CARBON AND OXYGEN ISOTOPE STUDY OF CARBONATES FROM WATLING’S BLUE HOLE AND BLUE HOLE FIVE, SAN SALVADOR, BAHAMAS

Carbonate platforms, such as the Bahamas, formed through deposition and sea level fluctuations. These platforms contain records of rapid interglacial climate change and are useful in studying the impacts of climate change on similar environments. Blue holes are dissolution lakes that may be beneficial for understanding climate change and anthropogenic impact. A δ¹³C and δ¹⁸O study was conducted on lake sediment core samples from Watling’s Blue Hole and Blue Hole Five on San Salvador Island, Bahamas. These lakes are located in a failed housing development and Watling’s Blue Hole was once part of an early 19th century plantation which modified the landscape of the surrounding watershed. These lakes are hydrologically connected to the ocean and are tidally influenced: seawater enters through karstic bedrock, while surface water is fresher because of rainwater inputs. Cores were collected from three sites in each lake. Initial studies included lithological core description, loss on ignition (LOI), x-ray fluorescence (XRF), and scanning electron microscopy (SEM) which together showed that sediments from the lakes differed from each other. Radiocarbon dating was used to produce an age model for each core. Two core was chosen based on the model and composition. Watling’s Blue Hole Site 2 had the older basal date at ~6,870 cal. yr. BP while Blue Hole Five Site 3 basal date was ~5,340 cal. yr. BP. These cores differed compositionally and may be a result of the anthropogenic impact in the top of the cores. The core from Watling’s Blue Hole was composed of fine to medium carbonate sands with few shells. The core from Blue Hole Five Site 3 was medium to coarse grained with shell beds. LOI data confirmed that the majority of the sediment for both lakes was carbonate, with varying amounts of terrestrial and aquatic organic material and very low, occasional inorganic pulses, probably a record of distal dust inputs. XRF analysis suggested a visual correlation between Fe and Ti. Pyrite, an indicator of oxygen-poor, sulfuric, reducing conditions was identified in cores from both lakes through SEM. The δ¹³C and δ¹⁸O study aided in understanding the climate change that occurred within the past 6,000 years in the Bahamas. The comparison of the lakes physically, compositionally, and isotopic data aid in understanding anthropogenic impacts on blue holes.