South Pole Coring for Volcanic Sulfates

It is well known that large, sulfur-rich explosive eruptions can influence the radiative budget of the atmosphere and the global climate. Less understood is the direct volcanic impact on atmospheric chemical processes, especially by massive eruptions that alter the composition of the entire atmosphere. Sulfur from volcanic eruptions is oxidized in the atmosphere to sulfate. Preliminary results of oxygen and sulfur isotope measurements in volcanic sulfate samples indicate that isotopic composition of the oxidation products (volcanic sulfate) contains abundant valuable information on atmospheric chemical processes (oxidation, photochemistry) and components (oxidants) that have not been previously investigated.

Samples of volcanic sulfate can be found and retrieved in Antarctica ice cores. A collaborative project by Jihong Cole-Dai (South Dakota State University) and Mark Thiemens (University of California San Diego) will aim to determine the oxygen and sulfur isotope composition of sulfate in South Pole snow from a number of large volcanic eruptions in the past 1000 years. The project objectives are: (1) recovery of a suite of shallow ice cores at South Pole; (2) extraction, purification of volcanic sulfate from at least 5 major eruptions; (3) measurement of oxygen and sulfur isotope composition of volcanic and background sulfate; and (4) data interpretation.

The study will use well-established analytical procedures to determine the oxygen and sulfur isotope composition of volcanic sulfate resulting from the atmospheric oxidation of sulfur dioxide from volcanic eruptions. The isotope composition will be investigated to address a number of atmospheric chemistry questions including

1. what impact do massive volcanic eruptions have on the oxidative capacity of the atmosphere?
2. what oxidants and mechanisms are involved in the oxidation or conversion of volcanic sulfur dioxide to sulfate in the stratosphere?
3. what isotopic criteria may be used to differentiate ice core signals of stratospheric eruptions from those of tropospheric eruptions?
4. what is the role of UV radiation in sulfur dioxide conversion in the atmosphere? and
5. does the photooxidation mechanism of volcanic sulfur dioxide depend on and reflect ozone/oxygen levels in past atmospheres?

ICDS will provide a 4" coring drill and two drillers (Beth Bergeron and Denise Braun) to work with the South Dakota State University team to obtain the shallow ice cores for this project. The plan is to collect four 40 m cores, one 100 m core and one 180 m core in the 2004-05 season at South Pole. The field work will be carried out during December, 2004 and January, 2005.