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High resolution measurements of carbon monoxide along a late Holocene Greenland ice core: evidence for in situ production

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  • We present high-resolution measurements of carbon monoxide (CO) concentrations from a shallow ice core of the North Greenland Eemian Ice Drilling project (NEEM-2011-S1). An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) coupled to a continuous melter system performed continuous, online analysis during a four-week measurement campaign. This analytical setup generated stable measurements of CO concentrations with an external precision of 7.8 ppbv (1σ), based on repeated analyses of equivalent ice core sections. However, this first application of this measurement technique suffered from a poorly constrained procedural blank of 48 ± 25 ppbv and poor accuracy because an absolute calibration was not possible. The NEEM-2011-S1 CO record spans 1800 yr and the long-term trends within the most recent section of this record (i.e., post 1700 AD) resemble the existing discrete CO measurements from the Eurocore ice core. However, the CO concentration is highly variable (75–1327 ppbv range) throughout the ice core with high frequency (annual scale), high amplitude spikes characterizing the record. These CO signals are too abrupt and rapid to reflect atmospheric variability and their prevalence largely prevents interpretation of the record in terms of atmospheric CO variation. The abrupt CO spikes are likely the result of in situ production occurring within the ice itself, although the unlikely possibility of CO production driven by non-photolytic, fast kinetic processes within the continuous melter system cannot be excluded. We observe that 68% of the CO spikes are observed in ice layers enriched with pyrogenic aerosols. Such aerosols, originating from boreal biomass burning emissions, contain organic compounds, which may be oxidized or photodissociated to produce CO within the ice. However, the NEEM-2011-S1 record displays an increase of ~0.05 ppbv yr−1 in baseline CO level prior to 1700 AD (129 m depth) and the concentration remains elevated, even for ice layers depleted in dissolved organic carbon (DOC). Thus, the processes driving the likely in situ production of CO within the NEEM ice may involve multiple, complex chemical pathways not all related to past fire history and require further investigation.
  • This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.climate-of-the-past.net/home.html.
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  • Faïn, X., Chappellaz, J., Rhodes, R. H., Stowasser, C., Blunier, T., McConnell, J. R., Brook, E. J., Preunkert, S., Legrand, M., Debois, T., and Romanini, D.: High resolution measurements of carbon monoxide along a late Holocene Greenland ice core: evidence for in situ production, Clim. Past, 10, 987-1000, https://doi.org/10.5194/cp-10-987-2014, 2014.
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  • 10
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  • This work was supported by the French AND programs RPD COCLICO (ANR-10-RPDOC-002-01) and NEEM (ANR-07-VULN-09-001), and by the EU FP7 IP PEGASOS (FP7-ENV-2010/265148). Support was also supplied by the US National Science Foundation (NSF) Office of Polar Programs (OPP) grants #0944552 and #0909541, and NSF Partnerships in International Research and Education (PIRE) grant #0968391. It received funding from the European Research Council under the European Community’s Seventh Framework Programme FP7/2007-2013 Grant Agreement #291062 (project ICE & LASERS). The NEEM project is directed by the Center for Ice and Climate at the Niels Bohr Institute, Copenhagen, and the US NSF OPP. It is supported by funding agencies and institutions in Belgium (FNRS-CFB and FWO), Canada (NRCan/GSC), China (CAS), Denmark (FIST), France (IPEV, CNRS/INSU, CEA and ANR), Germany (AWI), Iceland (RannIs), Japan (NIPR), Korea (KOPRI), The Netherlands (NWO/ALW), Sweden (VR), Switzerland (SNF), United Kingdom (NERC), and the USA (USNSF, OPP).
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