Revised records of atmospheric trace gases CO 2 , CH 4 , N 2 O, and δ 13 C-CO 2 over the last 2000 years from Law Dome, Antarctica

Abstract

Abstract. Ice core records of the major atmospheric greenhouse\ngases ( CO2 , CH4 , N2O ) and their isotopologues covering recent\ncenturies provide evidence of biogeochemical variations during the\nLate Holocene and pre-industrial periods and over the transition to the\nindustrial period. These records come from a number of ice core and firn air\nsites and have been measured in several laboratories around the world and\nshow common features but also unresolved differences. Here we present\nrevised records, including new measurements, performed at the CSIRO Ice Core\nExtraction LABoratory\xa0(ICELAB) on air samples from ice obtained at the high-accumulation site of Law Dome (East Antarctica). We are motivated by the\nincreasing use of the records by the scientific community and by recent\ndata-handling developments at CSIRO ICELAB. A number of cores and firn air\nsamples have been collected at Law Dome to provide high-resolution records\noverlapping recent, direct atmospheric observations. The records have been\nupdated through a dynamic link to the calibration scales used in the Global\nAtmospheric Sampling LABoratory\xa0(GASLAB) at CSIRO, which are periodically\nrevised with information from the latest calibration experiments. The\ngas-age scales have been revised based on new ice-age scales and the\ninformation derived from a new version of the CSIRO firn diffusion model.\nAdditionally, the records have been revised with new, rule-based selection\ncriteria and updated corrections for biases associated with the extraction\nprocedure and the effects of gravity and diffusion in the firn. All\nmeasurements carried out in ICELAB–GASLAB over the last 25\xa0years are now\nmanaged through a database (the ICElab dataBASE or ICEBASE), which provides\nconsistent data management, automatic corrections and selection of\nmeasurements, and a web-based user interface for data extraction. We present\nthe new records, discuss their strengths and limitations, and summarise their\nmain features. The records reveal changes in the carbon cycle and\natmospheric chemistry over the last 2 millennia, including the major\nchanges of the anthropogenic era and the smaller, mainly natural variations\nbeforehand. They provide the historical data to calibrate and test the next\ninter-comparison of models used to predict future climate change (Coupled\nModel Inter-comparison Project – phase\xa06, CMIP6). The datasets described in\nthis paper, including spline fits, are available at https://doi.org/10.25919/5bfe29ff807fb (Rubino et al., 2019).