Here we present a new method for obtaining radiocarbon dates for the organic compounds intrinsic ... more Here we present a new method for obtaining radiocarbon dates for the organic compounds intrinsic to diatom frustules. This method will improve age models for sediment cores that lack calcium carbonate and improve current interpretations of diatombased paleoproxies. In preparation for radiocarbon dating by Accelerator Mass Spectrometry, compounds intrinsic to diatom frustules are released from their opal matrix by dissolution in HF and then purified using preparative liquid chromatography-mass spectrometry (LC-MS). The method was applied to one sample from each of three cores (NBP9802 Station 7 GC2; TN057-13 PC4; Ell-2) and a plankton tow (CRS 746, FOODBANCS) collected in the Southern Ocean. In each sample, radiocarbon ages of diatom-bound organic compounds differed from those obtained from foraminiferal CaCO 3. Agreement between the foraminifera and compound-specific date was best in cores E11-2 and TN057-13. In contrast, compound-specific 14 C ages obtained from NBP9802 differed substantially from those measured for foraminiferal CaCO 3. The influence of background contamination was assessed throughout all stages of the method and cannot be responsible for the discrepancy observed. Possible reasons for the disagreement between the ages of foraminifera and diatom-bound compounds are discussed in the context of sediment dynamics. These preliminary results suggest that our diatom-based dating method represents a major step forward in our ability interpret sediment records in the Southern Ocean and therefore our understanding of the role of the Southern Ocean in past climate.
Radiocarbon has been an important constituent of radioactive wastes dumped in the open ocean and ... more Radiocarbon has been an important constituent of radioactive wastes dumped in the open ocean and marginal seas as well as wastes released from nuclear reprocessing plants. Therefore, in some regions these sources could have a greater impact on 14C concentration in seawater than global fallout. The high analytical sensitivity of 14C measurement by accelerator mass spectrometry (AMS) allows even tracer amounts of 14C to be found in seawater at radioactive waste dumping sites and their comparison with the global distribution of this radionuclide. Data on measurements of 14C in samples taken at former dumping sites in the northeast Atlantic and northwest Pacific Oceans and in the open ocean are discussed and compared with other anthropogenic radionuclides, namely 3H. Small increases in 14C concentrations observed in some bottom and surface seawater samples collected at the Northwest Pacific Ocean dumping sites require further 14C analyses before final conclusions can be made on possible...
Technological and theoretical advancements in modern radiocarbon chronology make the precise dati... more Technological and theoretical advancements in modern radiocarbon chronology make the precise dating of archaeological and geological events possible. Here, we show examples of how these state-of-the-art methods can be used to establish and refine the archaeological cultural chronology for the Shangluo area in the Qinling Mountains of central China. In this study, the Donglongshan and Zijing sites were dated using the high-precision accelerator mass spectrometry (AMS) 14C method. Also, detailed magnetic-susceptibility measurements were conducted at both sites to gain preliminary information about past climate changes. The 14C dates, after being treated with Bayesian statistics, provide a firm constraint on the archaeological chronological framework for this area. Within this framework, the Malan loess-Holocene soil transition can be placed at 10,400–10,090 BC, while the duration of the Yangshao and Longshan cultures was dated to ∼4200–2900 and ∼2900–2100 BC, respectively, revealing a...
Stratigraphic investigations together with climatic proxy data measurements and reliable radiocar... more Stratigraphic investigations together with climatic proxy data measurements and reliable radiocarbon dating show a history of fluctuations of dry and wet environmental conditions in the arid to semi-arid zone of northern China since the late Pleistocene. Based on these data, we are able to reconstruct shifts of the desert margin in two period extremes, the last glacial maximum (21–15 ka) and the Holocene Optimum (9–5 ka). We have compared the present desert margin with that for the two extremes. The results indicate that a southward shift of the present margin of about 3 degrees in latitude might be caused by anthropogenic impact. Hence the influence of human activity must be taken into consideration for sustainable development and environment protection. Future research will be to find a two-way feedback existing between climate and anthropogenic impacts.
We tested the feasibility of dating freshwater and terrestrial molluscs from the semiarid and ari... more We tested the feasibility of dating freshwater and terrestrial molluscs from the semiarid and arid zone in China, since these types of shell material deposit only aragonite to form their shell structure, and shell integrity can be easily observed using X-ray diffraction. We also tested the possibility of estimating microenvironmental changes from shell δ13C values, but variations within shell populations preclude the use of these values as a reliable indicator. Reservoir ages were calculated for living shells of the same species as fossil shells by using their measured 14C ages, which were recalculated using an average value of atmospheric 14C activity for the years spanning their time of collection as the modern standard. The results indicate that freshwater and terrestrial shells are potentially useful as dating material, provided extreme care is taken in their collection and other datable material (in this case wood and pollen) is within the profile to act as a comparison.
Nearly a decade ago, a different chronology than the conventional absolute chronology for the ear... more Nearly a decade ago, a different chronology than the conventional absolute chronology for the early Iron Age in Israel was suggested. The new, lower chronology “transfers” Iron Age I and Iron Age IIA contexts in Israel, traditionally dated to the 11th and 10th centuries BCE, to the 10th and 9th centuries, respectively. Thus, it places the Iron I|IIA transition at about 920–900 BCE. This alternative chronology carries important implications for Israelite history, historiography, and Bible research, as well as for the chronologies of other regions around the Mediterranean. Relevant radiocarbon data sets published to date, which were measured at different sites by different laboratories, were claimed to be incompatible. Therefore, the question of agreement between laboratories and dating methods needs to be addressed at the outset of any study attempting to resolve such a tight chronological dilemma. This paper addresses results pertaining to this issue as part of a comprehensive attem...
A method has been developed at the Arizona AMS facility for production of graphite directly from ... more A method has been developed at the Arizona AMS facility for production of graphite directly from CO2by catalytic reduction of CO/H2mixtures. The method is a modification of procedures discussed by Vogelet al(1984). Currents of12C−from these targets vary considerably, but have a median value which is 70% of that achieved from spectroscopic graphite. Precisions of ±60 to 100 yr are routinely achieved for14C ages of 5000-yr-old samples containing one milligram of carbon. The yield of14C from “blank” targets is 0.6 ± 0.1% of that from modern material.
Radiocarbon dating at the Arizona accelerator facility has improved substantially in the last thr... more Radiocarbon dating at the Arizona accelerator facility has improved substantially in the last three years. Since starting to use graphite targets (see Jull et al, 1986), we have been able to obtain routinely a precision of ca ± 1% (ca 80 yr) for relatively modern material. Our routine technique of tuning and operating the tandem accelerator mass spectrometer (TAMS) and our method of calculating 14C results are discussed in detail. Data on activity ratios of oxalic acid-II/oxalic-I are presented. Examples of the wide variety of projects on which we have collaborated are given. Brief discussions of three such projects are presented for our colleagues who were unable to attend this conference: an Arizona Indian archaeologic project, a study of megafaunal extinctions, and a study of the growth of phosphorite nodules on the sea floor off the Peruvian coast.
Vegetable remains are a rarity in Palueolithic contexts. These new determinations on material fro... more Vegetable remains are a rarity in Palueolithic contexts. These new determinations on material from southern Egypt establish securely the date of an intensive grass-tuber and fish economy in the Nile Valley towards 20,000 years ago.
The desert/loess transition zone in northern China is sensitive to climate variability, which is ... more The desert/loess transition zone in northern China is sensitive to climate variability, which is controlled mainly by the relative strengths of the East Asian summer and winter monsoons. Sandy loess layers found in the Loess Plateau and palaeosol sequences found in the sandy desert demonstrate latitudinal shifts of the southern desert margin over the last 20000 years. Stratigraphic investigations together with radiocarbon and some thermoluminescence dating, show that during the last glacial maximum the desert margin was at its most southerly position (38°N). During the early Holocene, it moved northward about three degrees in latitude (41°N). At present, the desert margin is again close to its most southerly position (38°21 N), yet the northern boundary position of modern summer monsoon activity is placed at 41°45 N, which is close to the estimated Holocene Optimum desert margin (41°N). This situation cannot be explained from natural climate models. Hence, an external driving mechan...
ABSTRACT Depleted shergotitte NWA 7635 has an ejection age of 1 m.y. and a 2.8-k.y. terrestrial. ... more ABSTRACT Depleted shergotitte NWA 7635 has an ejection age of 1 m.y. and a 2.8-k.y. terrestrial. Lead-lead isotopes are the least radiogenic measured for martian meteorites.
Page 1. [RADIOCARBON, VOL 32, No. 1, 1990, P 84-85] DISCUSSION RECOVERY FROM TRACER CONTAMINATION... more Page 1. [RADIOCARBON, VOL 32, No. 1, 1990, P 84-85] DISCUSSION RECOVERY FROM TRACER CONTAMINATION IN AMS SAMPLE PREPARATION A J T DULL, D J DONAHUE and L J TOOLIN NSF Accelerator Facility ...
Chinguetti is a 4.5 kg mesosiderite find recovered from the Adra region of Mauretania. In this pa... more Chinguetti is a 4.5 kg mesosiderite find recovered from the Adra region of Mauretania. In this paper the authors analyse a portion of the recovered sample for cosmogenic radionuclides to determine its terrestrial age, and to determine its pre-atmospheric radius. They determined the terrestrial age of Chinguetti to be < 30 ky. They constrain the pre-atmospheric radius to 50--80 cm and the shielding depths of 15--25 cm. These data indicate that Chinguetti is a comparatively recent fall.
Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of ... more Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of the city of Rı́o Cuarto, was suggested to be proximal ejecta related to a highly oblique impact event. We have identified about 400 additional elongate features in the area that indicate an aeolian, rather than an impact, origin. We have also dated fragments of glass found at the Rı́o Cuarto depressions; the age is similar to that of glass recovered 800 kilometers to the southeast. This material may be tektite glass from an impact event around 0.48 million years ago, representing a new tektite strewn field.
Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the... more Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the Antarctic meteorite LEW 85320(H5 chondrite). Antarctic meteorites have resided on the earth for periods of 10(4) to 10(6) years, but the time needed for weathering products to form has been uncertain. Isotopic measurements of delta(13)C and delta(18)O indicate that the nesquehonite formed at near freezing temperatures by reaction of meteoritic minerals with terrestrial water and carbon dioxide. Results from carbon-14 dating suggest that, although the meteorite has been in Antarctica for at least 3.2 x 10(4) to 3.3 x 10(4) years, the nesquehonite formed after A.D.1950.
Proceedings of the National Academy of Sciences, 1986
Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni , wer... more Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni , were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis , from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.
Here we present a new method for obtaining radiocarbon dates for the organic compounds intrinsic ... more Here we present a new method for obtaining radiocarbon dates for the organic compounds intrinsic to diatom frustules. This method will improve age models for sediment cores that lack calcium carbonate and improve current interpretations of diatombased paleoproxies. In preparation for radiocarbon dating by Accelerator Mass Spectrometry, compounds intrinsic to diatom frustules are released from their opal matrix by dissolution in HF and then purified using preparative liquid chromatography-mass spectrometry (LC-MS). The method was applied to one sample from each of three cores (NBP9802 Station 7 GC2; TN057-13 PC4; Ell-2) and a plankton tow (CRS 746, FOODBANCS) collected in the Southern Ocean. In each sample, radiocarbon ages of diatom-bound organic compounds differed from those obtained from foraminiferal CaCO 3. Agreement between the foraminifera and compound-specific date was best in cores E11-2 and TN057-13. In contrast, compound-specific 14 C ages obtained from NBP9802 differed substantially from those measured for foraminiferal CaCO 3. The influence of background contamination was assessed throughout all stages of the method and cannot be responsible for the discrepancy observed. Possible reasons for the disagreement between the ages of foraminifera and diatom-bound compounds are discussed in the context of sediment dynamics. These preliminary results suggest that our diatom-based dating method represents a major step forward in our ability interpret sediment records in the Southern Ocean and therefore our understanding of the role of the Southern Ocean in past climate.
Radiocarbon has been an important constituent of radioactive wastes dumped in the open ocean and ... more Radiocarbon has been an important constituent of radioactive wastes dumped in the open ocean and marginal seas as well as wastes released from nuclear reprocessing plants. Therefore, in some regions these sources could have a greater impact on 14C concentration in seawater than global fallout. The high analytical sensitivity of 14C measurement by accelerator mass spectrometry (AMS) allows even tracer amounts of 14C to be found in seawater at radioactive waste dumping sites and their comparison with the global distribution of this radionuclide. Data on measurements of 14C in samples taken at former dumping sites in the northeast Atlantic and northwest Pacific Oceans and in the open ocean are discussed and compared with other anthropogenic radionuclides, namely 3H. Small increases in 14C concentrations observed in some bottom and surface seawater samples collected at the Northwest Pacific Ocean dumping sites require further 14C analyses before final conclusions can be made on possible...
Technological and theoretical advancements in modern radiocarbon chronology make the precise dati... more Technological and theoretical advancements in modern radiocarbon chronology make the precise dating of archaeological and geological events possible. Here, we show examples of how these state-of-the-art methods can be used to establish and refine the archaeological cultural chronology for the Shangluo area in the Qinling Mountains of central China. In this study, the Donglongshan and Zijing sites were dated using the high-precision accelerator mass spectrometry (AMS) 14C method. Also, detailed magnetic-susceptibility measurements were conducted at both sites to gain preliminary information about past climate changes. The 14C dates, after being treated with Bayesian statistics, provide a firm constraint on the archaeological chronological framework for this area. Within this framework, the Malan loess-Holocene soil transition can be placed at 10,400–10,090 BC, while the duration of the Yangshao and Longshan cultures was dated to ∼4200–2900 and ∼2900–2100 BC, respectively, revealing a...
Stratigraphic investigations together with climatic proxy data measurements and reliable radiocar... more Stratigraphic investigations together with climatic proxy data measurements and reliable radiocarbon dating show a history of fluctuations of dry and wet environmental conditions in the arid to semi-arid zone of northern China since the late Pleistocene. Based on these data, we are able to reconstruct shifts of the desert margin in two period extremes, the last glacial maximum (21–15 ka) and the Holocene Optimum (9–5 ka). We have compared the present desert margin with that for the two extremes. The results indicate that a southward shift of the present margin of about 3 degrees in latitude might be caused by anthropogenic impact. Hence the influence of human activity must be taken into consideration for sustainable development and environment protection. Future research will be to find a two-way feedback existing between climate and anthropogenic impacts.
We tested the feasibility of dating freshwater and terrestrial molluscs from the semiarid and ari... more We tested the feasibility of dating freshwater and terrestrial molluscs from the semiarid and arid zone in China, since these types of shell material deposit only aragonite to form their shell structure, and shell integrity can be easily observed using X-ray diffraction. We also tested the possibility of estimating microenvironmental changes from shell δ13C values, but variations within shell populations preclude the use of these values as a reliable indicator. Reservoir ages were calculated for living shells of the same species as fossil shells by using their measured 14C ages, which were recalculated using an average value of atmospheric 14C activity for the years spanning their time of collection as the modern standard. The results indicate that freshwater and terrestrial shells are potentially useful as dating material, provided extreme care is taken in their collection and other datable material (in this case wood and pollen) is within the profile to act as a comparison.
Nearly a decade ago, a different chronology than the conventional absolute chronology for the ear... more Nearly a decade ago, a different chronology than the conventional absolute chronology for the early Iron Age in Israel was suggested. The new, lower chronology “transfers” Iron Age I and Iron Age IIA contexts in Israel, traditionally dated to the 11th and 10th centuries BCE, to the 10th and 9th centuries, respectively. Thus, it places the Iron I|IIA transition at about 920–900 BCE. This alternative chronology carries important implications for Israelite history, historiography, and Bible research, as well as for the chronologies of other regions around the Mediterranean. Relevant radiocarbon data sets published to date, which were measured at different sites by different laboratories, were claimed to be incompatible. Therefore, the question of agreement between laboratories and dating methods needs to be addressed at the outset of any study attempting to resolve such a tight chronological dilemma. This paper addresses results pertaining to this issue as part of a comprehensive attem...
A method has been developed at the Arizona AMS facility for production of graphite directly from ... more A method has been developed at the Arizona AMS facility for production of graphite directly from CO2by catalytic reduction of CO/H2mixtures. The method is a modification of procedures discussed by Vogelet al(1984). Currents of12C−from these targets vary considerably, but have a median value which is 70% of that achieved from spectroscopic graphite. Precisions of ±60 to 100 yr are routinely achieved for14C ages of 5000-yr-old samples containing one milligram of carbon. The yield of14C from “blank” targets is 0.6 ± 0.1% of that from modern material.
Radiocarbon dating at the Arizona accelerator facility has improved substantially in the last thr... more Radiocarbon dating at the Arizona accelerator facility has improved substantially in the last three years. Since starting to use graphite targets (see Jull et al, 1986), we have been able to obtain routinely a precision of ca ± 1% (ca 80 yr) for relatively modern material. Our routine technique of tuning and operating the tandem accelerator mass spectrometer (TAMS) and our method of calculating 14C results are discussed in detail. Data on activity ratios of oxalic acid-II/oxalic-I are presented. Examples of the wide variety of projects on which we have collaborated are given. Brief discussions of three such projects are presented for our colleagues who were unable to attend this conference: an Arizona Indian archaeologic project, a study of megafaunal extinctions, and a study of the growth of phosphorite nodules on the sea floor off the Peruvian coast.
Vegetable remains are a rarity in Palueolithic contexts. These new determinations on material fro... more Vegetable remains are a rarity in Palueolithic contexts. These new determinations on material from southern Egypt establish securely the date of an intensive grass-tuber and fish economy in the Nile Valley towards 20,000 years ago.
The desert/loess transition zone in northern China is sensitive to climate variability, which is ... more The desert/loess transition zone in northern China is sensitive to climate variability, which is controlled mainly by the relative strengths of the East Asian summer and winter monsoons. Sandy loess layers found in the Loess Plateau and palaeosol sequences found in the sandy desert demonstrate latitudinal shifts of the southern desert margin over the last 20000 years. Stratigraphic investigations together with radiocarbon and some thermoluminescence dating, show that during the last glacial maximum the desert margin was at its most southerly position (38°N). During the early Holocene, it moved northward about three degrees in latitude (41°N). At present, the desert margin is again close to its most southerly position (38°21 N), yet the northern boundary position of modern summer monsoon activity is placed at 41°45 N, which is close to the estimated Holocene Optimum desert margin (41°N). This situation cannot be explained from natural climate models. Hence, an external driving mechan...
ABSTRACT Depleted shergotitte NWA 7635 has an ejection age of 1 m.y. and a 2.8-k.y. terrestrial. ... more ABSTRACT Depleted shergotitte NWA 7635 has an ejection age of 1 m.y. and a 2.8-k.y. terrestrial. Lead-lead isotopes are the least radiogenic measured for martian meteorites.
Page 1. [RADIOCARBON, VOL 32, No. 1, 1990, P 84-85] DISCUSSION RECOVERY FROM TRACER CONTAMINATION... more Page 1. [RADIOCARBON, VOL 32, No. 1, 1990, P 84-85] DISCUSSION RECOVERY FROM TRACER CONTAMINATION IN AMS SAMPLE PREPARATION A J T DULL, D J DONAHUE and L J TOOLIN NSF Accelerator Facility ...
Chinguetti is a 4.5 kg mesosiderite find recovered from the Adra region of Mauretania. In this pa... more Chinguetti is a 4.5 kg mesosiderite find recovered from the Adra region of Mauretania. In this paper the authors analyse a portion of the recovered sample for cosmogenic radionuclides to determine its terrestrial age, and to determine its pre-atmospheric radius. They determined the terrestrial age of Chinguetti to be < 30 ky. They constrain the pre-atmospheric radius to 50--80 cm and the shielding depths of 15--25 cm. These data indicate that Chinguetti is a comparatively recent fall.
Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of ... more Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of the city of Rı́o Cuarto, was suggested to be proximal ejecta related to a highly oblique impact event. We have identified about 400 additional elongate features in the area that indicate an aeolian, rather than an impact, origin. We have also dated fragments of glass found at the Rı́o Cuarto depressions; the age is similar to that of glass recovered 800 kilometers to the southeast. This material may be tektite glass from an impact event around 0.48 million years ago, representing a new tektite strewn field.
Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the... more Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the Antarctic meteorite LEW 85320(H5 chondrite). Antarctic meteorites have resided on the earth for periods of 10(4) to 10(6) years, but the time needed for weathering products to form has been uncertain. Isotopic measurements of delta(13)C and delta(18)O indicate that the nesquehonite formed at near freezing temperatures by reaction of meteoritic minerals with terrestrial water and carbon dioxide. Results from carbon-14 dating suggest that, although the meteorite has been in Antarctica for at least 3.2 x 10(4) to 3.3 x 10(4) years, the nesquehonite formed after A.D.1950.
Proceedings of the National Academy of Sciences, 1986
Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni , wer... more Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni , were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis , from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.
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Papers by Ajt Jull