Relative sea-level changes during the last century recorded by coral microatolls in Belloc, Haiti

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 (HIS) 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 x 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 HIS is 1 cm below the HIS of the S. siderea killed in 2010. The record of 138, the diversity in shape of the S. siderea microatolls and the position of fossil D. strigosa corals overall indicate stable to slightly increasing relative sea-level (about 1 mm/yr). This is on the same order of magnitude, although slightly lower, as the rate we determined over the last 74 years by using eight tide gauge records around Hispaniola (1.63 +/- 0.20 mm/yr) and the mean rate of sea-level rise previously published (2.0 +/- 0.5 mm/yr) in the area. This study demonstrates that coral microatolls can be used to infer relative sea-level changes over the last decades or centuries in the Caribbean, where tide gauge records are often sparse, incomplete or nonexistent This is of prime importance for the numerous small and flat Caribbean islands, highly vulnerable to the threat of global sea-level rise. (C) 2016 Elsevier B.V. All rights reserved.