Enhanced deep Southern Ocean stratification during the lukewarm interglacials.

Area of Science:

• Paleoclimatology
• Oceanography
• Geochemistry

Background:

• Interglacial periods ~800-430 thousand years ago had lower CO2 and colder Antarctic temperatures than later interglacials.
• The Southern Ocean's role in climate regulation is significant but poorly understood due to limited proxy data.
• Ocean circulation changes during past interglacials are not well-constrained.

Purpose of the Study:

• To reconstruct Southern Ocean seawater isotope records over the past 800,000 years.
• To investigate ocean circulation changes during past interglacial periods.
• To understand the impact of Southern Ocean dynamics on atmospheric CO2 levels and climate.

Main Methods:

• Utilized a novel 2D laser ablation technique.
• Analyzed lead (Pb) isotopes (208Pb/206Pb and 206Pb/204Pb) from a ferromanganese crust.
• Obtained orbital-resolution records from the Antarctic margin at ~1.6 km water depth.

Main Results:

• First orbital-resolution Southern Ocean seawater Pb isotope records spanning 800,000 years.
• Systematically higher 208Pb/206Pb ratios observed during lukewarm interglacials compared to subsequent interglacials.
• Similar 206Pb/204Pb ratios across interglacial periods suggest changes in deep-water mixing, not source variations.

Conclusions:

• Lukewarm interglacials were characterized by reduced vertical deep-water mixing in the Southern Ocean.
• Strengthened deep Southern Ocean stratification likely enhanced deep-sea carbon sequestration.
• This process lowered atmospheric CO2, critically impacting lukewarm interglacial climates.