Bomb-produced radiocarbon in the shell of the chambered nautilus: rate of growth and age at maturity

The temporal pattern of bomb-produced radiocarbon in the oceans provides a chronometer to estimate the rate of growth of marine organisms. Radiocarbon measurements by tandem accelerator mass spectrometry of samples from the septa and shell wall of a mature specimen of Nautilus macromphalus reveal progressively increasing values in more recently formed shell material. This pattern is similar to that recorded in a banded coral from surface waters of the Great Barrier Reef, Australia. However, the pre-bomb values of Δ¹⁴C are lower in the nautilus than in the coral. This offset is probably due to the difference in the respective habitat depths of the two animals. Taking this difference into account, we have used the temporal pattern of Δ¹⁴C in the coral as a point of reference to help interpret the pattern of Δ¹⁴C in the nautilus. According to our calculations, the age of the specimen of N. macromphalus is 10-12 years and the timing of septal formation ranges from ≥ 80 to 240 days/septum.