PhD defense: Margaret Harlan

Insights from the Mount Brown South ice core: volcanic records, atmospheric transport, and iron fertilization

The Mount Brown South (MBS) ice cores were drilled in 2017-2018 in coastal East Antarctica. Covering 873-2017 CE, the 295 m MBS-Main core and 20-25 m shallow cores (MBS-Alpha, Bravo, and Charlie) have recently been studied for their climatological links to the southern Indian Ocean region and modes of global climate variability. Building on the growing body of work based on the MBS ice core array, this work presents continuous impurity measurements of the MBS-Main core and the first investigation of volcanic ash from the MBS-Alpha core. 

This dissertation proposes MBS as an important tephrochronological archive. A novel multi-faceted sampling strategy, combining atmospheric transport modeling, ice core chemistry records, and volcanic records from the region, was developed and employed for highly targeted cryptotephra sampling of MBS. Preliminary low-resolution sampling of MBS-Main was followed by high-resolution re-sampling of MBS-Alpha, and major-element geochemical analysis enabled the identification of two cryptotephra horizons, the 1985 eruption of Mt. Erebus and 1991 eruption of Cerro Hudson. The 1991 cryptotephra were analyzed using x-ray fluorescence microscopy and x-ray absorption near-edge structure (XANES) imaging as pilot study of synchrotron methods for determining bioavailability of iron in ice core cryptotephra. Qualitative interpretation of XANES results indicate that the 1991 Cerro Hudson ash in MBS-Alpha is a potentially significant source of bioavailable iron, with the potential to influence marine biological productivity. This work provides a strong proof of concept for both the sampling plan used in cryptotephra sampling and the use of synchrotron-XANES for analysis of ice core cryptotephra.

Committee: Professor Jens Hesselbjerg Christensen (Chair), Associate Professor Bess G. Koffman (Colby College), Associate Professor Barbara Delmonte (University of Milano-Bicocca)

Supervisors: Associate Professor Anders Svensson, Associate Professor Helle Astrid Kjær, Dr. Tessa Vance (University of Tasmania), Professor Delphine Lannuzel (University of Tasmania), Dr. Jodi Fox (University of Tasmania)