Brief communication: The anomalous winter 2019 sea ice conditions in McMurdo Sound, Antarctica

McMurdo Sound sea ice can generally be partitioned into two regimes: (1) a stable fast-ice cover, forming south of approximately 77.6◦ S around March / April, then breaking out the following January / February; and, (2) a more dynamic region north of 77.6◦ S that the McMurdo Sound and Ross Sea polynyas regularly impact. In 2019, a stable fast-ice cover formed unusually late due to repeated break-out events. We analyse the 2019 sea-ice conditions and relate them to southerly wind events using a 5 Katabatic Wind Index (KWI ::::::: Modified ::::: Storm ::::: Index ::::: (MSI). We find there is a strong correlation between ::: the ::::: timing ::: of break-out events and several unusually large KWI :::: MSI events. Copyright statement. This article is distributed under the Creative Commons Attribution 4.0 License.

and other supplies); a reduction in the number of sea ice :::::: sea-ice scientific field sites; and a two-month delay in the deployment of the University of Otago sea ice :::::: sea-ice mass balance station.
We are not aware of any studies directly investigating the causes of delayed freeze-up of sea ice in McMurdo Sound. Kim 25 et al. (2018) found that in years with higher mean annual wind speeds, the fast ice generally retreated earlier in the season, however, that study did not look at the impact of individual events on break up :::::::: break-up and retreat. At the event level, investigations by Banwell et al. (2017) into causes of the calving of the McMurdo Ice Shelf in 2016 suggested that strong (>10 m s -1 ) winds from the south and west contributed to the large fast ice :::::: fast-ice : break-up event that preceded the calving event. Brunt et al. (2006) investigated sea-ice break-out events in the southwest Ross Sea between 1996 and 2005 using satellite 30 imagery and automatic weather station data. They found that break-out events were correlated with a dimensionless "storm index", defined as the product of low pressure :::::::::: low-pressure : anomalies and anomalous temperature (lower temperatures in summer and higher temperatures in winter).
In years that were not iceberg-affected (2000; 2012 -2017), the fast ice ::::: fast-ice : cover in the Sound ::::: sound : generally reached a minimum in mid-March where it typically recedes :::::: receded : into a few pockets along the Victoria Land Coast in the west of 55 2 the Sound ::::: sound, around the Erebus Glacier Tongue along the west coast of Ross Island and into a wedge-shaped area between the tip of the Hut Point Peninsula on Ross Island and the McMurdo Ice Shelf. The fast ice ::::: fast-ice : cover south of 77.6 • S typically re-forms :::::::: re-formed sometime between mid-March and mid-April, with the exception of 2012, where it did not form until around the end of June. This is contrasted with 2019 when a stable fast-ice cover did not form until late July.
In :::::::: However, :: in : 2019, the frequency and intensity of : of ::::::: intense : storms in June and July were ::: was : such that the fast-ice 170 cover was too weak to withstand the southerly winds and was broken up and advected northwards on three separate occasions.
gov. ARTIST sea ice concentration data accessed from the University of Bremen data archive at https://seaice.uni-bremen.de/data/. Circum-Antarctic landfast sea ice extent data accessed from the Australian Antarctic Data Centre at https://data.aad.gov.au/metadata/records/AAS_ 4116_Fraser_fastice_circumantarctic.