Evolution of Melt Pond Fraction and Depth on Multiyear Ice in 2020 from
High Resolution Satellite Observations
Abstract
Observations reveal end of summer Arctic sea ice extent is declining at
an accelerating rate. Model projections underestimate this decline and
continue to have a broad spread in forecasted September sea ice extent.
This suggests some important summer processes, such as melt pond
formation and evolution, may not be properly represented in current
models. Melt ponds form on the sea ice surface as snow melts, and pools
in low lying areas on the sea ice surface. The evolution of the ponds
depends on snow depth, ice thickness, and surface conditions. Melt water
may spread across a level surface, or be confined to depressions between
sea ice ridges. Ponds decrease the albedo of the surface and enhance the
positive ice albedo feedback, accelerating further melt. Until recently,
Arctic-wide observations of individual melt ponds were not available.
ICESat-2, a photon counting laser altimeter launched in 2018, provides
high resolution detail of sea ice and snow topography due to its unique
combination of a small footprint (~12 m) and
high-resolution along-track sampling (0.7 m). The green laser (532 nm)
is able to penetrate water, enabling melt pond depth measurements. We
have developed methods to track the melt pond surface and bathymetry in
ICESat-2 data to determine melt pond depth. We also track melt pond
evolution through application of a sea ice classification algorithm to
10 m resolution Sentinel-2 imagery. The combination of these two
datasets allows for an evolving, three-dimensional view of the melting
sea ice surface. We focus on the evolution of summer melt on multiyear
ice in the Central Arctic north of Greenland and Canada in 2020. Our
findings are put in context of existing literature on melt pond depth,
volume, and evolution. We also discuss our results in relation to the
melt pond fraction north of the Fram Strait, where we expect different
ice conditions in the vicinity of the 2020 MOSAiC field studies.
Observational data products comprising melt pond fraction and pond depth
are being developed for public distribution. These products may be of
interest to those studying under-ice light and biology, as well as
modelers who are interested in understanding the evolution of melt pond
parameters for model initialization and validation.