A record of Holocene summer climate from a Canadian high-Arctic ice core

Abstract

MELT layers in ice cores are formed by melting on the snow-pack surface, which produces water that percolates down and refreezes in the colder snow layers below. Melt layers are distinguished by their 'bubble' texture. Because more ice forms in the snow pack in warm summers than in cool summers, the changing concentration with depth of melt layers in snow pits1,2 and ice cores3–5 is an indicator of past summer climate. Here we report on studies of melt layers in two Canadian high-Arctic surface-to-bedrock ice cores. Although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40% of the total climatic signal recorded in the melt layers, we interpret their varying concentrations in terms of changing summer temperatures over the past 10,000 years. The warmest summers occurred 8–10 kyr ago and the coldest only 150 years ago. The summers over the past 100 years have been the warmest for more than 1,000 years, but are still not as warm as those of the early Holocene. The melt-layer record is in broad agreement with geological records of glacier retreat during the Holocene6–8, indicating that these data also contain information of regional significance.