Northern Hemisphere atmospheric history of carbon monoxide since preindustrial times reconstructed from multiple Greenland ice cores

• Main Authors: Faïn, Xavier, Rhodes, Rachael H., Philip, Place, Petrenko, Vasilii V., Fourteau, Kévin, Chellman, Nathan, Crosier, Edward, McConnell, Joseph R., Brook, Edward J., Blunier, Thomas, Legrand, Michel, Chappellaz, Jérôme
• Format: Text
• Language: English
• Published: 2021
• Subjects: envir; geo; Greenland; Greenland ice cores; ice core; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-2021-28; https://cp.copernicus.org/preprints/cp-2021-28/

Carbon monoxide (CO) is a regulated pollutant and one of the key components determining the oxidizing capacity of the atmosphere. Obtaining a reliable record of atmospheric CO mixing ratios since pre-industrial times is necessary to evaluate climate-chemistry models in conditions different from today and to constrain past CO sources. We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet which experience a range of snow accumulation rates, mean surface temperatures, and different chemical compositions. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled to continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019. Overall, continuous flow analyses (CFA) of CO were carried out on over 700 m of ice. The CFA-based CO measurements exhibit excellent external precision (ranging 3.3-6.6 ppbv, 1sigma), and achieve consistently low blanks (ranging from 4.1+/-1.2 to 12.6+/-4.4 ppbv), enabling paleo-atmospheric interpretations. However the five CO records all exhibit variability too large and rapid to reflect past atmospheric mixing ratio changes. Complementary tests conducted on discrete ice samples demonstrate that these variations are not artifacts of the analytical method (i.e., production of CO from organics in the ice during melting), but very likely are related to in situ CO production within the ice before analysis. Evaluation of signal resolution and co-investigation of high-resolution records of CO and TOC show that past atmospheric CO variations can be extracted from the records’ baselines at four sites with accumulation rates higher than 20 cm water equivalent per year (weq yr-1). However, such baselines should be taken as upper bounds of past atmospheric CO burden. Baseline CO records from four sites are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from ...