THE PROGRESSION OF SEDIMENTOLOGICAL FACIES AND THEIR CONTROL OF BIOGEOCHEMICAL CYCLING IN THE BIOLUMINESCENT BAYS OF VIEQUES, PUERTO RICO

The interactions of sediment, macrofloral communities, and environmental conditions were examined in three bays along the southern coast of Vieques Island, Pueto Rico. One of these bays has an extraordinarily high population of the bioluminescent dinoflagellate Pyrodinium bahamense. Mapping of the distributions of sedimentary facies and macrofauna, extraction of cores, and the collection of geochemical data for various facies allowed for the reconstruction of sedimentary history and the definition of macrofloral communities in the three bays. We also used GIS to compare the distributions of sediment and macrofloral communities to each other in order to produce bay average net oxygen flux rate estimates.

The cores record a high-resolution history of late Holocene relative sea level for Vieques. Overall, relative sea level is shown to have increased over time. Shallow water and terrestrial facies are overlain by trangressive facies, which are in turn overlain by deeper water facies. Facies successions also record a series of second-order regression-transgression sequences. The timing of relative sea-level rise may be discordant with the relative sea-level history of other components of the Puerto Rico Virgin Islands Microplate.

Macrofloral communities appear to be primarily controlled by light availability, substrate type, and substrate stability. Sediment type appears to be controlled by water depth, amount of wave-action, macrofloral communities, and the amount of suspended sediment in the water. Estimated bay-average oxygen flux rates for the sediment range from -52.6 mmol O₂ m^-2 day^-1 to -64.72 mmol O₂ m^-2 day^-1. This study has shown that the key factor controlling differences between environmental conditions, particularly concentrations of Pyrodinium bahamense, of Puerto Mosquito, Puerto Ferro, and Bahia Tapon, are (1) bay morphology, which controls turbidity; (2) nutrient concentrations; and (3) the amount of wave energy in the bays.