128 / 2024-09-09 11:34:13

Combined control of polar stratification and iron fertilization on the Late Pliocene atmospheric pCO2 drawdown.

carbon cycle,CO2,Pliocene,PMOC

The late Pliocene witnessed profound global climate transition to the Pleistocene glacial cycles,  attributed partially a clear drawdown of the atmospheric CO2 levels from ~400 to around 280 ppm, the proposed threshold for Northern Hemisphere Glaciation. Yet, underlying processes that may drive this atmospheric carbon removal has yet to be found. With aid of biogeochemical modeling, we here propose that combination of diminished Pacific Meridional overturning circulation (PMOC) and enhanced global iron deposition substantially contribute to the late Pliocene pCO2atm reduction. The reduction of PMOC leads to substantial isolation of the deep Pacific, facilitating carbon sequestration in the abyssal cell. More dust deposition improves oceanic surface productivity, thereby lowering pCO2atm. By comparing with existing proxies, we further show that the weakened PMOC may result in the latitudinal heterogeneity of surface productivity, whereas the inter-basin difference of production may be attributed to the varied iron deposition pattern. Essentially, the intermediate-deep yet sufficiently strong PMOC simulated in this study can to some extent reconcile the conundrum that the late Pliocene North Pacific was associated with both sustained high production and no deep (>3000 m) water formation.