Title Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition; evidence from CFC-12 measurements in Antarctic firn air and ice cores
Author Aydin, M.; Montzka, S.A.; Battle, M.O.; Williams, M.B.; de Bruyn, W.J.; Butler, J.H.; Verhulst, K.R.; Tatum, C.; Gun, B.K.; Plotkin, D.A.; Hall, B.D.; Saltzman, E.S.
Author Affil Aydin, M., University of California, Department of Earth System Science, Irvine, CA. Other: NOAA, Earth System Research Laboratories; Bowdoin College; Chapman University; Rosenstiel School of Marine and Atmospheric Science; ICF International
Source Atmospheric Chemistry and Physics, 10(11), p.5135-5144. Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1680- 7316
Publication Date 2010
Notes In English. Published in Atmospheric Chemistry and Physics Discussions: 21 January 2010, http://www.atmos-chem-phys- discuss.net/10/1631/2010/acpd-10-1631- 2010.html ; accessed in May, 2011. 45 refs. GeoRef Acc. No: 310043. CRREL Acc. No: 65006809
Index Terms bubbles; chemical composition; diffusion; firn; gases; hydrocarbons; ice; porosity; recrystallization; sublimation; microelement content; Antarctica--Siple Dome; Antarctica--South Pole; Antarctica--West Antarctic ice sheet; air; aliphatic hydrocarbons; alkanes; Antarctic ice sheet; Antarctica; chlorofluorocarbons; dichlorodifluoromethane; geochemical anomalies; halogenated hydrocarbons; ice cores; Marie Byrd Land; methane; organic compounds; paleoatmosphere; Siple Dome; South Pole; trace elements; tracers; West Antarctic ice sheet
Abstract In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition.
URL http://www.atmos-chem-phys.net/10/5135/2010/acp-10-5135-2010.pdf
Publication Type journal article
Record ID 91469