Continued stimulation of Late Miocene cooling through phosphorus weathering

The Late Miocene cooling provides an opportunity to assess the sensitivity of Earth’s climate to ice volume changes and carbon cycle dynamics in warmer-than-modern conditions. Despite its relevance for the initial configuration of modern-day ecosystems, the driving mechanisms behind this carbon cycle perturbation event remains contentious. Here, it is presented magnetic and geochemical records from a hydrogenetic ferromanganese crust of the northwestern Pacific Ocean. Our findings show a striking 50% surge in deep ocean phosphorus concentrations from 7 to 4 million years ago, synchronous with changes in deep water oxygen consumption. Employing a global biogeochemical model, the proposed model demonstrates that the inferred rise in continental phosphorus weathering contributed to the late Miocene to early Pliocene cooling. Conversely, a comparable enhancement in silicate weathering would yield unreasonably low atmospheric CO2 level. These results support a potentially prominent decoupling between phosphorus and silicate weathering during this carbon cycling event.