ANSTO :: Browsing by Author "Curran, MAJ"

Browsing by Author "Curran, MAJ"

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10Be concentrations in snow at Law Dome, Antarctica following the 29 October 20 and 20 January 2005 solar cosmic ray events
(World Scientific, 2009-08) Pedro, JB; Smith, AM; Duldig, ML; Klekociuk, AR; Simon, KJ; Curran, MAJ; van Ommen, TD; Fink, D; Morgan, VI; Galton-Fenzi, BK
Recent model calculations have attempted to quantify the contribution of major energetic solar cosmic ray (SCR) events to 10Be production.1,2 In this study we compare modeled 10Be production by SCR events to measured 10Be concentrations in a Law Dome snow pit record. The snow pit record spans 2.7 years, providing a quasi-monthly 10Be sampling resolution which overlaps with the SCR events of 29 Oct 2003 and 20 Jan 2005. These events were calculated to increase monthly 10Be production in the polar atmosphere (>65° S geomagnetic latitude) by ~60% and ~120% above the GCR background, respectively2. A strong peak in 10Be concentrations (>4σ above the 2.7 y mean value) was observed ~1 month after the 20 Jan 2005 event. By contrast, no signal in 10Be concentrations was observed following the weaker 29 Oct 2003 series of events. The concentration of 10Be in ice core records involves interplay between production, transport, and deposition processes. We used a particle dispersion model to assess vertical and meridional transport of aerosols from the lower stratosphere where SCR production of 10Be is expected to occur, to the troposphere from where deposition to the ice sheet occurs. Model results suggested that a coherent SCR production signal could be transported to the troposphere within weeks to months following both SCR events. We argue that only the 20 Jan 2005 SCR event was observed in measured concentrations due to favorable atmospheric transport, relatively high production yield compared to the 29 Oct 2003 event, and a relatively high level of precipitation in the Law Dome region in the month following the event. This result encourages further examination of SCR signals in 10Be ice core data. © 2009 World Scientific Publishing
14-CO in glacial ice from Law Dome, Antarctica as a tracer of changes in atmospheric OH abundance from 1870 AD to present
(Australian Nuclear Science and Technology Organisation, 2021-11-15) Smith, AM; Neff, PD; Petrenko, VV; Etheridge, DM; Crosier, EM; Hmiel, B; Thornton, DP; Jong, LM; Beaudette, R; Harth, CM; Langenfelds, RL; Mitrevski, B; Curran, MAJ; Buizert, C; Murray, LT; Trudinger, CM; Dyonisius, MN; Ng, J; Severinghaus, JP; Weiss, RF
Hydroxyl, OH, is the main tropospheric oxidant and determines the lifetime of methane and most other trace gases in the atmosphere, thereby controlling the amount of greenhouse warming produced by these gases. Changes in OH concentration ([OH]) in response to large changes in reactive trace gas emissions (which may occur in the future) are uncertain. Measurements of 14C containing carbon monoxide (14CO) and other tracers such as methyl chloroform over the last ≈25 years have been successfully used to monitor changes in average [OH], but there are no observational constraints on [OH] further back in time. Reconstructions of 14CO from ice cores could in principle provide such constraints but are complicated by in-situ production of 14CO by cosmic rays directly in the ice. Recent work in Antarctica and Greenland shows that this in-situ component would be relatively small and can be accurately corrected for at sites with very high snow accumulation rates. A joint US and Australian team sampled and measured firn air and ice at Law Dome, Antarctica (2018-19 season, site DE08-OH, 1.2 m a-1 ice-equivalent snow accumulation), to a maximum depth of 240 m. Trapped air was extracted from the ice using an onsite large-volume ice melting system. Preliminary comparisons of methane measured in the samples to existing ice core records and atmospheric measurements suggest ice core air sample ages spanning from the 1870s to the early 2000s. Firn-air samples from the snow surface to 81 m depth capture air from the early 2000s to present. Analyses of [CO] and halocarbons in the samples show a relatively low and stable procedural CO blank and demonstrate that the samples are unaffected by ambient air inclusion. 14CO analyses in these firn and ice core air samples have been successfully completed. Corrections for in-situ 14CO production, validated against direct atmospheric measurements for the more recent samples, have allowed us to develop a preliminary 14CO history. This history will be interpreted with the aid of the GEOS-Chem chemistry-transport model to place the first observational constraints on the variability of Southern Hemisphere [OH] since ≈1870 AD. © The Authors
The 14CO2 bomb pulse in firn air at Aurora Basin, East Antarctica
(Australian Partnerships in Ice Core Sciences (APICS) Workshop, 2016-03-07) Thornton, DP; Etheridge, DM; Trudinger, CM; Rubino, M; Smith, AM; Curran, MAJ; Vance, TR; Chappellaz, J
The 14C isotope of CO2 produced in the atmosphere by nuclear weapons testing in the 1960’s is incorporated in air in open pores of firn before close-off in bubbles in Antarctic ice. The rapid growth and subsequent decline provides a unique test for the smoothing of atmospheric CO2 signals due to firn diffusion and bubble close off, and the level of smoothing quantifies the time resolution with which trace gas histories can be reconstructed from ice cores. The presence of a ‘bomb pulse’ in the record also permits accurate dating of CO2 and other gases in air. Aurora Basin North (ABN) will contribute new and valuable 2000-year atmospheric records from this data sparse region of inland East Antarctica. ABN has an annual snow accumulation up to 150 kgm-2 year-1, a low mean annual temperature and high elevation. Firn air samples were collected from ABN during December 2013 in stainless-steel canisters and cylinders and 0.5L glass flasks, from varying depths covering the whole firn column at the ABN site. Extraction of CO2 from ABN samples has been performed at the CSIRO ICELAB and transferred to ANSTO to derive the 14C activity of CO2 in ABN firn air. As expected, results suggest the age spread at ABN is wider than sites with higher accumulation, such as Law Dome. Firn modelling is also planned and the 14C results will be used as inputs for the modelling to help determine (with other gas measurements) the age and age spread of air in firn and ice at ABN.
7Be and 10Be concentrations in recent firn and ice at Law Dome, Antarctica
(Elsevier, 2000-10-01) Smith, AM; Fink, D; Child, DP; Levchenko, VA; Morgan, VI; Curran, MAJ; Etheridge, DM; Elliott, G
Over the past three years, the Australian National Tandem for Applied Research (ANTARES) AMS facility at ANSTO has been expanding its sample preparation and measurement capability, particularly for 10Be, 26Al and 36Cl. During this time, ANSTO has continued its collaboration with the AAD and CSIRO Atmospheric Research on the measurement of cosmogenic isotopes from Law Dome, Antarctica. This research program has been supported by the construction of a dedicated geochemistry laboratory for the processing of ice and rock samples for the preparation of AMS targets. Here we present our first results for 10Be concentrations measured in ice cores from three sites at Law Dome and describe the sample processing protocol and aspects of the AMS measurement procedure. These sites are characterised by an eightfold difference in accumulation rate with a common precipitation source. In combination with an established ice chronology, this has enabled some preliminary findings concerning the relationship between the snow accumulation rate and the measured 10Be concentration for Law Dome during recent times. Additionally, we present 7Be and 10Be/7Be measurements made for a few surface snow samples from Law Dome and Australia. © 2000 Elsevier Science B.V.
Atmospheric CO2 and d13C-CO2 reconstruction of the little ice age from antarctic ice cores
(Copernicus Publications, 2015-04-12) Rubino, M; Etheridge, DM; Trudinger, CM; Allison, CE; Rayner, PJ; Mulvaney, R; Steele, LP; Langenfelds, RL; Sturges, WT; Curran, MAJ; Smith, AM
The decrease of atmospheric CO2 concentration recorded in Antarctic ice around 1600 AD is one of the most significant atmospheric changes to have occurred during the last millennia, before the onset of the industrial period.Together with the temperature decrease, the CO2 drop has been used to derive the sensitivity of carbon stores to climate. However, the cause of it is still under debate because models are not yet able to reproduce either its magnitude, or its timing. Here we present new measurements of the CO2 concentration decrease recorded in an ice core from a medium accumulation rate site in Antarctica (DML). We show that the new record is compatible(differences <2 ppm) with the CO2 record from the high accumulation rate DSS site on Law Dome (East Antarctica), when the different age distributions are taken into account. We have also measured the d13C-CO2 change in DML ice, filling a gap around 1600 AD in the DSS d13C record. We use a double deconvolution of the CO2 and d13C records together to provide quantitative evidence that the CO2 decrease was caused by a change in the net flux to the terrestrial biosphere. Finally, we provide a new interpretation of a published record showing increasing atmospheric carbonyl sulphide during the CO2 decrease, suggesting that cooler LIA climate affected terrestrial biospheric fluxes. Altogether our findings support the hypothesis that reduced soil heterotrophic respiration is likely to have given the most significant contribution to the LIA CO2 decrease implying a positive CO2-climate feedback. © 2015, Authors.
Beryllium-10 transport to Antarctica: results from seasonally resolved observations and modeling
(John Wiley & Sons, Inc, 2011-12-15) Pedro, JB; Heikkilä, UE; Klekociuk, AR; Smith, AM; van Ommen, TD; Curran, MAJ
Cosmogenic 10Be measured in polar ice cores has important application in the reconstruction of past solar activity. However, the processes controlling its atmospheric transport and deposition to the ice sheets are not fully understood. Here we use the seasonal changes in 10Be concentrations in a 10 year monthly resolved ice core record from the Law Dome site (East Antarctica) in conjunction with ECHAM5-HAM general circulation model (GCM) simulations of 10Be and 7Be deposition as tools to examine this problem. Maximum 10Be concentrations are observed in the ice core during the austral late summer to early autumn (summer-autumn), while minimum concentrations are observed during the austral winter. The GCM simulations, corroborated by earlier observations of 10Be:7Be ratios in Antarctica from the Georg von Neumayer air sampling station, suggest that the 10Be concentration maximum is linked to direct input of stratospheric 10Be from the Antarctic stratosphere to the lower levels of the Antarctic troposphere during the austral summer-autumn. This result contrasts with the modeled transport of 10Be to Greenland, where the seasonal maximum in stratospheric input is seen in the late winter to spring, synchronous with the timing of the seasonal maximum in midlatitude stratosphere to troposphere exchange. Our results suggest that a different combination of processes is responsible for the transport of 10Be to the Antarctic and Greenland ice sheets. © 2011 American Geophysical Union
Characterization of insoluble nanoparticles in Antarctic ice cores
(American Geophysical Union, 2013-12-09) Ellis, A; Edwards, R; van Riessen, A; Saunders, M; Smith, AM; Curran, MAJ; Goodwin, ID; Feiteng, W
Insoluble nanoparticles in the form of aerosols have significant effects on climate and biogeochemical cycles. Records of these aerosols are essential for understanding paleoclimate forcing and future climate change. These particles and their precursors are emitted to the atmosphere from a variety of primary and secondary sources including biomass burning as well as biogenic, anthropogenic, volcanic, extraterrestrial, and terrestrial mineral emissions. While a large body of research exists with respect to mineral dust particles (on the micrometer scale) derived from ice and sediment cores, very little is known with regards to the history of insoluble particles on the nano scale. Ice core records are the only reliable way to study the past history of these particles. Here, we will present new data regarding the physical and chemical properties of nanoparticles found in ice cores from East Antarctica.
Characterization of insoluble nanoparticles in ice cores from Law Dome, East Antarctica
(Department of Environment Australian Antartic Division, 2013-06-24) Ellis, A; Edwards, R; van Riessen, A; Smith, AM; Curran, MAJ; Goodwin, ID; Feiteng, W
Insoluble nanoparticles, in the form of aerosols, have significant affects on climate and biogeochemical cycles. Records of these aerosols are essential for understanding paleoclimate forcing and future climate change. While a large body of research exists with respect to mineral dust particles (micron scale) derived from ice cores and sediment cores, very little is known with regards to the history of insoluble nanoparticles. These particles and their precursors are emitted to the atmosphere from a variety of primary and secondary sources including biomass burning, biogenic, anthropogenic, volcanic, and terrestrial mineral emissions. Ice core records are the only reliable way to study the past history of these particles. Here, we will present new data with regards to the physical and chemical properties of these particles as found in the Law Dome ice core, DSS0506 from East Antarctica.
Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy
(European Geosciences Union, 2015-01-01) Ellis, A; Edwards, R; Saunders, M; Chakrabarty, RK; Subramanian, R; van Riessen, A; Smith, AM; Lambrinidis, D; Nunes, LJ; Vallelonga, P; Goodwin, ID; Moy, AD; Curran, MAJ; van Ommen, TD
Antarctic ice cores have been used to study the history of black carbon (BC), but little is known with regards to the physical and chemical characteristics of these particles in the remote atmosphere. Characterization remains limited by ultra-trace concentrations in ice core samples and the lack of adequate methods to isolate the particles unaltered from the melt water. To investigate the physical and chemical characteristics of these particles, we have developed a tangential flow filtration (TFF) method combined with transmission electron microscopy (TEM). Tests using ultrapure water and polystyrene latex particle standards resulted in excellent blanks and significant particle recovery. This approach has been applied to melt water from Antarctic ice cores as well as tropical rain from Darwin, Australia with successful results: TEM analysis revealed a variety of BC particle morphologies, insoluble coatings, and the attachment of BC to mineral dust particles. The TFF-based concentration of these particles has proven to give excellent results for TEM studies of BC particles in Antarctic ice cores and can be used for future studies of insoluble aerosols in rainwater and ice core samples. © Author(s)
Cosmogenic radionuclides as signatures of past Solar storm events
(Australian National University, 2019-09-09) Smith, AM; Wilcken, KM; Simon, KJ; Dee, MW; Kuitems, M; Scifo, A; Moy, A; Curran, MAJ; Wallner, A; Fink, D; Fujioka, T
This collaborative project examines the relationship between the ‘Carrington Event’ (CE), the largest solar storm of modern times, and two recently discovered cosmic radiation events of greater magnitude, the ‘Miyake Events’ (ME). The intention is to construct cosmogenic isotope (14C, 10Be and 36Cl) profiles across the CE, so they can be compared with similar data that have already been obtained for the ME. We will use ice cores from Law Dome, East Antarctica, collected under Australian Antarctic Science awards, for the 10Be and 36Cl analyses. The large diameter DSS0506 ice core will permit high-resolution measurements at ANSTO of 10Be and 36Cl across the CE. Furthermore, we also intend to measure 10Be and 36Cl in the main DSS ice core across the ME. These measurements will complement existing data as both isotopes will be measured in the same ice core for each event for the first time and at high temporal resolution. New tree rings spanning the CE and ME, sourced from the Oxford Dendrochronology Laboratory, have been measured for 14C at the University of Groningen at mostly annual resolution. The ultimate goal of this study is to determine whether or not all three events are manifestations of the same phenomena. A secondary goal is to provide a check on the independent DSS-main ice core chronology. The CE of 1859 is known from geomagnetic data and contemporary records of the aurorae, which were observed as far south as the tropics. The event predated ground-based neutron detectors and routine cosmogenic isotope measurement, so the intensity of the incident particle radiation is still a matter of conjecture. Indeed, this question has been thrown into sharp focus recently by new discoveries in palaeoastronomy. Analyses of natural archives (tree-rings and ice-cores) have revealed that production of the cosmogenic isotopes 14C, 10Be and 36Cl spiked dramatically in the years 774-775 AD and 993-994 AD. Such anomalies could only have been generated by sudden bursts of cosmic radiation. Several sources were initially proposed for the radiation, however, the consensus now is that they were driven by solar activity. Here we discuss progress with the measurement of the cosmogenic radioisotopes and consider how the relative production rates of the cosmogenic radioisotopes may be used to substantiate a solar cause for the historical radiation events and to infer the spectral hardness of the initiating solar protons. © The Authors.
Cosmogenic radionuclides at Law Dome, East Antarctica, as signatures of past Solar storm events.
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Smith, AM; Curran, MAJ; Fink, D; Dee, MW; Kuitems, M; Levchenko, VA; Moy, A; Scifo, A; Simon, KJ; Wilcken, KM
This project investigates evidence for increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, during three extreme events. These events are the Carrington Event (CE) of 1859 AD [1], the largest solar storm of modern times, and two recently discovered cosmic radiation events of even greater magnitude, the Miyake Events (ME) of 774/5 AD [2] and 993/4 AD [3]. Our intention is to determine ¹⁴ C, ¹⁰ Be and ³⁶ Cl profiles, with the highest sub-annual temporal resolution to date, across these events to determine whether or not all three events are manifestations of the same phenomena. Understanding the frequency, origin and magnitude of these events is essential for future-proofing modern communication infrastructure against such high magnitude radiation impacts from space. Identification of the events also provides an independent check on the Law Dome ice chronology. New annual Δ¹⁴ C measurements in tree rings, in combination with earlier published data, show that the ME774 and the ME993 events occurred in close proximity to the point of maximum activity of the 11-year solar cycle [4]. Although it did not leave any radiocarbon signature, the CE1859 event was already known to have occurred around the point of maximum activity of the solar cycle from sunspot records. Ice samples for ¹⁰ Be and ³⁶ Cl analysis are derived from ice cores drilled near the summit of Law Dome, East Antarctica. This is the first time these radionuclides have been measured at the same site for these events, allowing a direct comparison of ME774, ME993 and CE1859 under similar transport conditions. Both ME samples were taken from sections of core where the amount of available ice was limited, and the CE samples were taken from a section where more ice was available. AMS measurements involved some method development at ANSTO, measuring both ¹⁰ Be and ³⁶ Cl in the same samples, with sample sizes challenging for the ME samples. Preliminary ¹⁰ Be results at annual resolution spanning 30 years allowed an exact location of the events. We have clearly identified the expected ME774 and ME993 ¹⁰ Be peaks, which were ~ 4 years and ~ 2 years, respectively, within the error of when the layer-counted DSS ice core chronology had suggested. Accordingly, a further set of ¹⁰ Be samples at sub-annual seasonal resolution have been taken to better define the fine structure and amplitude of the signal but are currently not processed. We will also prepare a set of ³⁶ Cl AMS targets from the sub-annual ice core samples and the initial annual survey samples. No discernible ¹⁰ Be peak or ³⁶ Cl peak was found for CE1859 at annual resolution. © The Authors
Dating Antarctic ice cores using high-temporal resolution black carbon records
(Antarctic Climate and Ecosystems Cooperative Research Centre, 2016-03-07) Edwards, R; Vallelonga, P; McConnell, JR; Bertler, NAN; Curran, MAJ; Sigil, M; Fudge, TJ; Anschuetz, H; Neff, PD; Emanuelsson, D; Bisiaux, M; Goodwin, D; Smith, AM; Taylor, KC; Moy, AD; Fetieng, W; Ellis, A
Black carbon aerosols (BC) emitted by fires in the Southern Hemisphere (SH) are transported to Antarctica and preserved in the Antarctic ice sheet. Recent efforts to develop ice core records of BC deposition to Antarctica show variability in BC over a broad range of time scales. The ~ monthly-resolution BC record from the WAIS divide deep ice core displayed strong seasonal variability in modern sections of the record consistent with the timing of SH biomass burning. The record was subsequently used as an annual layer dating proxy in conjunction with other chemical species. If the emissions and transport of BC to Antarctica are stable over long periods of time it may be useful as an annual layer proxy at sites other than WAIS. To date, a rigorous comparison of Antarctic ice core BC seasonality from different locations have not been conducted. Here we present a comparison of BC ice core data from the top sections of the WAIS divide deep core, the Roosevelt Island RICE core, and the Law Dome DSS1213 core. The RICE and Law Dome sites are separated from WAIS by large distances and experience different atmospheric circulation and climate regimes. A detailed description of the data uncertainties and its use in annual layer counting will be discussed.
High-resolution records of the beryllium-10 solar activity proxy in ice from Law Dome, East Antarctica: measurement, reproducibility and principal trends
(Copernicus Publications, 2011-07-12) Pedro, JB; Smith, AM; Simon, KJ; van Ommen, TD; Curran, MAJ
Three near-monthly resolution 10Be records are presented from the Dome Summit South (DSS) ice core site, Law Dome, East Antarctica. The chemical preparation and Accelerator Mass Spectrometer (AMS) measurement of these records is described. The reproducibility of 10Be records at DSS is assessed through intercomparison of the ice core data with data from two previously published and contemporaneous snow pits. We find generally good agreement between the five records, comparable to that observed between other trace chemical records from the site. This result allays concerns raised by a previous Antarctic study (Moraal et al., 2005) about poor reproducibility of ice core 10Be records. A single composite series is constructed from the three ice cores providing a monthly-resolved record of 10Be concentrations at DSS over the past decade (1999 to 2009). To our knowledge, this is the first published ice core data spanning the recent exceptional solar minimum of solar cycle 23. 10Be concentrations are significantly correlated to the cosmic ray flux recorded by the McMurdo neutron monitor (rxy = 0.64, with 95 % CI of 0.53 to 0.71), suggesting that solar modulation of the atmospheric production rate may explain up to ~40 % of the variance in 10Be concentrations at DSS. Sharp concentration peaks occur in most years during the summer-to-autumn, possibly caused by stratospheric incursions. Our results underscore the presence of both production and meteorological signals in ice core 10Be data. © Author(s) 2011.
Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall
(John Wiley & Sons, Inc, 2016-11-04) Ellis, A; Edwards, R; Saunders, M; Chakrabarty, RK; Subramanian, R; Timms, NE; van Riessen, A; Smith, AM; Lambrindis, D; Nunes, LJ; Vallelonga, P; Goodwin, ID; Moy, AD; Curran, MAJ; van Ommen, TD
Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large-scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC. ©2016. American Geophysical Union.
Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake
(Springer Nature, 2016-07-25) Rubino, M; Etheridge, DM; Trudinger, CM; Allison, CE; Rayner, PJ; Enting, I; Mulvaney, R; Steele, LP; Langenfelds, RL; Sturges, WT; Curran, MAJ; Smith, AM
Low atmospheric carbon dioxide (CO2) concentration1 during the Little Ice Age has been used to derive the global carbon cycle sensitivity to temperature2. Recent evidence3 confirms earlier indications4 that the low CO2 was caused by increased terrestrial carbon storage. It remains unknown whether the terrestrial biosphere responded to temperature variations, or there was vegetation re-growth on abandoned farmland5. Here we present a global numerical simulation of atmospheric carbonyl sulfide concentrations in the pre-industrial period. Carbonyl sulfide concentration is linked to changes in gross primary production6 and shows a positive anomaly7 during the Little Ice Age. We show that a decrease in gross primary production and a larger decrease in ecosystem respiration is the most likely explanation for the decrease in atmospheric CO2 and increase in atmospheric carbonyl sulfide concentrations. Therefore, temperature change, not vegetation re-growth, was the main cause of the increased terrestrial carbon storage. We address the inconsistency between ice-core CO2 records from different sites8 measuring CO2 and δ13CO2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO2 fluxes for the terrestrial biosphere (γL = −10 to −90 Pg C K−1), implying a positive climate feedback and providing a benchmark to reduce model uncertainties. © 2016, Nature Publishing Group.
Measurement of Pb in ancient Antarctic ice: implications for source regions of aerosols and past environmental conditions
(Elsevier; Cambridge Publications, 2010-06-16) Burn-Nunes, L; Rosman, KJR; Vallelonga, P; Loss, RD; Curran, MAJ; Smith, AM
The isotopic compositions and concentrations of Pb in ancient Antarctic ice cores has provided invaluable information in the investigation of past global climatic and environmental conditions, providing a useful method of fingerprinting sources of Pb deposited into the Antarctic environment. Whilst these studies have proved useful, they typically cover decadal to millennial time periods and relatively few data are available on annual or seasonal time scales. Such high-resolution studies are critical for the investigation of links between short-term meteorological conditions and the transport of impurities into the Antarctic environment which, in turn, complement the interpretation of the deep ice core records. However, to date, such studies have been unable to identify any regular seasonal variability in Pb concentrations and isotopes. Consequently, an improved ice core lathe technique has been developed that allows ice cores to be to be sampled with low contamination and high spatial resolution; concurrently mass spectrometry techniques have been refined permitting Pb isotopic ratios and concentrations of Pb to be measured with accuracy and precision equivalent to much larger sample amounts. This technique has been applied to the sectioning of selected Law Dome, Eastern Antarctic ice cores dated to ~56 ky, ~16 ky and, the late 18th and 19th centuries, to gain a greater understanding of the deposition of Pb, in coastal Antarctica, on short-term and seasonal scales.
Natural and anthropogenic changes in atmospheric greenhouse gases over the past 2 millennia
(Australian Antarctic Division, 2013-06-24) Etheridge, DM; Rubino, M; Trudinger, CM; Allison, CE; Steele, LP; Thornton, DP; Vollmer, M; Krummel, PB; Smith, AM; Curran, MAJ; Sturgess, WT
Millennial changes in atmospheric trace gas composition are best determined from air enclosed in ice sheets. Air extracted from the open pores in firn and the bubbles in ice is measured to derive the past concentrations and isotopic ratios of the long lived trace gases. The significant increases observed in CO2, CH4 and N2O since about 1750 and the more recent appearance of synthetic gases such as the CFCs in the atmosphere are a key feature of the anthropocene. The millennia preceding the anthropocene, the Late Pre-Industrial Holocene (LPIH), show evidence of natural changes in trace gases that can be used to constrain models and improve their ability to predict future changes under scenarios of anthropogenic emissions and climate change. Precise measurements and ice core air samples that are accurately dated and highly resolved in time are required to record the small and rapid trace gas signals of this period. The atmospheric composition records produced by CSIRO and collaborators using the Law Dome, Antarctica ice cores are widely used in models of climate, atmospheric chemistry and the carbon cycle over the anthropocene and the LPIH. Results from these studies have been influential in informing global policies, including the Montreal and Kyoto Protocols. We will present the recently revised trace gas records from Law Dome and new measurements of tracers from these and other ice sites that reveal the causes of atmospheric changes over the anthropocene and the LPIH.
A preliminary record of changes in Southern Hemisphere atmospheric OH abundance from 14CO in glacial ice (Law Dome, Antarctica, 1870 AD to present)
(American Geophysical Union (AGU), 2021-12-17) Neff, PD; Petrenko, VV; Etheridge, DM; Smith, AM; Crosier, EM; Hmiel, B; Thornton, DP; Jong, LM; Beaudette, R; Harth, CM; Langenfelds, RL; Mitrevski, B; Curran, MAJ; Buizert, C; Murray, LT; Trudinger, CM; Dyonisius, MN; Ng, J; Severinghaus, JP; Weiss, RF
Hydroxyl, OH, is the main tropospheric oxidant and determines the lifetime of methane and most other trace gases in the atmosphere, thereby controlling the amount of greenhouse warming produced by these gases. Changes in OH concentration ([OH]) in response to large changes in reactive trace gas emissions (which may occur in the future) are uncertain. Measurements of 14C-containing carbon monoxide (14CO) and other tracers such as methyl chloroform over the last ≈25 years have been successfully used to monitor changes in average [OH], but there are no observational constraints on [OH] further back in time. Reconstructions of 14CO from ice cores at sites with very high snow accumulation rates can provide such constraints, as rapid snow burial limits in-situ production of 14CO by cosmic rays directly in the ice. A joint US and Australian team sampled and measured firn air and ice at Law Dome, Antarctica (2018-19 season, site DE08-OH, 1.2 m a-1 ice-equivalent snow accumulation), to a maximum depth of 240 m. Trapped air was extracted from the ice using an on-site large-volume ice melting system. Preliminary comparisons of methane measured in the samples to existing ice core records and atmospheric measurements suggest ice core air sample ages spanning from the 1870s to the early 2000s. Firn-air samples from the snow surface to 81 m depth capture air from the early 2000s to present. Analyses of [CO] and halocarbons in the samples show a relatively low and stable procedural CO blank and demonstrate that the samples are unaffected by ambient air inclusion. 14CO analyses in these firn and ice core air samples have been successfully completed. Corrections for in-situ 14CO production, validated against direct atmospheric measurements for the more recent samples, have allowed us to develop a preliminary 14CO history. This history will be interpreted with the aid of the GEOS-Chem chemistry-transport model to place the first observational constraints on the variability of Southern Hemisphere [OH] since ≈1870 AD.
A quasi-monthly record of 10Be concentration at Law Dome, Antarctica, from 2000 to 2015
(Antarctic Climate and Ecosystems Cooperative Research Centre, 2016-03-07) Smith, AM; Curran, MAJ; Etheridge, DM; Galton-Fenzi, BK; Heikkilä, UE; Klekociuk, AR; Moy, AD; Pedro, JB; Simon, KJ; van Ommen, TD
This paper presents an overview of work undertaken over a number of Australian Antarctic Science projects, beginning in season 2001/02 with a shallow snow pit. In season 2005/06 this was augmented with a 260 m thermally drilled ice core and a 4.5 m snow pit. A core taken in 2008/09 overlapped the 2005/06 core and pit samples. From 2009/10, short cores spanning a few year’s deposition, along with snow pit samples spanning about half a year, have been taken each season. This has continued through to the current 2015/16 season. The cores permit an overlap with earlier years to match the chronology and to yield samples for 10Be analysis at the Australian Nuclear Science and Technology Organisation (ANSTO) by the technique of accelerator mass spectrometry (AMS). Together, the data provide a unique, continuous, quasi-monthly record over 2000 to 2015 as we have moved from Solar Cycle 23 to 24. The snow pits yield larger samples for 7Be analysis, earlier by gamma spectroscopy but lately by AMS. Along with comparison with neutron monitor data and GCM modelling, this unique, high-precision record has enabled us to learn much about the production, transport and deposition of 10Be to Law Dome and to improve our use of 10Be as a proxy for past solar variability.
A record of carbonyl sulfide from Antarctic ice over the last 1000 years
(Geochemical Society, 2013-01-01) Allin, SJ; Sturges, WT; Laube, JC; Etheridge, DM; Rubino, M; Trudinger, CM; Curran, MAJ; Smith, AM; Mulvaney, R
Carbonyl sulfide (COS) is a trace gas, present in the troposphere, and also in the stratosphere, where it contributes to the stratospheric sulfate aerosol layer. It has both natural and anthropogenic sources. Natural processes include uptake by plants, while oceans, wetlands, volcanism and biomass burning all contribute to natural COS emissions. We have measured COS in Antarctic ice cores from Dronning Maud Land, drilled in 1998, the DE08 core drilled at Law Dome in 1987, and the DSS0506 core drilled in 2006. Ice samples with COS gas ages between about 1050 AD and the early 20th centrury have been examined. A large volume ice crusher at the CSIRO Marine and Atmospheric Research laboratory was used to extract air from bubbles occluded in the ice cores. These air samples were analysed for CO2, CH4, CO and 13CO2 at CSIRO, and then for COS and several halocarbons at the University of East Anglia on a high sensitivity gas chromatograph/tri-sector mass spectrometer system. Initial results indicate that good sample integrity can be achieved. Measurements from the DML samples indicate low and uniform abundances across the last few hundred years, and at concentrations significantly below those in the modernday atmosphere. Measurements in more recent ice from DE08 show the start of increasing concentrations in the early 1900s, confirming earlier evidence that the global atmospheric abundance of COS has increased as a result of industrial activity during the 20th century.

Browsing by Author "Curran, MAJ"

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