Prof Christopher Ramsey

Abstract:

Contrasting Greenland and Antarctic temperatures during the last glacial period (115,000 to 11,650 years ago) are thought to have been driven by imbalances in the rates of formation of North Atlantic and Antarctic Deep Water (the ‘bipolar seesaw’). Here we exploit a bidecadally-resolved ¹⁴C dataset obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate datasets spanning iceberg-rafted debris event Heinrich 3 and Greenland Interstadial (GI) 5.1 in the North Atlantic (~30,400 to 28,400 to years ago). We observe no divergence between the kauri and Atlantic marine sediment ¹⁴C datasets, implying limited changes in deep water formation. However, a Southern Ocean (Atlantic-sector) iceberg rafted debris event appears to have occurred synchronously with GI-5.1 warming and decreased precipitation over the western equatorial Pacific and Atlantic. An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can be propagated globally via an atmospheric Rossby wave train.

Abstract:

AbstractThis study evaluates the radiocarbon dating of ceramic samples from Tupiguarani sites in Brazil, a settlement type dating up to 3000 cal BP. In this work, residues from ceramic samples from four archaeological sites in Rio de Janeiro (Morro Grande, Serrano, Barba Couto, and Bananeiras) were analyzed. In order to identify the most suitable sample preparation protocols, the humic fraction was isolated from the bulk material at the Oxford Radiocarbon Accelerator Unit (ORAU), whereas the acid-base-acid (ABA) residue fraction method was applied at the Radiocarbon Laboratory of the Fluminense Federal University (LAC-UFF). The dating results were compared to the current knowledge about the occupational periods of the sites. For the Morro Grande site, the results of humic and ABA residue fractions show a difference of more than 1500 yr. For the Serrano site, the 14C ages obtained from the two pretreatments are identical, and as with the Barba Couto and Bananeiras sites, indicate an occupation during the Brazilian colonial period of the 16th century AD and are compatible with the archaeological data.

Abstract:

AbstractThis study tested whether accurate dating by accelerator mass spectrometry (AMS) radiocarbon wiggle-matching of short tree-ring series (~30 annual rings) in the Medieval period could be achieved. Scientific dating plays a central role in the conservation of historic buildings in England. Precise dating helps assess the significance of particular buildings or elements of their fabric, thus allowing us to make informed decisions about their repair and protection. Consequently, considerable weight, both financial and legal, can be attached to the precision and accuracy of this dating. Dendrochronology is the method of choice, but in a proportion of cases this is unable to provide calendar dates. Hence, we would like to be able to use 14C wiggle-matching to provide a comparable level of precision and reliability, particularly on shorter tree-ring sequences (~30 annual growth rings) that up until now would not routinely be sampled. We present the results of AMS wiggle-matching five oak tree-ring sequences, spanning the period covered by the vast majority of surviving Medieval buildings in England (about AD 1180–1540) when currently we have only decadal and bidecadal calibration data.

Abstract:

In the context of unanswered questions about the nature and development of the Late Neolithic in Orkney, we present a summary of research up to 2015 on the major site at the Ness of Brodgar, Mainland Orkney, concentrating on the impressive buildings. Finding sufficient samples for radiocarbon dating was a considerable challenge. There are indications, from both features and finds, of activity pre-dating the main set of buildings exposed so far by excavation. Forty-six dates on thirty-nine samples are presented and are interpreted in a formal chronological framework. Two models are presented, reflecting different possible readings of the sequence. Both indicate that piered architecture was in use by the thirtieth century cal bc and that the massive Structure 10, not the first building in the sequence, was also in existence by the thirtieth century cal bc. Activity associated with piered architecture came to an end (in Model 2) around 2800 cal bc. Midden and rubble infill followed. After an appreciable interval, the hearth at the centre of Structure 10 was last used around 2500 cal bc, perhaps the only activity in an otherwise abandoned site. The remains of some 400 or more cattle were deposited over the ruins of Structure 10: in Model 2, in the mid-twenty-fifth century cal bc, but in Model 1 in the late twenty-fourth or twenty-third century cal bc. The chronologies invite comparison with the near-neighbour of Barnhouse, in use from the later thirty-second to the earlier twenty-ninth century cal bc, and the Stones of Stenness, probably erected by the thirtieth century cal bc. The Ness, including Structure 10, appears to have outlasted Barnhouse, but probably did not endure as long in its primary form as previously envisaged. The decay and decommissioning of the Ness may have coincided with the further development of the sacred landscape around it; but precise chronologies for other sites in the surrounding landscape are urgently required. The spectacular feasting remains of several hundred cattle deposited above Structure 10 may belong to a radically changing world, coinciding (in Model 2) with the appearance of Beakers nationally, but it was arguably the, by now, mythic status of that building which drew people back to it