Update on the cosmogenic in situ 14C laboratory at the Lamont-Doherty Earth Observatory
Résumé
Cosmogenic in situ C-14 in quartz is rapidly becoming a widely used geochronological tool for studying earth surface processes over the last 30,000 years. The Lamont-Doherty Earth Observatory houses one of the longest continuously-operating cosmogenic in situ C-14 laboratories; in this contribution, we provide an update on the status of the laboratory following Goehring et al. (2014). From 2010 to the present, our long-term average blank value is 119,000 +/- 37,000 C-14 atoms, with no statistically significant trend over the last nine years. While our average measured C-14 concentration of the CRONUS-A inter-laboratory comparison standard is in line with data published from other laboratories, we note a step increase between 2013 and 2015 that is still under investigation. Additionally, we report our first procedural blanks and CRONUS-A values analyzed on the gas source of the ANMICADAS at CEREGE, France. Many of the > 75 samples analyzed at Lamont for in situ C-14 from the Arctic, Antarctic, New Zealand, and the Alps have been paired with Be-10 analyses contributing to the increasing density of burial dating data covering the last 20,000 years. Currently we are working on increasing sample throughput, streamlining the C-14 extraction procedure, and considerably decreasing blank levels.