Atmospheric carbon dioxide variations across the middle Miocene climate transition

• Published in: Climate of the Past
• Main Authors: Raitzsch, Markus, Bijma, Jelle, Bickert, Torsten, Schulz, Michael, Holbourn, Ann, Kučera, Michal
• Format: Text
• Language: English
• Published: 2021
• Subjects: Antarctic; East Antarctic Ice Sheet; Antarc*; Antarctica; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-17-703-2021; https://cp.copernicus.org/articles/17/703/2021/

The middle Miocene climate transition ∼ 14 Ma marks a fundamental step towards the current “ice-house” 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 Ocean Drilling Program (ODP) Site 1092 in the South Atlantic, we show that long-term p CO 2 varied at 402 kyr periodicity between ∼ 14.3 and 13.2 Ma and follows the global δ 13 C variation remarkably well. This suggests a close link to precessional insolation forcing modulated by eccentricity, which governs the monsoon and hence weathering intensity, with enhanced weathering and decreasing p CO 2 at high eccentricity and vice versa. The ∼ 50 kyr lag of δ 13 C and p CO 2 behind eccentricity in our records may be related to the slow response of weathering to orbital forcing. A p CO 2 drop of ∼ 200 µ atm before 13.9 Ma may have facilitated the inception of ice-sheet expansion on Antarctica, which accentuated monsoon-driven carbon cycle changes through a major sea-level fall, invigorated deep-water ventilation, and shelf-to-basin shift of carbonate burial. The temporary rise in p CO 2 following Antarctic glaciation would have acted as a negative feedback on the progressing glaciation and helped to stabilize the climate system on its way to the late Cenozoic ice-house world.