Category Archives: Ice Island

What’s happened at Petermann Gletscher since the Industrial Revolution 150 years ago?

Posted on July 3, 2019 by | 4 comments

More than 15 years ago I first set sight on the floating Petermann Gletscher when the United States’ Coast Guard Cutter Healy visited north-west Greenland for the first time on 10th August of 2003. We only had to sail 20 km into the fjord to reach a flat expanse of glacier ice that stuck less than 5 m (15 feet) above the sea. In 2012 and 2015 we had to sail another 20 km, because two large calving events had shortened the glacier farther back than it has since first records were kept in 1876. The terminus was also much higher, almost 25 m (75 feet) above the sea:

DSCN4444

Terminus of Petermann Gletscher 5th August 2015 from aboard the Swedish icebreaker Oden. View is to the south-east. [Photo Credit: Andreas Muenchow]

I published more detailed results on observed glacier change and estimated melt rates with Drs. Laurie Padman and Helen Fricker in the Journal of Glaciology from which I take these two figures:

Muenchow2014_01

Petermann Gletscher’s two large calving events in 2010 and 2012 as seen from MODIS satellite. The glacier is floating on the ocean seaward of the grounding line indicated by the thick black line. Black areas are open ocean water, white is ice. Adapted from Muenchow et al., 2014.

Muenchow2014_02

Time series from 1876 to 2014 of the length of Petermann Gletscher as measured from its grounding line at y=0 km. Triangles are observations while lines indicate a steady 1 km per year advance. The insert shows three maps of observed glacier shapes. From Muenchow et al., 2014.

Back in 2003 the glacier advanced about 1 km each year and it does so still. Almost the same, but not exactly, because the removal of 6 “Manhattans” in 2010 and 2012 increased the forward speed some, that is, the glacier now moves faster forward than it did before. Many sensors placed on the glacier measured this speeding, but the glacier also gets thinner as it speeds up. It is stretched thin. I published this back in 2016 together with Drs. Laurie Padman, Keith Nicholls, and my PhD student Peter Washam in Oceanography:

Muenchow2016_03

Speed at which Petermann Gletscher moves out into the sea from many different measurements. The glacier moves more slowly over land (negative distances) than it does floating over the ocean (positive distances). Estimates made after 2012 are about 10-20 % higher than RADARSAT estimates before that date. From Muenchow et al., 2016.

With substantial help from the British Antarctic Survey we installed in 2015 a small ocean observing system under the floating glacier. It transmitted data from 800 meters (2400 feet) below the 100 m (300 feet) thick glacier ice via cables connected to a weather station. We sucessfully repaired the station (as well as a Danish weather station nearby) that stopped transmitting data via satellites in 2016. Two journalists of the Washington Post, Chris Mooney and Whitney Shefte joined Keith Nicholls and myself. Their outstanding and accurate reporting of our work includes video and graphics for a wider audience that you can find at this link:

Washington Post Video of 2016 Petermann Gletscher Site Visit

The ocean and glacier data were worked over carefully by Peter Washam who defended his dissertation last month. Dr. Washam moved to Georgia Tech in Atlanta to work with Dr. Britney Schmidt whose interests relate to the ice-covered oceans below some moons of Jupiter. Peter connected ocean temperature and salinity with ice radar and remote sensing data to estimate how much the glacier is melted by the ocean and how the ocean does this. His main result will be published later this year in the Journal of Glaciology [Added July-12, 2019: Published online as Washam et al., 2019 at the Journal of Glaciology.], that is

“… This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base…”

The next large calving will be no surprise: Large fractures cross much of the glacier. They are visible about 10-20 km behind the current terminus and are discussed and closely monitored almost every day at the excellent site of Greenland Enthusiasts from all walks of life who post at

https://forum.arctic-sea-ice.net/index.php/topic,53.600.html

Furthermore, a new sophisticated computer model of Petermann Gletscher reveals that the loss of this large “still attached” ice island is already gone from the glacier in terms of the friction that it provides along the sidewalls. Another way of putting this, all it takes is a little wiggle or bump and the separation will become visible. Dr. Martin Rueckamp just published this study in the Journal of Geophysical Research.

There is much more to be explored with regard to Petermann. Here are some of the readings and writings that I have done with many fellow sailors through uncertain climates:

Johnson, H.L., A. Muenchow, K.K. Falkner, and H. Melling: Ocean circulation and properties in Petermann Fjord, Greenland. Journal of Geophysical Research, 116, doi:10.1029/2010JC006519, 2011. .pdf

Muenchow, A., L. Padman, and H.A. Fricker: Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012 Journal of Glaciology, 60, doi:10.3189/2014JoG13J135, 2014. .pdf

Muenchow, A., L. Padman, P. Washam, and K.W. Nicholls, 2016: The ice shelf of Petermann Gletscher, North Greenland and its connection to the Arctic and Atlantic Oceans, Oceanography, 29, 84-95, 2016. .pdf

Rueckamp, M, N. Neckel, S. Berger, A. Humbert, and V. Helm: Calving induced speed-up of Petermann Glacier, Journal of Geophysical Research, 124, 216-228, 2019. .pdf

Shroyer, E., L. Padman, R. Samelson, A. Muenchow, and L. Stearns: Seasonal control of Petermann Gletscher ice-shelf melt by the ocean’s response to sea-ice cover in Nares Strait, Journal of Glaciology, 63, doi:10.1017/jog.2016.140, 2017. .pdf

Washam, P., A. Muenchow, and K.W. Nicholls: A decade of ocean changes impacting the ice shelf of Petermann Gletscher, Greenland, Journal of Physical Oceanography, 48, 2477-2493, 2018. source

Washam, P., K.W. Nicholls, A. Muenchow, and L. Padman: Summer surface melt thins Petermann Gletscher ice shelf by enhancing channelized basal melt, Journal of Glaciology, 65, doi:10.1017/jog.2019.43, 2019. .pdf

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

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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 Ice Shelf of Petermann Gletscher, North Greenland and its ocean below: Introductions

Posted on March 29, 2016 by | 3 comments

“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

Traveling by dog sled, Geologist Lauge Koch mapped Petermann Gletscher in 1921 after he and three Inuit companions crossed it on a journey to explore northern North Greenland. They discovered and named Steensby, Ryder, and H.C. Ostenfeld Glaciers that all had floating ice shelves as does Petermann (Ahnert, 1963; Higgins, 1990). In Figure 1 I reproduce the historic map of Koch (1928) that also contains his track in in 1917 and 1921 both across the terminus and across its upstream ice stream. In 1921 all four starved travelers returned safely after living off the land. Four years earlier, however, they were not so lucky: two traveling companions died on a similar journey in 1917 (Rasmussen, 1923).

Maps of Petermann Gletscher by Lauge Koch from 1917 and 1921 dog sleds and 2015 from MODIS-Terra.

Only 20 years after Lauge Koch’s expeditions by dog sled, air planes and radar arrived in North Greenland with the onset of the Cold War. The Arctic Ocean to the north became a battle space along with its bordering land and ice masses of northern Greenland, Ellesmere Island, Canada, Alaska, and Siberia. Weather stations were established in 1947 at Eureka by aircraft and in 1950 at Alert by US icebreaker to support military aviation (Johnson, 1990). In 1951 more than 12,000 US military men and women descended on a small trading post called Thule that Knud Rasmussen and Peter Freuchen had established 40 years earlier to support their own and Lauge Koch’s dog-sled expeditions across Greenland (Freuchen, 1935). “Operation Blue Jay” built Thule Air Force Base as a forward station for fighter jets, nuclear armed bombers, and early warning radar systems. The radars were to detect ballistic missiles crossing the Arctic Ocean from Eurasia to North America while bombers were to retaliate in case of a nuclear attack from the Soviet Union.

An F-102 jet of the 332d Fighter-Interceptor Squadron at Thule AFB in 1960. [Credit: United States Air Force]

An F-102 jet of the 332d Fighter-Interceptor Squadron at Thule AFB in 1960. [Credit: United States Air Force]

About another 60 years later, the jets, the bombers, and the communist threat were all gone, but the Thule Air Force Base is still there as the gateway to North Greenland. It is also the only deep water port within a 1,000 mile radius where US, Canadian, Danish, and Swedish ships all stop to receive and discharge their crews and scientists. Since 2009 Thule AFB also serves as the northern base for annual Operation IceBridge flights over North Greenland to map the changing ice sheets and glaciers.

The establishment of military weather stations and airfields in the high Arctic coincided with the discovery of massive ice islands drifting freely in the Arctic Ocean. On Aug.-14, 1946 airmen of the 46th Strategic Reconnaissance Squadron of the US Air Force discovered a moving ice islands with an area of about 200 square that was kept secret until Nov.-1950 (Koenig et al, 1950). Most of these ice islands originated from rapidly disintegrating ice shelves to the north of Ellesmere island (Jeffries, 1992; Copland 2007), however, the first historical description of an ice islands from Petermann Gletscher came from Franz Boas in 1883 who established a German station in Cumberland Sound at 65 N latitude and 65 W longitude as part of the first Polar Year.

Petermann Ice Island of 2012 at the entrance of Petermann Fjord. The view is to the north-west with Ellesmere Island, Canada in the background. [Photo Credit: Jonathan Poole, CCGS Henry Larsen]

Petermann Ice Island of 2012 at the entrance of Petermann Fjord. The view is to the north-west with Ellesmere Island, Canada in the background. [Photo Credit: Jonathan Poole, CCGS Henry Larsen]

Without knowing the source of the massive tabular iceberg the German physicist Franz Boas reported detailed measurements of ice thickness, extend, and undulating surface features of an ice island in Cumberland Sound that all match scales and characteristics of Petermann Gletscher (Boas, 1885). These characteristics were first described by Dr. Richard Croppinger, surgeon of a British Naval expedition in 1874/75 (Nares, 1876). Dr. Croppinger identified the terminus of Petermann Gletscher as a floating ice shelf when he noticed vertical tidal motions of the glacier from sextant measurements a fixed point (Nares, 1876). His observations on tides were the last until a group of us deployed 3 fancy GPS units on the glacier last summer.

These fancy GPS receivers give centimeter accuracy vertical motions at 30 second intervals. Here is what the deployment of 3 such units in August of 2015 gives me:

Vertical (top) and horizontal (bottom) motion of Petermann Gletscher from GPS referenced to a GPS base station on bed rock at Kap Schoubye. Note the attenuation of the tide from 26 km sea ward of the grounding line (red) to at the grounding line (black) and 15 km landward of the grounding line (blue). The horizontal location motion has the mean motion removed to emphasize short-term change over the much, much larger forward motion of the glacier that varies from about ~700 (black) to ~1250 meters per year (red).

Vertical (top) and horizontal (bottom) motion of Petermann Gletscher from GPS referenced to a GPS base station on bed rock at Kap Schoubye. Note the attenuation of the tide from 26 km sea ward of the grounding line (red) to at the grounding line (black) and 15 km landward of the grounding line (blue). The horizontal location motion has the mean motion removed to emphasize short-term change over the much, much larger forward motion of the glacier that varies from about ~700 (black) to ~1250 meters per year (red).

We have indeed come a far way during the last 150 years or so. Mapping of remote landscape and icescape by starvation and dog-sled has been replaced by daily satellite imagery. Navigation by sextant and a mechanical clock has been replaced by GPS and atomic clock whose errors are further reduced by a local reference GPS. These fancy units and advanced data processing allow me to tell the vertical difference between the top of my iPhone sitting on a table in my garden from the table.

Working at in the garden at home preparing for field work.

Working at in the garden at home preparing for field work near Petermann Fjord.

P.S.: This is the first in a series of 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.

Ahnert, F. 1963. The terminal disintegration of Steensby Gletscher, North Greenland. Journal of Glaciology 4 (35): 537-545.

Boas, F. 1885. Baffin-Land, geographische Ergebnisse einer in den Jahren 1883 und 1884 ausgeführten Forschungsreise. Petermann’s Mitteilungen Ergänzungsheft 80: 1-100.

Copland, L., D.R. Mueller, and L. Weir. 2007. Rapid loss of the Ayles Ice Shelf, Ellesmere Island, Canada. Geophysical Research Letters 34 (L21501): doi:10.1029/2007GL031809.

Freuchen, P. 1935. Arctic adventures: My life in the frozen North. Farrar & Rinehard, NY, 467 pp.

Higgins, A.K. 1990. North Greenland glacier velocities and calf ice production. Polarforschung 60 (1): 1-23.

Jeffries, M. 1992. Arctic ice shelves and ice islands: Origin, growth, and disintegration, physical characteristics, structural-stratigraphic variability, and dynamics. Reviews of Geophysics 30 (3):245-267.

Johnson, J.P. 1990. The establishment of Alert, N.W.T., Canada. Arctic 43 (1): 21-34.

Koch, L., 1928. Contributions to the glaciology of North Greenland. Meddelelser om Gronland 65: 181-464.

Koenig, L.S., K.R. Greenaway, M. Dunbar, and G. Hattersley-Smith. 1952. Arctic ice islands. Arctic 5: 67-103.

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.

Münchow, A., L. Padman, and H.A. Fricker. 2014. Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012. Journal of Glaciology 60 (221): doi:10.3189/2014JoG13J135.

Nares, G. 1876. The official report of the recent Arctic expedition. John Murray, London,

Rassmussen, K., 1921: Greenland by the Polar Sea: the Story of the thule Expedition from Melville Bay to Cape Morris Jessup, translated from the Danish by Asta and Rowland Kenney, Frederick A. Stokes, New York, NY, 327 pp.

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Posted in Arctic Glacier, Greenland, History, Ice Island, Petermann2015, Polar Exploration

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Coastal Oceanography off North-East Greenland

Posted on July 9, 2015 by | 1 comment

Greenland is melting, but it is not entire clear why. Yes, air temperatures continue to increase, but what does it matter, if those temperatures are below freezing most of the time. What if the ocean does most of the melting a few 100 m below the surface rather than the air above? It means that gut feeling and everyday experience can be poor guides for science, it means that there is more than meets the eye, and it means that some of Greenland’s melting happens out of sight without the dramatic imagery of a rapidly disintegrating glacier that sends icebergs out to sea.

Floating section of 79N Glacier in north-east Greenland as seen from LandSat in march 2014.

Floating section of 79N Glacier in north-east Greenland as seen from LandSat in march 2014.

In order to “see” where changes may happen out of sight American tax payers supported me via the National Science Foundation (NSF) to use available University of Delaware ocean sensors from an available German ship to investigate the ocean near two large glaciers off north-east Greenland. The sensors are in the water for over a year now and will stay there for another to collect data every half hour. The data are stored on computers inside the sensors and it is a marvel of smart engineering that we can measure water temperature, salinity, and velocity at the bottom of an ice-covered ocean. Now what would I do with such data?

Two ocean sensor packages ready for deployment near Isle de France, Greenland 10 June 2014.

Two ocean sensor packages ready for deployment near Isle de France, Greenland 10 June 2014.

First, one needs to know that in the Arctic Ocean temperature increases as one moves a thermometer from the surface towards the bottom for the first 900 feet or 300 meters. This only make sense, if the warm water is heavier than the cold water above. This is the case in the Arctic, because the warm water at depth is also very salty. The cold waters above contain less salt and that’s why they float. The warmest waters originate from the Atlantic Ocean to the south-east of Iceland. Lets call it Atlantic Water for this reason. The surface waters contain sea ice and its fresh melt water and thus are always close to the freezing point, so lets call them Polar Waters.

Vertical profiles of temperature and salinity across Norske Ore Trough, Greenland. The insert shows station locations for profiles (small symbols) and moorings (large circles). The red dot marks the location of the red profile.

Vertical profiles of temperature and salinity across Norske Ore Trough, Greenland. The insert shows station locations for profiles (small symbols) and moorings (large circles). The red dot marks the location of the red profile.

All along the East Coast of Greenland, we find a strong southward flow of ice and Polar Water called the East Greenland Current. On a rare clear day one can “see” this flow as a beautifully structured undulating band separating the deep Greenland Sea from the shallow and broad continental shelves. Now recall that the warmest waters are in the Atlantic layer way down and somewhat offshore. How do these waters cross the East Greenland current and the very wide continental shelf to reach the glaciers along the coast? It is this question my project tries to answer with lots of help from NSF and German friends.

Satellite image ocean current instabilities on Aug.-19, 2014 as traced by ice along the the shelf break, red lines show 500, 750, and 1000 meter water depth. Small blue triangles top left are ocean moorings.

Satellite image ocean current instabilities on Aug.-19, 2014 as traced by ice along the the shelf break, red lines show 500, 750, and 1000 meter water depth. Small blue triangles top left are ocean moorings.

We think that the warm and salty waters flow near the bottom below the East Greenland Current at deep bottom depressions such as canyons. Testing this idea, we placed our sensors in a line across the canyon with a small ice-capped island called the Isle of France on one side and Belgica Bank on the other. We deployed seven instrument as an array across the canyon to measure the speed and direction of the flow as well as its temperatures and salinities. Our canyon connects the deep Greenland Sea 150 miles to the east with two glaciers another 100 miles to the north-west. We all anxiously hope that no iceberg wiped out bottom moorings and that they all record data faithfully until the summer of 2016 when we plan to recover instruments and data.

Section of temperature across Norske Ore Trough with Isle de France, Greenland on the left and Belgica Bank towards Fram Strait on the right. The view is towards 79N Glacier.

Section of temperature across Norske Ore Trough with Isle de France, Greenland on the left and Belgica Bank towards Fram Strait on the right. The view is towards 79N Glacier.

Before and after the placement of our moored instruments, however, we did survey the section from the ship and I show the temperature and salinity across our canyon. We now see that the water below 200 m depth are indeed very warm and salty as expected, but there is a detail that I cannot yet explain: notice the slight upward sloping contours of salinity near km-80 at the rim of the canyon and the downward sloping contours on the other side near km-10. Such sloping contours represent a flow out of the page at km-80 and into the page at km-10 which is exactly the opposite of what I expected. All I can say at the moment is that this snapshot does not resolve motions caused by the tides, the winds, and the seasonal cycles properly, but our moorings do. So, there are still mysteries to be solved by the data sitting on the bottom of the ocean guarded by towering spectacles of ice.

Tabular iceberg and sea ice cover near Isle de France 10 June 2014

Tabular iceberg and sea ice cover near Isle de France 10 June 2014

[This entry will be submitted to NSF as a Final Outcome Report for award 1362109 “Shelf-Basin Exchange near 79N Glacier and Zachariae Isstrom, North-East Greenland.” The work would not have been possible without the generous support of NSF as well as the German Government as represented by the Alfred Wegener Institute who sponsored the expedition to North-East Greenland in 2014. Torsten Kanzow, Benjamin Rabe, and Ursula Schauer of AWI all deserve as much and even more credit for this work than do I.]

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

Reeh, N., Thomsen, H., Higgins, A., & Weidick, A. (2001). Sea ice and the stability of north and northeast Greenland floating glaciers Annals of Glaciology, 33 (1), 474-480 DOI: 10.3189/172756401781818554

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

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A Short Summary of Nares Strait Physics

Posted on September 21, 2014 by | 4 comments

The Arctic Ocean is a puddle of water covered by ice that melts, moves, and freezes. Grand and majestic rivers of Siberia and America discharge into the puddle and make it fresher than Atlantic Ocean waters. The fate of the Arctic freshwater helps decide if Europe and the US become warmer or colder, experience more or less storms, droughts, or floods, and if global sea level will rise or fall. In a nutshell: the fate of Arctic freshwater determines climate.

Arctic Ocean with Nares Strait study area (red box) with tide gauge locations as blue symbols and section of moored array as red symbol. Contours are bottom topography that emphasize ocean basins and continental shelf areas.

Arctic Ocean with Nares Strait study area (red box) with tide gauge locations as blue symbols and section of moored array as red symbol. Contours are bottom topography that emphasize ocean basins and continental shelf areas.

Nares Strait connects the Arctic and Atlantic Oceans to the west of Greenland. It is narrower than Fram Strait, but it transports as much fresh ocean water as does its wider sister facing Europe. Few people know this, including climate scientists who often model it with a bathymetry that is 10,000 years out of date from a time when Nares Strait did not yet exist. This is why the US National Science Foundation funded a group of oceanographers to use icebreakers, sensors, computers, and innovative engineering to collect and analyze data on the ice, the water, and the atmosphere.

Acoustic Doppler Current Profiler mooring deployment in Nares Strait from aboard the CCGS Henry Larsen in 2009.

Acoustic Doppler Current Profiler mooring deployment in Nares Strait from aboard the CCGS Henry Larsen in 2009.

Within days of the start of the grant I had to appear before the US Congress to answer questions on Petermann Glacier that discharges into Nares Strait. In 2010 a large 4-times Manhattan-sized ice islands broke off and people wanted to know if global warming was to blame. I was asked how ocean temperatures and currents relate to this and other events and what may happen next. My few data points were the only existing data for this remote region, but I had not yet had the time to analyze and publish much. Two years later another large 2-Manhattan sized ice island formed from the same glacier, but this time we were better prepared and people world-wide went directly to our data, thoughts, and stories when this blog was sourced in news papers in France, Germany, and China. Al Jezeraa, BBC, and PBS reported on it, too, giving me chance to connect via TV, radio, and pod-casting to a larger public.

Petermann Gletscher in 2003, 2010, and 2012 from MODIS Terra in rotated co-ordinate system with repeat NASA aircraft overflight tracks flown in 2002, 2003, 2007, and 2010. Thick black line across the glacier near y = -20 km is the grounding line location from Rignot and Steffen (2008).

Petermann Gletscher in 2003, 2010, and 2012 from MODIS Terra in rotated co-ordinate system with repeat NASA aircraft overflight tracks flown in 2002, 2003, 2007, and 2010. Thick black line across the glacier near y = -20 km is the grounding line location from Rignot and Steffen (2008).

While it was exciting and fun to share Nares Strait and Petermann Gletscher physics with a global audience, it is not what we had planned to do. Our goal was to put real numbers to how much water, ice, and freshwater was moving from the Arctic to the Atlantic via Nares Strait. So the next 3 years we labored through our extensive records to first describe and then to understand what was happening in Nares Strait. We found that ocean currents move water always to the south no matter if ice covers Nares Strait or not, no matter if the ice is moving or not, no matter which way the wind is blowing. The physical cause for this southward flow is that the sea level is always a few inches higher in the Arctic Ocean than it is in Baffin Bay and the Atlantic Ocean to the south.

Linear regression of volume flux through Nares Strait from current meters with along-strait sea level difference from tide gauges (unpublished).

Linear regression of volume flux through Nares Strait from current meters with along-strait sea level difference from tide gauges. (unpublished).

We know, because we measured this with tide gauges that we placed in protected coastal bays. We recovered 3 sensors; most rewarding was the recovery of one sensor that we had failed to reach in 2005, 2006, 2007, and 2009, but in 2012 we finally got the instrument and 9-years of very good data. Batteries and computers inside were still running and recording. I have never seen as clean and as long a time series.

Results from a 2003-12 tide record shows as power spectra with named tidal constituents at diurnal (~24 hours) and semi-diurnal (~12 hours) periods. The red line is a modeled red noise spectra (unpublished).

Results from a 2003-12 tide record shown as a power spectra with named tidal constituents at diurnal (~24 hours) and semi-diurnal (~12 hours) periods. Data are shown as the relative amplitudes of oscillations at frequencies in cycles per day or cpd. The red line is a modeled red noise spectra (unpublished).

From satellite data that we analyzed as part of this grant, we know when the ice moves and when it stops moving. The freeze-up of Nares Strait comes in one of three forms: 1. Ice stops moving in winter, because an ice barrier (ice arch or ice bridge) forms in the south that blocks all southward motion of ice; 2. only new and young ice moves southward, because an ice barrier forms in the north that blocks all entry of Arctic ice into Nares Strait; and 3. Arctic ice moves freely through Nares Strait, because no ice barriers are present. Our 2003-12 study period covers years for each of these different ice regimes. And each of these regimes leads to very different ocean (and ice) flux as a result of very different ocean physics.

Data alone cannot make definite statements on what will happen next with our climate, but we know much new physics. The physics suggest certain balances of forces and energy for which we have mathematical equations, but these equations must be solved on computers that can only approximate the true physics and mathematics. These computer models are our only way to make predictions ito the future. The data we here collected and our analyses provide useful checks on existing models and will guide improved models.

June-10, 2012 MODIS-Terra image showing location of moored array that was deployed in Aug. 2009 to be recovered in Aug. 2012.

June-10, 2012 MODIS-Terra image showing location of moored array that was deployed in Aug. 2009.

Johnson, H., Münchow, A., Falkner, K., & Melling, H. (2011). Ocean circulation and properties in Petermann Fjord, Greenland Journal of Geophysical Research, 116 (C1) DOI: 10.1029/2010JC006519

Münchow, A., Falkner, K., Melling, H., Rabe, B., & Johnson, H. (2011). Ocean Warming of Nares Strait Bottom Waters off Northwest Greenland, 2003–2009 Oceanography, 24 (3), 114-123 DOI: 10.5670/oceanog.2011.62

Münchow, A., Padman, L., & Fricker, H. (2014). Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012 Journal of Glaciology, 60 (221), 489-499 DOI: 10.3189/2014JoG13J135

Münchow, A., Falkner, K., & Melling, H. (2014). Baffin Island and West Greenland Current Systems in northern Baffin Bay Progress in Oceanography DOI: 10.1016/j.pocean.2014.04.001

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

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Posted in Global Warming, Greenland, Ice Arch, Ice Cover, Ice Island, Nares Strait 2012, Oceanography, Petermann Glacier

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