Sedimentary Mo isotope variability reflects climate-driven water column oxygenation changes in ferruginous Lake Towuti, Indonesia over the last ∼30 ka BP
Notice bibliographique
Résumé
Previous studies have shown the utility of Molybdenum (Mo) concentrations and isotopic compositions as sensitive recorders for changes in redox conditions in marine environments. Compared to marine settings, the much lower dissolved Mo concentrations in freshwater settings could result in enhanced sensitivity of Mo isotopic composition to the temporal variability in redox conditions. Additionally, unlike the dissolved Mo isotopic compositions in open marine environments, freshwater settings are highly influenced by site-specific factors such as catchment characteristics and in-lake processes. Here, we present sedimentary Mo concentration ([Mo]) and isotope (δ 98 Mo) data from presently stratified Lake Towuti (Indonesia) to provide insight into Mo behaviour in ferruginous (Fe-rich) and non-sulfidic freshwater settings. We find large variations in [Mo] (0.12–1.11 μg⋅g −1 ) and δ 98 Mo (−0.14 ‰ to −1.13 ‰) in lake surface sediments, which are distinct from previously reported variations found in weathering profiles of the ultramafic catchment. The [Mo] variation can partly be attributed to hydrodynamic sorting, with Mo enrichment at pelagic deep water sites distant from the major lake inflows. Sedimentary δ 98 Mo shows a distinct pattern, with generally higher values in sediments deposited in deep anoxic water compared to lower δ 98 Mo values in sediments deposited in shallow water sites above the oxycline. We attribute this δ 98 Mo pattern in Lake Towuti predominantly to redox-controlled processes. These involve the reductive dissolution of suspended laterite-sourced Fe oxides, with Mo liberation under anoxic conditions shortly below the sediment-water interface and/or water column oxycline. Above the oxycline, the formation of amorphous Fe oxides promotes the preferential adsorption of isotopically light Mo. This partial scavenging of isotopically light Mo leads to the formation of isotopically heavier dissolved Mo reservoirs. The scavenging of isotopically heavy dissolved Mo by organic matter (OM) coupled with higher OM burial rates in anoxic sediments promotes higher sedimentary δ 98 Mo ratios in sediment deposited below the oxycline, where OM is better preserved and amorphous Fe oxides are preferentially dissolved. When applying this framework of modern lake processes to a sediment piston core extending back ∼30 ka, we find δ 98 Mo variations that are similar to those observed in modern surface sediments, both above and below the oxycline. Low δ 98 Mo values in sediments deposited between ∼30 and ∼14 cal ka BP suggest deep oxygenation of the water column to the sediment-water interface. In contrast, Mo isotope signatures between ∼14 cal ka BP and the present are similar to those of present-day deep water anoxic sites, suggesting water column stratification throughout the Holocene. The water column oxygenation pattern inferred from δ 98 Mo aligns well with other independent sedimentary indicators that indicate a cooler, drier last glacial maximum with deep water column mixing, and a warmer, wetter Holocene with a stratified water column. Thus, our results imply that δ 98 Mo can be applied as an effective tracer of climate-driven changes in water column oxygenation in ferruginous and non-sulfidic settings. • Spatial [Mo] pattern in Lake Towuti is primarily controlled by hydrodynamic sorting. • Aquatic Mo isotope fractionation controlled by Fe redox cycling and OM preservation. • Sedimentary δ 98 Mo records long-term water column oxygenation.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,004 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 tête enseignante, pas un consensus.
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