Direct measurements of ice density at 1m depth in the Greenland Ice Sheet ablation zone during July 2016 from shallow ice cores

Ten shallow ice cores 0.9-1.1 m deep were collected with a 7.25 cm diameter Kovacs Mark III coring system (http://www.kovacsicedrillingequipment.com). Cores were collected and processed adjacent to the core sites on 11 July and 12 July between 14:00 and 21:00 local time. Core stratigraphy observations recorded in field notes include the presence of liquid water, ice lenses, and air bubbles. Natural breaks were used to separate the cores into individual segments. Each segment's length and diameter were measured to the nearest 0.1 cm with a calliper and weighed to the nearest 0.1 g on an Acculab digital scale to determine the ice density of each segment. The natural break segmentation yielded a 13 ± 6 cm mean sampling interval. Individual segments ranged from 3 to 40 cm in length. In addition to the shallow ice cores, ice density was measured with a snow sampler. Twenty-four samples were collected in total, one at each core site and fifteen additional sites at random along the study transect. Samples were weighed to determine their mass. Liquid water sourced from nearby flowing rills was then applied to the levelled ice-filled sampler until the water level was coincident with the ice surface (i.e., until the interconnected pore space was filled with water). Effective porosity was computed as the ratio of the water volume required to fill the sample to the 1000 cm3 ice sample volume. Elevation data and cryoconite hole geometry was measured. One-hundred cryoconite holes were measured. The depth of the hole with respect to the ice sheet surface and the depth to water in each hole with respect to the ice sheet surface were measured