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

Ellen R.M Druffel,Linda L King,Rebecca A Belastock,Ken O Buesseler

doi:10.1016/0016-7037(90)90174-j

Ellen R.M Druffel, Linda L King + Show 2 more

Open Access

https://doi.org/10.1016/0016-7037(90)90174-j

Copy DOI

Abstract

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.

Highlights

CONCENTRATIONOSFBOMEPRODUCIZtDransient tracers (r4C, 3H, 90Sr) in the water column have been used to estimate such processes as the mixing rate of water in the main thermocline (BROECKERet al., 1985), the ventilation rate of midocean gyms (JEN~NS, 1982; DRUFFE& 1989), and inter-ocean transfer of water (FINE, 1985)
Using excess “?b measurements, we show that the lifespan of our C. niobe specimen was about 180 4 40 a, assuming a constant growth rate for the trunk
The ground coral samples were acidified and the CO2 produced was analyzed for radiocarbon (GRIFFIN and DRUFFEL, 1989). *“‘POwas plated onto silver foil from the acid solutions and used to determine *“Pb activities (FLEER and BACON, 1984). 226Rawas measured using the *=Rn emanation method (MATHIEU et al, 1988)

Summary

Abstract-A deep-sea coral was studied to determine its growth rate and to reconstruct time histories of isotope distributions in the deep ocean. The growth rate of the calcitic coral trunk was determined using excess “OPb measured in concentric bands. The decrease observed in radiocarbon activities measured on the same bands (GRIFFIN and DRUFFEL, 1989) concurred with the growth rate estimated from excess ““Pb activity. We measured excess “OPb con~ntmtion in individual bands from a trunk of Coral~i~m niobe to determine the radial growth rate, similar to studies using surface corals (MOORE and KRISHNASWAMI1, 972; MOOREet al., 1973; DODGE and THOMSON, 1974). Using excess “?b measurements, we show that the lifespan of our C. niobe specimen was about 180 4 40 a, assuming a constant growth rate for the trunk Radiocarbon results corroborate this age estimate (GRIFFIN and DRUP~%L, 1989). Bomb radiocarbon was not detected in the A14Crecord from the coral (GRIPPIN and DRUFEEL, 1989), in agreement with the absence of bomb radiocarbon observed in seawater samples from similar isopycnals in the western North Atlantic

Corallium niobe Trunk

ISOTOPIC TECHNIQUES

Year of

RESULTS

DISCUSSION