The geometry of sea-level change across a mid-Pliocene glacial cycle

Abstract. Predictions of future sea-level change and ice-sheet stability rely on accurate reconstructions of sea levels for past warm intervals, such as the mid-Pliocene Warm Period (MPWP; 3.264–3.025 Ma). The magnitude of MPWP glacial cycles and the relative contribution of meltwater sources remain uncertain. We explore this issue by modeling processes of glacial isostatic adjustment for a wide range of possible MPWP ice-sheet melt zones, including North America, Greenland, Eurasia, and West Antarctica, as well as the Wilkes Basin, the Aurora Basin, and the embayment of Prydz Bay in East Antarctica. As a case study, we use a series of ice histories together with a suite of viscoelastic Earth models to predict global changes in sea level from the Marine Isotope Stage (MIS) M2 glacial to the MIS KM3 interglacial. At the Whanganui Basin (New Zealand), a location with stratigraphic constraints on Pliocene glacial–interglacial sea-level amplitude, the calculated local-sea-level (LSL) rise is on average ∼ 15 % lower than the associated change in the global mean sea level (GMSL) in the ice-sheet scenarios explored here. In contrast, the calculated LSL rise over the deglaciation from MIS M2 to MIS KM3 at Enewetak Atoll is systematically larger than the GMSL change by 10 %. While no single LSL observation (field site) can provide a unique constraint on the sources of ice melt observed during this period, combinations of observations have the potential to yield a stronger constraint on GMSL change and to narrow the list of possible sources.