Radiocarbon dating of porewater; correction for diffusion and diagenetic processes.

Abstract

Two simple algorithms are suggested here to correct for the effect of diffusion and diagenetic sulfate reduction on radiocarbon age determination of marine porewater. The correction algorithms were developed from mass balances of sulfate, dissolved inorganic carbon (DIC), and (super 14) C of the DIC ( (super 14) C (sub DIC) ) in vertical concentrations profiles in porewater starting from the sediment water interface. The algorithms were tested on data collected during our recent study of sediment porewaters extracted from the deep Eastern Mediterranean. The real ages of these porewaters varied from present (top of the core) to approximately 30 ka BP (bottom of the core) covering most of the dynamic range of the (super 14) C method (approximately 5 half lives). These ages were markedly older than the ages calculated from (super 14) C (sub DIC) analyses by the regular age equation. It is clearly demonstrated that in this case the correction of the apparent age for diffusion across the sediment/water interface is overwhelmingly larger than the correction for the effect of sulfate reduction. The correction for the effect of (super 14) C diffusion alone results in a perfect match between the calculated apparent (super 14) C ages and the real ages of porewater and therefore is the preferred algorithm for correcting apparent ages of porewater.