NOAA/WDS Paleoclimatology - Paleo-pCO2 Database: Meteor Rise, Atlantic Ocean Boron Isotope Data from the Late Miocene

The middle Miocene climate transition 14 Ma marks a fundamental step towards the current “ice-house” climate, with a 1‰ 18O increase and a 1‰ transient 13C 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 CO2 across the carbon-cycle perturbation has been intensely debated as proxy records of pCO2 for this time interval are sparse and partly contradictory. Using boron isotopes ( 11B) in planktonic foraminifers from Ocean Drilling Program (ODP) Site 1092 in the South Atlantic, we show that long-term pCO2 varied at 402 kyr periodicity between 14.3 and 13.2 Ma and follows the global 13C 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 pCO2 at high eccentricity and vice versa. The 50 kyr lag of 13C and pCO2 behind eccentricity in our records may be related to the slow response of weathering to orbital forcing. A pCO2 drop of 200 µatm before 13.9Ma may have facilitated the inception of icesheet expansion on Antarctica, which accentuated monsoondriven 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 pCO2 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.