5:15 PM - 6:30 PM
[BCG04-P09] Variations of land and oceanic organic carbon burial and their effects on atmospheric oxygen levels through Phanerozoic
Keywords:carbon cycle, C/S ratio, land plants, atmospheric oxygen level, Phanerozoic
Atmospheric oxygen levels through Phanerozoic time have been affected by emergence and evolution of land plants through production and burial of organic carbon, in addition to those derived from marine phytoplankton. Previous geochemical models using marine carbon and sulfur isotopic records, however, did not discriminate burial rates of organic carbon derived from land plants and marine phytoplankton. In this study, we modified a geochemical model for carbon and sulfur cycles (GEOCARBSULF) to calculate burial rates of land-derived and marine-derived organic carbon to consider this problem. Estimated ratio of global organic carbon and pyrite burial rates (C/S ratio) from the model, and compiled data of C/S ratio from sediments deposited under freshwater and oxygenated seawater environments, were used to separate global burial rates of organic carbon into land-derived and marine-derived rates. Monte Carlo approach was adopted because there are uncertainties in the isotopic record, initial values, and model parameters.
As a result, it is shown that the burial rate of land-derived organic carbon appeared for the first time in Silurian and Devonian, when vascular plants emerged and the first forests were formed. The burial rate of organic carbon derived from land plants reached its peak during the Late Carboniferous to the Early Permian, when a lot of coal was produced. There were substantial decreases of the burial rate of land-derived organic carbon at Frasnian/Famennian (F/F) and Permian/Triassic (P/T) mass extinction boundaries.
Atmospheric oxygen level remained low and was mainly affected by the burial of organic carbon derived from marine phytoplankton during Cambrian to Ordovician. However, it increased because of the addition of organic carbon burial derived from land plants during Silurian to Devonian, and Carboniferous to Permian. During Mesozoic and Cenozoic, both the burial of land-derived and marine-derived organic carbon affected atmospheric oxygen level.
As a result, it is shown that the burial rate of land-derived organic carbon appeared for the first time in Silurian and Devonian, when vascular plants emerged and the first forests were formed. The burial rate of organic carbon derived from land plants reached its peak during the Late Carboniferous to the Early Permian, when a lot of coal was produced. There were substantial decreases of the burial rate of land-derived organic carbon at Frasnian/Famennian (F/F) and Permian/Triassic (P/T) mass extinction boundaries.
Atmospheric oxygen level remained low and was mainly affected by the burial of organic carbon derived from marine phytoplankton during Cambrian to Ordovician. However, it increased because of the addition of organic carbon burial derived from land plants during Silurian to Devonian, and Carboniferous to Permian. During Mesozoic and Cenozoic, both the burial of land-derived and marine-derived organic carbon affected atmospheric oxygen level.