T315 Deciphering Climate Change and Climate Variability in the Geologic Record Using Palaeosols, Loess, Palaeoweathering Profiles, Pedosedimentary Sequences, and Polygenetic Soils: Their Applications and Limitations as Terrestrial Proxies in Understanding Impacts of Climatic Changes

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Skagit 3

PALEOSOL EVIDENCE FOR A SOIL-CO2 GLOBAL THERMOSTAT OVER THE PAST 300 MILLION YEARS

Paper number: T315-6
Program: Technical Sessions
Time: 9:15 AM – 9:35 AM

Authors

Abstract

CO2 greenhouse spikes in deep time from large perturbations, such as flood basalt eruptions and asteroid impacts, were cooled by carbon-sequestration in grasslands expanding into deserts and tropical forests migrating toward the poles. This is revealed by rare appearances of deep-calcic paleosols such as Alfisols and Vertisols in long sequences of Aridisols, and also of extratropical Oxisols in long sequences of Alfisols. A lower limit for CO2 was imposed by the spread of deserts (Aridisols) and ice caps (Gelisols) curbing plant productivity. This planetary thermostat is revealed by comparison of CO2 paleobarometers from paleosols and from stomatal index of Ginkgo. For most of the past 300 million years CO2 levels were between 400 and 600 ppm, but during life crises of the Permian-Triassic and Cretaceous-Tertiary and many other greenhouse crises, CO2 levels soared to beyond 1500 ppm. Such data from paleosols of Utah over the past 300 million years reveal 1.1oC increase in mean annual temperature and 110 mm increase in mean annual precipitation with doubling of CO2. Too much CO2 can be devastating for biodiversity: the pre-human amount of CO2 causing extinction of 50% of marine invertebrate genera (LD50) was 1355 ± 240 ppm. When CO2 is above 1500 ppm, many animals are culled to redress the balance.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-295895

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.