Biological fractionation of silicon isotopes in Southern Ocean surface waters
Bibliographic record
Abstract
The fractionation of silicon isotopes by diatoms during silicification (i.e., opaline cell wall formation) provides a new tool for paleoceanographic studies of the silicon cycle. Here we examine the natural variations of the 30 Si: 28 Si ratio in silicic acid (Si(OH) 4 ) and biogenic silica (bSiO 2 ) in surface waters of the Antarctic Circumpolar Current (ACC) along 170°W. The results provide direct evidence of biologically mediated fractionation of silicon isotopes, with an enrichment factor (ɛ) of between −1.1 and −1.9‰, depending on the model employed. Comparison of the mass flux of bSiO 2 captured in sediment traps deployed in the study area with the silicon isotopic composition of that material establishes a direct linkage between diatom dynamics in surface waters and the isotopic signature of exported particles. We calculated Si(OH) 4 :NO 3 − utilization ratios from variations in silicon and nitrogen isotopic ratios in surface waters and sediment traps that agree well with direct observations of 4:1 in this region. This work supports the use of variations in silicon isotopes in sedimentary opal as a proxy for relative Si(OH) 4 utilization in surface waters.
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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 | 0.000 |
| 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".