Seismic survey of the Blue Hole, Belize: a pre-study for ICDP-drilling

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A core study of the proponent has revealed that sediments at the bottom of the Blue Hole, a 125 m deep Pleistocene sinkhole located in the lagoon of Lighthouse Reef Atoll, Belize, consist of undisturbed, annually layered biogenic carbonate muds and silts with intercalated coarser grained storm beds. Sedimentation-rate of layered sections is 2.5 mm/yr on average, and our 6 m long core spans the past 1400 yrs. Oxygen isotopes of laminated sediment provide a late Holocene climate proxy: a highresolution 18O time series traces the Medieval Warm Period, the Little Ice Age, and the industrial temperature rise. Carbon isotopes (13C) decrease upcore and show the impacts of the decline of the Maya culture and the anthropogenic combustion of fossil fuel. Storm event beds are most common during AD 650-850, around AD 1000, during AD 1200-1300, and AD 1450-1550. Storm beds are rare during the past 500 years BP. Given the average sedimentation rate and the early Holocene marine inundation of the Lighthouse Reef lagoon, the total Holocene marine sediment record in the Blue Hole alone can be expected to cover about 8 kyrs. and more than 20 m of annually layered sediment. We plan to core this sediment package in the framework of the ICDP, and, therefore, need to perform a seismic pre-study in order to validate the layered nature and thickness of the late Quaternary sediments.