Glacial‐interglacial variability in the eastern tropical North Pacific oxygen minimum zone recorded by redox‐sensitive trace metals
Notice bibliographique
Résumé
Changes in the intensity of the oxygen minimum zone (OMZ) in the eastern tropical North Pacific over the past 140 kyr are recorded as enrichments and depletions of redox‐sensitive metals in sediments of two piston cores, one within and one below the modern OMZ, from the continental margin off Mazatlán, Mexico (22°41′N, 106°28′W). Concentrations of Al (7.7 ± 0.6%), Ti (0.37 ± 0.03%), Fe (3.1 ± 0.25%), Mn (320 ± 31 ppm), and Ba (560 ± 82 ppm) in core NH15P (within the OMZ at 420 m water depth) were relatively constant over the last 110 kyr. In contrast, concentrations of Cd (4.8 ± 2 ppm), Cu (29.8 ± 9.1 ppm), U (9.1 ± 3.7 ppm), Mo (12.1 ± 5.0 ppm), V (138.2 ± 51.9 ppm), and Re (45.8 ± 25.5 ppb) were all at least 30% higher in interglacial stages compared to glacial stages. Concentrations of Al (7.4 ± 0.3%), Ti (0.35 ± 0.03%), Fe (3.5 ± 0.4%), and Mn (385 ± 77 ppm) in core NH22P (below the OMZ at 2025 m water depth) were comparable to those in core NH15P, while concentrations of Ba (1662 ± 292 ppm) were about a factor of three higher. In contrast, concentrations of Cd (0.9 ± 0.3 ppm), U (6.6 ± 0.9 ppm), Mo (3.2 ± 1.2 ppm), V (81.8 ± 10.1 ppm), and Re (25.4 ± 12 ppb) were lower in sediments of comparable age than the concentrations of these same metals in the OMZ core, and the differences in their concentrations over glacial‐interglacial cycles were less pronounced than those in shallower core. Comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of Cu, Ba, and perhaps Cd to the sediment, whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions U, Re, Mo, and V. Changes in the depth at which Re and Mo precipitated in the sediments and in the Re/Mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time. Re and Mo removal depths were shallower and Re/Mo ratios were lower at the OMZ site than in deeper water, suggesting that a more reducing environment prevailed over time at the shallower site. Although the redox state of the waters and sediment at both sites varied over glacial‐interglacial cycles, the OMZ likely was never anoxic in the last 140 kyr. This variability in redox state could be attributed to changes in regional export productivity, changes in ocean circulation, or a combination of both processes. A paleoproductivity reconstruction from biogenic Ba data suggests that glacial productivity was considerable lower than it was during interglacial stages. Model results suggest that the oxygen penetration depth, an indicator of sediment redox state, changed less than 1 cm as a result of the change in productivity. Changes in oxygen penetration depth estimated from Re and U removal depths are significantly larger, suggesting that changes in ventilation are a more important control on sediment redox state. Overall, trace metal results confirm the tight coupling between ocean circulation, marine productivity, and global change.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».