Subseafloor nitrogen transformations in diffuse hydrothermal vent fluids of the Juan de Fuca Ridge evidenced by the isotopic composition of nitrate and ammonium
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Bibliographic record
Abstract
Little is known about dissolved inorganic nitrogen (DIN) transformations in hydrothermal vent (HV) fluids. Here, we present the first isotopic measurements of nitrate ( δ 15 N and δ 18 O) and ammonium ( δ 15 N) from three HV fields on the Juan de Fuca ridge (NE‐Pacific). The dominant process that drives DIN concentration variations in low‐T diffuse fluids is water mass mixing below the seafloor, with no effect on the DIN isotope ratios. Strong inter‐site variations in the concentration and δ 15 N of NH 4 + in high‐T fluids suggest different subsurface nitrogen (N) sources (deep‐sea nitrate versus organic sediments) for hydrothermally discharged ammonium. Low NH 4 + community N isotope effects (<3‰) for net NH 4 + consumption suggest an important contribution from gross ammonium regeneration in low‐T fluids. Elevation of HV nitrate 15 N/ 14 N and 18 O/ 16 O over deep‐sea mean isotope values at some sites, concomitant with decreased nitrate concentrations, indicate assimilatory or dissimilatory nitrate consumption by bacteria in the subsurface, with relatively low community N isotope effects ( 15 ε k < 3‰). The low N isotope effects suggest that nitrate assimilation or denitrification occur in bacterial mats, and/or in situ production of low δ 15 N nitrate. A significantly stronger relative increase for nitrate δ 18 O than for δ 15 N was observed at many sites, resulting in marked deviations from the 1:1 relationship for nitrate δ 15 N versus δ 18 O that is expected for nitrate reduction in marine settings. Simple box‐model calculation show that the observed un‐coupling of N and O nitrate isotope ratios is consistent with nitrate regeneration by either nitrite reoxidation and/or partial nitrification of hydrothermal ammonium (possibly originating from N 2 fixation). Our isotope data confirm the role of subsurface microbial communities in modulating hydrothermal fluxes to the deep ocean.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 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) | 0.000 | 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 it