Geological Society of America

T288 The Early Paleozoic World: Radiations, Extinctions, and Paleoenvironmental Change II

Wednesday, 28 September 2016
8:00 AM - 12:00 PM
Mile High Ballroom 3C

A MODEL FOR THE DECREASE IN AMPLITUDE OF CARBON ISOTOPE EXCURSIONS THROUGHOUT THE PHANEROZOIC

Paper number: T288-6
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Aviv Bachan Presenting Author
Stanford University, Stanford, CA
Kimberly V. Lau
Stanford University, Stanford, CA
Matthew Saltzman
The Ohio State University, Columbus, OH
Ellen Thomas
Yale University, New Haven, CT
Lee Kump
Penn State Univ - Univ ParkDept Geosciences, University Park, PA
Jonathan Payne
Stanford University, Stanford, CA

Abstract

The geological cycling of carbon ties the ocean-atmosphere carbon pool to Earth's biosphere and sedimentary reservoirs. Perturbations to this coupled system are recorded in the carbon-isotopic (δ¹³C) composition of marine carbonates. Large amplitude δ¹³C variations with durations of 0.5 – 10 m.y. are typically treated as individual events and interpreted accordingly. However, a recent compilation of Phanerozoic data reveals a decline in the variance of the δ¹³C record over time, suggesting a common underlying control.

Here we propose that the redox structure of the continental shelves was a key determinant of the sensitivity of the geologic carbon cycle: when oxygen minimum zones (OMZs) were large, shallow, and prone to expansion, recurrent physical forcings (such as sea level and tectonics) would have had the capacity to drive large changes in the areal extent of OMZs, resulting in a strong leverage on δ¹³C.

Using a simple model of the geologic carbon cycle, we demonstrate that interactions between the carbon and phosphate cycles can result in amplification of recurrent forcings with periods in the 0.5 – 10 m.y. range. Thus, rather than requiring that physical forcings have their largest amplitude of variation on those time scales, enhanced sensitivity of the carbon cycle can account for the characteristic duration of δ¹³C excursions.

Biologically mediated aspects of geologic carbon cycling, including the depth of bioturbation and evolution of pelagic calcifiers, likely drove a decline in the depth and extent of ocean anoxia over the Phanerozoic resulting in the stabilization of the geologic carbon cycle.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-281620

© Copyright 2016 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.