Paper No. 40-25
Presentation Time: 9:00 AM-5:30 PM
RECONSTRUCTING SEA SURFACE TEMPERATURES IN THE CARIBBEAN DURING THE EARLY-MID HOLOCENE FROM A REEF EXPOSURE IN CANADA HONDA, ENRIQUILLO VALLEY, DOMINICAN REPUBLIC
Temperatures during the Holocene are driven by seasonal changes in insolation; however, a better understanding of insolation mechanisms and how it affects tropical climate is still necessary. This study presents annual growth rates seasonally resolved oxygen and carbon isotopic and Sr/Ca trace elemental variations from five fossil Montrastraea sp. corals collected in growth position, in the erosional gully Cañada Honda located in the Enriquillo Valley, Dominican Republic. U/Th dates obtained from fossil corals in M1 facies indicate early-mid Holocene dates ranging from 8.0-8.9 ka B.P. Fossil corals from the Cañada Honda Reef Site are uniquely suited for paleoclimate reconstruction as high sedimentation rates during deposition and arid climate conditions helped preserve the coral’s skeleton integrity. The aragonite skeleton composition was confirmed by X-ray diffraction. Growth rates in Montrastraea sp. corals, with a record of 30-80 years, collected at this site, range from 2.07 ± 0.14 to 3.55 ± 0.37 mm/yr (n=5). This growth rates range is much lower than values reported from modern corals of the species Montrastraea sp in the Caribbean. High sedimentation rates in the reef were estimated to range from 1.53 ± 0.18 to 2.48 ± 0.45 mm/yr (n=8) based on sclerochronology measurements combined with morphological foliations in the coral skeleton interpreted to have been caused by sedimentation input stress. Measurements of δ18O and Sr/Ca from Montrastraea sp. corals were done along the skeleton in continuous transects at 1mm increments along the growth axis. δ18O measurements range from -0.69 to -2.41 (n=430), values that are heavier relative to modern corals from the tropics by ~2‰. This enrichment may be due to high saline environment. Sr/Ca measurements range from 9.07 to 9.70 mmol/mol (n=430) and provide values that are close, but more concentrated, than modern corals from the tropics. This is probably due to corals incorporating more strontium in colder waters and/or strontium enriched groundwater seepage into the system. Both proxies suggest temperature variations of 6⁰-7⁰C, values never reported from the Early Holocene, but may be explained by periods of freshwater influx. A low correlation index (R) estimated for both paleothermometers (0.26-0.85) suggests that they are reacting to different variables.