1 Ma of water mass provenance in the South Atlantic Ocean revealed by authigenic neodymium isotopes in ODP 1093

The deep Southern Ocean (SO) circulation is of major significance for understanding of the ocean´s impact on Earth’s climate as uptake and release of CO_­­­2 strongly depend on the redistribution of differently ventilated water masses.

Here, we present new authigenic neodymium isotope data (εNd) of the deep-sea sediment ODP1093 in the Southern Atlantic that reveals several systematic temporal glacial-interglacial changes in a range of 6.3 e-units. Assuming Nd-isotopes as mostly conservative tracer and neglecting possible reginal influences, the observed radiogenic εNd values of up to -2.5 during peak glacial periods suggest a predominance of glacial PDW at depths of >3 km. This results in a volume increase of carbon-rich water, aiding in atmospheric CO₂ drawdown during glacials.

The ability of εNd to trace water mass changes relies on the sensitivity of water masses to conservative Nd-isotope mixing. The εNd gradient ΔεNd is here defined as the North-South difference in εNd/10° latitude and is a measure for the sensitivity to changes in εNd signature over a given distance. Compared to further existing εNd records across the Atlantic Ocean the calculated mean εNd gradient for the Atlantic Ocean is approximately 0.89 ε-units/10° latitude and the εNd values of ODP1093 are constantly the most radiogenic. This suggests, that changes in ocean circulation during glacial-interglacial transitions are not purely induced by the Northern Hemisphere deep convection and southward flow but rather strongly influenced by equally strong changes of the SO circulation. This reinforces the importance of the SO in past and future climate changes.