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No description available.

Scleractinia (stony corals) are powerful tools in the field of paleoceanography, allowing researchers to reconstruct past ocean conditions based on variations in coral geochemistry. As corals regularly accrete their aragonite skeletons they preserve a history of climate on regional to global scales. Often able to provide centuries long continuous records of climate, an individual coral colony can provide insight into significant environmental perturbations. If preservation permits, fossil corals can be used to evaluate climate thousands of years in the past. Researchers use paleoclimate proxies, which are indirect geochemical fingerprints of environmental conditions, to create paleoclimate time series. Paleoclimate proxies are prevalent throught the literature and while many are well constrained by years to decades of use, individual conditions unique to study sites and timescale prevent the use of blanket assumptions regarding their interpretation. In this dissertation I illustrate the varied ways that the same or similar coral-based climate proxies can be used to reconstruct past ocean conditions. Part I (Ch. 2, 3) presents two studies based along of the Pacific Coast of Panamá to examine the influence of the seasonal migration of the Intertropical Convergence Zone (ITCZ). I analyzed a long-term coral δ18O time series from a living massive Porites colony to address low-frequency variation overprinted by the wet-dry seasonality. The coral record uncovered a clear decadal (~11 year) cycle in coral δ18O-inferred precipitation. I propose this mode is related to basin-wide processes, specifically a component of the Pacific Decadal Oscillation, which describes large-scale patterns in sea surface temperature (SST) and precipitation influencing marine ecosystems. In Chapter 2, I supplement the coral δ18O record with a coral Ba/Ca time series from a different coral colony. Coral Ba/Ca can be used as a proxy for river discharge (Q), although this practice is relatively new. Our coral record outlined seasonal variation in river Q and can also be used to identify past El Niño events and prolonged periods of drought. Uncovering a geochemical indicator of El Niño in this region is particularly powerful since conditions become warm and dry, which negate each other in coral δ18O rendering the proxy unable to consistently identify these climate events. This chapter furthers the community’s understanding of the many ways that trace metals can be used in paleoceanographic research, specifically to constrain local hydroclimate. In Part II (Ch. 4, 5) I present two studies in the Great Barrier Reef (GBR) based on coral δ18O and Sr/Ca records from modern and fossil Isopora, a coral species that is nearly completely absent from the paleoceanographic literature. Although this suite of climate proxies is similar to those used in Part I, in Part II the GBR corals provide a history of sea surface temperature rather than hydroclimate, which is due to prevailing local environmental conditions over a given timescale. In Chapter 4 I developed the first modern Sr/Ca- and δ18O-Sea Surface Temprature (SST) calibration using Isopora, which approaches those calculated for the commonly used Porites corals. Using Isopora in Pacific-based paleoceanographic research allows us to analyze coral records from reefs that might not be dominated by Porites. In Chapter 5 I applied the new Isopora Sr/Ca- and δ18O-SST calibrations to fossil corals recovered during Integrated Ocean Discovery Program (IODP) 25. The fossil corals date beyond the Last Glacial Maximum (LGM, ~20 kyr BP) to 25 kyr BP. In the Pacific SST change since the LGM is better constrained for more equatorial locations so our fossil samples from the GBR extend the geographic network of LGM-aged coral-based climate proxies. I measured ~5-7°C of cooling in the GBR at the LGM compared to today. The SST change through the LGM deglaciation provides valuable understanding of reef resilience and future risk of or adaptability to climate change. Each chapter in this dissertation uses similar strategies but provides a unique perspective on past climate change in the tropical Pacific. This dissertation identifies the many ways that coral proxies can be utilized with specific examples of the ways in which interpretation can vary. It is necessary to consider the environmental specifics of a given region before blindly interpreting paleo-proxy data. Furthermore, coral-based proxy records are supremely powerful tools in exploring and uncovering past climate histories of a given region. Coral-records can supplement and extend the limited instrumental record with centuries to millenia long information on SST and hydroclimate. These data can improve climate models, further our knowledge of coral reef growth, and deepen our understanding of regional hydroclimate, which are all vital to our understanding of global climate.

published_or_final_version / Zoology / Master / Master of Philosophy

Earth’s climate system has experienced significant changes throughout its history. Tropical, glacial and interglacial conditions have persisted across the globe during the Tertiary, and the present interglacial period with strong seasonality and episodes of warming and cooling has existed for the last several thousand years. However, rapid warming during the last century has highlighted the importance of understanding past climate behaviour, in order to predict the likely effects of such warming on our future climate. This has led to the use of proxies, such as sediment cores, tree rings, ice and carbonates, which provide high resolution palaeoclimate archives. Studies using a variety of proxies from around the globe have developed a network of site specific climate information, offering insights of climate fluctuations on a millennial scale, and identifying changing oceanic conditions as a major influence on global climate change. Coral skeletons are particularly sensitive recorders of ambient seawater conditions as they record fluctuations of oxygen and carbon in their aragonitic skeletons, which are caused by perturbations of sea surface temperature (SST) and sea surface salinity (SSS). Therefore, tropical oceans themselves provide a crucial record of climate change. Many of the coupled atmospheric-oceanographic processes that drive the global climate system occur in the Indo-Pacific, making it a particularly important region for data collection. Porites corals from the Indo-Pacific have been studied in detail and have revealed high resolution SST and SSS records, yet comprehensive investigations using other coral species are minimal. This study expands upon the current understanding of coral proxies by investigating three coral species of different ages, and provides new insights into the palaeoclimate history of the Indo-Pacific. Goniastrea retiformis, Platygyra pini and Platygyra lamellina corals have been retrieved from Timor Leste in the Indo-Pacific, and analysed using stable and radiogenic isotopic techniques. Sclerochronology was used to determine that the 4.5 year old, modern G. retiformis coral was living from 2006-mid 2010. Uranium-thorium (U/Th) analysis provided a mid Holocene age of 4.5 ± 0.092 (2σ) ka for the fossil P. pini. Uranium-lead (U/Pb) techniques were used to obtain a 2.7 ± 0.34 (2σ) Ma age for the fossil P. lamellina. A rigorous diagenetic screening process of X-ray diffraction (XRD), petrographic analysis of thin sections, and scanning electron microscopy (SEM) has been carried out to ascertain the extent of preservation in each coral. X-ray images allow annual density bands to be located and unique micromilling paths were developed for the three samples. This enabled us to obtain the first δ¹⁸O and δ¹³C stable isotope results for a G. retiformis coral, and the first fossil coral results for the Platygyra genus. Cross spectral analysis has been used to verify the periodicity of seasonal fluctuations visible in the data, and confirmed that these coral species are suitable for use as climate proxies. G. retiformis is an abundant reef coral distributed throughout the tropical Pacific, and has a robust skeletal configuration making it suitable for use as a climate proxy. The 4.5 year long record has revealed that δ¹⁸O and δ¹³C values range from -4.62‰ ± 0.03‰ (2σ) to -6.11‰ ± 0.02‰ (2σ), and 1.57‰ to -2.53‰, with means of -5.35‰ and -1.02‰, respectively. These values are in agreement with the average δ¹⁸O range of -5.1 to -5.6‰ in modern corals throughout the Indo-Pacific, predominantly of the Porites genus. Statistical analysis of the isotopic data has revealed a quasi-biennial signal in G. retiformis, typical of the temporal interaction between El Niño Southern Oscillation (ENSO) and the South Asian monsoon. Results have also been compared to the Southern Oscillation Index (SOI) in order to assess potential relationships between coral isotopes and ENSO. This has shown an accurate record of El Niño and La Niña events for the first half of the ~ 4.5 year record, from 2006 to mid 2008. Climate processes such as local rainfall and the Indian Ocean Dipole (IOD) are also reflected in the record, to varying extents. The use of Platygyra corals as climate proxies is limited to three investigations using modern samples, despite the fact that this genus has a much broader latitudinal range than the extensively studied Porites genus. This thesis provides the first examination of fossil samples, and provides analysis of both pristine and altered specimens. The 4.5 ka P. pini coral has allowed investigation of the palaeoclimate record in a sample that has been exposed to diagenesis. XRD, petrographic and SEM analyses have revealed widespread secondary aragonite growth, dissolution and secondary calcite within the coral, which would have occurred due to marine and freshwater diagenesis. However, primary growth textures have been retained in some areas of the coral. δ¹⁸O and δ¹³C values range from -3.47‰ ± 0.03‰ (2σ) to -5.45‰ ± 0.02‰ (2σ), and 3.43‰ to -0.49‰, with means of -4.82‰ and 1.12‰, respectively. These values are significantly more positive that the mean δ¹⁸O of four Platygyra corals from the Pacific region, which range from -4.82‰ to -5.10‰. There are two reasonable explanations for this. Secondary aragonite, which is detected throughout the milled section of coral, causes positive shifts in coral δ¹⁸O, an effect which is likely to have altered the geochemical record of this particular coral. But the fact that SST in the southern Indo Pacific Warm Pool (IPWP) during the mid Holocene were 1.2° C cooler than present must also be acknowledged, as cooler temperatures also impart a shift toward higher δ¹⁸O, due to equilibrium fractionation processes. SST reconstruction using the temperature dependence equation from a modern Platygyra coral reveals an SST range of 18.5-27.6° C, and mean of 24.7° C. The present day mean annual SST of 28° C suggests that mid Holocene temperatures less than 26.8° C are unrealistically cool, highlighting the fact that isotopic fractionation during diagenesis has affected coral chemistry. However, the presence of interannual periodicity indicates that ENSO was operating, and the magnitude of isotopic fluctuation through the 10 year record is similar to that found in modern and other Holocene corals. We suggest that although absolute isotopic and SST values are unreliable, prohibiting the extraction of high resolution climate records, insights into the behaviour of broad scale, seasonal and interannual climate processes may still be obtained. A strong annual periodicity has been detected when analysing the stable isotopic values recorded in the 2.7 Ma P. lamellina coral. This indicates that seasonal SST fluctuations were the dominant influence on this coral. Ranges of -4.67‰ ± 0.03‰ (2σ) to -5.48‰ ± 0.02‰ (2σ) and 0.88‰ to -1.12‰ for δ¹⁸O and δ¹³C, respectively, are similar to modern Platygyra coral results, suggesting that this coral has been preserved in pristine condition. Palaeo-SSTs have been reconstructed using a modern Platygyra temperature dependence equation, providing a range of 24-27.7° C and a mean of 25.9° C. Foraminiferal data from sediment cores in the greater Indo-Pacific suggest that mean annual SSTs at this time were ~ 2-3° C cooler than present. The coral record I present supports this statement, providing new insights into our understanding of tropical palaeoclimates. This coral has been entrained within a turbidite deposit on the sea floor that has subsequently been uplifted during the emergence of Timor, with U/Pb dating allowing further constraints of the stratigraphic age of the deposit. Tectonic narrowing is postulated to have caused major changes to the Indonesian Throughflow (ITF) from 4-2 Ma, and been a driver of major global climate change beginning in the late Pliocene. This means that fossil Platygyra corals Timor Leste could provide unique time slices of information about this important time in global climate history. This study confirms that G. retiformis, P. pini and P. lamellina corals are excellent candidates for further, detailed investigations. They provide the opportunity to develop new coral proxies which are both abundant throughout the tropics and distributed over a wide latitudinal range. Their prevalence in both modern and fossil reefs means that once modern samples of each species have been calibrated against modern SST and SSS, these corals will provide reliable, quantitative palaeoclimate proxies, with potential for data capture throughout the Indo-Pacific and mid latitudes. Geochemical coral archives are a crucial tool in the study of climate processes, and we believe that these species are ideally suited to enhancing and refining our current understanding of earth’s climate system.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 238-258). / Microfiche. / xv, 258 leaves, bound ill., photographs 29 cm

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

This thesis contains descriptions and illustrations of six genera and seven species of fossil corals collected by the writer on Mount Norquay, Banff National Park, Alberta. A brief discussion of the fossil locality and stratigraphy of the Rundle formation in that area is given. As a result of statistical research and graphic representation, a new species Faberophyllum multiseptatum is described. The new species is closely related to F. languidum, F. leathamense, F. pisgahense, and F. araneosum. The species Ekvasophyllnm banffense is proposed, and the species Lophyphyllum ? cascadense Warren is redescribed and referred to the genus Ekvasophyllum. The genera Triplophyllites and Cyathoclisia, which previously have not been described from Canada, are recognized and briefly discussed. The descriptions of Lithostrotion whitneyi and Lithostrotionella banffensis are revised and adequately illustrated. From the study of corals from the upper Rundle formation the writer concludes that these may be important horizon markers, and recommendations are made for more extensive and detailed work on this subject. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Lau, Pui Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 84-94). / Abstracts in English and Chinese. / Abstract (English) --- p.i / Abstract (Chinese) --- p.v / Acknowledgements --- p.ix / Contents --- p.x / List of Figures --- p.xiv / Chapter Chapter 1 --- General Introduction / Chapter 1.1 --- Regulations of gametogenesis and mass spawning in corals --- p.1 / Chapter 1.1.1 --- Endogenous cues --- p.2 / Chapter 1.1.2 --- Environmental cues --- p.3 / Chapter 1.2 --- Studies on black corals --- p.5 / Chapter 1.2.1 --- Introduction of black corals --- p.5 / Chapter 1.2.2 --- Black corals harvesting --- p.6 / Chapter 1.2.3 --- Biodiversity and distribution of black corals in Chinese and Hong Kong waters --- p.8 / Chapter 1.2.4 --- Threats to black corals --- p.9 / Chapter 1.3 --- Significance and objectives of the present study --- p.11 / Chapter 1.3.1 --- Objectives --- p.12 / Chapter 1.3.2 --- "The targeted species, Antipathes curvata and the study site" --- p.13 / Chapter 1.4 --- Thesis outline --- p.14 / Chapter Chapter 2 --- "Reproductive Biology of Antipatharian Black Coral, Antipathes curvata in Lan Giio Shui, Hong Kong" / Chapter 2.1 --- Introduction --- p.18 / Chapter 2.1.1 --- Coral Reproduction --- p.20 / Chapter 2.1.2 --- Sexual reproduction in black corals --- p.21 / Chapter 2.2 --- Materials and methods --- p.24 / Chapter 2.2.1 --- Sample collections and pre-treatment --- p.24 / Chapter 2.2.2 --- Histological processing --- p.25 / Chapter 2.2.3 --- Light microscopy --- p.26 / Chapter 2.2.4 --- Gametogenesis --- p.27 / Chapter 2.2.5 --- Environmental and statistical analysis --- p.27 / Chapter 2.3 --- Results --- p.28 / Chapter 2.3.1 --- General reproductive mode --- p.28 / Chapter 2.3.2 --- "Sex ratio, size at sexual maturity and density of gamete" --- p.28 / Chapter 2.3.3 --- Characteristics of polyps and gametes of A. curvata --- p.29 / Chapter 2.3.4 --- Changes in geometric diameter of gametes overtime --- p.30 / Chapter 2.3.5 --- Developmental stages of gametogenesis --- p.31 / Chapter 2.3.5.1 --- Oogenesis --- p.31 / Chapter 2.3.5.2 --- Spermatogenesis --- p.32 / Chapter 2.3.6 --- Development of oocytes and spermaries over time --- p.34 / Chapter 2.3.7 --- Correlation of black coral reproduction with seawater temperature --- p.35 / Chapter 2.3.8 --- Gametogenesis in individual colonies --- p.36 / Chapter 2.3.8.1 --- Female colonies --- p.37 / Chapter 2.3.8.2 --- Male colonies --- p.39 / Chapter 2.4 --- Discussion --- p.40 / Chapter 2.4.1 --- Asynchronization of gametogenic cycle --- p.40 / Chapter 2.4.2 --- Possible effect of seawater temperature on reproduction of A. curvata --- p.43 / Chapter Chapter 3 --- Detection of the Sex Steroid 17β-estradiol and its Possible Roles on Gametogenesis in Black Corals Antipathes curvata from Hong Kong / Chapter 3.1 --- Introduction --- p.55 / Chapter 3.1.1 --- "Roles of sex hormone, 17(3-estradiol (E2) in the reproduction of vertebrates" --- p.58 / Chapter 3.1.2 --- Roles of vertebrate-type sex steroids in Cnidaria --- p.59 / Chapter 3.2 --- Materials and methods --- p.63 / Chapter 3.2.1 --- Study site --- p.63 / Chapter 3.2.2 --- 17β-estradiol (E2) extraction --- p.63 / Chapter 3.2.3 --- 17β-estradiol (E2) assay --- p.65 / Chapter 3.2.4 --- Calculation and assay validation --- p.65 / Chapter 3.2.5 --- Gametogenesis of A. curvata --- p.66 / Chapter 3.2.6 --- Seawater temperature and statistical analysis --- p.67 / Chapter 3.3 --- Results --- p.67 / Chapter 3.3.1 --- Seasonal profile of E2 --- p.67 / Chapter 3.3.2 --- Gametogenesis --- p.68 / Chapter 3.3.3 --- Correlation with seawater temperature --- p.69 / Chapter 3.4 --- Discussion --- p.70 / Chapter Chapter 4 --- Summary and Perspectives --- p.78 / References --- p.84