Changes in atmospheric carbonyl sulfide over the last 54,000 years inferred from measurements in Antarctic ice cores

Abstract

We measured carbonyl sulfide (COS) in air extracted from ice core samples from the West Antarctic Ice Sheet (WAIS) Divide, Antarctica, with the deepest sample dated to 54,300 years before present. These are the first ice core COS measurements spanning the Last Glacial Maximum (LGM), the last glacial/interglacial transition, and the early Holocene. The WAIS Divide measurements from the LGM and the last transition are the first COS measurements in air extracted from full clathrate (bubble-free) ice. This study also includes new COS measurements from Taylor Dome, Antarctica, including some in bubbly glacial ice that are concurrent with the WAIS Divide data from clathrate glacial ice. COS hydrolyzes in ice core air bubbles, and the recovery of an atmospheric record requires correcting for this loss. The data presented here suggest that the in situ hydrolysis of COS is significantly slower in clathrate ice than in bubbly ice. The clathrate ice measurements are corrected for the hydrolysis loss during the time spent as bubbly ice only. The corrected WAIS Divide record indicates that atmospheric COS was 250-300 parts per trillion (ppt) during the LGM and declined by 80-100 ppt during the last glacial/interglacial transition to a minimum of 160-210 ppt at the beginning of the Holocene. This decline was likely caused by an increase in the gross primary productivity of terrestrial plants, with a possible contribution from a reduction in ocean sources. COS levels were above 300 ppt in the late Holocene, indicating that large changes in the COS biogeochemical cycle occurred during the Holocene.

Microbial metabolism directly affects trace gases in (sub) polar snowpacks

“…In particular, however it requires a reconsideration of the use of firn air to quantify pre-industrial levels of methyl halides [57] and dimethyl sulfide metabolism by-products (methane sulfonate: [58]; carbonyl sulfide: [59]). These measurements have not considered the impact of photochemistry [35] or biology (this study) on these long-term storage concentrations and until these impacts have been quantified and discounted, the reported values should be considered the net overall result of all possible biological, chemical and physical effects.…”

Reviews and Syntheses: Carbonyl Sulfide as a Multi-scale Tracer for Carbon and Water Cycles

“…OCS is the most abundant and stable of all the sulfur-containing gases. Ambient concentrations of OCS are relatively stable in the short term 15 (months), and in the longer term (millennia) may reflect large-scale changes in global plant cover (Aydin et al, 2016).…”

“…Ice core samples from the West Antarctic Ice Sheet Divide were used to produce a 54,300 year OCS record and an order of magnitude estimate of the change in GPP during the last glacial/interglacial transition (Aydin et al, 2016). Atmospheric OCS declined by 80 to 100 ppt during 5 the last glacial/interglacial transition.…”

“…Aydin et al (2014Aydin et al ( , 2016 developed the necessary corrections to take into account OCS hydrolysis within the ice core bubbles. Some ice core 5 material is not suitable for OCS analysis because the environment was too warm for long periods and OCS was continuously hydrolyzed for thousands of years.…”

“…For the rate-limiting step of hydrolysis in 25 near-room-temperature water, the pseudo-first order rate constant is around 2×10 -5 s -1 . The hydrolysis of OCS gains significance at longer time scales, such as in ice cores (Aydin et al, 2014(Aydin et al, , 2016 In typical environmental conditions, OCS adsorption and desorption is near steady state. OCS adsorbs onto various mineral surfaces at ambient temperatures and can be desorbed at higher temperatures (Devai and DeLaune, 1997).…”