Subsurface In Situ Detection of Microbes and Diverse Organic Matter Hotspots in the Greenland Ice Sheet

Abstract

We used a deep-ultraviolet fluorescence mapping spectrometer, coupled to a drill system, to scan from the surface to 105 m depth into the Greenland ice sheet. The scan included firn and glacial ice and demonstrated that the instrument is able to determine small (mm) and large (cm) scale regions of organic matter concentration and discriminate spectral types of organic matter at high resolution. Both a linear point cloud scanning mode and a raster mapping mode were used to detect and localize microbial and organic matter “hotspots” embedded in the ice. Our instrument revealed diverse spectral signatures. Most hotspots were <20 mm in diameter, clearly isolated from other hotspots, and distributed stochastically; there was no evidence of layering in the ice at the fine scales examined (100 μm per pixel). The spectral signatures were consistent with organic matter fluorescence from microbes, lignins, fused-ring aromatic molecules, including polycyclic aromatic hydrocarbons, and biologically derived materials such as fulvic acids. In situ detection of organic matter hotspots in ice prevents loss of spatial information and signal dilution when compared with traditional bulk analysis of ice core meltwaters. Our methodology could be useful for detecting microbial and organic hotspots in terrestrial icy environments and on future missions to the Ocean Worlds of our Solar System.

Perseverance’s Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Investigation

“…Salas et al (2015) demonstrated that the high radiance of a laser is necessary to observe these weak emissions and employed the technique in instruments for in situ measurements that observe trace organic and microbial detection in the ocean subsurface on the walls of igneous boreholes. More recently, laser-induced DUV native fluorescence was demonstrated to detect and locate and spatially resolve the stochastic nature of microbes and organics, including PAHs, in situ in Greenland ice (Malaska et al 2020).…”

Polar ice core organic matter signatures reveal past atmospheric carbon composition and spatial trends across ancient and modern timescales

“…Steps toward understanding future impacts of ice-sheet OM Ice core OM biogeochemistry is gaining more attention, using C characterization techniques commonly applied for aquatic and terrestrial ecosystems globally (Grannas and others, 2006;D'Andrilli and others, 2017b;Brogi and others, 2018;Xu and others, 2018;Vogel and others, 2019) and newly engineered systems designed for astrobiological research (Malaska and others, 2020). Engineering these techniques for flow through capabilities and/or in situ detection will advance ice core CFA measurements of C quality and quantity at high temporal resolution.…”

In situ organic biosignature detection techniques for space applications

“…For example, excitation and emission scanning fluorescence followed by PARAFAC enabled analysis of terrestrial humic-like species, marine humic-like species, and protein-like tryptophan in natural waters (Zielinski et al, 2018). Although no instrument is specifically being developed for space applications, EEMs have proven valuable for analyzing biological (Bhartia et al, 2008) and Ocean World (Malaska et al, 2020) analog samples, and may be a future spaceflight instrument avenue.…”

“…The absolute cell LOD was estimated to be < 300 cells, achieved through the spatial resolution (100 µm) and low interrogation volume, where each scan covers a 75 mm by 25 mm area. The instrument demonstrated that it could identify hot spots in the Greenland ice sheet containing organic matter from the surface down to 105 m depth (Malaska et al, 2020).…”