Subtropical Atlantic Climate Variability Record in Speleothems from the Bahamas

• Main Author: Arienzo, Monica
• Other Authors: Peter K. Swart, Kenneth Broad, Amy Clement, Philip (Flip) Froelich, Larry C. Peterson, Ali Pourmand
• Format: Other/Unknown Material
• Language: unknown
• Published: Scholarly Repository 2014
• Subjects: Speleothem; Bahamas; Heinrich; Glacial; North Atlantic
• Online Access: https://scholarlyrepository.miami.edu/oa_dissertations/1333; https://scholarlyrepository.miami.edu/cgi/viewcontent.cgi?article=2346&context=oa_dissertations

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 sub-tropical 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.