Timing and regional patterns of snowmelt on Antarctic sea ice from passive microwave satellite observations

Abstract

An improved understanding of the temporal variability and the spatial distribution of snowmelt on Antarctic sea ice is crucial to better quantify atmosphere-ice-ocean interactions, in particular sea-ice mass and energy budgets. It is therefore important to understand the mechanisms that drive snowmelt, both at different times of the year and in different regions around Antarctica. In this study, we combine diurnal brightness temperature differences (dT B (37 GHz)) and ratios (T B (19 GHz)/T B (37 GHz)) to detect and classify snowmelt processes. We distinguish temporary snowmelt from continuous snowmelt to characterize dominant melt patterns for different Antarctic sea-ice regions from 1988/1989 to 2014/2015. Our results indicate four characteristic melt types. On average, 38.9 6 6.0% of all detected melt events are diurnal freeze-thaw cycles in the surface snow layer, characteristic of temporary melt (Type A). Less than 2% reveal immediate continuous snowmelt throughout the snowpack, i.e., strong melt over a period of several days (Type B). In 11.7 6 4.0%, Type A and B take place consecutively (Type C), and for 47.8 6 6.8% no surface melt is observed at all (Type D). Continuous snowmelt is primarily observed in the outflow of the Weddell Gyre and in the northern Ross Sea, usually 17 days after the onset of temporary melt. Comparisons with Snow Buoy data suggest that also the onset of continuous snowmelt does not translate into changes in snow depth for a longer period but might rather affect the internal stratigraphy and density structure of the snowpack. Considering the entire data set, the timing of snowmelt processes does not show significant temporal trends.

Variability of Winter Snow Properties on Different Spatial Scales in the Weddell Sea

“…Consequently, the strong temperature gradients required for constructive metamorphism and the subsequent formation of faceted and depth hoar grains are intermittently interrupted (e.g., Colbeck, 1982). Instead, thaw-refreezing events might have developed the pronounced melt-freeze forms in the MYS during the previous spring-summer transition, which is supported by observation of multiple basal and internal thaw-refreezing events by satellite microwave observations in the area (Arndt et al, 2016;Willmes et al, 2006). In contrast, FYS is dominated by snow accumulation (wind slab) and fragmented grains, the prestate of depth hoar, dominated.…”

“…Furthermore, following our assumption that the density can be neglected for the variability analysis, an overall higher property variability is evident for MYS than for FYS. This might be attributed to diurnal thaw-freeze cycles in the upper snowpack as well as internal melt events in the previous summer in the area observed in a field studies on snow properties during the spring-summer transition by, for example, Nicolaus et al (2009) as well as identified by Arndt et al (2016) from passive microwave observations. In contrast, FYS is expected to be more homogenous.…”

“…Surface flooding is also thought to be seasonally and regionally dependent, with its occurrence increasing with the beginning of austral summer as basal ice melt increases due to high oceanic heat fluxes in the Southern Ocean (Martinson & Iannuzzi, 1998), while the thick snowpack remains. In addition, diurnal freeze-thaw cycles during spring and summer initiate the downward percolation of (fresh) meltwater through the snowpack, leading to formation of superimposed ice within the snowpack (Arndt et al, 2016;Haas et al, 2001Haas et al, , 2008Nicolaus et al, 2009;Willmes et al, 2006). Both snow-ice and superimposed ice formation are affected by snow metamorphism processes, which contribute to a strongly layered snowpack on Antarctic sea ice (M. Sturm & Massom, 2017).…”

Snow in the changing sea-ice systems

“…In addition to being younger, thinner and more dynamic, the Antarctic snow-sea ice system is also characterized by highly-variable meteorological conditions 10 in which heavy snowfall and synoptically-driven thaw events occur year-round 27,67 . The combined effect of heavy snowfall and thinner ice results in widespread flooding and snow-ice formation (Fig.…”

Influence of snow depth and surface flooding on light transmission through Antarctic pack ice

“…The results from nonflooded grid cells show high extinction coefficients for snow (31.76 ± 0.69 m −1 , section 3.3) revealing a strong scattering in the respective snowpack. Since Antarctic sea ice is covered with snow during most of the year [ Massom et al ., ], seasonal snowmelt processes [ Arndt et al ., ] lead to a snowpack consisting of highly compacted and metamorphic layers of snow with internal ice layers [ Nicolaus et al ., ]. This highly inhomogeneous snowpack and density structure leads to weak observed correlations of transmitted solar radiation with snow depth (Figure ).…”