Water mass gradients of the mid-depth Southwest Atlantic during the past 25,000 years

• Published in: Earth and Planetary Science Letters
• Main Authors: Pöppelmeier, F., Gutjahr, Marcus, Blaser, P., Oppo, D. W., Jaccard, S. L., Regelous, M., Huang, K.-F., Süfke, F., Lippold, J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: Antarctic; Antarc*
• Online Access: https://oceanrep.geomar.de/id/eprint/48328/; https://oceanrep.geomar.de/id/eprint/48328/1/Po%CC%88ppelmeier%20et%20al.pdf; https://oceanrep.geomar.de/id/eprint/48328/7/Po%CC%88ppelmeier%20et%20al.%20%282020%29%20EPSL%20supplement%201.pdf; https://oceanrep.geomar.de/id/eprint/48328/8/Po%CC%88ppelmeier%20et%20al.%20%282020%29%20EPSL%20supplement%202.xlsx; https://doi.org/10.1016/j.epsl.2019.115963

Highlights • Five new authigenic Nd isotope records from the mid-depth Southwest Atlantic. • The Holocene εNd depth gradient is indicative of the different water masses. • No Nd isotope depth gradient during the last glacial and early deglaciation. • Nd end member properties of Antarctic Intermediate Water potentially changed by dust. • Combination of C and εNd yield improved constraints on glacial water mass boundary. Abstract Antarctic Intermediate Water (AAIW) plays a central role in the Atlantic Meridional Overturning Circulation (AMOC) as the return flow of Northern Sourced Water (NSW) and is therefore of significant importance for the global climate. Past variations of the boundary between AAIW and NSW have been extensively investigated, yet available results documenting the prevailing depth of this boundary and the southern extent of NSW during the last ice age remain ambiguous. Here, we present five new timeseries focusing on the authigenic neodymium isotope signal in sediment cores retrieved from the Southwest Atlantic covering the past 25,000 years. The sites are situated along the southern Brazil Margin and form a bathymetric transect ranging between 1000 and 3000 m water depth, encompassing the modern water mass boundaries of AAIW and NSW and therefore allow their reconstruction since the Last Glacial Maximum (LGM). The new Nd isotope records show little change between the LGM and early deglaciation as well as relatively homogeneous values over the full depth range of the cores during these times. These results strongly contrast with epibenthic foraminiferal stable carbon isotope records ( C) from the same sites which exhibit highest glacial values at mid-depths, presumably related to NSW mixing into southern sourced water. We propose that the discrepancy between these two independent water mass proxies is partly related to changes in Nd end member properties of glacial AAIW. The combination of elevated glacial dust fluxes and, as a result, sustained export productivity caused high sinking particle ...