20-EPN2-025: Determining the C-14 ages of offshore groundwater by analysing fluid samples with small quantities
Visit by Nai-Chen Chen, University of Stockholm (Sweden) to TA2 Facility 16 – Carbon-14 Dating AMS Laboratory (Hungary).
Dates of visit: 14-25 March 2022
Report Summary: Submarine groundwater discharge (SGD) has been shown to be an important mechanism in transporting solutes from the terrestrial to the marine environment. Despite being a well-documented process, our knowledge about the timing of offshore groundwater emplacement is extremely scarce. We aim to develop an age-dependent numerical model in our study area to investigate the relationship between SGD and the carbon cycle, whereby the obtained 14C age of the groundwater is used as a constraint. Our goal is to analyze all the carbon pools present in our cores (i.e. TIC, TOC, DIC and CH4) for 14C, so that we can correct for possible interference with the 14C-DIC signal (used for groundwater age). This is a challenge however, as the carbon content for some of these samples is extremely low.
During this two-week visit, we not only learned about the 14C preparation methods and operation of Accelerator Mass Spectrometry (AMS), but also discussed and exchanged ideas with Isotoptech AMS C-14 group scientists. Preliminary 14C results indicate that 14C depleted DIC is observed closer to the sediment-water interface for cores with anticipated SGD. This can be explained by the advective upwards transport of older groundwater. The discrepancy between the TIC and TOC 14C content at similar core depths was found to be very large, indicating that these carbon pools are affected by different processes. This mismatch might be a result of the precipitation of authigenic carbonates or microbial activity.
