Variation in calcification of Reticulofenestra coccoliths over the Oligocene-Early Miocene
Bibliographic record
Abstract
Abstract. Coccolithophores are calcifying marine phytoplankton whose intracellularly produced calcite plates, or coccoliths, have been the dominant source of calcium carbonate in open ocean settings since the Cretaceous. An open question is whether their calcification has been affected by variation in environmental parameters such as the ocean carbon system over geological timescales. Previous methods using circular polarized light microscopy allowed only the thickness of small coccoliths thinner than 1.5 microns to be quantified but prior to the Pliocene, a significant fraction of the coccoliths exceed this thickness and have not been quantifiable. Here, we implement a new approach for calibration of circular polarized light microscopy enabling us to quantify coccoliths which feature calcite up to 3 microns thick. We apply this technique to evaluate the evolution of calcification in the Reticulofenestra from the Early Oligocene to Early Miocene in exceptionally well-preserved sediments from the Newfoundland margin. Through this time interval, coccolith thickness and the scale-invariant shape factor kse vary by about 20 % around the mean thickness of 0.37 µm and mean kse of 0.16. Lower shape factors characterize samples with higher relative abundance of dissolution-resistant nannoliths, suggesting that dissolution may contribute to thinning of placoliths. We therefore define temporal trends in calcification only in samples in which the assemblage suggests minimal dissolution. Lowest kse characterizes the Middle Oligocene, and highest kse around 18 Ma in the Early Miocene. High ocean DIC concentrations have been proposed for this period of the Miocene, and may be one factor contributing to high coccolith kse.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".