Hallmaier, Moritz, Rückert, Eva M., Chen, Yugeng, Link, Jasmin M., Lizio, Riccardo, Lohmann, Gerrit, Gutjahr, Marcus and Frank, Norbert (2025) Glacial Southern Ocean deep water Nd isotopic composition dominated by benthic modification. Scientific Reports, 15 (1). Art.Nr. 2586. DOI 10.1038/s41598-025-86350-y.

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Abstract

The deep Southern Ocean (SO) circulation plays a key role in the storage and release of CO2 in Earth's climate system. The uptake and release of CO2 strongly depend on the redistribution of well and poorly ventilated deep ocean water masses. Recently, evidence was found for possible stronger Pacific deep water overturning and subsequent intrusion into the SO during periods of reduced AMOC. Here, we present new authigenic neodymium isotope data (epsilon Nd) from two sites within the Atlantic sector of the SO to assess the distribution of water masses during the past 150 ka. PS 1768-8 (3299 m) and ODP 1093 (3624 m) feature unradiogenic interglacial epsilon Nd-signatures, which are typical for present-day Weddell Sea sourced Antarctic Bottom Water (AABW) (epsilon Nd similar to - 8.6). During peak glacial periods, radiogenic epsilon Nd-values ranging from similar to -2.5 to -3.5 are recorded. This may be the result of either a strong Pacific or benthic flux influence on the Nd budget in the Atlantic sector of the SO. However, an ocean circulation model indicates no stronger Pacific influence during glacials. Thus, we suggest that an increase in benthic flux influences the SO Nd budget, which is modulated by ACC strength. The more stratified and more sluggish deep water supports decreased vertical mixing and increased glacial carbon storage without the intrusion of poorly ventilated Pacific waters. The occurrence of highly radiogenic glacial bottom water or porewater signatures requires reassessment of the glacial Southern Hemisphere epsilon Nd-endmember for water mass sourcing reconstructions in the glacial Atlantic.

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