Subtropical Atlantic Climate Variability Record in Speleothems from the Bahamas

of a dissertation at the University of Miami. Dissertation supervised by Professor Peter K. Swart. No. of pages in text. (331) The last 100,000 years of climate consist of numerous abrupt millennial scale climate variations. Of interest to this study are Heinrich stadials which are extreme cold events in the North Atlantic. While a comprehensive picture of climate across Heinrich events is emerging for the North Atlantic, very few studies have been conducted in the subtropical western Atlantic, which may be important for the global propagation of these events. This study is the first study to determine paleoclimate of the Bahamas across Heinrich stadials. Cave deposits, in particular stalagmites, offer the opportunity to obtain high resolution records of past climate. Typically, stable oxygen and carbon isotopes of the calcite are analyzed. However, when interpreting the oxygen isotope record of carbonates there are several climatic factors which can lead to changes in the oxygen isotopes. The hydrogen and oxygen isotopic analysis (δ2H and δ18O) of water trapped within speleothem carbonate (fluid inclusions) can shed light on the drivers of the carbonate oxygen isotopes. The application of cavity ring-down spectroscopy to the δ2H and δ18O analysis of water in fluid inclusions was investigated at the University of Miami (this study) as an alternative to traditional δ2H and δ18O methods and results demonstrate acceptable precision and good agreement with previous results. In order to ascertain the climate expression across Heinrich events in the subtropical Atlantic, carbon and oxygen isotopes, fluid inclusion isotopes and minor elements have been measured on a series of U-Th dated speleothems from Dan’s Cave, Abaco Island, Bahamas. The analyses suggest that during Heinrich stadials 1-6 temperatures decreased by ~3 °C. These findings support previous work in other areas of the North Atlantic and are consistent with the climate response to a weakening of the Atlantic meridional overturning circulation. To support the findings in the ancient stalagmites, a monitoring study has been conducted. The goal of the monitoring study is to better understand the drivers of kinetic isotope fractionation. In particular, the focus of this study was the carbonate clumped isotope methodology which is a relatively recent geochemical development and therefore more calibration studies are necessary. Nearly 2 years of monitoring a currently active cave in the Bahamas has been conducted and results demonstrate that clumped isotope fractionation increases during periods of increased ventilation and growth rate. Modern studies of atmospheric dust demonstrate that currently there is seasonal deposition to the Caribbean derived from Africa. Iron concentrations within the cave in the modern are found to be heterogeneous in drip waters and calcite both temporally and spatially. The temporal variation is thought to be due annual variations in dust delivery and the amount of precipitation. Additionally, two stalagmites collected from the Bahamas exhibit iron concentrations which increase concurrently with Heinrich stadials, suggesting increased dust deposition to the Bahamas during these events. ACKNOWLEDGEMENT First I would like to thank my advisor Dr. Peter K. Swart. I have been extremely luckily to work with Peter, who taught me how to ask scientifically relevant questions, to write scientifically, and who also taught me how to solder. I also am grateful for his advice, in particular his rule of threes. I am extremely luckily to have had a committee which has pushed me, and supported me. Ali Pourmand provided me with the opportunity to utilize the Neptune, which has become extremely helpful in my post-doctoral research. I would also like to thank Amy Clement, who has helped me to better understand the climate as a system and to think about my paleoclimate reconstructions in a global perspective. I would also like to than Kenneth Broad, who I had the opportunity to work with in the field and at RSMAS. I am greatly appreciative of all of the numerous dives which were required to create such a unique collection of stalagmite samples. I would also like to thank Larry Peterson, who helped me understand the paleoclimate of the last glacial period and link my records to other records from around the world. Finally I would like to thank Flip Froelich, for pushing me to better understand speleothem geochemistry. This work could not have been conducted without the help from many others. In particular, I would like to thank Huber Vonhof, who allowed me to visit his laboratory, utilize his machine for fluid inclusion analysis and has provided insightful comments to our publications. I would also like to thank Brian Kakuk who acquired permits necessary for sampling in the Bahamas and who has also conducted numerous dives to collect samples as part of this project. The Cape Eleuthera Institute in particular I would like to thank Ron and Karen, who have provided me with help while I am in the Bahamas, allowed me to store materials in their house, and who made sure I returned after visiting