Impact of deglacial and Holocene AMOC changes on the mixed layer and deepwater hydrography of the subtropical North Atlantic
Notice bibliographique
Résumé
The Atlantic meridional overturning circulation (AMOC) transports warm saline water from low to high northern latitudes where it cools, sinks down and returns southward as deepwater flow. By the heat transfer from low to high latitudes, AMOC contributes in balancing the global energy budget and thus is an important part of global climate system. Within this study the impact of AMOC changes on surface and deepwater hydrography of the subtropical North Atlantic is investigated by the use of high-resolution sediment cores from a coring site located south of the Azores at the eastern flank of the Mid Atlantic Ridge. The Azores coring site is situated in the subtropical eastern North Atlantic (NA) at the boundary between warm Subtropical Gyre Water (STG) and temperate East North Atlantic Water (ENAW) at the surface. At depth the site is located at the interface between southern sourced Lower Deep Water (LDW) and North East Atlantic Deep Water (NEADW) that consists of a mixture of northern sourced Iceland-Scotland Overflow Water (ISOW) and Labrador Sea Water (LSW). Due to its location at water mass boundaries the coring position is ideal to reconstruct coupled surface and deepwater changes. Deglacial records in centennial to decadal resolution of changes in the mixed layer and the deepwater are established. Multiproxy sea surface temperature (SST) reconstructions using Mg/Ca surface of planktonic surface and subsurface dwelling foraminifera, the alkenone undersaturation index UK´37 and foraminifera transfer function (SIMMAX) are used to gain a reliable deglacial SST records from the subtropcial NA and to decipher environmental imprints other than temperature on SST reconstructions. The combination of these SST records with stable oxygen isotope records (δ18O) from planktonic surface and subsurface dwelling foraminifera are used to derive changes in the mixed layer salinity (18Ow-ice). Additionally, variations in the STG position are reconstructed by the use of foraminifera abundance data. Deglacial changes in deepwater composition are traced by its ventilation, temperature and salinity by the coupled use of stable isotope (δ18O and δ13C) and Mg/Ca bottom water temperature (BWT) reconstructions from benthic foraminifera. This new data indicates that the position of the NA subtropical Gyre (STG) was coupled with AMOC strength over the last deglaciation and the early to mid Holocene (16 -7 ka BP). During cold deglacial and Holocene weak AMOC phases (Heinrich event 1 (H1), Younger Dryas (YD), Preboreal and 8.2 event) the STG was displaced southward. This STG displacement most probably was driven by meltwater that reached southward to the Azores coring site (38°N) as indicated by salinity reconstructions (18Ow-ice) that indicate at least a salinity decrease of 1‰ Standard Mean Ocean Water (SMOW) for the H1 and 8.2 events. Additionally a southward extension of temperate ENAW led to a SST cooling of 4.5-6°C in comparison to modern values. On the contrary the presence of relatively warm subsurface water (14°C) during the YD might indicate subsurface heat storage during this event. The new high-resolution BWT, ventilation and δ18Ow-ice record from the subtropical eastern NA indicates that the deepwater composition in the eastern North Atlantic basin changed over the last 15 ka BP in parallel to deglacial changes in surface water hydrography. A general evolution toward a warmer better ventilated deepwater was disrupted during the H1 event, the YD and the early Holocene by a less ventilated (δ13C values between 0-0.5‰), cool (1.5°C minimum BWT) and freshened water (0.5 ‰ δ18Ow-ice depletion). The parallel evolution of BWT, δ13C and δ18Ow-ice with changes in deep- and surface water compositions in the subpolar NA and with the Greenland ice core record NGRIP indicates that variations in deepwater composition over the last 15 ka BP were triggered by high northern latitude climatic processes. This new results contradict the idea that southern sourced deepwater entered the subpolar NA during cold events. In consequence the new results would imply that the NA changes contributed even to deglacial changes in the Antarctic bottom water composition and finally had an impact on changes in the deepwater stratification mode as is discussed in a new conceptual model.\n
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 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 | 0,000 | 0,000 |
| 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 ».