SCLEROCHRONOLOGY AND SST CALCULATIONS FROM OXYGEN ISOTOPES IN CORALS FROM PUERTO RICO

This study aims to measure the growth rates of corals using Coral XDS software and measure δ¹⁸O values to use them as proxies for SST to determine the accuracy and resolution of the coral data. We cataloged the growth rate of 3 Orbicella sp. and used δ¹⁸O values of one coral to determine SST during the time of growth. Each coral represents a different environment in Puerto Rico. One Orbicella annularis from Mona Island, collected at 5 m, l showed a growth rate of 6.38 mm/yr (n=18). One Orbicella annularis from Buye, collected at 2 m, showed a similar growth rate of 7.65 mm/yr (n=14). Finally, one Orbicella faveolate from Mayaguez, collected at 10 m, showed the biggest growth rate 8.05 mm/yr (n=4). The growth rate results are between the range mentioned in the literature (Carricart-Ganivet, 2004; Hudson, 2003; Dustan, 1975). And the difference in the growth rates is due to changes in depth, with increasing depth the growth rate is less or age and size of the coral, younger and smaller corals have higher growth rates because they use more energy towards growth and less towards reproduction (Dustan, 1975; Page and Vaughan, 2014). For the δ¹⁸O derived SST we calculated a minimum temperature of 19.29 ^oC, a maximum temperature of 36.72 ^oC with an average of 23.59 ^oC. These were then compared with the HadISST1 data set which for the location and time shows a minimum temperature of 25.79 ^oC, a maximum of 29.34 ^oC with an average of 27.74 ^oC. Both temperature sets had an overall similar trend and low variance with respect to each other. The variance present can be attributed to an attenuation of the isotopic signal from physiological activity or strong winds that can shift the δ¹⁸O of precipitation and in turn change the δ¹⁸O of seawater (Yao et al., 2013). Overall, we determined that the δ¹⁸O technique is valid for paleoclimate reconstructions in places with low or no salinity changes and 2 that the growth rate calculations using Coral XDS fall within the expected global rates reported in the previous literature.