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Sea-level changes are of wide interest because they provide information about Earth's internal structure and the sensitivity of ice sheets to climate change. Here we illustrate the sensitivity of sea level to marine sedimentary water storage by modeling sea-level responses to a synthetic global sediment redistribution history in which rates and patterns of erosion and deposition are similar to those at present and steady in time from the Last Interglacial to present. Our simulations show that if sediment redistribution were accounted for but sedimentary water storage were neglected, modeled sea-level changes could be overestimated by similar to 2 +/- 1 m of global mean sea-level equivalent, a significant fraction of published estimates of 6-9 m of global mean sea-level change since the Last Interglacial. These results show that sedimentary water storage may significantly contribute to changes in Earth's long-term seawater budget over >10(5) year timescales and underscore the importance of accounting for it in modeling long-term sea-level changes.

Plain Language Summary Sea-level changes are of wide interest because they reflect changes in climate and affect coastal flooding hazards. Recent advances in sea-level modeling now make it possible to compute how sea-level changes are affected by the storage of water in the pore space of seafloor sediment, an effect that had not been included in previous models. To illustrate this effect, this study computes sea-level responses to simulated global erosion and deposition histories over a single ice-age cycle, from the Last Interglacial (similar to 120,000 years ago) to the present. These simulations show that if sea-level models accounted for sediment deposition but neglected water storage in seafloor sediment, modeled sea-level changes since the Last Interglacial could be overestimated by the globally averaged equivalent of about 2 +/- 1 m. This is a significant fraction of published estimates of globally averaged sea-level change (6-9 m) since the Last Interglacial. These results imply that water storage in sediment can significantly affect Earth's seawater volume over geologic time and demonstrate the importance of accounting for this effect in modeling long-term sea-level changes.