Tag Archives: Labrador

The Ice Shelf of Petermann Gletscher and its Ocean Below: Descriptions

Posted on April 11, 2016 by | 1 comment

“In 1921 owing to starvation I had to go directly from Cape Heiberg-Juergensen to our cache at Cape Agassiz … during this journey the greater part of the glacier was mapped.” –Lauge Koch, 1928

Petermann Fjord connects Petermann Gletscher to Nares Strait which in turn is connected to the Arctic Ocean in north and the Atlantic Ocean in the south (Figure-2). The track of Petermann ice island PII-2010A emphasizes this connection as the 60 meter thick section of the ice island reaches the Labrador Sea in the south within a year after its calving in 2010.

TOS2016-Fig2

PII-2010 left Petermann Fjord on the 9th of September in 2010 when it broke into segments A and B while pivoting around a real island. It flushed out of Nares Strait 10 days later when an ice-tracking beacon was placed to track the ice island. The ~60 m thick segment PII-2010A moved southward with the Baffin Island Current (Münchow et al., 2015) at an average speed of ~ 0.11 m/s past Davis Strait. Remaining on the continental shelf of the Labrador Sea, it passed Boas’ Cumberland Sound, Labrador, and reached Newfoundland in August 2011 when it melted away in a coastal cove about 3000 km from Petermann Fjord (Figure-2).

TOS2016-Fig7

Petermann Gletscher drains about 4% of the Greenland ice sheet via a network of channels and streams that extend about 750 km landward from the grounding line (Bamber et al., 2013). The glacier goes afloat at the grounding zone where bedrock, till, and ice meet the ocean waters about 600 meter below sea level (Rignot, 1996).

TOS2016-Fig3

Figure-3 shows a section of surface elevation from a laser altimeter flown on a repeat path along the glacier in April 2013 and May 2014 as part of NASA’s Operation IceBridge. Assuming hydrostatic balance, we also show basal topography below the sea surface that varies from 200 meters at the terminus to 600 meters at the grounding zone near distance zero (Figure-3). The 2013 profile has been shifted seaward by 1.25 km to match the terminus position. Note the close correspondence of large and small crevasses in 2013 and 2014 near 20, 40, and 45 km from the grounding zone.

The seaward shift of the 2013 relative to the 2014 profile implies a uniform glacier speed of about 1180 meters per year. This value is almost identical to the 1170 meters per year that we measure between 20th August of 2015 and 11th February of 2016 with a single-frequency GPS placed about 13 km seaward of the grounding zone as part of the ocean weather observatory.

We compare 2013/14 and 2015/16 velocity estimates in Figure-3 with those obtained from RadarSat interferometry between 2000 and 2008 (Joughin et al., 2010) of which I here only show three:

Figure-3 shows that glacier speeds before 2010 are stable at about 1050 m/y, but increased by about 11% after the 2010 and 2012 calving events. This increase is similar to the size of seasonal variations of glacier motions. Each summer Petermann Gletscher speeds up, because surface meltwater percolates to the bedrock, increases lubrication, and thus reduces vertical friction (Nick et al., 2012). Figure 3 presents summer velocity estimates for August of 2015 from three dual-frequency GPS. The along-glacier velocity profiles measured by these geodetic sensors in the summer follow the shape of the 2000 to 2008 winter record, however, its speeds are about 10% larger and reach 1250 m/y near the grounding zone (Figure 3).

Uncertainty in velocity of these GPS systems is about 1 m/y which we estimate from two bed rock reference stations 82 km apart. Our ice shelf observations are referenced to one of these two semi-permanent geodetic stations. Its location at Kap Schoubye is shown in Figure-1. Data were processed using the GAMIT/TRACK software distributed by MIT following methodology outlined by King (2004) to archive vertical accuracy of 2-3 centimeters which, we show next, is small relative to tidal displacements that reach 2 meters in the vertical.

TOS2016-Fig4

Figure-4 shows the entire 13 day long record of vertical glacier displacement from 30 seconds GPS measurements in August of 2015. The observed range of vertical glacier displacements diminishes from almost 2 meters about 26 km seaward of the grounding zone (GZ+26) via 0.6 meters in the grounding zone (GZ-00) to nil 20 km landward of the grounding zone (GZ-20). Anomalies of horizontal displacement are largest at GZ-00 with a range of 0.2 m (not shown) in phase with vertical oscillations (Figure-4).

More specifically, at GZ+26 we find the ice shelf to move up and down almost 2 meters roughly twice each day. This is the dominant semi-diurnal M2 tide which has a period of 12.42 hours. Notice that for each day there is also a diurnal inequality in this oscillation, that is, the two maximal (minimal) elevations oscillate from a higher to a lower High (Low) water. This is the diurnal K1 tide which has a period of 23.93 hours. And finally, all amplitudes appear modulated by some longer period that appears close to the record length of almost two weeks. This is the spring-neap cycle that is caused by a second semi-diurnal S2 tide that has a period of 12.00 hours. A formal harmonic analysis to estimate the amplitude and phases of sinusoidal oscillations at M2, K1, S2 and many more tidal constituents will be published elsewhere for both Petermann Fjord and Nares Strait. Preliminary results (not shown) reveal that the amplitudes and phases of the tidal signals at GZ+26 are identical to those observed off Ellesmere Island at 81.7 N latitude in both the 19th (Greely, 1888) and 21st century.

Hourly tidal observations at Discovery Harbor taken for 15 days by Greely in 1881 and Peary in 1909.

Hourly tidal observations at Discovery Harbor taken for 15 days by Greely in 1881 and Peary in 1909.

In summary, both historical and modern observations reveal real change in the extent of the ice shelf that moves at tidal, seasonal, and interannual time scales in response to both local and remote forcing at these times scales. Future studies will more comprehensively quantify both the time rate of change and its forcing via formal time series analyses.

P.S.: This is the second in a series of four essays that I am currently developing into a peer-reviewed submission to the Oceanography Magazine of the Oceanography Society. The work is funded by NASA and NSF with grants to the University of Delaware.

References:

Bamber, J.L., M.J. Siegert, J.A. Griggs, S. J. Marshall, and G. Spada. 2013. Palefluvial mega-canyon beneath the central Greenland ice sheet. Science 341: 997-999.

Greely, A.W. 1888. Report on the Proceedings of the United States Expedition to Lady Franklin Bay, Grinnell Land. Government Printing Office, Washington, DC.

Joughin, I., B.E. Smith, I.M. Howat, T. Scambos, and T. Moon. 2010. Greenland flow variability from ice-sheet wide velocity mapping. Journal of Glaciology 56 (197): 415-430.

King, B. 2004. Rigorous GPS data-processing strategies for glaciological applications. Journal of Glaciology 50 (171): 601–607.

Münchow, A., K.K. Falkner, and H. Melling. 2015. Baffin Island and West Greenland current systems in northern Baffin Bay. Progress in Oceanography 132: 305-317.

Nick, F.M., A. Luckman, A. Vieli, C.J. Van Der Veen, D. Van As, R.S.W. Van De Wal, F. Pattyn, A.L. Hubbard, and D. Floricioiu. 2012. The response of Petermann Glacier, Greenland, to large calving events, and its future stability in the context of atmospheric and oceanic warming. Journal of Glaciology 58 (208): 229-239.

Rignot, E. 1996. Tidal motion, ice velocity and melt rate of Petermann Gletscher, Greenland, measured from radar interferometry. Journal of Glaciology 42 (142): 476-485.

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Posted in Greenland, Ice Island, Oceanography, Petermann Glacier, Petermann2015, Polar Exploration

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The Turbulence of Van Gogh and the Labrador Shelf Current

Posted on May 8, 2013 by | 3 comments

Vincent Van Gogh painted his most turbulent images when insane. The Labrador Current resembles Van Gogh’s paintings when it becomes unstable. There is no reason that mental and geophysical instability relate to each other. And yet they do. Russian physicist Andrey Kolmogorov developed theories of turbulence 70 years ago that Mexican physicist applied to some of Van Gogh’s paintings such as “Starry Sky:”

Vincent Van Gogh's "Starry Sky" painted in June 1889.

Vincent Van Gogh’s “Starry Sky” painted in June 1889.

The whirls and curls evoke motion. The colors vibrate and oscillate like waves that come and go. There are rounded curves and borders in the tiny trees, the big mountains, and the blinking stars. Oceanographers call these rounded curves eddies when they close on themselves much as is done by a smooth wave that is breaking when it hits the beach in violent turmoil.

Waves come in many sizes at many periods. The wave on the beach has a period of 5 seconds maybe and measures 50 meters from crest to crest. Tides are waves, too, but their period is half a day with a distance of more than 1000 km from crest to crest. These are scales of time and space. There exist powerful mathematical statements to tell us that we can describe all motions as the sum of many waves at different scales. Our cell phone and computer communications depend on it, as do whales, dolphins, and submarines navigating under water, but I digress.

The Labrador Shelf Current off Canada moves ice, icebergs, and ice islands from the Arctic down the coast into the Atlantic Ocean. To the naked eye the ice is white while the ocean is blue. Our eyes in the sky on NASA satellites sense the amount of light and color that ice and ocean when hit by sun or moon light reflects back to space. An image from last friday gives a sense of the violence and motion when this icy south-eastward flowing current off Labrador is opposed by a short wind-burst in the opposite direction:

Ice in the Labrador Current as seen by MODIS-Terra on May 3, 2013.

Ice in the Labrador Current as seen by MODIS-Terra on May 3, 2013. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

Flying from London to Chicago on April 6, 2008, Daniel Schwen photographed the icy surface of the Labrador Current a little farther south:

Ice fields seen in Labrador Current April 6, 2008 from a plane. [Photo Credit: Daniel Schwen]

Ice fields seen in Labrador Current April 6, 2008 from a plane. [Photo Credit: Daniel Schwen]

Ice in the Labrador Current as seen by MODIS-Terra on April 6, 2008. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

Ice in the Labrador Current as seen by MODIS-Terra on April 6, 2008. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

The swirls and eddies trap small pieces of ice and arrange them into wavy bands, filaments, and trap them. The ice visualizes turbulent motions at the ocean surface. Also notice the wide range in scales as some circular vortices are quiet small and some rather large. If the fluid is turbulent in the mathematical sense, then the color contrast or the intensity of the colors and their change in space varies according to an equation valid for almost all motions at almost all scales. It is this scaling law of turbulent motions that three Mexican physicists tested with regard to Van Gogh’s paintings. They “pretended” that the painting represents the image of a flow that follows the physics of turbulent motions. And their work finds that Van Gogh indeed painted intuitively in ways that mimics nature’s turbulent motions when the physical laws were not yet known.

There are two take-home messages for me: First, fine art and physics often converge in unexpected ways. Second, I now want to know, if nature’s painting of the Labrador Shelf Current follows the same rules. There is a crucial wrinkle in motions impacted by the earth rotations: While the turbulence of Van Gogh or Kolmogorov cascades energy from large to smaller scales, that is, the larger eddies break up into several smaller eddies, for planetary-scale motions influenced by the Coriolis force due to earth’s rotation, the energy moves in the opposite direction, that is, the large eddies get larger as the feed on the smaller eddies. There is always more to discover, alas, but that’s the fun of physics, art, and oceanography.

Aragón, J., Naumis, G., Bai, M., Torres, M., & Maini, P. (2008). Turbulent Luminance in Impassioned van Gogh Paintings Journal of Mathematical Imaging and Vision, 30 (3), 275-283 DOI: 10.1007/s10851-007-0055-0

Ball, P. (2006). Van Gogh painted perfect turbulence news@nature DOI: 10.1038/news060703-17

Wu, Y., Tang, C., & Hannah, C. (2012). The circulation of eastern Canadian seas Progress in Oceanography, 106, 28-48 DOI: 10.1016/j.pocean.2012.06.005

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Posted in Oceanography

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Oceanography and Icebergs in Baffin Bay: LCDR Edward “Iceberg” Smith

Posted on March 27, 2013 by | 4 comments

In 1928 Edward H. “Iceberg” Smith took the 125 feet long Coast Guard Cutter “Marion” on an 8,100 mile journey from Boston, MA to New York City, NY via Disko Bay, Greenland. Along the way he defined operational Arctic Oceanography to explain and predict iceberg entering the busy sea lanes off North-America. The Titanic was sunk in 1912, the International Ice Patrol was formed in 1914, and LCDR Smith sailed to Greenland in 1928. The data are priceless 85 years later still. I used them to place modern observations from 2003 into a context of climate variations. First, however, let me give credit to one of the pioneers on whose scientific shoulders I stand:

Edward H. "Iceberg" Smith of the US Coast Guard with reversing thermometer.

Edward H. “Iceberg” Smith of the US Coast Guard with reversing thermometer.

“Iceberg” Smith entered the Coast Guard Academy at age 21 in 1910 and served during World War I as a navigator on Atlantic convoy escort duty. After this war his ship was detailed to the International Ice Patrol and he became one of its first scientific observers at age 32 in 1921. As such he was sent for a year to Bergen, Norway in 1925 to learn the latest theories in physical oceanography. Scandinavian explorers like Nansen, Ekman, Sverdrup, Bjerknes, and Helland-Hansen defined physical oceanography at this time by applying physics on a rotating earth to phenomena that they observed from ships sailing at sea or ships frozen in Arctic ice. Much of this revolutionary work is now elementary oceanography taught in introductory courses, but then, nobody knew much about why ice and ocean move they way they do. It was time to put ideas to a thorough test which is what “Iceberg” Smith did, when he got his ship and orders to explore in 1928.

USCGC Marion built in 1927 [from http://laesser.org/125-wsc/]

USCGC Marion built in 1927. Note the scale indicated by a person standing on the lower deck. [From http://laesser.org/125-wsc]

Armed with new ideas, knowledge, and the tiny USCGC Marion “Iceberg” Smith set to out to map seas between Labrador, Baffin Island, and Greenland to explain and predict the number of icebergs to enter the North-Atlantic Ocean. During his 10 weeks at sea he mapped ocean currents from over 2000 discrete measurements of temperature and salinity at many depths. This was before computers, GPS, and electronics. In 1928 this was slow to work with cold water collected in bottles with “reversing thermometers” that cut off the mercury to preserve temperatures measured in the ocean at depth to be read later aboard. Salinity was measured at sea by tedious chemical titrations. Imagine doing all of this from a rocking and rolling shallow draft cutter that bounces in icy seas for 10 weeks within fog much of the time. No radar to warn of icebergs either, and you want to study icebergs, so you move exactly where they are or where you think they are coming from. And they though that the Titanic was unsinkable.

Iceberg in the fog off Upernarvik, Greenland in July of 2003. [Photo Credit: Andreas Muenchow]

Iceberg in the fog off Upernavik, Greenland in July of 2003. [Photo Credit: Andreas Muenchow]

USCGC Healy in northern Baffin Bay in July 2003 with iceberg. Ellesmere Island is in the background.

USCGC Healy in northern Baffin Bay in July 2003 with iceberg. Ellesmere Island is in the background.

The 1928 Marion Expedition was the first US Coast Guard survey in Baffin Bay while the last such expedition took place 2003. Unlike “Iceberg” Smith we then had military grade GPS, radar, and sonar systems. These sensor systems allowed me to directly measure ocean currents from the moving ship every minute continuously from the surface to about 600 meters down. Oh, we also took water samples in bottles, but temperature, depth, and salinity are all measured electronically about 24 times every second. As a result we can actually test, if the physics that had to be assumed to be true in 1928 actually are true. As it turns out, the old theory to estimate currents from temperature and salinity sections works well off Canada, but not so well off Greenland. Furthermore, we found several eddies or vortices in the ocean from the current profiling sonars.

And finally, it took Edward H. “Iceberg” Smith only 3 years to publish most of his data and insightful interpretations while I am still working on both his and my own data 85 years and 10 years later, respectively. Sure, I got more data from a wider range of moored, ship-borne, and air-borne sensors, but I do wonder, if I really consider my data and interpretations as careful and think as thorough as LCDR Smith did. Furthermore, he had no computers and performed all calculations, crafted all graphs, and typed all reports tediously by hand. I would not want to trade, but all this makes me admire his skills, dedication, and accomplishments even more.

Dr Helen Johnson on acoustic Doppler current profiler (sonar to measure ocean velocity) watch aboard the USCGC Healy in Baffin Bay in 2003. [Photo credit: Andreas Muenchow]

Dr Helen Johnson on acoustic Doppler current profiler (sonar to measure ocean velocity) watch aboard the USCGC Healy in Baffin Bay in 2003. [Photo credit: Andreas Muenchow]

P.S.: The New Yorker has three stories on the subject published in 1938, 1949, and 1959. I eagerly await to read those.

ResearchBlogging.orgSmith, E. (1928). EXPEDITION OF U. S. COAST GUARD CUTTER MARION TO THE REGION OF DAVIS STRAIT IN 1928 Science, 68 (1768), 469-470 DOI: 10.1126/science.68.1768.469

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Nares Strait 2012: First Challenges and Petermann Ice Island Coming

Posted on July 31, 2012 by | 9 comments

Petermann Glacier’s 2012 ice island is heading south, the Canadian Coast Guard Ship Henry Larsen is heading north, and my passport went through the washer. Ticket agents at Philadelphia airport refused to accept my worn passport to get into Canada. My journey appeared at a dead-end, but ticket agents, U.S. State Department employees in downtown Philadelphia, and a Jordanian cab driver got me to Canada with a new passport, a new ticket, and a new lesson learnt in 4 hours. I did not believe it possible, but it was. I arrived in Canada with an entire day to spare.

Over the years I learnt to plan and budget generously for Arctic research, and then improvise with what is available. I was taught to bring spares of all critical equipment to prepare for loss and failure. I learnt to allow for extra time as missed planes, weather, and who knows what always make tight schedules tighter, like passports going through washers. I learnt that patience, civility, co-operations, and seeing the world through other people’s eyes and responsibilities get me farther than fighting. After I got my PhD in 1992, I learnt that the very people who cause troubles by enforcing rules and regulations are often also the most likely to know the way out of trouble. The ticket agent who denied my passport was also critical to help me get a new one. Thank you, Beth.

Our science party of eight from Delaware and British Columbia and the ship’s crew of 30-40 from Newfoundland will meet on the tarmac of St. John’s tomorrow at 4:30am, fly to and refuel at Iqaluit, Nunavut, and arrive at the U.S. Air Force Base at Thule, Greenland. The crew who got the ship from St. John’s to Thule will return with the plane home. It usually takes two days sailing north by north-west to reach Nares Strait from Thule, but this year the ice will be a challenge far greater than getting a new passport in 4 hours.

Western North-Atlantic and Arctic regions with Greenland in the west (top right) and Canada (left). Blue colors show bottom depth (light blue are shelf areas less than 200-m deep) and grey and white colors show elevations. Nares Strait is the 30-40 km wide channel to the north of Smith Sound, Baffin Bay is the body of water to the south of Thule.


The ice island PII-2012 is moving rapidly towards the outer fjord at a rate that increased from 1 km/day last week to 2 km/day over the weekend. I expect it to be out of the fjord an in Nares Strait by the weekend when we were hoping to recover the moorings with data on ocean currents, ice thickness, and ocean temperature and salinities that we deployed in 2009. The ice island is threatening us from the north: Without a break-up, it is big enough to block the channel as another large ice island did for almost 6 months in 1962.

Petermann Glacier, Fjord, and Ice Island on July 31, 2012 at 08:05 UTC. Nares Strait is to the top left. Petermann Glacier, Greenland is on bottom right. PII-2012 is at the center.


At the southern entrance to Nares Strait, lots of multi-year ice is piling up near the constriction of Smith Sound. Winds and currents from the north usually flush this ice into Baffin Bay to the south, however, the same winds and currents will move the ice island out of Petermann Fjord and into Nares Strait. We will need patience, humility, and luck to get where we need to be to recover our instruments and data. A challenge that cannot be forced, we will likely wait and go with the flow rather than fight nature. We will have to play it smart. We are the only search and rescue ship for others. I am nervous, because this year looks far more difficult than did 2003, 2006, 2007, or 2009. In 2005 we were defeated by the winds, but that is a story for a different day.

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Posted in Ice Island, Nares Strait 2012, Petermann Glacier

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Global Weight Watch: Slimmer Greenland and Fatter Tropics

Posted on August 6, 2011 by | 3 comments

An ice island four times the size of Manhattan separated from Petermann Glacier, Greenland last year. Today one of these Manhattans reached the coast of Newfoundland. Never before has as large a piece of ice from Greenland reached this far south. Does this show a warming climate taping into Greenland’s 20 feet potential to raise global sea level?

Track of Petermann Ice Island from Aug.-2010 through Aug.-2011 traveling in shallow water from northern Greenland along Baffin Island and Labrador to Newfoundland.

Greenland’s glaciers always melt with pieces breaking off. This raises sea level if Greenland receives less snow atop than it loses ice at the bottom. For the last 10 years Greenland lost about 200 trillion pounds of mass, net, per year. [At 5 cents per pound, this pays off the federal debt within a year.] Distributing this mass over all oceans, we raise global sea level by one inch in 75 years. Nothing to worry about, but there is a twist: Weight watching satellites show that Greenland becomes thinner, while the Tropic grow fatter. Records of weight gain and loss are too short to draw firm conclusions, yet, but they are consistent across the globe and the trends of gain and loss are increasing, too.

We do not understand the physics, stability, and uncertainty of these increasing gains and losses well enough to make reliable predictions. If the climate over Greenland is stable, as it has been for the last 10,000 years, then this matters little. If the present equilibrium reaches a tipping point, where a small change will kick us into different stable state, then we can expect sea level to increase 10 times or more. We understand tipping points in theory, but not in practice. In practical terms, we do not know if our children must deal with two inches of sea level from Greenland by the end of this century or 80 inches or none at all. We know only too well, however, that low-lying places like Bangladesh, the Netherlands, and New Orléans struggle with the sea level we have now.

Greenland’s ice island off Newfoundland indicates a globally connected world. Burning stuff over Europe, America, and increasingly Asia creates heat that melts Greenland at a rate that is increasing. What happens in Greenland does not stay in Greenland, but it impacts Rome, Miami, and Shanghai. More ice and rising sea level will come. To play it safe, let’s think smartly what and how we burn. To play it loose and reckless: burn, baby, burn … or was it drill?

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Posted in Global Warming, Ice Island

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