Controls on High Sedimentary Accumulation of Organic Matter During Cretaceous Oceanic Anoxic Event 2, Southeast Newfoundland Ridge, North Atlantic Ocean
Bibliographic record
Abstract
Deoxygenation and low-oxygen zones are occurring in modern oceans as a consequence of excessive nutrients in runoff. Solving this issue necessitates understanding the relationships between dissolved oxygen, ocean chemistry, inputs of atmospheric CO2, and climate change. As an analog, this study looks back 94 Ma to Oceanic Anoxic Event 2 (OAE2), a global geologic event triggered by greenhouse conditions from increased volcanism. The global carbon cycle was disrupted by OAE2, increasing burial of organic matter on the seafloor. Environmental changes were studied below, within, and above OAE2 sediments from deep-sea sediment cores drilled at Integrated Ocean Drilling Program Site U1407, Southeast Newfoundland Ridge. By analyzing the geochemistry and microscopic fossils, an interval of time within OAE2 was identified when excess nutrients led to oxygen levels so low that microorganisms could not survive on the seafloor and toxic sulfides were present in pore spaces of sediments. After OAE2, nutrient inputs declined, the ocean reoxygenated, and microorganism abundance and diversity recovered. The abnormal OAE2 environmental conditions impacted the sizes and community assemblages of benthic foraminifera, common protists in oceans over the past 500 Myr. To analyze foraminifera, correct sieve sizes for preparing them must be selected so that shell size does not bias results. Abundances recovered from sieves with standard >63 μm and 38-63 μm openings were compared to assess whether key environmental taxa or community trends were lost using larger-sized openings. General trends in both sizes were relatively similar, and no key taxa were lost, so counting large abundances of 38-63 μm shells was not proven time-effective. For >63 μm foraminifera, significant differences in their assemblages were observed at the Cenomanian–Turonian boundary hiatus at the base of the organic-carbon-rich layer deposited during OAE2. Many taxa presumed extinct after the Cenomanian were discovered further up-core in the Turonian, indicating they survived elsewhere and re-populated the area once conditions improved. Future organismal responses to ongoing climate changes that affect local environments will occur under multiple and cumulative stressors, both natural and anthropogenic. Therefore, studying analogs in the geological record provides empirical evidence for predictions of future climate change and deep-sea organismal responses.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.003 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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; both teacher heads agree on what is shown here.
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".