Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi
Bibliographic record
Abstract
Relating atmospheric CO 2 to δ 13 C of calcifying phytoplankton is often used as a proxy to reconstruct paleo-CO 2 .Therefore, a firm undertanding of how living cells fractionate carbon under different environmental conditions (known as vital effects) is necessary when interpreting δ 13 C values.In this study, we measured the isotopic fractionation of carbon in organic matter (ε p ) in the globally distributed, bloom-forming coccolithophorid Emiliania huxleyi grown in continuous culture under nutrient-replete conditions with growth rate limited by light or temperature.At a constant temperature of 18°C, growth followed a hyperbolic function of irradiance.At low irradiance levels, changes in ε p were highly correlated with growth rate.However, as growth became light-saturated, ε p declined with increasing light intensities.When temperature was increased from 7 to 18°C at a constant photon flux density, equilibrium partial pressure CO 2 concentrations ([pCO 2 ]) decreased from 17 to 13 µM, and ε p values declined from 25 to 19 ‰.As temperature was increased further to 26°C, [pCO 2 ] declined to 10 µM and ε p increased to 25 ‰.This non-linear pattern in isotopic fractionation is consistent with the induction of a carbon-concentrating mechanism at low [pCO 2 ] that replenishes the internal inorganic carbon pool with isotopically lighter carbon.In this study, we present an empirical model that predicts this non-linear behavior, and we validate this model with experimental data.These results suggest extreme variability in the isotopic fractionation of carbon in the bulk organic pool in E. huxleyi that precludes the reconstruction of pCO 2 from isotopic measurements without a priori knowledge of temperature.
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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".