Nice work on buoys! I didn't realize at first that it was a 2-frame animation. It looks good at the click-size. That is great to have the buoy network over a Sentinel base layer.
Compiled highlights (with edits and commentary in brackets) of the Polarstern cruise to Oct 23rd from screen scrapes of twitter, email, blogs, depts, BBC and newspapers. Too long but good to have it in one place (that won't get lost or deprecated to invisibility by google).
Most interesting information on thickness and near-loss of equipment and power line to ridging and shearing -- we knew from S1AB that things were morphing around on the selected floe but not exactly how. Is this going to get worse as time goes on, or will freezing solid help? (The too-fancy expedition web site does not allow text copying so screen shots have to be taken.)
First note a very important result from R Kwok et a; about overall Arctic Ocean calibration of IceSat2 by simultaneous airplane lidar: measured elevations agree to within 2-4 cm. The April flights did not quite reach the Polarstern/Mosaic floe but more recent Icesat-2 orbits may have.
ICESat‐2 surface height and sea‐ice freeboard assessed with ATM lidar acquisitions from Operation IceBridge
https://www.nasa.gov/feature/goddard/2019/laser-precision-nasa-flights-satellite-align-over-sea-icehttps://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084976 30 Sep 2019
Matthew Shupe: : how to get all of our different apparatus installations fitted into a limited and challenging space. Frozen melt ponds are to be avoided as they are likely to melt once again next summer. Plus some melted all the way through. Hummocks are safer for most equipment; the heavy stuff goes on the outer wall of the Fortress. with the Met Hut tucked up against a big plate of ice jutting up 2m inthe air. This may cause a drifting challenge.
We flagged a power line path out to all of the major installations. The ‘Ocean City’ type power hubs weigh 700 kg but are moveable as they are installed on top of 3 snowboards. The 700 m road out to Met City was smoothed out with picks and shovels.They are able to log in remotely from one station to the next to fix issues that arise.
Carrying a big breaker bar to probe the ice conditions, I learned back at SHEBA that if you lightly throw such a bar down to the surface from about 10 inches up and it DOES NOT break through, the ice is safe to walk on. Deep snow at places, making walking difficult.
But inside the Fortress was actually quite appealing. Nice courtyards of flat ice surrounded by sturdy walls. Eventually we made our way to a broad valley heading out to the far end of the floe, with a gateway to exit the fortress. Heading south we found wide, open and mostly flat plains made of frozen over melt ponds (30 cm thick ice) and some older hummocks (~100 cm thick). At the southern extreme we looked out over a narrow lead of open water, perhaps 15-20m across.
Took the ship’s helicopter over to AkF to give a lecture on “coupled system research” to the MOSAIC School.
https://blogs.agu.org/thefield/2019/10/20/postcards-from-a-frozen-icebreaker-part-5/October 16, 2019 Janek Uin, Brookhaven Lab/ARM Instrument
84° 45.440' N 133° 08.236' E
IThe ARM instruments are set up and will hopefully run smoothly for the rest of the campaign during the drift. In case of any trouble, our amazing technicians will be there to tackle any issues. Even today new cracks and pressure ridges appeared in the ice in the middle of a power line, challenging our efforts to set up our camp. We prepare ourselves for the next ARM adventure on Andoya, a Norwegian island located within the Arctic Circle.
October 5, 2019 Matt Boyer, Brookhaven Lab/ARM Instrument Mentor
85° 06.187' N, 133° 50.678' E
BBC x 2:
“With other floes we’ve encountered [data on 16 floes studied not released] we have clipped a piece off the edge with the ship to see how thick it is. A red and white two-meter stick, painted at 50cm intervals, sticks out from a lower deck to help judge how thick it is. The solid layer of blue ice in between snow on top and mushy rotten ice below [incompletely melted in summer, not newly forming], has rarely made it past 0.5 m.
The new layer [FYI from last winter not affected by past melt season] at the top can support equipment weight. The older rotten ice below [ice accretes to the bottom; this is newer than the ice above, is new ice on the floe edge meant?] is unreliable, although there is a question about whether a thicker layer of it helps or hinders refreezing during winter.
The investigated floe’s surface is level with the water that is freezing at its edges [freeboard should be 10% of total thickness if it were solid ice: Bernouli]. There is no protection or refuge. Instead, the floe merges seamlessly with the sea around it, rising in the distance to what could be a more rugged area towards the centre.
“The thing is, I’m not sure this piece of ice is even safe to walk on. That ridged area has holes and gaps. Take survival suits and floats,” says atmospheric physicist Markus Rex.
“In that ridged area there are holes and gaps,” says Rex, gesturing towards the central region. “It would be good to have those survival suits. Take flotation too.”
The Polarstern parks well away from a floe of interest so as not to damage it. A refrozen lead is covered by a thin layer of blackish-grey ice. The ship’s bridge radar augments what they can see. They don’t clip any ice off the edge with the ship to see how thick it is.
The edges of the "fortress" ice floe seem thin and waterlogged but in the distance the ice rises up and becomes thicker.
But the ship has to cut through a neighboring piece of ice instead. Large fragments bob vertically next to the hull to reveal a cross-section over 1 m. The sea ice in the region where the Mosaic mission have been searching has turned out to be much thinner than they were expecting. Floes are large but drill easily and could easily have disintegrated. [Only anecdotal data from EmBird surveys and drilling has been released].
Foes identified as >80cm thick from satellite images [IceSat2? Smos?] have turned out <40 cm from sled EM transects and drilling “Put that ship alongside such a floe and the first storm will press this ship right through it sideways. We budgeted to look at 20 floes,” says Rex.
The selected floe has a strong central section, with ice depths of up to 5m. It appears to have been created from several floes merging under high pressure. It appears as a luminous, bright patch in the otherwise dark grey satellite pictures the team are using. The inhomogeneous rugged jumble has drop-offs of 3m.
Beyond the fortress, there are two large flatter zones. The larger of these two [south side] appears to be made of ice typical of the region. It would allow the expedition to study what is happening to the ordinary, fast-disappearing young Arctic sea ice.
The ice around the ship started forming about 300 days ago – around two months later than the usual onset of the Arctic winter freeze. Those two months of missing freezing make a big difference, reducing the ice thickness by around half.
After two days, the floe, clearly very dynamic, has already changed. A large crack runs through the ice from west to east, almost severing about a fifth of the floe beyond the northern edge of the fortress. The floe is in a shear zone, with currents [a misunderstanding: no water currents exist in the central AO] pulling it in different directions. This section of the floe is not expected to last long.
The Polarstern moors to the fortress floe at 85ºN, 137ºE on Oct 4th but not as originally planned by gently lining the ship up to an edge but instead by ramming 500m towards the fortress. The captain wants to the ship securely embedded to get the robust mooring. “This may be one of the last years we can do this kind of expedition,” says Matt Shupe.
Some ice terms: frazil, shuga, nilas, pancake, grease, cake ice and frost flowers.
As sea water freezes, it first forms crystal discs known as frazil, eventually forms a suspension in the water known as grease ice, which creates an iridescent sheen like an oil slick. Waves and wind can compress the ice crystals together to form pancake ice that floats on the ocean surface. As these pancakes grow bigger they become cakes. On calmer seas, the frazils grow to form a continuous expanse of dark, glassy layer of ice, like a windowpane on top of a black sea. Shuga ice is slushy mess created by spongy white lumps that bob in the water.
Researchers at Russia’s AARI have been tracking ice floes for Mosaic in the Central Arctic Ocean all summer. They have been using data from several satellites[?], hoping to find those which survive the storms and melting.
Rex points out a darker oval in the image – the darker the ice appears, the thinking goes, the thicker and more robust the ice should be. The ice in the target region is looking like it will be 80cm thick, according to the data available. “We’d prefer one meter, one meter 20 (3 to 4ft) – but 80cm can work,” says Rex.
They will drift with the floe on an unpredictable path across the polar region, creeping on average from east to west through the year. But, choose a bad floe, or even a good floe in the wrong place, and the camp is at risk of collapse.
“What happened to N-ice would be really, really bad [4 forced relocations as Atlantic swells and melt broke up their floes]. We need to avoid that. A large fraction of model trajectories ends up in the N-ice area [2º north of Svalbard].
But other drift trajectories end their year’s drift stuck at the North Pole. Another gets into a danger zone off the coast of Greenland. [Floes never pile up against land in Greenland; floes never pass through the Nares Strait from their starting position.]
Another promising floe has 30 cm of compact snow over a deep layer of translucent blue ice that transitions to brownish mushy honeycomb that easily sloughs off as sludge. However the Akademik Federov has sailed straight through it leaving a track visible on satellite. However it turned out to be only 30 or 40cm thick so worthless for an ice camp.
Re-interpretation of radar imagery: the discovery of so many thin floes lead the team to rethink satellite imagery. Previously the idea was that the thicker ice absorbs more radar signal from satellites overhead and so appear darker in the resulting image. But tests on those floes shows that this interpretation is wrong. The dark patches on the images are in fact showing something else entirely.
On the first floe, there was very little freeboard. “When you remove the snow, the surface was wet,” says Stefan Hendricks. The floe was flooded with seawater. The layer of salt water reduces the reflection of the radar back to the satellite. “Our idea is dark floes are actually the thin ones having low freeboard.”
September 29, 2019
84° 29' 44.2" N 128° 44' 12.1" E
Last couple of days were spent retrieving four Ocean Bed Seismometers that had been collecting data for the past year at the bottom of the ocean, almost 4 kilometers (2.5 miles) deep. The scientists responsible for these devices had remotely triggered their release from the ocean bed and had to find them among the ice once they surfaced. It took almost two days, but finally all four were found and hoisted on board.
https://www.awi.de/en/science/geosciences/geophysics/methods-and-tools/ocean-bottom-seismometer.html