Geomorphology of the Belize Barrier Reef margin: a survey for IODP drilling

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As precondition for IODP drilling along the Belize Barrier Reef, a detailed bathymetric study using multibeam and shallow seismic techniques is planned along selected section of the forereef area between ca. 20-150 m water depth of this major reef margin. To date, no detailed and GPS-controlled bathymetry and continuous high-resolution seismic data of this barrier reef margin exists. Based on the data to be acquired, we intend to select suitable sites for IODP drilling. We hypothesize that postglacial lowstand and transgressive reefs mark clear topographic lineaments / terraces along the platform margin. We aim at locating fore-reef sites, which will be suitable to recover postglacial (20-10 kyr BP) and underlying older Pleistocene deposits along a series of core traverses. Furthermore, an international workshop is planned to bring together interested scientists in order to explore the possibilities of developing a drill proposal for the IODP. The subsequent IODP proposal could have four potential objectives including the reconstruction of postglacial sea-level rise, to analyze and quantify postglacial reef composition and architecture as response to sea-level and climate change, and to obtain environmental data on temperature and carbonate saturation during that time window. In addition, aspects of Pleistocene reef initiation and paleoecology may be investigated, depending on recovery in older Pleistocene succession. In the light of the modelled 21st century increase in sea-level rise, postglacial drowned reef sequences along the Belize margin can potentially be used for future sea-level projections. In contrast to the Indo-Pacific region where several highly resolved and scientifically robust reef-based postglacial sea-level records have been acquired (Huon Peninsula, Tahiti, Great Barrier Reef), there is only one such record in the tropical western Atlantic (Barbados, eastern Caribbean). The Barbados record is curious however, in the light of the fact that of meltwater pulses (MWP) 1A and 1B only the former has been detected in the recently acquired sea-level data from Tahiti (IODP leg 310) and the Great Barrier Reef (IODP leg 325). Also, abundant postglacial microbialite facies found in the Tahiti and Great Barrier is apparently absent in Barbados for hitherto unknown reasons. Proxy data (thickness, volume) from these comparably simple organisms (bacteria) are largely environmentally controlled and presumably easier to interpret as proxy data (sclerochronology, d18O, Sr/Ca) from encymatically controlled reefal framebuilders such as corals. It has been debated whether microbialite abundance is linked to the nature of the hinterland, carbonate saturation, and rate of sea-level rise. In summary, a second postglacial reefal archive from the tropical Atlantic would certainly help to answer these open and debated questions and to constrain the nature of postglacial sea-level rise in the western Atlantic.