Carbonyl sulfide hydrolysis in Antarctic ice cores and an atmospheric history for the last 8000 years

M Aydin,T J Fudge,K R Verhulst,E D Waddington,M R Nicewonger,E S Saltzman

doi:10.1002/2014jd021618

Abstract

©2014. American Geophysical Union. All Rights Reserved. Carbonyl sulfide (COS) was measured in Antarctic ice core samples from the Byrd, Siple Dome, Taylor Dome, and West Antarctic Ice Sheet Divide sites covering the last 8000 years of the Holocene. COS levels decrease downcore in most of these ice cores. The magnitude of the downcore trends varies among the different ice cores and is related to the thermal histories of the ice sheet at each site. We hypothesize that this is due to the temperature-dependent hydrolysis of COS that occurs in situ. We use a one-dimensional ice flow and heat flux model to infer temperature histories for the ice core samples from different sites and empirically determine the kinetic parameters for COS hydrolysis. We estimate e-folding lifetimes for COS hydrolysis ranging from 102 years to 106 years over a temperature range of 0°C to -50°C. The reaction kinetics are used to estimate and correct for the in situ COS loss, allowing us to reconstruct paleoatmospheric COS trends during the mid-to-late Holocene. The results suggest a slow, long-term increase in atmospheric COS that may have started as early as 5000 years ago. Given that the largest term in the COS budget is uptake by terrestrial plants, this could indicate a decline in terrestrial productivity during the late Holocene.

Highlights

Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere, with a global average mixing ratio of 480–490 parts per trillion and a lifetime of 2–3 years [Montzka et al, 2007]
We present new ice core COS measurements from the previously unsampled Byrd, Taylor Dome, and West Antarctic Ice Sheet (WAIS) Divide sites in Antarctica and from the deep Siple Dome A ice core (Figure 1 and Table 1)
The COS measurements from the WAIS Divide 05A and 06A ice cores compare well with each other and with the previously published data from the South Pole during the last 1 kyr (Figure 3a)

Summary

Introduction

Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere, with a global average mixing ratio of 480–490 parts per trillion (ppt) and a lifetime of 2–3 years [Montzka et al, 2007]. COS is emitted from a variety of natural and anthropogenic sources It is produced directly in the surface ocean through photochemical breakdown of organosulfur compounds. The oceans are a large indirect source of COS via the emission and atmospheric oxidation of carbon disulfide (CS2) and dimethylsulfide (DMS) [Watts, 2000; Kettle, 2002]. Both COS and CS2 are emitted as a result of industrial activities linked to synthetic fiber manufacturing [Sturges et al, 2001; Montzka et al, 2004]. Based on recent top down estimates of the atmospheric COS fluxes [Suntharalingam et al, 2008; Berry et al, 2013], the COS levels in the preindustrial atmosphere would largely reflect a balance between the net oceanic source and the terrestrial uptake

Methods

Results

Conclusion