Recent increase in H 2 O 2 concentration at Summit, Greenland

Prior measurements of hydrogen peroxide (H 2 O 2 ) in Greenland ice suggested a 50% increase of the H 2 O 2 concentration during the last 200 years, where most of the increase occurred between 1960 and 1988 [ Sigg and Neftel , 1991]. In this work we present data from two shallow cores drilled at Summit, Greenland in 1995 that confirm the H 2 O 2 increase found earlier and that show a further increase of the H 2 O 2 concentration since 1988, leading to an overall increase of 60±12% during the last 150 years. The new shallow cores were drilled 6 years after the Eurocore, which allowed us to identify the influence of the firnification process on the mean annual H 2 O 2 concentration recorded in the firn. We found that the H 2 O 2 concentration in the upper snow/firn decreased until the layer was buried with at least 1 m of snow and that the mean annual H 2 O 2 concentrations in deeper layers stayed essentially unchanged. Besides the increase in the mean annual concentration, the annual amplitude between winter minima and summer maxima has tripled since 1970. Since there has been no significant change in temperature during either the last 150 years or last 25 years, it is unlikely that the increasing H 2 O 2 concentrations are temperature related. We cannot rule out the possibility that seasonal accumulation patterns at Summit have changed, which could make a small contribution toward the increase. A small part of the increase of both the mean annual concentration and the annual amplitude of H 2 O 2 in recent years could be due to increasing UV‐B radiation caused by the depletion of stratospheric ozone, but a combination of changes in tropospheric chemistry apparently is involved.