5400 carbon isotope ratios from the late-wood alpha-cellulose of individual rings from 18 modern oak trees and 50 building timbers spanning the 9th to 21st centuries. After a very short (c.5 years) juvenile phase with slightly elevated values, the number of series that show rising and falling trends is almost equal (33:35) and the average trend is almost zero. These results are based upon measuring and averaging the trends in individual time-series; the ‘mean of the slopes’ approach. We demonstrate that the more conventional ‘slope of the mean’ approach can produce strong but spurious ‘age-trends’ even when the constituent series are flat, with zero slope and zero variance. We conclude that it is safe to compile stable carbon isotope chronologies from UK oaks without de-trending. The isotope chronologies produced in this way are not subject to the ‘segment length curse’, which applies to growth measurements, such as ring width or density, and have the potential to retain very long-term climate signals.

Abstract:

© 2020 Elsevier Ltd The Lake Baikal region of southern Siberia has a rich mortuary record that has provided the most comprehensive isotopic database for palaeodietary studies of north-temperate hunter-gatherers in the world, permitting more detailed reconstructions and finer-grained research questions than are usually possible. Building on previous work, this study contributes new δ13C, δ15N, and AMS radiocarbon dating results from the cemeteries of Verkholensk (n = 44) in the Upper Lena River micro-region and Ulan-Khada (n = 19) in the Little Sea micro-region. Our results reveal that the Late Neolithic (LN, 5570–4600 cal BP) individuals at Verkholensk exhibit higher δ15N values than in the Early Bronze Age (EBA, 4600–3700 cal BP), suggesting a shift to a more terrestrial diet, possibly in response to climate-induced environmental changes. In addition, EBA individuals at Verkholensk differ in both δ13C and δ15N from those at the nearby site of Obkhoi, suggesting territorial divisions at a surprisingly small scale, although there is a diachronic component that needs to be considered, highlighting the need for additional work on freshwater reservoir corrections for the Upper Lena micro-region. The Ulan-Khada EBA results are consistent with the ‘Game-Fish’ and ‘Game-Fish-Seal’ dietary patterns previously identified in the Little Sea micro-region. The now substantial Little Sea micro-region EBA dataset—— allows for more subtle differences in diet to be identified, namely that EBA females with Game-Fish-Seal diets for the whole of the Little Sea sample display significantly lower mean δ13C values than their male counterparts, providing some of the first evidence for sex-based dietary distinctions in Lake Baikal. A small number of δ13C and/or δ15N outliers were identified at both Verkholensk and Ulan-Khada that may support previous suggestions of individual mobility between the Upper Lena and Little Sea micro-regions. Exploratory use of δ18O isotopes in bone collagen offers a novel line of support for this scenario, confirming a number of independently identified outliers.