Time-Domain Reflectometry Measurements and Modelling of Firn Meltwater
Infiltration at DYE-2, Greenland
Abstract
Meltwater infiltration and refreezing in snow and firn are important
processes for Greenland Ice Sheet mass balance, acting to reduce
meltwater runoff and mass loss. To advance understanding of meltwater
retention processes in firn, we deployed vertical arrays of time-domain
reflectometry sensors and thermistors to continuously monitor meltwater
infiltration, refreezing, and wetting-front propagation in the upper 4 m
of snow and firn over the 2016 melt season at DYE-2, Greenland. The
dataset provides a detailed record of the co-development of the firn
wetting and thawing fronts through the melt season. These data are used
to constrain a model of firn thermodynamics and hydrology that is then
used in simulations of the long-term firn evolution at DYE-2, forced by
ERA5 climate reanalyses over the period 1950-2020. Summer 2016 meltwater
infiltration reached a depth of 1.8 m below the surface, which is close
to the modelled long-term mean at this site. Modelled meltwater
infiltration increased at DYE-2 from 1990-2020, driving increases in
firn density, ice content, and temperature; 10-m firn temperatures
increased by 1°C per decade over this period. Modelled meltwater
infiltration reached 6 to 7 m depth during extreme melt seasons in
Greenland such as 2012 and 2019, causing 3-4°C increases in 10-m firn
temperatures which persist for several years. A similar event occurred
in 1968 in the model reconstructions. These deep infiltration events
strongly impact the firn at DYE-2, and may be more influential than the
background warming trend in governing meltwater retention capacity in
the Greenland percolation zone.