Accretion patterns of Belize barrier and atoll reefs: an archive of environmental change during the Holocene

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The status of tropical coral reefs has been declining due to warming, ocean acidification, pollution, and disease (Pandolfi et al. 2003, 2011; Hughes et al. 2017; Eyre et al. 2018). This is also visible in reefs of the Caribbean realm in that live coral cover has diminished (Gardner et al. 2003), many reefs are no longer dominated by corals but fleshy algae (Hughes 1994), reef-building acroporid and massive faviid corals are reduced in abundance and replaced by weedy, generalistic taxa (Perry et al. 2015; Kuffner and Toth 2016), and reef accretion potential has decreased (Perry et al. 2018). As millions of people are living along tropical coasts and on reef islands and because these people are dependent on coral reefs socio-economically, this issue is not purely scientific. The study of drill core material extracted from modern coral reefs allows detailed reconstructions of environmental conditions during the Holocene based on sedimentological, paleoecological, and geochronological analyses. Based on these data, previous ecological and environmental changes can be reconstructed that may allow to decide whether or not current declines are unprecedented and serve also as basis for future predictions. It is proposed to revisit existing core material from Belize barrier and atoll reefs, the largest reef system in the Atantic, and to perform additional age dating to constrain patterns of reef accretion, date faunal changes, and identify possible reef gaps. This will be achieved by quantitatively analyzing reef composition and by obtaining some 50 new U/Th-dates from corals in 22 drill cores (total Holocene length 213.4 m) and to add these to 58 existing age dates. As a valuable side-effect, the regional Holocene sea-level curve of Belize can be refined based on the new age data.