PALEOTEMPESTOLOGY AND DEPOSITIONAL HISTORY OF CLEAR POND, SAN SALVADOR ISLAND, BAHAMAS A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Mark R. Dalman December, 2009 PALEOTEMPESTOLOGY AND DEPOSITIONAL HISTORY OF CLEAR POND, SAN SALVADOR ISLAND, BAHAMAS Mark R. Dalman Thesis Approved: Accepted: ______________________ ________________________ Advisor Dean of the College Lisa E. Park Chand K. Midha ______________________ ________________________ Faculty Reader Dean of the Graduate School Ira D. Sasowsky George R. Newkome ______________________ ________________________ Faculty Reader Date John Peck ________________________ Department Chair John P. Szabo ii ABSTRACT The field of paleotempestology has gained more awareness in the past decade as a result of increased hurricane intensity, quantity, and duration within the late Holocene. One of the best localities to find records of hurricane overwash deposits is in the Bahamian islands. San Salvador Island, Bahamas (SSI) is a small (150km2), isolated carbonate platform, that contains shallow (0.5-3m) saline lakes that occur in between interdune areas of arcuate dune ridges. Due to San Salvador Island’s location within the Bahamian archipelago and the Atlantic Ocean, the island is poised to record hurricane strikes and the record of these events can be found in coastal lakes. Clear Pond is a shallow (~1m), variably saline (16-30 ppt) lake in the southwestern edge of the island, that is separated from the Atlantic Ocean by Holocene dunes. It was a previously uncharacterized pond, but like many other depositional environments on San Salvador, it is constantly recording climatic and anthropogenic changes on the island. This study addresses the following questions: 1) Is there a seasonal salinity variation within the pond and what is the general limnology of the pond, 2) Can we identify large storm events in the sedimentary record of Clear Pond, and 3) What is the depositional history for Clear Pond for the past 4000 years? Nine sediment cores, ranging in length from 50 to 150 cm, were recovered from Clear Pond. The cores were analyzed for organic and carbonate content, dry bulk density, iii grain size, sediment fabric, and mollusk and ostracode composition. Additionally, x-ray fluorescence, spectrophotometry, and x-radiography were carried out on sediment cores. Salinity varied from brackish conditions in the summer and fall to more marine during the winter and spring seasons. It was also influenced by a previously uncharacterized karst conduit. Large storm events were identified through an increase in grain size and dry bulk density, and additionally by x-radiographs. A catastrophic hurricane recurrence interval of 478 years and an annual landfall probability of 0.21% were found as well. The record of Clear Pond indicates an average sedimentation rate of 2.3 cm/ 100 years which suggests the record recovered is at least 5200 years old. These cores record a major climatic shift occurring at 1460 ybp which correlates with the end of a documented Caribbean dryness period. The facies shift is from a sand and mud laminated facies to a recent, massive bioturbated facies. The record documents multiple hurricane strikes from 1600-3400 ybp which supports a hurricane "hyperactivity period" from 1000- 3000 ybp from other areas in the Atlantic and Gulf of Mexico. These large storm events are linked to two large-scale climate mechanisms, the location of the Bermuda high and the strength of the North Atlantic Oscillation. The ability to characterize and identify past overwash deposits in the Bahamas may be useful in climate reconstruction and landfall probability assessments. These results are the first proxy records for hurricane strikes on the west coast of San Salvador Island. iv ACKNOWLEDGEMENTS This research could not have been conducted nor facilitated if weren't for my advisor Dr. Lisa Park. Her knowledge, patience, and focus were indispensable and steadfast through my Master’s. She provided a venue to understand the geological sciences in a way I never thought possible. I would like to thank the Department of Geology and Environmental Science at The University of Akron for internal grants that provided for the transportation and housing to and from my research site in the Bahamas and for ultimately picking "me." Special thanks to Mr. Tom Quick for his expert technical knowledge and Ms. Elaine Butcher for her omniscient properties when it came to paperwork that needed to be filled out. I would also like to thank Dr. John Peck for allowing me to not only use but also make a copy of his coring equipment for future students to use. Thanks are also in order to Dr. Joseph Ortiz from Kent State University for allowing me to utilize his lab and equipment. I would also like to thank Dr. Ira Sasowsky for being a part of my thesis committee and helping facilitate my interest in hydrogeology. I would also like to thank my Paleo-Pirates for their support and help in the field, especially Sara Sipahioglu, Andy Michelson, and honorary member, Melisa Bishop for their help. I would also like to thank Renee Crane at Kent State University. Thanks to the Gerace Research Centre and Dr. Tom Rothfus for housing and laboratory space at the v field station along with a 2008 Gerace Research Centre Grant. Thank you to Dr. Fred Siewers for help in the field and Dr. Tina Neimi for putting "everything" she had into this project. I would also like to thank Unit Director, Mr. Tony Carpenter for excellent X-rays at the Aultman West Hospital. Ultimately, I would like to thank Dr. Hays Cummins at Miami University for taking a Zoology major under his wing. He let me catch the "bug" they call research beginning with an Undergraduate Summer Scholars award to San Salvador Island, Bahamas. Special thanks to my parents, Rick and Melody, for being the cornerstones of my life, standing unwaveringly by my side through thick and thin, for they have given me opportunities I cherish every day. I would like to thank my twin girls, Isabella and Mackensie, for never letting me forget why I push myself. You both are truly the Sun that fuels my growth. Lastly, I would like to thank my one and only Sara for empathizing with my research, understanding the trials and tribulations of school work, and encouraging me to excel in life. vi TABLE OF CONTENTS Page LIST OF TABLES...............................................................................................................x LIST OF FIGURES ........................................................................................................... xi CHAPTER I. INTRODUCTION ...................................................................................................1 Geology of the Bahamas and San Salvador Island ..................................................4 Hurricanes................................................................................................................5 San Salvador Climate.............................................................................................11 Lakes on San Salvador Island................................................................................15 Clear Pond..............................................................................................................15 Clear Pond Biota Overview ...................................................................................19 Ostracoda in Clear Pond ........................................................................................19 II. METHODS ............................................................................................................23 Dune Profiles.........................................................................................................23 Physical Limnology ...............................................................................................23 Piston Coring.........................................................................................................26 X-radiography........................................................................................................26 X-ray fluorescence.................................................................................................27 Spectrophotometry.................................................................................................27 vii Loss on Ignition .....................................................................................................28 Grain Size...............................................................................................................29 Microfossil Analysis ..............................................................................................29 Radiometric Dating................................................................................................30 III. RESULTS ..............................................................................................................31 Dune Profiles.........................................................................................................31 Physical Limnology ...............................................................................................33 Description of Core Facies.....................................................................................37 X-radiography........................................................................................................38 X-ray fluorescence.................................................................................................44