Great Blue Hole: a sedimentological archive of tropical cyclone frequency covering the Holocene at annual resolution

Sedimentary archives from marine sinkholes enable long-term reconstructions of past storm activity. In the last years, numerous cyclone-frequency reconstructions have been obtained from sediment cores collected in blue holes located in the circum-Caribbean region. Such structures work as sediment traps for allochthonous particles, mobilized through storm waves and surges from adjacent areas by passing cyclones. The 320 m wide and 125 m deep Great Blue Hole (Lighthouse Reef, Belize) is an outstanding cyclone-frequency archive worth exploring due to anoxic bottom-water conditions and the opportunity to recover annual deposits spanning the Holocene interglacial and even parts of the late Pleistocene. In June 2022, a 30-m-long sediment core (BH8) was extracted from the sinkhole and dated to 12.5 ka BP at its base. Sedimentological and palynological analyses point to an initial cenote-like setting that experienced a rising marine influence starting around 7.2 ka BP, which led to brackish and restricted marine conditions until 5.7 ka BP. Afterwards, full marine conditions have persisted in the Great Blue Hole to present day. Our sediment-core analysis resulted in a 12000-years-long paleoenvironmental reconstruction at annual resolution. Several warm climate periods of this timeline represent past equivalents for the current situation of rising ocean temperatures. In the SW Caribbean, cyclone frequency changed from a rather variable and less active stage (12.5-3.5 ka BP) to a more stable and active state (3,5-0 ka BP). This bipartite pattern is surprisingly best explained by latitudinal changes of the Intertropical Convergence Zone (ITCZ) from a northern towards a southern location.