Prof Christopher Ramsey

Abstract:

Radiocarbon dating can be applied to archaeological materials which contain radiocarbon from the atmosphere or the oceans. In order to interpret radiocarbon measurements as dates, it is necessary to compare them against measurements on known‐age samples which have been dated by other methods. This allows calibration onto a timescale derived from either dendrochronology or uranium series dating. Multiple analyses can be interpreted through the use of Bayesian statistical methods, allowing for the incorporation of relative age constraints and the grouping of events in phases.

Abstract:

During the last glacial period Northern Hemisphere climate was characterized by extreme and abrupt climate changes, so-called Dansgaard–Oeschger (DO) events. Most clearly observed as temperature changes in Greenland ice-core records, their climatic imprint was geographically widespread. However, the temporal relation between DO events in Greenland and other regions is uncertain due to the chronological uncertainties of each archive, limiting our ability to test hypotheses of synchronous change. In contrast, the assumption of direct synchrony of climate changes forms the basis of many timescales. Here, we use cosmogenic radionuclides ( 10 Be, 36 Cl, 14 C) to link Greenland ice-core records to U∕Th-dated speleothems, quantify offsets between the two timescales, and improve their absolute dating back to 45 000 years ago. This approach allows us to test the assumption that DO events occurred synchronously between Greenland ice-core and tropical speleothem records with unprecedented precision. We find that the onset of DO events occurs within synchronization uncertainties in all investigated records. Importantly, we demonstrate that local discrepancies remain in the temporal development of rapid climate change for specific events and speleothems. These may either be related to the location of proxy records relative to the shifting atmospheric fronts or to underestimated U∕Th dating uncertainties. Our study thus highlights the potential for misleading interpretations of the Earth system when applying the common practice of climate wiggle matching.

Abstract:

ABSTRACTThere is increasing awareness of the need to correct for freshwater as well as marine reservoir effects when undertaking radiocarbon (14C) dating of human remains. Here, we explore the use of stable hydrogen isotopes (δ2H), alongside the more commonly used stable carbon (δ13C) and nitrogen isotopes (δ15N), for correcting 14C freshwater reservoir offsets in 10 paired human-faunal dates from graves at the prehistoric cemetery of Shamanka II, Lake Baikal, southern Siberia. Excluding one individual showing no offset, the average human-faunal offset was 515±175 14C yr. Linear regression models demonstrate a strong positive correlation between δ15N and δ2H ratios, supporting the use of δ2H as a proxy for trophic level. Both isotopes show moderate but significant correlations (r2 ~ 0.45, p < 0.05) with 14C offsets (while δ13C on its own does not), though δ2H performs marginally better. A regression model using all three stable isotopes to predict 14C offsets accounts for approximately 65% of the variation in the latter (r2=0.651, p=0.025), with both δ13C and δ2H, but not δ15N, contributing significantly. The results suggest that δ2H may be a useful proxy for freshwater reservoir corrections, though further work is needed.

Abstract:

© 2018 The Authors Osteobiographies of four individuals whose skeletal remains were recovered in 2015–16 from the Stonehenge World Heritage Site are constructed, drawing upon evidence from funerary taphonomy, radiocarbon dating, osteological study, stable isotope analyses, and microscopic and biomolecular analyses of dental calculus. The burials comprise an adult from the Middle Neolithic period, immediately prior to the building of Stonehenge, and two adults and a perinatal infant dating from the Middle Bronze Age, shortly after the monument ceased to be structurally modified. The two Middle Bronze Age adults were closely contemporary, but differed from one another in ancestry, appearance and geographic origin (key components of ethnicity). They were nevertheless buried in very similar ways. This suggests that aspects they held in common (osteological analysis suggests perhaps a highly mobile lifestyle) were more important in determining the manner of deposition of their bodies than any differences between them in ethnicity. One of these individuals probably came from outside Britain, as perhaps did the Middle Neolithic adult. This would be consistent with the idea that the Stonehenge landscape had begun to draw people to it from beyond Britain before Stonehenge was constructed and that it continued to do so after structural modification to the monument had ceased.