Os and Tl isotope measurements from 109D-C and ODP Hole 121-756B

• Main Authors: Nielsen, Sune G, Gannoun, Abdelmouhcine, Marnham, Charles, Burton, Kevin W, Halliday, Alex N, Hein, James R
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2011
• Subjects: 121-756B; ANTIPODE; ANTP-109D-C; Dredge; DRG; DRILL; Drilling/drill rig; Joides Resolution; Leg121; Melville; Ocean Drilling Program; ODP; South Indian Ridge; South Indian Ocean; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.817623; https://doi.org/10.1594/PANGAEA.817623

This study presents a high-resolution record of osmium and thallium isotopes in a ferro-manganese (Fe-Mn) crust from the Indian Ocean, Antipode 109D-C. These results, when combined with additional new Os isotope data from ODP Hole 756B in the southeast Indian Ocean, define a new best estimate for the age at the base of this crust of ~6.5 Ma, which is significantly different from a previous estimate of ~15 Ma based on Co-flux modeling. The Tl isotope record obtained for the Indian Ocean resembles that for the Pacific Ocean with a small but well-defined increase occurring over the last ~5 Myr. This contrasts with two records from the Atlantic Ocean which do not have resolvable variations. Ocean basin-scale Tl isotope variation may be inconsistent with the inferred modern marine residence time for Tl of ~20 kyr but could be explained by an increase in ocean crust production rates in the Pacific and Indian oceans since ~10 Ma. The improved age model for 109D-C reveals that the Hf isotope composition of Indian Ocean bottom waters has remained homogenous over the last ~6 Myr. Thus, this isotope system does not bear any evidence that the influence of North Atlantic Deep Water in the formation of Indian Ocean bottom waters has changed during that time. However, because of the lack of knowledge about Hf isotopes as a tracer of ocean circulation, we cannot conclude that export of NADW decreased over the last 6 Myr.