USAP-DC

In the past, Earth's climate underwent dramatic changes that influenced physical, chemical, geological, and biological processes on a global scale. Such changes left an imprint in Earth's atmosphere, as shown by the variability in abundances of trace gases like carbon dioxide and methane. In return, changes in the atmospheric trace gas composition affected Earth's climate. Studying compositional variations of the past atmosphere helps us understand the history of interactions between global biogeochemical cycles and Earth?s climate. The most reliable information on past atmospheric composition comes from analysis of air entrapped in polar ice cores. This project aims to generate ice-core records of relatively short-lived, very-low-abundance trace gases to determine the range of past variability in their atmospheric levels and investigate the changes in global biogeochemical cycles that caused this variability. This project measures three such gases: carbonyl sulfide, methyl chloride, and methyl bromide. Changes in carbonyl sulfide can indicate changes in primary productivity and photosynthetic update of carbon dioxide. Changes in methyl chloride and methyl bromide significantly impact natural variability in stratospheric ozone. In addition, the processes that control atmospheric levels of methyl chloride and methyl bromide are shared with those controlling levels of atmospheric methane. The measurements will be made in the new ice core from the South Pole, which is expected to provide a 40,000-year record.

The primary focus of this project is to develop high-quality trace gas records for the entire Holocene period (the past 11,000 years), with additional, more exploratory measurements from the last glacial period including the period from 29,000-36,000 years ago when there were large changes in atmospheric methane. Due to the cold temperatures of the South Pole ice, the proposed carbonyl sulfide measurements are expected to provide a direct measure of the past atmospheric variability of this gas without the large hydrolysis corrections that are necessary for interpretation of measurements from ice cores in warmer settings. Furthermore, we will test the expectation that contemporaneous measurements from the last glacial period in the deep West Antarctic Ice Sheet Divide ice core will not require hydrolysis loss corrections. With respect to methyl chloride, we aim to verify and improve the existing Holocene atmospheric history from the Taylor Dome ice core in Antarctica. The higher resolution of our measurements compared with those from Taylor Dome will allow us to derive a more statistically significant relationship between methyl chloride and methane. With respect to methyl bromide, we plan to extend the existing 2,000-year database to 11,000 years. Together, the methyl bromide and methyl chloride records will provide strong measurement-based constraints on the natural variability of stratospheric halogens during the Holocene period. In addition, the methyl bromide record will provide insight into the correlation between methyl chloride and methane during the Holocene period due to common sources and sinks.

Person	Role
Aydin, Murat	Investigator and contact

Antarctic Glaciology

Award # 1443470

USAP-1443470_1

DataManagementPlan.doc

Repository	Title (link)	Format(s)	Status
USAP-DC	SPC14 carbonyl sulfide, methyl chloride, and methyl bromide measurements from South Pole, Antarctica	Excel	exists
USAP-DC	SP19 Gas Chronology	Excel	exists
USAP-DC	South Pole ice core (SPC14) discrete methane data	Excel	exists

1. Hartman, L. H., Kurbatov, A. V., Winski, D. A., Cruz-Uribe, A. M., Davies, S. M., Dunbar, N. W., … Yates, M. G. (2019). Volcanic glass properties from 1459 C.E. volcanic event in South Pole ice core dismiss Kuwae caldera as a potential source. Scientific Reports, 9(1). (doi:10.1038/s41598-019-50939-x)
2. Epifanio, J. A., Brook, E. J., Buizert, C., Edwards, J. S., Sowers, T. A., Kahle, E. C., … Kennedy, J. A. (2020). The SP19 chronology for the South Pole Ice Core - Part 2: gas chronology, Δage, and smoothing of atmospheric records. (doi:10.5194/cp-2020-71)
3. Aydin, M., Britten, G. L., Montzka, S. A., Buizert, C., Primeau, F. W., Petrenko, V. V., … Saltzman, E. S. (2020). Anthropogenic impacts on atmospheric carbonyl sulfide since the 19th century inferred from polar firn air and ice core measurements. (doi:10.1002/essoar.10503126.1)
4. Aydin, M., Britten, G. L., Montzka, S. A., Buizert, C., Primeau, F., Petrenko, V., … Saltzman, E. S. (2020). Anthropogenic Impacts on Atmospheric Carbonyl Sulfide Since the 19th Century Inferred From Polar Firn Air and Ice Core Measurements. Journal of Geophysical Research: Atmospheres, 125(16). (doi:10.1029/2020jd033074)
5. Epifanio, J. A., Brook, E. J., Buizert, C., Edwards, J. S., Sowers, T. A., Kahle, E. C., … Kennedy, J. A. (2020). The SP19 chronology for the South Pole Ice Core – Part 2: gas chronology, Δage, and smoothing of atmospheric records. Climate of the Past, 16(6), 2431–2444. (doi:10.5194/cp-16-2431-2020)
6. Aydin, M. (2023). Increase in atmospheric carbonyl sulphide since the last glacial period. (doi:10.21203/rs.3.rs-2692937/v1)