USAP-DC

The summit crater of Mt. Moulton, in West Antarctica, contains a 600-m thick horizontally-exposed section of ice with intercalated tephra layers from nearby Mt Berlin. Argon-40/Argon-39 dating of the thick, near-source tephra indicates that the age of the horizontal ice section ranges between 15,000 and 492,000 years. Thus, the Mt Moulton site offers an unparalleled repository of ancient West Antarctic snow and trapped air that can be used to investigate West Antarctic climate over much of the past 500,000 years. The planar nature and consistent dips of the tephra layers suggests that, although the ice section has thinned, it is otherwise undeformed. The Mt. Moulton site was visited during the 1999/2000 field season, at which time a horizontal ice core representing approximately 400 meters of ice was collected, ranging in age from 15,000 to older than 480,000 years. In addition to this horizontal core, samples of ice at a range of depths were collected in order to test the quality of the climate record in the ice. Forty tephra layers intercalated in the ice were also collected in order to provide chronology for the ice section. The results of this first effort are extremely encouraging. Based on the d?18 O of ice, for example, there is clearly a useable record of past climate at Mt. Moulton extending back beyond 140,000 years. There is work to do, however, to realize the full potential of this horizontal ice core. The elemental and isotopic composition of trapped gases suggest some contamination with modern air, for example. As gas cross-dating of ice cores is the current standard by which climate records are intercompared, we need to understand why and how the gas record is compromised before adding Moulton to our arsenal of ice core paleoclimate records. This award supports a collaborative effort between three institutions with following objectives: 1) to evaluate more thoroughly the integrity of the climatic record through shallow drilling of the blue ice area, as well as the snow field upslope from the blue ice; 2) to improve the radioisotopic dating of specific tephra layers; 3) to obtain baseline information about modern snowfall deposition, mean annual temperature, and wind pumping around the summit of Mt. Moulton; and 4) to study how firn densification differs when surface accumulation changes from net accumulation to net ablation.

Person	Role
White, James	Co-Investigator
Popp, Trevor	Co-Investigator
Dunbar, Nelia	Investigator
Sowers, Todd A.	Investigator
Steig, Eric J.	Investigator
Bauer, Rob	TBD

Antarctic Glaciology	Award # 0230348
Antarctic Glaciology	Award # 0230316
Antarctic Glaciology	Award # 0230021

NSIDC-0640_1
Sowers_0230021
dunbar_NSF0230348

None in the Database

Repository	Title (link)	Format(s)	Status
USAP-DC	Mount Moulton Isotopes and Other Ice Core Data	None	exist

1. Steig, E. J., Huybers, K., Singh, H. A., Steiger, N. J., Ding, Q., Frierson, D. M. W., … White, J. W. C. (2015). Influence of West Antarctic Ice Sheet collapse on Antarctic surface climate. Geophysical Research Letters, 42(12), 4862–4868. (doi:10.1002/2015gl063861)
2. Dunbar, N. W., Iverson, N. A., Smellie, J. L., McIntosh, W. C., Zimmerer, M. J., & Kyle, P. R. (2021). Chapter 7.4 Active volcanoes in Marie Byrd Land. Geological Society, London, Memoirs, 55(1), 759–783. (doi:10.1144/m55-2019-29)