Paper No. 51-7
Presentation Time: 3:20 PM
A GLOBALLY WETTER MIDDLE MIOCENE WITH A NARROWER INTERTROPICAL CONVERGENCE ZONE (ITCZ)
GIBSON, Martha, Department of Geology and Geography, West Virginia University, 98 Beechurst Ave, Morgantown, WV 26506; Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom, O'KEEFE, Jen, Earth and Space Sciences, Morehead State University, 404-A Lappin Hall, Morehead, KY 40351, NUÑEZ OTAÑO, Noelia, Laboratoria de Geología de Llanuras, Facultad de Ciencia y Tacnologia, Universidad Autónoma de Entre Ríos, CONICET, Sede Diamante, Argentina, ROMERO, Ingrid, Morehead State University, Department of Physics, Earth Science, and Space Systems Engineering, 405-C Lappin Hall, Morehead, MS 40351, WARNY, Sophie, Department of Geology and Geophysics, and Museum of Natural Science Baton Rouge, USA, Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, NKAU, Iola, Jesmond Park Academy, Jesmond Park West, Newcastle upon Tyne, United Kingdom, TODD, Chloe, Southmoor Sixth Form, Ryhope Road, Sunderland, United Kingdom and POUND, Matthew J., Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom
Future changes to the global hydrological cycle will have profound environmental and societal impacts. Changes in precipitation will be a cause of concern for flood defence and accompanied infrastructural and financial challenges, water scarcity and agricultural productivity, as well as for ecosystem functioning and biodiversity. Past climates, including that of the Miocene, are routinely used to explore how climates have changed under elevated atmospheric CO
2 in the past, and may continue to change in the future.
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 pCO2 was slightly 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 still developing as there are difficulties reconciling proxy-based climate reconstructions with climate models.
Here we present the first global reconstruction of mean annual precipitation and precipitation seasonality for the warmer-than-present Middle Miocene (~16-11.6 Ma) using CREST (Climate Reconstruction SofTware), a probability-based terrestrial paleoclimate reconstruction technique. Using 187 paleobotanical sites we 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 (ITCZ) that, due to the asymmetric distribution of ice in the Middle Miocene, was located in the northern hemisphere over a yearly average.
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.
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