Completeness and compensational sedimentation of ANDRILL AND-2A through the Miocene Climate Optimum

The response of ice sheets to warming is a critical unknown in projections of ongoing climate change. The Miocene Climate Optimum is one of the best analogs for modern warming. The response of the Antarctic ice sheet to Miocene warming, and subsequent cooling in the Mid-Miocene Climatic Transition, is recorded in the ANDRILL AND-2A sediment core. To accurately interpret these records of ice growth and loss, we must understand the distribution of time within the core. We develop a theory for statistical quantities that dictate time’s distribution in stratigraphy— completeness and the compensation time scale and length scales—for glaciomarine sedimentation. We hypothesize that the compensation length scale, which quantifies the relief on the sedimentary surface, is set by the vertical amplitude of grounding line motion. This value should be tens of meters for astronomically forced Miocene ice sheets. We develop a novel Bayesian age modeling methodology that probabilistically constrains hiatus duration throughout the stratigraphy. This method yields a new age model for AND-2A and constrains the compensation time scale—the longest hiatus resulting from sedimentary dynamics—to 197−478 k.y. This time scale exceeds the time scales of most astronomical forcings and most reported values for fluvio-deltaic systems. The corresponding compensation length scale is 29−71 m, which aligns with our hypothesis that astronomically forced grounding line motion sets the compensation length scale for glaciomarine sedimentation. Our new age model suggests complete Miocene sedimentation from ca. 16 Ma to ca. 14.5 Ma, followed by a decline in accumulation rates during the expansion of the Antarctic ice sheet during the Mid-Miocene Climatic Transition.