DEEP UV-FLUORESCENCE MAPPING OF A GLACIAL ICE CORE

We are developing a down-borehole deep-UV (248 nm) fluorescence/Raman instrument coupled to an ice drill for the in situ analysis and characterization of glacial ice microenvironments. The ultimate goal of our program is to develop in situ techniques for exploration of Ocean Worlds ice crust surfaces or the polar caps of Mars. As part of this effort, we conducted a field campaign to the Greenland ice sheet near Kangerlussuaq, Greenland. We used a manual coring drill to remove several 14-cm and 9-cm ice cores at several locations on the ice sheet. Each of the core sections was scanned in the field using a UV-fluorescence system coupled with photomultiplier tube (PMT) arrays. The cores were then shipped and stored at the Montana State University subzero research facility. After shipment and storage, the core sections were rescanned using the same UV-fluorescence system. Following initial rescanning, a 2-cm deep tangential lengthwise longitudinal cut was made and the freshly cut interior surface of the core rescanned. The removed section was further divided and submitted for total organic carbon (TOC) and total dissolved nitrogen (TDN) analysis in addition to epifluorescence microscopy for cell counting.

Our preliminary results show that we can identify zonation in glacial ice using fluorescence wavelengths from 320-360 nm, with the region from 340-360 nm being particularly noise-free. We identified broad enhanced fluorescent bands that were 8 cm wide. These did not correlate to visible features in the ice. We determined that these zones were not artifacts by noting the same bands were present after scraping the core lengthwise to 1 cm depth, and cutting the core to removing an additional 2 cm from the scraped surface. Preliminary total dissolved nitrogen analysis showed an enhanced nitrogen signal in the region correlated with the enhanced fluorescence at 340-360 nm. This is consistent with the detection of either nitrogenated fluorescent (likely aromatic) organic molecules or microbial cells. Our results show that we were able to use UV-fluorescence to determine a band of organic/biological materials in the ice and follow up with more detailed analytical techniques.