Researchers from Laoshan Laboratory and GEOMAR analyzed Southern Ocean sediment cores and found that Antarctic Bottom Water expanded in two phases between about 18,000 and 10,000 years ago. Increased vertical mixing during those phases released deep-ocean carbon to the atmosphere, helping to end the last Ice Age. The study, published in Nature Geoscience, warns that similar processes could amplify modern warming as Antarctic ice shelves melt. Understanding these past ocean responses can improve projections of future Antarctic ice-sheet loss and associated risks.
Signals From the Past: Southern Ocean's Deep-Carbon Release Offers a Warning About Antarctic Warming
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New research into ancient Southern Ocean sediments reveals that expansions of Antarctic Bottom Water (AABW) tens of thousands of years ago stirred deep ocean carbon back into the atmosphere — a process that helped end the last Ice Age and may offer a cautionary analogue for modern Antarctic warming.
Study and Methods
Researchers from the Laoshan Laboratory in Qingdao, China, together with Germany's GEOMAR Helmholtz Centre for Ocean Research Kiel analyzed sediment cores recovered from the Southern Ocean, reaching thousands of meters below the surface. Their results, published in Nature Geoscience, reconstruct changes in Antarctic Bottom Water during the last deglaciation (roughly 18,000–10,000 years ago) and examine how those changes affected the global carbon cycle.
Key Findings
The team found that Antarctic Bottom Water expanded in two distinct phases as the planet warmed and ice sheets retreated. These expansions increased vertical mixing in the Southern Ocean, allowing deep, carbon-rich waters that had been isolated for millennia to vent CO2 back to the atmosphere. That release of stored carbon contributed to further warming and helped drive the transition out of the last Ice Age.
“We wanted to understand how the influence of Antarctic Bottom Water...changed during the last deglaciation, and what role it played in the global carbon cycle,” Huang Huang, lead author of the study, said in a GEOMAR press release.
The research indicates that the deepest ocean layers remained relatively isolated during glacial conditions until warming events re-entrained them. When those deep reservoirs were mixed upward, they released substantial amounts of carbon dioxide into the atmosphere, amplifying climate change at the time.
Why This Matters Today
Modern observations show that deep Southern Ocean waters have warmed faster than many other ocean regions over the past half-century. If continued Antarctic warming and ice-sheet loss replicate the physical processes seen in the paleo record, a comparable return of deep-ocean carbon to the atmosphere could magnify future temperature rise.
“Comparisons with the past are always imperfect, but ultimately it comes down to how much energy is in the system,” GEOMAR geochemist Marcus Gutjahr said. “If we understand how the ocean responded to warming in the past, we can better grasp what is happening today as Antarctic ice shelves continue to melt.”
Implications and Next Steps
Understanding past Southern Ocean behavior improves projections of Antarctic ice-sheet response and helps quantify risks such as accelerated sea level rise, disruptions to fisheries and food systems, and changing disease patterns linked to shifting climates. The authors call for continued monitoring of AABW, improved climate models that capture deep-ocean processes, and efforts to limit future warming through mitigation and clean-energy transitions.
Note: This study reconstructs past events and does not predict exact future outcomes, but it highlights a physical mechanism—deep-ocean carbon release—that could amplify warming if similar ocean and ice-sheet changes occur.
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