Natural and anthropogenic bismuth in Central Greenland

We report here Bismuth (Bi) measurements in recent snow and ancient ice from Central Greenland. The results indicate that during the last 26,000 years, the relative importance of the different sources of atmospheric Bi has strongly varied. From 26,000 to 20,000 years ago, Bi mainly originated from both rock and soil dust ( 50%) and volcanic activity ( 50%). Bi concentration in ice was 1 pg g−1. From 20,000 to 8000 years ago, Bi concentration decreased down to very low values close to 0.03 pg g−1 while the Bi/Al ratio strongly increased up to 40×10−6 indicating that other sources became predominant. Rock and soil dust contribution strongly decreased to represent only 5%. Volcanism stays at that time the main contributor of Bi. Finally, Bi concentrations remained very low from 8000 to 6000 years ago, with contribution from rock and soil dust reaching again 50%. Bi contribution from volcanism fall down to 0.015 pg g−1 and represent 50% of natural sources. Enhanced Bi concentrations are observed for ice and snow dated from the time of the fallout from known major volcanic events such as the big eruption of Laki (1783–1784). During this last event, 0.14 metric tonnes of volcanic Bi were deposited onto the Greenland ice sheet. During the last three decades, Bi/Al ratio is as high as 25×10−6, i.e. 6 times natural Holocene values. This recent increase is attributed to the influence of anthropogenic emissions from oil and coal combustion, refuse incineration and ferromanganese alloys and aluminium production.