Constraints on Atmospheric CO2 Obtained from Fossil Metasequoia for the Middle Eocene Polar Forests on Axel Heiberg Island, Nunavut, Canada
Bibliographic record
Abstract
Fossils from Paleogene High Arctic deposits provide some of the clearest evidence of greenhouse climates and offer the potential to improve our understanding of Earth system dynamics in a largely ice-free world. One of the most well-known and stunningly-preserved polar forests, Napartulik, crops out of middle Eocene (47.9-37.8 Ma) sediments on eastern Axel Heiberg Island, Nunavut, Canada. An abundance of data from Napartulik suggest mean annual temperatures over 30 °C warmer than today and atmospheric water loads 2× above current levels. Despite decades of intensive paleobotanical, paleoecological, and paleoclimatological work, there are currently no constraints on atmospheric CO2 levels from Napartulik or from any other High Arctic forest site. This lack of CO2 information strongly limits our ability to understand high-latitude climate dynamics during globally-warm times. Here, I test a new gas-exchange based approach for reconstructing paleo-CO2 on living Metasequoia glyptostroboides Hu et Cheng and then apply the model to fossil M. occidentalis (Newberry) Chaney from six forest layers at Napartulik. Reconstructed modern CO2 of 445 ppm (354-558 ppm at 95% confidence) is in good agreement with the current ambient CO2 (396 ppm) and validates model application to Metasequoia Miki. Individual fossil forest layer reconstructions vary between 405-489 ppm with a site mean reconstruction of 437 (337-564 ppm at 95% confidence). These reconstructions provide the first direct evidence for CO2 from a High Arctic polar forest and indicate that the warm, equable conditions present at Napartulik during the middle Eocene were maintained under CO2 concentrations ~1.6× above pre-industrial levels. These results are consistent with high long-term climate sensitivity to CO2, even during times with little ice, suggesting that some fundamental climate feedbacks and/or forcings for enhancing polar warmth during greenhouse periods remain poorly understood.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".