USAP-DC

Gases trapped in ice cores have revealed astonishing things about the greenhouse gas composition of the past atmosphere, including the fact that carbon dioxide concentrations never rose above 300 parts per million during the last 800,000 years. This places today's concentration of 400 parts per million in stark contrast. Furthermore, these gas records show that natural sources of greenhouse gas such as oceans and ecosystems act as amplifiers of climate change by increasing emissions of gases during warmer periods. Such amplification is expected to occur in the future, adding to the human-produced gas burden. The South Pole ice core will build upon these prior findings by expanding the suite of gases to include, for the first time, those potent trace gases that both trapped heat and depleted ozone during the past 40,000 years. The present project on inert gases and methane in the South Pole ice core will improve the dating of this crucial record, to unprecedented precision, so that the relative timing of events can be used to learn about the mechanism of trace gas production and destruction, and consequent climate change amplification. Ultimately, this information will inform predictions of future atmospheric chemical cleansing mechanisms and climate in the context of our rapidly changing atmosphere. This award also engages young people in the excitement of discovery and polar research, helping to entrain the next generations of scientists and educators. Education of graduate students, a young researcher (Buizert), and training of technicians, will add to the nation?s human resource base.

This award funds the construction of the gas chronology for the South Pole 1500m ice core, using measured inert gases (d15N and d40Ar--Nitrogen and Argon isotope ratios, respectively) and methane in combination with a next-generation firn densification model that treats the stochastic nature of air trapping and the role of impurities on densification. The project addresses fundamental gaps in scientific understanding that limit the accuracy of gas chronologies, specifically a poor knowledge of the controls on ice-core d15N and the possible role of layering and impurities in firn densification. These gaps will be addressed by studying the gas enclosure process in modern firn at the deep core site. The work will comprise the first-ever firn air pumping experiment that has tightly co-located measurements of firn structural properties on the core taken from the same borehole.

The project will test the hypothesis that the lock-in horizon as defined by firn air d15N, CO2, and methane is structurally controlled by impermeable layers, which are in turn created by high-impurity content horizons in which densification is enhanced. Thermal signals will be sought using the inert gas measurements, which improve the temperature record with benefits to the firn densification modeling. Neon, argon, and oxygen will be measured in firn air and a limited number of deep core samples to test whether glacial period layering was enhanced, which could explain low observed d15N in the last glacial period. Drawing on separate volcanic and methane synchronization to well-dated ice cores to create independent ice and gas tie points, independent empirical estimates of the gas age-ice age difference will be made to check the validity of the firn densification model-inert gas approach to calculating the gas age-ice age difference. These points will also be used to test whether the anomalously low d15N seen during the last glacial period in east Antarctic ice cores is due to deep air convection in the firn, or a missing impurity dependence in the firn densification models.

The increased physical understanding gained from these studies, combined with new high-precision measurements, will lead to improved accuracy of the gas chronology of the South Pole ice core, which will enhance the overall science return from this gas-oriented core. This will lead to clarification of timing of atmospheric gas variations and temperature, and aid in efforts to understand the biogeochemical feedbacks among trace gases. These feedbacks bear on the future response of the Earth System to anthropogenic forcing. Ozone-depleting substances will be measured in the South Pole ice core record, and a precise gas chronology will add value. Lastly, by seeking a better understanding of the physics of gas entrapment, the project aims to have an impact on ice-core science in general.

Person	Role
Severinghaus, Jeffrey P.	Investigator and contact
Sowers, Todd A.	Investigator and contact
Brook, Edward J.	Investigator and contact

Antarctic Glaciology	Award # 1443710
Antarctic Glaciology	Award # 1443472
Antarctic Glaciology	Award # 1443464

USAP-1443710_1

Data_Management_Plan.pdf

Repository	Title (link)	Format(s)	Status
USAP-DC	South Pole (SPICECORE) 15N, 18O, O2/N2 and Ar/N2	Excel	exist
USAP-DC	South Pole CH4 data for termination	Excel	exists
USAP-DC	South Pole ice core total air content	Excel	exists
USAP-DC	SP19 Gas Chronology	Excel	exists
USAP-DC	South Pole ice core (SPC14) discrete methane data	Excel	exists
USAP-DC	South Pole Ice Core Isotopes of N2 and Ar	Excel	exists

1. 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)
2. 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)
3. Kahle, E. C., Steig, E. J., Jones, T. R., Fudge, T. J., Koutnik, M. R., Morris, V., … White, J. W. C. (2020). Reconstruction of temperature, accumulation rate, and layer thinning from an ice core at South Pole using a statistical inverse method. (doi:10.1002/essoar.10503447.1)
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. Buizert, Christo; Fudge, T.J.; Roberts, William H. G.; Steig, Eric J.; Sherriff-Tadano, Sam; Ritz, Catherine; Lefebvre, Eric; Edwards, Jon; Kawamura, Kenji; Oyabu, Ikumi; Motoyama, Hideaki; Kahle, Emma C.; Jones, Tyler R.; Abe-Ouchi, Ayako; Obase, Takashi; Martin, Carlos; Corr, Hugh; Severinghaus, Jeffrey P.; Beaudette, Ross; Epifanio, Jenna; Brook, Edward J.; Martin, Kaden; Chappellaz, Jérôme; Aoki, Shuji; Nakazawa, Takakiyo; Sowers, Todd A.; Alley, Richard; Ahn, Jinho; Sigl, Michael; Severi, Mirko; Dunbar, Nelia W.; Svensson, Anders; Fegyveresi, John; He, Chengfei; Liu, Zhengyu; Zhu, Jiang; Otto-Bliesner, Bette; Lipenkov, Vladimir Y.; Kameda, Takao; Schwander, Jakob. 2021 in press. Antarctic surface temperature and elevation during the Last Glacial Maximum. Science, 372(6546), 1097–1101 (doi:10.1126/science.abd2897)
7. Kahle, E. C., Steig, E. J., Jones, T. R., Fudge, T. J., Koutnik, M. R., Morris, V., … White, J. W. C. (2021). Reconstruction of temperature, accumulation rate, and layer thinning from an ice core at South Pole using a statistical inverse method. (doi:10.1002/essoar.10503447.2)
8. Kahle, E. C., Steig, E. J., Jones, T. R., Fudge, T. J., Koutnik, M. R., Morris, V. A., … White, J. W. C. (2021). Reconstruction of Temperature, Accumulation Rate, and Layer Thinning From an Ice Core at South Pole, Using a Statistical Inverse Method. Journal of Geophysical Research: Atmospheres, 126(13). (doi:10.1029/2020jd033300)
9. Morgan, J. D., Buizert, C., Fudge, T. J., Kawamura, K., Severinghaus, J. P., & Trudinger, C. M. (2022). Gas isotope thermometry in the South Pole and Dome Fuji Ice Cores provides evidence for seasonal rectification of ice core gas records. (doi:10.5194/tc-2022-49)
10. Kahle, E. C., Steig, E. J., Jones, T. R., Fudge, T. J., Koutnik, M. R., Morris, V., Vaughn, B., Schauer, A., Stevens, C. M., Conway, H., Waddington, E. D., Buizert, C., Epifanio, J., & White, J. W. C. (2021). Reconstruction of temperature, accumulation rate, and layer thinning from an ice core at South Pole using a statistical inverse method. (doi:10.1002/essoar.10503447.3)
11. Morgan, J. D., Buizert, C., Fudge, T. J., Kawamura, K., Severinghaus, J. P., & Trudinger, C. M. (2022). Gas isotope thermometry in the South Pole and Dome Fuji ice cores provides evidence for seasonal rectification of ice core gas records. The Cryosphere, 16(7), 2947–2966. (doi:10.5194/tc-16-2947-2022)
12. Epifanio, J. A., Brook, E. J., Buizert, C., Pettit, E. C., Edwards, J. S., Fegyveresi, J. M., Sowers, T. A., Severinghaus, J. P., & Kahle, E. C. (2023). Millennial and orbital-scale variability in a 54,000-year record of total air content from the South Pole ice core. (doi:10.5194/egusphere-2023-578)
13. Epifanio, J. A., Brook, E. J., Buizert, C., Pettit, E. C., Edwards, J. S., Fegyveresi, J. M., Sowers, T. A., Severinghaus, J. P., & Kahle, E. C. (2023). Millennial and orbital-scale variability in a 54 000-year record of total air content from the South Pole ice core. The Cryosphere, 17(11), 4837–4851. (doi:10.5194/tc-17-4837-2023)