Recent and Most-Cited Papers by Michael W Dee
Annually resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp ... more Annually resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp rises in carbon-14 production. These 'Miyake events' are likely produced by rare increases in cosmic radiation from the Sun or other energetic astrophysical sources. The radiocarbon produced is not only circulated through the Earth's atmosphere and oceans, but also absorbed by the biosphere and locked in the annual
PNAS, 2020
Inadequate resolution is the principal limitation of radiocarbon dating. However, recent work has... more Inadequate resolution is the principal limitation of radiocarbon dating. However, recent work has shown that exact-year precision is attainable if use can be made of past increases in atmospheric radiocarbon concentration or so-called Miyake events. Here, this nascent method is applied to an archaeological site of previously unknown age. We locate the distinctive radiocarbon signal of the year 775 common era (CE) in wood from the base of the Uyghur monument of Por-Bajin in Russia. Our analysis shows that the construction of Por-Bajin started in the summer of 777 CE, a foundation date that resolves decades of debate and allows the origin and purpose of the building to be established. radiocarbon dating | exact-year precision | archaeology |
Scientific Reports, 2019
Extreme cosmic radiation events occurred in the years 774/5 and 993/4 CE, as revealed by anomalie... more Extreme cosmic radiation events occurred in the years 774/5 and 993/4 CE, as revealed by anomalies in the concentration of radiocarbon in known-age tree-rings. Most hypotheses point towards intense solar storms as the cause for these events, although little direct experimental support for this claim has thus far come to light. in this study, we perform very high-precision accelerator mass spectrometry (AMS) measurements on dendrochronological tree-rings spanning the years of the events of interest, as well as the Carrington Event of 1859 CE, which is recognized as an extreme solar storm even though it did not generate an anomalous radiocarbon signature. Our data, comprising 169 new and previously published measurements, appear to delineate the modulation of radiocarbon production due to the Schwabe (11-year) solar cycle. Moreover, they suggest that all three events occurred around the maximum of the solar cycle, adding experimental support for a common solar origin. Since the discovery of annual anomalies in the radiocarbon record, also known as Miyake Events, much effort has been undertaken to determine their cause 1-4. Detected through the analysis of tree-ring archives, the events comprise sudden and globally synchronous increases in the atmospheric concentration of radiocarbon (Δ 14 C). The first two verified anomalies occurred in the years 775 and 994 CE (henceforth Event-775 and Event-994). The uplifts were quickly attributed to increases in cosmic radiation, as radiocarbon is produced by means of nuclear reactions associated with the cosmic ray cascade 5,6. The rate of production is proportional to the cosmic ray flux entering the Earth's magnetosphere, which is in turn modulated by the interplanetary magnetic field in accordance with the Schwabe cycle. In fact, this solar cycle is inversely related to radiocarbon production as, during periods of maximal solar activity, the shielding of cosmic rays by the solar plasma in the interplanetary and the geomagnetic fields is enhanced. In such cases, a decrease in radiocarbon production occurs, and vice versa 7-9. This sinusoidal variation has already been measured in tree-ring samples by various groups, and exhibits a peak-to-trough amplitude of around 4-6‰ 8,10-12. Despite this anticorrelation, the most widely accepted theory for the cause of the anomalous increases in Δ 14 C is extreme solar storms 3,13. This is largely because of the occurrence frequency of the events, as several have now been attested and others predicted during the Holocene 4,14,15 , but it is also the conclusion of modelling studies of isotopic signatures in natural archives 16. However, to date few direct connections have been made between the Miyake Events and established solar behavior, or instrumentally monitored solar storms. Indeed, some analyses still contradict the claim of a solar origin altogether 17,18. Here, our results suggest that Event-775 and Event-994 both occurred during the period of the 11-year solar cycle when the Sun was most active. This provides additional support for the hypothesis that these anomalies were instigated by powerful solar emissions.
Radiocarbon, 2019
Information about the global climate, the carbon cycle, changes in solar activity, and a number o... more Information about the global climate, the carbon cycle, changes in solar activity, and a number of other atmospheric processes are preserved in the carbon-14 and the beryllium-10 records. However, these isotope datasets are large and cumbersome to work with. We have designed a self-contained, easy-to-use application that allows for more efficient analysis of different periods and patterns of interest. For several applications in atmospheric modelling, a pre-processing stage is applied to the isotope datasets in order to interpolate the data and mitigate their low temporal resolution. In CHRONOscope, we included linear and non-linear methods of interpolation with interactive parameter optimization. The resultant interpolated data can be extracted for further use. The main functionalities of CHRONOscope include the importation and superimposition of external data, quick navigation through the data with the use of markers, expression of the carbon-14 results in both ∆ 14 C and yr BP form, separation of the data by source, and the visualization of associated error bars. We make this free software available in standalone applications for both Windows and Macintosh operating systems.
IEEE Access, 2019
Extreme bursts of radiation from space result in rapid increases in the concentration of radiocar... more Extreme bursts of radiation from space result in rapid increases in the concentration of radiocarbon in the atmosphere. Such rises, known as Miyake Events, can be detected through the measurement of radiocarbon in dendrochronological archives. The identification of Miyake Events is important because radiation impacts of this magnitude pose an existential threat to satellite communications, aeronautical avionics, and may even be detrimental to human health. However, at present radiocarbon measurements on tree-ring archives are generally only available at decadal resolution, which smooths out the effect of a possible radiation burst. The Miyake Events discovered so far, in tree-rings from the years 3372-3371 BCE, 774-775 CE and 993-994 CE, have essentially been found by chance, but there may be more. In this work, we use signal processing techniques, in particular COSFIRE, to train filters with data on annual changes in radiocarbon (∆ 14 C) around those dates. Then, we evaluate the trained filters and attempt to detect similar Miyake Events in the past. The method that we propose is promising, since it identifies the known Miyake Events at a relatively low false positive rate (FPR). Using the findings of this study, we propose a list of 26 calendar years that our system persistently indicates are Miyake Event-like. We are currently examining a shortlist of five of the newly identified dates, and intend to perform single-year radiocarbon measurements over them. Signal processing techniques, such as COSFIRE filters, can be used as guidance tools since they are able to identify similar patterns of interest, even if they vary in time or in amplitude.
STOTEN, 2019
• Miyake events are natural phenomena causing failures to telecommunication systems. • We investi... more • Miyake events are natural phenomena causing failures to telecommunication systems. • We investigated computational techniques that effectively model such events. • COSFIRE filters are effective for model-ing Miyake events. • Spectral features are also suitable for identifying Miyake events. • Our methods identify 75% of the known Miyake events with FPR b10%. Rapid increments in the concentration of the radiocarbon in the atmosphere (Δ 14 C) have been identified in the years 774-775 CE and 993-994 CE (Miyake events) using annual measurements on known-age tree-rings. The level of cosmic radiation implied by such increases could cause the failure of satellite telecommunication systems, and thus, there is a need to model and predict them. In this work, we investigated several intelligent computational methods to identify similar events in the past. We apply state-of-the-art pattern matching techniques as well as feature representation, a procedure that typically is used in machine learning and classification. To validate our findings, we used as ground truth the two confirmed Miyake events, and several other dates that have been proposed in the literature. We show that some of the methods used in this study successfully identify most of the ground truth events (~1% false positive rate at 75% true positive rate). Our results show that computational methods can be used to identify comparable patterns of interest and hence potentially uncover sudden increments of Δ 14 C in the past.
PNAS, 2018
The extent to which climate change causes significant societal disruption remains controversial. ... more The extent to which climate change causes significant societal disruption remains controversial. An important example is the decline of the Akkadian Empire in northern Mesopotamia ∼4.2 ka, for which the existence of a coincident climate event is still uncertain. Here we present an Iranian stalagmite record spanning 5.2 ka to 3.7 ka, dated with 25 U/Th ages that provide an average age uncertainty of 31 y (1σ). We find two periods of increased Mg/Ca, beginning abruptly at 4.51 and 4.26 ka, and lasting 110 and 290 y, respectively. Each of these periods coincides with slower vertical stalagmite growth and a gradual increase in stable oxygen isotope ratios. The periods of high Mg/Ca are explained by periods of increased dust flux sourced from the Mesopotamia region, and the abrupt onset of this dustiness indicates threshold behavior in response to aridity. This interpretation is consistent with existing marine and terrestrial records from the broad region, which also suggest that the later, longer event beginning at 4.26 ka is of greater regional extent and/or amplitude. The Q:9 chronological precision and high resolution of our record indicates that there is no significant difference, at decadal level, between the start date of the second, larger dust event and the timing of North Mesopotamia settlement abandonment, and furthermore reveals striking similarity between the total duration of the second dust event and settlement abandonment. The Iranian record demonstrates this region's threshold behavior in dust production, and its ability to maintain this climate state for multiple centuries naturally.
Ecology Letters, 2016
Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; 3... more Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; 38 however their relative importance remains unclear. We assessed the extent to which mega-39 herbivore species controlled plant community composition and nutrient cycling, relative to other 40 factors during the Late Quaternary extinction event in Britain and Ireland, when two-thirds of the 41 region's mega-herbivore species went extinct. Warmer temperatures, plant-soil and plant-plant 42 interactions, and reduced burning contributed to the expansion of woody plants and declining 43 nitrogen availability in our five study ecosystems. Shrub biomass in particular was consistently one 44 of the strongest predictors of ecosystem change, equaling or exceeding the effects of other biotic 45 and abiotic factors. In contrast, there was relatively little evidence for mega-herbivore control on 46 plant community composition and nitrogen availability during this time. The ability of plants to 47 determine the fate of terrestrial ecosystems during periods of global environmental change may 48 therefore be greater than previously thought.
Radiocarbon, 2015
Papyri 10012A and 10012B from Illahun, Egypt, provide the earliest astro-chronological datum in h... more Papyri 10012A and 10012B from Illahun, Egypt, provide the earliest astro-chronological datum in history and, while calculated to various years in the 19th century BCE, have never been independently verified. As this datum enables the Middle Kingdom (MK) section of Egyptian historical chronology to be anchored in absolute time, it establishes the principal calendrical timeline for the eastern Mediterranean Bronze Age in the first half of the 2nd millennium BCE. AMS radiocarbon measurements of Papyrus 10012B establish its date range to 1886–1750 BCE, confirming the astronomical calculations and the essential reliability of Egyptian historical chronology for this period. Furthermore, all three leading estimates for the calendar year attribution of the document are supported by this analysis, with the role of a possible growing season effect determining which is most favored.
Nature Geoscience, 2016
Mantle flow can cause the Earth's surface to uplift and subside, but the rates and durations of t... more Mantle flow can cause the Earth's surface to uplift and subside, but the rates and durations of these motions are, in general, poorly resolved due to the diiculties in making measurements of relatively small vertical movements (hundreds of metres) over suuciently large distances (about 1,000 km). Here we examine the eeect of mantle upwelling through a study of Quaternary uplift along the coast of Angola. Using both optically stimulated luminescence on sediment grains, and radiocarbon dating of fossil shells, we date a 25 m coastal terrace at about 45 thousand years old, when sea level was about 75 m lower than today, indicating a rapid uplift rate of 1.8–2.6 mm yr −1 that is an order of magnitude higher than previously obtained rates averaged over longer time periods. Automated extraction and correlation of coastal terrace remnants from digital topography uncovers a symmetrical uplift with diameter of more than 1,000 km. The wavelength and relatively short timescale of the uplift suggest that it is associated with a mantle process, possibly convective upwelling, and that the topography may be modulated by rapid short-lived pulses of mantle-derived uplift. Our study shows that stable continental regions far from the eeects of glacial rebound may experience rapid vertical displacements of several millimetres per year.
Radiocarbon, 2017
Single-year spikes in radiocarbon production are caused by intense bursts of radiation from space... more Single-year spikes in radiocarbon production are caused by intense bursts of radiation from space. Supernovae emit both high-energy particle and electromagnetic radiation, but it is the latter that is most likely to strike the atmosphere all at once and cause a surge in 14 C production. In the 1990s, it was claimed that the supernova in 1006 CE produced exactly this effect. With the 14 C spikes in the years 775 and 994 CE now attributed to extreme solar events, attention has returned to the question of whether historical supernovae are indeed detectable using annual 14 C measurements. Here, we combine new and existing measurements over six documented and putative supernovae, and conclude that no such astrophysical event has yet left a distinct imprint on the past atmospheric 14 C record.
The date of the Late Bronze Age Minoan eruption of the Thera volcano has provoked much debate amo... more The date of the Late Bronze Age Minoan eruption of the Thera volcano has provoked much debate among archaeologists, not least in a recent issue of Antiquity (‘Bronze Age catastrophe and modern controversy: dating the Santorini eruption’, March 2014). Here, the authors respond to those recent contributions, citing evidence that closes the gap between the conclusions offered by previous typological, stratigraphic and radiometric dating techniques. They reject the need to choose between alternative approaches to the problem and make a case for the synchronisation of eastern Mediterranean and Egyptian chronologies with agreement on a ‘high’ date in the late seventeenth century BC for the Thera eruption.
The simple method of graphite target development, ®rst presented at AMS-7 has been further develo... more The simple method of graphite target development, ®rst presented at AMS-7 has been further developed and re®ned. Experiments have been performed to study the range of possible reaction conditions and the eect of these on the nature of the graphite generated. The results from these experiments have been used to make the method as robust as possible with a high success rate, a quick reaction time and very simple apparatus requirements. This paper covers the details of the experiments, the conclusions drawn from them, and the technique now employed for routine graphite sample preparation at ORAU.
Between 1500 and 1850, more than 12 million enslaved Africans were transported to the New World. ... more Between 1500 and 1850, more than 12 million enslaved Africans were transported to the New World. The vast majority were shipped from West and West-Central Africa, but their precise origins are largely unknown. We used genome-wide ancient DNA analyses to investigate the genetic origins of three enslaved Africans whose remains were recovered on the Caribbean island of Saint Martin. We trace their origins to distinct subcontinental source populations within Africa, including Bantu-speaking groups from northern Cameroon and non-Bantu speakers living in present-day Nigeria and Ghana. To our knowledge, these findings provide the first direct evidence for the ethnic origins of enslaved Africans, at a time for which historical records are scarce, and demonstrate that genomic data provide another type of record that can shed new light on long-standing historical questions. ancient DNA | genomics | slave trade
Radiocarbon dates on samples susceptible to inbuilt age are common in the chronological record of... more Radiocarbon dates on samples susceptible to inbuilt age are common in the chronological record of many archaeological and environmental sites. Indeed, fragments of charcoal and wood are sometimes the only materials sufficiently well preserved for dating. However, where high-precision estimates are required the extra uncertainty associated with such measurements often renders them unusable. This article tests three Bayesian modeling approaches that are designed to tackle this problem. The findings of our study suggest that successful corrections can be made for the inherent age offsets. The most effective and versatile approach was based on a version of outlier analysis. It is hoped that this method will become more widely employed and enable samples susceptible to inbuilt age to be included in high-precision chronologies.
The Egyptian state was formed prior to the existence of verifiable historical records. Convention... more The Egyptian state was formed prior to the existence of verifiable historical records. Conventional dates for its formation are based on the relative ordering of artefacts. This approach is no longer considered sufficient for cogent historical analysis. Here, we produce an absolute chronology for Early Egypt by combining radiocarbon and archaeological evidence within a Bayesian paradigm. Our data cover the full trajectory of Egyptian state formation and indicate that the process occurred more rapidly than previously thought. We provide a timeline for the First Dynasty of Egypt of generational-scale resolution that concurs with prevailing archaeological analysis and produce a chronometric date for the foundation of Egypt that distinguishes between historical estimates.
Keywords: Radiocarbon Egypt Reservoir Effect Seasonal Effect Egyptian Historical Chronology Nile ... more Keywords: Radiocarbon Egypt Reservoir Effect Seasonal Effect Egyptian Historical Chronology Nile a b s t r a c t Some radiocarbon dates for ancient Egypt have been significantly offset from the established historical chronology (see Bonani et al., 2001). In this paper, short-lived plant species collected in Egypt between 1700 and 1900 AD were used to investigate the possibility that the radiocarbon record had been influenced by reservoir effects. AMS radiocarbon measurements were made on 66 known-age samples, resulting in an average offset from expected values of 19 years. The implications of this minor discrepancy on the likelihood of a reservoir process are discussed, and the agreement of the data with recent models of radiocarbon seasonality is also considered.
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Recent and Most-Cited Papers by Michael W Dee