Isotopic dynamics between methane-derived authigenic carbonates and gas hydrates: Insights from two deep-sea cold seeps
Bibliographic record
Abstract
The use of clumped isotopes (Δ 47 ) as a geothermometer in carbonates has become widespread in geosciences because carbonates are ubiquitous in the environment and this technique also constrains the precipitating fluid δ 18 O composition. However, in some contexts, Δ 47 values cannot be used as a geothermometer. Instead, they provide insights into processes affecting the isotopic composition of CO 2 and dissolved inorganic carbon (DIC) prior to and during precipitation, as observed in speleothems, corals, and cold seep-associated authigenic carbonates. Among all these precipitates, authigenic carbonates associated with cold seeps stand out, as the measurement of their clumped isotopic abundances has revealed an unprecedented range of isotopic ordering, and several explanations were put forward to explain the various signals observed. To get a firmer understanding of the cause of natural variability in modern cold seeps, here we report δ 13 C, δ 18 O and Δ 47 results performed on carbonates from two deep-sea cold seeps offshore Nova Scotia, Canada, i.e., >2300 m water depth and within the gas hydrate stability zone. We report a broad Δ 47 range ( i.e., 0.502–0.663 ‰ I-CDES) that differs from values expected at isotopic equilibrium at seafloor temperatures ( i.e. , 0.671–0.672 ‰ I-CDES). Using micro computed X-ray tomography, micro-X-ray fluorescence, and micro sampling, we demonstrate that methane-derived authigenic carbonates at these deep-water sites are closely associated with colocalized methane-hydrate dissolution. The isotopic composition of these authigenic carbonates are influenced by the complex mixing of different dissolved inorganic carbon (DIC) pools at various stages of isotopic re-equilibration, resulting in fine-scale isotopic variability. We propose several mixing models and stages of DIC re-equilibration to explain this isotopic variability and apply them to evaluate the contributions of the proposed sources of DIC. The isotopic domains resulting from this exercise encompass the entire range of dual isotopic values (δ 18 O and Δ 47 ) ever observed in cold seeps and suggests that the isotopic diversity observed in these environments may be broader than that observed to date
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".