New Ocean Observations in Petermann Fjord

A new ice island separated from Petermann Glacier on July 16, 2012 as reported here first. Less than 4 weeks later, the Canadian Coast Guard Ship Henry Larsen reconnoitered the ice island on Aug.-9 when it blocked the northern half of the entrance of the fjord.

Petermann Ice Island 2012 (PII-2012) as seen Aug.-11, 2012 at the entrance of Petermann Fjord. The view is to the north-west. [Photo Credit: Canadian Coast Guard Ship Henry Larsen.]

I was aboard this ship when Captain Wayne Duffett decide to break into the largely ice-free fjord behind the ice-island after consultations with Ice Services Specialist Erin Clarke. The ice observer had just returned from her second helicopter survey in 2 days with pilot Don Dobbin to assess both ice cover and its time rate of change. From the time the ship entered the fjord behind the ice island, hourly flights to a fixed point at the south-western corner of the ice island ensured that its movement would not cut off the ship’s exit. This approach worked and it gave the science crew of 8 aboard about 18 hours to conduct the very first survey of a previously ice-covered ocean:

Petermann Glacier, Fjord, and Ice Island as seen by MODIS at 865 nm on Aug. 07, 2012 overlaid with survey lines of CCGS Henry Larsen on Aug.-9/10/11, 2012 in red.

We were not funded to do enter the fjord, but our main mission to recover an array of ocean moorings with 3-year long data records covering the 2009-12 period about 100 km to the south in Nares Strait has already been accomplished. So, what does a physical oceanographer do when in uncharted and unknown territory? He drops a number of CTDs, that is, measuring conductivity (C), temperature (T), and depth (D, pressure, really) as the instrument (the CTD) is lowered at a constant rate from the surface to the bottom of the ocean at a number of stations. The results from such work next to the present front of Petermann Glacier was a surprise for which we do not yet have a satisfactory explanation: The waters inside the fjord are much warmer at salinities 32.5-34.25 than they are outside the fjord:

Temperature as a function of salinity from 9 stations across Petermann Fjord next to the current seaward edge of Petermann Glacier on Aug.-10, 2012 in red. For comparison I show in blue a station done outside the fjord on Aug.-9, 2012. Note that temperatures increase with increasing salinity which is expected for waters that are a mixture of cold and fresh polar and saltier and warmer Atlantic waters. Density deviations from 1000 kg/m^3 are shown as solid contours along with the freezing temperature that decreases with increasing salinity.

Another way to show the same data is to actually plot the section, that is, the distribution of temperature and salinity in physical space across the fjord as a function of depth:

Section across the seaward edge Petermann Glacier on Aug.-10, 2012 for salinity (left panel) and temperature (right panel). Symbols indicate station locations from which color contours are drawn. Note that the display is cropped to the top 300 meters while real recordings extend to the bottom which exceeds 1000 meters. The view is eastward towards the glacier with north to the left.

Note the doming salinity contours which to classically trained oceanographers suggest a flow out of the page on the right and into the page on left with maximum at about 90 meter depth relative to no flow at, say, 500 meter depth. Another way to view this distinct property distribution is that the flow above 90 meters is clockwise (outflow on left, inflow on right) relative to the more counter-clockwise flow below this depth. This feature, too, comes as a surprise and requires more thought and analyses to explain.

There is much more work to be done to figure out what all this means. I feel like scratching the surface of a large iceberg half-blind. The data from below 300 meter depth, too, contain clues on how some this glacier interacts with the ocean. As for the purpose of this post, I merely wanted to report that the ice island is presently having a hitting or scratching tiny Hans Island. The latter is unlikely to move, but Petermann’s Ice Island will slow on impact, swivel counter-clockwise, bump into Ellesmere, and pretend nothing has happened on its merry way south. This is the latest image I have:

Petermann Ice Island 2012 on Aug.-22, 2012 as seen by MODIS Terra at 21:45 UTC. The tiny red dot marks Hans Island, the location of a weather station in the Kennedy Channel section of Nares Strait. Petermann Fjord is towards the top right out of view.

ADDENDUM Sept.-1, 2012: PII-2010B had a maximum thickness of at least 144 meters as it passed over a mooring that measures ocean currents from the Doppler shift of acoustic backscatter that is shown here for one of four beams:

Time-depth series of acoustic scatter from a bottom-mounted acoustic Doppler current profiler for 24 hours starting Sept-22, 2010 9:30 UTC. Red colors indicate high backscatter from a “hard” surface like ice. The vertical axis depth in meters above the transducers while the horizontal is ensemble number into the record (0.5 hours between ensembles). The 2010 ice island from Petermann Glacier (PII-2010B) passed over the mooring. When PII-2010B was attached to the glacier it was adjacent to the segment that became PII-2012 this year.

10 responses to “New Ocean Observations in Petermann Fjord

  1. Andreas, as I was replying to a comment of yours on Dr. Pelto’s page it dawned on me that possibly what’s causing the abnormal profile you’re mentioning above might be enhanced halo siphoning sucking more of the deeper, warmer water up the fjord.

    Terry

    BTW Thanks so much for this page – your adventures and your writing style would make it a must read even without the scientific content.

  2. As I understand your post and the profile shown, what you are finding is that the water upstream of the sill is warmer than would be expected for the depth/salinity.
    If a strong siphon was pulling deeper, warmer, more saline waters from beyond the sill, and mixing them to some extent with the out flowing fresh current, would this give the profile you are finding?
    Could a sill with an uneven height project a greater influx of water to one side or the other giving rise to clockwise/counterclockwise flow patterns at different depths in the fjord upstream?

    I’m assuming that Halo Siphoning would increase at least proportionally to the amount of melt water being disgorged through the fjord

    If i’m missing something rudimentary please let me know, I’ve very little ego invested in this supposition, so brutal honesty is welcomed.

    Terry

  3. That’s an interesting idea that people have applied and used over the sills leading into Pudget Sound in Washington State, I believe. The problem that it may not apply here is that the sill at Petermann Fjord is very deep, somewhere between 350-450 meters. So the subsurface temperature maximum has little trouble making into the fjord without much need of dynamically lifting it over the sill.

    The salinity where the two temperature-salinity (T-S) curves (inside/outside) meet/cross is near a salinity of 34.2 to 34.3 or so. This salinity is found at a depth of 140-150 meter below the surface. So the mixing lines (straight lines in T-S space) is with water above that depth. The thickness of the ice island is about the same, so my gut feeling tells me to think about what a moving 150-m thick wall of ice does to the water column. I’ll also need to check how the downstream Nares Strait temperature and salinity structures look. We took sections both to the north in Robeson Channel as well as several sections to south in Kennedy Channel and Smith Sound.

  4. Thanks Andreas

    I’d found a fjord in South America where they were considering the siphoning action, but concluded that tidal action was far more important. At that local as I recall the sill was very close to the surface and had an almost vertical face of the seaward side.

    The flow around PII2012 as it crossed the sill must be ridiculously complex.

    I think I recall the island turning sideways at about that point, possibly allowing the outflowing fresh water to pass without having to displace the warm saline layers.

    Does anyone know the shape of the keel on structures such as this?

    I’ll be very interested in your conclusions when you’ve had time to work through all the new data, and as a Canadian I’m proud of the services of the officers and crew aboard the Henry Larsen. It sounds as though they went way beyond the minimums required of them.

    Terry

  5. Ohhhh, I cannot agree more with you on the superior skill, experience, and efficiency of the crew and officers of the Candian Coast Guard that I had the pleasure to work and live with (I am still planing to write a blog on that). They have a natural knack for all things related to the sea combining ancient seamanship with modern electronics and aviation with the social glue that brings diverse people and skills together in a no-nonsense way. I do not think, however, that they always have the support and appreciation at the political level, that they deserve within Canada, because much of what they do, sadly, is out-of-sight.

    We will have partial profiles of underice topography from the 2010 ice island that passed over the array that we recovered this year. The instruments, moored at 75 meter depth were actually hit hard by the ice island that was much thicker than that. One instrument stopped recording as a result while the second kept recording until July 2012.

    Two Ice Profiling Sonars (IPS) aboard the CCGS Henry Larsen in Aug.-2012. The protective stainless steel frame was bent by the 2010 ice island that hit both instruments in Sept.-2010. [Photo Credit: Andreas Muenchow]

  6. Andreas

    Some of us (Canadians), have far more appreciation for the work of the Coast Guard than for the work of the politicians

    I’ll be interested when you’ve found out the bottom configuration of PII2012. From the way it reacts to wind and current I’d suspect 2 fairly deep keels with a hollow between them. One keel is possible and more than two seems unlikely.

    Without keel shapes I’d expect it to turn it’s narrowest face into the wind, but so far it seems to be presenting it’s broadest face to the wind and aligning itself to the current.

    Terry

    BTW – Did you purposefully align yourself with such alliterative companions?

  7. The bottom configuration of PII-2012 that is now in Kane Basin I do not know, but just this afternoon I processed some very early and preliminary data of PII-2010B that was attached to what this year became PII-2012. I am planning a more detailed blog post on these data and placing it all into a wider context, but since you asked … here it is, nobody has seen this yet:

    Time-depth series of acoustic scatter from a bottom-mounted acoustic Doppler current profiler for 24 hours starting Sept-22, 2010 9:30 UTC. Red colors indicate high backscatter from a “hard” surface like ice. The vertical axis depth in meters above the transducers while the horizontal is ensemble number into the record (0.5 hours between ensembles). The 2010 ice island from Petermann Glacier (PII-2010B) passed over the mooring. When PII-2010B was attached to the glacier it was adjacent to the segment that became PII-2012 this year.

    P.S.: Learning a new word “alliterative.” Short answer, yes. Working with friends on getting back with the same company on a different project, they are just too good and too much fun.

  8. Andreas
    What a thrilling image!

    The island appears to have gone over your profiler with the northern edge (as it had been positioned in the fjord) leading if I’m reading the ASAR images and your profiler chart correctly, and the southern end would be the far deeper keel dragging along in the stern. I’m sending the URL’s for the 22nd at 0044 & 1554, they bracket the time the island passed over.

    I’m sure you’ve got much better images, but these gave me some idea of what was happening.

    Were you able to capture the passage of the first piece that broke off? It should have been close to your location around noon on the 11th, the closest ASAR I could find was

    from 1645, and the island had passed over earlier.

    Terry

  9. Pingback: Petermann and Ryder Glacier Ice Island | Icy Seas

  10. Pingback: Land-Fast Ice Cover off North Greenland: Will NASA bite? | Icy Seas

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