Browsing by Author "Langenfelds, RL"
Now showing 1 - 10 of 10
Results Per Page
Sort Options
- Item14-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, RFHydroxyl, 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
- ItemAtmospheric 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, AMThe 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.
- ItemComposition of clean marine air and biogenic influences on VOCs during the MUMBA campaign(MDPI AG, 2019-07-10) Guérette, ÉA; Paton-Walsh, C; Galbally, IE; Molloy, SB; Lawson, S; Kubistin, D; Buchholz, R; Griffith, DWT; Langenfelds, RL; Krummel, PB; Loh, Z; Chambers, SD; Griffiths, AD; Keywood, MD; Selleck, PW; Dorminick, D; Humphries, R; Wilson, SRVolatile organic compounds (VOCs) are important precursors to the formation of ozone and fine particulate matter, the two pollutants of most concern in Sydney, Australia. Despite this importance, there are very few published measurements of ambient VOC concentrations in Australia. In this paper, we present mole fractions of several important VOCs measured during the campaign known as MUMBA (Measurements of Urban, Marine and Biogenic Air) in the Australian city of Wollongong (34°S). We particularly focus on measurements made during periods when clean marine air impacted the measurement site and on VOCs of biogenic origin. Typical unpolluted marine air mole fractions during austral summer 2012-2013 at latitude 34°S were established for CO2 (391.0 ± 0.6 ppm), CH4 (1760.1 ± 0.4 ppb), N2O (325.04 ± 0.08 ppb), CO (52.4 ± 1.7 ppb), O3 (20.5 ± 1.1 ppb), acetaldehyde (190 ± 40 ppt), acetone (260 ± 30 ppt), dimethyl sulphide (50 ± 10 ppt), benzene (20 ± 10 ppt), toluene (30 ± 20 ppt), C8H10 aromatics (23 ± 6 ppt) and C9H12 aromatics (36 ± 7 ppt). The MUMBA site was frequently influenced by VOCs of biogenic origin from a nearby strip of forested parkland to the east due to the dominant north-easterly afternoon sea breeze. VOCs from the more distant densely forested escarpment to the west also impacted the site, especially during two days of extreme heat and strong westerly winds. The relative amounts of different biogenic VOCs observed for these two biomes differed, with much larger increases of isoprene than of monoterpenes or methanol during the hot westerly winds from the escarpment than with cooler winds from the east. However, whether this was due to different vegetation types or was solely the result of the extreme temperatures is not entirely clear. We conclude that the clean marine air and biogenic signatures measured during the MUMBA campaign provide useful information about the typical abundance of several key VOCs and can be used to constrain chemical transport model simulations of the atmosphere in this poorly sampled region of the world. © 2019 The Authors
- ItemLaw Dome 14CH4 measurements confirm revised fossil methane emissions estimates(American Geophysical Union (AGU), 2021-12-17) Etheridge, DM; Petrenko, VA; Smith, AM; Neff, PD; Hmiel, B; Trudinger, CM; Crosier, EM; Thornton, DP; Langenfelds, RL; Jong, LM; Harth, CM; Mitrevski, B; Buizert, C; Yang, B; Weiss, RF; Severinghaus, JPMethane is a powerful greenhouse gas and has significant roles in the chemistry of the atmosphere. Its global concentration has risen by 240% since 1750 AD. Atmospheric 14CH4 is an independent and potentially unambiguous tracer of fossil CH4 emissions from anthropogenic and natural geologic sources, however 14C from nuclear weapons tests and 14CH4 from nuclear power plants complicate its interpretation after the late 1950s. Measurements before then rely on air extracted from polar ice and firn. Hmiel et al. (Nature, 2020) measured 14CH4 in air extracted from firn and ice in Greenland and Antarctica and found that the natural global fossil CH4 source is very small (<6 Tg CH4 yr-1). This is inconsistent with bottom-up geological CH4 emissions estimates (40-60 Tg CH4 yr-1) and implies a significant upward revision of anthropogenic fossil source emissions, emphasising the need for further measurements. We present new 14CH4 measurements of air extracted from the high accumulation site DE08-OH on the Law Dome ice sheet in 2018/19, including firn air to 81 m depth and large ice samples combined from parallel ice cores to 240 m. Measurements of trace gases confirm that the samples were uncontaminated and only minor corrections are required for sample processing. The correction for cosmogenic in-situ production of 14CH4 is very small at DE08-OH due to its high accumulation rate and relatively low elevation. The new 14CH4 results compare closely with the previous measurements from the other sites. An atmospheric 14CH4 history is reconstructed from inverse modelling of the combined ice and firn data. The pre-industrial 14CH4 level is almost identical to that expected from contemporaneous biogenic sources, confirming very minor natural fossil CH4 emissions. 14CH4 decreases to a minimum in about 1940 as anthropogenic fossil methane is emitted followed by an increase during the nuclear era from 1950 to present. The record since the 1950s would allow the evolution of the anthropogenic fossil source to be quantified when improved nuclear 14CH4 emissions estimates become available. The larger emissions from anthropogenic fossil sources implied by this result highlight opportunities for methane emissions reductions.
- ItemLow 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, AMLow 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.
- ItemThe Macquarie Island (LoFlo2G) high-precision continuous atmospheric carbon dioxide record(Copernicus Publications, 2019-02-21) Stavert, AR; Law, RM; van der Schoot, M; Langenfelds, RL; Spencer, DA; Krummel, PB; Chambers, SD; Williams, AG; Werczynski, S; Francey, RJ; Howden, RTThe Southern Ocean (south of 30∘ S) is a key global-scale sink of carbon dioxide (CO2). However, the isolated and inhospitable nature of this environment has restricted the number of oceanic and atmospheric CO2 measurements in this region. This has limited the scientific community's ability to investigate trends and seasonal variability of the sink. Compared to regions further north, the near-absence of terrestrial CO2 exchange and strong large-scale zonal mixing demands unusual inter-site measurement precision to help distinguish the presence of midlatitude to high latitude ocean exchange from large CO2 fluxes transported southwards in the atmosphere. Here we describe a continuous, in situ, ultra-high-precision Southern Ocean region CO2 record, which ran at Macquarie Island (54∘37′ S, 158∘52′ E) from 2005 to 2016 using a LoFlo2 instrument, along with its calibration strategy, uncertainty analysis and baseline filtering procedures. Uncertainty estimates calculated for minute and hourly frequency data range from 0.01 to 0.05 µmol mol−1 depending on the averaging period and application. Higher precisions are applicable when comparing Macquarie Island LoFlo measurements to those of similar instruments on the same internal laboratory calibration scale and more uncertain values are applicable when comparing to other networks. Baseline selection is designed to remove measurements that are influenced by local Macquarie Island CO2 sources, with effective removal achieved using a within-minute CO2 standard deviation metric. Additionally, measurements that are influenced by CO2 fluxes from Australia or other Southern Hemisphere land masses are effectively removed using model-simulated radon concentration. A comparison with flask records of atmospheric CO2 at Macquarie Island highlights the limitation of the flask record (due to corrections for storage time and limited temporal coverage) when compared to the new high-precision, continuous record: the new record shows much less noisy seasonal variations than the flask record. As such, this new record is ideal for improving our understanding of the spatial and temporal variability of the Southern Ocean CO2 flux, particularly when combined with data from similar instruments at other Southern Hemispheric locations. © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemA new pilot Australian tropical atmospheric research station (ATARS)(CSIRO Marine and Atmospheric Research, 2014-01-01) van der Schoot, MV; Fraser, PJ; Krummel, PB; Spencer, DA; Loh, ZM; Langenfelds, RL; Steele, LP; Gregory, RL; Meyer, CP; Keywood, MD; Lawson, S; Fedele, R; Atkinson, B; Klau, D; Zahorowski, W
- ItemA 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, RFHydroxyl, 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.
- ItemRevised records of atmospheric trace gases CO2, CH4, N2O, and δ13C-CO2 over the last 2000 years from Law Dome, Antarctica(Copernicus Publications, 2019-04-11) Rubino, M; Etheridge, DM; Thornton, DP; Howden, R; Allison, CE; Francey, RJ; Langenfelds, RL; Steele, LP; Trudinger, CM; Spencer, DA; Curran, MAJ; van Ommen, TD; Smith, AMIce core records of the major atmospheric greenhouse gases (CO2, CH4, N2O) and their isotopologues covering recent centuries provide evidence of biogeochemical variations during the Late Holocene and pre-industrial periods and over the transition to the industrial period. These records come from a number of ice core and firn air sites and have been measured in several laboratories around the world and show common features but also unresolved differences. Here we present revised records, including new measurements, performed at the CSIRO Ice Core Extraction LABoratory (ICELAB) on air samples from ice obtained at the high-accumulation site of Law Dome (East Antarctica). We are motivated by the increasing use of the records by the scientific community and by recent data-handling developments at CSIRO ICELAB. A number of cores and firn air samples have been collected at Law Dome to provide high-resolution records overlapping recent, direct atmospheric observations. The records have been updated through a dynamic link to the calibration scales used in the Global Atmospheric Sampling LABoratory (GASLAB) at CSIRO, which are periodically revised with information from the latest calibration experiments. The gas-age scales have been revised based on new ice-age scales and the information derived from a new version of the CSIRO firn diffusion model. Additionally, the records have been revised with new, rule-based selection criteria and updated corrections for biases associated with the extraction procedure and the effects of gravity and diffusion in the firn. All measurements carried out in ICELAB–GASLAB over the last 25 years are now managed through a database (the ICElab dataBASE or ICEBASE), which provides consistent data management, automatic corrections and selection of measurements, and a web-based user interface for data extraction. We present the new records, discuss their strengths and limitations, and summarise their main features. The records reveal changes in the carbon cycle and atmospheric chemistry over the last 2 millennia, including the major changes of the anthropogenic era and the smaller, mainly natural variations beforehand. They provide the historical data to calibrate and test the next inter-comparison of models used to predict future climate change (Coupled Model Inter-comparison Project – phase 6, CMIP6). The datasets described in this paper, including spline fits, are available at https://doi.org/10.25919/5bfe29ff807fb (Rubino et al., 2019). © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemTerrestrial uptake due to cooling responsible for low atmospheric CO2 during the Little Ice Age(Antarctic Climate and Ecosystems Cooperative Research Centre, 2016-03-07) Rubino, M; Etheridge, DM; Trudinger, CM; Allison, CE; Rayner, PJ; Enting, I; Mulvaney, R; Steele, LP; Langenfelds, RL; Sturges, WT; Curran, MAJ; Smith, AMModels of future carbon cycle-climate changes predict a large range in atmospheric CO2, mainly because of uncertainties in the response of the land carbon cycle to the future temperature increase. The Little Ice Age (LIA, 1500-1750 AD) CO2 decrease is the most significant pre-industrial atmospheric change over the last millennia and has been used to derive the climate sensitivity of the global carbon cycle (δ). While a recent study confirms that pre-industrial CO2 variations were caused by changes in land carbon stores, there are open questions about the size of the atmospheric LIA CO2 decrease reconstructed from ice cores, and about what caused the land to sequester CO2. To quantify the size of the LIA CO2 decrease, we have produced new CO2 measurements from DML ice, that support the DSS LIA CO2 decrease as a real atmospheric feature. To partition the contribution of ocean and land, we have measured the δ 13C-CO2, showing that the cause of the CO2 drop was uptake by the terrestrial biosphere. To identify whether the land uptake was caused by temperature, or by a decline in farming due to pandemics, we have simulated the effect of a temperature perturbation on atmospheric Carbonyl Sulfide (COS). In agreement with the previously published positive COS anomaly, our results indicate that Global Primary Productivity (GPP) decreased during the LIA, ruling out the early anthropogenic land use change hypothesis as the dominant cause of increased terrestrial carbon storage. This allows us to obtain a new, more coherent estimation of δ in the range -10/-60 Pg of C K-1.