Temporal Variability of Nepheloid Layer Structures on Continental Slope Environments: Natural and Anthropogenic Processes
Notice bibliographique
Résumé
This Thesis aims to investigate the contribution of the deep-sea trawling activities, besides that of natural processes, to the sediment dynamics in different continental slope areas, particularly in the NW Mediterranean and the NE Pacific basins. The temporal and spatial variability of the water column turbidity structure in the Foix Canyon (NW Mediterranean) are studied by analysing two months of hydrographic profiles collected by an autonomous hydrographic profiler. The water column turbidity structure consists in intermediate nepheloid layers (INLS) developed between 300 and 500 m water depth and above the canyon rims, and INLs and near-bottom nepheloid layers (BNLs) confined inside the canyon between 650 and 800 m water depth. Data from fishing vessels positioning during the deployment period reveals that the presence and depths of the observed INLs and BNLs depend on the operating depths of bottom trawlers and on the specific fishing grounds being exploited by the local trawling fleet. This data strongly suggests that bottom trawling activities in the study area are the main driver of the turbidity increases observed in the water column. The spatial and temporal variations on the water column turbidity structure and near- bottom suspended sediment transport associated to both natural processes (storms, river floods, and dense shelf water cascading, DSWC) and bottom trawling activities are also analysed for three months in the Palamós Canyon (NW Mediterranean) using an autonomous hydrographic profiler and near-bottom instrumentation installed in a mooring, covering a trawling closure period, and an active trawling period. Periods of enhanced water turbidity during the trawling closure period are associated with storms and DSWC events, transporting turbid dense waters into the canyon. In absence of such energetic events, the water column remains unchanged, displaying the lowest suspended sediment concentrations of the recording period, until the trawling season began. INLs (250 and 350 m depth) and BNLs (> 500 m depth) are found at the water depths where trawling grounds from the Palamós Canyon are located. High near-bottom suspended sediment fluxes are sporadically registered during the trawling closure associated with a major wet eastern storm and a DSWC event, whereas smaller but more frequent increases in near-bottom suspended sediment fluxes are recorded during trawling activities. However, the continued bottom trawling activity, at least for 30 days of monitoring, produces an accumulated suspended sediment transport similar to that generated by a major DSWC event. Considering that bottom trawling in Palamós Canyon is practised on a daily basis throughout the year, except for the 2-month trawling closure period, a much larger contribution of anthropogenically derived suspended sediment transport can be expected. The temporal evolution of the hydrographic and nepheloid layer structure in the upper slope of Vancouver Island (British Columbia, Cascadia margin, NE Canadian Pacific) is also assessed by analysing four months of sensor data from the NEPTUNE observatory. The water column turbidity structure during the study period consists in surface nepheloid layers (SNLs) (<100 m depth) associated to primary and secondary productivity, INLs between 150 and 300 m depth at the shelf-break and upper slope domain, and BNLs developed at deeper continental slope regions (~400 m depth). Strong fall storms occurring during the monitored months seem to generate the more intense INLs found at shelf-break depths. However, not all the recorded INLs coincide with the more intense storms, indicating that other sediment resuspension mechanisms might be modulating these INL detachments. Results from this study suggest that, in combination with the regional currents, the presence of continuous fishing along the continental slope off Vancouver Island, contributes to the advection of suspended sediment particles, playing a major role in their transference along the margin as nepheloid layers.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
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 | 0,000 | 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 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,004 | 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.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».