Palaeoecological implications from an 11,500 year old thermokarst lake in Northwest Canada (Herschel Island, Yukon) \n \n
Notice bibliographique
Résumé
A thermokarst lake sediment core from the centre of Herschel Island was analysed in order to reconstruct post-glacial palaeoenvironmental changes and landscape dynamics in this part of the Western Canadian Arctic. The ice-rich island in the Southern Beaufort Sea is of outstanding scientific interest since it archives the northernmost terrestrial lake record of the Yukon Territory. Besides previously published sedimentological and biogeochemical analyses, we applied micropaleontology and hydrochemistry on pore waters. \nThe formation of the lake occurred during the Holocene Thermal Maximum, around 11.5 to 10.0 cal ka BP. Here, brackish shallow water ostracods (Heterocyprideis sorbyana) and foraminifers (Cribroelphidium excavatum) prevailed and electrical conductivity of pore waters of approximately 13,000 µS/cm demonstrates a marine influence. Reworking from older sediments, however, cannot be ruled out completely. The lake development until about 7.0 cal ka BP was associated with a period of intense thermokarst activity and the pollen-based temperature reconstruction shows that TJuly was greater than 8°C during the early Holocene at the initial stage of Lake Herschel. The freshwater ostracod Cytherissa lacustris was the dominant species. \nPollen concentrations and influx were low prior to 6.0 cal ka BP and subsequently increased, especially in the past thousand years. The ostracod association became more diverse in the Mid-Holocene; Fabaeformiscandona levanderi is the dominant species besides C. lacustris. The reconstructed TJuly were lower from 7.0 to 5.5 cal ka BP and relatively high but variable until 1.8 cal ka BP. Pollen of Cyperaceae and Poaceae were generally the most abundant taxa. However, Poaceae pollen increased in sediments younger than 3.0 cal ka BP and Cyperaceae pollen decreased after 1.8 cal ka BP. Pollen from several shrubs were found in relatively high quantities, including Alnus, Juniperus and Betula; only the latter is found in the recent tundra environment. The ostracod associations show a persistent lake with high input of allochthonous material and possibly elevated salinity. \nA change in the sedimentation rate between 1.8 to 0.9 cal ka BP is explained either by a hiatus due to modified drainage conditions or slumping. Bioproductivity increased, as shown by a richer fauna (Chironomidae). Foraminifers are abundant and occur together with fresh and brackish water ostracods reflecting elevated salinity. The change of facies is also recorded in pore waters chemistry characterized by lower pH values, slightly higher electrical conductivity and increased Ca, Mg, Mn, Sr and SO4 ion content. \nThe final late-Holocene phase, beginning by 0.9 cal ka BP, was characterized by an elevated and variable NO3 ion content in pore waters, a poorer ostracod fauna and disappearance of foraminifers, as well as pollen-based TJuly below 7°C. \n
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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 | 0,002 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| 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 ».