Orbital forcing over 3.5 billion years - Implications for cyclostratigraphy

Orbital (or Milankovic) forcing of the Earth system is key to understanding rhythmic climate change and its expression in stratigraphic sequences on time scales >10 kyr. Stratigraphic applications concerned with past orbital forcing rely on astronomical solutions, which represent the backbone of cyclostratigraphy and astrochronology. Here we present new deep-time astronomical solutions from state-of-the-art solar system integrations for orbital eccentricity, inclination, obliquity, and precession over the past 3.5 Gyr. We performed long-term ensemble integrations to explore the possible solution/phase space of the system. Our study provides multiple astronomical solutions and characteristic long-term features of Milankovic forcing. Importantly, we integrate the equations of motion for Earth's spin axis over 3.5 Gyr, yielding full solutions for Earth's obliquity and climatic precession. We found startling results regarding the primary astronomical cycle (405 kyr in the recent past) utilized in deep-time paleoclimate analyses and for constructing age models, aka the long eccentricity cycle. The widely accepted and long-held view is that the long eccentricity cycle was practically stable in the past and may hence be used as a "metronome" to reconstruct accurate chronologies. However, we found that the LONG ECCENTRICITY CYCLE CAN BECOME UNSTABLE over long time scales, rendering Earth's orbital eccentricity and climate-forcing spectrum unrecognizable compared to the recent past. Furthermore, our computations show that Earth's obliquity was lower and its amplitude (variation around the mean) significantly reduced in the past. We therefore predict weaker climate forcing at obliquity frequencies in deep time and a trend toward reduced obliquity power with age in stratigraphic records. Our findings have multiple, fundamental implications for cyclostratigraphy, astrochronology, and paleoclimatology, which will be discussed in this presentation.