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Investigating the impact of aerosol deposition on snowmelt over the Greenland Ice Sheet using a large-ensemble kernel

Abstract. Accelerating surface melt on the Greenland Ice Sheet (GrIS) has led to a
doubling of Greenland's contribution to global sea level rise during recent
decades. Black carbon (BC), dust, and other light-absorbing impurities (LAIs)
darken the surface and enhance snowmelt by boosting the absorption of solar
energy. It is therefore important for coupled aerosol–climate and ice sheet
models to include snow darkening effects from LAI, and yet most do not. In
this study, we conduct several thousand simulations with the Community Land
Model (CLM) component of the Community Earth System Model (CESM) to
characterize changes in melt runoff due to variations in the amount, timing,
and nature (wet or dry) of BC deposition on the GrIS. From this large matrix
of simulations, we develop a kernel relating runoff to the location, month,
year (from 2006 to 2015), and magnitudes of BC concentration within
precipitation and dry deposition flux. BC deposition during June–August
causes the largest increase in annually integrated runoff, but winter
deposition events also exert large (roughly half as great) runoff
perturbations due to reexposure of impurities at the snow surface during
summer melt. Current BC deposition fluxes simulated with the atmosphere
component of CESM induce a climatological-mean increase in GrIS-wide runoff
of ∼ 8 Gt yr−1, or +6.8 % relative to a paired simulation
without BC deposition. We also provide linear equations that relate the
increase in total runoff to GrIS-wide wet and dry BC deposition fluxes. It is
our hope that the runoff kernel and simple equations provided here can be
used to extend the utility of state-of-the-art aerosol models.
