Axial obliquity control on the greenhouse carbon budget through middle‐ to high‐latitude reservoirs

Abstract

Carbon sources and sinks are key components of the climate feedback system, yet their response to external forcing remains poorly constrained, particularly for past greenhouse climates. Carbon-isotope data indicate systematic, million-year-scale transfers of carbon between surface reservoirs during and immediately after the Late Cretaceous thermal maximum (peaking in the Cenomanian-Turonian, circa 97-91 million years, Myr, ago). Here we calibrate Albian to Campanian (108-72 Myr ago) high-resolution carbon isotope records with a refined chronology and demonstrate how net transfers between reservoirs are plausibly controlled by~1 Myr changes in the amplitude of axial obliquity. The amplitude-modulating terms are absent from the frequency domain representation of insolation series and require a nonlinear, cumulative mechanism to become expressed in power spectra of isotope time series. Mass balance modeling suggests that the residence time of carbon in the ocean-atmosphere system is-by itself-insufficient to explain the Myr-scale variability. It is proposed that the astronomical control was imparted by a transient storage of organic matter or methane in quasi-stable reservoirs (wetlands, soils, marginal zones of marine euxinic strata, and potentially permafrost) that responded nonlinearly to obliquity-driven changes in high-latitude insolation and/or meridional insolation gradients. While these reservoirs are probably underrepresented in the geological record due to their quasi-stable character, they might have provided an important control on the dynamics and stability of the greenhouse climate.

An astronomically calibrated stratigraphy of the Cenomanian, Turonian and earliest Coniacian from the Cretaceous Western Interior Seaway, USA: Implications for global chronostratigraphy

“…This interval in particular was characterized by the widespread deposition of organic-rich, fine-grained sediment marked by a globally recognized positive carbon isotope excursion (CIE) reflecting the widespread removal of 12 C-enriched organic matter in marine sediments under global anoxic conditions (see Jenkyns, 2010 and references therein). However, the exact timing of this inferred global OAE-2 event is still debated with recent studies showing diachroneity between the deposition of the organic-rich sediment and the CIE (e.g., Sageman et al, 1997;Tsikos et al, 2004;Meyers et al, 2005;Meyers, 2007;Trabucho Alexandre et al, 2010;Eldrett et al, 2014), whereas interpretations vary on the precise timing and origin of the trigger (Mitchell et al, 2008;Turgeon and Creaser, 2008;Du Vivier et al, 2014;Eldrett et al, 2014;Laurin et al, 2015).…”

Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic

“…A first explanation for the long-term amplification in the carbon cycle could be a "memory" effect produced by the long residence time of carbon in the ocean (i.e., ∼100,000 y), transferring power from high-to low-frequency cycles (9,30). However, recent massbalance models suggest that this process alone would be insufficient to amplify the modulation terms at million-year time scales (31). Alternative nonlinear mechanisms could involve cumulative sequestrations of organic carbon in quasi-stable (over millions of years) terrestrial reservoirs from high latitudes (e.g., wetlands, peats, and marginal zones) (31).…”

“…However, recent massbalance models suggest that this process alone would be insufficient to amplify the modulation terms at million-year time scales (31). Alternative nonlinear mechanisms could involve cumulative sequestrations of organic carbon in quasi-stable (over millions of years) terrestrial reservoirs from high latitudes (e.g., wetlands, peats, and marginal zones) (31). In this hypothesis, geological periods with greenhouse conditions favoring production and preservation of organic matter (i.e., high pCO 2 levels, warm and equable climates, and high precipitation rates toward high latitudes) should be especially sensitive to eccentricity.…”

Chapter 1: Integrated, High-Resolution Allostratigraphic, Biostratigraphic and Carbon-Isotope Correlation of Coniacian Strata (Upper Cretaceous), Western Alberta and Northern Montana

“…Centimeter-scale fine sandstone beds in CA21 to CA23 are planar laminated and wave rippled. Laurin et al, 2015). The Cutpick section, and corresponding carbon-isotope curve, has been "expanded" to show the location of hiatuses determined on the basis of regional subsurface correlation (i.e., fig.…”