Climate-forced sea-level lowstands in the Indian Ocean during the last two millennia

Sea-level reconstructions over the past two millennia provide a pre-industrial context to assess whether the magnitude and rate of modern sea-level change is unprecedented. Sea-level records from the Indian Ocean over the past 2,000 years are sparse, while records from the Atlantic and Pacific Oceans show variations less than 0.25 m and no significant negative excursions. Here, we present evidence of two low sea-level phases in the Maldives, Indian Ocean, based on fossil coral microatolls. Microatoll growth is constrained by low water levels and, consequently, they are robust recorders of past sea level. U-Th dating of the Maldivian corals identified lowstands at AD 234-605 and AD 1481-1807 when sea level fell to maximum depths of -0.88 m and -0.89 m respectively. These lowstands are synchronous with reductions in radiative forcing and sea surface temperature associated with the Late Antiquity Little Ice Age and the Little Ice Age. Our results provide high-fidelity observations of lower sea levels during these cool periods and show rates of change of up to 4.24 mm yr(-1). Our data also confirm the acceleration of relative sea-level rise over the past two centuries and suggest that the current magnitude and rate of sea-level rise is not unprecedented.