T105 Surf’s Up: New Insights on the Geology, Karst, and Paleontology of Carbonate Systems of the Bahama Archipelago (Posters)

Monday, 5 November 2012
9:00 AM - 6:00 PM
Hall B

GEOCHEMICAL AND PHYSICAL COMPARISON OF WATLING'S BLUE HOLE AND BLUE HOLE FIVE, SAN SALVADOR, BAHAMAS

Paper number: T105-3
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Blue holes are lakes on carbonate platforms that are formed by dissolution and may be related to sea level fluctuations. Two blue holes on San Salvador Island, Bahamas were studied for records of anthropogenic impacts and climate change. These lakes are among many on the island, and were chosen based upon past research, field observations, and historical evidence of anthropogenic impacts. Watling’s Blue Hole and Blue Hole Five are both located in a failed housing development on the island’s south end and Watling’s was once part of an early nineteenth century cotton plantation which modified the landscape of the surrounding watershed.

Watling’s Blue Hole and Blue Hole Five vary physically and chemically. Watling’s Blue Hole is circular in shape and has a depth of 8 meters and Blue Hole Five is keyhole shaped with a depth of 6 meters. These blue holes are hydrologically connected to the ocean and are tidally influenced: seawater enters deep in the lakes through karstic bedrock, while surface water is fresher because of rainwater inputs. Watling’s Blue Hole has a conduit located in the central basin whileBlue Hole Five’s conduit is located toward one side of the blue hole with a shallow bench on the other side. The blue holes are brackish (21 to 22 g/L for Watling’s Blue Hole and 16 to 17 g/L for Blue Hole Five), with haloclines at depths of 2.5-3 meters for Watling’s Blue Hole and 11.5 meters below lake surface for Blue Hole Five.

Lake sediment cores were collected from three sites (deep to shallow) in each blue hole. Lithological core description, loss on ignition (LOI), x-ray fluorescence (XRF), and scanning electron microscopy (SEM) show that sediments from Watling’s Blue Hole and Blue Hole Five varied from each other. LOI data confirmed that the majority of the sediment for both blue holes was carbonate, with varying amounts of terrestrial and aquatic organic material and very low, occasional inorganic pulses, probably a record of distal dust inputs. Diagenetic pyrite is present in both lakes. XRF data indicates differences in elemental analysis of cores from the blue holes.