Millennial-scale cycles (1–15 kyr periods) are extensively documented in Quaternary climate proxies and linked to complex interhemispheric earth system feedbacks associated with dynamic behavior of large continental-scale ice sheets at both poles. Here, we identify millennial-scale variability in the East Antarctic ice sheet in the early Miocene, a time characterized by warmer climates, higher atmospheric pCO 2, and no large Northern Hemisphere ice sheets. These millennial-scale cycles are modulated by astronomical climate forcing, despite there being no a priori reason to expect such patterns to arise from a linear response to Milankovitch Cycles. These patterns likely arise from nonlinear interactions between the atmosphere, ocean, and ice that appear to have characterized Earth’s cryosphere for at least the past 20 My.
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 pCO 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.
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