T33 New Advances in Geobiology (Posters)

Sunday, 22 September 2024
8:00 AM - 5:30 PM
Hall D

DID ATMOSPHERIC CARBON DIOXIDE REALLY DECLINE IN THE LATE PALEOZOIC AS SUGGESTED BY CARBON CYCLE MODELS?

Paper number: T33-2
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The hypothesized decline in atmospheric carbon dioxide concentration (pCO2) during the Late Paleozoic Era (approximately 420 to 300 million years ago) remains unresolved, despite the predictions of seminal geologic pCO2 modeling studies such as the GEOCARB model (Berner, 1992; Berner & Kothavala, 2004). These models suggest a pCO2 drawdown driven by biological innovations on land, particularly the evolution of deep soil-forming roots that enhanced the sensitivity of silicate weathering, thereby reducing pCO2. However, empirical verification of this modeled decline has been contentious. While some proxy studies, such as those utilizing paleosol carbonate proxies by Mora et al., 1996, support the modeled stepwise decrease in pCO2, others do not (Witkowski et al., 2018). Moreover, recent modeling studies by D’Antonio et al., 2020 argue against a change in silicate weathering during this period, citing carbon budget mass balance constraints.

To address this conundrum, we propose an alternative approach. If a decline in pCO2 occurred during the Late Paleozoic due to enhanced soil formation (as suggested by the GEOCARB model), it should correspond to a significant increase in terrestrial chemical weathering observable in the rock record. We aim to reconstruct terrestrial silicate weathering through this period by analyzing a high-quality proxy of chemical weathering, i.e. Lithium isotopes preserved in brachiopods, at a high stratigraphic resolution. This reconstruction will allow us to determine whether the hypothesized pCO2 model(s) such as GEOCARB, that base pCO2 drawdown during this period on enhanced chemical weathering, need reevaluation (no change or depletion in Lithium isotopes over this record) or if plant root evolution did result in enhanced rates of silicate weathering, resulting in lower pCO2 during the Late Paleozoic (enriched Lithium isotopes over this record).

This research is crucial in understanding the geological carbon cycle as the Late Paleozoic is thought to represent a state-shift in pCO2, from a world of elevated CO2 to the relatively low CO2 realm we inhabit today. In addition, this work will shed light on the hypothesized role of organisms (trees with deep roots) in shaping the Earth's physical structure (particularly the atmospheric composition), during its past.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402567

© Copyright 2024 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.