Radiolytically reworked Archean organic matter in a habitable deep ancient high-temperature brine

Abstract

Investigations of abiotic and biotic contributions to dissolved organic carbon (DOC) are required to constrain microbial habitability in continental subsurface fluids. Here we investigate a large (101–283 mg C/L) DOC pool in an ancient (>1Ga), high temperature (45–55 °C), low biomass (102−104 cells/mL), and deep (3.2 km) brine from an uranium-enriched South African gold mine. Excitation-emission matrices (EEMs), negative electrospray ionization (–ESI) 21 tesla Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and amino acid analyses suggest the brine DOC is primarily radiolytically oxidized kerogen-rich shales or reefs, methane and ethane, with trace amounts of C3–C6 hydrocarbons and organic sulfides. δ2H and δ13C of C1–C3 hydrocarbons are consistent with abiotic origins. These findings suggest water-rock processes control redox and C cycling, helping support a meagre, slow biosphere over geologic time. A radiolytic-driven, habitable brine may signal similar settings are good targets in the search for life beyond Earth.

Characterization of PP and PE Waste Pyrolysis Oils by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…For analysis, 2 × 10 6 charges were accumulated for ∼1–5 ms in an external multipole ion trap equipped with automatic gain control (AGC) . Ion depletion, a method for mass filtering or gas-phase depletion of contaminant ions, was employed to enhance the signal-to-noise ratio by dampening the abundance of species with a mass-to-charge ratio ( m / z ) between 306 and 334 Da due to an unknown impurity in the samples as will be discussed further in Section . Ions were transferred to the ICR cell as a function of m / z and then excited to a m / z -dependent radius to maximize the dynamic range and number of detected peaks.…”

“…50 Ion depletion, a method for mass filtering or gas-phase depletion of contaminant ions, was employed to enhance the signal-to-noise ratio by dampening the abundance of species with a mass-to-charge ratio (m/z) between 306 and 334 Da due to an unknown impurity in the samples as will be discussed further in Section 3. 51 Ions were transferred to the ICR cell as a function of m/z and then excited to a m/z-dependent radius to maximize the dynamic range and number of detected peaks. Excitation and detection were performed on the same pair of electrodes of the dynamically harmonized ICR, operated with 6 V trapping potential.…”

Hydrogeological controls on microbial activity and habitability in the Precambrian continental crust

“…Organic matter reworked by the effects of radiolysis is proposed as the primary source of the DOC in Moab Khotsong brines (Nisson, Walters, et al, 2023). In that study, DOC composition analysis in fluids from a shallower depth (1.2 km) revealed, by comparison to deeper and older fluids, greater abundance of larger and more oxidized compounds, which had lower salinity and much higher cell abundance (10 7 cells mL −1 ), indicating higher heterotrophic utilization (Nisson, Walters, et al, 2023). Possible sources of dissolved organic carbon in the deep subsurface include the Proterozoic metasedimentary rocks which are rich in organic carbon (Strauss, 1986), as…”

“…or as suggested for the subsurface fluids of South Africa, mixtures of microbial necromass and metabolic products (Kieft et al, 2018), and organic matter reworked by the effects of radiolysis (Nisson, Walters, et al, 2023). The similarity of the δ 13 C value of DOC for the adjacent Birchtree mine (−23.6‰ to −34.3‰) to that of organic carbon in the surrounding host rocks suggests that regardless of the specific processes involved, the ultimate origin of dissolved organic carbon in the fluids at Thompson is most likely derived from the host rocks (Sherwood .…”