Title

Tropical Atlantic climate variability recorded in corals from the Cape Verde Islands and the eastern Caribbean

Date of Award

2005

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Geology and Geophysics

First Committee Member

Peter K. Swart, Committee Chair

Abstract

Stable isotopes, minor elements, and trace elements in coral skeletons from the Cape Verde Islands and the eastern Caribbean were used as proxies for climate variability in the tropical North Atlantic. Coral cores were collected by divers on two expeditions to the Cape Verde Islands in June 2001 and July 2002, and one cruise throughout the Lesser Antilles in October and November 2002. These coral cores were then slabbed and microsampled for geochemical analysis by several methods. The analyses provided chronological records of stable isotopes (delta18O and delta13 C), minor elements (Sr and Mg), and trace elements (Ba, Al, Fe, Zn, Ni, U) from the coral skeletons.This dissertation represents the first geochemical work with the zooxanthellate coral Siderastrea radians from the Cape Verde Islands. Initial observation of their slow annual growth rate of 1--1.5 mm yr-1 held hopes for their potential to contain lengthy paleoclimate records. However, the oldest specimen collected was limited to just over 100 years. Special sampling designs were implemented to adjust for the time-transgressive nature of sampling corals with such slow growth rates and small skeletal structures.Records of coral skeletal delta18O from 1900--2000 revealed salinity fluctuations in the eastern tropical North Atlantic, including a 0.5 psu increase since 1950. The salinity variability is significantly correlated to sea surface temperature (SST) and the North Atlantic Oscillation (NAO) through evaporation and regional upwelling. The greatest correlation with salinity trends is captured by an index based on the strength and phase of the relationship between SST and the NAO, explaining more than 60% of the salinity variability. This data supports similar suggestions from the western Atlantic that the there have been substantial basin-wide changes in the freshwater balance of the Atlantic.Minor and trace element records from corals on Sal and Sao Vicente in the Cape Verde Islands, and from Bequia, St. Vincent in the Lesser Antilles display striking similarities despite being on opposite sides of the Atlantic. In particular, Al and Mg both exhibit significant deviations far above mean values at the same times in all three corals. Magnesium, is found in these peaks at concentrations almost an order of magnitude higher than expected in relation to such environmental parameters as sea surface temperature (SST). Comparison of some of these records with African dust production over the last 30--40 years yields a significant correlation.

Keywords

Biogeochemistry; Physics, Atmospheric Science

Link to Full Text

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