Neodymium isotope constraints on provenance, dispersal, and climate‐driven supply of Zambezi sediments along the Mozambique Margin during the past ∼45,000 years

Abstract

Marine sediments deposited off the Zambezi River that drains a considerable part of the southeast African continent provide continuous records of the continental climatic and environmental conditions. Here we present time series of neodymium (Nd) isotope signatures of the detrital sediment fraction during the past 45,000 years, to reconstruct climate-driven changes in the provenance of clays deposited along the Mozambique Margin. Coherent with the surface current regime, the Nd isotope distribution in surface sediments reveals mixing of the alongshore flowing Zambezi suspension load with sediments supplied by smaller rivers located further north. To reconstruct past changes in sediment provenances, Nd isotope signatures of clays that are not significantly fractionated during weathering processes have been obtained from core 64PE304-80, which was recovered just north of the Zambezi mouth at 1329 m water depth. Distinctly unradiogenic clay signatures (E Nd values <214.2) are found during the Last Glacial Maximum, Heinrich Stadial 1, and Younger Dryas. In contrast, the Nd isotope record shows higher, more radiogenic isotope signatures during Marine Isotope Stage 3 and between 15 and 5 ka BP, the latter coinciding with the timing of the northern hemisphere African Humid Period. The clay-sized sediment fraction with the least radiogenic Nd isotope signatures was deposited during the Holocene, when the adjacent Mozambique Shelf became completely flooded. In general, the contribution of the distinctly unradiogenic Zambezi suspension load has followed the intensity of precession-forced monsoonal precipitation and enhanced during periods of increased southern hemisphere insolation and high-latitude northern hemispheric climate variability.

South African Climates (Agulhas LGM Density Profile)

“…A particularly intriguing feature of records from both stalagmites in coastal caves in South Africa (Bar-Matthews et al, 2010) and marine sediment cores at the southeast African continental margin (Schefuß et al, 2011;Wang et al, 2013;Ziegler et al, 2013;Just et al, 2014;van der Lubbe et al, 2014van der Lubbe et al, , 2016Weldeab et al, 2014;Simon et al, 2015b) is the indication of recurrent but spatially variable millennial oscillations of rainfall patterns. Such variability demands highly resolved spatial and temporal records as well as numerical simulations.…”

“…This fluvial sediment mixes with current-transported and biogenic material and forms a major component of the extensive current-controlled sedimentary deposits that characterize the Mozambique margin. Recent work on shorter cores demonstrates that the strata here have the potential to provide comprehensive proxy records of regional oceanographic changes as well as changes in hydrological conditions of the African precipitation belt in southeastern Africa (e.g., Schefuß et al, 2011;Schulz et al, 2011;Wang et al, 2013;Weldeab et al, 2013Weldeab et al, , 2014Just et al, 2014;van der Lubbe et al, 2014van der Lubbe et al, , 2016.…”

Untitled

“…A more distal, deeper coring site ~200 km north of the Zambezi River mouth at ~1300 m water depth provides continuous sedimentary records spanning the last ~40 ky. A high-resolution record of neodymium isotopes (εNd) in the lithogenic clay fraction from one of the cores (64PE304-80) is interpreted to reflect changes in Zambezi sediment discharge relative to sediment transported from more northern sources by the strong net southward eddy-induced flow through the Mozambique Channel (van der Lubbe et al, 2016). The reconstructed intervals of enhanced Zambezi discharge are in agreement with the δD rainfall record obtained from a parallel core (GIK16160-30; Wang et al, 2013) after correction for the C 3 -C 4 vegetation abundances.…”

“…A particularly intriguing feature of both emergent records from stalagmites in coastal caves in South Africa (Bar-Matthews et al, 2010) and marine sediment cores at the southeast African continental margin (Schefuß et al, 2011;Wang et al, 2013;Ziegler et al, 2013;Just et al, 2014;van der Lubbe et al, 2014van der Lubbe et al, , 2016Weldeab et al, 2014;Simon et al, 2015b) is the indication of recurrent but spatially variable millennial oscillations of rainfall patterns.…”

“…This fluvial sediment mixes with current-transported and biogenic material and form a major component of the extensive current-controlled sedimentary deposits that characterize the Mozambique margin. This sediment has the potential to provide comprehensive proxy records of regional oceanographic changes as well as changes in hydrological conditions of the African precipitation belt in southeastern Africa (e.g., Just et al, 2014;Schefuß et al, 2011;Schulz et al, 2011;Wang et al, 2013;Weldeab et al, 2013Weldeab et al, , 2014van der Lubbe et al, 2014van der Lubbe et al, , 2016.…”