Search for: All records

This archive contains firn temperature data collected at two sites in the western Greenland Ice Sheet percolation zone. The sites, T3 and Crawford Point (CP), are located along the Expéditions Glaciologiques Internationales au Groenland (EGIG) line. The data are time series of firn temperature measured in boreholes drilled to 100 m depth. The boreholes were drilled by hot water methods. The CP measurements span the period June to August, 2019. This borehole was drilled in 2018, so the temperature profile had fully recovered from the drilling thermal disturbance by the start of the time series. The T3 data span the period June 2019 to September 2021. This borehole was drilled in June 2019, so the time series of measurements includes the thermal recovery from drilling (several months) and two subsequent years. The dataset was collected as part of projects funded by the U.S. National Science Foundation. These measurements are associated with additional datasets collected as part of a NSF Arctic Observing Network project, and include measurements at multiple sites on the EGIG line of firn temperature and firn density/ice content. 

Abstract Processes governing meltwater penetration into cold firn remain poorly constrained. Here, in situ experiments are used to develop a grain-scale model to investigate physical limitations on meltwater infiltration in firn. At two sites in Greenland, drilling pumped water into cold firn to >75 m depth, and the thermo-hydrologic evolution of the firn column was measured. Rather than filling all available pore space, the water formed perched aquifers with downward penetration halted by thermal and density conditions. The two sites formed deep aquifers at ~40 m depth and at densities considerably less than the air pore close-off density (~725 kg m −3 at −18°C, and ~750 kg m −3 at −14°C), demonstrating that some pore space at depth remains inaccessible. A geometric grain-scale model of firn is constructed to quantify the limits of a descending fully saturated wetting front in cold firn. Agreement between the model and field data implies the model includes the first-order effects of water and heat flow in a firn lattice. The model constrains the relative importance of firn density, temperature and grain/pore size in inhibiting wetting front migration. Results imply that deep infiltration, including that which leads to firn aquifer formation, does not have access to all available firn pore space. 

Abstract The intermixed thermal and structural framework of cold firn, water-saturated firn and ice layers in Greenland's percolation zone can be challenging to penetrate with core drills. Here, we present our experiences using a hot water drill for research on the firn layer of the percolation zone. We built and deployed a lightweight and easily transportable system for drilling a transect of ~15 cm diameter boreholes through the full firn column thickness, to depths exceeding 100 m. An instrumented drill stem provides a scientific measurement of the firn properties while drilling. The system was successful at gaining rapid access to the firn column with mixed wet and cold conditions, was easily transported to the site and across the glacier surface, and required a small field crew to operate. The boreholes are well suited for in situ investigations of firn processes in Greenland percolation zone.