Southern ocean glacial-interglacial variations in delta- 238 U

• Main Author: Kuzminov, Amy Marie
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2018
• Subjects: Southern Ocean
• Online Access: https://dx.doi.org/10.7282/t3-54sn-2m80; https://rucore.libraries.rutgers.edu/rutgers-lib/59149/

Sedimentary uranium (U) abundance peaks have been aligned with changes in glacial-interglacial cycles in the Southern Ocean sediment record. These peaks have been interpreted to reflect changes in the biological pump efficiency, with high U abundance associated with high carbon burial. Uranium isotopic composition (238U/235U; δ238U) may provide additional information about the depositional conditions and biogeochemical cycling. In this study, I measured δ238U from samples spanning glacial-interglacial cycles at RC13-254 (48.57oS, 5.127oE, 3636 mbss), an Atlantic sector Southern Ocean core, which has previously documented pronounced U peaks. Uranium-isotope composition showed a broad range, with a positive excursion (0.07 to 0.31 ‰) in the glacial period and a seawater-like signal in the interglacials (-0.67 to -0.30 ‰). The glacial positive excursion coincided with the elevated authigenic U concentrations. The magnitude of the δ238U excursion is similar to published values for the Black Sea. Unlike the euxinic conditions in the Black Sea, studies from nearby locations show that the bottom water remained oxygenated during glacial periods. In previous studies, δ238U has been applied as a global redox proxy to reconstruct the extent of anoxia, owing to the conservative oceanic behavior of U. My results show that variability in δ238U reflects local processes, including carbon burial rate. Therefore, rather than being a global ocean redox proxy, δ238U should be treated as a localized signature of the carbon burial rate.