Recent precipitation decrease across the western Greenland ice sheet percolation zone

Abstract

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest in the context of future sea level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius–Clapeyron relationship, compensating for some of the melt-induced mass loss throughout the western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the western GrIS percolation zone, providing new accumulation rate estimates in regions with sparse in situ data or data that do not span the recent accelerating surface melt. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground-penetrating radar, covering the past 20–60 years of accumulation, collected across the western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation rates of 2.4±1.5 % a−1 over the 1996–2016 period, which we attribute to shifting storm tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously strong summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation rates.

Firn cold content evolution at nine sites on the Greenland ice sheet between 1998 and 2017

“…Also, should the decrease of precipitation in Western Greenland continue (Fig. 3 and Lewis and others, 2019), one can expect an increase of near-surface cold content in these regions due to denser near-surface firn and enhanced firn cooling in the winter.…”

“…The firn characteristics are greatly dependent on the local net snow accumulation: snowfall plus deposition minus sublimation. To ensure that the firn model is provided with accurate accumulation values, we compare the net snow accumulation calculated from weather station measurements to 14 firn-core derived accumulation records: Nine cores from PARCA (Mosley-Thompson and others, 2001; Bales and others, 2009), the ACT-11D core at Dye-2 (Forster and others, 2014), Core 14 at NASA-U (Lewis and others, 2019), a core from 2012 at South Dome (Ørum, 2015), the Owen core at Summit (Hawley and others, 2014) and a core from 2007 at CP1 (Porter and Mosley-Thompson, 2014). Some of these cores do not overlap with our study period but can nevertheless be used to ensure that the station-derived accumulation has a realistic magnitude and variability.…”

The role of blocking circulation and emerging open water feedbacks on Greenland cold‐season air temperature variability over the last century

“…Of note, the local sea ice influence on air temperatures tends to be confined to low‐elevation areas due to mesoscale wind features, such as katabatic flows, that frequently prevent the penetration of turbulent heat from the local marine environment upslope past the lower ablation zone (Ballinger et al ., 2019). In addition to GBI and local oceanic mechanisms, atmospheric river frequency and intensity (Mattingly et al ., 2018) and local storm activity (Lewis et al ., 2019; Oltmanns et al ., 2019) within the coastal areas represent a couple of the energy balance‐related factors not explicitly integrated into our statistical models that likely contribute some residual temperature variance and precondition the ice sheet and peripheral glaciers for the subsequent melt season.…”

Surface accumulation in Northern Central Greenland during the last 300 years

“…While the spatially extensive data coverage from the airborne campaigns have returned numerous important insights, the spatially confined ground-based surveys can in turn yield information with higher spatial resolution within targeted areas. Examples include data acquired by Hawley and others (2014) during a traverse from Thule, North Greenland, to Summit Station, data collected by Miège and others (2013) from a high accumulation area in Southeast Greenland and a recent study by Lewis and others (2019) using data from West Greenland. One area that may specifically benefit from the increased resolution of a ground-based survey is the region around major ice divides.…”