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

Abstract

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.

Annual Greenland accumulation rates (2009–2012) from airborne snow radar

“…First, to characterize density across the GrIS, we extract the snow/firn density measurements ranging in depth from the snow surface to 15 m (the depth to which MAR predicts firn density), which contains over 1500 measurements from snow pits and cores at 62 sites. At each site, the number of measurements ranges in number between 8 and 170 and maximum depths range from 1 to 15 m. (Koenig et al, 2014;Koenig and SUMup, 2015;Miège et al, 2013;Mosley-Thompson et al, 2001;Hawley et al, 2014;Baker, 2012) (Fig. 1).…”

“…1). Second, to compare radar-derived and in situ accumulation rates, we consider only accumulation-rate measurements within 5 km of OIB snow radar data, a criterion that includes 11 cores from the SUMup dataset (Mosley- Thompson et al, 2001). To expand this comparison, an additional dataset of 71 cores was included (J. McConnell, personal communication, 2015), providing 23 additional cores within 5 km of OIB snow radar data ( Fig.…”

“…Only two major accumulation-rate measurement campaigns have been undertaken across the GrIS: the first in the 1950s when the US Army collected pit data along long traverse routes (Benson, 1962) and the second in the 1990s when the Program on Arctic and Regional Climate Assessment (PARCA) collected an extensively distributed set of ice cores (e.g. Mosley-Thompson et al, 2001). A recent traverse and study by Hawley et al (2014) reports a 10 % increase in accumulation rate since the 1950s and highlights the need to monitor how Greenland precipitation is evolving in the midst of ongoing climate change.…”

Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land

“…They store information on past changes in temperature in the form of stable water isotopes (EPICA community members, 2006), in greenhouse gas concentrations via trapped air (Raynaud et al, 1993) and in many other parameters such as accumulation rates (e.g. Mosley-Thompson et al, 2001) or aerosols (e.g. Legrand and Mayewski, 1997).…”

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

“…In the late 1990s, PARCA collected scores of shallow firn and ice cores to quantify spatial and temporal variability of annual accumulation rates over the GrIS (e.g. McConnell et al, 2000;Bales et al, 2001;Mosley-Thompson et al, 2001).…”