ANNUAL ACCUMULATION AT 2 SITES IN NORTHWEST GREENLAND DURING RECENT CENTURIES

During summer 1995; 150-m firn and ice cores were drilled to determine annual accumulation rates at two Greenland sites, 73.84 degrees N, 49 .49 degrees W (NASA-U site) and 78.53 degrees N, 56.83 degrees W (Humb oldt glacier site). Annual layers were identified in the cores using m ultiple parameters: delta(18)O 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 unce rtainty. For the lower-accumulation Humboldt core, the dating uncertai nty is about 5 years over the 852-year period of record, with no uncer tainty over the past 200 years. Annual accumulation over the periods o f record at the two sites averaged about 0.34 and 0.14 m water equival ent, respectively. A set of 20-m firn cores drilled near the main 150- m cores showed that interannual variability of accumulation exceeded s patial variability at NASA-U. The Humboldt cores showed equal spatial and interannual variability. The accumulation rates at both sites show ed 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 ind icating a changed circulation pattern for the more northern part of Gr eenland in that period.