ASTRONOMICALLY INFLUENCED MILLENNIAL-SCALE CYCLICITY OF THE ANTARCTIC CRYOSPHERE DURING THE EARLY MIOCENE

Millennial-scale ice sheet variability shorter than precession (1-15 kyr periods) is well-documented in the Pleistocene, providing insight into critical atmosphere-ocean-cryosphere interactions that can inform the mechanism and pace of future climate change. Similar variability is comparatively less established and understood in the Miocene, where higher atmospheric pCO₂ 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 representing ice rafted debris, from an early Miocene succession of clastic mudstone at ANDRILL 2A – a proximal marine depositional environment in the Ross Sea, Antarctica. In addition to preserving a record of precession and eccentricity variability in clast abundance, the sedimentation rates are of appropriate resolution to characterize the signature of robust, sub-precessional cyclicity. A particularly strong semi-precession-scale (~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 non-linear interactions (combination or difference tones) between each other and the Milankovitch cycles. The presence of these Pleistocene-like cycles during the Miocene reveals the ubiquity of millennial-scale ice sheet variability, even at times when large ice sheets were generally restricted to the Southern Hemisphere.