Dark zone of the Greenland Ice Sheet controlled by
distributed biologically-active impurities
Jonathan C. Ryan
, Alun Hubbard
, Marek Stibal
, Tristram D. Irvine-Fynn
, Joseph Cook
Laurence C. Smith
, Karen Cameron
& Jason Box
Albedo—a primary control on surface melt—varies considerably across the Greenland Ice
Sheet yet the speciﬁc surface types that comprise its dark zone remain unquantiﬁed. Here we
use UAV imagery to attribute seven distinct surface types to observed albedo along a 25 km
transect dissecting the western, ablating sector of the ice sheet. Our results demonstrate that
distributed surface impurities—an admixture of dust, black carbon and pigmented algae—
explain 73% of the observed spatial variability in albedo and are responsible for the dark zone
itself. Crevassing and supraglacial water also drive albedo reduction but due to their limited
extent, explain just 12 and 15% of the observed variability respectively. Cryoconite, con-
centrated in large holes or ﬂuvial deposits, is the darkest surface type but accounts for <1% of
the area and has minimal impact. We propose that the ongoing emergence and dispersal of
distributed impurities, ampliﬁed by enhanced ablation and biological activity, will drive
future expansion of Greenland's dark zone.
Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK.
Department of Geography,
University of California, Los Angeles, Los Angeles, CA 90095, USA.
Institute at Brown for Environment and Society, Brown University, Providence, RI
Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, University of Tromsø, 9037 Tromsø, Norway.
of Ecology, Faculty of Science, Charles University, 12844 Prague, Czech Republic.
Department of Geochemistry, Geological Survey of Denmark and
Greenland, 1350 Copenhagen, Denmark.
Department of Geography, University of Shefﬁeld, Shefﬁeld S10 2TN, UK.
Institute of Biological, Environmental
and Rural Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK.
Department of Glaciology and Climate, Geological Survey of Denmark and
Greenland, 1350 Copenhagen, Denmark. Correspondence and requests for materials should be addressed to A.H. (email: firstname.lastname@example.org)