Quadruple sulfur isotope biosignatures from terrestrial Mars analogue systems
Bibliographic record
Abstract
In this study, we present quadruple sulfur isotope values (QSI: 32 S, 33 S, 34 S, 36 S) measured in sediments from two sulfur-rich Mars analogue environments: i) the glacially-fed hydrothermal pools in Iceland (Kerlingarfjöll and Kverkfjöll), and ii) the Lost Hammer hypersaline spring from Axel Heiberg Island, Nunavut, Canada. The localities host different physical and geochemical characteristics, including aqueous geochemistry , volcanic input, temperature, pH and salinity . The δ 34 S values of sulfur compounds from the Lost Hammer hypersaline spring exhibit large fractionations typical of microbial sulfate reduction (MSR) with or without additional oxidative sulfur cycling and microbial sulfur disproportionation (MSD) ( 34 ε SO4-CRS from −49.5 to −43.5‰), contrary to the small S isotope fractionations reported for the Icelandic hydrothermal sites ( 34 ε SO4-CRS from −9.9 to −0.7‰). Lost Hammer minor S isotope values (Δ 33 S and Δ 36 S), interpreted within the context of a sulfur cycling box model, are consistent with a biogeochemical S cycle including both MSR and MSD. In contrast, the small range in δ 34 S values within the Iceland hydrothermal pools are consistent with a large volcanic H 2 S flux and minimal biological S cycling. The minor S isotope values recorded in the hydrothermal pools, however, indicate further biogeochemical sulfur cycling. Our results demonstrate that contrasting physical and chemical characteristics between sites support different microbial S cycling processes, as recorded in the QSI sedimentary values. The QSI data and the derived models support the strong potential for QSI values to be used as biosignatures in the search for life in Martian S-rich environments. These results also suggests that extreme, metabolic energy-limited environments with low abiotic sulfur fluxes could be more likely to produce unequivocal biological QSI signals than those with more moderate conditions or abundant available energy. This finding carries significant implications for targeting sites on Mars for in situ measurements or future sample return missions .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".