Survival strategies of Antarctic vegetation during extensive glacial expansion across the Oligocene/Miocene Transition
Bibliographic record
Abstract
Abstract. Antarctica’s terrestrial ecosystems are at risk from a rapidly changing climate. Investigating how Antarctica’s vascular plants responded to major climatic variations in the geological past, especially under atmospheric CO2 values similar to modern and future projections, may provide insight into how organisms could migrate across the continent as conditions change. Here, we investigate vegetation trends across the Oligocene/Miocene Transition (OMT, ~23 Myr), one of the largest transient glaciations of the Cenozoic. Despite extensive ice sheet expansion, Antarctic vegetation survived throughout this glacial episode. We use compound specific isotope trends (δ13C and δ2H) of plant waxes in an Antarctic proximal sediment core from the Ross Sea (Deep Sea Drilling Project site 270) to investigate the response and survival mechanisms of Antarctic vegetation during this event. We detect the first observation of a marked negative n-alkane δ13C excursion over the OMT, coupled with a shift to more positive n-alkane δ2H. We interpret this as plants sacrificing water use efficiency to maintain photosynthesis and carbon uptake during increasing glacial conditions, as atmospheric CO2 decreased and orbital configurations favoured shorter, colder growing seasons with lower light intensity. We consider further drivers of these isotopic trends to be enhanced aridity, and a shift to a stunted, low elevation vegetation. These findings establish the adaptability of ancient Antarctic vegetation under atmospheric CO2 conditions comparable to modern, and mechanisms that allowed vegetation to keep a foothold on the continent despite prolonged hostile conditions.
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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 | 0.001 |
| 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) | 0.001 | 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".