Biogeochemical proxies of environmental change in surface and deep-sea corals from the Pacific

This dissertation research aims to develop and test biogeochemical proxies of environmental change in both massive hermatypic reef building corals (surface corals), and azooxanthellate corals (deep-sea corals) from the Pacific. The research on surface corals focused on the use of stable isotopic (delta 13C, delta18O) and trace element (Sr/Ca) proxies to reconstruct the frequency of past bleaching events and the associated stressors, increased sea surface temperatures (SST) and decreased salinities due to flood events, on the Great Barrier Reef (GBR) and French Polynesia. The results suggest there is a clear and discernable decrease in the delta13 C values of a coral head that was known to have bleached during the 1998 large-scale bleaching event on the GBR when the coral is sampled at a high (near-weekly) resolution. The rapid decrease in delta13C values is also of value for reconstructing unknown bleaching events that have occurred in the past in a particular coral head, but our results suggest that different corals within the same reef may not record the same delta 13C shift due to multiple factors that affect the carbon isotopic signature. In addition delta18C and Sr/Ca measurements are able to reconstruct the increased SST and salinity changes that caused the bleaching events. Overall, these results show that it is possible to reconstruct past bleaching events and the associated stressors: increased SST, increased solar radiation, and decreased salinity, using stable isotopic and trace element proxies. By using these proxies in multiple cores, it should be possible to develop a record of the minimum number of bleaching events that have occurred on a reef.;Research on deep-sea corals focused on the development of radiocarbon based ages and growth rates of four different deep-sea coral species from the Pacific Ocean in order to develop age models for new proxy time-series. The radial growth rates and ages of three different groups of Hawaiian deep-sea corals were determined. Using time markers associated with bomb 14 C, growth rates on the order of 100s of mum/year and life spans ranging from ∼20 to ∼100 years were calculated for Corallium secundum and Antipathes dichotoma samples. A growth rate of 16 mum/year and an age of 770 +/-30 was calculated from a high resolution 14C radial transect on a live collected Gerardia. With a growth rate of <10 mum/year and an age of ∼2330 years, the Leiopathes glaberrima is also extremely long lived. The primary source of carbon to the C. secundum samples was dissolved inorganic carbon (DIC) while particulate organic carbon (POC) is the primary source of carbon to the Gerardia, A. dichotoma, and L. glaberrima samples. Delta14C data suggest that bamboo corals from the Gulf of Alaska are long-lived (75-126 years) and that they acquire skeletal carbon from two distinct sources. Surface-derived POC is the primary source of carbon for the gorgonin nodes while ambient DIC is the primary source of carbon for the calcareous internodes. Independent verification of the growth rate estimates and coral ages is obtained by counting seasonal Sr/Ca cycles and probable lunar cycle growth bands.