Atmospheric radiocarbon calibration to 45,000 yr B.P.: late glacial fluctuations and cosmogenic isotope production

A 35 ka record of groundwater recharge in south-west Australia using stable water isotopes

The isotopic composition of groundwater can be a useful indicator of recharge conditions and may be used as an archive to infer past climate variability. Groundwater from two largely confined aquifers in south-west Australia, recharged at the northernmost extent of the westerly wind belt, can help constrain the palaeoclimate record in this region. We demonstrate that radiocarbon age measurements of dissolved inorganic carbon are appropriate for dating groundwater from the Leederville aquifer and Yarragadee aquifer within the Perth Basin. Variations in groundwater δ¹⁸O values with mean residence time were examined using regional and flow line data sets, which were compared. The trends in the regional groundwater data are consistent with the groundwater flow line data supporting the hypothesis that groundwater δ¹⁸O is a robust proxy for palaeo-recharge in the Perth Basin. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. The Southern Perth Basin groundwater isotopic record also indicates a trend towards higher volume and/or intense rainfall during the Mid- to Late Holocene. The long-term stable water isotope record provides an understanding of groundwater palaeo-recharge. Knowledge of recharge dynamics over long time scales can be used to improve current water sharing plans and future groundwater model predictions.

New electron spin resonance (ESR) ages from Geißenklösterle Cave: A chronological study of the Middle and early Upper Paleolithic layers

Geißenklösterle Cave (Germany) is one of the most important Paleolithic sites in Europe, as it is characterized by human occupation during the Middle and early Upper Paleolithic. Aurignacian layers prior to 37-38 ka cal BP feature both musical and figurative art objects that are linked to the early arrival in Europe of Homo sapiens. Middle Paleolithic layers yielded lithic artifacts attributed to Homo neanderthalensis. Since human occupation at the site is attributed to both Neanderthals and modern humans, chronology is essential to clarify the issues of Neanderthal disappearance, modern human expansion in Europe, and the origin of the Aurignacian in Western Europe. Electron spin resonance (ESR) dating was performed on fossil tooth enamel collected from the Middle Paleolithic layers, which are beyond the radiocarbon dating range, and from the nearly sterile 'transitional' geological horizon (GH) 17 and the lower Aurignacian deposits, to cross-check ESR ages with previous radiocarbon, thermoluminescence and ESR age results. The Middle Paleolithic layers were dated between 94 ± 10 ka (GH 21) and 55 ± 6 ka (GH 18) by ESR on tooth enamel. Mean ages for GH 17, at 46 ± 3 ka, and for the lower Aurignacian layers, at 37 ± 3 ka, are in agreement with previous dating results, thus supporting the reliability of ESR chronology for the base of the sequence where dating comparisons are not possible. These results suggest that Neanderthals occupied the site from Marine Isotope Stage (MIS) 5 to the second half of MIS 3 and confirm the antiquity of early Aurignacian deposits. The presence of an almost sterile layer that separates Middle and Upper Paleolithic occupations could be related to the abandonment of the site by Neanderthals, possibly during Heinrich Stadial 5 (ca. 49-47 ka), thus before the arrival of H. sapiens in the area around 42 ka cal BP. These dates for the Middle Paleolithic of the Swabian Jura represent an important contribution to the prehistory of the region, where nearly all of the excavations were conducted decades ago and prior to the development of reliable radiometric dating beyond the range of radiocarbon.

A 14C age calibration curve for the last 60 ka: the Greenland-Hulu U/Th timescale and its impact on understanding the Middle to Upper Paleolithic transition in Western Eurasia

This paper combines the data sets available today for 14C-age calibration of the last 60 ka. By stepwise synchronization of paleoclimate signatures, each of these sets of 14C-ages is compared with the U/Th-dated Chinese Hulu Cave speleothem records, which shows global paleoclimate change in high temporal resolution. By this synchronization we have established an absolute-dated Greenland-Hulu chronological framework, against which global paleoclimate data can be referenced, extending the 14C-age calibration curve back to the limits of the radiocarbon method. Based on this new, U/Th-based Greenland(Hulu) chronology, we confirm that the radiocarbon timescale underestimates calendar ages by several thousand years during most of Oxygen Isotope Stage 3. Major atmospheric 14C variations are observed for the period of the Middle to Upper Paleolithic transition, which has significant implications for dating the demise of the last Neandertals. The early part of "the transition" (with 14C ages > 35.0 ka 14C BP) coincides with the Laschamp geomagnetic excursion. This period is characterized by highly-elevated atmospheric 14C levels. The following period ca. 35.0-32.5 ka 14C BP shows a series of distinct large-scale 14C age inversions and extended plateaus. In consequence, individual archaeological 14C dates older than 35.0 ka 14C BP can be age-calibrated with relatively high precision, while individual dates in the interval 35.0-32.5 ka 14C BP are subject to large systematic age-'distortions,' and chronologies based on large data sets will show apparent age-overlaps of up to ca. 5,000 cal years. Nevertheless, the observed variations in past 14C levels are not as extreme as previously proposed ("Middle to Upper Paleolithic dating anomaly"), and the new chronological framework leaves ample room for application of radiocarbon dating in the age-range 45.0-25.0 ka 14C BP at high temporal resolution.

Single particle characterization of ultrafine and accumulation mode particles from heavy duty diesel vehicles using aerosol time-of-flight mass spectrometry

The aerodynamic size and chemical composition of individual ultrafine and accumulation mode particle emissions (Da = 50-300 nm) were characterized to determine mass spectral signatures for heavy duty diesel vehicle (HDDV) emissions that can be used for atmospheric source apportionment. As part of this study, six in-use HDDVs were operated on a chassis dynamometer using the heavy heavy-duty diesel truck (HHDDT) five-cycle driving schedule under different simulated weight loads. The exhaust emissions were passed through a dilution/residence system to simulate atmospheric dilution conditions, after which an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS) was used to sample and characterize the HDDV exhaust particles in real-time. This represents the first study where refractory species including elemental carbon and metals are characterized directly in HDDV emissions using on-line mass spectrometry. The top three particle classes observed with the UF-ATOFMS comprise 91% of the total particles sampled and show signatures indicative of a combination of elemental carbon (EC) and engine lubricating oil. In addition to the vehicle make/year, the effects of driving cycle and simulated weight load on exhaust particle size and composition were investigated.

A new radiocarbon revolution and the dispersal of modern humans in Eurasia

Radiocarbon dating has been fundamental to the study of human cultural and biological development over the past 50,000 yr. Two recent developments in the methodology of radiocarbon dating show that the speed of colonization of Europe by modern human populations was more rapid than previously believed, and that their period of coexistence with the preceding Neanderthal was shorter.

Direct dating of human fossils

The methods that can be used for the direct dating of human remains comprise of radiocarbon, U-series, electron spin resonance (ESR), and amino acid racemization (AAR). This review gives an introduction to these methods in the context of dating human bones and teeth. Recent advances in ultrafiltration techniques have expanded the dating range of radiocarbon. It now seems feasible to reliably date bones up to 55,000 years. New developments in laser ablation mass spectrometry permit the in situ analysis of U-series isotopes, thus providing a rapid and virtually non-destructive dating method back to about 300,000 years. This is of particular importance when used in conjunction with non-destructive ESR analysis. New approaches in AAR analysis may lead to a renaissance of this method. The potential and present limitations of these direct dating techniques are discussed for sites relevant to the reconstruction of modern human evolution, including Florisbad, Border Cave, Tabun, Skhul, Qafzeh, Vindija, Banyoles, and Lake Mungo.

Receptor modeling of toronto PM2.5 characterized by aerosol laser ablation mass spectrometry

Urban Toronto fine particulate matter (PM2.5) was physically and chemically characterized by online aerosol laser ablation mass spectrometry (LAMS) between January 2002 and February 2003. The mass spectra from the analysis of individual aerosol particles were classified according to chemical composition by a neural network approach called adaptive resonance theory (ART-2a). Temporal trends of the hourly analysis rate of over 120 different particles types were constructed and subjected to positive matrix factorization (PMF). This receptor modeling technique enabled the identification of nine distinct emission sources responsible for these particle types: biogenic, mixed crustal, organic nitrate, construction dust, Toronto soil/road salt, secondary salt, wood burning, intercontinental dust, and an unknown source of aluminum fluoride dust. Episodic events occurred with the wood burning, intercontinental dust, and unknown dust sources. This is the first paper reporting the application of PMF to single-particle spectral data.

Reagentless detection and classification of individual bioaerosol particles in seconds

The rapid chemical analysis of individual cells is an analytical capability that will profoundly impact many fields including bioaerosol detection for biodefense and cellular diagnostics for clinical medicine. This article describes a mass spectrometry-based analytical technique for the real-time and reagentless characterization of individual airborne cells without sample preparation. We characterize the mass spectral signature of individual Bacillus spores and demonstrate the ability to distinguish two Bacillus spore species, B. thuringiensis and B.atrophaeus, from one another very accurately and from the other biological and nonbiological background materials tested with no false positives at a sensitivity of 92%. This example demonstrates that the chemical differences between these two Bacillus spore species are consistently and easily detected within single cells in seconds.

14C Activity and Global Carbon Cycle Changes over the Past 50,000 Years

A series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed 14C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Mono Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

Radiocarbon dating the appearance of modern humans and timing of cultural innovations in Europe: new results and new challenges

New radiocarbon dates from the sites of Bockstein-Törle, Geissenklösterle, Hohle Fels, Hohlenstein-Stadel, Sirgenstein, and Vogelherd in the Swabian Jura of southwestern Germany indicate that the Aurignacian of the region spans the period from ca. 40-30ka BP. If the situation at Vogelherd, in which skeletal remains from modern humans underlie an entire Aurignacian sequence, is viewed as representative for the region, the dates from the Swabian Jura support the hypothesis that populations of modern humans entered the region by way of the "Danube Corridor." The lithic technology from the lower Aurignacian of Geissenklösterle III is fully developed, and classic Aurignacian forms are well represented. During the course of the Aurignacian, numerous assemblages rich in art works, jewelry, and musical instruments are documented. By no later than 29ka BP the Gravettian was well established in the region. These dates are consistent with the "Kulturpumpe" hypothesis that important cultural innovations of the Aurignacian and Gravettian in Swabia predate similar developments in other regions of Europe. The radiocarbon dates from Geissenklösterle corroborate observations from other non-archaeological data sets indicating large global fluctuations in the atmospheric concentrations of radiocarbon between 30 and 50ka calendar years ago. These fluctuations lead to complications in building reliable chronologies during this period and cause the "Middle Paleolithic Dating Anomaly" and the "Coexistence Effect," which tend to exaggerate the temporal overlap between Neanderthals and modern humans.

Asynchronous climate changes in the North Atlantic and Japan during the last termination

Pollen records from the annually laminated sediment sequence in Lake Suigetsu, Japan, suggest a sequence of climate changes during the Last Termination that resembles that of the North Atlantic region but with noticeable differences in timing. An interstadial interval commenced a few centuries earlier [approximately 15,000 years before the present (yr B.P.)] than the North Atlantic GI-1 (Bölling) event. Conversely, the onset of a Younger Dryas (YD)-like cold reversal (12,300 to 11,250 yr B.P.) postdated the North Atlantic GS-1 (YD) event by a few centuries. Climate in the Far East during the Last Termination reflected solar insolation changes as much as Atlantic influences.

Accelerator mass spectrometry at Arizona: geochronology of the climate record and connections with the ocean

There are many diverse uses of accelerator mass spectrometry (AMS). Carbon-14 studies at our laboratory include much research related to paleoclimate, both with 14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments and many terrestrial records. Terrestrial records such as forest fires can also show the influence of oceanic oscillations, whether they are short-term such as ENSO, or on the millennial time scale. In tracer applications, we have developed the use of 129I as well as 14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson for several of these fields and hope to give some idea of the breadth of these studies.

Detection of pesticide residues on individual particles

An aerosol time-of-flight mass spectrometer (ATOFMS) is used to analyze the size and composition of individual particles containing pesticides. Pesticide residues are found in the atmosphere as a result of spray drift, volatilization, and suspension of coated soils. The ability of the ATOFMS to identify the presence of these contaminants on individual particles is assessed for particles created from pure solutions of several commonly used pesticides, as well as pesticides mixed with an organic matrix, and coated on soils. The common names of the pesticides studied are 2,4-D, atrazine, chlorpyrifos, malathion, permethrin, and propoxur. Analysis of the mass spectra produced by single- and two-step laser desorption/ionization of pesticide-containing particles allows for identification of peaks that can be used for detection of pesticide residues in the ambient aerosol. The identified marker peaks are used to approximate detection limits for the pesticides applied to soils, which are on the order of a fraction of a monolayer for individual particles. Results suggest that this technique may be useful for studying the real-time partitioning and distribution of pesticides in the atmosphere immediately following application in agricultural regions.

Quantitative time-resolved monitoring of nitrate formation in sea salt particles using a CCSEM/EDX single particle analysis

Progress of the nitrate formation in individual sea salt particles was detected as a function of time using aerosol samples collected during the TexAQS 2080 experiment We demonstrate that the time-resolved collection approach coupled with the automated EDX single particle analysis made it possible to follow in detail the time evolution of sea salt particles within a diverse aerosol mixture. Using a custom built Time-Resolved Aerosol Collector (TRAC), particulate samples were taken sequentially on grid-supported 50 nm carbon films with a time resolution of 10 min between two consecutive samples. The samples were analyzed in the laboratory using Computer Controlled Scanning Electron Microscopy with Energy-Dispersed analysis of X-rays (CCSEM/EDX). Between midnight of 08/16/00 and the early morning of 08/17/00, a steady, particularly sea salt rich aerosol was observed at the measurement site, which later showed the effects of atmospheric processing. During the night of 08/17/00 the sea salt particles were almost unprocessed, having elemental composition close to that of seawater. By 12 noon, the evolving atmosphere was able to completely convert them, predominantly to sodium nitrate particles. During the next night this process had nearly stopped and fairly virgin sea salt particles appeared again.

A field-based approach for deterimining ATOFMS instrument sensitities to ammonium and nitrate

Aerosol time-of-flight mass spectrometry (ATOFMS) instruments measure the size and chemical composition of individual particles in real-time. ATOFMS chemical composition measurements are difficult to quantify, largely because the instrument sensitivities to different chemical species in mixed ambient aerosols are unknown. In this paper, we develop a field-based approach for determining ATOFMS instrument sensitivities to ammonium and nitrate in size-segregated atmospheric aerosols, using tandem ATOFMS-impactor sampling. ATOFMS measurements are compared with collocated impactor measurements taken at Riverside, CA, in September 1996, August 1997, and October 1997. This is the first comparison of ion signal intensities from a single-particle instrument with quantitative measurements of atmospheric aerosol chemical composition. The comparison reveals that ATOFMS instrument sensitvities to both NH4+ and NO3- decline with increasing particle aerodynamic diameter over a 0.32-1.8 microm calibration range. The stability of this particle size dependence is tested overthe broad range of fine particle concentrations (PM1.8) = 17.6 +/- 2.0-127.8 +/- 1.8 microg m(-3)), ambient temperatures (23-35 degrees C), and relative humidity conditions (21-69%), encountered during the field experiments. This paper describes a potentially generalizable methodology for increasing the temporal and size resolution of atmospheric aerosol chemical composition measurements, using tandem ATOFMS-impactor sampling.

Single-particle characterization of urban aerosol particles collected in three Korean cites using low-Z electron probe X-ray microanalysis

A recently developed single-particle analytical technique, called low-Z electron probe X-ray microanalysis (low-Z EPMA), was applied to characterize urban aerosol particles collected in three cities of Korea (Seoul, CheongJu, and ChunCheon) on single days in the winter of 1999. In this study, it is clearly demonstrated that the low-Z EPMA technique can provide detailed and quantitative information on the chemical composition of particles in the urban atmosphere. The collected aerosol particles were analyzed and classified on the basis of their chemical species. Various types of particles were identified, such as soil-derived, carbonaceous, marine-originated, and anthropogenic particles. In the sample collected in Seoul, carbonaceous, aluminosilicates, silicon dioxide, and calcium carbonate aerosol particles were abundantly encountered. In the CheongJu and ChunCheon samples, carbonaceous, aluminosilicates, reacted sea salts, and ammonium sulfate aerosol particles were often seen. However, in the CheongJu sample, ammonium sulfate particles were the most abundant in the fine fraction. Also, calcium sulfate and nitrate particles were significantly observed. In the ChunCheon sample, organic particles were the most abundant in the fine fraction. Also, sodium nitrate particles were seen at high levels. The ChunCheon sample seemed to be strongly influenced by sea-salt aerosols originating from the Yellow Sea, which is located about 115 km away from the city.

Links between climate and sea levels for the past three million years

The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth -- the ice sheets and the oceans. Since the latest of these oscillations, the Last Glacial Maximum (between about 30,000 and 19,000 years ago), approximately 50 million cubic kilometres of ice has melted from the land-based ice sheets, raising global sea level by approximately 130 metres. Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere, oceans, ice sheets and solid earth, all of which have different response timescales. The trigger for the sea-level fluctuations most probably lies with changes in insolation, caused by astronomical forcing, but internal feedback cycles complicate the simple model of causes and effects.

Chronometric dating in archaeology: a review

Most archaeological dating methods are based on decay of a naturally occurring radioisotope. (14)C activity of fossil bones and charcoal decreases with age, but must be calibrated for past changes in atmospheric activity. Uranium absorbed by shells and stalagmites is used to date on a 10(5)-year scale by observing the decay of (234)U to (230) Th. Thermoluminescence, optical luminescence, and electron spin resonance detect trapped electronic charges generated by natural radioactivity in burned flint, beach sands, shells, and tooth enamel. Rate of racemization of amino acids in fossil shells is constant at constant T, and age can be tracked from an increase in the D/L ratio.

Effects of meteorological conditions on aerosol composition and mixing state in Bakersfield, CA

Particle and meteorological instrumentation were used to characterize ambient atmospheric conditions, aerosol size distributions, aerosol mass concentrations, and single particle size and chemical composition in Bakersfield, CA for the period January 9, 1999 through January 28, 1999. The sampling period included four distinct meteorological periods of stagnation, clearing, haze, and rain. Particle number and mass concentrations were the highest during the stagnation episode when a heavy and extensive fog developed. Mass and number concentrations also approached these high levels during the haze period. Single particle size and composition data from an aerosol time-of-flight mass spectrometer (ATOFMS) are used to provide unique continuous information on the diversity in types of particles present, the effects of meteorology on particle size and composition, and the distribution of important chemical species within individual particles. Aerosol composition and mixing state are found to vary with meteorological conditions. Single particle data show that carbonaceous aerosol with secondary ammonium, nitrate, and sulfate dominate the aerosol concentration during a stagnation period with a dramatic composition shift occurring to sodium type particles during the haze period. The aerosol is internally mixed with respect to carbon, nitrate, sulfate, and ammonium during the stagnation period. The mixing state changes significantly over the haze period when much greater diversity in the associations of chemical species within individual particles occurs.

Measurement of individual particle atomic composition by aerosol mass spectrometry

Advances in instrumentation used for particle compositional analysis have enabled real-time identification and classification of individual particles. However, precise quantitation of individual particle compositions has been elusive. Here, we demonstrate that real-time quantitative single-particle compositional analysis is possible. This is illustrated for individual particles of sodium chloride (70 nm), ammonium sulfate (70 nm), and silica (40-2000 nm) using a real-time aerosol mass spectrometer. Atomic fractions for major components (> 1% concentration) of individual multicomponent particles have been measured within +/-20% accuracy. Trace element detection limits of 20 ppm are also demonstrated when individual particle compositions are ensemble averaged.

Single-particle analysis of aerosols at Cheju Island, Korea, using low-Z electron probe X-ray microanalysis: a direct proof of nitrate formation from sea salts

A recently developed electron probe X-ray microanalysis (EPMA), called low-Z EPMA, employing an ultrathin window energy-dispersive X-ray detector, was applied to characterize aerosol particles collected at two sampling sites, namely, Kosan and 1100 Hill of Cheju Island, Korea, on a summer day in 1999. Since low-Z EPMA can provide quantitative information on the chemical composition of aerosol particles, the collected aerosol particles were classified and analyzed based on their chemical species. Many different particle types were identified, such as marine-originated, carbonaceous, soil-derived, and anthropogenic particles. Marine-originated particles, such as NaNO3- and Na2SO4-containing particles, are very frequently encountered in the two samples. In this study, it was directly proven that the observed nitrate particles were from sea salts. In addition, two types of nitrate particles from sea salts were observed, with and without Mg. The sodium nitrate particles without Mg were believed to be collected as crystalline form, either with the sodium nitrate particles being fractionally recrystallized within evaporating seawater drops or with recrystallized sodium chloride particles having reacted with gaseous nitrogen species in the air to form the crystalline sodium nitrate particles. The other seemed to be collected as seawater drops, where the atmospheric reaction had occurred in the droplets, and thus sodium as well as magnesium nitrates were observed. Carbonaceous particles are the most abundant in the samples at both sites. From this study, it was found that about three-quarters of the carbonaceous particles in the samples were biogenic, which partially explains a previously reported observation of a large concentration of organic carbon particles as compared to elemental carbon. Various soil-derived particles were also observed. In addition to aluminosilicate- and iron oxide-containing particles, which are ubiquitous components in soil-derived particles, CaCO3-, Al2O3- and Cr-containing particles were also frequently encountered.

Heterogeneity assessment in individual CaCO3-CaSO4 particles using ultrathin window electron probe X-ray microanalysis

In our previous studies, it has been demonstrated that both the excitation interactions between electrons and the atoms of the matrix and the matrix and geometric effects of electron-induced X-ray signals can be described by Monte Carlo simulation for low-Z elements, such as carbon, nitrogen, and oxygen, in individual atmospheric microparticles. In addition, by the application of a quantification method, which employs Monte Carlo simulation combined with successive approximations, at least semi-quantitative specification of the chemical compositions could be done. This has enlarged the scope of electron probe X-ray microanalysis (EPMA) for the single particle analysis of atmospheric environmental aerosol particles. In this work, we demonstrate that the heterogeneity of individual particles, even of micrometer size, can be characterized by the application of EPMA. X-ray photons obtained with different primary electron beam energies carry information on the chemical compositions for different regions in the particles. Artificially generated heterogeneous CaCO3-CaSO4 individual particles were measured at different accelerating voltages, and it was found that the Monte Carlo calculation is a powerful technique to extract the information on the heterogeneity of the particles that is contained in the measured X-ray data. Our approach can even estimate the thickness of the surface CaSO4 species by the application of the Monte Carlo calculation. A preliminary result for carbon-coated glass particles is also presented. The complexity involved in the analysis of real world particles is briefly mentioned with a result for heterogeneous SiO2 particle.

Ornaments of the earliest Upper Paleolithic: new insights from the Levant

Two sites located on the northern Levantine coast, Uçağizli Cave (Turkey) and Ksar 'Akil (Lebanon) have yielded numerous marine shell beads in association with early Upper Paleolithic stone tools. Accelerator mass spectrometry (AMS) radiocarbon dates indicate ages between 39,000 and 41,000 radiocarbon years (roughly 41,000-43,000 calendar years) for the oldest ornament-bearing levels in Uçağizli Cave. Based on stratigraphic evidence, the earliest shell beads from Ksar 'Akil may be even older. These artifacts provide some of the earliest evidence for traditions of personal ornament manufacture by Upper Paleolithic humans in western Asia, comparable in age to similar objects from Eastern Europe and Africa. The new data show that the initial appearance of Upper Paleolithic ornament technologies was essentially simultaneous on three continents. The early appearance and proliferation of ornament technologies appears to have been contingent on variable demographic or social conditions.

Lateglacial and Early Holocene vegetation history of the northern Wetterau and the Amöneburger Basin (Hessen), central-west Germany

The Lateglacial and Early Holocene vegetation history of the northern Wetterau and Amöneburger Basin, two intra-montane basins in Hessen, central-west Germany, is reconstructed by means of pollen and macrofossil analyses. Regional pollen assemblage zones are defined for the Lateglacial and Early Holocene. After calibration of the radiocarbon dates and establishment of age/depth relationships, the ages of the pollen zone boundaries are calculated. The regional vegetation changes correlate closely with the major fluctuations in the delta18O curve of the Greenland ice cores spanning the same time period. During the early Lateglacial, the open herbaceous vegetation with dwarf shrubs in the northern Wetterau was replaced by woodlands. Initially these woodlands consisted of birch, but after the immigration of pine, mixed forests of pine and birch developed. Soon after its immigration pine became dominant and pine woodlands largely replaced the birch forests. Only on the locally wetter substrates of the river floodplain did Betula stands persist. Gradually the importance of herbaceous communities declined and the pine woodlands lost their open character. During the Lateglacial two regressive phases in the vegetation succession are reflected in the data which are equated with the Older- and Younger Dryas biozones. At the beginning of the Younger Dryas, the forest-limit was lowered and the importance of herbaceous communities increased. Later, pine woodlands thinned and Ericales became part of the vegetation, indicating the development of more acid, nutrient-poor soils. A subdivision of the Younger Dryas biozone into a wetter, colder first part and a drier, warmer second part is suggested. At the beginning of the Early Holocene, pine woodlands became more closed and soils more stabilised. The transition between the Younger Dryas and Preboreal biozones is indicated by a lithological change to organic (-rich) deposits. Betula stands persisted on the locally wetter substrates of the fluvial plains. At the end of the early Preboreal, there was an extension of Betula stands on the river floodplains. This is interpreted as a phase in which climate was temporarily wetter, perhaps a reflection of a short-term climatic oscillation, the so-called Preboreal oscillation. During the Preboreal biozone, ferns became more important in the local vegetation of the mires, and later during the Boreal they formed the undergrowth of swamp forests. During the Boreal biozone, a major expansion of hazel took place in both areas. On the hills and slopes of the northern Wetterau and the Amöneburger Basin, open pine forests and hazel scrub developed with grasses and Pteridium in the field layer. In the river valleys, pine forests were replaced by deciduous mixed forests with oak, elm and later also with lime.

Application of the ART-2a algorithm to laser ablation aerosol mass spectrometry of particle standards

Single-particle mass spectrometers are now commonly used to analyze atmospheric particles and generate tens of thousands of spectra from typical measurement campaigns. The ART-2a spectrum algorithm has been used to classify these spectra. In this work, we generate a range of particles that are models of those that are common in the atmosphere. A single-particle mass spectrometer is used to analyze these known particles, and the spectra are classified using ART-2a. The optimum vigilance parameter is approximately 0.5 while the optimum learning rate is approximately 0.05. The classifications elucidate limitations in generation of test particles, their analysis by single-particle techniques, and their classification by ART-2a.

Source apportionment of fine particulate matter by clustering single-particle data: tests of receptor model accuracy

The source apportionment accuracy of a neural network algorithm (ART-2a) is tested on the basis of its application to synthetic single-particle data generated by a source-oriented aerosol processes trajectory model that simulates particle emission, transport, and chemical reactions in the atmosphere. ART-2a successfully groups particles from the majority of sources actually present, when given complete data on ambient particle composition at monitoring sites located near the emission sources. As particles age in the atmosphere, accumulation of gas-to-particle conversion products can act to disguise the source of the primary core of the particles. When ART-2a is applied to synthetic single-particle data that are modified to simulate the biases in aerosol time-of-flight mass spectrometry (ATOFMS) measurements, best results are obtained using the ATOFMS dual ion operating mode that simultaneously yields both positive and negative ion mass spectra. The results of this study suggest that the use of continuous single-particle measurements coupled with neural network algorithms can significantly improve the time resolution of particulate matter source apportionment.

Extremely Large Variations of Atmospheric 14C Concentration During the Last Glacial Period

A long record of atmospheric 14C concentration, from 45 to 11 thousand years ago (ka), was obtained from a stalagmite with thermal-ionization mass-spectrometric 230Th and accelerator mass-spectrometric 14C measurements. This record reveals highly elevated Delta14C between 45 and 33 ka, portions of which may correlate with peaks in cosmogenic 36Cl and 10Be isotopes observed in polar ice cores. Superimposed on this broad peak of Delta14C are several rapid excursions, the largest of which occurs between 44.3 and 43.3 ka. Between 26 and 11 ka, atmospheric Delta14C decreased from approximately 700 to approximately 100 per mil, modulated by numerous minor excursions. Carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle.

Synchronous radiocarbon and climate shifts during the last deglaciation

Radiocarbon data from the Cariaco Basin provide calibration of the carbon-14 time scale across the period of deglaciation (15,000 to 10, 000 years ago) with resolution available previously only from Holocene tree rings. Reconstructed changes in atmospheric carbon-14 are larger than previously thought, with the largest change occurring simultaneously with the sudden climatic cooling of the Younger Dryas event. Carbon-14 and published beryllium-10 data together suggest that concurrent climate and carbon-14 changes were predominantly the result of abrupt shifts in deep ocean ventilation.

Interpretation of mass spectra from organic compounds in aerosol time-of-flight mass spectrometry

Organic compounds containing a variety of functional groups have been analyzed using aerosol time-of-flight mass spectrometry. Both positive and negative laser desorption/ionization mass spectra have been acquired for compounds of relevance to ambient air particulate matter, including polycyclic aromatic hydrocarbons, heterocyclic analogues, aromatic oxygenated compounds such as phenols and acids, aliphatic dicarboxylic acids, and reduced nitrogen species such as amines. In many cases, positive ion mass spectra are similar to those found in libraries for 70-eV electron impact mass spectrometry. However, formation of even-electron molecular ions due to adduct formation also plays a major role in ion formation. Negative ion mass spectra suggest that organic compounds largely disintegrate into carbon cluster fragments (C(n)- and C(n)H-). However, information about the heteroatoms present in organic molecules, especially nitrogen and oxygen, is carried dominantly by negative ion spectra, emphasizing the importance of simultaneous analysis of positive and negative ions in atmospheric samples.

Variations of Younger Dryas atmospheric radiocarbon explicable without ocean circulation changes

The concentration of radiocarbon, 14C, in the atmosphere depends on its production rate by cosmic rays, and on the intensity of carbon exchange between the atmosphere and other reservoirs, for example the deep oceans. For the Holocene (the past approximately 11,500 years), it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field. Recent progress in extending the radiocarbon record backwards in time has indicated especially high atmospheric radiocarbon concentrations in the Younger Dryas cold period, between 12,700 and 11,500 years before the present. These high concentrations have been interpreted as a result of a reduced exchange with the deep-ocean reservoir, caused by a drastic weakening of the deep-ocean ventilation. Here we present a high-resolution reconstruction of atmospheric radiocarbon concentrations, derived from annually laminated sediments of two Polish lakes, Lake Gosciaz and Lake Perespilno. These records indicate that the maximum in atmospheric radiocarbon concentrations in the early Younger Dryas was smaller than previously believed, and might have been caused by variations in solar activity. If so, there is no indication that the deep-ocean ventilation in the Younger Dryas was significantly different from today's.

Relative sensitivity factors for alkali metal and ammonium cations in single-particle aerosol time-of-flight mass spectra

A variety of factors have been investigated with regard to the quantitation of chemical species within individual ambient aerosol particles analyzed by laser desorption time-of-flight mass spectrometry. Spectrum to spectrum differences in the interaction of the particle with the ionization laser beam, which affect the absolute peak areas in the mass spectra, can be minimized by using relative peak areas instead of absolute peak areas in each spectrum. Whereas absolute peak areas vary by an average of 59% for a given ion peak in single particle mass spectra of a monodisperse aerosol of particles formed from the same solution, relative peak areas in the same mass spectra vary only by an average of 16%. Relative sensitivity factors (RSF) relating the mass spectral ion intensity of NH4+ and the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ in single particle aerosol time-of-flight mass spectrometry to their bulk concentrations have been determined. The values for Li+/Na+, K+/Na+, Rb+/Na+, Cs+/Na+, and NH4+/Na+ are found to be 0.14, 5.1, 6.0, 7.9, and 0.014, respectively. The higher response for heavier cations of the alkali metals is consistent with the periodic trends of both ionization potential and lattice energies of the species of interest. The response factor for sodium and potassium cations has been used to accurately determine the relative amounts of Na+ and K+ in sea-salt particles, by analyzing a sample of approximately 360 ambient sea-salt particles. The relative amounts of Na+ and K+ are found to be 97 and 3% in particles, respectively, whereas in seawater they are, on average, 98 and 2%.

Deep-Sea coral evidence for rapid change in ventilation of the deep north atlantic 15,400 years Ago

Coupled radiocarbon and thorium-230 dates from benthic coral species reveal that the ventilation rate of the North Atlantic upper deep water varied greatly during the last deglaciation. Radiocarbon ages in several corals of the same age, 15.41 +/- 0.17 thousand years, and nearly the same depth, 1800 meters, in the western North Atlantic Ocean increased by as much as 670 years during the 30- to 160-year life spans of the samples. Cadmium/calcium ratios in one coral imply that the nutrient content of these deep waters also increased. Our data show that the deep ocean changed on decadal-centennial time scales during rapid changes in the surface ocean and the atmosphere.