Deep circulation changes in the South Atlantic since the Last Glacial Maximum from Nd isotope and multi-proxy records

• Published in: Earth and Planetary Science Letters
• Main Authors: Wei, R., Abouchami, W., Zahn , R., Masque , R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2016
• Subjects: Southern Ocean; NADW; North Atlantic Deep Water; North Atlantic; Planktonic foraminifera
• Online Access: http://hdl.handle.net/11858/00-001M-0000-002A-2246-4

We report down-core sedimentary Nd isotope (epsilon(Nd)) records from two South Atlantic sediment cores, MD02-2594 and GeoB3603-2, located on the western South African continental margin. The core sites are positioned downstream of the present-day flow path of North Atlantic Deep Water (NADW) and close to the Southern Ocean, which makes them suitable for reconstructing past variability in NADW circulation over the last glacial cycle. The Fe-Mn leachates epsilon(Nd) records show a coherent decreasing trend from glacial radiogenic values towards less radiogenic values during the Holocene. This trend is confirmed by epsilon(Nd) in fish debris and mixed planktonic foraminifera, albeit with an offset during the Holocene to lower values relative to the leachates, matching the present-day composition of NADW in the Cape Basin. We interpret the epsilon(Nd) changes as reflecting the glacial shoaling of Southern Ocean waters to shallower depths combined with the admixing of southward flowing Northern Component Water (NON). A compilation of Atlantic epsilon(Nd) records reveals increasing radiogenic isotope signatures towards the south and with increasing depth. This signal is most prominent during the Last Glacial Maximum (LGM) and of similar amplitude across the Atlantic basin, suggesting continuous deep water production in the North Atlantic and export to the South Atlantic and the Southern Ocean. The amplitude of the epsilon(Nd) change from the LGM to Holocene is largest in the southernmost cores, implying a greater sensitivity to the deglacial strengthening of NADW at these sites. This signal impacted most prominently the South Atlantic deep and bottom water layers that were particularly deprived of NON during the LGM. The epsilon(Nd) variations correlate with changes in Pa-231/Th-230 ratios and benthic delta C-13 across the deglacial transition. Together with the contrasting Pa-231/Th-230: epsilon(Nd) pattern of the North and South Atlantic, this indicates a progressive reorganization of the AMOC to full strength ...