E. S. Mosley-Thompson

Local to regional‐scale variability of annual net accumulation on the Greenland ice sheet from PARCA cores

A suite of spatially distributed cores collected under the Program for Arctic Regional Climate Assessment (PARCA) provides an unprecedented opportunity to assess local to regional variability of annual accumulation rates over the Greenland ice sheet. PARCA cores are unique in their broad spatial distribution and accurate dating of annual layers using multiple seasonally varying indicators. The core data provide (1) a more rigorous evaluation of spatial and temporal variations in accumulation rates, (2) critical input to ice sheet mass balance estimates, (3) ground truth measurements for satellite observations and climate model-based precipitation estimates, and (4) important constraints on paleoclimatic interpretations from ice cores. Multiple closely spaced cores demonstrate that signals of high-frequency (annual to possibly decadal scale) climate variability preserved in the ice sheet are partially masked by glaciological noise. Two 350-year accumulation histories, one from northwest Greenland and one from the summit area, reveal significant multidecadal variability. The regional trends show long periods (60–90 years) of strong positive correlation and an equally long period of strong negative correlation. Since 1940 the trends have been decoupled. This spatial variability reflects the strong modulation of Greenland precipitation (and the climate information it contains) by changes in North Atlantic atmospheric circulation patterns. Proxy records from the PARCA cores document that climate reconstructions from a single core must be interpreted cautiously, with application of appropriate filters to reduce local noise and careful extrapolations from local to regional scales. Richer, more robust ice core-derived data sets should result from combining multiple, more widely spaced cores to produce regional stacked records.

Accumulation map for the Greenland Ice Sheet: 1971–1990

An updated accumulation map for the Greenland Ice Sheet for the period 1971–1990, based on kriging of accurate point estimates developed during the past decade at over 40 points plus over 200 historical points, shows an average water accumulation of 30 g cm−2yr−1. Average uncertainty (standard deviation) in estimates of point accumulation for the interior part of the ice sheet, where the kriging drift surface is well constrained, is approximately 7 g cm−2yr−1, or 24% of mean accumulation. Because there are multiple cores in most regions, the regional uncertainty in accumulation should be considerably lower than the 7 g cm−2yr−1 average uncertainty at a point. There are still many areas on the ice sheet, including northwest and southern Greenland, where annual accumulation remains poorly constrained.