Comparing Long-Term Atmospheric 14C and 3H Records near Groningen, The Netherlands with Fruholmen, Norway and Izaña, Canary Islands 14C Stations

We present the results of the (CO2)-C-14 atmospheric monitoring station at the Smilde observation station, near Groningen, the Netherlands, a typical continental station. We compared these data, for absolute values and annual variation, with data from Fruholmen, Nordkapp, Norway and Izana, Tenerife, Canary Islands, which are situated in areas less influenced by fossil-fuel CO2. The 20-yr Smilde record shows much seasonal variation (peak-to-trough variation is similar to 30% in contrast to similar to 12% for Fruholmen, and similar to 55% for Izana) and a lower overall value due to fossil-fuel consumption, in accordance with findings from similar stations in continental Western Europe. The Fruholmen and Izana data show fairly equal mean Delta(14)C levels, but differ in seasonal amplitude. This difference could be due partly to the elevation difference between the stations. The Izana station also has a slow exchange with the ground-level air because of an inversion layer. It is speculative whether annual injection of C-14 from the stratosphere also plays a role. We give the Groningen long record of tritium in precipitation, showing profound seasonality