Online radiocarbon analysis of carbonates with laser ablation AMS

The fastest way of analyzing carbonate samples for their radiocarbon content is using a novel laser ablation (LA)n accelerator mass spectrometer (AMS) technique (Welte et al. 2016). By focusing a pulsed laser beam (ArF excimer laser 193 nm, 200 - 250 Hz) on the sample's surface, CO and CO2 is produced, which is directly and continuously introduced into the gas ion source of the AMS and analyzed online for radiocarbon. A positioning system allows precise movement of the sample relative to the laser beam. Hence, scanning along the growth axis of a naturally grown carbonate sample such as stalagmites, corals, shells etc. allows recording a continuous 14C profile with high spatial resolution down to 75μm. Therefore, the LA-AMS setup installed at ETH Zurich combines the advantages of high sample throughput, high spatial resolution and minimal material consumption compared to standard 14C sample preparation methods. Here, we present the novel LA-AMS system and apply it for the analysis of marine shells (Arctica islandica). In less than one hour a 14C profile along the growth axis of an individual specimen was established revealing the complete 14C bomb peak. The LA-AMS results are in agreement with the 14C-AMS analysis of micro-drilled samples that had been done previously (Witbaard et al. 1994). The new technique now can be applied in broader field studies e.g. to monitor the distribution of 14C in many specimens and with large geographic coverage.