Gerry McCormac | University of Stirling (original) (raw)

Papers by Gerry McCormac

Research paper thumbnail of IntCal04: A New Consensus Radiocarbon Calibration Dataset from 0-26 ka BP

Abstract Because atmosphere 14C levels have not been constant through time, it is necessary to ca... more Abstract Because atmosphere 14C levels have not been constant through time, it is necessary to calibrate radiocarbon dates with known age radiocarbon datasets in order to compare paleorecords based on 14C ages and those based on other timescales. The ...

Research paper thumbnail of A 30,000-Year Pollen and Radiocarbon Record from Highland Sumatra as Evidence for Climatic Change

Radiocarbon

We examine the pollen analytical and14C sequences from two Sumatra highland sites, Pea Bullok (2°... more We examine the pollen analytical and14C sequences from two Sumatra highland sites, Pea Bullok (2°15'N,…

Research paper thumbnail of Radiocarbon to Calendar Date Conversion: Calendrical Band Widths as a Function of Radiocarbon Precision

Radiocarbon

Accurate high-precision14C dating (i.e.,± 20 yr precision or less on the14C date) provides the na... more Accurate high-precision14C dating (i.e.,± 20 yr precision or less on the14C date) provides the narrowest calendrical band width and, hence, the best age range determination possible. However, because of the structure in the14C calibration curve, the calendar age range for a given14C precision is not constant throughout the calibration range. In this study, we quantify the calendar band widths for a range of14C precisions throughout the calibration range. We show that an estimate of the likely calendar band width in years can be obtained from the expression: Band width (yr) = 2.12 x14C precision (1 σ) + 54.6. We also show that calendar band widths are widest around 4000 BP at the start of the Bronze Age, and become narrow through the later Bronze Age and Iron Age and back into the Neolithic.

Research paper thumbnail of Precise dating of the Norfolk timber circle

Nature

, the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was disc... more , the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was discovered within the intertidal zone at Holme-nextthe-Sea, Norfolk (52.58°N, 00.33°E). The circle, the first surviving example discovered in Britain, was in serious danger of destruction by tidal erosion, so it was imperative that detailed archaeological investigations be undertaken, including dating. Information provided by tree-ring analysis and radiocarbon measurements was combined using a bayesian approach 1 , resulting in a precise absolute dating for the structure. The timber circle (Fig. 1) was dated by taking six samples (four from the ring of posts and duplicate samples from the central tree) for dendrochronological analysis 2. The ring sequence from the central stump and the four ring sequences from the posts crossmatched and were combined to form a 168-year site chronology. This tree-ring sequence was compared with a series of reference chronologies. The highest, but statistically non-significant, correlation was against the East Anglia chronology 3 (tǃ3.98; higher t-values are more significant 4), giving an end date for the site chronology of 2050 BC. It also produced lower correlations against East Anglia ending at 2454 BC (tǃ3.17) and 2019 BC (tǃ3.14). Running the ring pattern against the Irish master 5 gave correlations of tǃ3.39 at 2050 BC, but only tǃ0.96 at 2454 BC and tǃ1.7 at 2019 BC. Thus, although not statistically significant, dendrochronology suggested that 2050 BC is the most likely end date for the site chronology. However, although the consistency of the t-values was encouraging, the correlation values were too low for definitive dating.

Research paper thumbnail of New Scientific Dating of the Later Bronze Age Wells at Swalecliffe, Kent

The Antiquaries Journal, Aug 31, 2004

The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquar... more The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquaries Journal. The site comprised seventeen wells cut into the base of a previously reduced hollow. Groundwater could thus have been more readily accessed within the subsequently cut well pits. The depth of the base of the wells, at up to 2.5m below ground level, and their consequent waterlogged nature, allowed exceptional preservation of wooden linings and plank steps. Application of dendrochronological and radiocarbon dating suggested that the individual wells were used in sequence over a period of around 500 years, from an origin probably in the late thirteenth century BC to abandonment probably within the seventh century BC. The earlier phases (1–4) were dated mainly by dendrochronology, a 348-year sequence known as SWALECLF 1, whilst the later phases (5–7) were dated by a series of five radiocarbon dates.

Research paper thumbnail of High-precision 14C measurements of contemporaneous tree-ring dated wood from the British Isles and New Zealand: AD 1850 to 950

Radiocarbon

The University of Waikato, Hamilton, New Zealand and The Queen's University of Belfast, North... more The University of Waikato, Hamilton, New Zealand and The Queen's University of Belfast, Northern Ireland radiocarbon dating laboratories have undertaken a series of high-precision measurements on decadal samples of dendrochronologically dated oak (Quercus petraea) from Great Britain and cedar (Libocedrus bidwillii) and silver pine (Lagarostrobos colensoi) from New Zealand. The results show an average hemispheric offset over the 900 yr of measurement of 40 ± 13 yr. This value is not constant but varies with a periodicity of about 130 yr. The Northern Hemisphere measurements confirm the validity of the Pearson et al. (1986) calibration dataset.

Research paper thumbnail of Radiocarbon Calibration of the Anglo-Saxon Period: AD 495-725

Radiocarbon

Radiocarbon dating has been rarely used for chronological problems relating to the Anglo-Saxon pe... more Radiocarbon dating has been rarely used for chronological problems relating to the Anglo-Saxon period. The "flatness" of the calibration curve and the resultant wide range in calendrical dates provide little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology have, however, created the possibility of refining and checking the established chronologies, based on typology of artifacts, against 14C dates. The calibration process, within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have there- fore re-measured, at decadal intervals, a section of the Irish oak chronology for the period AD 495-725. These measurements have been included in IntCal04.

Research paper thumbnail of The Norfolk Bronze Age Timber Circle

Nature

, the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was disc... more , the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was discovered within the intertidal zone at Holme-nextthe-Sea, Norfolk (52.58°N, 00.33°E). The circle, the first surviving example discovered in Britain, was in serious danger of destruction by tidal erosion, so it was imperative that detailed archaeological investigations be undertaken, including dating. Information provided by tree-ring analysis and radiocarbon measurements was combined using a bayesian approach 1 , resulting in a precise absolute dating for the structure. The timber circle (Fig. 1) was dated by taking six samples (four from the ring of posts and duplicate samples from the central tree) for dendrochronological analysis 2. The ring sequence from the central stump and the four ring sequences from the posts crossmatched and were combined to form a 168-year site chronology. This tree-ring sequence was compared with a series of reference chronologies. The highest, but statistically non-significant, correlation was against the East Anglia chronology 3 (tǃ3.98; higher t-values are more significant 4), giving an end date for the site chronology of 2050 BC. It also produced lower correlations against East Anglia ending at 2454 BC (tǃ3.17) and 2019 BC (tǃ3.14). Running the ring pattern against the Irish master 5 gave correlations of tǃ3.39 at 2050 BC, but only tǃ0.96 at 2454 BC and tǃ1.7 at 2019 BC. Thus, although not statistically significant, dendrochronology suggested that 2050 BC is the most likely end date for the site chronology. However, although the consistency of the t-values was encouraging, the correlation values were too low for definitive dating.

Research paper thumbnail of Liquid Scintillation Counter Characterisation, Optimisation and Benzene Purity Correction

Radiocarbon

In liquid scintillation counting (LSC), small variations in benzene purity can cause 14C pulse-he... more In liquid scintillation counting (LSC), small variations in benzene purity can cause 14C pulse-height spectra to move with respect to the counting window. Thus, one must carefully monitor the purity of each benzene sample and apply corrections for spectral shifts. I describe here the techniques used at Queen's University Belfast for deriving correction factors for observed small variations in benzene purity. I also describe the methods used at our laboratory to fine-tune our Quantulus LS counters for high-precision dating. The tuning of the instruments minimizes the effect of fluctuations in gain that may occur during the long counting periods required for high-precision dating. Any remaining influences on efficiency owing to gain changes are corrected for, along with the purity correction, by continuous monitoring of the spectrum produced by the external source.

Research paper thumbnail of Experimental Confirmation of a high-resolution double-etalon modulator (DEM)

Research paper thumbnail of Dating Stonehenge

Research paper thumbnail of The influence of IMF B sub y on the high-latitude thermospheric circulation during northward IMF

Journal of Geophysical Research Atmospheres

Thermospheric neutral wind data, obtained by the Fabry-Perot Interferometer and Wind and Temperat... more Thermospheric neutral wind data, obtained by the Fabry-Perot Interferometer and Wind and Temperature Spectrometer on the Dynamics Explorer 2 satellite during periods of northward interplanetary magnetic field (IMF B{sub z} positive), show a dependence of the circulation on the magnitude and sign of the east-west component (B{sub y}) of the IMF. Averaged thermospheric neutral wind vector fields, for the northern hemisphere, and data from several sets of satellite orbits, that illustrate the variation in the neutral wind structure as a function of time and IMF orientation, are presented and discussed. The results show that near December solstice, at solar maximum: (1) sunward neutral winds develop inside the geomagnetic polar cap during periods of persistent positive B{sub z} and relatively low B{sub y}; (2) typical time delays in the establishment of sunward winds following a northward turning of the IMF are approximately 4 hours; (3) sunward winds are not observed when the magnitude...

Research paper thumbnail of The generation of vertical thermospheric winds and gravity waves at auroral latitudes—I. Observations of vertical winds

Planetary and Space Science, 1984

... 30 (1968), p. 1505. Abstract | PDF (1007 K) | View Record in Scopus | Cited By in Scopus (0).... more ... 30 (1968), p. 1505. Abstract | PDF (1007 K) | View Record in Scopus | Cited By in Scopus (0). PB Hays, TL Killeen, NW Spencer, LE Wharton, RG Roble, TJ Fuller-Rowell and D. Rees, Observations of the dynamics of the polar thermosphere, J. geophys. Res. (1983) (in press).. ...

Research paper thumbnail of An illustrated guide to measuring radiocarbon from archaeological samples

Physics Education, 2004

Radiocarbon dating has been central to the construction of archaeological chronologies for over 5... more Radiocarbon dating has been central to the construction of archaeological chronologies for over 50 years. The archaeological, scientific and (increasingly) statistical methods for interpreting radiocarbon measurements to produce these chronologies have become ever more sophisticated. The accurate measurement of the radiocarbon content of an archaeological sample is, and always has been, fundamental to any interpretation. This article provides an overview of the different approaches adopted for measuring radiocarbon from archaeological samples by laboratories at the start of the 21st century.

Research paper thumbnail of New Scientific Dating of the Later Bronze Age Wells at Swalecliffe, Kent

The Antiquaries Journal, 2004

The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquar... more The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquaries Journal. The site comprised seventeen wells cut into the base of a previously reduced hollow. Groundwater could thus have been more readily accessed within the subsequently cut well pits. The depth of the base of the wells, at up to 2.5m below ground level, and their consequent waterlogged nature, allowed exceptional preservation of wooden linings and plank steps. Application of dendrochronological and radiocarbon dating suggested that the individual wells were used in sequence over a period of around 500 years, from an origin probably in the late thirteenth century BC to abandonment probably within the seventh century BC. The earlier phases (1–4) were dated mainly by dendrochronology, a 348-year sequence known as SWALECLF 1, whilst the later phases (5–7) were dated by a series of five radiocarbon dates.

Research paper thumbnail of Excavations on the Lower Terrace, Site C, Tintagel Island 1990–94

The Antiquaries Journal, 1997

This article reports excavations undertaken between 1990 and 1994 on a small cliff terrace, at Ti... more This article reports excavations undertaken between 1990 and 1994 on a small cliff terrace, at Tintagel Island in Cornwall. This terrace (the Lower Terrace) lies below Site C (the Middle Terrace), where a building was excavated by Dr C.A.R. Radford in the 1930s. The remains uncovered on the Lower Terrace comprise several phases of ephemeral stone and turf structures with associated hearths, floor deposits and stakeholes. These are separated by periods of shillet (tiny flakes of slate in sandy clay soil) levelling. With the collapse of the last structure the terrace was buried by layers of scree and slate slip from the slope above. Artefact groups of fire-lighting stones, whetstones and worked flint and quartz were recovered predominantly from earlier phases, together with Romano-British Native pottery. Later phases mainly comprised sherds of Imported Mediterranean pottery (84 per cent of all finds) and slate disc pot lids. The results of an extensive programme of environmental sampl...

Research paper thumbnail of Thermospheric neutral wind signatures dependent on the east-west component of the interplanetary magnetic field for Northern and Southern Hemispheres as measured from Dynamics Explorer-2

ABSTRACT DE-2 neutral-wind measurements obtained between November and January 1981-1982 and 1982-... more ABSTRACT DE-2 neutral-wind measurements obtained between November and January 1981-1982 and 1982-1983 were analyzed to investigate the effect of the sign of the IMF By component on neutral thermosphere dynamics at F-region altitudes. Maps of the mean neutral circulation for the northern (winter) and southern (summer) polar regions were derived for By positive and negative using polar geomagnetic coordinates. The mean neutral winds demonstrate clear By-dependent neutral wind signatures in both hemispheres.

Research paper thumbnail of Extended Radiocarbon Calibration in the Anglo-Saxon Period, AD 395-485 and AD 735-805

Radiocarbon

Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon... more Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon archaeology. Primarily, this is because the uncertainty of calibrated dates provides little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology in conjunction with high-precision 14 C dating have, however, created the possibility of both testing and refining the established Anglo-Saxon chronologies based on typology of artifacts. The calibration process within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have previously reported decadal measurements on a section of the Irish oak chronology for the period AD 495-725 (McCormac et al. 2004). In this paper, we present decadal measurements for the periods AD 395-485 and AD 735-805, which extends the original calibration set.

Research paper thumbnail of INTCAL98 radiocarbon age calibration, 24,000-0 cal BP

The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the in... more The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to 14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the A14C values of INTCAL98.

Research paper thumbnail of Interhemispheric Variation in the Response to Solar Forcing Over the Past 1000 Years

ABSTRACT The difference in atmospheric 14C levels in the Northern and Southern Hemispheres (NS of... more ABSTRACT The difference in atmospheric 14C levels in the Northern and Southern Hemispheres (NS offset) has recently been shown to vary between 1 and 10 % over the last millennium (1, 2). More than 80 % of the variation is explained by three quasi-periodic cycles with ca. 200, 130, and 80-year periods. The 205-year de Vries cycle in atmospheric 14C levels can confidently be ascribed to a solar origin based on comparisons to cosmogenic isotope records, (3, 4). Additionally, a significant 130-year cycle is found in the 10Be ice core record of the South Pole. Observing these cycles in the NS offset requires either variable input of 14C into the troposphere in each hemisphere or a differential response of the carbon reservoirs to solar variations. The amplitude of the de Vries cycle increases throughout the past millennium in the individual records of Northern and Southern Hemisphere tree-ring 14C. The Southern Hemisphere amplitudes are smaller until ca. AD 1500 when the amplitudes in both hemispheres are roughly the same. This interhemispheric difference in amplitudes results in pseudo-cyclic behavior in the NS offset that disappears after AD 1400. Because the de Vries cycle in the South Pole 10Be record has nearly constant amplitude during this same time period, the increase in the amplitude in the atmospheric 14C records must include a climatic component possibly related to millennial-scale ocean circulation changes. 1. A. G. Hogg et al., Radiocarbon (submitted). 2. F. G. McCormac et al., Radiocarbon (submitted). 3. E. Bard, G. M. Raisbeck, F. Yiou, J. Jouzel, EPSL 150:453-462 (1997). 4. G. Wagner et al., GRL 28:303-306 (2001).

Research paper thumbnail of IntCal04: A New Consensus Radiocarbon Calibration Dataset from 0-26 ka BP

Abstract Because atmosphere 14C levels have not been constant through time, it is necessary to ca... more Abstract Because atmosphere 14C levels have not been constant through time, it is necessary to calibrate radiocarbon dates with known age radiocarbon datasets in order to compare paleorecords based on 14C ages and those based on other timescales. The ...

Research paper thumbnail of A 30,000-Year Pollen and Radiocarbon Record from Highland Sumatra as Evidence for Climatic Change

Radiocarbon

We examine the pollen analytical and14C sequences from two Sumatra highland sites, Pea Bullok (2°... more We examine the pollen analytical and14C sequences from two Sumatra highland sites, Pea Bullok (2°15'N,…

Research paper thumbnail of Radiocarbon to Calendar Date Conversion: Calendrical Band Widths as a Function of Radiocarbon Precision

Radiocarbon

Accurate high-precision14C dating (i.e.,± 20 yr precision or less on the14C date) provides the na... more Accurate high-precision14C dating (i.e.,± 20 yr precision or less on the14C date) provides the narrowest calendrical band width and, hence, the best age range determination possible. However, because of the structure in the14C calibration curve, the calendar age range for a given14C precision is not constant throughout the calibration range. In this study, we quantify the calendar band widths for a range of14C precisions throughout the calibration range. We show that an estimate of the likely calendar band width in years can be obtained from the expression: Band width (yr) = 2.12 x14C precision (1 σ) + 54.6. We also show that calendar band widths are widest around 4000 BP at the start of the Bronze Age, and become narrow through the later Bronze Age and Iron Age and back into the Neolithic.

Research paper thumbnail of Precise dating of the Norfolk timber circle

Nature

, the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was disc... more , the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was discovered within the intertidal zone at Holme-nextthe-Sea, Norfolk (52.58°N, 00.33°E). The circle, the first surviving example discovered in Britain, was in serious danger of destruction by tidal erosion, so it was imperative that detailed archaeological investigations be undertaken, including dating. Information provided by tree-ring analysis and radiocarbon measurements was combined using a bayesian approach 1 , resulting in a precise absolute dating for the structure. The timber circle (Fig. 1) was dated by taking six samples (four from the ring of posts and duplicate samples from the central tree) for dendrochronological analysis 2. The ring sequence from the central stump and the four ring sequences from the posts crossmatched and were combined to form a 168-year site chronology. This tree-ring sequence was compared with a series of reference chronologies. The highest, but statistically non-significant, correlation was against the East Anglia chronology 3 (tǃ3.98; higher t-values are more significant 4), giving an end date for the site chronology of 2050 BC. It also produced lower correlations against East Anglia ending at 2454 BC (tǃ3.17) and 2019 BC (tǃ3.14). Running the ring pattern against the Irish master 5 gave correlations of tǃ3.39 at 2050 BC, but only tǃ0.96 at 2454 BC and tǃ1.7 at 2019 BC. Thus, although not statistically significant, dendrochronology suggested that 2050 BC is the most likely end date for the site chronology. However, although the consistency of the t-values was encouraging, the correlation values were too low for definitive dating.

Research paper thumbnail of New Scientific Dating of the Later Bronze Age Wells at Swalecliffe, Kent

The Antiquaries Journal, Aug 31, 2004

The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquar... more The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquaries Journal. The site comprised seventeen wells cut into the base of a previously reduced hollow. Groundwater could thus have been more readily accessed within the subsequently cut well pits. The depth of the base of the wells, at up to 2.5m below ground level, and their consequent waterlogged nature, allowed exceptional preservation of wooden linings and plank steps. Application of dendrochronological and radiocarbon dating suggested that the individual wells were used in sequence over a period of around 500 years, from an origin probably in the late thirteenth century BC to abandonment probably within the seventh century BC. The earlier phases (1–4) were dated mainly by dendrochronology, a 348-year sequence known as SWALECLF 1, whilst the later phases (5–7) were dated by a series of five radiocarbon dates.

Research paper thumbnail of High-precision 14C measurements of contemporaneous tree-ring dated wood from the British Isles and New Zealand: AD 1850 to 950

Radiocarbon

The University of Waikato, Hamilton, New Zealand and The Queen's University of Belfast, North... more The University of Waikato, Hamilton, New Zealand and The Queen's University of Belfast, Northern Ireland radiocarbon dating laboratories have undertaken a series of high-precision measurements on decadal samples of dendrochronologically dated oak (Quercus petraea) from Great Britain and cedar (Libocedrus bidwillii) and silver pine (Lagarostrobos colensoi) from New Zealand. The results show an average hemispheric offset over the 900 yr of measurement of 40 ± 13 yr. This value is not constant but varies with a periodicity of about 130 yr. The Northern Hemisphere measurements confirm the validity of the Pearson et al. (1986) calibration dataset.

Research paper thumbnail of Radiocarbon Calibration of the Anglo-Saxon Period: AD 495-725

Radiocarbon

Radiocarbon dating has been rarely used for chronological problems relating to the Anglo-Saxon pe... more Radiocarbon dating has been rarely used for chronological problems relating to the Anglo-Saxon period. The "flatness" of the calibration curve and the resultant wide range in calendrical dates provide little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology have, however, created the possibility of refining and checking the established chronologies, based on typology of artifacts, against 14C dates. The calibration process, within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have there- fore re-measured, at decadal intervals, a section of the Irish oak chronology for the period AD 495-725. These measurements have been included in IntCal04.

Research paper thumbnail of The Norfolk Bronze Age Timber Circle

Nature

, the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was disc... more , the site of a subcircular ring of 55 oak timbers surrounding a large inverted oak tree was discovered within the intertidal zone at Holme-nextthe-Sea, Norfolk (52.58°N, 00.33°E). The circle, the first surviving example discovered in Britain, was in serious danger of destruction by tidal erosion, so it was imperative that detailed archaeological investigations be undertaken, including dating. Information provided by tree-ring analysis and radiocarbon measurements was combined using a bayesian approach 1 , resulting in a precise absolute dating for the structure. The timber circle (Fig. 1) was dated by taking six samples (four from the ring of posts and duplicate samples from the central tree) for dendrochronological analysis 2. The ring sequence from the central stump and the four ring sequences from the posts crossmatched and were combined to form a 168-year site chronology. This tree-ring sequence was compared with a series of reference chronologies. The highest, but statistically non-significant, correlation was against the East Anglia chronology 3 (tǃ3.98; higher t-values are more significant 4), giving an end date for the site chronology of 2050 BC. It also produced lower correlations against East Anglia ending at 2454 BC (tǃ3.17) and 2019 BC (tǃ3.14). Running the ring pattern against the Irish master 5 gave correlations of tǃ3.39 at 2050 BC, but only tǃ0.96 at 2454 BC and tǃ1.7 at 2019 BC. Thus, although not statistically significant, dendrochronology suggested that 2050 BC is the most likely end date for the site chronology. However, although the consistency of the t-values was encouraging, the correlation values were too low for definitive dating.

Research paper thumbnail of Liquid Scintillation Counter Characterisation, Optimisation and Benzene Purity Correction

Radiocarbon

In liquid scintillation counting (LSC), small variations in benzene purity can cause 14C pulse-he... more In liquid scintillation counting (LSC), small variations in benzene purity can cause 14C pulse-height spectra to move with respect to the counting window. Thus, one must carefully monitor the purity of each benzene sample and apply corrections for spectral shifts. I describe here the techniques used at Queen's University Belfast for deriving correction factors for observed small variations in benzene purity. I also describe the methods used at our laboratory to fine-tune our Quantulus LS counters for high-precision dating. The tuning of the instruments minimizes the effect of fluctuations in gain that may occur during the long counting periods required for high-precision dating. Any remaining influences on efficiency owing to gain changes are corrected for, along with the purity correction, by continuous monitoring of the spectrum produced by the external source.

Research paper thumbnail of Experimental Confirmation of a high-resolution double-etalon modulator (DEM)

Research paper thumbnail of Dating Stonehenge

Research paper thumbnail of The influence of IMF B sub y on the high-latitude thermospheric circulation during northward IMF

Journal of Geophysical Research Atmospheres

Thermospheric neutral wind data, obtained by the Fabry-Perot Interferometer and Wind and Temperat... more Thermospheric neutral wind data, obtained by the Fabry-Perot Interferometer and Wind and Temperature Spectrometer on the Dynamics Explorer 2 satellite during periods of northward interplanetary magnetic field (IMF B{sub z} positive), show a dependence of the circulation on the magnitude and sign of the east-west component (B{sub y}) of the IMF. Averaged thermospheric neutral wind vector fields, for the northern hemisphere, and data from several sets of satellite orbits, that illustrate the variation in the neutral wind structure as a function of time and IMF orientation, are presented and discussed. The results show that near December solstice, at solar maximum: (1) sunward neutral winds develop inside the geomagnetic polar cap during periods of persistent positive B{sub z} and relatively low B{sub y}; (2) typical time delays in the establishment of sunward winds following a northward turning of the IMF are approximately 4 hours; (3) sunward winds are not observed when the magnitude...

Research paper thumbnail of The generation of vertical thermospheric winds and gravity waves at auroral latitudes—I. Observations of vertical winds

Planetary and Space Science, 1984

... 30 (1968), p. 1505. Abstract | PDF (1007 K) | View Record in Scopus | Cited By in Scopus (0).... more ... 30 (1968), p. 1505. Abstract | PDF (1007 K) | View Record in Scopus | Cited By in Scopus (0). PB Hays, TL Killeen, NW Spencer, LE Wharton, RG Roble, TJ Fuller-Rowell and D. Rees, Observations of the dynamics of the polar thermosphere, J. geophys. Res. (1983) (in press).. ...

Research paper thumbnail of An illustrated guide to measuring radiocarbon from archaeological samples

Physics Education, 2004

Radiocarbon dating has been central to the construction of archaeological chronologies for over 5... more Radiocarbon dating has been central to the construction of archaeological chronologies for over 50 years. The archaeological, scientific and (increasingly) statistical methods for interpreting radiocarbon measurements to produce these chronologies have become ever more sophisticated. The accurate measurement of the radiocarbon content of an archaeological sample is, and always has been, fundamental to any interpretation. This article provides an overview of the different approaches adopted for measuring radiocarbon from archaeological samples by laboratories at the start of the 21st century.

Research paper thumbnail of New Scientific Dating of the Later Bronze Age Wells at Swalecliffe, Kent

The Antiquaries Journal, 2004

The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquar... more The Swalecliffe later Bronze Age well complex was reported in detail in volume 83 of the Antiquaries Journal. The site comprised seventeen wells cut into the base of a previously reduced hollow. Groundwater could thus have been more readily accessed within the subsequently cut well pits. The depth of the base of the wells, at up to 2.5m below ground level, and their consequent waterlogged nature, allowed exceptional preservation of wooden linings and plank steps. Application of dendrochronological and radiocarbon dating suggested that the individual wells were used in sequence over a period of around 500 years, from an origin probably in the late thirteenth century BC to abandonment probably within the seventh century BC. The earlier phases (1–4) were dated mainly by dendrochronology, a 348-year sequence known as SWALECLF 1, whilst the later phases (5–7) were dated by a series of five radiocarbon dates.

Research paper thumbnail of Excavations on the Lower Terrace, Site C, Tintagel Island 1990–94

The Antiquaries Journal, 1997

This article reports excavations undertaken between 1990 and 1994 on a small cliff terrace, at Ti... more This article reports excavations undertaken between 1990 and 1994 on a small cliff terrace, at Tintagel Island in Cornwall. This terrace (the Lower Terrace) lies below Site C (the Middle Terrace), where a building was excavated by Dr C.A.R. Radford in the 1930s. The remains uncovered on the Lower Terrace comprise several phases of ephemeral stone and turf structures with associated hearths, floor deposits and stakeholes. These are separated by periods of shillet (tiny flakes of slate in sandy clay soil) levelling. With the collapse of the last structure the terrace was buried by layers of scree and slate slip from the slope above. Artefact groups of fire-lighting stones, whetstones and worked flint and quartz were recovered predominantly from earlier phases, together with Romano-British Native pottery. Later phases mainly comprised sherds of Imported Mediterranean pottery (84 per cent of all finds) and slate disc pot lids. The results of an extensive programme of environmental sampl...

Research paper thumbnail of Thermospheric neutral wind signatures dependent on the east-west component of the interplanetary magnetic field for Northern and Southern Hemispheres as measured from Dynamics Explorer-2

ABSTRACT DE-2 neutral-wind measurements obtained between November and January 1981-1982 and 1982-... more ABSTRACT DE-2 neutral-wind measurements obtained between November and January 1981-1982 and 1982-1983 were analyzed to investigate the effect of the sign of the IMF By component on neutral thermosphere dynamics at F-region altitudes. Maps of the mean neutral circulation for the northern (winter) and southern (summer) polar regions were derived for By positive and negative using polar geomagnetic coordinates. The mean neutral winds demonstrate clear By-dependent neutral wind signatures in both hemispheres.

Research paper thumbnail of Extended Radiocarbon Calibration in the Anglo-Saxon Period, AD 395-485 and AD 735-805

Radiocarbon

Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon... more Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon archaeology. Primarily, this is because the uncertainty of calibrated dates provides little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology in conjunction with high-precision 14 C dating have, however, created the possibility of both testing and refining the established Anglo-Saxon chronologies based on typology of artifacts. The calibration process within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have previously reported decadal measurements on a section of the Irish oak chronology for the period AD 495-725 (McCormac et al. 2004). In this paper, we present decadal measurements for the periods AD 395-485 and AD 735-805, which extends the original calibration set.

Research paper thumbnail of INTCAL98 radiocarbon age calibration, 24,000-0 cal BP

The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the in... more The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to 14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the A14C values of INTCAL98.

Research paper thumbnail of Interhemispheric Variation in the Response to Solar Forcing Over the Past 1000 Years

ABSTRACT The difference in atmospheric 14C levels in the Northern and Southern Hemispheres (NS of... more ABSTRACT The difference in atmospheric 14C levels in the Northern and Southern Hemispheres (NS offset) has recently been shown to vary between 1 and 10 % over the last millennium (1, 2). More than 80 % of the variation is explained by three quasi-periodic cycles with ca. 200, 130, and 80-year periods. The 205-year de Vries cycle in atmospheric 14C levels can confidently be ascribed to a solar origin based on comparisons to cosmogenic isotope records, (3, 4). Additionally, a significant 130-year cycle is found in the 10Be ice core record of the South Pole. Observing these cycles in the NS offset requires either variable input of 14C into the troposphere in each hemisphere or a differential response of the carbon reservoirs to solar variations. The amplitude of the de Vries cycle increases throughout the past millennium in the individual records of Northern and Southern Hemisphere tree-ring 14C. The Southern Hemisphere amplitudes are smaller until ca. AD 1500 when the amplitudes in both hemispheres are roughly the same. This interhemispheric difference in amplitudes results in pseudo-cyclic behavior in the NS offset that disappears after AD 1400. Because the de Vries cycle in the South Pole 10Be record has nearly constant amplitude during this same time period, the increase in the amplitude in the atmospheric 14C records must include a climatic component possibly related to millennial-scale ocean circulation changes. 1. A. G. Hogg et al., Radiocarbon (submitted). 2. F. G. McCormac et al., Radiocarbon (submitted). 3. E. Bard, G. M. Raisbeck, F. Yiou, J. Jouzel, EPSL 150:453-462 (1997). 4. G. Wagner et al., GRL 28:303-306 (2001).