Arana-Morales, Ashlyann

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    Middle holocene SST record (6,200 +/- 80 to 4,760 +/- 90 yr B.P.) based on corals from Cañada Honda, Dominican Republic
    (2018-05) Arana-Morales, Ashlyann; Ramírez-Martínez, Wilson R.; College of Arts and Sciences - Sciences; Winter, Amos; Mendez Tejeda, Rafael; Santos Mercado, Hernán; Rodríguez Iglesias, Lizzette; Department of Geology; Grove, Kurt A.
    It is important to understand climate change in the past, present, and future. The Holocene was initially considered to have a relative stable climate, however, significant climate variations have been observed in several paleoclimate records studies. Previous studies have shown that coral proxy records can provide past archives of paleoclimate variations in the tropics. Using both Sr/Ca and δ18O analysis should lead to a higher precision and resolution of the SST reconstruction. The subaerial exposure of the Cañada Honda fossil coral reef, located in the Enriquillo Valley of the Dominican Republic, provides remarkable well-preserved corals that lived in a shallow water reef environment during the Holocene. Although many coral species are present in the Cañada Honda reef, the Orbicella sp. corals are the main focus of this project. The U/Th dates from MZ facies range from 5152 ± 30 to 6833 ± 31 yr B.P. The average growth rate obtained for all MZ coral facies zone ranges from 4.43 ± 0.03 to 5.18 ± 0.04 mm/yr with an average value of 4.73 ± 0.03 mm/yr (n from 21 to 32 years). Based on the measurements of the corals the estimated sedimentation rate in the reef at the time of accretation was 6.29 ± 0.15 to 5.76 ± 0.15 mm/yr with an average value of 6.03 ± 0.15 mm/yr (n = 1 to 3 years). The presence of the expected aragonite XRD spectra and absence of all the possible calcite peaks in the diffractograms indicates the coral samples studied have retained the original aragonitic mineralogical composition. The Sr/Ca values obtained from coral samples range from 9.1 to 9.5 mmol/mol, similar to Holocene samples from the tropics. The δ18O values obtained from the MZ Orbicella sp. in this study (6 kya B.P) range from -2.84 to -3.11 ‰. Having a more positive δ18O from the fossil corals than modern corals is a result of the corals being exposed to a salinity environment. The Sr/Ca ratios measured in corals of the facies MZ resulted relatively higher than Sr/Ca measurements reported for modern corals but similar to Holocene samples from different locations. By measuring higher Sr/Ca ratios, the temperatures obtain were colder than anticipated.