Thesis (M.S.)--University of Akron, Dept. of Geology, 2008. / "December, 2008." Title from electronic thesis title page (viewed 12/13/2009) Advisor, Lisa E. Park; Faculty Readers, Ira D. Sasowsky, John Peck; Department Chair, John P. Szabo; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

San Salvador Island is a small Bahamian island located in the subtropics just north of the Tropic of Cancer. Due to its subtropical location, the island is influenced by both mid-latitude and tropical weather patterns. These weather patterns vary in scale from localized convective uplift to synoptic-scale systems. This study compares satellite-derived estimates of precipitation and rain gauge observations from June 2019 through September 2021 to evaluate the relationship between the two datasets. This study then uses the satellite-derived estimates of precipitation over a 20-year period to quantify annual and seasonal variability in precipitation on San Salvador. Corroborating past research, the island exhibits a bimodal pattern of precipitation during the year, but rainfall is highly variable across seasons and between years. Atmospheric fields from a reanalysis dataset indicate the North Atlantic subtropical high influences summertime rainfall, but a relationship between upper-level wind patterns and rainfall is less clear.

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Located in the subtropical central-eastern Bahamas, San Salvador Island is impacted by both synoptic-scale weather systems as well as local features and the North Atlantic Subtropical High. This study explores rainfall variability via one year of daily rain gauge observations in relation to daily weather patterns identified from 18 UTC surface analyses. Satellite-derived rainfall estimates are then compared to gauge observations to look at days when gauge data was missing. Though non-synoptic classifications comprised 61.1% of the days and synoptic classifications comprised 38.9% of the days, more rainfall was produced by synoptic days. Unlike other studies done on San Salvador, this study uses multiple observations—in situ, surface analyses, and satellite—to further our understanding of San Salvador’s rainfall. This study also establishes methods to explore synoptic and non-synoptic impacts on the island’s rainfall using additional years as more rain gauge data become available.

A major economic constraint in the Bahamas, and other small carbonates islands world-wide, is the lack of fresh water resources. To combat these socio-economic problems on San Salvador Island I sought to gain a more detailed understanding of the extent, behavior, and controls on the island’s fresh-water lens. DC electrical resistivity tomography and time-series geochemical data are used to study the fresh water lens at the Line Hole well field. Electrical Resistivity profiles are used to image the extent of fresh water resources. Time-series geochemical data provide information on the behavior of the fresh water resources as a function of time. The inversion models of the electrical resistivity profiles illustrate a fresh water lens less than 3 meters thick on average. The mixing zone is diffuse in nature, and substantially thicker than the fresh water lens. The geochemical results corroborate the fresh water lens dimensions predicted by the electrical resistivity model. In addition, mixed semi-diurnal and spring/neap tidal cycles are the primary control on the water level. Statistical analysis of specific conductance and temperature illustrate a positive and negative correlation with water level, respectively. Analysis of precipitation with respect to water level and geochemistry indicate low effective recharge rates during the period of study. The current state of the water resources at the Line Hole well field is strained. Despite moderate levels of freshening since the termination of pumping in December 2006; the system continues to be in a state of disequilibrium. The problem is compounded by abnormal thickening of the mixing zone due to communication of the well field with the ocean, and a limited volume of fresh water. In conclusion, the two techniques used in conjunction provide a non-invasive method of estimating fresh water resources in this type of setting. Conversely, the high RMS and L2 values for the electrical resistivity models and limited time-series data create a high level of uncertainty in the interpretation of results.

Understanding modern carbonate depositional systems gives valuable insights into the interpretation of ancient carbonate systems. Ancient carbonate strand plains have the potential to act as productive hydrocarbon reservoirs because of their relatively high porosity. Unfortunately, they are difficult to identify in the rock record because of the lack of work done on modern analogues. San Salvador Island in the Bahamas hosts a well-exposed and easily accessible Holocene strand plain, ideal as a modern analogue. Sandy Hook, located on the southeast part of the island, consists of approximately 35 ridge-swale features that show signs of four distinct zones of deposition. In this study, 20 sediment samples were collected from one meter in depth, and throughout each zone. The sediment analysis reveals remarkably consistent grain-size distributions across the four zones. Carbon-14 ages were taken from the sediment samples. They revealed ages decreasing from 2617 ± 188 YBP to modern moving seaward through zone 4. The ages reveal depositional rates of 0.08 to 0.29 meters of accretion per year. Four pseudo-3D GPR surveys were acquired in Zones B, C, and D, and a 2D GPR survey was acquired that spanned the three zones. The pseudo-3D surveys revealed consistent reflectors through the width of the survey indicating that the 2D surveys represent more than the single line. The 2D survey reveals semi-parallel seaward-dipping reflectors (representing fair-weather deposits) that are truncated by sigmoidal seaward-dipping reflectors (high-energy storm deposits). Indicating that Sandy Hook was built through both fair-weather deposits and high-energy storm events.

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