Prof Christopher Ramsey

Abstract:

This is the thirty‐sixth list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst some of the sites included here are the latest series of determinations from the key sites of El Mirón (Spain) and Sutton Courtney (UK), as well as others dating to the Palaeolithic, Mesolithic and later periods. Submitters of the material provide comments on the significance of the results.

Abstract:

White Rose University Press (WRUP) is an open access digital publisher of peer-reviewed academic journals and books, publishing across a wide range of academic disciplines. We are run jointly by the Universities of Leeds, Sheffield and York. We are committed to open access dissemination of research and teaching materials, ensuring academic quality, and supporting innovation in publishing.

Abstract:

Here we present the results of the first cryptotephra investigation of two Late glacial-Holocene lake records from the Southern Carpathian Mountains in Romania, Lake Brazi and Lake Lia. The discovery of an important Icelandic tephrostratigraphic marker, the Askja-S, in the sedimentary records of both sites significantly extends the known ash dispersal from this Plinian eruption. Bayesian age-depth modelling of available radiocarbon (14C) data from both sedimentary records allows us to further refine the depositional age of this ultra-distal tephra. In combination with age constraints on the tephra from other well-dated European sites, we produce an updated age for this key tephrostratigraphic marker of 10,824 ± 97 cal yrs BP (95.4% range). The Askja-S tephra is stratigraphically positioned after the palaeoenvironmental proxy response to the Preboreal Oscillation at both sites. The widespread distribution of this tephra across Europe offers the potential to assess spatio-temporal variability of this climatic signal. The discovery of the Askja-S in lake records from the Southern Carpathians highlights the likelihood of finding other ultra-distal (Icelandic) cryptotephra marker layers within the region. Additionally, given the location of the Carpathian region, it offers the opportunity to further enhance and integrate tephrostratigraphic frameworks of north-western Europe with those of the Mediterranean and Anatolia regions, which will enable a more precise comparison of palaeoenvironmental archives across Europe.

Abstract:

When a carbon reservoir has a lower content of radiocarbon relative to the atmosphere, this is referred to as a reservoir effect. This is expressed as an offset between the radiocarbon ages of samples from the two reservoirs at a single point in time. The marine reservoir effect (MRE) has been a major concern in the radiocarbon community, as it introduces an additional source of error that is often difficult to accurately quantify. For this reason, researchers are often reluctant to date marine material where they have another option. The influence of this phenomenon makes the study of the MRE important for a broad range of applications. The advent of Accelerator Mass Spectrometry (AMS) has reduced sample size requirements and increased measurement precision, in turn increasing the number of studies seeking to measure marine samples. These studies rely on overcoming the influence of the MRE on marine radiocarbon dates through the worldwide quantification of the local parameter ΔR, i.e. the local variation from the global average MRE. Furthermore, the strong dependence on ocean dynamics makes the MRE a useful indicator for changes in oceanic circulation, carbon exchange between reservoirs and the fate of atmospheric CO2, as well as their impact on Earth's climate. This article explores data from the Marine Reservoir Database and reviews the place of natural radiocarbon in oceanic records, focusing on key questions (e.g., changes in ocean dynamics) that have been answered by MRE studies and on their application to different subjects.