{"id":445173,"date":"2026-05-19T04:48:51","date_gmt":"2026-05-19T11:48:51","guid":{"rendered":"https:\/\/climatescience.press\/?p=445173"},"modified":"2026-05-19T06:46:54","modified_gmt":"2026-05-19T13:46:54","slug":"warmer-saltier-antarctic-waters-unlocked-higher-atmospheric-co%e2%82%82-after-the-mid-brunhes-event","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=445173","title":{"rendered":"Warmer, Saltier Antarctic Waters Unlocked Higher Atmospheric CO\u2082 After the Mid- Brunhes Event"},"content":{"rendered":"\n
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The Mid-Brunhes Event (MBE, or Mid-Brunhes Transition, ~424\u2013478 ka, around the MIS 12\u201311 boundary) marks a major step-change in Pleistocene climate: post-MBE interglacials became warmer, with higher sea levels, smaller ice volumes, and elevated atmospheric CO\u2082 (roughly +30\u201340 ppm baseline shift, from ~240 ppm to ~280 ppm range in interglacials), while glacial CO\u2082 levels remained comparably low.<\/strong><\/p>\n\n\n\n

The MBE likely resulted from interacting orbital triggers amplified by Southern Ocean processes (sea ice, AABW, AAIW, winds, and freshwater). No single mechanism fully explains the ~35 ppm CO\u2082 jump; deep and intermediate water changes, plus wind\/sea ice feedbacks, worked together.<\/p>\n\n\n\n

Researchers from National Taiwan University<\/strong> (led by Dr. Ra\u00fal Tapia and Assoc. Prof. Sze Ling Ho<\/strong>) and international partners analyzed sediment cores from the South Pacific. They reconstructed temperature, salinity, and other properties of AAIW (a water mass at ~500\u20131,500 meters depth<\/strong>) over the past ~600,000 years<\/strong>.<\/p>\n\n\n\n

In the Tapia et al. (2026) study and broader paleoceanographic records, AAIW during glacial periods shows characteristic glacial-interglacial variability, but the key long-term shift across the Mid-Brunhes Event (MBE) is primarily in interglacial properties.<\/strong><\/p>\n\n\n\n

Glacial-Interglacial Oscillations<\/strong><\/p>\n\n\n\n

Surface waters (SAMW-influenced):<\/strong> Glacials typically feature cooler sea surface temperatures (SST), as seen in the G. bulloides Mg\/Ca proxy at the study site. These follow orbital-scale cycles with larger amplitudes in some intervals.<\/p>\n\n\n\n

Subthermocline \/ AAIW (recorded by G. inflata):<\/strong> Glacials generally align with cooler and often fresher conditions compared to interglacials within each cycle. However, the study highlights that glacial CO\u2082 levels and associated deep\/intermediate water states remained relatively stable across the MBE<\/strong>, unlike the clear step-change in interglacials.<\/p>\n\n\n\n

The paper\u2019s reconstructions focus on interglacial AAIW variability (selecting samples from peak interglacials), but downcore data and comparisons (e.g., Fig. 2F in the paper for MIS 2\u20136) show persistent glacial-interglacial contrasts. Glacial AAIW was generally colder than post-MBE interglacial AAIW.<\/p>\n\n\n\n

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Shifts in Antarctic Intermediate Water properties coincide with atmospheric CO2<\/sub> rise across the Mid-Brunhes Event<\/strong><\/p>\n\n\n\n

Shifts in Antarctic Intermediate Water properties coincide with atmospheric CO2 rise across the Mid-Brunhes Event is the title of a key 2026 paper published in Science Advances by Ra\u00fal Tapia, Sze Ling Ho, and colleagues.<\/strong><\/p>\n\n\n\n

Core Evidence and Methods<\/strong><\/p>\n\n\n\n

The study uses sediment core SO213-60-1 (45\u00b0S, 119\u00b0W, South Pacific, ~3471 m depth) \u2014 a key but data-sparse AAIW formation\/source region.<\/p>\n\n\n\n

They reconstruct properties over ~600 kyr using:<\/p>\n\n\n\n