Oxygen and Carbon Isotopes and Coral Growth in the Gulf of Mexico and Caribbean Sea as Environmental and Climate Indicators

Abstract

The Gulf of Mexico and Caribbean Sea comprise a sensitive and important region, both oceanographically and climatically. A better understanding of the history of climate and marine environmental conditions in this region provides valuable insight into the processes that affect climate globally. This dissertation furthers our understanding of these factors via investigations of the isotopes of corals and seawater, as well as coral growth. Results improve our understanding of how the isotope and coral growth records from the Gulf of Mexico and Caribbean Sea reflect recent environmental conditions, enhancing our ability to reconstruct the history of climate in this important region. Analysis of the relationship between salinity and oxygen isotopic composition of seawater from the Texas/Louisiana continental shelf and Flower Garden Banks yield improved understanding of the relative contribution of the fresh water sources into the northern Gulf of Mexico, and also the oxygen isotopic composition of open-ocean seawater in this region. Variations in the growth of long-lived coral cores from the Flower Garden Banks are compared to local and regional climate conditions, particularly winter air temperatures. During the latter half of the twentieth century, a close correlation has existed between slow coral growth and cold wintertime air temperatures along the Gulf Coast, which are due to a meridional orientation of the North American jet stream (associated with the Pacific/North American climate pattern). Existing long coral growth records are too limited to assess this relationship during earlier years. Knowledge of the marine radiocarbon (14C) reservoir age is important for understanding carbon cycling and calibrating the radiocarbon ages of marine samples. Radiocarbon concentrations in corals from the Flower Garden Banks, Veracruz, and the Cariaco Basin are measured and used to determine the surface ocean 14C reservoir ages for the Gulf of Mexico and Caribbean Sea. Results also indicate that the post-nuclear weapons testing Delta 14-C values of the Gulf of Mexico and Caribbean Sea differ. This difference is attributed to the advection of 14C-depleted surface water from the Southern Hemisphere into the Caribbean Sea. The results reported in this dissertation provide valuable information for understanding the marine environment when using carbonate proxies to study and reconstruct past climate and marine conditions in the Gulf of Mexico and Caribbean.