Mihaela Glamoclija

Equatorial layered deposits in Arabia Terra, Mars: Facies and process variability

We investigated the equatorial layered ndeposits (ELDs) of Arabia Terra, Mars, in nFirsoff crater nand on the adjacent plateau. nWe produced a detailed geological map that nincluded a survey of the relative stratigraphic nrelations and crater count dating. We reconstructed nthe geometry of the layered deposits nand inferred some compositional constraints. nELDs drape and onlap the plateau materials nof late Noachian age, while they are unconformably ncovered by early and middle nAmazonian units. ELDs show the presence nof polyhydrated sulfates. The bulge morphology nof the Firsoff crater ELDs appears to be nlargely depositional. The ELDs on the plateau ndisplay a sheet-drape geometry. ELDs nshow different characteristics between the ncrater and the plateau occurrences. In the ncrater they consist of mounds made of breccia nsometimes displaying an apical pit laterally ngrading into a light-toned layered unit ndisrupted in a meter-scale polygonal pattern. nThese units are commonly associated nwith fissure ridges suggestive of subsurface nsources. We interpret the ELDs inside the ncraters as spring deposits, originated by fluid nupwelling through the pathways likely provided nby the fractures related to the crater nformations, and debouching at the surface nthrough the fissure ridges and the mounds, nleading to evaporite precipitation. On the nplateau, ELDs consist of rare mounds, flat-lying ndeposits, and cross-bedded dune fields. nWe interpret these mounds as possible nsmaller spring deposits, the flat-lying deposits nas playa deposits, and the cross-bedded ndune fields as aeolian deposits. Groundwater nfluctuations appear to be the major factor ncontrolling ELD deposition.

Microbial Diversity of Hypersaline Sediments from Lake Lucero Playa in White Sands National Monument, New Mexico, USA

Lake Lucero is a gypsum-rich, hypersaline, ephemeral playa located on the southern part of the Alkali Flat at the White Sands National Monument (WSNM), New Mexico, USA. This modern playa setting provides a dynamic extreme environment that changes from a freshwater lake to a hypersaline dry desert during the year. We investigated the microbial diversity (bacteria, archaea, and microbial eukaryotes) of the Lake Lucero sediments using 16S- and 18S-based amplicon sequencing approach and explored the diversity patterns in different geochemical microenvironments. Our results indicated that similar microbial communities, in particular bacterial communities colonized, were remarkably consistent across our depth profiles. Therefore, these communities show a first-order relevance on the environmental conditions (moisture content, oxygen content, and mineral composition). We found that Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Gemmatimonadetes were the major bacterial phyla, while Cyanobacteria were present in relatively low abundances and appeared only at the surface. Genus level assessment reflected that Truepera, Delftia, and Pseudomonas were the predominant bacterial genera across all samples. Euryarchaeota was the major archaeal phylum in all the samples, while Candidatus Halobonum and Candidatus Nitrososphaera were the main genera. Diatoms were the dominant eukaryotic group in surface samples and Fungi, Ciliophora, Metazoa, and Nematodes were the other major groups. As expected, metabolic inference indicated that aerobic microbial communities were near surface colonizers, with anaerobic communities dominating with increasing depth. We demonstrated thatxa0these microbial communities could be used to characterize unique geochemical microenvironments enabling us to extrapolate these results into other terrestrial and possibly extraterrestrial environments with comparable geochemical characteristics.

Astrobiology, the Emergence of Life, and Planetary Exploration

Astrobiology brings together scientific disciplines focused on deciphering the origin of life, its nature, evolution, and distribution in the universe. Exceptionally rapid progress in our understanding has been made over the past four decades, including new insights into how life could have emerged on Earth, the revelation that life can thrive in the most hostile terrestrial environments, evidence of the presence of liquid water throughout the universe, a controversial discovery of past life in a Martian meteorite that reinvigorated the search for life on Mars, and the discovery of Earth-like planets orbiting stars other than our Sun in the Milky Way. Although Earth is the only planet known to host life in our Solar System, continued advances in the field of astrobiology stimulate the search for life and its origin beyond our planet.

Insignificant impact of freezing and compaction on iron solubility in natural snow

To explore the freezing effect on iron (Fe) solubility in natural environments, especially in Polar regions, event based freshly fallen snow samples were collected at Newark, New Jersey on the US East Coast for two consecutive winter seasons (2014–2015 and 2015–2016). These samples were analyzed for the concentrations of soluble iron (Fesol) using UV-Vis Spectroscopy and filterable iron (Fefil) and total iron (Fetot) using Atomic Absorption Spectroscopy. The average fractional solubility of the Fesol (the portion that passes through a 0.22xa0μm pore-size filter) with respect to the total Fe in the samples was 23.3u2009±u200912.2%, with the majority of the soluble Fe being present as Fe(III). Approximately 48.5% of the total Fe existed as Fefil (the portion that passes through 0.45xa0μm pore size filter media). No significant correlation was found between the soluble ionic species and soluble Fe. Six snow events were kept frozen for 10xa0days, and analyzed in periodic intervals to study the post-freezing modification in Fe solubility. Events 1 and 2 showed increasing trend in the soluble Fe concentrations; however, the events 5, 6, 7, and 8 showed no noticeable increments. The pattern shown in Events 1 and 2 is associated with high fraction of Fefil and one unit pH drop, suggesting that the freeze-induced modification in Fe solubility could be linked with the amount of Fefil and the acidity change in the samples. To further investigate the freeze-induced compaction of particles, samples from three events 6, 7, and 10 were analyzed by SEM-STEM-EDS microscopy, and the results showed that due to freezing, in general, the particles in the ice-melt counterparts tend to compact and cluster and form larger aggregates compared to the particles in snow-melt. These results show, despite the freeze-induced compaction in snow was observed from STEM images, the snow freezing might not have significant effect in increasing Fe solubility from materials in the snow. These results further suggest that freezing process with fresh snow in high-latitude regions may not impose significant modification on Fe solubility in snow.