Prof Christopher Ramsey

Abstract:

Radiocarbon (14C), as a consequence of its production in the atmosphere and subsequent dispersal through the carbon cycle, is a key tracer for studying the Earth system. Knowledge of past 14C levels improves our understanding of climate processes, the Sun, the geodynamo, and the carbon cycle. Recently updated radiocarbon calibration curves (IntCal20, SHCal20, and Marine20) provide unprecedented accuracy in our estimates of 14C levels back to the limit of the 14C technique (~55,000 years ago). Such improved detail creates new opportunities to probe the Earth and climate system more reliably and at finer scale. We summarize the advances that have underpinned this revised set of radiocarbon calibration curves, survey the broad scientific landscape where additional detail on past 14C provides insight, and identify open challenges for the future.

Abstract:

A considerable amount of bioarchaeological research – including AMS ¹⁴C dating and stable carbon and nitrogen isotope analyses (δ¹³C and δ¹⁵N) – has been undertaken on the hunter-gatherers from the area west of Lake Baikal, known as Cis-Baikal. No such work has previously been reported for the east side of the lake, Trans-Baikal. Here, we present new radiocarbon dates and isotopic results for twenty individuals from the Fofanovo cemetery, located along the Selenga River on the southeast coast of Lake Baikal.

Once corrected for an old carbon effect using regression equations developed for Cis-Baikal, the radiocarbon results form 4 chronological clusters: 1) Late Mesolithic (LM), around 7950 cal BP (n = 3); 2) Late Neolithic (LN), between ca. 6000 and 5500 cal BP (n = 5); 3) LN to Early Bronze Age (EBA), between ca. 4900 and 4500 cal BP (n = 2); and the largest cluster 4) later EBA, around 3700 cal BP (n = 10). The LM Cluster 1 dates indicate that formal cemetery use in Trans-Baikal may have begun earlier than in Cis-Baikal. Clusters 2 and 3 reveal a previously unidentified LN component to the cemetery. Additionally, the EBA Cluster 4 appears to be largely synchronous with the EBA in Cis-Baikal.

As a group, the Fofanovo individuals are isotopically distinct from the Middle-Holocene hunter–gatherers in the microregions of Cis-Baikal, exhibiting a combination of low δ¹³C values (−19.4 ± 0.9‰) but high δ¹⁵N values (15.2 ± 0.8‰). This likely reflects the distinctive isotopic ecology of the lower Selenga River, combined with use of aquatic resources from Lake Baikal itself. While further sampling is needed to test its robustness, a statistically significant difference between the LN (n = 6) and EBA (n = 11) was found, suggesting a greater reliance on the seasonal resources of the Selenga River during the EBA.

Further analyses on these and other individuals from the cemetery are planned and will undoubtably provide additional insights into hunter-gatherer subsistence adaptations and dietary variation in Trans-Baikal, highlighting both differences and similarities with those of Cis-Baikal.

Abstract:

Stable oxygen isotope dendrochronology is an effective precision-dating method for fast grown, invariant (complacent) tree-rings and for trees growing in moist, temperate climatic regions where growth may not be strongly controlled by climate. The method works because trees preserve a strong common isotopic signal, from summer precipitation, and therefore do not need to be physiologically stressed to record a dating signal. This study explores the working hypothesis that whilst tree species may differ in their eco-physiology, leaf morphology and wood anatomy they will record an isotopic signal in their growth rings that is sufficiently similar to enable their precise dating against isotopic reference chronologies developed using dated oak tree rings from the same region. Modern and historical samples from six species (sweet chestnut, English elm, ash, alder, European beech and black poplar) were analysed and their oxygen isotopic variability was compared against an oak master chronology previously developed for central southern England. Whilst differences in the relative strength of the agreement between the different species and the master chronology are apparent, the potential for interspecies dating is demonstrated convincingly. The ability to date non-oak species using stable oxygen isotopes opens-up new opportunities for science-based archaeology and will improve understanding of a largely-unexplored, but significant part of the European historical buildings archive.

Abstract:

Sea-level change is thought to influence the frequencies of volcanic eruptions on glacial to interglacial timescales. However, the underlying physical processes and their importance relative to other influences (for example, magma recharge rates) remain poorly understood. Here we compare an approximately 360-kyr-long record of effusive and explosive eruptions from the flooded caldera volcano at Santorini (Greece) with a high-resolution sea-level record spanning the last four glacial–interglacial cycles. Numerical modelling shows that when the sea level falls by 40 m below the present-day level, the induced tensile stresses in the roof of the magma chamber of Santorini trigger dyke injections. As the sea level continues to fall to −70 or −80 m, the induced tensile stress spreads throughout the roof so that some dykes reach the surface to feed eruptions. Similarly, the volcanic activity gradually disappears after the sea level rises above −40 m. Synchronizing Santorini’s stratigraphy with the sea-level record using tephra layers in marine sediment cores shows that 208 out of 211 eruptions (both effusive and explosive) occurred during periods constrained by sea-level falls (below −40 m) and subsequent rises, suggesting a strong absolute sea-level control on the timing of eruptions on Santorini—a result that probably applies to many other volcanic islands around the world.

Abstract:

Sea-level change is thought to influence the frequencies of volcanic eruptions on glacial to interglacial timescales. However, the underlying physical processes and their importance relative to other influences (for example, magma recharge rates) remain poorly understood. Here we compare an approximately 360-kyr-long record of effusive and explosive eruptions from the flooded caldera volcano at Santorini (Greece) with a high-resolution sea-level record spanning the last four glacial–interglacial cycles. Numerical modelling shows that when the sea level falls by 40 m below the present-day level, the induced tensile stresses in the roof of the magma chamber of Santorini trigger dyke injections. As the sea level continues to fall to −70 or −80 m, the induced tensile stress spreads throughout the roof so that some dykes reach the surface to feed eruptions. Similarly, the volcanic activity gradually disappears after the sea level rises above −40 m. Synchronizing Santorini’s stratigraphy with the sea-level record using tephra layers in marine sediment cores shows that 208 out of 211 eruptions (both effusive and explosive) occurred during periods constrained by sea-level falls (below −40 m) and subsequent rises, suggesting a strong absolute sea-level control on the timing of eruptions on Santorini—a result that probably applies to many other volcanic islands around the world.