A∼9 myr cycle in Cenozoic δ13C record and long-term orbital eccentricity modulation: Is there a link?

The similar to 65-myr-long Cenozoic carbon isotope record (delta C-13) of Zachos et al. (2001, 2008) documents a strong long-term cycle with a mean pseudoperiodicity close to similar to 9 myr. This cyclicity modulates the similar to 2.4 myr eccentricity cycle amplitude, hinting at a possible link between long-term astronomical and geological variations. Some phase shifts between similar to 9-myr delta C-13 and astronomical cycles suggest that additional processes (e.g., tectonics) contribute to these long-term carbon-cycle variations. The strong response of delta C-13 to long-term eccentricity periods (similar to 9 myr, similar to 2.4 myr, similar to 400 kyr) supports the hypothesis that the long time-residence of carbon in the oceans amplifies lower frequency or dampens higher frequency orbital variations. Additionally, the strong expression of low-amplitude similar to 9 myr eccentricity cycle in the delta C-13 record could be explained by energy-transfer process from higher to lower frequency cycles, and all eccentricity components modulate the carrier climatic precession cycles. Finally, the Paleocene-Eocene Thermal Maximum (PETM, 55.9 Ma) event, which corresponds to a pronounced delta C-13 negative excursion, is situated within a strong decrease in the most prominent similar to 9 myr delta C-13 cycle, hinting at a link between accelerated rates in delta C-13 variations and the PETM. This specific similar to 9 myr delta C-13 cycle seems to be amplified by non-orbital mechanisms in atmosphere-continent-ocean system, such as previously suggested methane release from gas hydrate and volcanism. (C) 2011 Elsevier B.V. All rights reserved.