Indian-Atlantic subsurface- and deep-water mass exchange over the past 600 kyrs
Résumé
The water-mass exchange between Indian and Atlantic oceans, occurring through Agulhas current and its leakage, is one of the return flows of global thermohaline circulation. To investigate the Indian-Atlantic subsurface- and deep-water mass exchange
over the last 600 kyrs, we analyzed Nd isotopic composition (εNd) on planktic foraminiferal authigenic fraction, epibenthic foraminiferal stable carbon isotopes ( δ13C), and planktic foraminiferal warm species in the sediment core MD96-2077 (SW Indian Ocean, 3,781 m). At present, this sedimentary sequence is bathed by modified Circumpolar Deep Water and it is below the flow path of the Agulhas current. The obtained εNd and δ13C records show glacial/interglacial variability ranging between -8.0 and -10.3, and between -1.1 and 0.7 ‰, respectively, with higher εNd values coinciding with more depleted δ13C values and vice versa. Planktic warm species relative abundances vary from 1.2 to 37.6 % with a marked increase during terminations. The most striking feature of our record is systematic very low glacial δ13C values similar to
records from the deep SE Atlantic (ODP Site 1090). Relationship between εNd and δ13C of the studied core compared with existing records indicates similar trends with deep SE Atlantic water masses, suggesting that deep glacial carbon-rich water extended
from the SE Atlantic into the SW Indian Ocean. Contribution of Indian deep water cannot account for the low benthic δ13C values observed at the study site. The increases in warm planktic species relative abundances during the terminations are coincident with
reconstructed Agulhas leakage peaks, suggesting a possible link between Agulhas current and Agulhas leakage during terminations. To better constrain the deep-water variability of the northern and southern source water masses arriving at the SW
Indian Ocean, we are analyzing the foraminiferal εNd in core MD96-2052 (2,627 m water depth) from the Mozambique Channel. This core is currently occupied by North Atlantic Deep Water (NADW) as confirmed by an εNd value of -11.7 in the core-top sample, in the range expected from present-day NADW. Based on this new record, we will investigate the changes in northern and southern source waters together with subsurface water conditions
Domaines
Sciences de la TerreOrigine | Fichiers produits par l'(les) auteur(s) |
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