Measurements of solar light transmission in bare glacier ice: Implications for subsurface meltwater production in the Greenland Ice Sheet ablation zone
Abstract
Transmission and absorption of solar radiation in bare ice can produce subsurface meltwater and create a porous layer of near-surface weathered ice that slows the delivery of surface meltwater runoff to supraglacial rivers and streams. We collected measurements of spectral solar flux transmission in bare glacier ice in the spectral range 300-900 nm at 12-77 cm depth below the ice surface on 20 July 2018 in the western Greenland Ice Sheet ablation zone (840 m a.s.l, 67.15 oN, 50.02 oW). These measurements are used to calculate flux scattering, absorption, and extinction coefficients, which describe the attenuation of transmitted solar radiation with depth in ice following a Beer-Bouguer exponential decay law. We compare our empirical coefficients and predicted flux transmission to theoretical values calculated using two-stream radiative transfer theory. Empirical flux extinction coefficients are nearly one order of magnitude larger than predicted by two-stream theory. We suggest the discrepancy is due to embedded light absorbing impurities in the measured ice that enhance visible light absorption. We also find transmitted solar flux is overestimated by ~3-4x depending on wavelength at all measured depths, which we attribute to enhanced scattering from near-surface weathered ice that imparts a non-linear extinction rate with depth at distances very near the ice surface. Consequently, flux transmission is overestimated by the Beer-Bouguer model, which assumes a constant extinction rate with depth. Future work will incorporate our solar flux extinction coefficient values into a surface energy balance model to quantify subsurface meltwater production in the GrIS ablation zone and its effect on surface meltwater runoff.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C34A..01C
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 0728 Ice shelves;
- CRYOSPHERE;
- 0736 Snow;
- CRYOSPHERE;
- 0762 Mass balance;
- CRYOSPHERE