Spatial and temporal oxygen isotope variability in northern Greenland - implications for a new climate record over the past millennium

We present for the first time all 12 δO records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland. The cores cover an area of 680 km× 317 km, 10 % of the Greenland ice sheet. Depending on core length (100–175 m) and accumulation rate (90–200 kg m a) the single records reflect an isotope–temperature history over the last 500–1100 years. Lowest δO mean values occur north of the summit and east of the main divide as a consequence of Greenland’s topography. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources. A stack of all NGT records and the NGRIP record is presented with improved signal-to-noise ratio. Compared to single records, this stack represents the mean δO signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δO stack indicates distinctly enriched δO values during medieval times, about AD 1420± 20 and from AD 1870 onwards. The period between AD 1420 and AD 1850 has depleted δO values compared to the average for the entire millennium and represents the Little Ice Age. The δO values of the 20th century are comparable to the medieval period but are lower than that about AD 1420.