Bomb radiocarbon dating - Leatherback
Unpublished - Negative results
Bomb radiocarbon dating of leatherback turtle (Dermochelys coriacea): A feasibility study
In this study, we investigated the use of bomb radiocarbon dating on core material extracted from ossicles of leatherback turtles. Based on microstructural observations of ossicle cross sections, some material from the first few years of growth appear to be conserved with time. Reconstructed bone has been observed at the center of some ossicles with increased tissue porosity, but some ossicle cores appeared to have bone that was not reworked or removed. This material may have retained carbon-14 that is an accurate representation of the environmental signal at the time of formation. Hence, it is hypothesized that 14C measured from ossicles can provide an independent means of determining age for leatherback turtles.
Above is a reconstruction of a leatherback turtle skull by Larisa Avens (NOAA Fisheries) with the ossicles positioned as they would be in the eye of this individual. The ossicles have been sections and age estimated to exceed 40 years based on growth zone counting (See Avens et al. 2009).
The plot below is of northern Atlantic ∆14C reference chronologies from various marine organisms used for a comparison with leatherback turtle measurements. Regional hermatypic corals have recorded the highest ∆14C levels and are most representative of the rapid uptake of bomb-produced carbon-14 from the atmosphere and tropical exposures to ∆14C (Druffel and Linick 1978, Druffel 1989). Otoliths from known collection year juvenile fishes (haddock, redfish, and yellowtail flounder), referred to as the Northwest Atlantic Reference (NWA) by Campana et al. (2002), and a relatively deep water mollusk provided a record that is more temperate in distribution. Juvenile Arcto-Norwegian cod provided an intermediate signal that is representative of the Arctic Ocean end of the spectrum (Kalish et al. 1991). A more complicated record was measured from porbeagle shark from the Northwestern Atlantic providing evidence for a trophic level effect on the ∆14C signal as a phase lag of a few years, with an attenuated peak. Also plotted is a series of ocean water carbon-14 data points from the western edge of the Sargasso Sea (Druffel et al. (2008), and a recent coral record from Puerto Rico (Moyer and Grottoli 2011). The mean ∆14C level recorded from leatherback ossicle cores is marked as a solid line at 77‰. This level indicated bomb radiocarbon was present, but the proper reference record for bomb radiocarbon is not known. In addition, no difference was notable between core material and edge material (near time of death/capture). Hence, conclusions about age could not be drawn. However, the findings of this study indicate further study could yield meaningful results, especially if ossicles can be collected from a leatherback turtle with a birth year prior to the mid-1960s.
This work was a collaborative effort with Larisa Avens (NOAA Fisheries, Beaufort Laboratory).
We thank Scott Benson of NOAA Fisheries for his foresight on linking the potential application of bomb radiocarbon dating to the ossicle age estimation work that was in progress. We acknowledge Thomas Brown at the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratories for radiocarbon processing of the sample series and Irene Kelly, Sea Turtle Recovery Coordinator at the Pacific Islands Fisheries Science Center, for providing the funding for this exploratory work. We also thank Robin Leroux of NOAA Fisheries and Moss Landing Marine Laboratories for assistance with handling project funds and infrastructure support. This project was funded under Order #JG133F08SE4102, Requisition #NFFR7000-8-47756.
For a synopsis of the concerns associated with this species, see the synopsis at IUCN.
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