A seven-year study of oxygen isotopes in daily precipitation at a site close to the Arctic Circle, Tustervatn, Norway: Trajectory analysis and links with the North Atlantic Oscillation

Daily precipitation δ18O values were recorded through a 7-year period at Tustervatn, Norway, close to the Arctic Circle. Seasonal variations were superimposed on an overall rising trend. Cluster analysis of air mass trajectories revealed five principal moisture source areas and transport routes to Tustervatn. Both daily precipitation amounts and δ18O values differed between the trajectory clusters. Seasonal differences of the frequency of trajectory clusters were reflected in the relationship of precipitation δ18O values to regional temperatures, which was strongest in winter (DJF). Monthly precipitation totals varied with the North Atlantic Oscillation (NAO) index. The relationship of DJF precipitation to the NAO index was particularly strong, but varied between air mass trajectory clusters. The relationship of DJF precipitation and NAO index at Tustervatn differs from that at Tasiilaq, southeast Greenland, which is at around the same latitude. DJF precipitation totals at Tustervatn tend to be higher when the NAO index is higher; at Tasiilaq, the trend is for lower DJF precipitation at higher NAO index values. The contrasting NAO/climate relations reflect the location of the two sites with respect to that of the Icelandic low.