A combined approach in determining late Quaternary fluctuations in deep water masses derived from neodymium isotopes, faunal variations and d13C in foraminifera along the western continental slope of South Africa

The Meridional Overturning Circulation is crucial in regulating Earth‘s climate and is composed of various ocean currents, playing an important role in heat exchange and the distribution of water masses. The transfer of water masses also affects regional carbon storage, nutrient contents, temperature, evaporation and precipitation balances in the oceans. The advancement in our understanding of the interaction between these water masses can contribute to our current knowledge on the state of the oceans. The use of foraminiferal isotope geochemistry and faunal analyses has greatly contributed to understanding the changes our oceans have undergone in the Quaternary. The purposes of this study are to determine what the timescales were at which the bottom water masses were changing and to determine at which periods the influence of these water masses were the strongest. A combination of neodymium and δ¹³C isotopes, as well as faunal abundance records in this study, were derived from foraminifera in cores recovered at 3522 m and 3631 m water depths along the western margin of South Africa to investigate deep water mass variability in the southeast Atlantic Ocean during the last two glacial terminations. The neodymium isotope composition (¹⁴³Nd/¹⁴⁴Nd), expressed as εNd, were measured in planktic foraminifera from the western continental slope of South Africa. This isotopic tracer is useful in tracking deep water masses on the sub-millennial scale owing to the short residence time of Nd in seawater. Foraminifera (single-celled protists) microfossils acquire the bottom water Nd signature upon burial that can be useful in providing insight into the variability of deep water masses. In addition to the εNd records, the foraminiferal δ¹³C results also support the results of the neodymium isotopes. These records in this study are largely correlative with the abundances of benthic species Cibicidoides wuellerstorfi, reflecting shifts between the southern-sourced Antarctic Bottom Water (AABW) and the northern-sourced North Atlantic Deep Water (NADW) during the last two glacial terminations at ~130 ka and ~18 ka. The εNd, δ¹³C results and C. wuellerstorfi relative abundances indicate an intensified inflow of southern-sourced water masses and weakened NADW inflow along the margin during peak glacial periods MIS 6 and MIS 2. The terminations of these peak glacials were more beneficial to stronger penetration of NADW into the southeast Atlantic.