Yesterday's MODIS shows the first melt water puddles at the mouths of the Mackenzie delta. The Lena on the Sib side isn't that far yet.
Extent is slipping fast with another almost century loss.
yesterday also cleared clouds from the open water in that part of the Beaufort giving the before view for what the next few days will bring
Can someone with closer experience of these rivers than me explain how breakup occurs? from watching the satellite imagery it seems there is water flowing under the ice even in those permafrost regions. Occasionally water appears (above the ice I assume) which later disappears (under the ice ?) Or are we seeing loose ice floes in these images at this time of the year? http://go.nasa.gov/1OlfINc
The Ob seems to be the Siberian River to watch at the moment by the way. http://go.nasa.gov/1WXezSD
Been living next to Ob for 2 years of my life, in 1990s. The process is rather simple. Indeed there is liquid water under the river's winter ice, throughout the winter. It's a BIG river. In fact, it's so big that where i lived - Surgut, - one can't see the other shore when Ob goes summer flood. It's some 6+ kilometers wide. Like a sea. By the autumn, though, all the melt water is gone (went to the Arctic), and so levels drop and Ob becomes "just a river" - still some ~1...2 kilometers wide, that is. Then winter frost comes, and freezes its surface at _that_ low level. It's still quite deep, so it never freezes to the bottom; far from it.
Then comes next spring. You may notice Ob, Lena, Enisei and lots more rivers all through Siberia are generally going northwards. This means it's warmer where they start, colder in the middle, and even colder next to Arctic shore - on average. So the usual situation is, lots of snow and ice turned into liquid water in the "starting parts" of those rivers, and then that water starts to flow out. Where to? Through the rivers, of course. But since ice is lighter than water, that "extra new" water goes under (the still-remaining ice further north, in general).
And then, as more and more water goes "through" under the remaining ice, it simply breaks the ice mechanically "from down under", - there becomes not enough space for _all_ that additional water to freely go "under" the solid ice cover.
The process is usually quite abrupt at any given place: whole winter there is thick ice (it is usual deal to have heavy vehicles crossing those rivers winter-times, for example), but then one day during spring time - or sometimes just over a night, - the river turns into quickly expanding stream of water with lots and lots of ice pieces floating next to each other (sorta slash thing, but with _big_ pieces initially). It then may remain in such a state for a few days, some years - i was told by locals, - for over a week.
This is how siberian rivers can break their ice cover for hundreds and even thousands kilometers of their length _way_ before that ice would in fact be weakened to the point of fragmenting - it's just a matter of "not enough space for extra flow under the ice" and resulting mechanical pressure which breaks the ice from being connected to any (shore) soil as river levels rise.
P.S. In the middle part of Ob, where Surgut city stands, soil permafrost is absent few kilometers to both north and south from the river itself, but then present even further south. The river itself is the cause of this. Unless that southern permafrost area has disappeared in the last ~20 years, that is - the last time i've seen there detailed local permafrost map was that long ago...
P.P.S. Sidenote. DoomInTheUK - thank you, i guess. If it wasn't sarcastic. If it was - hehehe, yeah, i ain't no big deal. Alas, when dinosaurs went extinct, it is small mouse-like mammals who survived and became our ancestors, so there are benefits... Say, your nickname, - i think UK will have it better than most places around this little planet. Eventually. I even heard it described as "Europe's lifeboat" in the context of the ATM, the latter being "anthropogenic thermal maximum" which we are going into.
