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SUMMARY:Antarctic Ice-Sheet Geometry Set the Interglacial CO₂ Ceiling in
  the Late Pleistocene - Xu Zhang\, British Antarctic Survey
DTSTART:20260304T173000Z
DTEND:20260304T190000Z
UID:TALK243682@talks.cam.ac.uk
CONTACT:91369
DESCRIPTION:During the Late Pleistocene\, the climate system experienced a
  persistent shift in interglacial intensity during the Mid-Brunhes Transit
 ion (~425 ka)\, with post-MBT interglacials exhibiting higher atmospheric 
 CO₂ and warmer Antarctic and global ocean temperatures than earlier “l
 ukewarm” interglacials. Whether this systematic difference reflects chan
 ges in ice-sheet configuration remains uncertain owing to ambiguities in 
 δ¹⁸O-based reconstructions and persistent model–data discrepancies. 
 Here we integrate Antarctic ice-core temperature and δ¹⁸O records\, th
 e benthic δ¹⁸O stack\, marine sediment constraints\, and isotope-enabl
 ed climate model simulations to reconcile the systematic contrasts between
  pre- and post-MBT interglacials. Simulations forced solely by orbital par
 ameters and greenhouse-gas concentrations systematically underestimate the
  observed isotopic and thermal contrasts\, including global benthic δ¹
 ⁸O variability\, implying a substantial ice-volume deficit during lukewa
 rm interglacials if temperature effects are held constant. Consistent agre
 ement across Antarctic temperature and isotopic signals\, deep-ocean tempe
 rature\, and global benthic δ¹⁸O stack records is achieved only when a
  higher Antarctic ice-sheet surface elevation is prescribed. Using a marin
 e biogeochemical general circulation model\, we further show that increase
 d Antarctic ice-sheet elevation strengthens Antarctic Bottom Water formati
 on and enhances Southern Ocean stratification\, thereby suppressing deglac
 ial deep-ocean carbon release and limiting interglacial atmospheric CO₂ 
 levels. These results identify Antarctic ice-sheet elevation as a necessar
 y physical constraint on lukewarm interglacials and suggest that the inter
 val spanning Termination 5 and Marine Isotope Stage 11c marks a threshold 
 shift in the coupled ice–ocean–carbon system.
LOCATION:Latimer Room\, Clare College
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