Growth rate of a deep-sea coral using 210Pb and other isotopes

A deep-sea coral was studied to determine its growth rate and to reconstruct time histories of isotope distributions in the deep ocean. The specimen was collected at a depth of 600 m off Little Bahama Banks using the Deep Submergence Vehicle (DSV) Alvin. The growth rate of the calcitic coral trunk was determined using excess 210Pb measured in concentric bands. Excess 210Pb was found in the outer half of the coral's radius, and a growth rate of 0.11 ± 0.02 mm/a is calculated. Assuming a constant growth rate during formation of the entire trunk, an age of 180 ± 40 a is estimated for the coral. The decrease observed in radiocarbon activities measured on the same bands (Griffin and Druffel, 1989) concurred with the growth rate estimated from excess 210Pb activity. 239,240pu activities measured by mass spectrometry were also detected in the outer two bands of the coral, as expected from the 210Pb chronology. Stable oxygen and carbon isotopes measured in samples collected by a variety of techniques are positively correlated. This is evidence of a variable kinetic isotope effect most likely caused by variations in the skeletal growth rate. Long-lived corals such as this specimen have the potential for serving as integrators of seawater chemistry in the deep-sea over several century timescales. © 1990