A while back we had a section where various thoughts were presented on the dark ice bands in the ESS and elsewhere. A few competing ideas were presented with no conclusions, but the white in this image is probably more intact flows of ice with a bit greater thickness than the surrounding rubble.
The dark ice may have active algae growth, sea floor sediment, river sediment, particulate deposits from smoke, or simply be thin enough/fragmented enough to be absorbing more light/passing it through to the ocean below.
The sediment above would have been integrated into the ice either by wave action while it formed in shallow water, or picked up when the ice froze to the river delta/ocean floor.
Fundamentally, there are a lot of ways to make ice dark. There are considerably fewer ways to make ice
white. More or less, it comes down to two options: relics of older ice embedded in a weaker matrix (such that they retain albedo while the surrounding material goes to slush) or the weathered remains of pressure ridges (for much the same reason). Or both.
The pattern of fairly small linear features in that ice near the New Siberian Islands suggests the latter.
Since we're on the topic... Pressure ridges are an extremely important aspect of Arctic sea ice, but don't get much discussion here because the large-scale models gloss over them. Basically, where floes are forced together by currents or winds, the ice shatters into blocks. Some of these blocks are pushed upward, in a small-scale equivalent of orogeny, to form visible ridges that can peak several meters above the floes' "ground level". But more importantly in many regards, this process also forces ice blocks
below sea level, somewhat akin to the keel of an iceberg writ large. Leppäranta (2005) argued that these pressure ridges, in total, amounted for about half of ASI volume. We can quibble about that number, but the ridging process unquestionably provides for hidden stores of ice.
Also, these large pressure-ridge keels help to stabilize the pack against wind and current. The apparent cryosphere-scale rotation strongly suggests that there has been widespread erosion of this hidden volume store. In areas where sea ice abuts fast ice, the shallow water depth can allow pressure ridges to actually anchor to the sea floor. These structures are called stamukha; I suspect that the persistence of stamukha immediately north of the Sverdrup Islands is what has protected the Prince Gustav Adolf Sea and nearby channels from melt ... but that the shearing off of the sea ice from these anchors is what as allowed the CAA/CAB crack to torque open.
It's hard to back up any of my suspicions about pressure ridge keel behavior because these structures, despite historically being huge volume reserves, are individually too small-scale to be easily identified in the pack, and certainly too small-scale to be represented by most models. I suspect that, system-wide, most of that hidden volume is now gone, and the self-evident increases in motility and dispersion are the consequence.