The seasonal evolution of albedo across glaciers and the surrounding landscape of Taylor Valley, Antarctica

Abstract

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.

Modeling of Mass Balance Variability and Its Impact on Water Discharge from the Urumqi Glacier No. 1 Catchment, Tian Shan, China

“…Since bare-ice albedo can vary temporally and spatially [41][42][43], constant value for ice albedo presents a shortcoming in energy balance models. However, albedo values deduced from Landsat images are very low and require adjustment before integration into COSIPY.…”

“…As the melting season proceeds, exposure time of already snow-free areas prolongs. As a consequence, accumulation of impurities grows [41,96] and englacial debris increasingly melts out [97], which highly affects albedo [42,45,49,63]. An additional drawback from the sole employment of images from the ablation season is the influence of meltwater on albedo.…”

“…Glacier-runoff responses to climate change are manifold depending on general setting and climate both concerning the expected long-term overall annual changes and their seasonal patterns (e.g., [5][6][7][8]). snow as the top layer as well as its thickness and aging [27,41]. Once the snow has melted away, the bare-ice albedo is commonly assumed constant but can in fact vary spatially and temporally [41][42][43].…”

“…snow as the top layer as well as its thickness and aging [27,41]. Once the snow has melted away, the bare-ice albedo is commonly assumed constant but can in fact vary spatially and temporally [41][42][43]. This variability arises mainly from changes of the physical properties like density, liquid water content, stratification, crystal structure, and surface roughness [42] but also from the emergence of englacial debris due to melt or from increasing exposure of supraglacial debris [44] and from impurities [42,43,45].…”

Long‐term shifts in feedbacks among glacier surface change, melt generation and runoff, McMurdo Dry Valleys, Antarctica

“…From an energy balance perspective, the drainage network creates centimetre to meter scale surface roughness. This small‐scale roughness can trap wind‐blown sediment, which lowers albedo (Bergstrom et al, 2020; Johnston et al, 2005; MacClune et al, 2003) increases total surface area available for melt, and creates an ice surface with multiple aspects (rather than a uniform sloping surface with a single aspect). Increased roughness overall can increase the potential for increased direct, rather than diffuse, radiation (Cathles et al, 2011; Rippin et al, 2015), and increases turbulent heat transfer into the ice (Hoffman et al, 2016).…”