Associations Between the Seasonal Darkening of the Greenland Ice Sheet and the Duration of Bare Ice

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Abstract
Darkening of the Greenland ice sheet is known to amplify surface melting. Here, analysis of automatic weather station (AWS) data around the ice sheet and satellite‐derived albedo data reveals that the bare ice duration (BID) is a predictor of the average albedo during summer (June through August, JJA, ). Inverse correlation between the two is found in both the AWS ( = 0.74) and satellite ( = 0.55) data, meaning that longer periods of bare ice result in lower average albedo. The average decrease in measured by AWS is −0.0044 ± 0.0002 (mean ± standard error (SE)), associated with an additional ∼9 cm ablation (∼8 cm w.e.) for each 0.01 decrease in . Satellite observations reveal that lowers −0.0032 ± 0.0000 (mean ± SE) across the ice sheet, increasing season‐total melt by ∼4 cm w.e. for each 0.01 decrease in . The simple correlation between BID and offers a convenient expression for current Greenland ice sheet melt modeling, but we advise caution when using this expression for predictive melt modeling because the data scatter in versus BID plots become more dispersed around the best fit linear regression line as BID increases. We contend that this scattering is most likely due to spatial variability in the dominant darkening processes, which differ in their albedo‐lowering capacity, and that this variability will become increasingly important to constrain in a warming climate as larger surface areas of the ice sheet are exposed and the melt seasons lengthen.
Funding Information
  • Horizon 2020 Framework Programme (856416)
  • Villum Fonden (42069)
  • Novo Nordisk Fonden (NNF24OC0094957)
  • Centre for Water Technology, Aarhus University

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