Ordovician climate simulations with an earth system model: Focus on the impact of atmospheric O2 and CO2 on deep ocean oxygen concentrations

Daniel Frank D'Amico, Ohio State University, Department of Geography, Columbus, United States, Alvaro Montenegro, Ohio State University, Department of Geography, Columbus, OH, United States and Michael Eby, University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada

Contact First Author: Daniel Frank D'Amico; damico@ucar.edu

Previously Published Material: N/A

Abstract ID#: 33836

 

English Abstract:
Stratigraphic evidence from the Ordovician suggests that widespread oceanic anoxia existed during the late-Middle to Late Ordovician (460-443 million years ago). While numerous observational studies have examined this issue, there have been relatively few numerical experiments attempting to model the conditions that might have contributed to the recorded low oxygen levels during the period. Previous Ordovician modeling efforts have focused on atmospheric concentration of CO2 and its impacts on extreme climate change, including a short lived glaciation during the Hirnantian (~445 million years ago). Here we utilize the University of Victoria Earth System Climate Model, a model of intermediate complexity, to simulate the impacts of paleogeography and atmospheric CO2 and O2 concentrations on Ordovician deep ocean oxygen. Simulations were performed with two different CO2 levels (14 and 20 times the preindustrial atmospheric level) and two distinct atmospheric O2 concentrations (5 and 12% by volume). Modeled meridional overturning transport, sea surface and surface air temperatures are in general agreement with previous simulations of the period. The overturning is dominated by two cells with maximum transports ranging from -42 Sv around 20oN to 58 Sv around 10oS. While atmospheric CO2 variability influences both ocean temperature and overturning, it has no significant impact on modeled deep ocean O2. Experiments with the lower atmospheric O2 concentration show fairly widespread anoxia, here defined as O2 concentrations below 10 µmol L-1, for the northern hemisphere with an average oxygen concentration of 4.39 µmol L-1. Counter to many of the observations, the majority of the deep ocean in the southern hemisphere, where most continents are located, remains well oxygenated. Future simulations will further evaluate the impact of changes in biological activity and nutrient input on deep-ocean anoxia during the period.
Back to: The Geologic History of Atmospheric Oxygen: Models and Proxies