Cenozoic Carbon Dioxide: The 66 Ma Solution.

The trend in partial pressure of atmospheric CO₂, P(CO₂), across the 66 MYr of the Cenozoic requires elucidation and explanation. The Null Hypothesis sets sea surface temperature (SST) as the baseline driver for Cenozoic P(CO₂). The crystallization and cooling of flood basalt magmas is proposed to have heated the ocean, producing the Paleocene–Eocene Thermal Maximum (PETM). Heat of fusion and heat capacity were used to calculate flood basalt magmatic Joule heating of the ocean. Each 1 million km³ of oceanic flood basaltic magma liberates ~5.4 × 10²⁴ J, able to heat the global ocean by ~0.97 °C. Henry's Law for CO₂ plus seawater (H_S) was calculated using δ¹⁸O proxy-estimated Cenozoic SSTs. H_S closely parallels Cenozoic SST and predicts the gas solute partition across the sea surface. The fractional change of Henry's Law constants, H n − H i H n − H 0 is proportional to ΔP(CO₂)_i, and H n − H i H n − H 0 × ∆ P (C O 2) + P (C O 2 ) m i n , where ΔP(CO₂) = P(CO₂)_max − P(CO₂)_min, closely reconstructs the proxy estimate of Cenozoic P(CO₂) and is most consistent with a 35 °C PETM ocean. Disparities are assigned to carbonate drawdown and organic carbon sedimentation. The Null Hypothesis recovers the glacial/interglacial P(CO₂) over the VOSTOK 420 ka ice core record, including the rise to the Holocene. The success of the Null Hypothesis implies that P(CO₂) has been a molecular spectator of the Cenozoic climate. A generalizing conclusion is that the notion of atmospheric CO₂ as the predominant driver of Cenozoic global surface temperature should be set aside. [ABSTRACT FROM AUTHOR]