An attempt to understand δ13C cycles with a simple conceptual model.

A correct understanding of the human perturbation on the carbon cycle is a fundamental prerequisite of future climate modelling on large timescales.

However, « classical » carbon cycle theories barely take into account the « organic » part of the carbon cycle and are not able to reproduce past δ¹³C data.

Analysis of sediment data reveals the presence of cycles in the δ¹³C 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.

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 δ¹³C.

The net organic matter burial has a key role on δ¹³C, as terrestrial and marine biology preferentially use ¹²C during photosynthesis. Therefore if the burial of (¹²C rich) organic matter is relatively more important, the δ¹³C of the superficial system will decrease, and inversely.

However, this conceptual model was not able to explain longer term cycles at 4.6 and 9 Myr.

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.

With this new conceptual model coupling carbon and oxygen cycle, it is possible to obtain 400 kyr, 2.4 Myr, but also longer cycles.

 

References :

[1] Sexton et al, 2011, Eocene global warming events driven by ventilation of oceanic dissolved organic carbon

[2] Pälike et al, 2006 The Heartbeat of the Oligocene Climate System

[3] Billups et al, 2004 Astronomic calibration of the late Oligocene through early Miocene geomagnetic polarity time scale

[4]Wang et al, 2010, Obscuring of long eccentricity cyclicity in Pleistocene oceanic carbon isotope records

[5] Boulila et al, 2012, A ~9 myr cycle in Cenozoic δ13C record and long-term orbital eccentricity modulation: Is there a link?

[6] Ikeda et al, 2014, 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic–Jurassic geochronology.

[7] Martinez et al, 2015, Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic

[8] Sprovieri M, et al. (2013) Late Cretaceous orbitally-paced carbon isotope stratigraphy from the Bottaccione Gorge (Italy).

[9] Paillard, 2017, The Plio-Pleistocene climatic evolution as a consequence of orbital forcing on the carbon cycle.