Glacial Southern Ocean deep water Nd isotopic composition dominated by benthic modification

Area of Science:

• Oceanography
• Paleoclimatology
• Geochemistry

Background:

• Deep Southern Ocean circulation is crucial for regulating atmospheric CO2 through deep water mass redistribution.
• Understanding water mass origins and mixing is key to reconstructing past climate dynamics and carbon cycling.
• Previous studies suggested increased Pacific deep water influence in the Southern Ocean during glacial periods with reduced Atlantic Meridional Overturning Circulation (AMOC).

Purpose of the Study:

• To investigate deep water mass distribution in the Atlantic sector of the Southern Ocean over the past 150,000 years.
• To test the hypothesis of increased Pacific deep water influence during glacial periods.
• To understand the drivers of carbon storage in the deep ocean.

Main Methods:

• Analysis of authigenic neodymium isotope ratios (ɛNd) from sediment cores at two Southern Ocean sites (PS 1768-8 and ODP 1093).
• Comparison of paleoceanographic data with results from an ocean circulation model.
• Interpretation of ɛNd signatures to infer water mass sources and mixing.

Main Results:

• Interglacial periods show unradiogenic ɛNd signatures, consistent with present-day Weddell Sea-sourced Antarctic Bottom Water (AABW).
• Glacial periods exhibit highly radiogenic ɛNd values, suggesting a different water mass influence.
• Ocean circulation modeling indicates no significant increase in Pacific water influence during glacials.

Conclusions:

• Increased benthic flux, modulated by Antarctic Circumpolar Current (ACC) strength, likely explains the radiogenic glacial ɛNd signatures.
• Stratified and sluggish glacial deep water limited vertical mixing, enhancing glacial carbon storage without Pacific water intrusion.
• Glacial Southern Hemisphere ɛNd endmembers need re-evaluation for accurate paleoceanographic reconstructions in the Atlantic sector.