Figure 1
(a) The month-wise ranking of sea ice extents for each year from 1979 to 2023, represented from dark to light shades in increasing order, where a high rank represents high ice extents and lower ranks means lesser sea ice extents. (b) The month-wise ranking of surface air temperature for each year from 1979 to 2023, where a high rank represents higher warming. (c) The annual mean sea ice extents from 1979 to 2022, the corresponding anomalous surface air temperature (SAT), and sea surface temperature (SST) are represented in the blue, red, and green line plots. The green (red) shading represents the dominant positive (negative) IPO phases while green (red) dots represent the annual mean positive (negative) SAM index (Marshall, 2003). The blue (yellow) shading highlights the strong La-Niña (El-Niño) years (d) The yearly sea ice extent anomalies for observational (blue) and the Coupled Model Intercomparison Project Phase 6 (CMIP6) (red) were simulated for the entire Southern Ocean. Anomalies are calculated with respect to the mean from 1979–2015. Observations are based on the merged data from multiple passive microwave satellite sensors available from 1979 to 2022. The dashed blue line indicates the linear trend for observational records from 2010 to 2022 while the dashed red line highlights the long-term trend of sea ice from 1979 to 2022. The CMIP6 sea ice extent anomalies are the r1 ensemble outputs from 20 models (grey) for historical and future simulations with the mean ice extent from multiple models. The yellow-colored points in (a) represent the record low values while it represents extreme high temperatures in (b). The recent decline in sea ice from 2016 to 2023 is highlighted in the magenta-bordered box.
Table 1
Slopes and standard deviations of linear least-squares fit for annual and seasonal sea ice extents in the total Southern Ocean and each of the 5 sectors both for the 43-y record (1979–2022) and in parentheses, for the 37-y record (1979–2015). The values highlighted in bold (bold italic) indicate significance at 99% (95%) or above. The 5 sectors apart of Total Southern Ocean (SO) are, WS: Weddell Sea, IO: Indian Ocean, WP: Western Pacific, RS: Ross Sea, BAS: Amundsen-Bellingshausen Sea.
| SO | WS | IO | WP | RS | BAS | |
|---|---|---|---|---|---|---|
| Annual mean (103 km2/decade) | 14.10 ± 54.65 (235.92 ± 40) | (–0.68 ± 32.17) (80.17 ± 37.18) | 8.47 ± 16.36 (53.20 ± 17.75) | 12.35 ± 11.91 (28.69 ± 15.35) | 34.28 ± 25.44 (110.98 ± 28.40) | (-40.31 ± 15.43) (-37.13 ± 20.26) |
| Annual mean (%/decade) | 0.11 ± 0.45 (1.95 ± 0.33) | (–0.16 ± 0.73) (1.80 ± 0.83) | 0.43 ± 0.83 (2.67 ± 0.89) | 0.99 ± 0.96 (23.02 ± 12.32) | 1.18 ± 0.87 (3.78 ± 0.96) | (–2.72 ± 1.04) (–2.48 ± 1.35) |
| DJF (103 km2/decade) | 7.07 ± 71.73 (250.85 ± 71.37) | 34.22±48.69 (159.66 ± 56.90) | 19.10 ± 18.82 (49.89 ± 23.33) | 15.25 ± 11.47 (29.70 ± 15.25) | 0.90 ± 34.14 (107.48 ± 38.74) | (–62.38 ± 18.08) (–95.87 ± 22.06) |
| DJF (%/decade) | 0.11 ± 1.10 (3.78 ± 1.07) | 1.30 ± 1.85 (5.95 ± 2.12) | 2.52 ± 2.48 (6.48 ± 3.03) | 2.46 ± 1.85 (4.77 ± 2.45) | 0.056 ± 2.14 (6.52 ± 2.35) | (–6.88 ± 1.99) (–10.52 ± 2.42) |
| MAM (103 km2/decade) | 35.75 ± 78.69 (285.69 ± 77.31) | 51.11 ± 45.52 (178.44 ± 53.08) | 25.33 ± 14.67 (52.34 ± 18.56) | 31.94 ± 13.32 (51.21 ± 17.73) | 8.69 ± 37.03 (107.89 ± 42.65) | (–81.34 ± 20.89) (–104.20 ± 23.34) |
| MAM (%/decade) | 0.47 ± 1.05 (3.75 ± 1.01) | 1.88 ± 1.68 (6.47 ± 1.93) | 3.02 ± 1.75 (6.21 ± 2.20) | 3.74 ± 1.56 (6.018 ± 2.08) | 0.39 ± 1.69 (4.83 ± 1.91) | (–8.76 ± 2.25) (–11.02 ± 2.46) |
| JJA (103 km2/decade) | 31.67 ± 55.07 (212.86 ± 48.24) | (–36.80 ± 39.11) (–14.59 ± 49.14) | 2.91 ±26.37 (65.06 ± 31.70) | 16.39 ± 16.76 (24.30 ± 22.70) | 63.21 ± 28.38 (110.59 ± 36.65) | (–14.05 ± 27.05) (27.50 ± 34.32) |
| JJA (%/decade) | 0.19 ± 0.34 (1.31 ± 0.29) | (–0.62 ± 0.66)) (–0.24 ± 0.83) | 0.11 ± 0.96 (2.35 ± 1.14) | 0.96 ± 0.98 (1.43 ± 1.33) | 1.65 ± 0.74 (2.88 ± 0.95) | (–0.70 ± 1.35) (1.36 ± 1.69) |
| SON (103 km2/decade) | 6.59 ± 51.80 (194.72 ± 46.19) | (–4.48 ± 36.48)) (–12.33 ± 46.14) | 4.24 ± 25.84 (59.40 ± 30.20) | (–1.14 ± 22.81)) (8.84 ± 29.54) | 72.23 ± 29.43 (124.35 ± 35.98) | (–5.29 ± 28.49) (14.45 ± 37.22) |
| SON (%/decade) | 0.04 ± 0.29 (1.08 ± 0.26) | (–0.70 ± 0.57)) (–0.19 ± 0.72) | 0.12 ± 0.73 (1.66 ± 0.84) | (–0.63 ± 1.27)) (0.48 ± 1.63) | 1.79 ± 0.73 (3.08 ± 0.89) | (–0.25 ± 1.36) (0.68 ± 1.77) |
Figure 2
The reoccurrence of Maud Rise polynya (Red rectangle) from 20th November 2021 to 10th December 2021.
Figure 3
(a) The tracks of selected ARGO floats (id- 5904468 and 5904472) in the Weddell Sea (WS) during the period of consideration, (b) the mixed layer temperature (MLT) and (c) Potential temperature (°C) for float-5904468, (d) the mixed layer temperature (MLT) and (e) Potential temperature (°C) for float-5904472. The white solid line in Figure 3c and Figure 3e shows the variability of ocean mixed layer depth. The black solid boxes indicate the profiles for the austral summer seasons while the black dashed boxes highlight the polynya formation period.
Figure 4
(a-l) Sea ice concentration (SIC) for the 15th day of each month sequentially from January to December 2022 in the western Antarctic region. The yellow line represents the sea ice edge for the 15th day of each month from January to December 2022. The red line indicates the daily climatological sea ice edge (median) from 1979 to 2015. The magenta square highlights the region of western part of Antarctic Peninsula that remained nearly ice-free throughout 2022 with the sea ice concentrations below the long-term median values.
Figure 5
The seasonal average anomaly of sea ice concentration (SIC) (%) composite from 2016 to 2022 overlaid by the anomalies of mean sea level pressure (MSLP) contours and wind directions (grey arrows) for (a) summer (DJF), (b) autumn (MAM), (c) winter (JJA), and (d) spring (SON). The atmospheric pressure lows are indicated with the ‘L’ symbol in red. The dashed line contours represent the negative MSLP anomaly and the solid line contours represent the positive MSLP anomaly. The anomaly is computed with respect to the climatology from 1979 to 2015.
Figure 6
(a) Normalized anomaly of 500 hPa geopotential height (GH) composite from 2016 to 2022 relative to the climatology from 1979 to 2015. White dots represent the locations used for computing the ZW3 index. ZW3 index computed using daily geopotential height at 500 hPa for (b) 2016, (c) 2017, (d) 2018, (e) 2019, (f) 2020, (g) 2021, (h) 2022 based on the methodology by Raphael (2004). The black line represents the ZW3 index computed for the climatological mean from 1979 to 2015. The three ridge points for the analysis are 79.5°E, 32.25°W, and 139.5°W at 45°S latitude (Francis et al., 2019). (i) Monthly SAM index from 2016 to 2022.
Figure 7
The seasonal average anomaly of total column water vapor (a-b-c-d) and, surface air temperature (e-f-g-h) composite from 2016 to 2022 for (a and e) Summer (DJF), (b and f) Autumn (MAM), (c and g) Winter (JJA), and (d and h) Spring (SON) seasons. The anomaly is computed with respect to the climatology from 1979 to 2015.
Figure 8
The seasonal average anomaly of sea surface temperature (a-b-c-d) and, mixed layer temperature (e-f-g-h) composite from 2016 to 2022 for (a and e) Summer (DJF), (b and f) Autumn (MAM), (c and g) Winter (JJA), and (d and h) Spring (SON) seasons. The anomaly is computed with respect to the climatology from 1979 to 2015.