Decreasing density and ice content in shallow firn cores at DYE-2, Southwest Greenland from 2013-2019

Abstract:

The porous structure of firn allows meltwater to percolate downwards where it may refreeze and form ice lenses. These ice lenses can coalesce forming thick ice layers (more than tens of centimeters thick), which prevent further infiltration and increase runoff. Several years of low melt, however, would likely lead to firn regeneration, slow the formation of thick ice layers and absorb surface meltwater. To investigate the temporal variation of density and ice layer distribution in near-surface firn (top 5-20 m), we compare 14 firn cores drilled at DYE-2 in Southwest Greenland during 2013-2019. The ice content and the average density of the cores have decreased over this period. An exception to this trend took place following the melting season of 2016, which triggered an increase of the ice content and the average density. The cores also exhibit large variability in ice layer distribution with depth. However, several pronounced thick ice layers can be traced across the years, with thickness remaining roughly similar and depth gradually increasing. Prior research shows that an extreme melt season can result in a sudden increase of refrozen ice in firn. Here we show how several years without extreme melt can regenerate porous firn near the surface and cause the downward advection of thick ice layers.