The sun rises over A23 as it crosses the "Antarctic Circle". It is at a distance beyond 1,000km from where it was 12 months ago. It traveled northward in excess of 600km during 4 months of sundown. Surface air temps fluctuating between above zero and below -30°C.
A23 calved from the Filchner Ice Shelf in the winter of 1986 at a section where the ice was thicker than most of the surrounding ocean. Movement was constrained by bathymetry for 3 decades to about 200km off shore before eventually thinning and gouging the seabed enough to force passage across shallower depths last year. Between 1990 to 1991, A24 from the same calving had made a similar trajectory around the gyre once in deeper water. From this point it headed north to warm water between the peninsula and South Orkney Islands breaking apart near the Falkland Islands. Originating from the deeper segment of the ice shelf to A23, it was thought to be close to 400m thick, with drift impacted by deeper currents than most bergs. A map tracks its path on this USGS page via underscored link within the body of text:
https://eros.usgs.gov/media-gallery/earthshot/the-1986-filchner-calvingA81 from the January Brunt calving has drifted down past Filchner close to where A74 was 12 months ago, which calved from Brunt in February 2021. A23 was perhaps quite significantly obstructing currents such as now rotate the Brunt bergs around with full pack momentum. The sea is less inclined to retain ice.
The quick clear out of icebergs also signals mass clear out of multi year ice as it follows the flows. According to AMSR2 ice age map, perhaps three quarters of ice 3 years old or more, spirals out high eastward through the early sunlight hours above the polar circle. Recent years seem to push a lot of MYI out of the zone of what remains at seasonal minimum extent. When strong winds move the pack north in the winter, new ice formation blocks strong winds pushing it back down southward. Freezing season has been quite damaging as well as slow in ice formation and it could leave the sea ice prone to go.
The strip of fast ice north of Berkner Island between Filchner and Ronne Ice Shelves, broke off as the sun went down late March. It had persisted through 2022. In recent years, the area in front of Filchner had tended to consist of older ice, slower to clear the bay or melt, and receiving MYI import from the Indian Ocean. For extended periods of time it consisted largely of fast ice while A23 staked its position in the bay. Now other than icebergs, it's filled with young ice. An extended cold surrounding anomaly now history. Future giant ice bergs are awaiting calving events.
A lot of icebergs have headed around the northern Weddell ice edge and perhaps they disturb surrounding ice formation rather than encourage it. More temps -30°C required. Time is short. If outer ice coverage is destined to shift from being a month behind in freeze, to being a month ahead in melt, an imminent bare ocean event outpacing the Arctic is far from inconceivable. Icebergs will be plain to see on dark seas.
I added an arrow to the bathymetry map to show roughly where A23 was caught up for so long. Original map found from here:
https://phys.org/news/2019-12-team-high-precision-antarctic-ice-sheet.html
