| The arc exhumation hypothesis states that new basalt-rich sources lifted during arc-continent collisions cause atmospheric PCO{dollar}sb2{dollar} drawdown and global cooling. Drawdown lags the early release of CO{dollar}sb2{dollar} and {dollar}sp{lcub}187{rcub}{dollar}Os from uplifted continental margin sediments. It generally precedes release of {dollar}sp{lcub}87{rcub}{dollar}Sr from continental crust exhumed later.; During the Miocene, Australia collided with New Guinea, lifting up a composite arc terrane around 15 Ma. Benthic foraminiferal {dollar}deltasp{lcub}18{rcub}{dollar}O values increased from 1 to 2{dollar}perthous{dollar} in response to polar cooling between 14.8 and 12.8 Ma. Marine {dollar}sp{lcub}187{rcub}{dollar}Os/{dollar}sp{lcub}186{rcub}{dollar}Os ratios began to increase at 0.1/my while the rate of change of {dollar}sp{lcub}87{rcub}{dollar}Sr/{dollar}sp{lcub}86{rcub}{dollar}Sr ratios decreased at 16 Ma. Bulk carbonate {dollar}deltasp{lcub}13{rcub}{dollar}C values began to decrease at 0.3{dollar}perthous{dollar}/my after 14 Ma.; A new coupled C-Os-Sr isotopic mass balance model calculates atmospheric PCO{dollar}sb2{dollar} from the {dollar}sp{lcub}87{rcub}{dollar}Sr/{dollar}sp{lcub}86{rcub}{dollar}Sr ratio of weathered silicates (following a large correction for weathering of intermediate and radiogenic carbonates) based on the lithology-dependent time constant associated with Ca and Mg release. Seafloor-spreading rate constrains the metamorphic carbon fluxes, and the riverine flux of Os, associated with organic matter, constrains the weathering of sedimentary carbon.; Model atmospheric PCO{dollar}sb2{dollar} mimics the proxy for climate (inverse benthic foraminiferal {dollar}deltasp{lcub}18{rcub}{dollar}O values). The rate of change of basalt weathering generally increases at times expected from independent records of basalt exhumation. Calculated organic C burial accelerates at 16 Ma, perhaps triggered by high rates of sedimentation of fine-grained material from Indonesia, and the organic C cycle is a net CO{dollar}sb2{dollar} sink (1-2 ocean reservoirs of C). Carbonate burial results, which decrease from 20 to 15 Ma and then increase, resemble the time evolution of the CCD.; Arc exhumation operated at other times of global cooling, including the Pliocene (northern Andes and central America?), middle Miocene (Indonesia), Eo-Oligocene (proto-Himalayas), Permo-Carboniferous (Urals-Varisco-Hercynides), late Ordovician (Taconics), and late Precambrian (early Pan-African). Related organic C burial events may explain biologically important steps in the evolution of atmospheric PO{dollar}sb2.{dollar} During exhumational events, especially in the Archean, silicate weathering must have fractionated accreted mafic terranes, with the sialic by-products contributing to growth of andesitic continental crust. |
