Radiocarbon Dating Marine Shells in South Australia

Abstract

Recent Australian coastal research in archaeology and geomorphology has employed 14 C dating as an analytical tool in determining the age structure of anthropogenic and natural sedimentary deposits. The majority of these studies have applied an Australian 'Oceanic Reservoir Correction Factor' in order to compensate for depletion of 14 C in the ocean, relative to the land environment. This lower marine 14 C activity is caused by variable mixing in the surface ocean of much older 14 C from deep ocean water masses with contemporary 14 C from the atmosphere (Mangerud 1972). The result is an 'apparent' age for marine organisms (compared with terrestrial organisms) which varies around the world, depending on proximity to areas of deep ocean water upwelling and local oceanographic factors (Gillespie 1975; Mangerud and Gulliksen 1975). This figure varies between 410 years for New Zealand coastal waters (Rafter et al. l972), 440 years for Norway, 510 years for Spitzbergen and 750 years for arctic Canada (Mangerud and Gulliksen 1975). Deduction of an appropriate oceanic correction factor from radiocarbon dates of marine organisms is intended to produce compatibility with dates derived from terrigenous samples which were originally in equilibrium with the uniform distribution of 14c in the atmosphere (Mangerud 1972).