The Development and Use of the Berkeley Fluorescence Spectrometer to Characterize Microbial Content and Detect Volcanic Ash in Glacial Ice
- Author(s): Rohde, Robert Andrew
- Advisor(s): Price, P. Buford
- et al.
The Berkeley Fluorescence Spectrometer (BFS) was designed and implemented to provide rapid non-destructive characterizations of the organic / microbial content in glacial ice. The resulting information is general, aiming at bulk microbial concentration and a few identifiable classes of microbes, but nonetheless can provide orders of magnitude more data than can be reasonably obtained via the slow process of cutting and sampling. This instrument has now scanned ice cores segments from a variety of Antarctic and Greenland sites including a majority of the 580 m of the WAIS Divide Core (WDC) that has been archived at the National Ice Core Laboratory (NICL). A sustained scanning rate of 4 minutes per ice core meter has been achieved with seven channel fluorescence spectra collected every 750 microns.
These scans have provided the largest collection of data on the microbial content of glacial ice ever assembled. They show the microbial content of the ice to be fairly homogenous in bulk but heterogeneous at the fine scale. We further discovered that the observed fluorescence declines ~95% during the top ~100m of all ice cores for which scans have been conducted. This decline corresponds to the transition from snow to fully dense ice and the signal response may reflect a combination of changes in the microbial population of the ice mixed with changes in the optical properties of the ice itself. Thus far microbial deposits have not shown the kind of the large-scale continuity that would be required to coordinate events over large scales or make them useful for dating. However, the BFS has revealed an unexpected sensitivity to volcanic ash that makes it a very sensitive non-destructive system for detecting faint ash layers in archived ice cores.