# Ice Production in Ross Ice Shelf Polynyas during 2017-2018 from Sentinel-1 SAR Images
## 4 Results  
The extent/outline of each wind-driven polynya was manually digitized and the ice volume of each event was calculated based on the polynya area and ice thickness. The results are presented in Figure 6 and Table 2. During these two years of 2017 and 2018, the wind-driven polynya events occurred during March-November with no ice-production events observed during austral summertime (December, January, or February). The occurrence frequency of wind-driven polynya events was 90 in 2017, lower than 114 in 2018. Among them, there were 64 RISP events and 26 MSP events in 2017 (events occurred between 15 March and 15 November 2017), and 84 RISP and 30 MSP events in 2018 (events occurred from 12 March to 12 November 2018). The polynya area and the ice production show large fluctuations (Figure 6). The areas of wind-driven polynya for each event varied from 343 km\({}^{2}\) to 86,419 km\({}^{2}\) for RISP, and from 159 km\({}^{2}\) to 23,654 km\({}^{2}\) for MSP. The yearly cumulative ice area in MSP was 93,327 km\({}^{2}\) in 2017 and 87,682 km\({}^{2}\) in 2018, and that of RISP were 1,066,520 km\({}^{2}\) and 1,013,906 km\({}^{2}\) (Figure 6, Table 2), respectively. The yearly cumulative ice productions were 14 km\({}^{3}\) and 17 km\({}^{3}\) for MSP in 2017 and 2018, and 188 km\({}^{3}\) and 179 km\({}^{3}\) for RISP in 2017 and 2018, respectively. Thus, it can be seen, although the occurrence frequency in 2017 was smaller than that in 2018, the yearly cumulative polynya areas and ice productions in 2017 were close to (even slightly larger than) those in 2018. The cumulative polynya area is the area sum of all polynya events, and thus its value depends on occurrence frequency and each polynya area. Figure 6 shows the occurrence frequency in 2017 was smaller than that in 2018, but the frequency of polynya with an area of more than 3000 km\({}^{2}\) was 9 in 2017, larger than 5 in 2018. Therefore, the average polynya area was 19,749 km\({}^{2}\) (16,159 km\({}^{2}\) for RISP and 3590 km\({}^{2}\) for MSP) in 2017, much larger than 14,993 km\({}^{2}\) (12,070 km\({}^{2}\) for RSP and 2923 km\({}^{2}\) for MSP) in 2018. Compared with the results in the previous studies, the polynya ice production in RSP is 1/2-2/3 of previous results, implying that previous studies might have significantly overestimated the ice production in RSP. Figure 5: Polynya area (green polygons) mapped from the Sentinel-1 SAR image on 20 August 2017, and the ice thicknesses (dots) within the polynya area derived from AMSR2 on 20 August 2017 (**a**) and 22 August 2017 (**b**). Figure 6: Wind-driven ice production areas, average thickness, and volumes for every event at the McMurdo Sound and Ross Ice Shelf polynyas (RISP) in 2017 (**a**) and 2018 (**b**). (The polynya area and polynya ice production of RISP on 5 July 2017, exceed the top scale. They are 86,419 km\({}^{2}\), and 24 km\({}^{3}\), respectively). The cumulative polynya ice production is controlled by both polynya area/extent and ice thickness. The variability in average ice thicknesses of RISP and MSP in 2017 and 2018 (Figure 6) shows that during 2017, the minimum ice thicknesses of all ice production events at the RISP and MSP are 0.05 m and 0.03 m, respectively; the maximum ice thicknesses are 0.29 m and 0.3 m, respectively; and the average thicknesses are 0.18 m and 0.16 m, respectively. During 2018, the minimum ice thicknesses of all ice-production events in RISP and MSP were 0.05 m and 0.06 m, respectively; the maximum ice thicknesses are 0.30 m and 0.30 m, respectively; and the average thicknesses were 0.16 m and 0.18 m, respectively. Although ice thickness was quite variable over time, there was an apparent seasonal change of increase-stable-decrease, i.e., increase from March to May, relatively stable from May to September, and decrease from September onwards.