Coral growth records 20^th Century sea-level acceleration and climatic variability in the Indian Ocean

Empirical observations of the rate of sea-level rise (SLR) and the timing of its recent acceleration are critical for validating ensemble methods used to determine global mean sea level trends. Such records are critically important at far-field locations where instrumental datasets are scarce. Here we construct a continuous 90-year sea level record (1930-2019) from the central tropical Indian Ocean derived from the incremental growth of a coral microatoll, which is demonstrated to reflect changes in sea level at annual timescales. Our record, which overlaps with tide gauge observations, extends the instrumental record by six decades and reveals climatic variability and marked changes in sea level behaviour across the twentieth century characterised by: (1) an increase in sea level of 0.30 m between 1930 and 2019; (2) low rates of SLR in the early twentieth century (1.42 ± 0.42 mm.yr^-1); (3) a marked acceleration in SLR to ~3.44 ± 0.68 mm.y^-1 in the late 1950's; and (4) a further increase to 4.39 ± 0.48 mm.y^-1 over the past three decades. Our results provide empirical evidence for a mid-century SLR acceleration in the central Indian Ocean, which is earlier than instrumental records indicate for coastal sites at the continental margins.