A giant underwater stalactite from the Blue Hole, Belize, revisited: a complex history of carbonate accretion under changing meteoric and marine conditions

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The aim of this project is to investigate a unique sample of a submarine stalactite, collected by Jacques Cousteau and the crew of the RV CALYPSO in the Blue Hole of Lighthouse Reef, Belize, in 1970. The sample offers the opportunity to study meteoric and especially extensive marine carbonate formation in a special environment and to obtain a highly resolved climate achive for a time window during the early Holocene. Preliminary studies have shown that the late Pleistocene-Holocene speleothem consists of a meteoric core, thick crust of marine aragonite cement, and a thin outher biogenic crust. The planned project has three objectives including (1) to reconstruct the history and conditions of formation of the stalactite in detail, (2) to assess the influence of organisms (microbes) in carbonate formation, and (3) to test the usability of the speleothem as postglacial climate archive. To achieve this, petrography and composition, precise U-series ages, geochemical signatures (d18O, d13C, Sr/Ca), as well as lipid biomarkers and CAS isotopes shall be analyzed systematically.