The role of scavenging and early diagenesis in controlling hydrothermal fluxes into the ocean along the Endeavour segment of the Juan de Fuca ridge
Bibliographic record
Abstract
Mixing of high-temperature hydrothermal vent fluids with seawater leads to the precipitation of a large fraction of the non-conservative element load and scavenging of elements from seawater onto the particles formed. This substantially modifies hydrothermal fluxes into the ocean relative to the flux across the seafloor at vents. However, the particles formed in the plume are rarely in equilibrium within the uppermost sediments, and scavenged elements may be loosely bound to particle surfaces, meaning that the net flux from the ocean can be readily modified by processes operating during early diagenesis. Using bulk geochemistry, and progressive leaching experiments, we characterize sediments from around the Endeavour segment of the Juan de Fuca ridge to investigate scavenging and early diagenetic processes. Changes in bulk sediment composition with distance from the ridge (e.g., decreases in Fe/Ti) support a decreased hydrothermal input off-axis. Bulk-sediment and leachate data are interpreted as indicating substantial scavenging of elements such as P, V, Cr and REEs as previously suggested, with different elements scavenged with different efficiencies in different parts of the plume. Correlations of these elements with Fe in the HCl leachates, suggests their uptake is associated with Fe-oxyhydroxides. Water column scavenging is overprinted by fluxes associated with benthic scavenging for V and REE. In contrast, early diagenesis leads to complete loss of scavenged P back to the ocean. Leaching the samples with NaOH and acetic acid provides evidence for recrystallization of reactive (biogenic and hydrothermal) silica and CaCO 3 during early diagenesis in all locations. The fraction of Fe and Mn leached by 1 M HCl in 1 h versus 24 h, and the amount leached in 24 h, vary systematically; these data can be explained by progressive recrystallization of hydrothermally-derived Fe and Mn minerals during early diagenesis. These early diagenetic reactions release almost all hydrothermally-derived Mn back into the ocean, while Fe remains largely fixed in the sediment. Large-scale loss of Co, Zn, Mo, Ag and Cd also occurs during early diagenesis, with some evidence As, Pb and U are also lost. In deeper, more reducing, sediments there is uptake of As, Mo, Ag, Cd and U, presumably via diffusion through the shallow oxic sediments. Such diagenetic processes mean that the net fluxes of elements into and out of the ocean associated with hydrothermal systems differ from those estimated from studies of either vent fluids or hydrothermal plumes. • Progressive leaching helps unravel the evolution of hydrothermal particles. • The fraction of reactive Fe varies systematically with distance from axis. • The fraction of reactive Fe varies systematically with depth in cores. • Early diagenesis plays a key role in controlling hydrothermal fluxes.
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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 | 0.000 | 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 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".