No detectable Weddell Sea Antarctic Bottom Water export during the Last and Penultimate Glacial Maximum

Huang Huang,Anton Eisenhauer,Marcus Gutjahr,Gerhard Kuhn

doi:10.1038/s41467-020-14302-3

Abstract

Weddell Sea-derived Antarctic Bottom Water (AABW) is one of the most important deep water masses in the Southern Hemisphere occupying large portions of the deep Southern Ocean (SO) today. While substantial changes in SO-overturning circulation were previously suggested, the state of Weddell Sea AABW export during glacial climates remains poorly understood. Here we report seawater-derived Nd and Pb isotope records that provide evidence for the absence of Weddell Sea-derived AABW in the Atlantic sector of the SO during the last two glacial maxima. Increasing delivery of Antarctic Pb to regions outside the Weddell Sea traced SO frontal displacements during both glacial terminations. The export of Weddell Sea-derived AABW resumed late during glacial terminations, coinciding with the last major atmospheric CO2 rise in the transition to the Holocene and the Eemian. Our new records lend strong support for a previously inferred AABW overturning stagnation event during the peak Eemian interglacial.

Highlights

The Southern Ocean (SO) has long been identified as the key driver in regulating atmospheric CO2 concentrations on glacial–interglacial timescales, mediating ocean
We generated seawater Pb isotope records (206Pb/204Pb and 208Pb/204Pb) from a sediment core in the Atlantic sector of the SO (ODP Leg 177, Site 1094, 53.2°S, 5.1°E, water depth 2807 m; Fig. 1), and the corresponding bottom water Nd isotope records (143Nd/144Nd, expressed as εNd) from authigenic Fe–Mn oxyhydroxides of two additional sediment cores: one located very close to ODP Site 1094 (PS1768-8, 53.6°S, 4.5°E, water depth 3299 m) and another located on the northern continental slope of the Antarctic Filchner–Rønne Ice Shelf (PS15993, 74.1°S, 27.7°W, water depth 2487 m; Fig. 1)
Least radiogenic Pb isotope compositions at ODP Site 1094 were recorded during the Last Glacial Maximum (Fig. 2b, c)

Summary

Results

Least radiogenic (lowest) Pb isotope compositions at ODP Site 1094 were recorded during the Last Glacial Maximum (Fig. 2b, c) Both 206Pb/204Pb and 208Pb/204Pb experienced a major change to significantly more radiogenic Pb isotopic compositions during the early deglaciation until the onset of the Antarctic Cold Reversal (~15 ka BP) during which the ambient εNd at Site PS1768-8 was invariant (Fig. 2g), suggesting changes in the upper SO-overturning cell only. The clearly defined change in εNd was associated with a second smaller excursion toward more radiogenic Pb isotopic compositions (Fig. 2b, c), an increase in East Antarctic ice core EDML δ18O33 (Fig. 2j), and the second rise in atmospheric pCO2 (Fig. 2a), and coincided with increasing Ross Sea AABW export in the Pacific sector of the SO34 (Fig. 2h)

Discussion

TN057–13PC

18.9 ODP 1094