The MOSAiC Drift: Ice conditions from space and comparison with previous years

Abstract

Abstract. We combine satellite data products to provide a first and general overview of the sea-ice conditions along the MOSAiC drift and a comparison with previous years. We find that the MOSAiC drift was around 25 % faster than the climatological mean drift, as a consequence of large-scale low-pressure anomalies prevailing around the Barents-Kara-Laptev Sea region between January and March. In winter (October–April), satellite observations show that the sea-ice in the vicinity of the Central Observatory (CO) was rather thin compared to the previous years along the same trajectory. Unlike ice thickness, satellite-derived sea-ice concentration, lead frequency, and snow thickness during winter month were close to the long-term mean with little variability. With the onset of spring and decreasing distance to Fram Strait, variability in ice concentration and lead activity increased. In addition, frequency and strength of deformation events (divergence and shear) were higher during summer than during winter. Overall, we find that sea-ice conditions observed close (~ 5 km) to the CO are representative for the wider (50 km and 100 km) surroundings. An exception is the ice thickness: Here we find that sea-ice near the CO (50 km radius) was 4 % thinner than sea-ice within a 100 km radius. Moreover, satellite acquisitions indicate that the formation of large melt ponds began earlier on the MOSAiC floe than on neighbouring floes.

Meteorological conditions during the MOSAiC expedition

“…During summer, T2M near the melting point of ice persisted from late May until early September during MOSAiC. This period of near melting point conditions was more than a month longer than the 1979-2019 median (Figure 1) and is consistent with lower than normal seaice concentration along the MOSAiC drift track during the summer (Krumpen et al, 2021). The MOSAiC temperatures in July and August 2020 were especially anomalous (Table 1, Figures 1, 4, and S4) and the warmest of the 1979-2020 period (Figure 3).…”

“…This relates with the changed background state, often called the "New Arctic." Compared to earlier years, the Polarstern has seen thinner sea ice in winter and lower sea-ice concentration in summer (Krumpen et al, 2021). The main findings for the meteorological conditions along the yearlong MOSAiC track based on ERA5 reanalysis data and compared to the past 4 decades are as follows:…”

“…In earlier years, MOSAiC would have been deep in the ice pack, while in recent years, the sea-ice extent is greatly reduced (e.g., Stroeve and Notz, 2018). Accordingly, MOSAiC was closer to the sea-ice edge (e.g., with a distance less than 200 km at the beginning of July; Krumpen et al, 2021) than earlier in the climatology, which is generally linked with warmer and wetter conditions.…”

“…These cyclones' central MSLP ranked in the top 25th percentile of all March storms from 1979 to 2019 (Table S6). The location of these cyclones, to the south and east of the Polarstern, resulted in persistent northerly winds during mid-March (Figure 6), which caused a rapid southward drift of the Polarstern (Krumpen et al, 2021). The warm and moist conditions occurring in mid to late April 2020 were associated with three cyclone tracks impacting the Polarstern from April 16 to 19 whose intensities ranked in or near the top 25th percentile, in terms of wind speed at the Polarstern and central MSLP (Figure S2, Table S7).…”

Estimation of thermodynamic and dynamic contributions to sea ice growth in the Central Arctic using ICESat-2 and MOSAiC SIMBA buoy data

“…1). Since the floes of the CO and DN were formed around November to December 2018, the buoys were dominantly deployed at the area of second-year ice (Krumpen et al, 2021(Krumpen et al, , 2020. The deployment sites had initial snow depth and ice thicknesses ranging from 0.05-0.30 m and 0.40-1.70 m, respectively.…”