Carbonyl sulfide hydrolysis in Antarctic ice cores and an atmospheric history for the last 8,000 years
A Department of Atmospheric and Oceanic Sciences Seminar featuring Dr. Murat Aydin, Associate Researcher, Department of Earth System Science, University of California, Irvine
Wednesday, October 09, 2013
Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere with a global average mixing ratio of about 500 parts per trillion (ppt) and a lifetime of 3 years. It is produced by a variety of natural and anthropogenic sources. Oceans are the largest source, emitting COS and precursors carbon disulfide and dimethyl sulfide. The most important atmospheric removal process of COS is uptake by terrestrial plants during photosynthesis. Interest in the atmospheric variability of COS is primarily due to its potential value as a proxy for changes in gross primary productivity of the land biosphere.
We measured COS in ice core samples from Byrd, Siple Dome, Taylor Dome, and West Antarctic Ice Sheet (WAIS) Divide sites in Antarctica that covers the last 8,000 years of the Holocene. The measurements display a site-dependent downcore decline in COS, apparently driven by hydrolysis within the ice matrix. We use one dimensional ice and heat flow models to infer temperature histories for the ice core samples from different sites that are used to determine the kinetic parameters of ice core COS hydrolysis and to correct for the in situ COS loss. The reaction is strongly temperature dependent. The estimated ice core hydrolysis lifetimes (1/k) vary from 100 y to 1,000,000 y over a temperature range of 0°C to -50°C. The “corrected” COS records suggest a slow, long-term increase in atmospheric COS during the late Holocene that may have started as early as 5,000 years ago. Atmospheric CO2 was also rising during this time period, suggesting the atmospheric levels of both trace gases might have changed as a response to a long-term decline in terrestrial productivity during the late Holocene.
SEMINAR TEA: 4:30-5:00PM (MSB 7124B)