Annual accumulation at two sites in northwest Greenland during recent centuries

Abstract

During summer 1995, 150‐m firn and ice cores were drilled to determine annual accumulation rates at two Greenland sites, 73.84°N, 49.49°W (NASA‐U site) and 78.53°N, 56.83°W (Humboldt glacier site). Annual layers were identified in the cores using multiple parameters: δ18O and concentrations of dust, H2O2, NH4+, Ca2+, and NO3−. Using all parameters together to define annual layers resulted in a 350‐year record for the NASA‐U core with no dating uncertainty. For the lower‐accumulation Humboldt core, the dating uncertainty is about 5 years over the 852‐year period of record, with no uncertainty over the past 200 years. Annual accumulation over the periods of record at the two sites averaged about 0.34 and 0.14 m water equivalent, respectively. A set of 20‐m firn cores drilled near the main 150‐m cores showed that interannual variability of accumulation exceeded spatial variability at NASA‐U. The Humboldt cores showed equal spatial and interannual variability. The accumulation rates at both sites showed a low‐frequency variation of about 100 years, and both sites showed 200‐year cumulative fluctuations of about 2 m from mean accumulation rates. Compared to central Greenland and to NASA‐U, the Humboldt core showed higher annual accumulation rates around 1760–1810, possibly indicating a changed circulation pattern for the more northern part of Greenland in that period.