Eccentricity-paced atmospheric carbon-dioxide variations across the middle Miocene climate transition

• Main Authors: Raitzsch, Markus, Bijma, Jelle, Bickert, Torsten, Schulz, Michael, Holbourn, Ann, Kučera, Michal
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; East Antarctic Ice Sheet; Antarc*; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-2020-96; https://cp.copernicus.org/preprints/cp-2020-96/

The middle Miocene climate transition ~ 14 Ma marks a fundamental step towards the current “icehouse” climate, with a ~ 1 ‰ δ 18 O increase and a ~ 1 ‰ transient δ 13 C rise in the deep ocean, indicating rapid expansion of the East Antarctic Ice Sheet associated with a change in the operation of the global carbon cycle. The variation of atmospheric CO 2 across the carbon-cycle perturbation has been intensely debated as proxy records of p CO 2 for this time interval are sparse and partly contradictory. Using boron isotopes (δ 11 B) in planktonic foraminifers from drill site ODP 1092 in the South Atlantic, we show that long-term p CO 2 variations between ~ 14.3 and 13.2 Ma were paced by 400 k.y. eccentricity cycles, with decreasing p CO 2 at high eccentricity and vice versa. Our data support results from a carbon-cycle model study, according to which increased monsoon intensity at high eccentricity enhanced weathering and river fluxes in the tropics, resulting in increasing carbonate and organic carbon burial and hence decreasing atmospheric CO 2 . In this scenario, a combination of the eccentricity-driven climatic cycle and enhanced meridional deep-ocean circulation during Antarctic ice-sheet expansion may have both contributed to the p CO 2 rise following Antarctic glaciation, acting as a negative feedback on the progressing glaciation and helping to stabilize the climate system on its way to the late Cenozoic “icehouse” world.