Category Archives: Ice Cover

Icebergs, Islands, and Instruments off Isle de France, North-East Greenland

Andreas Muenchow

Leaving all land behind when FS Polarstern sailed for Greenland almost 2
weeks ago, we saw land again for a few hours last Sunday. A small
ice-capped island called Isle de France was ahead of us. Solid ice was to
the west, open water to the east, and Greenland proper appeared just
faintly above the western horizon. We arrived at 5 am in the morning, but
the northern summer light changes more with the clouds, absent this day,
than it does as day becomes night. We are more than 1000 km to the north
of the Arctic Circle and about half-way between Bremerhaven and the North
Pole.

Image

Image

Waiting for the mooring work to begin, we sailed along a row of large
and grounded tabular icebergs and ice islands that appeared strung out
like pearls on a line where the ocean’s water was about 100 meters deep.
Sea- and ice-scape looked the same eons ago when massive ice-sheets
covered much of northern Europe and North-America before people invented
agriculture and turned from nomadic hunters and gatherers to settled
farmers and peasants. And while everyone awake admired Greenland’s beauty
and serenity that Sunday morning, I had only one thought: Here go my
moorings.
Image

The ship paused for a few hours to wait for me and Jonathan to ready
instruments that we needed to placed on the ocean floor. They are
designed to measure ocean currents for the next 2-3 years and will give
us better ideas on how ocean heat and currents melt
Greenland’s glaciers from below. We already had deployed four such
instruments the day before out of sight of land and icebergs. Now we were off Isle de France to complete our shelf mooring program with 3
instruments placed across the south-western slope of Norske Ore Trough.

ModisMoorBath

This ‘trough” is really a broad and deep submarine valley that connects
the deep Fram Strait 150 km to the east to Greenland’s largest glaciers
100 km in the West and North. The valley may act as a pathway, so we
think, to move warm ocean waters from Fram Strait near the bottom across
the broad and confused continental shelf of Greenland. It is coastal oceanography that we do, but the heat that our coastal flows
transport towards the glaciers does impact a changing climate that
changes land, sea, and icescape both here around Greenland and
elsewhere as ocean sea level rises when ice on land becomes ice on water
and eventually water in the ocean.

As fast-flowing floating glaciers disappear, such as Zachariae Isstrom did
the last 10 years, the ice-sheet behind them on land often accelerates and
thins because ice-shelves attached to glaciers act a little like a cork
does to a bottle of Champagne. The bubbly inside exerts a high pressure
against the cork separating the Champagne from the lower pressure outside,
especially if shaken. If you loose the cork or remove it explosively, then
the bubbly will spill out quickly. The friction of an ice-shelf may have
retarded the advancement of the ice-sheet behind in a subtle balance of
forces. Now, as the ice shelf is removed, a new
balance of forces will have to establish itself. The transition from one
to another stable state usually occurs via accelerations: The glacier
speeds up, stretches, and as it stretches, it thins and may allow the sea
water to advance deeper shoreward to melt more ice that was before not
in contact with the ocean. It is a positive feedback and the potential
exists, that the glacier keeps retreating faster as a result. Both
Jacobshavn Glacier in South-West Greenland and Pine Island Glacier in
Antarctica do this now.

Image

But I digress and want to return to Isle de France with its pearl string
of tabular icebergs within about 5 km off our first moorings. At 170
meters below the surface a strike by one of these stunning mountains and
islands of hard ice will perhaps wipe out a mooring, but perhaps the
goddess of the sea will steer the perhaps 50,000 year old towers of ice into shallow
water where they will ground for a few years. Either way, I will be
watching these icy islands from afar for the next few years in what
becomes a most exciting and pleasurable puzzle with many pieces. Some may
fit and some may be missing. Perhaps the best we can hope for is
a sketch or an outline. Control of nature is vanity, we are merely
temporary sailors on a mighty ocean with ice that will last longer than
either us or whatever sensor we may place in her ways.

posted by Pat Ryan for Andreas Muenchow

Measuring Ice Thickness From The Ocean

Ice floats and moves abouts. It melts in summer, it freezes in winter, but it moves from here to there driven by winds and currents. Some ice leaves the Arctic Ocean via Fram Strait to the east of Greenland and some leaves via Nares Strait to the west of Greenland. For the last 11 years I worked with Canadian friends in Nares Strait, but this summer I will work on the other side of Greenland with German, Polish, and perhaps Norwegian colleagues in Fram Strait. This opportunity already helps me solve puzzles in Nares Strait and more generally how ocean currents around Greenland impact ice cover, thickness, and flux.

Jonathan Poole in 2012 with ice profiling sonar hit by ice.

Jonathan Poole in 2012 with ice profiling sonar that was hit by ice.

One of our many instruments measures the thickness of ice. Our sensor package is moored on the ocean floor and quietly sends out a single ping every few seconds. Think of this ping as the sound you make when you tap your desk with a finger. The sound travels from the desk to your ear where you hear it, because your inner ear has a drum that picks up the vibrations that the taping makes when it hits your ear-drum. Well, our ice-profiling sonar sends out this ping that travels through the water to the ice above, bounces off the ice, and returns to our sensor. We then measure the time it takes for our ping to travel to the ice and back. If we know the speed of sound in the water, if we know the density of the water, if we know the pointing direction of the sonar, and if we know how much water is above our sensor, then we can estimate the thickness of the ice. The sketch below shows design details that go into keeping such a sensor system in the ocean recording data for 2-3 years at a time.

Sketch of ice-profiling sonar mooring deployed on the bottom of the ocean. Design by Dr. Humfrey Melling of Fisheries and Oceans, Canada.

Sketch of ice-profiling sonar mooring deployed on the bottom of the ocean. Design by Dr. Humfrey Melling of Fisheries and Oceans, Canada.

There are lots of challenges to deploy such a sensor system, there are more challenges to find and recover it in later years, and then there are the challenges to analyze and interpret the data writing the software that does it all. None of the many parameters such as speed of sound, ocean density, atmospheric pressure, and amount of water above the sensor are known very well, all of them change with time from day-to-day and sometimes even hour to hour. In order to measure ice thickness within a few inches (10 centimeters, say), we need good estimates of these things. I work with PhD student Patricia Ryan on this and we are almost done to untangle these many data strands for all of 3,300 days that we have observations in Nares Strait. Lets start with a random day exactly 10 years ago:

Ice draft below sea surface for May 30, 2004 in Nares Strait. Data shown are 15 second averages.

Ice draft below sea surface for May 30, 2004 in Nares Strait. Data shown are 15 second averages.

The bottom of the ice is about 1 meter (~ 3 feet) below the surface, but at about 6 pm (18:00) it becomes 0.2 meter thinner to return to its original thickness near midnight. A thicker piece of ice must have moved in and out of the “view” of our sensor. So far, so good, but you can already see that ideally I also would want to know the motion of the ice in addition to its thickness, but that is another story. Also, please recall that we got about 9 years of such data or about 3,300 plots, so, let me show you a second one, but this one is really bad:

Ice draft below sea surface for April 18, 2005 in Nares Strait.

Ice draft below sea surface for April 18, 2005 in Nares Strait.

The ice here is a little thicker, but not by much. What stands out are three funky looking, abrupt jumps every 6 hours precisely. How can this be? Well, it cannot and I must have done something bad to the data. Recall that we need speed of sound and water density estimates to convert acoustic travel time to ice draft. On April 18, 2005 my estimates perhaps were off. But why? And how can this be fixed?

The first clue is revealed in a month-long series of speed of sound that I estimated from a different mooring that measures temperature, salinity, and pressure along a string. Using some fancy math that a prior PhD student of mine developed (Dr. Berit Rabe), I estimate the vertical sound speed averaged from 100-m depth where the ice-profiling sensor is located to the surface where the ice is located. The plot below shows how this speed varies during the month of April 2005. It has some wild undulations near April-18:

Vertically averaged sound speed for the month of April 2005. Black curve is for 6-hourly and blue curve is for 24-hourly estimates.

Vertically averaged sound speed for the month of April 2005. Black curve is for 6-hourly and blue curve is for 24-hourly estimates.

For most of the month the speed of sound is about 1440 meters per second (m/s), but it spikes to almost 1446 m/s on April-18. It is this unrealistic spike that causes the estimated draft of the ice to go up and down by 20 to 30 centimeters.

The second clue and likely fix to my “ice offset problem” is the blue curve in the above plot. Using the same fancy math, I there come up with an estimate of the speed of sound only once a day rather than once every six hours. There are still fluctuations, but they are much smaller without a big spike. So, to conclude, I pushed my fancy math too far and it crashed the same way that a flashy muscle car driven too fast will crash as either the car or the driver cannot handle the road anymore. I here crashed the car as physicists are prone to do. Ideally we do it in a safe environment such as crunching numbers on a computer … as I did here.

Hansen, E., Gerland, S., Granskog, M., Pavlova, O., Renner, A., Haapala, J., Løyning, T., & Tschudi, M. (2013). Thinning of Arctic sea ice observed in Fram Strait: 1990-2011 Journal of Geophysical Research: Oceans, 118 (10), 5202-5221 DOI: 10.1002/jgrc.20393

Rabe, B., Johnson, H., Münchow, A., & Melling, H. (2012). Geostrophic ocean currents and freshwater fluxes across the Canadian polar shelf via Nares Strait Journal of Marine Research, 70 (4), 603-640 DOI: 10.1357/002224012805262725

North Greenland Glacier Ice-Ocean Interactions 2014

I will travel to Spitsbergen in six weeks to board the German research icebreaker Polarstern. She will sail west across the Fram Strait towards northern Greenland where some of the last remaining glaciers exist that still discharge their ice via extensive floating ice-shelves. If all goes well, we will deploy instruments on the bottom of the ocean across a 30 km wide submarine canyon (Norske Ore Trough). The instruments profile ocean velocities from the bottom to the surface of the canyon that connects the deep (warm) ocean to the shallow continental shelf areas which then connect to two large outlet glaciers, Zachariae and 79N Glaciers. These are two of three glacier that terminate the North-East Greenland Ice Stream (NEGIS) which contains about 15 per cent of Greenland’s ice sheet:

Speed of Greenland's ice sheet movements. NE indicates the fast-moving (red) North-East Greenland Ice Stream with 3 branches connecting it to the ocean. [From Mauri Pelto's blog]

Speed of Greenland’s ice sheet movements. NE indicates the fast moving (red) North-East Greenland Ice Stream with 3 branches connecting it to the ocean. [From Mauri Pelto's blog]

The most southern is Storstrommen Glacier, a tidewater glacier with an almost vertical glacial front attached to the bedrock. The next one up north is Zachariae Glacier which lost its extensive ice-shelf during the last 3 years in a dramatic collapse reported on Mari Pelto’s blog. Presumably, there is little floating ice-shelf left that is attached to the lacier. And only 30 km to the north, we have 79N Glacier whose real name is the Danish Nioghalvfjerdsfjorden. It rivals Petermann Gletscher in ice discharge, areal coverage, thickness, and more with one exception: Nioghalvfjerdsfjorden’s ice-shelf appears remarkabe stable, nobody knows why exactly, but it may provide clues on how Greenland’s ice sheet interacts with and responds to forcing by the oceans. I show a recent Landsat image taken from Neven’s Arctic Sea Ice Forum; the floating glacier is on the left (east) of the image with a set of 5-7 out-cropping islands towards the right (west) providing some pinning support for the ~30 km wide front of the glacier:

Landsat image of Nioghalvfjerdsfjorden on Mar.-22, 2014.

Landsat image of Nioghalvfjerdsfjorden on Mar.-22, 2014.

Our 2014 study area is actually to the east, just outside the frame of the above image. The reason is lack of ship time, as this year’s deployment is just a small pilot study to better prepare and understand a larger German-led experiment that will take place both on the glacier and its adjacent ocean and land in 2016 and, I hope, beyond. Furthermore, we are scheduled to be there in June, a tad early for all the sea ice to clear out of the area (79N Glacier MODIS summer imagery) which also explains my intense interest in how the ice develops. And a first fairly clear MODIS image came about yesterday morning:

Ice-covered coastal waters off northeast Greenland April 14, 2014. Red contour indicates 100-m water depth. The "horseshoe" shaped red island is Belgica Bank with Norske Oer Trough to its south-west.

Ice-covered coastal waters off northeast Greenland April 14, 2014. Red contour indicates 100-m water depth. The “horseshoe-shaped red island is Belgica Bank with Norske Oer Trough to its south-west.

Belgica Bank is about as big as the Georges Bank in the Gulf of Maine. In past decades rafted multi-year ice and tabular icebergs often grounded over shallow Belgica Bank and thus provided an anchor to maintain stability for a year-round land-fast ice cover called the Norske Oer Ice Barrier. This year-round land-fast ice area, however, disintegrated in 2003 and has become an intermittent and not a regular feature for unknown reasons.

Before I can get onto the German icebreaker in Spitsbergen, my 3500 kg of equipment had to be repaired, rebuilt, re-powered, and shipped from British Columbia to Germany via rail, ocean freighter, and truck. It all arrived in 86 pieces only last friday, two weeks behind schedule, because of ice and confused shipping schedules in the Canadian Gulf of St. Lawrence. Lots of great people in Canada, the USA, and Germany made it happen. Wish us luck for the next step in this exciting scientific exploration to reveal one of many of Greenland’s glacier and ocean mysteries.

Hughes, N., Wilkinson, J., & Wadhams, P. (2011). Multi-satellite sensor analysis of fast-ice development in the Norske Øer Ice Barrier, northeast Greenland Annals of Glaciology, 52 (57), 151-160 DOI: 10.3189/172756411795931633

Wadhams, P., Wilkinson, J., & McPhail, S. (2006). A new view of the underside of Arctic sea ice Geophysical Research Letters, 33 (4) DOI: 10.1029/2005GL025131

Fram Strait Ice, Oil, and Glaciers

Tomorrow I fly to Germany to prepare for an ocean experiment in the shallow waters off northern Greenland. Together with oceanographers from the Alfred Wegener Institute (AWI), Germany, I hope to deploy 5 ocean current measuring devices on the bottom of the ocean for 2-3 years in Norske Oer Trough to the west of Belgica Bank inside the little black box to measure the ocean heat moving deep below the surface towards 79N Glacier, one of the last remaining glaciers of Greenland with an attached ice shelf floating atop the ocean:

Map of North Greenland with shallow (red/yellow) and deep (blue) oceans. Future study area are black boxes on the continental shelf of north-east Greenland.

Map of North Greenland with shallow (red/yellow) and deep (blue) oceans. Future study area are black boxes on the continental shelf of north-east Greenland. Small box is the area shown via MODIS imagery below.

Anotated MODIS images of 79N Glacier and Zachariae Icestream in September 2009 (left) and 2013 (right). Thick red line is 100-m depth with icebergs grounded on Belgica Bank often supporting extensive land-fast ice such as in 2009 but not 2013.

Anotated MODIS images of 79N Glacier and Zachariae Icestream in September 2009 (left) and 2013 (right). Thick red line is 100-m depth, thin red lines 200 and 300-m depth. Icebergs often ground on Belgica Bank (<100- deep) supporting extensive land-fast ice such as in 2009 but not 2013.

To do this, I need about 7000 pounds of equipment to get from western Canada to northern Greenland. All this stuff sits in the Port of Montreal (Canada) waiting for the freighter “Montreal Express” to ship it all to Hamburg and Bremerhaven to be loaded onto the R/V Polarstern, AWI’s research icebreaker. All ships are tracked via https://www.marinetraffic.com/en/ in real time and, I just checked, she just left Hamburg for Montreal this morning.

The Arctic research community is tiny and I try my darnest to share data, news, and developments without breaking confidences. A good friend and colleague of mine, Prof. Preben Gudmandsen, lives and works in Denmark. He is as excited as am I about all things related to Greenland which includes the upcoming experiment(s) in Fram Strait. By training Preben is an electrical engineer and helped developed some of the first radars with which to probe Greenland’s ice-sheet. We visit and e-mail each other as often as our professional and private lives allow, but he just sent me these images of western Fram Strait off Greenland:

And on related matters, I discovered earlier this week that Norway’s StatOil has a license to explore this very shelf area for oil and gas exploration as explained in this official StatOil press release that also includes this map

Norway's StatOil lease area on the continental shelf off north-east Greenland from their Dec.-20, 2013 press release.

Norways StatOil lease area on the continental shelf off north-east Greenland just to the south-east of Belgica Bank, taken from their Dec.-20, 2013 press release.

I also learnt that they sponsored mooring deployments in 2012/13 and 2013/14 with the Norwegian Polar Institute and the Norwegian University of Science and Technology in Trondheim. A 5-minute video of the cruise is posted at

There is much more to explore and think about here, but this will have to await a future blog when my mind is less cluttered by ship and travel schedules, paper and proposal writing, data and computer chasing, or just keeping a crazy life of working across 9 time zones together. Scientific life is good and fun, but exhausting and nerve-wrecking at times.

Budéus, G., & Schneider, W. (1995). On the hydrography of the Northeast Water Polynya Journal of Geophysical Research, 100 (C3) DOI: 10.1029/94JC02024

Hughes, N., Wilkinson, J., & Wadhams, P. (2011). Multi-satellite sensor analysis of fast-ice development in the Norske Øer Ice Barrier, northeast Greenland Annals of Glaciology, 52 (57), 151-160 DOI: 10.3189/172756411795931633

Wadhams, P., Wilkinson, J., & McPhail, S. (2006). A new view of the underside of Arctic sea ice Geophysical Research Letters, 33 (4) DOI: 10.1029/2005GL025131

Arctic Heart Beat and Disappearing Old Ice

Have a look at this beautiful movie that shows how the Arctic Ocean moves its oldest and thickest ice around from 1987 through 2013:


[Credits: Dr. Mark Tschudi, University of Colorado and NOAA's climate.gov.]

The Beaufort Gyre moves ice off western Canada and Alaska clockwise while the Fram Strait outflow between eastern Greenland and Spitsbergen exports much of the ice into the North Atlantic Ocean with the East Greenland Slope Current. The dividing line between the westward flux (into the Beaufort Gyre) and the eastward flux (into Fram Strait) stretch out to the north of the Canadian Archipelago and Greenland.

My only quibble is that, according to the movie, no old ice exits via Nares Strait or the Canadian Archipelago which is not true. During our field work in Nares Strait from 2003 through 2012 we always met rather heavy, thick, and old ice streaming south:

A graduate student in our oceanography program, Autumn Kidwell, is credited with directing me to this movie. Oh, and the Norwegian Ice Service in Tromso has a job opening for a smart remote sensing person ;-)