Insight from the Depths of the Straits of Florida: Assessing the Utility of Atlantic Deep-water Coral Geochemical Proxy Techniques

• Main Author: Rosenberg, Angela D.
• Other Authors: Peter K. Swart, Gregor P. Eberli, Chris Langdon
• Format: Other/Unknown Material
• Language: unknown
• Published: Scholarly Repository 2011
• Subjects: Deep-water corals; geochemistry; stable isotopes; Straits of Florida; temperature; salinity; Antarctic; Antarc*
• Online Access: https://scholarlyrepository.miami.edu/oa_theses/244; https://scholarlyrepository.miami.edu/cgi/viewcontent.cgi?article=1243&context=oa_theses

This thesis addresses the utility of deep-water coral geochemistry and its potential to reconstruct oceanographic conditions in the Straits of Florida. Through stable isotope and elemental analyses of the carbonate skeletons and use of available geochemical proxy calibration equations, present and past environmental parameters were determined. Over the last several years, scientific expeditions to the bottom of the Straits of Florida have revealed hundreds of deep-water coral mounds and led to the collection of extensive oceanographic data, sediment samples, and deep-water coral specimens. In 2005-2006, an Autonomous Underwater Vehicle (AUV) was used to map the coral mound fields at five sites with the use of geophysical imaging technology, and the manned Johnson-Sea-Link II submersible was deployed for further exploration and sample collection. The AUV and the submersible CTD also measured numerous environmental parameters, including temperature and salinity. With the goal of reconstructing environmental parameters across the Straits of Florida, Scleractinian and gorgonian deep-water coral specimens were selected from three sites spanning the Straits. Each coral was sampled at the highest resolution possible and analyzed for stable isotopes and elemental concentrations. Resulting geochemical data, specifically d18O, d13C, Sr/Ca, and Mg/Ca, was then used with previously published and newly developed calibration equations to calculate temperature, salinity, and seawater density. Kinetic and vital effects were also examined and taken into account while reconstructing environmental parameters using the coral geochemistry. Additional reconstructions using stable isotopic values from benthic foraminifera corroborated the geochemical reconstructions, and analyses of pteropods and surface sediment samples provided further insight into the oceanographic conditions at the bottom of the Straits of Florida. Results from geochemical reconstructions agreed with in situ data, indicating that slightly warmer bottom temperatures exist on the eastern side of the Straits and salinity variability among the three sites is minimal. This suggests that the deep-water coral skeletons are sensitive recorders of the environmental conditions in which they lived. Ultimately, in situ measurements and reconstructed parameters showed that there is little variability across the bottom of the Straits and that Antarctic Intermediate Water (AAIW) is the only apparent water mass in the area at that depth. Moreover, comparison of the coral habitat from this study with others from around the world demonstrated that certain conditions are required for deep-water coral growth, and that these same parameters are common to deep-water reef systems throughout the globe. Further sampling and geochemical analyses of deep-water corals in the region may be used to gain additional insight into the oceanographic conditions surrounding the coral mounds both presently and in the past. As with other previously studied deep-water coral systems, this highlights the potential for the reconstruction of paleo environmental records from deep-water corals in the Straits of Florida.