The effect of the Pliocene temperature pattern on silicate weathering and Pliocene-Pleistocene cooling

The warmer early Pliocene climate featured changes to global sea surface temperature (SST) patterns, namely a reduction in the Equator-pole gradient and the east-west SST gradient in the tropical Pacific, the so-called "permanent El Nino". Here we investigate the consequences of the SST changes to silicate weathering and thus to atmospheric CO2 on geological timescales. Different SST patterns than today imply regional modifications of the hydrological cycle that directly affect continental silicate weathering in particular over tropical "hotspots" of weathering, such as the Maritime Continent, thus leading to a "weatherability pattern effect". We explore the impact of Pliocene-like SST changes on weathering using climate model and silicate weathering model simulations, and we deduce CO2 and temperature at carbon cycle equilibrium between solid Earth degassing and silicate weathering. In general, we find large regional increases and decreases in weathering fluxes, and the net effect depends on the extent to which they cancel. Permanent El Nino conditions lead to a small amplification of warming relative to the present day by 0.4 degrees C, suggesting that the demise of the permanent El Nino could have had a small amplifying effect on cooling from the early Pliocene into the Pleistocene. For the reduced Equator-pole gradient, the weathering increases and decreases largely cancel, leading to no detectable difference in global temperature at carbon cycle equilibrium. A robust SST reconstruction of the Pliocene is needed for a quantitative evaluation of the weatherability pattern effect.