Tag Archives: oceanography

How oceans interact with Greenland’s last floating glaciers

Testifying before the US Congress back in 2010, I refused to endorse the view that a first large calving at Petermann Gletscher in North Greenland was caused by global warming. When a second Manhattan-sized iceberg broke off in 2012, I was not so sure anymore and looked closely at all available data. There was not much, but what little I found suggested that ocean temperatures were steadily increasing. Could it be that warm waters 1000 feet below the surface could melt the glacier at all times of the year? Did this melting from below thin the glacier? Did these changes increase the speed at which it moves ice from land into the ocean? These were the questions that motivated a number of projects that began in earnest in 2015 aboard the Swedish icebreaker I/B Oden. Professional videos of this expeditions are at https://icyseas.org/2019/07/04/petermann-glacier-videos-science/

Scientists and technicians from the British Antarctic Survey drilled three holes through the floating section of Petermann Gletscher to access the ocean and ocean sediments below it. The ocean temperature and salinity profile confirmed both the warming trend observed in the fjord and ocean adjacent to the glacier, but more importantly, we placed ocean sensors below the glacier ice to measure temperature and salinity every hour for as long as the sensors, cables, and satellite data transmission would work. This has never been done around Greenland, so our data would be the first to report in real time on ocean properties below 100 to 300 m thick glacier ice at all times. What we saw when the data started to come in after 2 weeks, a month, and half a year stunned us, because (a) the ocean waters under the glacier changed by a very large amount every two weeks. Nobody has ever seen such regular and large changes in tempertures (and salinity) under a glacier bathed in total darkness at air temperatures of -40 degrees Celsius and Fahrenheit, but then our station went offline after 6 months and did not report any data to us via satellite.

Helicopter flight path on 27/28 August 2016 to reach Petermann Gletscher (PG) via southern (Fuel-S) and northern (Fuel-N) fuel stops in northern Inglefield and southern Washington Land, respectively. Background color is ocean bottom depth in meters.

Refurbished Petermann Glacier Ocean Weather station on 28. August 2016 with Greenland Air helicopter and British Antarctic radar station in the background.

The first work on the grant was to visit our station by helicopter in 2016 using two fuel caches that we placed the year prior from the Swedish icebreaker. At this point Petermann Gletscher and our projects attracted the attention of journalists of the Washington Post who had read some of the blog articles at this site. The two journalists accompanied us for a week and produced a beautiful visual report of our work that is posted at

https://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/

A detailed news report on our science and new findings appeared on page-1 of the Washington Post on January 1, 2017 [Broader Impacts]. I briefly summarize the results and findings of our subsequent data analyses of all data from August of 2015 through October of 2017 [Intellectual Merit]:

1a. Ocean temperatures increase at all five depths below the 100-m thick floating ice shelf of the glacier. These warmer waters are also saltier which demonstrates their Atlantic origin.

1b. Surface sensors indicate short, but intense pulses of meltwater passing our ocean array at spring-neap tidal cycles.

2a. Melt rate data reveal that these pulses occur during reduced tidal amplitudes and follow peaks in glacier melting that exceeded 30 feet per year.

2b. Statistical analyses indicate that the melt waters originate from a location near where the glacier sits on bed rock and that the melt water then moves seaward towards the ocean.

3a. Ocean melting below the glacier varies from summer (strong) to winter (weak) rising from a winter mean of 6 feet per year to a maximum of 240 feet per year during the summer.

3b. The large summer melting is caused by the increased discharge of subglacial runoff into the ocean near the grounding line.

3c. The larger discharge strengthens ocean currents under the floating glacier that drive ocean heat toward the glacier’s ice base.

The work formed one basis for the dissertation of PhD student Peter Washam who published the items #2 and #3 in the Journal of Physical Oceanography and Journal of Glaciology, respectively. He helped to drill holes and install sensors for the project that we first described at #1 in Oceanography. These three peer-reviewed journal articles are all published by not-for-profit professional organizations and societies dedicated to higher learning and public outreach. Furthermore we placed three separate data sets (1 | 2 | 3) at the Arctic Data Center that is funded by the National Science Foundation. More will come as we continue to work on the hard-won data from below Petermann Gletscher.

Look down the 0.3 meter wide drill hole. Yellow kevlar rope supports cable and ocean sensors.

Post Scriptum:
A modified version of the above was submitted the US National Science Foundation as part of the final reporting on grant 1604076 (“Glacier-Ocean interactions at a Greenland ice shelf at tidal to interannual time scales”) that funded this work with $360,400 at the University of Delaware from August 2016 through July 2019.

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

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

Germany 1985 to 2018

I left my native Germany in 1985 to study oceanography in North Wales. I returned in 2018 as an American Professor of polar oceanography.  

  Much has changed in 33 years. For one, the divided country that I left is no more. The largely peaceful unification of Germany and Europe removed barbed wires, concrete walls, and shoot-to-kill orders along a violent border. The Cold War was over, I saw the scenes of joy on TV in a bar in Newark, Delaware more than 4100 miles (5600 km) away:

https://abcnews.go.com/Archives/video/nov-10-1989-celebration-berlin-wall-8980622

I experienced the “new” Germany for the first time when sailing aboard Germany’s icebreaker R/V Polarstern in 2014 to deploy ocean moorings. At the time I counted four distinct German cultures.  

  Today is a national holiday that celebrates the “Tag der Deutschen Einheit” or “Day of German Unity.” It is very much work in progress as Germany is becoming more diverse with its over 10 Million people born in countries other than Germany. Turkey (1.5 Mil), Poland (0.9 Mil), and Syria (0.7 Mil) field the most foreign-born people as of 2017. From my American perspective Germany has become a more normal country with its recent politics, troubles, inconveniences, and strengths that these diverse backgrounds entail.

Dragonfly and I arrived in Bremerhaven three months ago to live and work here for at least a year. It took us two days to get bicycles and another two days to find a well-furnished apartment. My parents visited the second weekend and we became Bremerhaven tourists for two days. We purchased the required catastrophic health insurance from a credible company for about €550/year each, but after 3 months we are still waiting for the installation of an internet connection at our home, but we are hopeful that this may change soon.

Author aboard German research vessel F/S Maria S. Merian in port of Longyearbyen, Svalbard in the fall of 2018. [Photo by Dragonfly Leathrum.]

Author aboard German research vessel F/S Maria S. Merian in port of Longyearbyen, Svalbard in the fall of 2018. [Photo by Dragonfly Leathrum.]

 

Northern Winds and Currents off North-East Greenland

I spent 6 weeks aboard the German research icebreaker R/V Polarstern last year leaving Tromso in Norway in early September and returned to Bremerhaven, Germany in October. We successfully recovered ocean sensors that we had deployed more than 3 years before. It felt good to see old friends, mates, and sensors back on the wooden deck. Many stories, some mysterious, some sad, some funny and happy could be told, but today I am working on some of the data as I reminisce.

The location is North-East Greenland where Fram Strait connects the Arctic Ocean to the north with the Atlantic Ocean in the south. We worked mostly on the shallow continental shelf areas where water depths vary between 50 and 500 meters. The map shows these areas in light bluish tones where the line shows the 100 and 300 meter water depth. Fram Strait is much deeper, more than 2000 meters in places. I am interested how the warm Atlantic water from Fram Strait moves towards the cold glaciers that dot the coastline of Greenland in the west.

Map of study area with 2014-16 mooring array in box near 78 N across Belgica Trough. Red triangles place weather data from Station Nord (81.2 N), Henrik Kr\o yer Holme (80.5 N), and Danmarkhaven (76.9 N). Black box indicates area of mooring locations.

There is also ice, lots of sea icebergs, and ice islands that we had to navigate. None of it did any harm to our gear that we moored for 1-3 years on the ocean floor that can and often is scoured by 100 to 400 meter thick ice from glaciers, however, 2-3 meter thick sea ice prevented us to reach three mooring locations this year and our sensors are still, we hope, on the ocean floor collecting data.

Ahhh, data, here we come. Lets start with the weather at this very lonely place called Henrik Krøyer Holme. The Danish Meteorological Institute (DMI) maintains an automated weather station that, it seems, Dr. Ruth Mottram visited and blogged about in 2014 just before we deployed our moorings from Polarstern back in 2014:

Weather station on Henrik Kroeyer Holme [Credit: Dr. Ruth Mottram, DMI]

It was a little tricky to find the hourly data and it took me more than a day to process and graph it to suit my own purposes, but here it is

Winds (A) and air temperature (B) from an automated weather station at Henrik Kroeyer Holme from 1 June, 2014 through 31 August, 2016. Missing values are indicated as red symbols in (A).

The air temperatures on this island are much warmer than on land to the west, but it still drops to -30 C during a long winter, but the end of July it reaches +5 C. The winds in summer (JJA for June, July, and August) are weak and variable, but they are often ferociously strong in winter (DJF for December, January, February) when they reach almost 30 meters per second (60 knots). The strong winter winds are always from the north moving cold Arctic air to the south. The length of each stick along the time line relates the strength of the winds, that is, long stick indicates much wind. The orientation of each stick indicates the direction that the wind blows, that is, a stick vertical down is a wind from north to south. I use the same type of stick plot for ocean currents. How do these look for the same period?

Ocean current vectors at four selected depths near the eastern wall of Belgica Trough. Note the bottom-intensified flow from south to north. A Lanczos low-pass filter removes variability at time scales smaller than 5 days to emphasize mean and low-frequency variability.

Ocean currents and winds have nothing in common. While the winds are from north to south, the ocean currents are usually in the opposite direction. This becomes particular clear as we compare surface currents at 39 meters below the sea surface with bottom currents 175 or even 255 meters below the surface. They are much stronger and steadier at depth than at the surface. How can this be?

Image of study area on 15 June 2014 with locations (blue symbols) where we deployed moorings a few days before this satellite image was taken by MODIS Terra. The 100-m isobath is shown in red.

Well, recall that there is ice and for much of the year this sea ice is not moving, but is stuck to land and islands. This immobile winter ice protects the ocean below from a direct influence of the local winds. Yet, what is driving such strong flows under the ice? We need to know, because it is these strong currents at 200 to 300 meter depth that move the heat of warm and salty Atlantic waters towards coastal glaciers where they add to the melting of Greenland. This is what I am thinking about now as I am trying to write-up for my German friends and colleagues what we did together the last 3 years.

Oh yes, and we did reach the massive terminus of 79 North Glacier (Nioghalvfjerdsfjorden) that features the largest remaining floating ice shelf in Greenland:

We recovered ocean moorings from this location also, but this is yet another story that is probably best told by scientists at the Alfred-Wegener-Institute who spent much time and treasures to put ship, people, and science on one ship. I am grateful for their support and companionship at sea and hopefully all of next year in Bremerhaven, Germany.

Is Petermann Gletscher Breaking Apart this Summer?

I am disturbed by new ocean data from Greenland every morning before breakfast these days. In 2015 we built a station that probes the ocean below Petermann Gletscher every hour. Data travels from the deep ocean via copper cables to the glacier surface, passes through a weather station, jumps the first satellite overhead, hops from satellite to satellite, falls back to earth hitting an antenna in my garden, and fills an old computer.

A 7-minute Washington Post video describes a helicopter repair mission of the Petermann data machine. The Post also reported first result that deep ocean waters under the glacier are heating up.

Sketch of Petermann Gletscher’s ice shelf with ocean sensor stations. The central station supports five cabled sensors that are reporting hourly ocean temperatures once every day. Graphics made by Dani Johnson and Laris Karklis for the Washington Post.

After two years I am stunned that the fancy technology still works, but the new data I received the last 3 weeks does worry me. The graph below compares ocean temperatures from May-24 through June-16 in 2017 (red) and 2016 (black). Ignore the salinity measurements in the top panel, they just tell me that the sensors are working extremely well:

Ocean temperature (bottom) and salinity (top) at 450-m depth below Petermann Gletscher from May-25 through June-16 2017 (red) and 2016 (black). Notice the much larger day-to-day temperature ups and downs in 2017 as compared to 2016. This “change of character” worries me more than anything else at Petermann right now.

The red temperature line in the bottom panel is always above the black line. The 2017 temperatures indicate waters that are warmer in 2017 than in 2016. We observed such warming for the last 15 years, but the year to year warming now exceeds the year to year warming that we observed 10 years ago. This worries me, but three features suggest a new ice island to form soon:

First, a new crack in the ice shelf developed near the center of the glacier the last 12 months. Dr. Stef Lhermitte of Delft University of Technology in the Netherlands discovered the new crack two months ago. The new rupture is small, but unusual for its location. Again, the Washington Post reported the new discovery:

New 2016/17 crack near the center of Petermann Gletscher’s ice shelf as reported by Washington Post on Apr.-14, 2017.

Second, most Petermann cracks develop from the sides at regular spaced intervals and emanate from a shear zone at the edge. Some cracks grow towards the center, but most do not. In both 2010 and 2012 Manhattan-sized ice islands formed when a lateral crack grew and reached the central channel. The LandSat image shows such a crack that keeps growing towards the center.

Segment of Petermann Gletscher from 31 May 2017 LandSat image. Terminus of glacier and sea ice are at top left.

And finally, let’s go back to the ocean temperature record that I show above. Notice the up and down of temperature that in 2017 exceeds the 2016 up and down range. Scientists call this property “variance” which measures how much temperature varies from day-to-day and from hour-to-hour. The average temperature may change in an “orderly” or “stable” or “predictable” ocean along a trend, but the variance stays the same. What I see in 2017 temperatures before breakfast each morning is different. The new state appears more “chaotic” and “unstable.” I do not know what will come next, but such disorderly behavior often happens, when something breaks.

I fear that Petermann is about to break apart … again.