Spatially variable sea level response to erosion and deposition in Aotearoa New Zealand

Surface processes alter sea level by warping Earth’s surface and modifying the gravitational field. Recent studies show that paleo-sea level indicators are depressed by sedimentation near major depocenters, such as the Mississippi and Indus deltas, and raised by the erosion of rock in rapidly eroding coastal regions such as Taiwan. The South Island of Aotearoa New Zealand poses an interesting combination of these endmembers because the Southern Alps are eroding rapidly on the west coast, while high sediment loads are deposited along the eastern margin. Here, we use a global, gravitationally self-consistent sea-level model to demonstrate that sediment redistribution on the South Island drastically alters interpretations of sea level change since the Last Interglacial (Marine Isotope Stage 5e) by as much as +100 m on the west coast and –30 m on the east coast. The influence of sediment redistribution on sea level is highly sensitive to geodynamic properties such as effective elastic thickness, which we reconcile using the abundance of paleo-shoreline markers available.