In my last post I mentioned that the Russian icebreaker Kapitan Dranitsyn had to battle thick sea-ice to resupply the Polarstern at the MOSAiC site. Contact was successful, and cranes began to unload and load supplies that were hauled by tractor between the two ships.
A fresh crew of scientists relieved the crew that has been working there.
With temperatures down around -30ºC, the open water in the wake of the Kapitan Dranitsyn froze over swiftly. Men could walk on the new ice within 24 hours.
By the time the transfer of men and supplies was complete the ship was frozen so fast it could not extract itself. The news is now that the Russians are sending a second icebreaker, the Admiral Makarov, to help the first icebreaker free itself. (Note the twilight in the above picture. The are located close enough to the Pole to see a very swift transition from noontime night to midnight day. Currently it is dark at midnight, but the twilight is bright enough at noon to read by. In around a week the sun will peek over the horizon, and a few weeks more will see the daylight become constant. But the chilly sun remains so low that no thawing occurs until the end of April.)
Despite the ice trapping the icebreaker, it is important to remember we are talking about sea-ice, a mass of ice in constant motion with enough “leads” (cracks) to allow seals to breathe and be seen hunting arctic cod, by the MOSAiC underwater cameras. Sea-ice is by no means stable. The Polarstern radar recently saw a lead open roughly a mile from the ship.
And the infrared view of the Pole shows plenty of cracks in the sea-ice,
In other words, sea-ice is not the same thing as the gigantic icebergs that make life interesting for fishermen in Newfoundland, icebergs that are so vast that they can run aground in water 300 feet deep.
These giant, awesome bergs calve off glaciers, (largely Greenland’s), and, while they have been seen in the Arctic Ocean, they usually head south down either side of Greenland, and are rare up north. For the most part the sea-ice affecting the icebreakers is thin in comparison, roughly six feet thick.
The problem is that, besides cracking apart, which is helpful to icebreakers, the ice claps back together again. In such cases the baby-ice which swiftly forms in the open water, (as we saw in the wake of the Kapitan Dranitsyn), has little hope of resisting the compression it undergoes; even if it is two feet thick it is clamped in the jaws of ice at least three times as thick, which has the power of wind pressing across miles and miles of fetch. Consequently the new ice in leads crumples up like eggshells between elephants, and what was open water on Monday may become a pressure ridge of crumbled slabs of ice by Friday. And, because this process goes on all winter long, the surface of the Arctic Sea is far from smooth. There are smooth areas, basically big slabs, but finding a smooth area large enough for the yearly Barneo blue-ice airstrip often involves a considerable search.
Considering the sea-ice is constantly tortured and contorted, the “thickness” maps portray an average, for in fact the ice can vary between open water and a towering pressure ridge in a hundred yards. (This was made visual back in the days we had cameras on buoys bobbing about the Pole.) Because both pressure ridges and leads are often too narrow to be seen by satellite, and also because how numerous they are varies a lot between stormy years and calm years, a certain amount of guess-work (also called “modelling”) goes into the creation of “thickness” maps…..which in turn leads to disagreements. For example the NRL map can show ice six feet thick
Whereas the DMI map shows sea-ice twelve feet thick:
These disagreements suggest the captains of icebreakers face uncertainty, as they face the sea-ice. Not only are the captain’s initial maps to some degree “modeled”, but the circumstances they are sailing into are in constant flux. Though their radar may show an open lead ahead, a shift in the winds may turn that lead into a pressure ridge in a mere hour.
One then is led to wonder why these icebreakers are not ever crushed like a nut in a nutcracker. The compression involved when wind-shear creates two masses of sea-ice converging is hard to imagine. We are talking about fifty miles of ice colliding headlong with fifty miles of ice; even sea-ice nine feet thick can buckle, creating the arctic’s biggest pressure ridges, thirty feet high and (because nine tenths of an iceberg is under water) with “keels” extending downwards 270 feet. A 1880’s ship like the Jeanette, with a greatly reinforced hull, might survive 21 months clamped in sea-ice, but it stood little chance when the sea-ice concentrated its squeeze. (Descriptions of the moaning noise the Jeanette made as it went down are amazing.) Therefore men learned to structure hulls in a manner that caused squeezing from the side to lift the ships upward, rather than crushing inward. Icebreakers utilize such uplift, as the entire ship rides up and over the ice, which is then crushed down and broken by the sheer weight of the ship.
The Russian icebreakers are huge. The Kapitan Dranitsyn has seven stories of windows above the main deck. Let’s look at the picture again:
Besides riding up over the ice moving forward, such ships are designed to ride over ice when moving astern. When the ice is especially thick they can back up and plow forward repetitively, crunching the ice downwards and making their way to where radar indicates a lead may provide an easier path.
The fact Kapitan Dranitsyn requires help indicates, to me at least, that the sea-ice is especially thick in the Central Arctic this year.