The CAA breakup continues. Prince Gustav Adolf Sea broke up within the last few days:
https://go.nasa.gov/33oqdyi
The situation in the Prince Gustav Adolf Sea is uglier than it looks on Worldview, which already isn't good. There are three striking aspects to this breakup.
First, the speed of the event. On July 28, the PGAS was essentially intact. A single large floe (some 50 km x 10 km) spalled off the north side. All of the Arctic-facing CAA basins had been losing occasional floes to the Crack throughout the season, though, so there was no immediate reason to expect that the separation of this long, but thin, piece of ice was a harbinger of rapid change. The next several days were under cloud, although there was evidence of further disintegration visible by the 31st. On August 1, clear skies showed that the breakup had advanced some 50 km south of the Crack, but there was some reason to suspect that it might not continue to propagate, at least on the western side of the basin (which is historically more stable due to local hydrodynamics). A few more days interlude under cloud, and when we get sunshine again on the 4th, effectively the entire PGAS has shattered. The only substantially intact pack ice in the area is now confined to Ballantyne Strait and Wilkins Strait, but visibility has been poor, and so I'm likely overrating the quality of the remaining ice, especially in the Ballantyne.
Second, the condition of these floes is clearly very poor. The initial floe generated on July 28th had an obvious weak point, and was certain to break in two from its formation. But floe tracking has been impossible; even by the end of July it was impossible to conclusively distinguish the remains of that floe from the rubble of the Crack. The floes generated by the next breakup cycle, circa August 1, are mostly indistinguishable as early as August 4. Admittedly, it's possible to identify the August 4th floes in the August 5th satellite pass, but that's little comfort; it is clear that many of them have suffered measurable areal reduction in only one day of further melt action. None of the cloudy periods have represented anything like a GAC; rather, it's just normal cloud and storm activity, but the floes can't hold up to it at all.
Third, comparing the August 4th and August 5th images, it is clear that there is
northward drift in the PGAS. This caught me very much by surprise. Historically, PGAS ice moves south; over a period of several years, it is one of the "garlic press" vectors that supplies (formerly) MYI to the Parry Channel. Additionally, what limited studies have been done suggest that the PGAS itself supported a local clockwise current (which is the reason for the lesser stability in the east half of the basin -- see the melt patterns in 2012). I had assumed that the northward flow of ice from the Crack-adjacent CAA was the consequence of the fairly rapid clockwise rotation that the CAB pack had been experiencing. But the last few days suggest that rotation has stalled, or even reversed slightly. This changes the fate of ice in the regional system substantially. Even in years, like 2012, where the PGAS saw considerable melt, lost ice was resupplied from the north. If this northward drift of PGAS ice continues, it would require resupply from the south, but Belcher Channel and the Maclean Strait are likely to melt out (if they haven't already; they have been under cloud since July 29th), or nearly so; there is no ice there to resupply a depleted PGAS.
I'm not convinced that these regions will melt entirely. There's a lot of ice left in the northern CAA, just in terms of area, and pushing all the way to zero is costly in terms of energy. Weather will out, of course. But to some extent it doesn't matter. If the pack ice is reduced to kilometer-scale rubble, it might technically be considered "multi-year" ice, but in reality it will be badly compromised material that will not behave like true MYI should. Rather, it paints a picture of the total collapse of the traditional "cold pole" of the CAA and its associated ice stores.
