Abstract: The shell weights of planktonic foraminifera from marine sediments are influenced by both upper-ocean calcification and deep-ocean calcium carbonate dissolution, and are potential paleoceanographic proxies. Based on the global surface-sediment calibrations, dissolution begins to significantly affect planktonic foraminiferal shell weight when the deep-ocean carbonate ion saturation degree (CISD) is below 20 μmol·kg⁻¹. The shell weights of dissolution-susceptible species are more sensitive to CISD changes, and thus can be used as reliable deep-ocean CISD proxies. When the deep-ocean CISD is above 20 μmol·kg⁻¹, the shell weights of planktonic foraminifera can reflect the changes of their calcification degree. Previous paleoceanographic studies based on the shell weight proxies reveal that the calcifications of planktonic foraminifera mainly respond to the changes in seawater carbonate system and temperature during glacial-interglacial cycles. The evolutions of deep Pacific CISD since the Pliocene is controlled by the changes in sea level height, Southern Ocean ice-sheet/sea ice, and global thermohaline circulation. The planktonic foraminiferal shell weight proxy provides a powerful tool for exploring the evolution of ocean carbon cycle.