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Volume 16, issue 17 | Copyright
Atmos. Chem. Phys., 16, 10899-10910, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Sep 2016

Research article | 01 Sep 2016

A comprehensive estimate for loss of atmospheric carbon tetrachloride (CCl4) to the ocean

James H. Butler1, Shari A. Yvon-Lewis2,7, Jurgen M. Lobert3,7, Daniel B. King4,7, Stephen A. Montzka1, John L. Bullister5, Valentin Koropalov6, James W. Elkins1, Bradley D. Hall1, Lei Hu1,2, and Yina Liu2,8 James H. Butler et al.
  • 1Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA
  • 2Department of Oceanography, Texas A&M University, College Station, Texas 77840, USA
  • 3Entegris Inc., Franklin, Massachusetts 02038, USA
  • 4Chemistry Department, Drexel University, Philadelphia, Pennsylvania 19104, USA
  • 5NOAA Pacific Marine and Environmental Laboratory, Seattle, Washington 98115, USA
  • 6Roshydromet, Moscow, 123242, Russia
  • 7Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, USA
  • 8Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Massachusetts, USA

Abstract. Extensive undersaturations of carbon tetrachloride (CCl4) in Pacific, Atlantic, and Southern Ocean surface waters indicate that atmospheric CCl4 is consumed in large amounts by the ocean. Observations made on 16 research cruises between 1987 and 2010, ranging in latitude from 60°N to 77°S, show that negative saturations extend over most of the surface ocean. Corrected for physical effects associated with radiative heat flux, mixing, and air injection, these anomalies were commonly on the order of −5 to −10%, with no clear relationship to temperature, productivity, or other gross surface water characteristics other than being more negative in association with upwelling. The atmospheric flux required to sustain these undersaturations is 12.4 (9.4–15.4)Ggyr−1, a loss rate implying a partial atmospheric lifetime with respect to the oceanic loss of 183 (147–241)yr and that  ∼ 18 (14–22) % of atmospheric CCl4 is lost to the ocean. Although CCl4 hydrolyzes in seawater, published hydrolysis rates for this gas are too slow to support such large undersaturations, given our current understanding of air–sea gas exchange rates. The even larger undersaturations in intermediate depth waters associated with reduced oxygen levels, observed in this study and by other investigators, strongly suggest that CCl4 is ubiquitously consumed at mid-depth, presumably by microbiota. Although this subsurface sink creates a gradient that drives a downward flux of CCl4, the gradient alone is not sufficient to explain the observed surface undersaturations. Since known chemical losses are likewise insufficient to sustain the observed undersaturations, this suggests a possible biological sink for CCl4 in surface or near-surface waters of the ocean. The total atmospheric lifetime for CCl4, based on these results and the most recent studies of soil uptake and loss in the stratosphere is now 32 (26–43)yr.

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This study was conducted to understand the influence of the ocean on the lifetime of atmospheric carbon tetrachloride, a strong, ozone-depleting gas. Data from 16 research cruises conducted between 1987 and 2010 show that, unlike the unreactive chlorofluorocarbons, carbon tetrachloride is undersaturated in surface waters regardless of temperature, wind, or biological regime, but with larger undersaturations with upwelling. Results suggest that the ocean consumes about 18 % of atmospheric CCl4.
This study was conducted to understand the influence of the ocean on the lifetime of atmospheric...