Background levels of formate and other ions in ice cores from inland Greenland

Concentration levels of the organic acids HCOO − and CH 3 SO 3 − , inorganic acids NO 3 − and excess SO 4 2− and ammonium were measured in pre‐1900 AD ice layers from seven geographically dispersed inland sites in Greenland. Average multiple‐year background concentration levels are calculated for each ion at each site from laboratory measurements of continuous core samples representing from 4 to 10 years of snow accumulation (32 to 80 individual measurements) from various time intervals. The HCOO − concentration level increases from 6 ng/g in the most northern colder site to 36 ng/g in the most southern warmer site; CH 3 SO 3 − increases from 0.9 ng/g to 2.8 ng/g; NO 3 − decreases from 83 ng/g to 37 ng/g; excess SO 4 2− decreases from 43 ng/g to 19 ng/g, all with variability. The distribution of the NH 4 + ion shows a nearly constant level at about 6 ng/g for all sites except Dye‐2 where it reaches 10 ng/g. The deposition patterns for HCOO − and NH 4 + on the ice sheet suggest major contributions arrive from sources originating from the southwest of Greenland.