Browsing by Author "Spencer, DA"

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    A 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
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    Revised 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, AM
    Ice 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.
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    Speculation on the origin of sub-baseline excursions of CH4 at Cape Grim
    (NOAA Earth System Research Laboratory, 2016-01-01) Loh, ZM; Krummel, PB; Gregory, RL; Steele, LP; Stavert, AR; Schoot, MVVD; Spencer, DA; Mitrevski, B; Thornton, DP; Galbally, IE; Ward, JZ; Somerville, NT; Chambers, SD; Williams, AG
    The Advanced Global Atmospheric Gases Experiment (AGAGE) program has historically measured in situ methane (CH4 ) at Cape Grim via gas chromatography with flame ionization detection (GC-FID) in 40 minutely grab samples. By adding continuous, high precision in situ measurements of CH4 (Picarro cavity ring-down spectroscopy [CRDS]) at both Cape Grim, Tasmania, and Casey, Antarctica, a new feature has become apparent in the Cape Grim CH4 record. During the austral summer (December to February), the Cape Grim CH4 record periodically drops below baseline. For example, in Figure 1, a number of sustained episodes of depressed CH4 concentration can be seen below the baseline selected data shown in red. Notably, these episodes are also seen in the GC-FID record. In this presentation, we examine these sub-baseline excursions of CH4 . In conjunction with meteorology and a variety of other chemical species measured at Cape Grim, including radon, ozone, hydrogen and ethane, we speculate on a number of possible mechanisms that might be responsible for these dips in CH4 mixing ratio.