A globally wetter Middle Miocene with a narrower intertropical convergence zone

GIBSON, MARTHA E.; O'KEEFE, JENNIFER M. K.; NUÑEZ OTAÑO, NOELIA B.; ROMERO, INGRID C.; WARNY, SOPHIE; NKAU, I; TODD, C; POUND, MATTHEW J.

Manizales

Congreso; 54th AASP Meeting - Manizales 2022; 2022

The palynological society

The Middle Miocene Climatic Optimum (MCO; 16.9-14.7Ma) was the warmest interval of the Neogene and is a potential analogue for the IPCC RCP 4.5-6.0 (intermediate scenarios). Global mean annual temperatures are estimated to have been 4–6°C warmer and pCO 2 wasslightly higher than present day (above 500 ppm), with an asymmetric latitudinal temperature gradient, tropical temperatures in the mid- latitudes and reduced polar ice sheets. However, our understanding of Middle Miocene terrestrial climate at broad spatial scales is stilldeveloping as there are difficulties reconciling proxy-based climate reconstructions with climate models. One of the current views of Miocene terrestrial climate is based on the Co-existence Approach which has given a broad view of global temperature and precipitation across the Neogene. However, the Co- existence Approach reconstructs an equal likelihood range for climateparameters that can be wide and therefore hampers our understanding the water cycle. These reconstructed ranges also hinder quantitative data-model comparisons (proxy-ranges vs. climate model uncertainty). Here we present the first global reconstruction of mean annual precipitation and seasonality from 188 Middle Miocene sites. We use two probability-based terrestrial paleoclimate reconstruction techniques, CREST (Climate Reconstruction SofTware) and CRACLE(Climate Reconstruction Analysis using Coexistence Likelihood Estimation), that employ Bayesian and likelihood estimation probability respectively to generate 2σ confidence intervals.This is the first application of these models at a global scale. Our results show a globally wetter than present-day world, with the exception of a narrow band around the equator. This we attribute to a narrower Intertropical Convergence Zone that, due to the asymmetric distribution of ice in the Middle Miocene, was also located in the northern hemisphere over a yearly average. The impacts of climate change on the global hydrological cycle will have profound impacts on society. Changes in precipitation will be a cause of concern for flood defense and accompanied infrastructural and financial challenges, water scarcity and agricultural productivity, ecosystem functioning and biodiversity. This statistically generated terrestrial climate reconstruction for the MCO will aid in the evaluation of climate reconstruction models in deep time, enabling an understanding of hydrology in the globally warmer conditions of the MCO. This new reconstruction will also contextualize botanical and fungal biodiversity during the MCO.