Abstract. The McMurdo Dry Valleys (MDVs) of Antarctica are a polar desert
ecosystem consisting of alpine glaciers, ice-covered lakes, streams, and
expanses of vegetation-free rocky soil. Because average summer temperatures
are close to 0 ∘C, the
MDV ecosystem in general, and glacier melt dynamics in particular, are both closely linked to the energy balance. A slight
increase in incoming radiation or change in albedo can have large effects on
the timing and volume of meltwater. However, the seasonal evolution or
spatial variability of albedo in the valleys has yet to fully characterized.
In this study, we aim to understand the drivers of landscape albedo change
within and across seasons. To do so, a box with a camera, GPS, and
shortwave radiometer was hung from a helicopter that flew transects four to five
times a season along Taylor Valley. Measurements were repeated over three
seasons. These data were coupled with incoming radiation measured at six
meteorological stations distributed along the valley to calculate the
distribution of albedo across individual glaciers, lakes, and soil
surfaces. We hypothesized that albedo would decrease throughout the austral
summer with ablation of snow patches and increasing sediment exposure on the
glacier and lake surfaces. However, small snow events (<6 mm water
equivalent) coupled with ice whitening caused spatial and temporal
variability of albedo across the entire landscape. Glaciers frequently
followed a pattern of increasing albedo with increasing elevation, as well as
increasing albedo moving from east to west laterally across the ablation
zone. We suggest that spatial patterns of albedo are a function of landscape
morphology trapping snow and sediment, longitudinal gradients in snowfall
magnitude, and wind-driven snow redistribution from east to west along
the valley. We also compare our albedo measurements to the MODIS albedo product
and found that overall the data have reasonable agreement. The mismatch in
spatial scale between these two datasets results in variability, which is
reduced after a snow event due to albedo following valley-scale gradients of
snowfall magnitude. These findings highlight the importance of understanding
the spatial and temporal variability in albedo and the close coupling of
climate and landscape response. This new understanding of landscape albedo
can constrain landscape energy budgets, better predict meltwater generation
on from MDV glaciers, and how these ecosystems will respond to changing
climate at the landscape scale.
Review to Bergstrom et al. (2019): "The seasonal evolution of albedo across glaciers and the surrounding landscape of the Taylor Valley, Antarctica" submitted to The Cryosphere.
