Multi-million-year cycles in modelled [delta].sup.13C as a response to astronomical forcing of organic matter fluxes

• Published in: Earth system dynamics 2023-03, Vol.14 (2), p.291
• Main Authors: Leloup, Gaëlle, Paillard, Didier
• Format: Article
• Language: English
• ISSN: 2190-4979

Along with 400 kyr periodicities, multi-million-year cycles have been found in [delta].sup.13 C records over different time periods. An â¼ 8-9 Myr periodicity is found throughout the Cenozoic and part of the Mesozoic. The robust presence of this periodicity in [delta].sup.13 C records suggests an astronomical origin. However, this periodicity is barely visible in the astronomical forcing. Due to the large fractionation factor of organic matter, its burial or oxidation produces large [delta].sup.13 C variations for moderate carbon variations. Therefore, astronomical forcing of organic matter fluxes is a plausible candidate to explain the oscillations observed in the [delta].sup.13 C records. So far, modelling studies forcing astronomically the organic matter burial have been able to produce 400 kyr and 2.4 Myr cycles in [delta].sup.13 C but were not able to produce longer cycles, such as 8-9 Myr cycles. Here, we propose a mathematical mechanism compatible with the biogeochemistry that could explain the presence of multi-million-year cycles in the [delta].sup.13 C records and their stability over time: a preferential phase locking to multiples of the 2.4 Myr eccentricity period. With a simple non-linear conceptual model for the carbon cycle that has multiple equilibria, we are able to extract longer periods than with a simple linear model - more specifically, multi-million-year periods.