Understanding the sources and transformations of mercury (Hg) in the free troposphere is a critical aspect of global Hg research. Here we present one year of observations of atmospheric Hg speciation and gaseous elemental Hg (GEM) isotopic composition at the high-altitude Pic du Midi Observatory (2860 m above sea level) in France. Biweekly integrated GEM from February 2012 to January 2013 revealed significant variations in delta Hg-202(GEM) (-0.04 parts per thousand to 0.52 parts per thousand) but not in Delta Hg-199(GEM) (-0.17 parts per thousand to -0.27 parts per thousand) or Delta Hg-200(GEM) (-0.10 parts per thousand to 0.05 parts per thousand). delta Hg-202(GEM) was negatively correlated with CO and reflected air mass origins from Europe (high CO, low delta Hg-202(GEM)) and from the Atlantic Ocean (low CO, high delta Hg-202(GEM)). We suggest that the delta Hg-202(GEM) variations represent mixing of recent low delta Hg-202(GEM) European anthropogenic emissions with high delta Hg-202(GEM) northern hemispheric background GEM. In addition, Atlantic Ocean free troposphere air masses showed a positive correlation between delta Hg-202(GEM) and gaseous oxidized Hg (GOM) concentrations, indicative of mass-dependent Hg isotope fractionation during GEM oxidation. On the basis of atmospheric delta Hg-202(GEM) and speciated Hg observations, we suggest that the oceanic free troposphere is a reservoir within which GEM is readily oxidized to GOM.