An attempt to understand &#948;13C cycles with a simple conceptual model.
Authors: Leloup Gaelle , Paillard Didier 
Published: March 2021

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&lt;p&gt;A correct understanding of the human perturbation on the carbon cycle is a fundamental prerequisite of future climate modelling on large timescales.&lt;/p&gt;
&lt;p&gt;However, &amp;#171;&amp;#160;classical&amp;#160;&amp;#187; carbon cycle theories barely take into account the &amp;#171;&amp;#160;organic&amp;#160;&amp;#187; part of the carbon cycle and are not able to reproduce past &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C data.&lt;/p&gt;
&lt;p&gt;Analysis of sediment data reveals the presence of cycles in the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C record. A 400 kyr cycle has been observed at several time periods, from the Eocene to present [1-4]. Moreover, longer cycles have been observed : 2.4, 4.6 and 9 Myr [5-8]. The 9 Myr cycle is present since the start of the Mesozoic. These periodicities seem linked to eccentricity periods.&lt;/p&gt;
&lt;p&gt;By forcing astronomically the (net) organic matter burial in a carbon cycle conceptual model, Paillard [9] reproduced 400 kyr and 2.4 Myr cycles in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C.&lt;/p&gt;
&lt;p&gt;The net organic matter burial has a key role on &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, as terrestrial and marine biology preferentially use &lt;sup&gt;12&lt;/sup&gt;C during photosynthesis. Therefore if the burial of (&lt;sup&gt;12&lt;/sup&gt;C rich) organic matter is relatively more important, the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C of the superficial system will decrease, and inversely.&lt;/p&gt;
&lt;p&gt;However, this conceptual model was not able to explain longer term cycles at 4.6 and 9 Myr.&lt;/p&gt;
&lt;p&gt;Here, we develop a new conceptual model based on Paillard [9], which includes the role of oxygen. Indeed, oxygen also influences the organic matter burial.&lt;/p&gt;
&lt;p&gt;With this new conceptual model coupling carbon and oxygen cycle, it is possible to obtain 400 kyr, 2.4 Myr, but also longer cycles.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;References&amp;#160;:&lt;/p&gt;
&lt;p&gt;[1] Sexton et al, 2011, Eocene global warming events driven by ventilation of oceanic dissolved organic carbon&lt;/p&gt;
&lt;p&gt;[2] P&amp;#228;like et al, 2006 The Heartbeat of the Oligocene Climate System&lt;/p&gt;
&lt;p&gt;[3] Billups et al, 2004 Astronomic calibration of the late Oligocene through early Miocene geomagnetic polarity time scale&lt;/p&gt;
&lt;p&gt;[4]Wang et al, 2010, Obscuring of long eccentricity cyclicity in Pleistocene oceanic carbon isotope records&lt;/p&gt;
&lt;p&gt;[5] Boulila et al, 2012, A ~9 myr cycle in Cenozoic &amp;#948;13C record and long-term orbital eccentricity modulation: Is there a link?&lt;/p&gt;
&lt;p&gt;[6] Ikeda et al, 2014, 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic&amp;#8211;Jurassic geochronology.&lt;/p&gt;
&lt;p&gt;[7] Martinez et al, 2015, Orbital pacing of carbon fluxes by a &amp;#8764;9-My eccentricity cycle during the Mesozoic&lt;/p&gt;
&lt;p&gt;[8] Sprovieri M, et al. (2013) Late Cretaceous orbitally-paced carbon isotope stratigraphy from the Bottaccione Gorge (Italy).&lt;/p&gt;
&lt;p&gt;[9] Paillard, 2017, The Plio-Pleistocene climatic evolution as a consequence of orbital forcing on the carbon cycle.&lt;/p&gt;
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