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Discussion papers
https://doi.org/10.5194/tc-2019-65
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-65
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Apr 2019

Research article | 10 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

The surface albedo of the Greenland Ice Sheet between 1982 and 2015, and its relationship to the ice sheet’s surface mass balance and ice discharge

Aku Riihelä1, Michalea D. King2, and Kati Anttila1 Aku Riihelä et al.
  • 1Finnish Meteorological Institute, Helsinki, FI-00560, Finland
  • 2Byrd Polar and Climate Research Center, Columbus, USA

Abstract. The Greenland Ice Sheet is losing mass at a significant rate, primarily driven by increasing surface melt-induced runoff. Because the ice sheet’s surface melt is closely connected to changes in the surface albedo, studying multidecadal changes in the ice sheet’s albedo offers insight into surface melt and associated changes in its surface mass balance. Here, we first analyse the CLARA-A2 SAL satellite-based surface albedo dataset, covering 1982–2015, to obtain decadal albedo trends for each summer month. We also examine the rates of albedo change during the early summer, supported with atmospheric reanalysis data from MERRA-2, to discern changes in the intensity of early summer melt, and their likely drivers. We find that rates of albedo decrease during summer melt have accelerated during the 2000s relative to early 1980s, and that the surface albedos now often decrease to values typical of bare ice at elevations 50–100 m higher on the ice sheet. The southern margins exhibit the opposite behaviour, though, and we suggest this is due to increasing snowfall over the area.

We then correct the mass balance estimates observed by the GRACE satellite mission with state-of-the-art ice discharge estimates to obtain observation-based estimates for the surface mass balance. The CLARA albedo changes are regressed with this data to obtain a proxy surface mass balance timeseries for the summer periods 1982–2015. This proxy timeseries is compared with latest regional climate model estimates from the MAR model. We show that the proxy timeseries agrees with MAR through the analyzed period within the associated uncertainties of the data and methods, demonstrating and confirming that surface runoff has dominated the rapid mass loss period between 1990s and 2010s.

Finally, we extend the analysis to GrIS basin scale to examine discharge-albedo relationships in order to ascertain if the surface melt contributes to discharge acceleration via basal lubrication. While there is little evidence of surface melt-induced ice flow acceleration at annual timescales, we find time lags between seasonal maximum runoff production and seasonal maximum discharge rate to be in agreement with recent modelling results.

Aku Riihelä et al.
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Aku Riihelä et al.
Data sets

CLARA-A2: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data – Edition 2 K.-G. Karlsson, K. Anttila, J. Trentmann, M. Stengel, J. F. Meirink, A. Devasthale, T. Hanschmann, S. Kothe, E. Jääskeläinen, J. Sedlar, N. Benas, G.-J. van Zadelhoff, C. Schlundt, D. Stein, S. Finkensieper, N. Håkansson, R. Hollmann, P. Fuchs, and M. Werscheck https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002

Aku Riihelä et al.
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Short summary
We used a 1982–2015 time series of satellite observations to examine changes in the surface reflectivity (albedo) of the Greenland Ice Sheet. We found notable decreases in albedo over most of the ice sheet margins in July & August, but particularly over the west coast and between 2000–2015. The results also indicate that significant melt now occurs in areas 50 to 100 m higher up the ice sheet relative to early 1980s. The meltwaters also temporarily accelerate glacier flow via basal lubrication.
We used a 1982–2015 time series of satellite observations to examine changes in the surface...
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