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Millennial-scale ice sheet variability (1-15 kyr periods) is well documented in the Quaternary, providing insight into critical atmosphere-ocean-cryosphere interactions that can inform the mechanism and pace of future climate change. Ice sheet variability at similar frequencies is comparatively less known and understood prior to the Quaternary during times, where higher atmospheric p CO 2 and warmer climates prevailed, and continental-scale ice sheets were largely restricted to Antarctica. In this study, we evaluate a high-resolution clast abundance dataset (ice-rafted debris) that captures East Antarctic ice sheet variability in the western Ross Sea during the early Miocene. This dataset is derived from a 100 m-thick mudstone interval in the ANtarctic DRILLing (ANDRILL or AND) core 2A, which preserves a record of precession and eccentricity variability. The sedimentation rates are of appropriate resolution to also characterize the signature of robust, subprecession cyclicity. Strong sub-precession (~10 kyr) cyclicity is observed, with an amplitude modulation in lockstep with eccentricity, indicating a relationship between high-frequency Antarctic ice sheet dynamics and astronomical forcing. Bicoherence analysis indicates that many of the observed millennial-scale cycles (as short as 1.2 kyr) are associated with nonlinear interactions (combination or difference tones) between each other and the Milankovitch cycles. The presence of these cycles during the Miocene reveals the ubiquity of millennial-scale ice sheet variability and sheds light on the interactions between Earth's atmosphere, ocean, and ice in climates warmer than the Quaternary.

The geologic record of Milankovitch climate cycles provides a rich conceptual and temporal framework for evaluating Earth system evolution, bestowing a sharp lens through which to view our planet's history. However, the utility of these cycles for constraining the early Earth system is hindered by seemingly insurmountable uncertainties in our knowledge of solar system behavior (including Earth-Moon history), and poor temporal control for validation of cycle periods (e.g., from radioisotopic dates). Here we address these problems using a Bayesian inversion approach to quantitatively link astronomical theory with geologic observation, allowing a reconstruction of Proterozoic astronomical cycles, fundamental frequencies of the solar system, the precession constant, and the underlying geologic timescale, directly from stratigraphic data. Application of the approach to 1.4-billion-year-old rhythmites indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ), an Earth-Moon distance of 340,900 ± 2,600 km (2σ), and length of day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results confirm reduced tidal dissipation in the Proterozoic. A complementary analysis of Eocene rhythmites (∼55 Ma) illustrates how the approach offers a means to map out ancient solar system behavior and Earth-Moon history using the geologic archive. The method also provides robust quantitative uncertainties on the eccentricity and climatic precession periods, and derived astronomical timescales. As a consequence, the temporal resolution of ancient Earth system processes is enhanced, and our knowledge of early solar system dynamics is greatly improved., Competing Interests: The authors declare no conflict of interest.

Periodic fluctuations in past biodiversity, speciation, and extinction have been proposed, with extremely long periods ranging from 26 to 62 million years, although forcing mechanisms remain speculative. In contrast, well-understood periodic Milankovitch climate forcing represents a viable driver for macroevolutionary fluctuations, although little evidence for such fluctuation exists except during the Late Cenozoic. The reality, magnitude, and drivers of periodic fluctuations in macroevolutionary rates are of interest given long-standing debate surrounding the relative roles of intrinsic biotic interactions vs. extrinsic environmental factors as drivers of biodiversity change. Here, we show that, over a time span of 60 million years, between 9 and 16% of the variance in biological turnover (i.e., speciation probability plus species extinction probability) in a major Early Paleozoic zooplankton group, the graptoloids, can be explained by long-period astronomical cycles (Milankovitch "grand cycles") associated with Earth's orbital eccentricity (2.6 million years) and obliquity (1.3 million years). These grand cycles modulate climate variability, alternating times of relative stability in the environment with times of maximum volatility. We infer that these cycles influenced graptolite speciation and extinction through climate-driven changes to oceanic circulation and structure. Our results confirm the existence of Milankovitch grand cycles in the Early Paleozoic Era and show that known processes related to the mechanics of the Solar System were shaping marine macroevolutionary rates comparatively early in the history of complex life. We present an application of hidden Markov models to macroevolutionary time series and protocols for the evaluation of statistical significance in spectral analysis., Competing Interests: The authors declare no conflict of interest.