A MULTIDECADAL RECORD OF D18O CORAL VARIATION AND THE RELATIONSHIP TO SUN SPOT CYCLES

Scleractinian corals can be excellent recorders of paleoenvironmental change because the coral skeleton can contain a broad array of geochemical tracers that can provide a record of paleoceanographic and paleoclimatic change. For example, seasonal density bands can be used to establish timelines of coral annual growth cycles, and the internal banding can carry isotopic and chemical indicators that archive information about ambient water temperature, salinity, and isotopic composition. The oxygen isotopic composition (d¹⁸O_coral) of the coral skeleton is a function of sea surface temperature (SST) and the d¹⁸O of ambient seawater (d_w), which is related to sea surface salinity (SSS). Other explanations for d¹⁸O_coral variability include other environmental variables (insolation), physiological effects, or growth rate (density band extension). This study considers the interpretation of skeletal d¹⁸O, d¹³C, and density band extension values obtained from two coral heads of Orbicella annularis from similar water depths in Curaçao, and additional sites from San Salvador, Bahamas. Coral core samples were obtained using SCUBA diving, and a coring apparatus that uses compressed air in SCUBA tanks to drive a pneumatic drill gun with a coring attachment. We report on multidecadal variations in the d¹⁸O_coral from Curacao, demonstrate the correspondence between the isotopic data from the corals with historical records of sun spot cycles, and describe the collapse of this correspondence in the 1990s. The latter observation suggests to us that long-term trends in global warming, particularly of SST in the Caribbean Sea, now trump the natural effect of decadal scale solar cycle variations on the d¹⁸O composition of these coral skeletons.