| Summary: | We present here the first study of coral microatolls in the Caribbean. An exceptional site (Belloc reef) where dozens of microatolls were growing was uplifted and exposed during the 12 January 2010 Mw 7 Haiti earthquake. Total station measurements of the old pre-earthquake and the new post-earthquake coral highest level of survival (HLS) on two generations of Siderastrea siderea corals allowed us to estimate a value of 45 ± 14 cm for the coseismic uplift. In this small 90 m × 70 m reef, microatolls of different shapes (cups, hats or flats) coexist, indicating long term submergence, emergence or stable relative sea-level. This variability in coral shape is uncommon. Two slices of microatolls, one cup-shaped (B8) and one hat-shaped (B10) were sampled with a chain saw and X-rayed to study their stratigraphy. B10 recorded a mean relative sea-level decrease of about - 1 mm/yr over the last five decades, whereas B8 has grown in a context of relative sea-level rise at a rate of about 1 mm/yr over nine decades. Several sudden and temporary die downs simultaneously disrupted the growth of both corals in 1940 ± 2, 1963 ± 2, 1983 ± 2, 1992 ± 1, 2001 ± 1 and 2009 and may be caused by oceanographic/climatic phenomena occurring in the tropical North Atlantic. The last one, in 2009, was associated with a clear sea-level height decrease (about 10 cm) in the satellite data. B10 was strongly affected by these events and records die downs of systematically larger amplitude, which tended to delay its upward growth compared to B8. This makes B10 less reliable for the evaluation of the relative sea-level trend, its emergence rate being only an apparent estimate due to die downs. Fossil coral microatolls of Diploria strigosa which died between 1958 and 1966 (according to U/Th dating), probably during one of the strongest hurricane reported in Haiti (Flora, 1963), display a cup shape attesting for submergence. Their HLS is 1 cm below the HLS of the S. siderea killed in 2010. The record of B8, the diversity in shape of the S. siderea ...
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