Spatial Variability of the Snowmelt‐Albedo Feedback in Antarctica

• Published in: Journal of geophysical research. Earth surface Vol. 126; no. 2
• Main Authors: Jakobs, C. L., Reijmer, C. H., van den Broeke, M. R., van de Berg, W. J., van Wessem, J. M.
• Format: Journal Article
• Language: English
• Published: 01.02.2021
• Subjects: albedo; Antarctica; climate modeling; grain size; surface melt
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2020JF005696

Surface melt is an important process for the stability of ice shelves, and therewith the Antarctic ice sheet. In Antarctica, absorption of solar radiation is mostly the largest energy source for surface melt, which is further enhanced by the snowmelt‐albedo feedback (SMAF): Refrozen snow has a lower albedo than new snow, which causes it to absorb more solar radiation, further increasing the energy available for surface melt. This feedback has previously been shown to increase surface melt by approximately a factor of 2.5 at Neumayer Station in East Antarctica. In this study, we use a regional climate model to quantify SMAF for the entire Antarctic ice sheet. We find that it is most effective on ice shelves in East Antarctica, and is less important in the Antarctic Peninsula and on the Ross and Filchner‐Ronne ice shelves. We identify a relationship between SMAF and average summer 2 m air temperatures, and find that SMAF is most important around 265 ± 2 K. On a subseasonal scale, we identify several parameters that contribute to SMAF: the length of dry periods, the time between significant snowfall events and snowmelt events, and prevailing temperatures. We then apply the same temperature dependency of SMAF to the Greenland ice sheet and find that it is potentially active in a narrow band around the ice sheet, and finally discuss how the importance of SMAF could change in a warming climate. Plain Language Summary The Antarctic ice sheet is surrounded by ice shelves: floating extensions that prevent it from flowing into the oceans. The stability of these ice shelves is mainly affected by the melting of snow and ice, leading to a potential disintegration of the entire ice shelf. To properly simulate the climate, models should therefore be able to accurately reproduce snowmelt rates. Snowmelt in Antarctica is mainly driven by the absorption of solar radiation. This is subject to a positive feedback: when snow melts, it becomes darker, causing it to absorb more radiation. This leads to more energy that is available for snowmelt, which further darkens the surface. In this study, we use a climate model to quantify the importance of this feedback for the Antarctic ice sheet. We find that it is most important in regions with an average summer 2 m air temperature around 265 K. We furthermore find that during a long, dry period in summer, the feedback is more effective, and that the timing between snowfall and snowmelt partly determines how much the feedback will affect snowmelt. As a final step, we estimate how important this feedback is in Greenland, and how the observed patterns could change in a warming climate. Key Points We use a regional climate model to quantify the snowmelt‐albedo feedback for the Antarctic ice sheet We find that this feedback is most active on East Antarctic ice shelves Precipitation frequency, timing, and summer 2 m air temperature are key parameters for its importance